Titanium dioxide-cobalt magnetic film and its production method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a titanium dioxide / cobalt magnetic film and a method for producing the same, and further relates to a photocatalyst using this magnetic film, a semiconductor material having electric / optical / magnetic functions, a material useful for a transparent magnet, etc., and a method for producing the same. is there.

【0002】

[Conventional technology]

Titanium dioxide (TiO₂) Is a material that has been put to practical use for photocatalytic activity of water and decomposition and removal of harmful substances due to its photocatalytic function, and further improvement of the photocatalytic activity of titanium dioxide in the future is desired from the viewpoint of energy problems and environmental problems. ing. In addition, Si and GaAs are the mainstream semiconductor materials, and these conventional semiconductor materials are materials that can realize electrical functions by carrier control or optical / electrical functions such as laser diodes and photodiodes. However, there is no semiconductor material that can realize magnetic functions such as magnetic memory. Titanium dioxide is a semiconductor crystal having an optical / electrical function whose band gap energy is in the ultraviolet region. However, if the optical / electrical function can be maintained and the magnetic function can be provided, the optical / electrical function can be provided. It is possible to obtain a semiconductor material that can realize both electrical and magnetic functions.

【0003】

Conventionally, a substance called a magnet is a black substance that does not transmit visible light. If a transparent magnet can be realized, it is clear that it will be useful in a wide range of industrial fields, not to mention that it is convenient for applications such as paper scissors. By the way, as a conventional technique for adding magnetism to a transparent insulator, there is an example shown in FIG. Al₂O₃This is a non-magnetic insulating powder that is transparent with visible light and is hardened by mixing magnetic metal particles made of Co or the like. In such a transparent magnet, when the amount of magnetic metal particles is increased, the non-magnetic insulator becomes amorphous due to the inclusion of the magnetic metal particles, the crystallinity is lost, and the original transparent insulator which is the base material is originally formed. The properties of transparency and insulation are lost. As magnetic semiconductors, there are those in which Mn is mixed with GaAs and those based on CdMnTe, and there are those having a magnetic function and an optical function such as Faraday rotation. However, these conventional magnetic semiconductors are not transparent to visible light. As described above, conventionally, there has been no semiconductor material that is transparent to visible light and has a magnetic function.

【0004】

[Problems to be Solved by the Invention]

In view of the above problems, the present invention has added a magnetic function without losing the crystallinity of titanium dioxide, a photocatalyst, a semiconductor material having both optical, electrical and magnetic functions, and a titanium dioxide / cobalt magnetic film that can be used as a transparent magnet. And its manufacturing method.

【0005】

[Means for solving problems]

In order to achieve the above object, the titanium dioxide-cobalt magnetic film of the present invention can be used. Chemical formula: Ti_1-xCo_xO₂However, it is characterized by being a titanium dioxide-cobalt magnetic film represented by 0 <x 0.3, in which Co is substituted at the Ti lattice position, and which is epitaxially grown on a single crystal substrate. The crystal structure of the magnetic film is preferably an anatase structure. The crystal structure of the magnetic film is preferably a rutile structure. The titanium dioxide-cobalt magnetic film having the anatase structure is characterized in that the band gap energy changes in the range of 3.13 eV to 3.33 eV depending on the Co concentration (X) substituted at the Ti lattice position. The titanium dioxide-cobalt magnetic film can further retain its magnetization even at a temperature of room temperature or higher, and is transparent with visible light. The single crystal substrate is preferably LaAlO when the crystal structure is an anatase structure.₃(001) It is a substrate. The single crystal substrate is preferably Al when the crystal structure is a rutile structure.₂O₃It is a board. The single crystal substrate preferably has a rutile crystal structure when the crystal structure is a rutile structure.₂It is a board.

【0006】

According to the above configuration, since titanium dioxide has a magnetic function without losing its crystallinity as a semiconductor crystal, it can be used as a photocatalyst, a semiconductor material having both optical, electrical and magnetic functions, and a transparent magnet.

【0007】

In the method for producing a titanium dioxide-cobalt magnetic film of the present invention, TiO mixed at a predetermined mixing ratio in a vacuum chamber in an oxygen-pressure atmosphere.₂The target consisting of and Co is irradiated with a predetermined laser beam under predetermined irradiation conditions, and TiO₂And Co are evaporated to form a film on a single crystal substrate heated to a predetermined substrate temperature. Preferably, the oxygen pressure is 10^-5~10^-6Torr, substrate temperature 500-700 ° C, laser light KrF excimer laser light (248 nm), irradiation conditions, laser light pulse power 1-2 joules / cm², And the irradiation speed of this laser pulse can be 1 to 10 Hz. Furthermore, TiO mixed at a predetermined mixing ratio₂And a target consisting of Co and TiO₂A target made of only chisel may be alternately irradiated with a predetermined laser light pulse at a pulse number ratio corresponding to a predetermined Co concentration to form a titanium dioxide-cobalt magnetic film having a predetermined Co concentration. According to the above configuration, the titanium dioxide-cobalt magnetic film of the present invention having a desired Co concentration can be obtained.

【0008】

If the titanium dioxide-cobalt magnetic film of the present invention is used as a photocatalyst, the catalytic activity is high.

【0009】

By using the titanium dioxide-cobalt magnetic film of the present invention as a semiconductor material, it is possible to manufacture a semiconductor device having both an electrical function by carrier control, a light emitting / receiving function, and a magnetic function by magnetic control.

【0010】

If the titanium dioxide-cobalt magnetic film of the present invention is used as a transparent magnet, it is useful, for example, as a paper scissors.

【0011】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the titanium dioxide-cobalt magnetic film of the present invention will be described with reference to FIGS. 1 to 13. FIG. 1 is a schematic view of the titanium dioxide / cobalt dioxide magnetic film manufacturing apparatus of the present invention. In FIG. 1, the manufacturing apparatus 10 is configured as a laser ablation deposition apparatus, and a substrate 11 and a target 12 arranged to face the substrate 11 are mounted in the vacuum chamber 17, and the vacuum chamber 17 is mounted. From the outside, a laser device 13 that irradiates the target 12 with a pulsed laser through a window and a heating device 14 for heating the substrate 11 are arranged. Further, a mask 15 is movably supported on the surface of the substrate 11 facing the target 12 so as to partially cover the substrate 11. Reference numeral 16 denotes a nozzle for introducing oxygen.

【0012】

The substrate 11 is LaAlO, which is a transparent substrate having a relatively small lattice mismatch when epitaxially growing a titanium dioxide-cobalt magnetic film having an anatase crystal structure.₃It is made of a (001) substrate and is molded so that its surface is the (001) surface. Further, when the substrate 11 is epitaxially grown of a titanium dioxide-cobalt magnetic film having a rutile crystal structure, Al₂O₃, Or TiO with a rutile crystal structure₂It may be a single crystal substrate. The target 12 is, for example, a TiO having a rutile crystal structure.₂It is obtained by sintering 10 mol% of Co and sintering it at 1000 ° C. The target 12 is a target having the above composition and a rutile crystal structure of TiO.₂Two targets, one consisting only of a single target, may be used, and these targets may be produced by alternately irradiating a predetermined number ratio of laser light pulses. In this case, each target is held on a multi-target holder 18 capable of supporting a plurality of targets, and the rotating shaft 19 of the multi-target holder 18 selectively brings each target to the laser irradiation position of the laser device 13. It has become so.

【0013】

The laser used in the laser device 13 is, for example, a KrF excimer laser that emits a laser beam of 248 nm, and the optical energy density of the pulse of this laser beam is 1 to 2 J / cm.²This laser pulse is irradiated at 1 to 10 pulses / sec, that is, at a speed of 1 to 10 Hz.

【0014】

The heating device 14 is a substrate heating device using an Nd: YAG laser, and can heat the substrate 11 to a high temperature even in an oxidizing atmosphere. The substrate heating device may be a normal lamp heater. The inside of the above vacuum chamber is 1 x 10^-9After being held in a vacuum of about Torr, 10^-5~10^-6Oxygen is introduced through the gas introduction valve 16 so that the oxygen partial pressure is about Torr.

【0015】

Next, the crystal structure of the titanium dioxide-cobalt magnetic film of the present invention will be described. Figure 2 shows titanium dioxide (TiO).₂) Is schematically shown, FIG. 2 (a) shows the Ti coordination position (black circle) in the anatase crystal structure and the rutile crystal structure, and FIG. 2 (b) shows the anatase. The arrangement of the octahedral ligand composed of Ti and O in the crystal structure and the rutile crystal structure is schematically shown. In addition, FIG. 2 (c) shows a bond model of Ti and O in the anatase crystal structure and the rutile crystal structure.

【0016】

FIG. 3 shows the X-ray diffraction measurement results of the titanium dioxide-cobalt magnetic film having an anatase crystal structure produced by the production method of the present invention. FIG. 3 (a) shows a diffraction pattern by XRD (XRAY Diffract Meter). FIG. 3 (b) shows the RHEED (reflected electron diffraction) result at the time of film formation. The titanium dioxide-cobalt magnetic film used for the measurement is LaAlO.₃(001) TiO with a rutile crystal structure on the substrate₂10 mol% Co-doped target and rutile crystal structure TiO₂It is a titanium dioxide-cobalt magnetic film having a Co concentration of 5.8%, which is formed by alternately irradiating a target composed of chisel with the above laser light pulses having a predetermined number ratio. The Co concentration was determined by EPMA (Electron Probe Micro Analysis). Substrate temperature and oxygen partial pressure are 650 ° C and 10 respectively.^-5Torr.

【0017】

From the diffraction pattern of FIG. 3 (a), it can be seen that the titanium dioxide-cobalt magnetic film produced by the production method of the present invention has an anatase crystal structure and is c-axis oriented on the substrate. In addition, from the RHEED result in Fig. 3 (b), it can be seen that epitaxial growth occurs in each monolayer.

【0018】

FIG. 4 shows the X-ray diffraction measurement results of the titanium dioxide-cobalt magnetic film having a rutile crystal structure produced by the production method of the present invention. The titanium dioxide-cobalt magnetic film with a rutile crystal structure used for this measurement is an Al on an epitaxial single crystal substrate.₂O₃Substrate or TiO with rutile crystal structure₂Except for using a substrate, the conditions are the same as those for producing a titanium dioxide-cobalt magnetic film having an anatase crystal structure. From the diffraction pattern of FIG. 4, it can be seen that the titanium dioxide-cobalt magnetic film produced by the production method of the present invention has a rutile crystal structure and is (101) axially oriented on the substrate. Although not shown, it is confirmed from the RHEED measurement results that epitaxial growth occurs in each monolayer.

【0019】

FIG. 5 is a diffraction image showing the TEM (transmission electron diffraction) measurement result in the cross-sectional direction of the titanium dioxide-cobalt magnetic film having the anatase crystal structure. As is clear from FIG. 5, since regularly arranged diffraction points based on the lattice arrangement of Ti and Co can be seen, in the titanium dioxide-cobalt magnetic film of the anatase crystal structure of the present invention, Co is located at the lattice point position of Ti. It can be seen that is replaced. Further, although not shown, it has been confirmed that Co is substituted at the lattice point position of Ti in the titanium dioxide-cobalt magnetic film having a rutile crystal structure. FIG. 6 is a graph showing the results of measuring the lattice constant in the c-axis direction of the titanium dioxide-cobalt magnetic film of the anatase crystal structure prepared by variously changing the Co concentration. As is clear from FIG. 6, it can be seen that the lattice constant increases almost in proportion to the Co concentration. From this result, it can be seen that Co is substituted at the grid point position of Ti. As is clear from FIGS. 5 and 6, it can be seen that the titanium dioxide-cobalt magnetic film of the present invention maintains the crystal structure as a semiconductor even if it contains Co atoms having magnetic properties.

【0020】

FIG. 7 is a graph showing the results of measuring the transmittance of the titanium dioxide-cobalt magnetic film having the above anatase crystal structure having a Co concentration of 8%. From this figure, it can be seen that the titanium dioxide-cobalt magnetic film of the present invention is transparent in visible light. Further, although not shown, it has been confirmed that the titanium dioxide-cobalt magnetic film having a rutile crystal structure is also transparent in visible light.

【0021】

Figure 8 were taken using a scanning SQUID microscope, Image represents the measurement results of the magnetic domain structure of a titanium dioxide-cobalt magnetic film of anatase crystal structure is a di-view. In FIG. 8, the concentration scale on the horizontal axis indicates the strength of magnetization represented by microtesla, and + and-indicate the direction of magnetization. This measurement was performed using a scanning SQUID microscope, and the measurement temperature was 3K, 30K and 60K, and the measurement area was 200 μm × 200 μm. FIG. 9 is an image diagram showing the measurement results of the magnetic domain structure of the titanium dioxide-cobalt magnetic film having a rutile crystal structure, taken with a scanning SQUID microscope. The concentration scale on the vertical axis shows the strength of magnetization expressed in microtesla, the measurement temperature is 3K, and the measurement area is 200 μm × 200 μm. The titanium dioxide-cobalt magnetic film having a rutile crystal structure used for this measurement was prepared by continuously changing the Co concentration from left to right in the figure. The Co concentration at the left end is 14.6%, and the Co concentration at the right end is 15.4%.

【0022】

FIG. 10 shows the magnetic domain structure of the titanium dioxide-cobalt magnetic film having various Co-concentration anatase crystal structures measured by the same means as in FIG. The concentration scale on the horizontal axis indicates the strength of magnetization expressed in microtesla, and + and-indicate the direction of magnetization. As is clear from FIG. 10, it can be seen that the magnetization increases as the Co concentration increases. FIG. 11 is a graph showing the magnetization characteristics of the titanium dioxide-cobalt magnetic film having the anatase crystal structure, FIG. 11 (a) is a diagram showing the magnetic hysteresis characteristics, and the vertical axis is the magnetic moment per Co atom. Μ_BExpressed in units, the horizontal axis represents the magnetic field strength applied parallel to the surface of the magnetic film, and the measurement temperature is 300K. Further, FIG. 11 (b) shows the residual magnetic moment, that is, the degaussing characteristic depending on the temperature of the residual magnetization. FIG. 12 is a graph showing the temperature dependence of the magnetization characteristics of the titanium dioxide-cobalt magnetic film having the anatase crystal structure. The applied magnetic field strength is 200 Gauss, and the measurement temperature range is 0 to 400 K.

【0023】

As is clear from FIGS. 7 to 12, the titanium dioxide-cobalt magnetic film of the present invention has a magnetic domain structure, and its magnetization increases as the Co concentration increases. In addition, remanent magnetization can be generated in the temperature range of 0 to 400 K. That is, it can be magnetized, and its magnetization does not disappear even at a high temperature of 400 K.

【0024】

FIG. 13 is a graph showing the light absorption characteristics of the titanium dioxide-cobalt magnetic film of the anatase crystal structure having different Co concentrations of the present invention. Each absorption curve shows that it is a good semiconductor crystal, and the bandgap energy obtained from the absorption edge is 3.13 to 3.33 eV. As is clear from FIG. 14, it can be seen that the titanium dioxide-cobalt magnetic film of the present invention is a good semiconductor crystal in which the bandgap energy changes depending on the Co concentration.

【0025】

As can be understood from the above description, the titanium dioxide-cobalt magnetic film of the present invention is a semiconductor crystal in which Co atoms are substituted at Ti lattice positions, has a magnetic domain structure, and can form remanent magnetization. This remanent magnetization does not disappear even at 400K. Further, it is transparent in visible light, the band gap energy can be changed depending on the Co concentration to be doped, and according to the method for producing a titanium dioxide-cobalt magnetic film of the present invention, the titanium dioxide-cobalt magnetic film of the present invention Can be produced.

【0026】

TiO₂Photocatalytic reaction by TiO₂It is a redox reaction by holes and free electrons generated by absorbing photons with energy equal to or higher than the bandgap energy of the above, but these holes and free electrons are recombined at the same time as they are generated, and the photocatalytic efficiency is high. It wasn't too expensive. When the titanium dioxide-cobalt magnetic film of the present invention is used as a photocatalyst, the recombination ratio of holes and electrons can be reduced by magnetization by Co. Therefore, the photocatalytic efficiency is high.

【0027】

Conventionally, data used in a computer or the like has been recorded and held on a magnetic thin film disk or the like. However, in such a conventional method, it is necessary to provide such a recording device outside the CPU, and a mechanical drive part is required, so that the compactness and reliability are lacking. .. If the titanium dioxide-cobalt magnetic film of the present invention is used as a semiconductor material, the CPU and the data recording unit can be integrated on the same substrate. Therefore, the compactness and reliability of this type of device can be improved. Furthermore, it is expected to be used as a transparent element material for circuit drives such as transparent displays and electronic papers, taking advantage of its transparency.

【0028】

[Effect of the invention]

As described above, by using the titanium dioxide / cobalt dioxide magnetic film of the present invention, it is possible to provide a photocatalyst having high catalytic ability, a semiconductor material having optical / electrical / magnetic functions, and a transparent magnet. Further, according to the method for producing a titanium dioxide-cobalt magnetic film of the present invention, the titanium dioxide-cobalt magnetic film can be reliably produced.

[Simple explanation of drawings]

[Figure 1]

It is the schematic of the manufacturing apparatus of the titanium dioxide-cobalt magnetic film of this invention.

[Figure 2]

It is a figure which showed typically the anatase crystal structure and rutile crystal structure of titanium dioxide.

[Fig. 3]

It is a figure which shows the X-ray diffraction measurement result of the titanium dioxide-cobalt magnetic film of the anatase crystal structure produced by the manufacturing method of this invention.

[Fig. 4]

It is a figure which shows the X-ray diffraction measurement result of the titanium dioxide-cobalt magnetic film of the rutile crystal structure produced by the manufacturing method of this invention.

[Fig. 5]

It is a diffraction image by a micrograph which shows the TEM (transmission electron diffraction) measurement result in the cross-sectional direction of the titanium dioxide-cobalt magnetic film of the anatase crystal structure of this invention.

[Fig. 6]

It is a graph which shows the result of having measured the lattice constant in the c-axis direction of the titanium dioxide-cobalt magnetic film of the anatase crystal structure produced by changing the Co concentration of this invention variously.

[Fig. 7]

It is a graph which shows the transmittance measurement result of the titanium dioxide-cobalt magnetic film of the anatase crystal structure of the Co concentration 8% of this invention.

[Fig. 8]

It is a figure which shows the magnetic domain structure of the titanium dioxide-cobalt magnetic film of anatase crystal structure photographed using the scanning SQUID microscope.

[Fig. 9]

It is a figure which shows the magnetic domain structure of the titanium dioxide-cobalt magnetic film of the rutile crystal structure photographed using the scanning SQUID microscope.

[Fig. 10]

It is a figure which shows the magnetic domain structure of the titanium dioxide-cobalt magnetic film of the anatase crystal structure of various Co concentrations, which was photographed using the scanning SQUID microscope.

[Fig. 11]

It is a figure which shows the magnetization hysteresis characteristic of the titanium dioxide-cobalt magnetic film of the anatase crystal structure of this invention.

[Fig. 12]

It is a figure which shows the temperature dependence of the magnetization property of the titanium dioxide-cobalt magnetic film of the anatase crystal structure of the anatase crystal structure of this invention.

[Fig. 13]

It is a figure which shows the light absorption property of the titanium dioxide-cobalt magnetic film of the anatase crystal structure with different Co concentration of this invention.

[Fig. 14]

It is a figure explaining the prior art which adds magnetism to a transparent insulator.

[Explanation of symbols]

10 Manufacturing equipment 12 targets 13 Laser device 14 Substrate heating device 15 mask 16 nozzles 17 Vacuum chamber 18 Multi-target holder 19 rotating shaft