Method and system for ultrafast photoelectron microscope

[Related application] This application was filed on April 2, 2004, with a US provisional application number 60 / 559,234 entitled "Ultrafast High Electron Microscope" and a US provisional application on June 7, 2004, entitled "Space". And claims the benefits commonly assigned to the US provisional application No. 60 / 577,902, entitled "Diffraction, Crystallography, and Microscopy Beyond Three-dimensional Structural Dynamics in Time." These are included here as references.

[Statement on the rights of inventions made under government-sponsored R & D] The studies described here are partially supported by NSF grant CHE-0117850. The US Government may therefore have some rights to the invention.

The present invention generally relates to the imaging of an object. In particular, the present invention uses one or more pulses of a particle containing approximately 1 to 10000 electrons, preferably approximately 10 to 100 electrons in a transmission electron microscopy system to create one or more objects. Provides a method and system for imaging. Furthermore, the present invention provides methods and systems for recognizing information about one or more transient elements associated with one or more spatial features of some ceramic objects being imaged. To do. As merely an example, the present invention applies to imaging specific chemical, physical, or biological objects. However, the present invention relates to, for example, other areas of biology, chemistry (eg, organic chemistry, physical chemistry, biochemistry), medicine (eg, medical equipment, diagnosis, analysis, treatment), physical science, electronic engineering, semiconductors. Elements and materials (eg silicon, germanium, III / V group semiconductors, II / VI group semiconductors), chemicals (eg industrial chemicals), petrochemicals (eg gas, oil), any combination thereof , And other uses. The present invention relates to specific compounds and / or such as oligomers, peptides, nucleic acids, oligosaccharides, phospholipids, polymers, proteins, a drug congener preparation, other species and / or entities. It may be applied to applications including molecular processing and screening. Further, the present invention may be applied to diffraction, spectroscopy, other regions and the like. Furthermore, the present invention may be applied to monitor the formation / decomposition of materials, films, compounds, and / or other species, depending on the examples.

The 20th century was a witness to certain important developments in our ability to glimpse the world of molecules with a microscope, and as a result we were given unparalleled insight into their static behavior. .. For example, electron microscopy, especially transmission electron microscopy (TEM), provides a means of directly imaging the static structure of macromolecules with a few angstrom spatial resolutions. These conventional electron microscopy systems have been employed, for example, to image biopolymer crystals. Despite the development of these imagings, the insights desirable for understanding the dynamic aspects and functions of structural evolution are no longer available from the available static images. This is due to the lack of temporal resolution in conventional electron microscopy.

<p> Often attention must be paid to the nature of three-dimensional (3D) molecular structures when chemical, especially biological changes, involve complex and temporary structures with various possible conformations. , Each must pay attention to different times during the change. In most biologically important processes, structural changes are reversible. That is, a repeatable non-destructive reaction occurs at the self-proclaimed initiation and associated response. Unfortunately, there are limits to traditional microscopy techniques. For example, conventional electron microscopes are generally unable to produce images with spatial resolution on the biological length scale (nanometers to micrometers) with the desired time resolution. These or other limitations in the prior art are described herein and are further described below.</p><p> Therefore, there is a technical need for improved methods of imaging physical, chemical, biological, and other samples on an atomic scale.</p>

<p> According to the present invention, a technique for visualizing an object is provided. In particular, the present invention uses one or more pulses of a particle containing approximately 1 to 10000 electrons, preferably approximately 10 to 100 electrons in a transmission electron microscopy system to create one or more objects. Provides a method and system for imaging. Furthermore, the present invention provides methods and systems for recognizing information about one or more transient elements associated with one or more spatial features of some object being imaged. As merely an example, the present invention applies to imaging specific chemical, physical, or biological objects. However, the present invention relates to, for example, other areas of biology, chemistry (eg, organic chemistry, physical chemistry, biochemistry), medicine (eg, medical equipment, diagnosis, analysis, treatment), physical science, electronic engineering, semiconductors. Elements and materials (eg silicon, germanium, III / V group semiconductors, II / VI group semiconductors), chemicals (eg industrial chemicals), petrochemicals (eg gas, oil), any combination thereof , And other uses. The present invention comprises the treatment and screening of specific compounds and / or molecules such as oligomers, peptides, nucleic acids, oligosaccharides, phospholipids, polymers, proteins, drug congener preparations, and other species and / or entities. It may be applied. Further, the present invention may be applied to diffraction, spectroscopy, other regions and the like. Furthermore, the present invention may be applied to monitor the formation / decomposition of materials, films, compounds, and / or other species, depending on the examples.</p><p> According to some examples, at subcellular levels, the invention may be applied to the interaction of a peptide or chemical compound (drug) with the active site of an enzyme, a peptide or small molecule and a protein surface. It may be applied to any reversible interaction with. The present invention may be applied to nucleic acid interactions that bind proteins or enzymes to target nucleic acids. For example, it may be applied to the binding of a transcription factor to a specific DNA sequence, or the interaction of an enzyme with DNA, binding and scanning along the surface of DNA, or insertion into DNA. The present invention may be applied to nucleic acid-nucleic acid interactions. For example, it may be applied to the interaction of ribozymes with RNA according to specific examples.</p><p> According to some examples, at the cellular level, the invention is a compound, protein, virus or cell-membrane interaction such that when a compound, protein, virus or cell touches the membrane, it crosses the membrane. It may also be applied to various interactions. These or other applications are described in detail below.</p><p> In certain embodiments, the present invention provides, for example, a system for imaging one or more biological, chemical, and physical samples. The system has a stage assembly, which contains the sample to be imaged. Preferably, the system has a laser source capable of emitting optical pulses with a duration less than one picosecond (ps). The system has a cathode linked to a laser source. In a preferred embodiment, the cathode can emit electron pulses with a duration less than 1 picosecond and can also emit pulses with other durations. Electron lens assembly (An electron lens) assembly) is adapted to focus the electron pulse on the sample placed on the stage. The detector is adapted to capture one or more electrons that have passed through the sample. One or more electrons that have passed through the sample are representative of the image of the sample. The detector provides a signal (eg, a data signal) associated with one or more electrons that have passed through the sample on behalf of the image of the sample. This system has a processor linked to a detector. In a preferred embodiment, the processor is adapted to process the data signal associated with one or more electrons that have passed through the sample to output the information associated with the image represented by the sample. The output device is attached to the processor. The output device is adapted to output the information associated with the image represented by the sample.</p><p> In a particular alternative embodiment, the present invention provides a method of operating a transmission electron microscope consisting of a laser source, a cathode, and an electronic lens assembly. The method involves forming a train-like connected optical pulse. Each optical pulse is characterized by a Full Width Half Maximum (FWHM) pulse length with a duration of less than 1 picosecond. In this method, a sample for imaging placed on the stage assembly and a train-like connected electron pulse generated by a train-like connected optical pulse colliding with the cathode are generated. including. An electronic pulse connected like a train is associated with an optical pulse connected like a train. Each train-like connected electron pulse is characterized by a FWHM pulse length of less than 1 picosecond. The method captures a portion of a train-like connected electron pulse by using a sensing device to extract information associated with the image of the sample. The method processes the information associated with the image of the sample.</p><p> In yet another specific embodiment, the present invention provides a transmission electron microscope (TEM) system capable of obtaining time-resolved images. The system has a laser that produces photon pulses and a beam splitter adapted to split the photon pulses into electron-generated photon pulses and initiation photon pulses. The cathode is adapted to generate an electron pulse in response to being activated by an electron-generating photon pulse. The optical delay stage is adapted to introduce a time delay between the start photon pulse and the electron pulse. The system has a sample irradiated by a start photon pulse and an electron pulse. The system has an electron detector that produces an image of the sample in response to irradiation of the sample by an electron pulse. Instead, the electron detector, in other embodiments, produces other information in the material in response to the irradiation of the sample by the electron pulse.</p><p> Furthermore, the present invention provides a method of forming an image from one or more samples using an electron beam pulse. The method comprises providing features of the sample to be imaged. Its features have a size of about 100 nanometers or less, according to certain examples. The method includes placing the sample in the stage assembly and maintaining the sample in the stage assembly in a vacuum environment. The method involves directing one or more electron pulses in the direction of the feature of the sample. Preferably, according to a particular embodiment, each one or more electron pulses has about 10 to about 1000 electrons, even though each can have another number of electrons. The method uses a detector to capture a portion of one or more electron pulses. Some of the one or more electron pulses are associated with images of sample features. The method involves transferring information associated with a portion of one or more electron pulses associated with an image of a sample feature from a detector to a processing device. The method outputs a visual image associated with a sample feature, using at least the information associated with a portion of one or more electron pulses associated with the image of the sample feature.</p><p> In a further embodiment, the present invention provides a method of obtaining time-resolved images using an electron microscope. The method comprises providing features of the sample to be imaged. The method includes placing the sample in the stage assembly and maintaining the sample on the stage assembly in a vacuum environment. The method involves directing one or more electron pulses in the direction of the feature of the sample. In a preferred embodiment, each one or more electron pulses has about 1 to about 1000 electrons. The method comprises capturing the first portion of one or more electron pulses using a detector during the first portion of time. The portion of one or more electron pulses is associated with the first image of sample features during the first portion of time. The method involves transferring the first information associated with the first part of one or more electron pulses associated with the first image of the sample features of the first part of time from the detector to the processing device. .. The method uses a detector to capture a second portion of one or more electron pulses during the second portion of time. The portion of the one or more electron pulses is associated with a second image of the sample features during the second portion of time. The method comprises transferring a second piece of information associated with a second part of one or more electron pulses associated with a second image of a sample feature during a second part of time. In a preferred embodiment, the first image may have different characteristics from the second image.</p><p> In yet another special embodiment, the invention provides a system for characterizing one or more samples. The system has a stage assembly, which has a sample to be characterized. The system has a laser source capable of emitting light pulses with a duration of less than 1 picosecond. The system has a cathode connected to a laser source. In a specific embodiment, the cathode can emit an electron pulse with a duration of less than 1 picosecond. The system has an electronic lens assembly adapted to focus the electron pulse on a sample placed on the stage. The system has a detector adapted to capture one or more electrons passing through the sample. One or more electrons passing through the sample represent the structure of the sample. This system has a processor connected to a detection unit. The processor is adapted to process the data signal associated with one or more electrons passing through the sample in order to output the information associated with the structure of the sample. The system has an output device attached to the processor. The output device is adapted to output information associated with the structure of the sample.</p><p> Furthermore, the present invention provides a method for obtaining information from one or more samples using electron beam pulses. The method is electromagnetic radiation (electromagnetic) It is derived from each pulse of radiation), for example a laser pulse. The method comprises providing features of the sample to be imaged. The method involves placing the sample on a stage assembly maintained in a vacuum environment. The method involves directing one or more electron pulses in the direction of the feature of the sample. In a particular embodiment, each one or more electron pulses has about 1 to about 1000 electrons, or 10 to 100 electrons, depending on the application. The method involves capturing a portion of one or more electron pulses using a detector. Some of the one or more electron pulses are associated with the characterization of the sample characteristics (eg, image, diffraction characteristics). The method involves transferring information associated with a portion of one or more electron pulses associated with characterization of a sample from a detector to a processing device. Optionally, the method comprises processing information using a processing device. The method outputs at least one or more indicators associated with a sample feature using information associated with at least a portion of one or more electron pulses associated with an image of the sample feature.</p><p> In an alternative special embodiment of the present invention, a method of obtaining a time-resolved image using an electron microscope is provided. The method comprises supplying features of the sample to be imaged, the features having size and placing the sample on the stage assembly. The method also includes maintaining the sample on the stage assembly in a vacuum environment and guiding the first electron pulse train towards the characteristics of the sample, with the first electron pulse train having an average time of less than 1 picosecond. Has a pulse width. In addition, the method comprises capturing the first part of the first electron pulse train using a detector during the first part of the time, where the first part of the electron pulse train is the sample during the first part of the time. Processes the first information from the detector associated with the first image of the feature and also the first part of the first electron pulse train associated with the first image of the sample feature during the first part of time. Transfer to device. The method further comprises directing a second electron pulse train in the direction of the feature of the sample. The second electron pulse train has an average time pulse width of less than one picosecond and uses a detector during the second part of time to capture the second part of the second electron pulse train. The portion of the second electron pulse train is associated with the second image of the sample features during the second portion of time. In addition, the method processes the second information associated with the second part of the second electron pulse train associated with the second image of the sample features during the second part of time from the detector. Including forwarding to.</p><p> Yet another alternative, particular embodiment of the invention, provides a method of performing time-resolved characterization of a sample. The method involves providing a photon pulse and adapting the beam splitter to split the photon pulse into an electron-generating photon pulse and a start photon pulse. In a special embodiment of the present invention according to this aspect, the photon pulse is on a train-like connected ultrafast photon pulse. The method adapts the cathode to generate an electron pulse in response to activation by an electron-generating photon pulse and sets the optical delay stage to capture the time delay between the start photon pulse and the electron pulse. Including adapting and so on. The method further provides a sample irradiated by a start photon pulse and an electron pulse, and adapts the electron detector to generate an image of the sample in response to irradiation of the sample by the electron pulse. And include.</p><p> Also, in another alternative embodiment according to the invention, a spectroscopic system is provided. The system has a laser that produces photon pulse trains, a beam splitter adapted to separate the photon pulse trains into electron-generated photon pulse trains and spectrophoton pulse trains, and to adjust the wavelength of the spectrophoton pulse trains to the starting wavelength. Includes adapted non-linear optical elements. The system is adapted to generate a time delay between the spectrophoton pulse train and the electron pulse train with the cathode adapted to generate the electron pulse train in response to being activated by the electron-generated photon pulse train. Also includes a light delay stage. Further, the system includes a sample irradiated by a spectrophoton pulse train and an electron pulse train, and an electron detector that generates an image of the sample in response to the sample being irradiated by the electron pulse train.</p><p> In addition, the examples of the present invention provide a method of determining the temporal characteristics of the features of one or more objects using an electron microscope assembly. The method comprises providing a sample containing one or more features. The sample is placed on the stage assembly and generates one or more electron pulses. One or more electron pulses have a FWHM pulse length of less than 1 picosecond in duration. The method derives one or more electron pulses in the direction of one or more features of the sample during the time cycle associated with one cycle of detection and extracts the information associated with the characteristics of one or more features of the sample. It also includes capturing a portion of one or more electron pulses using a detector. The method further comprises processing at least the information for identifying the temporal characteristics of one or more features of the sample (eg, features that change or may not change with respect to time).</p><p> Many benefits go beyond the prior art via the present invention. For example, current techniques provide techniques and systems for imaging materials and biological structures with the structural mechanics of samples described in terms of both space and time, according to specific embodiments. Furthermore, the present invention provides, in some embodiments, methods and systems that may use conventional electronic techniques, including computer code that is easy to implement. The present invention also provides, in other embodiments, operable methods and systems for capturing images of a sample at a temperature compatible with the biological material. Depending on the examples, some methods and systems may be applied to diffraction, imaging, crystallography, spectroscopy and other techniques. In some embodiments, the present invention heats small features of biological and / or chemical objects in a manner that does not avoid them, i.e., objects that are often low energy and often delicate to excessive thermal energy. Provide methods and systems for imaging in a way that does not cause damage. In some embodiments, the methods and systems include processes that are "insulated" in their properties. Depending on the embodiment, one or more of these benefits may be obtained. These and other benefits are further described herein, and more particularly below.</p><p> Various further objectives, features, and advantages of the present invention can be better understood by reference to the detailed description and accompanying drawings below.</p>

<figref num="1A">It is a simplified figure of the ultrafast photoemission electron microscope system which concerns on one Example of this invention.</figref><figref num="1B">It is a simplified perspective view of the ultrafast photoemission electron microscope system which concerns on one Example of this invention.</figref><figref num="1C">It is a simplified figure of the computer system which controls the ultrafast high electron microscope system which concerns on one Example of this invention.</figref><figref num="1D">It is a simplified block diagram of the computer hardware which controls the ultrafast photoemission electron microscope system which concerns on one Example of this invention.</figref><figref num="2">It is a series of figures which concerns on one Example of this invention.</figref><figref num="3">It is an image obtained by using the electron pulse which concerns on one Example of this invention.</figref><figref num="4">It is an image obtained by using the diffraction mode of the operation which concerns on one Example of this invention.</figref><figref num="5">It is an image of a biological sample obtained using one embodiment of the present invention.</figref><figref num="6">It is a simplified timing diagram which illustrates the use of the method which concerns on this invention.</figref><figref num="7">It is a simplified flow chart of the imaging method which concerns on one Example of this invention.</figref><figref num="8">It is a simplified flow chart of the alternative imaging method which concerns on one Example of this invention.</figref><figref num="9A">It is a simplified flow chart of the further alternative imaging method which concerns on one Example of this invention.</figref><figref num="9B">It is a simplified timing diagram which illustrates the pulse train which concerns on one Example of this invention.</figref><figref num="9C">It is a simplified flowchart which illustrates the image collection which concerns on one Example of this invention.</figref><figref num="10">It is a simplified flow chart of the further alternative imaging method which concerns on one Example of this invention.</figref><figref num="11">It is a simplified figure of the experimental result which concerns on one Example of this invention.</figref><figref num="12">It is a simplified figure of the experimental result which concerns on one Example of this invention.</figref><figref num="13">It is a simplified figure of the experimental result which concerns on one Example of this invention.</figref><figref num="14">It is a simplified figure of the experimental result which concerns on one Example of this invention.</figref><figref num="15">It is a simplified figure of the experimental result which concerns on one Example of this invention.</figref><figref num="16">It is a simplified figure of the experimental method which concerns on one alternative example of this invention.</figref><figref num="17">It is a simplified figure of the experimental result which concerns on the alternative example of this invention.</figref><figref num="18">It is a simplified figure of the experimental result which concerns on the alternative example of this invention.</figref><figref num="19">It is a simplified figure of the experimental result which concerns on the alternative example of this invention.</figref><figref num="20">It is a simplified figure of the experimental result which concerns on the specific embodiment of this invention.</figref>

According to the present invention, there is provided a technique for imaging an object. In particular, the present invention uses one or more pulses of a particle containing approximately 1 to 10000 electrons, preferably approximately 10 to 100 electrons in a transmission electron microscopy system to create one or more objects. Provides a method and system for imaging. Furthermore, the present invention provides methods and systems for recognizing information about one or more transient elements associated with one or more spatial features of some object being imaged. As merely an example, the present invention applies to imaging specific chemical, physical, or biological objects. However, the present invention relates to, for example, other areas of biology, chemistry (eg, organic chemistry, physical chemistry, biochemistry), medicine (eg, medical equipment, diagnosis, analysis, treatment), physical science, electronic engineering, semiconductors. Elements and materials (eg silicon, germanium, III / V group semiconductors, II / VI group semiconductors), chemicals (eg industrial chemicals), petrochemicals (eg gas, oil), any combination thereof , And other uses. The present invention comprises the treatment and screening of specific compounds and / or molecules such as oligomers, peptides, nucleic acids, oligosaccharides, phospholipids, polymers, proteins, drug congener preparations, and other species and / or entities. It may be applied. Further, the present invention may be applied to diffraction, spectroscopy, other regions and the like. Furthermore, the present invention may be applied to monitor the formation / decomposition of materials, films, compounds, and / or other species, depending on the examples. Details of the embodiments of the present invention can be found in the specification, and more particularly below. Before discussing the details of the various examples, we provide some information. That information is what we know and / or discover and may be applied to the description of the examples below.

Beginning with X-rays at the turn of the 20th century, diffraction techniques have made it possible to determine three-dimensional equilibrium structures with atomic resolution. In the system, it ranges from two molecules (NaCl) to complex aggregates such as DNA, proteins, and viruses. In terms of mechanics, the resolution of time has similarly reached basic atomic-scale movements. With the advent of femtosecond time resolution 20 years ago, it has become possible to study the dynamics of non-equilibrium molecular systems in real time: from the smallest (NaI) to the very large (DNA, proteins, theirs). Up to (aggregate). This will be described below.

With this ability to capture static structures as well as the time behavior of chemical bonds, the hope of inspiring researchers around the world now is the real-time, all-individual primitive coordinates during the reaction. Arrange in detail, for example, when it is revealed that a molecule forms a selected structure, or when a protein docks on the cell surface. These transient structures provide important insight into the function of chemical or biological molecules. Knowing the static structure of a molecule, as its function is intimately associated with its underlying structural dynamics, often leads to elucidating how the molecule works, especially in the world of biology. It's just the first step towards. Therefore, revealing the real-time "structural mechanics" of structures far from atomic-scale equilibrium is essential for understanding the basic mechanisms of complex chemical and biological systems.

Time-resolved experiments with femtosecond resolution have been performed in the past with probe wavelengths ranging from the ultraviolet to the infrared and far infrared. At this time scale, the local structures of space (wave packets) can be frozen and their evolution can be seen in time-hence, in chemistry and biology, binding changes via transition states. The initial process becomes clear.

Several advances have been made in multidimensional spectroscopy to relate the frequency of light transitions to temporal evolution, thus scrutinizing structural changes in different relaxation processes. However, for complex molecular structures, the positions of all atoms at a given time can only be obtained if the probe can "see" the interference of all atoms. Diffraction methods using X-rays or electrons have the only possibility of revealing the coordinates between all nuclei with very high spatial resolution, and therefore ultrafast time-scale structures with atomic level details. Provides a complete picture of change.

Diffraction techniques using electron or X-ray pulses can, in principle, be used to obtain several time-varying molecular structures. These pulses often have to be short enough to freeze the movement of atoms, but bright enough to provide an identifiable diffraction pattern. In the case of X-rays, photons are scattered by electrons in the molecular sample, so the opening intensity depends directly on the electron concentration. This is because most of the electrons are concentrated in atoms, and these electron concentrations indicate the position of the nucleus, especially in heavy atoms. Ultrafast pulsed X-ray sources include third-generation synchrotron radiation, laser-excited plasma sources, generation of higher harmonics in gas and on solid surfaces, and free electron lasers. While the high neutron flux X-ray pulse from the synchrotron source is relatively long (tens of picoseconds, determined by the duration of the electron flux in the storage ring), the lower picoseconds (sub) by other generation mechanisms -picosecond) X-ray pulses suffer from fairly low flux. As a result, ultrafast X-ray diffraction studies have focused primarily on solid samples where the intrinsic long-range order enhances the signal-to-noise ratio of the interference pattern. X-ray absorption spectroscopy (XAS) techniques, such as extended X-ray absorption fine structure (EXAFS) and X-ray absorption edge structure (XANES) spectroscopy, provide local structural information on a nanosecond time scale and in solution. Or used to obtain in ultrafast time scale and in gas or liquid.

Electron diffraction offers many benefits. For example, the cross section of electron scattering is about 6 orders of magnitude larger than that of X-ray scattering. In addition, the experiments are done on a "desktop" scale and can be implemented using ultrafast (femtosecond or picosecond) laser sources. Electrons do less damage to the swatch per useful elastic scattering event than X-rays. Since the penetration depth of electrons generated from the strong interaction with an object is short, it is possible to clarify the transient structure of gas, surface, and (thin) crystals. Electrons can be focused on obtaining images in microscopy. By using a sequence of exact timings of the electron pulses, sometimes referred to as a frame referencing, it is possible to "isolate" changes in the transient structure, as more fully described below. it can. Depending on the embodiment, other benefits may also exist.

Examples of the present invention include temporally and spatially decomposed transient structures, including structures in non-radiative transitions, structures in non-concerted organic reactions, and non-concerted organic metals. Methods and systems for structures, carbene intermediate structures, dynamic pseudorotary structures, unbalanced and conformational structures on complex energy landscapes, and hydrogen-bonded structures of reciprocal reactions. provide. Just as an example, the reaction of pyridine has been believed to form a valence structure, but it has been shown that this reaction has a course of reaction with the formation of diradical intermediates as well as the opening of the ring.

Photomicroscopy has provided a means of visualizing what is happening outside the body or inside the cell, using fluorescent probes, such as green fluorescent protein. However, while the optical method can, in principle, provide femtosecond-scale temporal resolution, the reachable spatial resolution is typically 200 nanometers, up to the resolution on the order of the wavelength of light used in the microscope. Limited to meters. Other limitations may also exist by using photomicroscopy.

Direct imaging of polymer static structures with 2-3 angstrom resolutions has been adopted with great success in many conventional electron microscopy systems, including biological polymer crystals. But the dynamics of structural change, which is absolutely essential for us to understand its function, cannot be obtained without temporal resolution. The development of strobe-based methodologies has made it possible to explore structural mechanics with a time scale limited solely by the temporal characteristics of electron probes. This time-scale separation limits the energy dissipation that usually leads to structural degradation over longer periods of time. Importantly, atomic movements can be ignored on the lower picosecond time scale. In some embodiments of the invention, a three-dimensional (3D) spatial structure is imaged, for example, as a function of time (4D) that provides insight into structural mechanics.

The embodiments of the present invention solve the problem of the time-energy uncertainty principle in that samples are coherently prepared and limited to information obtained from femtosecond to picosecond time resolutions. To. Moreover, for any mechanical process, the change as a function of time is continuous, and some overall events occur over a longer period of time, sometimes referred to as the "related time scale". Events are caused by changes that occur early. The first event is an integral part of any complete description of terrain and mechanics. Therefore, the notion that "related" biological events occur far beyond the ultrafast time domain gives an incomplete picture and may substantiate misunderstandings in cases such as the early notion of chemical reactions. unknown.

In some embodiments of the invention, the term "ultrafast" is used to characterize the various components of the system described herein. Those skilled in the art will fully understand that the term ultrafast refers to a pulse containing either a photon or an electron with a duration of less than one pico (ps) second. The pulse width measurement is generally performed at the full width at half maximum (FWHM) of the pulse. Generally, pulses with a width on the order of 100 femtoseconds are used in the examples of the present invention, but below the threshold of 1 picosecond, which defines the term ultrafast, is sufficient. Of course, other variants, improvements, and alternatives are also possible. Some details of current methods and systems can be found herein, and more particularly below.

FIG. 1A is a simplified view of the ultrafast photoemission electron microscope system according to an embodiment of the present invention. This figure is just an example and the scope of the claims in it should not be overly limited. Those skilled in the art will recognize many modifications, improvements and alternatives. As shown in FIG. 1, the femtosecond laser 110 is guided through the pocket cell 112, which acts as a controllable shutter. The gran deflector 114 is used in some embodiments to select the force of the laser propagated by the optical path 115. Beam splitters (not shown) are used to supply several laser beams to different parts of the system. The system illustrated in FIG. 1A is described for imaging applications, which is not generally required by the present invention. Those skilled in the art will fully understand that the embodiments of the present invention provide systems and methods for imaging, diffraction, crystallography, and related fields. In particular, the experimental results discussed below provide insights that can be used in a variety of applications by using the examples of the present invention.

The femtosecond laser source 110 can generally generate a sequence of light pulses of a predetermined pulse width. An example of such a laser system is a diode-pumped mode-locked Ti: Sapphire laser oscillator, which operates at 800 nanometers and produces 100 femtosecond pulses. The number of repetitions is 80 MHz and the average force is 1 watt, resulting in a period of 12.5 nanoseconds between pulses. In one example, the spectral bandwidth of the laser pulse is 2.35 nanometers in FWHM. An example of such a laser is the Mai Tai One Box Femtosecond Ti: Sapphire Laser, which can be procured from Spectra-Physics Lasers in Mountain View, California. In alternative embodiments, other laser sources with different wavelengths, different pulse widths, and different repeat numbers of light pulses are used. Those skilled in the art will appreciate many variants, improvements and alternatives.

The first part of the output of the femtosecond laser 110 is a second harmonic generation (SHG) device 116, such as barium borate (BaB).₂O₄) Connected to the crystal. Barium borate crystals are typically referred to as BBO crystals and are also available from a variety of doubling crystal manufacturers. The frequency of the SHG device doubles a row of optical pulses to produce a row of 400 nanometers, producing 100 femtosecond pulses with 80 MHz iterations. SHG devices typically utilize non-linear crystals that preserve the pulse width while doubling the frequency of the input pulse. In some embodiments, the SHG is a device that triples the frequency, resulting in the generation of light pulses of ultraviolet wavelength. Of course, the wavelength for the light pulse of the desired output will depend on the particular application. The doubled optical pulse generated by the SHG device propagates along the electron generation path 118.

The CW diode laser 120 is coupled with an optical pulse whose frequency is doubled by using a beam splitter 122. The light produced by the CW diode laser and now on the same line as the light pulse generated by the SHG device acts as an alignment marker beam and also tracks one of the light pulse trains in the electron generation path. Used. A laser beam on the same line enters chamber 130 through the inlet window 132. In the embodiment illustrated in FIG. 1A, the entrance window is made of a material that is thick enough to provide high transparency at 400 nanometers and provide mechanical strength. For example, anti-reflective coating, for example MgF₂Alternatively, BK-7 glass with a thickness of 6 mm, sapphire, is used in various embodiments. Those skilled in the art will appreciate that there are many modifications, improvements and alternatives.

The optical system, partly supplied to the outside of the chamber 130 and partly to the inside of the chamber 130, electron-generates a frequency-doubled optical pulse train so that the optical pulse affects the cathode 140. Guide to the inside of chamber 130 along. As shown in the figure, the optical system has a mirror 144, which acts as a reflector inside the chamber 130. In the embodiments of the present invention, a polished metal mirror is used inside the chamber 130, because electron irradiation may damage the mirror coating used in some optical mirrors. In certain embodiments, the mirror 144 is made from an aluminum substrate that is a diamond that has been turned to create the surface of the mirror. In some examples, the aluminum mirror is uncoated. In another embodiment, another metal mirror, such as a mirror made of platinum, is used as the mirror 144.

In one example, the region of interaction on the cathode was chosen to be a plane with a diameter of 300 micrometers. Further, in the illustrated embodiment, the frequency-doubled optical pulse was shaped to deliver a beam with a predetermined beam waist on the surface of the cathode. In certain examples, the waist of the beam was about 50 micrometers. In an alternative embodiment, the waist of the beam had a width from 30 micrometers to 200 micrometers. Of course, the special dimensions will depend on the special use. In certain embodiments, the frequency-doubled optical pulse train was guided into the chamber using a computer-controlled mirror.

In a particular embodiment, the optical pulse train is in the direction of the front-illuminated photocathode, where the laser cathode irradiation ends up generating electron pulses via the photoelectron effect. Be guided. Irradiating the cathode with light having energy exceeding the work function of the cathode leads to the emission of photoelectrons. That is, according to a preferred embodiment, a pulse of electromagnetic energy that exceeds the work function of the cathode emits an electron pulse. Generally, the cathode is maintained at a temperature of 1000K, but below the threshold of thermal radiation of about 1500K is sufficient. However, this is not required in the present invention. In an alternative embodiment, the cathode is maintained at room temperature. In some embodiments, the cathode is adapted to generate an electron pulse of a given pulse width. The orbit of the electron after emission follows the design of the TEM lens: the capacitor, the object, the lens of the projector. Depending on the embodiment, there may also be other settings.

In the example shown in the figure, the cathode is an MVM (Mini-Vogel mount) single crystal lanthanum hexaboride (LaB).₆) At the cathode, shaped into a truncated cone, with a plane of apex of 300 micrometers and a cone angle of 90 degrees, which can be sourced from Applied Physics Technologies, Inc. in McMinnville, Oregon. As is often known, LaB₆Cathodes are used in the transmission and scanning of electron microscopes in the century. LaB₆Quantum efficiency of cathode is about 10^-3And these cathodes are 10^-13It is possible to generate an electron pulse with a temporal pulse width on the order of seconds. In some examples, the brightness of the electron pulse generated by the cathode is 10.⁹A / cm²/ rad²The energy spread of the electron pulse is on the order of 0.1 eV. In another embodiment, the pulse energy of the laser pulse is suppressed to 500pJ per pulse, resulting in about 1 electron / pulse.

In general, the quality of an image obtained using a TEM is proportional to the number of electrons passing through the sample. That is, as the number of electrons passing through the sample increases, the image quality improves. Some pulsed lasers, such as some Q-switched lasers, reduce the total number of pulses to produce a smaller number of pulses characterized for higher maximum output per pulse. Therefore, some laser amplifiers control the number of iterations to 1 kHz and generate pulses with energy ranging from about 1 μJ to about 2 mJ per pulse. However, when such a high maximum power laser is used to generate an electron pulse using the photoelectron effect, among other things (among other) issues), both the spatial and temporal spreads of the electron pulse, conversely, affect the pulse width of the generated electron pulse or packet. In some embodiments of the invention, the laser is operated to output low power pulses at higher iterations, eg 80 MHz. This mode of operation provides the benefits available by using low power per pulse, which is described below. Moreover, this high number of iterations makes it possible to obtain a high quality image with a sufficient number of electrons.

In some embodiments of the invention, the laser power is maintained at a level of less than 500 pJ per pulse to prevent damage to the photocathode. As a benefit, the robustness of the photo emitter is increased. In addition, these force level laser pulses prevent the spread of space-charge in the electron pulse width during the flight time from cathode to sample, thus preserving the desired femtosecond time resolution. It is. Moreover, the low total number of electrons provided per pulse provided by some embodiments of the invention reduces the effect of space charge repulsion within the electron pulse. Therefore, the focusing characteristics of the system are enhanced. As will be appreciated by those skilled in the art, the low total number of electrons per pulse, coupled with the high number of iterations up to 80 MHz provided by femtosecond lasers, is capped, as commonly used in imaging applications. Is 1 electron / ŲProvides the total dose that is.

In alternative embodiments, other suitable cathodes capable of delivering ultrafast electron pulses in response to ultrafast light pulses of appropriate wavelength are used. In an embodiment of the invention, the cathode is selected to provide a work function that correlates with the wavelength of the optical pulse delivered by the SHG device. The wavelength of radiation is the well-known relationship λ (μm) 1.24 ÷ ν (eV), where λ is the wavelength expressed in microns and ν is the energy expressed in eV. , This relationship is related to the energy of photons. In one embodiment of the invention, for example, a LaB with a work function of 2.7 eV.₆The cathode is adapted to an optical pulse with a wavelength of 400 nanometers (ν = 3.1 eV). As shown, the cathode is placed in a vacuum chamber 130, for example, in the housing of a transmission electron microscope (TEM). Generally, the vacuum of chamber 130 is 1x10.^-6Maintained at levels below torr. In an alternative embodiment, the vacuum level is about 1x10.^-6About 1x10 from torr^-10It fluctuates up to torr. Special vacuum levels may be a feature of different applications.

In an embodiment of the invention, a short period of light pulse leads to the emission of photoelectrons before a significant amount of stored energy is transferred to the spatial lattice of the cathode. Generally, the characteristic time for thermalization of the energy stored in the metal is less than 2-3 picoseconds. Therefore, by using the examples of the present invention, it happens that the cathode is not heated.

The electrons produced by the cathode 140 are accelerated past the anode 142, parallelized and focused by the electronic lens assembly 146, and guided along the electronic imaging path 148 in the direction of the sample 150. The electronic lens assembly generally includes a large number of electromagnetic lenses, apertures, and other components, as will be appreciated by those skilled in the art. Electronic lens assemblies suitable for the embodiments of the present invention are often used in TEMs. The electron pulse propagating along the electron imaging path 148 is, in the embodiments of the present invention, a controller that supplies an electron beam of a given dimension (not shown, but in more detail with reference to some figures below). Controlled by), the electron beam constitutes an ultrafast electron pulse train.

Electron wavelength in an electron microscope (λ_deBroglie) And the acceleration voltage (U) are λ_deBroglie= h / (2m₀EU)^1/2It is expressed by the relationship. Where h is Planck's constant and m₀Is the mass of the electron and e is the elementary charge. As an example, the de Broglie wavelength of an electron pulse at 120 kV corresponds to 0.0335 Å, and the de Broglie wavelength can vary depending on other applications. The bandwidth or energy spread of an electronic packet is a function of the bandwidth of the optical pulse used for optoelectronic processing and generation of the electronic packet or pulse.

Electrons passing through the sample or sample 150 are focused on the detector 154 by the electronic lens assembly 152. Although two electronic lens assemblies 146 and 152 are illustrated in FIG. 1A, the invention is not limited to this arrangement and may have other lens assembly or lens assembly settings. In alternative embodiments, additional electromagnets, diaphragms, other components, etc. are utilized to focus the electron beam before, after, or both of the interaction with the sample.

Detection of electrons passing through a sample, which involves detection of one electron, is particularly suitable for small applications in one particular embodiment, and is an ultrasensitive phosphorus coupled with a digital CCD camera. Achieved through phosphor scintillator detector 154. In a special embodiment, the CCD camera is an UltraScan manufactured by Gatan, Inc. in Pleasanton, California.^TM It was a 1000 UHS camera. UltraScan^TM The 1000 CCD camera is a 4 megapixel (2048 x 2048) camera with a pixel size of 14 μm x 14 μm, 16-bit digitization, and a read speed of 4 megapixels / second. In the illustrated embodiment, the digital CCD camera is mounted on-axis below the microscope and below the position of the chamber. In some embodiments, the CCD camera chip is electrically cooled to about -25 ° C using a Peltier cooler to reduce noise and adverse artifacts. Images from the CCD camera are also available from Gatan, Inc. Tecnai^TMDigital Micrograph embedded in the user interface^TMObtained in software. Of course, various other variants are possible in CCD cameras, coolers, and computer software.

FIG. 1B illustrates an embodiment of the invention in which the TEM has been modified to supply a thermionic radiation source used for imaging a sample, as well as an electron pulse train used for imaging. Is. FEI Tecnai, just one example^TM G² 12 TWIN can be sourced from FEI Company in Hillsboro, Oregon, which can be modified according to the embodiments of the present invention. Tecnai^TM G² 12 TWIN is an all-in-one 120kV (λ_deBroglie= 0.0335 Å) high resolution TEM optimized for 2D and 3D imaging at both room temperature and liquid nitrogen temperature. The embodiments of the present invention utilize features provided by commercial TEMs such as automation software, detectors, data transfer technology, and tomography.

In particular, in some embodiments of the invention, an automated specimen tilt in which a precision goniometer powered by a 5-axis motor is linked to automated acquisition of images as part of a computer tomographic (CT) imaging system. Used with computer software that provides. In these examples, a series of 2D images are captured from various swatch locations and are concatenated by using computer software that produces a reconstructed 3D image of the swatch. In some embodiments, the CT software is combined with other TEM software, and in other embodiments, the CT software is provided offline. Those skilled in the art will understand many variants, improvements and alternatives.

In some embodiments where low-electron content electron pulses are used to image the sample, irradiation damage is limited to the passage of electrons within the electron pulse through the sample. The sample is typically on the order of 100 nanometers, although it will move at other thicknesses as long as some electrons may pass through the sample. Therefore, the effect of irradiation damage on the images of these low-electron-capacity electron pulses is limited to the damage that occurs during this transit time. Radiation-induced structural damage that occurs on a time scale longer than the transit time will not affect the collected images, because these damage events will occur after structural information has been collected. is there.

By using the instruments described so far, the embodiments of the present invention have spatial and temporal spatial resolutions on the order of 1 nanometer and temporal resolutions on the order of 100 femtoseconds. Provides imaging systems and methods for materials and biological swatches. At these time scales, energy randomization is limited and atoms are frozen almost in place (frozen). Therefore, the method according to the present invention opens the door to the study of time-resolved structural mechanics on an atomic scale in space and time. Details of the current computer system according to an embodiment of the present invention may be described according to the following description.

FIG. 1C is a simplified diagram of a computer system 210 that monitors the systems of FIGS. 1A and 1B according to an embodiment of the present invention. This figure is just an example and the scope of the claims here should not be overly limited. Those skilled in the art will understand many improvements, alternatives and variants. As shown, the computer system 210 includes a display device 220, a display screen 230, a cabinet 240, a keyboard 250, and a mouse 270. The mouse 270 and keyboard 250 represent "user input devices". The mouse 270 includes a button 280 for button selection on a graphical user interface device. Other examples of user input devices are touch screens, light pens, trackballs, data gloves, microphones and the like.

The present system is merely one type of system for practicing the present invention and is merely representative. It will soon be apparent to those skilled in the art that many system types and settings are suitable for use in conjunction with the present invention. In one preferred embodiment, the computer system 210 is a Pentium.^TMA class computer, Microsoft's Windows^TM Includes those running NT or XP. However, the system is readily adapted by those skilled in the art to other operating systems such as open source systems and architectures without leaving the scope of the invention. As mentioned above, the mouse 270 can have one or more buttons, such as the button 280. Cabinet 240 houses familiar computer components such as disk drives, processors, storage devices and more. Storage devices include, but are not limited to, disk drives, magnetic tapes, semiconductor memories, bubble memories, and the like. The cabinet 240 is like an input / output (I / O) interface card for connecting a computer system to the computer system 210, as well as external devices, external storage, other computers, and other peripherals described below. Can include additional hardware.

FIG. 1D is a more detailed view of the hardware elements of the computer system of FIG. 1C according to an embodiment of the present invention. This figure is just an example and the scope of the claims here should not be overly limited. Those skilled in the art will understand many improvements, alternatives and variants. As shown, the basic subsystem is contained within computer system 210. In certain embodiments, the subsystems are interconnected via system bus 275. Additional subsystems such as printer 274, keyboard 278, fixed disc 279, monitor 276 connected to display adapter 282, and more are shown. Peripherals and input / output (I / O) devices are connected to the I / O controller 271, but are connected to the computer system by any number of technically known means, such as serial port 277. be able to. For example, serial port 277 can be used to connect a computer system to modem 281, which connects to each other a wide area network such as the Internet, mouse input devices, or scanners. By interconnecting via the system bus, the central processor 273 can communicate with each subsystem and controls the execution of instructions from system memory 272 or fixed disk 279 as well as exchanging information between subsystems. can do. Other subsystems or interconnected devices can be readily implemented by those skilled in the art. System memory and fixed disks are examples of tangible media for storing computer programs, and other types of tangible media are floppy disks®, removable hard disks, CD-ROMs and bar codes. Includes optical storage media, semiconductor memory such as flash memory and read-only memory (ROM), and battery backup memory.

Although the above has been shown in terms of specific hardware characteristics, it will be understood that there can be many variants, alternatives and improvements. For example, the characteristics of any hardware can be further summarized or even separated. Features can also be implemented, in part, through software or a combination of hardware and software. Hardware and software can be further integrated or less integrated, depending on the application. Although performed by using a combination of hardware and / or software elements, further details of the functionality of the present invention can be outlined below with reference to the figures.

2A to 2D are a series of images obtained using an embodiment of the present invention. To characterize the system performance, calibration swatches were placed in the system described above and imaged using a variety of methodologies. In the example illustrated in FIG. 2, the swatch was a replica of a 2160 line / mm waffle-pattern diffraction grating. The distance between the sample lines was 0.462 μm. This plaid becomes first visible at a magnification of 2500x.

FIG. 2A is an image obtained using the electrons emitted via thermionic emission from the electron gun. As is known to those skilled in the art, conventional electron guns used in TEMs emit thermionic electrons that are accelerated away from the cathode and produce a flow of electrons focused on the beam directed towards the sample. Use. In Figure 2A, the voltage between the cathode and the anode was 120 kV, and the magnification of the imaging system was 4400 times. The scale marker shows 0.5 μm, which is the same as the distance between approximately adjacent lines of 0.463 μm.

FIG. 2B is an image obtained using electrons emitted via the photoelectric effect from the same cathode used to generate the image of FIG. 2A. As described above , using the embodiments of the present invention, a row of lattice pulses is guided onto the cathode to generate a row of electron pulses that move along the imaging path. By operating the microscope at the same voltage of 120 kV, the flow of electron pulses encounters a sample with some of the electron pulses passing through the sample, resulting in the image shown in Figure 2B. Therefore, by using the method and system according to the embodiment of the present invention, it is possible to obtain a static sample image.

For calibration purposes, the background "image" was obtained by turning off the cathode (ie, no thermionic emission) and blocking the femtosecond pulse before entering chamber 130. These "images" consist of an opaque background composed of readout noise, that the image shown in Figure 2B is the result of a photoelectron effect, and that the generation of electrons by the thermionic emission process can be ignored. It was to show what to show. Thermoelectrons may be generated by laser heating of the cathode and / or as a result of resistance overheating of the cathode, but calibration measurements have eliminated these possibilities.

2C and 2D are images obtained using thermionic emission sources and electron pulses, respectively. Scale marker 292 indicates a distance of 100 nm, about 1/5 between adjacent lines. The movement of the sample between measurements is observed from the image.

FIG. 3 is an image obtained by using an electron pulse according to an embodiment of the present invention. The object shown is graphitized carbon on a porous carbon grid. The magnification of the image shown is 110,000 times and the scale bar 310 is 20 nm. The calibration "image" was obtained by blocking the femtosecond pulse before entering the chamber. The result is an opaque background that is calibrated from readout noise.

4A to 4C are images obtained by using the diffraction operation mode according to an embodiment of the present invention. To obtain the image shown in the figure, the intermediate lens (not shown in FIG. 1A) was adjusted to select the posterior focal plane of the objective lens as its object. Diffraction patterns were collected at 120 kV in both thermionic emission and electron pulse modes for polycrystalline aluminum and single crystal gold samples. Figure 4A shows the 5 nm obtained by using thermionic emission from a polycrystalline aluminum sample.^-1It is a diffraction pattern of the scale 410 of. Figure 4B shows a commentary pattern of the same scale obtained using a sequence of ultrafast electron pulses on the same polycrystalline aluminum. Similar diffraction patterns were collected by using thermionic emission (Fig. 4C) and by using a sequence of ultrafast electron pulses with a single crystal gold sample (Fig. 4D). The diffraction patterns shown may be indexed to provide atomic plane spacing and symmetry, depending on the embodiment.

Those skilled in the art will appreciate that the embodiments of the present invention are not limited to imaging applications, but may also include diffraction and crystallographic applications. Optically initiated diffraction experiments are provided by the examples of the present invention, as described with reference to some of the figures below, but are not limited to this particular application. .. Therefore, it will be understood that the examples of the present invention incorporate imaging and diffraction experiments using electron pulses. In addition, imaging and diffraction experiments in which the sample is optically initiated or spectroscopically activated are also incorporated into the examples of the present invention. Of course, there can be other variants, improvements and alternatives.

FIG. 5 is an image of a biological sample obtained using an embodiment of the present invention. In FIG. 5, positively-stained (uranyl acetate) biological cells embedded in resin, especially the rat intestine, were imaged using the system shown in FIG. 1A. Samples were prepared for this example using conventional positive staining methods, but this is not required in the present invention. Figure 5A was obtained using an electron beam generated using thermionic emission. Figure 5B was obtained using a row of ultrafast electron pulses. The image shown in Figure 5B was obtained in just a few seconds and used a femtosecond electron pulse with a power outage usage of about 1 electron per pulse, but not available with a thermionic emission source. Provides a decomposed image.

The ultrafast temporal resolution provided by the ultrafast electron microscope (UEM) according to the examples of the present invention has unique results. Due to the image shown in FIG. 5B, the random energy is limited, because the strobe-based method provided by the embodiments of the present invention causes the atoms to be mostly fixed and frozen. Because. Therefore, studies of intact biological samples are made possible by the examples of the present invention. Using the methods and systems described herein, it is characterized by a cryo-electron microscope (millisecond order resolution) for studying polymer structure, assembly, and mechanics with ultrafast (regime) time resolution. However, the resolution can be extended by using (depending on the freezing / thawing rate at that time). The low electron count of each ultrafast pulse, along with the established cryofixation method, provides a huge advance in limiting the damage from electron irradiation discussed earlier.

For samples with biological structure recovery longer than 12.5 ns, pulse pickers such as Pulse-Picker 9200, available from Coherent, Inc. in Santa Clara, California, are suitable for such recovery. It may be used to select a pulse from a row by velocity. In addition, as shown in FIGS. 2, 4A-4D, 5, the embodiments of the present invention use some conventional TEM operating modes, or either images or diffraction patterns in UEM mode. Provide methods and systems for obtaining alternatives. Therefore, with minimal system modification and training, the embodiments of the present invention provide many benefits.

Referring again to the optical path 115 of FIG. 1A, the second portion of the optical pulse generated by the laser 110 is connected to the optical parameter oscillator (OPO) 160. The OPO160 parametrically oscillates two long wavelength grids from a single short wavelength photon. Generation) provides adjustable femtosecond pulses in the infrared region from about 1.1 μm to about 2.25 μm. In addition, doubling the frequency of the infrared pulse generated by the OPO extends access to the visible region of the spectrum. In some embodiments, the OPO enhances the versatility of the ultrafast titanium sapphire laser by extending its output to the visible and infrared regions of the spectrum. In some embodiments of the invention, OPO160 is used to regulate photon beams for spectroscopic applications. For example, in some spectroscopic applications, the frequency associated with the pump light, for example used to initiate a chemical reaction within the sample, is selected to maximize the interaction between the pump light and the sample. To. Therefore, in this special application, OPO is used to adjust the frequency of the photon beam in path 164 as desired. The spectroscopic applications available through the examples of the present invention are not limited to chemical reactions and may include absorptiometry, electron energy loss spectroscopy (EELS), and other applications.

The optical delay stage 162 is supplied into the change-initiating path 164 to introduce a predetermined delay in the optical path of the optical pulse propagating along the path 164. One of ordinary skill in the art will understand the technique of introducing and controlling an optical delay stage as illustrated in Figure 1A. In some embodiments, the optical delay stage 162 was adapted so that the optical pulse in the change-initiating path 164 and the electronic pulse in the electronic imaging path 148 reach sample 150 simultaneously in time and space. Used to determine "zero time". In other embodiments, the optical delay is either positive (the optical pulse is behind the selected time period for the electron pulse) or negative (the optical pulse is ahead of the selected time period for the electron pulse). You can choose to introduce. Those skilled in the art will understand many variants, improvements and alternatives. The optically delayed pulse enters chamber 130 through window 166, is reflected by mirror 168, and is directed towards sample 150. In some embodiments, the coaxial illuminator (coaxial) An imaging system 170 is provided that includes an illuminator) 172 and a CCD camera 174 for monitoring the sample using light that is drawn down and scattered from the surface of the sample 150. As will be appreciated by those skilled in the art, many modifications, improvements and alternatives are available for the imaging system 170. In some embodiments, the window 166 and the mirror 168 are identical to the window 132 and the mirror 144, but this is not required in the present invention.

In the above discussion, the optical delay stage within the optical path 164 has been described, but this is not required in the present invention. Depending on the embodiment, the light delay stage may be combined with an electron generation path 118 that delays the generation of the electron beam with respect to the light beam in the change-inducing path 164. As mentioned above, the delay of the electron generation path may be positive or negative. This is because the stage is generally set to one end for negative delays, the other end for positive delays, and the middle part of the stage for zero time delays.

In an embodiment of the invention utilizing an optical pulse in a change inducing path 164 to initialize changes in a sample, the time coordinates for the reaction are generally between the optical start pulse and the electron pulse. Established on the basis of reference to relative time delays. This reference point has a common zero time (t)₀), The zero time is the time when both pulses cross the sample at the same time. One approach to determining the zero time is based on careful measurement of photon and electron beam paths. This technique can typically narrow the window at zero time to within 100ps.

Another approach utilized in some embodiments of the present invention is the crossed-beam geometry of an actual diffraction experiment that determines the zero time via the "lensing effect". Is to use. For example, CF₃During the study of the dissociation reaction of I, we observed dramatic changes in the undiffracted electron beam image in the presence of the excitation laser. The beam spots strengthened along one axis, with a corresponding slight increase in overall width. This effect occurred when both the excitation laser and the molecular beam were present. The stripped strip is parallel to the laser axis and be considered up or down in the beam spot by adjusting the vertical tilt of the excitation laser entrance lens. I was able to. Defocusing the laser reduced the intensity of the stripes. We refer to this phenomenon as photoionization-induced lensing. This effect is similar to plasma lensing, which is a technique in which a high-energy charged beam in a particle accelerator is focused by passing through a plasma field.

In yet another embodiment of the invention, an in-situ synchronization method is used with an energy filter tuned in the region corresponding to the resonating plasmon loss. This is because the electron-electron scattering constants are on the order of 2-3 femtoseconds and the position of the plasmon peak is a natural marker of experimental synchronization. In particular, the position of the peak in the energy loss spectrum corresponds to the plasmon frequency and is proportional to the free carriers in the sample. Plasmon resonance is the strongest feature in the energy loss spectrum and has an intensity 2-3% higher than the zero loss peak. Using this same technique, measurements of the electron pulse width can be obtained.

An example of an example application of the present invention is the imaging of a non-concerted elimination reaction of dihaloethanes. FIG. 6 is a simplified timing diagram illustrating the use of the method according to the present invention. FIG. 6 illustrates the method of the invention using different electron pulse sequences for isolating the structures of reactants, transitional intermediates and products. As illustrated, the particular reaction studied is to eliminate two elemental atoms from the reactants, resulting in a product.

Reactants, such as diiodoethane, are shown at time-t and t in FIG. 6A.₀Illustrated in. As illustrated at time -t, the electron pulse 610 was timed to arrive at the sample before the light start pulse 620. By utilizing the delay stage illustrated in FIG. 1A, the delay between the start pulse and the electron pulse is modified so that images can be collected at different reaction times. Time t₀In, the light initiation pulse 620 and the probe pulse 612 simultaneously affect the sample containing diiodoethane. In the embodiment illustrated in FIG. 6, the starting pulse is an optical pulse, which initiates a non-cooperative erasing reaction of diiodoethane. Of course, the use of OPO160 provides the adjustment of the light initiation pulse as required, for example, chemical reactions, spectroscopic analysis, etc.

Figure 6B shows the time after the light start pulse affected the sample.₁It is a snapshot of the erasure reaction in. Time t₁In, as illustrated, diiodoethane eliminates the first iodine atom. As time progresses, time t as illustrated in Figure 6C₂The second iodine atom is erased at. C₂F₄The molecular structure of the I intermediate was determined from the frame referencing and the diffraction-difference curve ΔsM (t; 5ps; s). Bridge C₂F₄I structure and classic C₂F₄The I structure was considered from the diffraction data. The theoretical curve of the classical structure reproduces the experimental data very well, but the fit provided by the theoretical bridge structure is very poor. Therefore, we are C₂F₄We conclude that the structure of the I-radical intermediate is, in fact, classical in nature, that is, the iodine atom does not bridge the two carbons.

In addition, we are C₂F₄The CI and CC distances of the I intermediates are longer and shorter than the distances in the reactants, respectively, while the radical site (-CF'₂) Is the internuclear distance of C-F'-CF₂It was decided that it was shorter than the internuclear distance of the I site. This result is C at the time of transition₂F₄From the results of the structure of I, the increased CC and decreased CI binding orders were elucidated. In addition, the angles of CCF'and F'CF'are greater than the angles of the corresponding reactants (~ 9 ° and ~ 12 °, respectively). This is C₂F₄It is suggested that the radical center of the I intermediate mitigates the loss of the first iodine atom that occurs next. We believe that the structure and mechanics reported in this reaction are important in describing the retention of stereochemistry in the field of such reactions. Moreover, we believe this is the first example of elucidating such a complex structure in transition.

In FIGS. 6A-6C, the time scale is not drawn on the scale, but the time scale is provided merely to illustrate a series of time-resolved measurements. In the non-consonant erasure reaction of dihaloetan, time t₁Is about 250fs and time t₂Is 26 ± 7ps. Of course, there can be other variants, improvements and alternatives. Some methods according to the embodiments of the present invention are described herein, and in particular more described below.

A method of imaging an object according to an embodiment of the present invention may be outlined as follows: 1. Prepare a transmission electron microscope consisting of a laser source, a cathode, and an electron lens assembly. 2. Form a row of optical pulses. Each optical pulse is characterized by a full width at half maximum (FWHM) pulse length and a duration of less than 100 fs. 3. Prepare a sample for imaging (eg, chemical, biological, physical) placed on the stage assembly 4. Generate a row of electron pulses by affecting the cathode with the relevant row of optical pulses. Each electron pulse is characterized by a FWHM pulse length of less than 1 ps. 5. Guide the electron pulse train towards the sample, at least using the electronic lens assembly 6. Use a detector to capture part of the electron pulse train 7. Extract information related to the sample image 8. Process the information related to the sample image 9. Output a visual representation of the sample image, at least with the processed information 10. Perform other steps as requested

The procedure of the steps described above provides a method according to an embodiment of the present invention. As shown, the method uses a combination of steps that includes a method of imaging the characteristics of one or more samples using one or more electron pulses with a short predetermined duration according to a particular embodiment. Many other methods and systems are also included. Of course, other variants are also provided in which steps are added, one or more steps are removed, and one or more steps are provided in different sequences, without departing from the claims described herein. To. In addition, various methods can be implemented by using computer code, code in software, firmware, hardware, or any combination thereof. Other variants, improvements, and alternatives can exist, depending on the embodiment. Further details of the method can be found herein, and more particularly below.

FIG. 7 is a simplified flow diagram 700 of an imaging method according to an embodiment of the present invention. This figure is merely an example and should not overly narrow the scope of the claims described herein. Those skilled in the art will understand many variants, improvements and alternatives.

Although the methods described above have been exemplified for specific software and / or hardware features, it will be appreciated that there can be many variants, alternatives, and improvements. For example, the features of any hardware can be further summarized and even separated. This feature can also be implemented in part by software or hardware in collaboration with software. Depending on the application, hardware and software can be more integrated or less integrated. Of course, those skilled in the art will understand other improvements, variants and alternatives.

The method of imaging an object according to an alternative embodiment of the present invention may be outlined as follows: 1. Prepare the characteristics of the sample to be imaged (for example, 100 nanometers or less) 2. Place the sample on the stage assembly 3. Maintain the sample on the stage assembly in a vacuum environment 4. Derivation of one or more electron pulses (eg, 1 to about 1000 electrons per pulse) towards the characteristics of the sample 5. Use a detector to capture a portion of one or more electron pulses associated with the characteristics of the sample. 6. Transfer information related to the portion of one or more electron pulses associated with the image of the feature of the sample from the detector to the processing device. 7. The processing device receives information related to the portion of one or more electronic pulses 8. Process information related to parts of one or more electron pulses 9. Output a visual image associated with the sample feature, using at least the information associated with some of the one or more electron pulses associated with the sample feature image. 10. Perform other steps as requested

The procedure of the steps described above provides a method according to an embodiment of the present invention. As shown, the method uses one or more electron pulses directed to a feature and some of the electrons captured by a detector according to a particular embodiment to image an image of the feature of the sample. It uses a combination of steps that includes a method of capture. Many other methods and systems are also included. Of course, other alternatives in which steps are added, one or more steps are deleted, or one or more steps are provided in different sequences are also provided without departing from the claims set forth herein. In addition, various methods can be implemented using computer code, code in software, firmware, hardware, and combinations thereof. Other variants, improvements, and alternatives can exist, depending on the embodiment. Further details of the method can be found herein, more particularly below.

FIG. 8 is a simplified flow diagram 800 of an alternative imaging method according to an embodiment of the present invention. This figure is merely an example, and the scope of the claims described herein should not be overly limited. Those skilled in the art will understand many variants, improvements and alternatives.

Although the methods described above are exemplary for specific software and / or hardware features, it will be appreciated that there can be many variants, alternatives, and improvements. For example, the features of any hardware can be further summarized and even separated. This feature can be implemented in part by software or hardware in collaboration with software. Depending on the application, hardware and software can be further integrated or less integrated. Of course, those skilled in the art will understand many variants, improvements and alternatives.

In a further embodiment, the invention provides a method of obtaining time-resolved images using an electron microscope. Such a method may be outlined as follows: 1. Prepare the characteristics of the sample to be imaged for temporal characteristics 2. Place the sample on the stage assembly of the electron microscope 3. Place the sample on the state assembly in a vacuum environment 4. Guide one or more first electron pulses, each with 10 to 1000 electrons, towards the characteristics of the sample 5. During the first part of time, a detector is used to capture the first part of one or more first electron pulses. That part is associated with the first image of sample features during the first part of time 6. From the detector to the processing device, the first information related to the first part of one or more first electron pulses related to the first image of the sample features during the first part of time. Forward 7. Guide one or more second electron pulses, each with 10 to 1000 electrons, towards the characteristics of the sample 8. During the second part of time, a detector is used to capture the second part of one or more second electron pulses. That part is associated with a second image of sample features during the second part of time 9. Transfer the second information related to the second part of one or more second electron pulses related to the second image of the sample features during the second part of time from the detector to the processing device. 10. Process the first information using a processing device 11. Process the second information using a processing device 12. Output a first visual image related to the features of the first part of time 13. Output a second visual image related to the features of the second part of time 14. Perform other steps as requested

The procedure of the steps described above provides a method according to an embodiment of the present invention. As shown, the method uses a combination of steps, including a method of capturing images of a large number of features in different time domains, according to a particular embodiment. According to a particular example, the combination of one or more ultrafast electron pulses leads to determine the temporal variation of sample characteristics. Of course, other alternatives in which steps are added, one or more steps are deleted, or one or more steps are provided in different sequences are also provided without departing from the claims set forth herein. In addition, various methods can be implemented using computer code, code in software, firmware, hardware, and combinations thereof. Depending on the embodiment, there may be other modifications, improvements, and alternatives. Further details of the method can be found herein, more particularly below.

FIG. 9A is a simplified flow diagram of an alternative imaging method according to an embodiment of the present invention. This figure is merely an example, and the scope of the claims described herein should not be overly limited. Those skilled in the art will understand many variants, improvements and alternatives.

Although the methods described above are exemplary for specific software and / or hardware features, it will be appreciated that there can be many variants, alternatives, and improvements. For example, the features of any hardware can be further summarized and even separated. This feature can be implemented in part by software or hardware in collaboration with software. Depending on the application, hardware and software can be further integrated or less integrated. Of course, those skilled in the art will understand many variants, improvements and alternatives.

In a further alternative special embodiment, a method for capturing information from one or more samples using electron beam pulses is briefly described as follows. 1. Prepare the characteristics of the sample to be imaged 2. Place the sample on the stage assembly 3. Place the sample on the stage assembly in a vacuum environment 4. Irradiate the cathode with one or more pulses of electromagnetic radiation 5. Guide one or more electron pulses, each with about 10 to about 1000 electrons, towards the characteristics of the sample derived from electromagnetic radiation 6. Use a detector to capture a portion of one or more electron pulses related to sample characterization. 7. Transfer the information associated with the portion of one or more electron pulses related to the characterization of the sample from the detector to the processing device. 8. Process the information 9. Output one or more indicators related to the sample features, using at least the information associated with some of the one or more electron pulses associated with the image of the sample features. 10. Perform other steps as requested

The steps in the above steps provide a method according to an embodiment of the present invention. As shown, the method uses a detector such as a CCD array and uses a combination of steps that includes a method of identifying the nature of a sample feature using one or more electron pulses. Depending on the examples, the method can be used for imaging, diffraction, and other analytical techniques. Many other methods and systems are also included. Of course, other alternatives in which steps are added, one or more steps are deleted, or one or more steps are provided in different sequences are also provided without departing from the claims set forth herein. In addition, various methods can be implemented using computer code, code in software, firmware, hardware, and combinations thereof. Other variants, improvements, and alternatives can exist, depending on the embodiment. Further details of the method can be found herein, more particularly below.

In some embodiments of the invention, methods are provided for determining the temporal characteristics of an object's 1st and subsequent features using an electron microscope assembly. By way of example only, a sample may be imaged at various times during the transition period between multiple states. FIG. 9B is a simplified timing diagram illustrating a pulse train according to an embodiment of the present invention. During period 920, a large number of electron pulses 922 are supplied as a pulse train. In a special embodiment, the time width of each pulse is 100 fs and the delay between adjacent pulses is 12.5 ns. In addition, each pulse is relative to a reference time, eg, the time when the separately provided start pulses arrive at the sample. In one embodiment, sensors (sensing elements), such as a CCD camera, are operating for a period of 920 to obtain an image as a result of the interaction of the electrons in the pulse train with the sample. As an example, protein denaturation is imaged by using a system according to an embodiment of the present invention. Unfolding process process) is operated by pump light pulse. As mentioned above, the timing between the pump and the electron pulse is chosen to provide a collection of images at one time during the deployment process. As an example, in one embodiment, the pulse 922 lags the pump pulse by 100 ps. During the time between adjacent pulses, for example, 12.5 ns, the protein returns to steady-state conditions. The unfolding process is repeated when initiated by the next pump pulse during period 920, with additional electron pulses interacting with the sample after the same delay time. In an embodiment where the period 920 is on the order of seconds, millions of electron pulses with the same delay time interact with the sample to form the first set of images. In some embodiments, the period 920 is on the order of seconds. Those skilled in the art will appreciate that there are many modifications, improvements and alternatives.

The second period 930 is illustrated in Figure 9B. In another embodiment, the delay time between the start pulse and pulse 932 is the second delay time, for example 200 ps. In the embodiment illustrated in FIG. 9B, the above process is repeated to obtain an image of the unfolding process at a second time during the unfolding process, eg 200ps. As shown, an additional period of 940 is supplied in some examples to produce a series of time-resolved images in the combination of the samples. There are n additional periods in some examples. n is a predetermined number.

FIG. 9C is a simplified flowchart illustrating a set of images according to an embodiment of the present invention. In step 950, a partial image of the sample is obtained with the sample in state 1. In step 955, a further image of some of the sample is obtained with the sample in state 2. In step 960, an image of a portion of the sample added n times is obtained with the sample in the state of being added n times. By using the methods and systems according to the present invention, the ultrafast electron pulses used in obtaining images are characterized by low electron capacitance. These electron pulses reduce the spread of the pulse both in time and space, providing low electron fluences. This is beneficial in minimizing damage during imaging of biological samples. In the embodiment of the present invention, the number of pulses included in each period is a predetermined number. In general, the choice of pulse number balances the number of electrons preferred for imaging, damage to the sample, the time required to collect the image, and so on.

FIG. 10 is a simplified flow diagram 1000 of a further alternative imaging method according to an embodiment of the present invention. This figure is merely an example and should not overly narrow the scope of the claims described herein. Those skilled in the art will understand many variants, improvements and alternatives.

Although the methods described above are exemplary for specific software and / or hardware features, it will be appreciated that there can be many variants, alternatives, and improvements. For example, the features of any hardware can be further summarized and even separated. This feature can be implemented in part by software or hardware in collaboration with software. Depending on the application, hardware and software can be further integrated or less integrated. Of course, those skilled in the art will understand many variants, improvements and alternatives.

Although some figures are provided for the particular embodiments, those skilled in the art will appreciate many variations, alternatives and improvements. Of course, there can be many variations without departing from the claims set forth herein.

To prove the principles and behavior of the present invention, we have conducted experiments for several uses of the examples of the present invention. The present invention used the current ultrafast electron microscopy system described above. That is, according to a particular embodiment, the ultrafast system includes various parameters such as one or more ultrafast optical pulses to generate one or more ultrafast electron pulses. These parameters are used, but there can be many other variants, improvements, and alternatives.

In a particular example, we studied the molecular assembly on the surface of the sea on a nanometer scale. This is important for chemical and biological phenomena using current methods and systems. With respect to water, from non-crystalline to crystalline, directional molecular structures and possible different structures make, until our discovery, a lesser understanding of the collective assembly of interfaces on the mesoscopic scale. It is supposed to be. Structurally, the nature of water on a substrate is determined by the force of orientation at the interface and the net (net) charge density, which defines the hydrophilic or hydrophobic nature of the substrate. However, the transformation from aligned structures to messy structures and their coexistence decisively depend on the timescale of atomic movement locally and at long distances. Therefore, it is desirable to elucidate the nature of these structures and the timescale of their equilibrium.

In an experiment made using an embodiment of the invention, we make a direct determination of the structure of the water at the interface with atomic-scale resolution, an ultrafast infrared (IR) laser-initiated temperature rise ( It was performed using the dynamics and diffraction that received the temperature jump). As shown in FIG. 11, the interfacial water is formed in a controlled ultra high vacuum (UHV) environment on a hydrophilic surface (silicon, chlorine termination). The atomic-scale spatial, temporal, and energy resolutions provided by the embodiments of the present invention monitor the evolution of non-equilibrium structures, create their aligned or messy properties, and break long-range bonds and A new structural form of time scale has been determined. As discussed below, we confirmed the water at the structured or aligned interface from Bragg diffraction and the layered crystalline structure from the Debeischeler ring. The temporal evolution of interfacial water and layered ice after temperature rise was studied by submonolayer sensitivity. We compared these results with those obtained from hydrophobic surfaces such as hydrogen-terminated silicon or silver substrates.

FIG. 11 shows the structure of water in a hydrophilic interface. As shown, the chlorine termination on the Si (111) substrate forms a hydrophilic layer that orients the water bilayer. The close-packing distance (4.43 Å) between oxygen atoms in the bottom layer of water is similar to the distance (4.50 Å) between the top of the chlorine layer and the interstitial position, a silicon substrate. Specific bilayer orientations (± 30 °) with respect to. This aligned stacking continues from 3 to 4 bilayers until disorientation occurs, resulting in crystallite islands, forming a layered structure. As shown, the size of the atom does not exceed the van der Waals radius (not to scale for).

Spectroscopic techniques such as internal reflection and non-linear (eg, second harmonic generation and sum frequency generation (SFG)) optics are sensitive to changes in surface molecules. For example, the presence of polar ordering of the ice film on the Pt (111) surface is indicated by having a decay length of 30 monolayers, D on the CO / Pt (111) surface.₂The transitional SFG reaction from the O ice crystals showed the presence of non-desorption-free melting and recrystallization. Here, the structure was determined using diffraction with ultrafast temporal resolution, providing a spatial resolution of 0.01 Å. We can monitor changes in the internuclear distances of selective hydrogen bond networks, such as OH ... O and O ... O, which are 2.75 Å and 4.5 Å, respectively. .. Unlike previous studies on supramolecular surface reconstruction and subnanosecond melting, we can scrutinize the structural dynamics of supramolecular supramolecular on the surface, cleaning the diffraction of interfacial water from substrate diffraction. It can be observed to separate.

Using the examples of the present invention, water was prepared on a single crystal Si (111) surface terminated with chlorine atoms to create a hydrophilic interface. The crystals were mounted on an ultra-high vacuum (UHV) environment with an angular precision of 0.005 ° on a goriometer. The crystals can be cooled to a temperature of 100 K or other suitable temperature. Layer preparation on the surface generally requires low-energy electron diffraction and substrate characterization by Aussie spectroscopy, as well as in-situ monitoring of layer growth by reflective high-energy electron diffraction. In our case, the electron bundle (~ 1pA / mm)²) Is relatively small, which reduces damage and charge to the molecular layer. The optical pulse generated by a femtosecond laser (typically 120 femtoseconds at a repetition rate of ~ 1 mJ, 800 nm, 1 kHz) is guided to the scattering chamber at a 30 ° angle and onto the substrate to initiate a temperature rise. It was focused.

The weaker beam is separated from the photon pulse beam, the frequency is tripled (at ~ 10nJ, 266nm) in certain embodiments, and after a correctable time delay to generate an electron pulse via the photoelectron effect. Focused on the back-illuminated silver photocathode. The electron pulse in this example has a de Broglie wavelength λ = 0.07 Å at 30 keV. A series of deflectors and apertures are θ for the incident_iA &lt;1 ° surface, which is typically suitable for obtaining high sensitivity with respect to nanometer-scale surface assemblies, was used to guide towards this. The arrival of an electron pulse is controlled to define a series of images recorded by a set of image-intensified charge-coupled device (CCD) cameras with low noise capable of detecting a single electron. Was done.

We first characterized the diffraction of the Si substrate prior to dosing with water. By rotating the crystal, we θ_iWe obtained the dependence of rocking curves and diffraction patterns on. These diffraction patterns represent the intersection between the Ewald's sphere and the reciprocal lattice as defined by the substrate. Therefore, the momentum movement coordinate (s) is defined by s = 4π / λ · sin (θ / 2), where θ is the scattering angle, but the event angle θ._iAny given diffraction image in can be precisely set, and the in-situ zero-of-time was also determined by using the temperature rise on the substrate surface. Diffraction images showed a transition from the Bragg point of the substrate to the new points and rings characteristic of water, as the interfacial ice formed on the surface at 110 K. To separately image the evolution of water structure after substrate temperature rise, we used different sequences of electron pulses. This difference in diffraction method allows only one transition structure to be involved. Because the reference time (t_ref) Can be selected before or after the arrival of the start pulse, or different times during the change.

FIG. 12 shows a diffracted image obtained using an ultrashort electron pulse but not using a start laser pulse (t at negative time)._refIs the same as). The process of in-situ growth of aligned ice is shown through the deposition of water on a cold (110K) silicon substrate. Adsorption of water on the substrate causes the disappearance of 111 Bragg points of silicon (see, eg, Figure 12A) and the composition of 111 Bragg points of crystalline ice with the diffractive ring of non-crystalline ice (see, eg, Figure 12B). Seen from. Annealing promotes the formation of long-range crystalline structures (see, for example, Figures 12C and D), as shown by the increased brightness of the points and the sharpening of the rings. Its structure is stable in rings, dots and fringes with little change in diffraction (see, for example, Figures 12E and F). Figures 12G and 12I show experimentally observed diffraction and simulation of points from orientated cube (Ic) and hexagonal (Ih) structures on a substrate with a thickness of nanometers. is there. FIG. 12J shows that the experimental diffraction ring when averaging radially in the s space creates a one-dimensional diffraction intensity curve. Figures 12K and L show the theoretical diffraction intensity curve, along with peaks identified as Bragg reflections. The clear distinction of different orderings in annealing and the early appearance of points (not rings) suggest that dissimilar layers are on the surface, along with crystals layered by water at the aligned interface. To do. In addition, the diffractive points are sharp, indicating that the water at the interface has a well-defined orientation; in contrast, the diffractive ring is circular, which coincides with perfectly randomly oriented crystals. Shown.

As shown, the diffraction pattern consists of rings, dots and stripes. The disappearance of substrate diffraction and the appearance of surface water diffraction as monolayers of ice after annealing are evident. The observed Bragg points indicate that the water molecules are oriented by the substrate on the order of long distances. The rings coincide with points in the reciprocal lattice space (s space), and these rings show the appearance of crystallite structures: that is, aligned water islands but messy in orientation. The ring is sharp enough to define crystallites that are non-crystalline. The structural evolution of water at the interface as a function of temperature was calibrated in near equilibrium conditions (temperature ramp, ~ 2 ° / min). Crystallization of uncrystallized ice that we deposited early on the nanometer scale begins near 140K and is the highest on the order of long distances. It was found that saturation was reached at ~ 150K at degree). Sublimation of the water layer occurs at 157 ± 1K. From Bragg points and rings, we can determine the structure by comparing these diffracted images with the diffracted images predicted by the contrast of the ice grid.

The intensity of the diffractive ring when plotted against s gives the corresponding Bragg reflection peak. The theoretical diffraction patterns of cubes and hexagonal structures are shown in Figures 2K and L. These plots were obtained by adding the phases of 3D (3D) crystals (cells of 5nm dimension in each direction) and by averaging all orientations. The peaks illustrated in Figure 12J closely match the reflections of the cube's ice from planes such as 111, 220, 311 (see, eg, Figure 12K), which is the dominant structure (for comparison, for comparison). Hexagonal ice diffraction (see, for example, Figure 12L). From the value of s in Fig. 12J, we set the distance between the planes to 3.80 ± 0.23 Å for the (111) plane, 2.27 ± 0.15 Å for the (220) plane, and 1.93 ± 0.07 for the (311) plane, respectively. It was decided to be Å. This is consistent with the results of powder diffraction of the cubic structure. Uncertainty is dominated by the width of the observed diffraction peaks.

Surface-oriented water has a well-defined crystalline structure (ie, epitaxially grown from the substrate), which is associated with sharp Bragg points. We theoretically relative to the position of the Bragg point by adding the phases of the water at the interface on the order of long distances (10 nm, 1.5 nm thick layers for every 10 nm width), as illustrated in Figure 12H. Reproduced with strength. In hydrophilic substrates, we find that the close-packed distance between oxygen atoms in the bottom layer of water (4.5 Å) is the distance between the on-top of the chlorine layer and the interstitial position (4.43). I found it similar to Å). This allows for long distance packing of the water bilayer on the surface, leading to a unique 30 ° rotation with respect to the substrate layer. Therefore, a two-dimensional (2D) surface unit cell of water can be described as a superlattice as illustrated. This arrangement was derived from the symmetry and position of the Bragg point of the substrate and the symmetry and position of the water. Examination of the Bragg points on ice confirms two domains within the satellites of the main Bragg peak (ie 111); one set is formed by 022, 111, 311; the other The set of is formed by 202, 111, 131 (see Figure 12H). Water probably overlaps with three chlorine atoms sp³It interacts with the substrate at two positions, either through oxygen at interstitial positions with hybrid orbitals or through hydrogen that sits on top of the chlorine atom.

From the diffraction results, we found that water was constructed primarily as a cube on a hydrophilic surface (see the theory of cube orientation (Ic) and hexagonal orientation (Ih) and a comparison with the illustrated experiments), Pt (111). ) It was proved to be different from the structure (hexagonal) found on the substrate. Our theoretical modeling of the position of the 111-part rug point has set the space between layers to 3.66 ± 0.26 Å. This is in perfect agreement with the value obtained from the ring (3.80 ± 0.23 Å). The apparent brightness and width of the Bragg points are inherent reflections of the size of the interferences, from which we obtained nanometer-scale thickness. This thickness is also consistent with theory.

FIG. 13 shows the data collected in the experiments performed using the positional examples of the present invention. In FIGS. 13A and 13B, diffraction difference images at negative time (-30ps) and positive time (100ps) are illustrated. t_refIs -70ps in Figures 13C to H. ((C) -30ps, (D) 10ps, (E) 20ps, (F) 100ps, (G) 530ps, (H) 1130ps) Radially averaged diffraction difference intensity curves at some delay times Substrate energy fluence is 22 mJ / cm²The structural dynamics of the stratified crystallites are shown. Note the decrease (negative difference) and increase (positive difference) in the clear s value. FIG. 13I shows a diffraction difference image at 111 Bragg points. The vertical axis is s in the reciprocal lattice space, and the horizontal axis is the azimuth scattering angle.

Due to the dynamics of the system, we tracked diffraction as a function of time after temperature rise of the substrate, as shown in Figure 13. t_refWhen is a negative time (-70ps), the image at -30ps (see the case of -70ps in Figure 13A) does not show the diffraction difference intensity as expected. At positive times, as shown in Figures 13B and 13I, both Bragg points and rings appear, but with noticeable structural changes (note the displacement between rings). Different panels show evolution with a clear indication of the disappearance of "old" structures and the emergence of "new" structures. However, the behavior is similar in appearance to the behavior of "phase transition": in a short time (10ps (Fig. 13D) and 20ps (Fig. 13E)), we observed the phenomenon of old structure. On the other hand, in the middle time (Figs. 13F and 13G), a region of coexistence of messy water and crystalline water appeared. Over time (Fig. 13H), the system returned to its original structure, but there were some differences in bond length. In the isolated freezing and cooling experiment, we changed the temperature of the substrate by ramping near the thermodynamic equilibrium (near-thermodynamic), just below the sublimation temperature (157K), and also of ice. It should be noted that we have found that the structures match those obtained after being reconstructed over a long period of time. This behavior of crystals away from the surface (ring) is in contrast to the behavior of (point) structured crystal-like water on the surface. Figure 13I shows the evolution of one point showing the same tendency over time-decrease and reconstruction-but the mechanics are very different.

FIG. 14 shows the temporal evolution of gated diffraction in the 111 reflection region. As shown in FIG. 14, 111 diffraction points and ring reductions at an early time (100 ps) at some energy fluences are shown. In FIG. 14B, the new 111 diffraction points and rings are also shown at an early time. Note that the apparent delay of zero time is independently determined with an error of 3 ps. Corresponding changes over time are shown in Figures 14C and 14D.

Examining the rate of change at different temperatures, which is controlled by changes in the fluence of the heating pulse of the substrate, by which we test 111, as shown in Figure 14. Gating in the reflection region shows a decrease in old peaks (see Figures 14A and 14C) and an increase in corresponding new peaks (see Figures 14B and 14D). This behavior reflects the breakage of old bonds (due to melting) and the formation of new structures. Melting of layer crystals occurs within 5 ps of laser excitation on the surface of the substrate. In contrast, from the same data, gated images on 111 Bragg points have the same energy fluence (22 mJ / cm).²) Had a delay time of 36 ± 3 ps of water at the interface. Because water does not absorb light directly at 800 nm, the relatively fast reaction of layer crystals exhibits high efficiency of heating by non-diffusive vibrational couplings on this ultra-short timescale; if diffuse. For example, the layered ice should melt after the interfacial ice. As the fluence increases, the delay decreases in the water at the interface, but the time remains similar at 37 ± 5 ps and the decrease is constant. The results suggest the existence of a high-energy (friction) barrier of structured water caused by long-range orders of hydrophilic substrates and dipole orientation forces.

These observations were made at the highest temperature of the substrate (fluence, 42 mJ / cm).²), The water at the interface continues to lose long-range orders, and only when the maximum change arrives will the reconstruction illustrated in Figures 14A and 14B begin. However, in the vicinity of the largest change, a new structure begins to form in the region of coexistence, which follows the reconstruction (see Figures 14C and 14D). In long-term reconstruction, energy dissipation (cooling) occurs through redistribution and heat diffusion. In this type, from the solution of the thermal diffusion equation, we estimate the surface temperature to be ~ 150K at 1ns; the maximum change temperature is ~ 370K. It was found that thermal desorption was not important during the overall timescale of structural change. This is because, as shown in FIG. 14, we have observed that the diffractive rings and points recover to almost their original intensities from the invariance of the reference at negative time in all fluences. The lack of effective desorption, which is also seen in ice on the surface of CO / Pt, reflects the difference between the desorption temperature at most equilibrium and the desorption temperature far from equilibrium. .. In high fluence for the phenomenon of old structures and the generation of new structures (42 mJ / cm)²The appearance of regions in the stable period suggests the involvement of collective modes in reconstruction, as well as the coexistence of old and new structures, similar to phase transitions.

Figure 15 shows that the radial distribution function (RDF) of Ic is shown along with the internuclear distance density. Local distances at 2.75 Å (OH ... O) and 4.5 Å (O ... O) in diamond tetrahedral units are marked for data comparison (Figures 15B-E). The experimental differential RDF curve was obtained by performing a sinusoidal transformation from the corresponding differential intensity curve (see Figure 13). The change in distance density was apparent in the three positive times, while no change was observed in the negative time. The gray-white curve on the panel is the Ic curve, measured and super-imposed for comparison. Changes in RDF clearly indicate a decrease in old structures and the formation of new structures, but here we confirm the binding involved. In Figure 15F, the corresponding structural changes are -5, +10, and + 1130ps, as shown.

In supramolecular systems, as discussed here, local structures within a unit cell are added to the order of long distances, but can be experimented with by inverting the diffraction curve into real space (Fourier transform). .. Figures 15A to E show that such a obtained radial distribution function [f (r)] reveals the density of internuclear distances. In cubic ice, the second closest O ... O distance (4.50 Å) is associated with the diamond tetrahedral hydrogen bond OH ... O distance (2.75 Å). The temporal variation of the densities of these two distances therefore provides the dynamics of the reconstruction of the hydrogen bond network at the local molecular level. At negative time (-5ps, see Figure 15B), no change in density was observed, as expected. At 10 ps (Fig. 15C), a change in the OH ... O peak is not significant, but a decrease in the O ... O peak is observed. This decrease indicates network rupture (to non-crystalline) at 10 ps. At a delay of 150 ps (Fig. 15D), a significant but moved reduction coexists with the emergence of new distances. At the longest delay, 1130 ps (Fig. 15E), the original cube-like structure is restored, as evidenced by the reduction in diffraction difference, but the new structure due to the slow diffusion rate (ns to μs). Yes still slightly "hot". In such a structure, we determined the interplane distances to be 4.22 ± 0.37 Å (111 planes), 2.42 ± 0.20 Å (220 planes), and 1.97 ± 0.05 Å (311 planes). A structural diagram of local molecular changes is drawn in Figure 15F.

The water at the interface on the substrate of the hydrophilic surface has a characteristic structure and dynamics and is compared with the layer of water on the hydrophobic surface. The timescale of long-term failure of the interfacial layer (37ps) is on the order of a longer scale than the timescale of hydrogen bond failure in bulk liquid water, with local OH ... O and O from diffraction. ... O bond length is directly involved in the change. These results suggest that the timescale of energy flow in the aggregate water structure is shorter than the timescale of energy localization for the desorption of individual molecules. The maximum transient temperature is 370K; the equilibrium desorption temperature is 157K. In addition, the reconstruction time, including long-term orders, is decrystallization, a process that loses the O ... O correlation before the OH ... O correlation, but more than that time. long. Perhaps the timescale for losing hydrogen bond networks (37ps) is similar to the timescale reported for water at the interface near the surface of hydrophilic proteins (20-50ps), and the timescale for bulk water (700fs-1.5ps). ) Is not a coincidence. In another experiment, we also studied hydrophobic surfaces such as hydrogen-terminated substrates and silver-coated substrates. He discovered that the ordering of the interface changed to the distribution around the former (110) orientation and that it was absent for the latter.

Therefore, by using the examples of the present invention, it becomes possible to study the structure of nanometer-scale supramolecular, along with the structure of non-crystalline and crystallite solids, with unprecedented resolution and sensitivity. This demonstrates that by using the embodiments of the present invention, it can be used for various purposes, especially for interface and surface scrutiny with atomic resolution. Of course, these results are merely examples and should not overly limit the scope of the claims described herein. Those skilled in the art will appreciate many variants, improvements and alternatives.

In another experiment, we demonstrated the potential of methods and systems according to the present invention for the direct determination of the surface structural mechanics of solid crystals (GaAs) with impact femtosecond laser excitation. From changes in Bragg diffraction (movement, width, and intensity), we find that direct inversion of diffraction data causes atomic compression and expansion on a scale of -0.01 Å to + 0.02 Å, respectively, and that it is temporary. The fact that the temperature reaches its maximum value (1565K) in 7ps is shown in the accompanying discussion. The onset of structural change lags behind the rise in temperature, demonstrating the evolution of non-equilibrium structures. The results of these structural mechanics are compared with the results of non-thermal femtosecond photo-examination, and the agreement with the temperature reaction due to the fluence dependence of the dielectric function is impressive. The success of direct observation of the structural mechanics of a surface (monolayer) with connected ultrafast temporal resolution and atomic-scale spatial resolution promises many new uses for the embodiments of the present invention.

GaAs is an ideal system for demonstrating this possibility of the embodiments of the present invention for surface studies. In particular, the properties of the crystallites and semiconductors are well-quantified. This allows for a wide range of ultrafast optical experiments that vary from scrutiny of carrier properties to symmetric electronic irregularities or changes. In addition to these optical studies, recent ultrafast X-ray experiments on GaAs have revealed the bulk lattice dynamics associated with femtosecond laser excitation. However, in these ultrafast X-ray experiments, the invasion of X-rays into crystals, typically several μm, could not be examined due to the large invasion. On the other hand, optical technology, which scrutinizes the surface on a scale of 2 to 3 nanometers, could not directly determine the structure with atomic-scale resolution, but it is valuable for the reaction of the dielectric function and lattice irregularity. Information was given. The large scattered cross section of the electrons combined with ultrafast temporal resolution allows this gap to be bridged in the addressing of the dynamics of the surface structure in real time.

The experiments described below were performed using, for example, the system shown in FIG. Ultra high vacuum (typically 10^-10Under torr), with low-energy electron diffraction and surface characterization by Aussie spectroscopy, the sample is brought to a scattering position where the laser pulse excitation beam and electron pulse probe intersect in space and can be modified. It was accompanied by a time delay Δt (zero time was determined by the method described above used in situ). In some embodiments of the invention, the chamber comprises a sputtering and cleaning tool. We terminated the semi-insulating GaAs (111) crystals with a monolayer of chlorine with Cl atoms above each Ga atom to saturate the other Ga dangling bonds. The surface maintained its integrity throughout the experiment. This is evidenced by the fact that the diffraction patterns (symmetry, point profiles, and intensities) well described below retain their invariant quality. Crystals placed on a goniometer with 3 degrees of freedom in translation and 2 axes of rotation were placed in space with a precision of 0.01 ° in rotation and a precision of 10 μm in translation. The experiment was conducted at room temperature.

FIG. 16 is a conceptual diagram illustrating an embodiment of the present invention and the structure of a chlorine-terminated GaAs (111) crystal. The output of the Ti: Sapphire femtosecond amplifier (120fs, 800nm, 2mJ, 1kHz) was tripled in frequency to produce a 266nm beam (400μJ, &lt;300fs, 1kHz). This UV beam was delivered to the scattering chamber to supply the initial heating pulse at t = 0. A tiny piece of this beam was synchronously guided onto a back-illuminated Ag light cathode to generate an electron pulse. These electron pulses were led to the crystal after acceleration and focusing, where they were heating in space and time (delay Δt). It overlapped with pulse). The electron pulse was created as short as 500 fs, but at this specular incident, the spatial range reduces this resolution to tens of ps. However, thanks to the sensitivity obtained (20 per frame), we were able to reduce the experimental time cross-correlation to 7 ps; along with the convolution and at the signal level reported here. , We easily got a 1-2ps response. This was made possible by reducing the spatial range of the substrate to 400 μm by masking technology, resulting in an elapsed time of 4 ps. The sample mounted on a 5-axis high-precision goriometer has an electron beam selected incident angle (θ)._iAt &lt;5 °), it was placed so as to collide along the azimuth in the &lt;112&gt; direction. In the figure, L0 and L1 refer to 0th and 1st order Laue zones. The resulting diffraction pattern was recorded in a non-proximity field by an imaging CCD camera system. In the inset of FIG. 16, the space between the two layers is 3.26 Å and the crystal structure is shown.

Femtosecond laser heating at t = 0 initiated mechanics. It was then scrutinized by a 30 keV ultra-short electronic packet (λ)._deBroglie 0.07 Å). The electrons collided with the surface at a small incident angle (θi1 °). In addition, the reflected high-energy electron diffraction method was the only application for this near-incident incident, and was used for the study of heating with a time resolution of 100 ps. The electron pulse was generated by a modified Williamson-Mourou streak camera arrangement. In the system used for this experiment, we obtained pulses as short as 500 ps in duration. However, in the system for experimental grazing geometry, the time cross-correlation was 7 ps. By controlling the arrival of the electron pulse (Δt in Figure 16), we can scrutinize the structure before or after the heating pulse. Structural changes followed in real-time monitoring of Bragg reflections and rocking curves, recorded by a CCD (charge-coupled device) imaging assembly capable of detecting a single electron. The three features of diffraction were associated as a function of time: Bragg peak movement, width, and intensity.

Figures 17 (A and B) show static diffraction images of the surface of the crystal (111) obtained by ultrashort electron pulse without time decomposition. In FIG. 17A (reference letter a), a diffracted image showing strong (0,0) in-phase reflections is illustrated with streaks and dots in the rowe zone. FIG. 17B (reference letter b) shows the experimental locking curve of the (0,0)-(111) work surface. Those skilled in the art will understand that periodicity allows a clear distinction of Bragg reflexes and provides spacing between layers.

Figures 17 (A and B) provide typical static diffraction images displaying very strong (0,0) and other Bragg reflections. FIG. 17A shows the diffraction pattern, and due to the diffraction pattern, the angle of incidence was adjusted to represent the higher diffraction peaks as well as the diffraction fringes in the 0th order Rawe zone. These, or similar data, determine the exact distance of the camera from the dispersion position (170 ± 1) by direct inversion of the angular separation between the streaks at low angles, or by Bragg spots in the higher Rawe zone. This inversion is direct, because the rods have a radius of 2πλ of the Ewald sphere in the reciprocal lattice space.^-1= 90Å^-1In-plane reverse distance along the intersection with 3.14Å^-1Because it is separated by. (0,0) By gating the detection of Bragg points and following the diffraction position as a function of the angle of incidence, we obtained an experimental locking curve. The locking curve gives the periodicity of the GaAs lattice along the (111) direction (n = 1, 2, ...). This was seen in Figure 17B, where the angle of incidence diversified several times. 0.60 ° ± 0.02 ° θ_iThe experimental periodicity in is quantitatively consistent with the expected value of 0.61 ° obtained from 3.26 Å of lattice bilayer space.

FIG. 18 shows the time dependence of the center position, intensity and width of Bragg reflection with laser heating excitation at t = 0. In Figure 18A, the center position of the Bragg point as a function of time and fluence is plotted. The vertical axis on the right gives the angular displacement, the left shows the corresponding changes in grid spacing, and is perpendicular to the (111) surface plane. The contraction occurs at an early time (Δd &lt;0) and follows the lattice expansion (Δd&gt; 0). The inset in Figure 18 shows evolution over time. In Figure 18B, the integrated intensity of Bragg points (temperatures), the change in lattice spacing, and 2 mJ cm.^-2A comparison with the change in lattice spacing by the dataset obtained in is illustrated. The right axis uses a logarithmic scale to give the time-dependent integrated intensity (I) of Bragg points as a percentage of its counterpart (Io) in negative delay, from which the temperature scale is obtained. Lattice expansion is also shown at that scale on the left axis, along with the expansion of Bragg points depicted by the dashed line. Its apparent delay between temperature rise and lattice expansion is noted by the two arrows shown below.

In the time-resolved experiment graphically depicted in FIG. 16, the excitation pulse at t = 0 defines the initial temperature and structural changes. In Figure 18, we track the center position and intensity of the n = 2 (0,0) Bragg point as a function of time. We also monitor the width shown in Figure 18B. Figure 18A provides a change in peak center position, which precisely plans the change in lattice spacing in the (111) direction. Experimentally determined damage threshold at 266 nm 4.5 mJ cm^-2Results at 9% and 45% fluence are shown. The angular displacement (Δθ) of the Bragg point is directly a change in the interstitial distance (Δd).₁₁₁), And the change is Δd₁₁₁=-Δθ d₁₁₁ {2sin (θ / 2)}^-1It is given from the relation (θ is the total scattering angle). Displacements with respect to larger or smaller angles (Δθ&gt; 0 or Δθ &lt;0) are therefore evidence of lattice contraction or expansion.

From the results shown in FIG. 18A, the top surface layer of the crystal shrinks immediately with excitation at t = 0. The amplitude of this initial contraction is given by the two fluences, the full fluence dependence is shown in FIG. After the first contraction (-0.015 Å), the system expands to the maximum amplitude (+ 0.025 Å), which is strongly fluence dependent: the greater the fluence, the wider the expansion. The data also shows the start time and the rate of expansion (ms)^-1) And strongly depend on fluence: expansion occurs faster and faster at higher fluence. After reaching its maximum expansion, the system contracts again on a longer time scale, a scale greater than 50ps, towards the lower lattice spacing, but a smaller expansion with a limit persists for at least a few nanoseconds. Observations were also made with 800 nm femtosecond excitation at various laser fluences, but with similar behavior. That is, the first contraction with expansion and the next return towards the first interstitial spacing. This formal similarity indicates that the observed structural mechanics, compared to the 266 nm experiment, is not governed by surface charging by photoelectron emission. This is because excitation at 800 nm and / or low fluence results in similar behavior.

Figure 19 illustrates the fluence dependence of structural mechanics demonstrated experimentally. In Figure 19A, the experimental tracking of a set of data at the indicated fluence is illustrated. In Figure 19B, the amplitude at maximum change is shown as a function of excitation fluence. Time dependence is shown in the inset (1: 0.04, 2: 0.2, 3: 1, 4: 3 mJ cm^-2). In particular, the time resolution is lower than that in FIG. This is because these fluence-dependent measurements were made without masking to determine the minimum possible range of fluence.

Its temporary temperature is significant in the change in diffraction-integrated intensity over time. This is the excitation at 45% of the damage threshold and is provided in Figure 18B, which plots the evolution of the integrated intensity of Bragg points as a function of time. By using the tabulated Debye-Waller factor in the bulk GaAs list and considering the two-dimensionality of the surface, we obtained the initial temperature rise to 1563 ± 83 K. The system cooled on a time scale of 2 to 300 picoseconds and reached 510 K after 1 ns. The first temperature rise has a rise time of 7 ps (10 ps before deconvolution), which is in perfect agreement with the results from femtosecond light studies of the dielectric function. Moreover, the maximum temperatures reported above are close to the values extrapolated from these optical studies (1300-1500K) at the corresponding fluence. Lower fluence type shown in Figure 18A (0.4 mJ cm)^-2), We find a temperature rise to 420 ± 18K after 1 ns with leveling of attenuation at 320 ± 5K. Again, the rise time and maximum temperature are consistent with optical studies.

The evolution of lattice expansion and the evolution of temperature are parallel with width in Figure 18B. Obviously, temperature evolution precedes lattice expansion, and we have measured a 15 ps delay between temperature rise and structural expansion. This delay in structural expansion provides direct evidence of the proposed delayed lattice changes associated with the impulsive initial temperature. We note that the temperature rise to 1565 ± 83K resembles (or even exceeds) the melting point of 1513K, while the excitation fluence is only half the damage threshold. However, as is clear from Figure 18B, the peak temperature does not last for a long time and the system does not lose its crystalline structure.

The delayed structural change reaches its maximum expansion of 0.025 Å at a temperature of approximately 1000 K (see Figure 18B). This nanometer-scale lattice extension may now be compared to the bulk GaAs extension. From the coefficient of linear extension of the bulk crystal, a temperature of 1000 K can correspond to a linear lattice extension of 0.013 Å, and this value is our experimental value of 0.025 ± 0.001 Å due to two factors. different. Over a longer period of time (1 ns), the temperature of 510 K corresponds to a linear extension of 0.0038 Å, and our experimental value is 0.0032 Å ± 0.0005 Å (Fig. 18B). reference). This temporary decrease in spacing differences indicates a surface change to bulk behavior. Modeling of strain propagation in X-ray studies inferred that the 0.0082 Å surface strain amplification was that of GaAs. Our measurements show greater deformation (by 3 factors).

Due to the small angle of incidence, the scrutinized electrons have a very small penetration depth (θ)._i2-3 Å for electrons at 30 keV at 1 °), and therefore only the very upper surface layer of the crystal is examined; in the geometry of our experiments, the excitation pulse (incident angle is 30 °) has a vertical penetration depth. Also on the nm scale (3.5 nm at 266 nm). The small or equivalent penetration depths of these photons and electrons are the only situation for monitoring the local structural mechanics of these surface layers. In X-ray experiments, heating pulses typically have an absorption length of 0.3 μm, and scrutinized X-ray pulses have a micron-scale penetration depth. Such scales generally require consideration of strain propagation in bulk or beyond the order of microns. Obviously, a direct scrutiny of the surface movement of an atom provides an insight into the initial understanding of the dynamics of the surface and an insight into the connection (fluence) to bulk propagation at different temperatures. The effects of fluence on structural changes are elaborately planned in Figure 19A, and a representative example of experimental tracking associated with time-dependent Bragg reflexes is shown in Figure 19B.

Further experiments were conducted on silicon to eliminate the effects of chlorination and to test the generality of the approach and scope of application. Chlorinated and unchlorinated silicon (111) surfaces followed the same experimental conditions (excitation wavelength and fluence). Similar behavior to that of GaAs was found-on the other hand, hydrogen-terminated silicon showed no noticeable surface shrinkage prior to expansion, while chlorinated surfaces showed rapid shrinkage prior to expansion. The overall phase of the signal in FIG. 18 depends on the overlap in the mask and it is possible that the optical phonon formation at t = 0 contributes to the observed scattering. It should be noted that the phase corresponding to the expansion is unclearly established and confirmed by the temporal evolution of temperature and structural mechanics at different fluences. However, observations with chlorine are consistent with the earliest potential-driven changes that precede the generation of coherent acoustic phonons.

Based on these experiments, possible mechanisms are proposed. The embodiments of the present invention are not limited to this proposed mechanism. It can be argued that pictures of general structural mechanics emerge from observations of structural changes and timescales of motion (see Figure 18B), and from observations on silicon surfaces. In the non-thermal form, the temporary excitation of the first femtosecond creates a pair of electron holes, which distorts the potential and, as experimentally verified above, the structural change is an ultrashort timescale. Caused by this deformation prior to significant movements in the lattice (phonons). This highly non-equilibrium state of the solid is associated with energy dissipation and redistribution, which leads to complete lattice expansion and reconstruction over time. With this in mind, only surface atom expansion can be expected, as opposed to the contractions and expansions observed in the studies reported here. However, on the surface with a short chlorine odor, a large electronegativity shifts the charge distribution towards chlorine (ion potential). The next Coulomb force interaction with the underlying layer contracts the interatomic layer, as observed at the early rise of ultrafast contraction (see Figure 18A), and also on this timescale. Mechanics is driven by changes in potential. With the observations made in the case of silicon and this proposed mechanism supporting in shrinkage, we note that atomic chlorine adsorption on GaAs was found to be an electron acceptor.

Following contraction, expansion proceeds on a similar timescale. Through the auger process that occurs within 2-3ps (density is 10)²¹ cm^-3), The carrier density decreases, but the overall electron energy does not change. The dip in Coulomb force potential with electron-phonon coupling now moves the system from the opposite movement towards expansion (see Figure 18A). Lattice expansion typically requires 7 ps to define the temperature of the surface layer, which is also evident in the rise in density profile (see Figure 18B); after this rise. Only we can define the temperature obtained through the electron-phonon bond. The structural change (expansion) is accompanied by an increase in temperature, but after an apparent delay of 15 ps, its maximum expansion of +0.025 angstroms is reached in a longer time. This thermal expansion in the (111) direction is probably due to the anharmonicity of lattice vibrations. In particular, the width of the Bragg point reaches its maximum before the peak of structural lattice expansion. Lattice mechanics is initially driven by the coherent population of phonons associated with the isotropic expansion that follows when anharmonicity is in effect. This emerging lattice expansion should generally overcome the ongoing contraction first (see Figure 18A). From our data, we obtained a start of 5 ps expansion after the temperature had risen to half of its maximum, and an additional delay of 10 ps to overcome the initial contraction. It should be noted that this picture of structural mechanics is robust at low fluence, as demonstrated in Figure 19. However, in the low fluence type, the initial temperature decreases, the electron-phonon bond dominates, and the diffusion process becomes prominent over a longer period of time.

Restoration to the original structure is Δd₁₁₁This reconstruction occurs on a longer timescale, although it is observed with a decrease of +0.025 Å to + 0.003 Å (see Figure 18). We say that the diffusion process typically begins above 50 ps, until this time Δd₁₁₁Is increasing-the cooling of the surface by diffusion is Δd₁₁₁It is mentioned that this is because it leads to a decrease in the number of people. Therefore, the extended value Δd₁₁₁The structure at = 0.025 Å is oscillatingly in a non-equilibrium state of collective mode, which cools for a longer time due to energy rearrangement and diffusion. The theoretical calculation of thermal diffusivity using the known thermal properties of GaAs (heat capacity and thermal conductivity) provides good agreement with the temperature behavior from the leveling point shown in Figure 18B.

Therefore, this experiment demonstrates that a new dimension of ultrafast electron crystallography on the scale of time, length, and sensitivity is ideally suitable for atomic-scale structural mechanics of surfaces and interfaces. One reason this is achieved is directly-from the periodicity of diffusion and changes over time-in atomic space (Bragg peak position), transition temperature (Bragg integrated intensity), and coherence. This is due to the possibility that the involvement of lattice vibration (Bragg peak width) can be directly determined. Timescales of non-equilibrium surface structures, and longer time reconstructions, are desirable for understanding surface reduction and propagation of bulk materials. We now believe that the examples of the present invention provide the development of many applications in this general area of surface science and nanometer-scale materials, as well as polymer structures.

In another experiment using the system according to one embodiment of the present invention, the temporal evolution of bulk and surface structures was studied at atomic scale spatial resolution. As just one example, in one experiment, silicon crystals with adsorbates and silicon crystals without adsorbates were studied. Figure 20 illustrates the transitions of condensed phases, such as crystalline and solid-liquid phases, obtained during the study. In FIG. 20A, diffraction from a Si crystal is illustrated. In FIG. 20B, a diffraction frame with reference to the Bragg point is shown. FIG. 20C illustrates a diffraction frame that references the transition from non-crystalline to liquid.

Reference to the diffraction difference illustrated in FIG. 20 for the ground state is the observed change in the positive time from the ground state pattern in the negative time, the change in the structure caused by the starting pulse. Shown. The structural change is apparent in the time shift of the in-phase Bragg peak of the locking curve, while the increase in vibration amplitude is reflected in the broadening. The change occurs as a maximum shift and then a decline to the coordinates of the original structure. By gating Bragg points, we can track changes over time. These results show instantaneous structural changes (2ps change steps; total 10ps); uniform 2.35 Å Si-Si coupling of the lattice by raising to 0.04A at a level of 50% of damaging fluence. It is an extension. This is accompanied by lattice relaxation from a highly parallel structure to the final ground state with a Si-Si distance of 2.35 Å. Many time constants of reconstruction describe the expansion and oscillation temperature in the real interval.

Further studies on the surface structure (and with hydrogen or chlorine) have produced outstanding results. By gate the fringes in the heterogeneous state, the embodiments of the present invention allow for a direct elucidation of the structural interference of surfaces and their evolution over time. In particular, the two points change over time and differently, but maintain phase coherence. Therefore, we can display the spatial, temporal, and phase consistency changes of the surface structure, and the spatial pattern is within the framework of the diffraction (kinematic) theory of condensate. Can be described in. Changes in structure are evident in changes in the amplitude of the surface of Si atoms. Unlike the result of bulk displacement (0.04 Å), the expansion of atoms on the surface is greater on the order of magnitude (0.4 Å). Surface structure cooling occurs on a different timescale than the bulk timescale. We also studied the structural changes involved in the phase transition when the temperature of the lattice is high enough to cause large amplitude randomness. The initiation of an ultrashort temperature rise in the non-crystalline structure with an infrared femtosecond pulse creates a new pattern of diffractive rings. We tracked the pattern as a function of time by reference to the ground state image (see Figure 20). The structural change is a phase transition to the liquid state.

In yet another experiment using the method according to the embodiment of the present invention.

The examples and examples described herein are for illustrative purposes only. Various amendments and their apparent changes will be suggested to those skilled in the art and are within the spirit of the present application and within the scope of the present application and the claims added. The present invention is not intended to be limited, except as indicated in the additional claims.