JP5246900B1 - Method for making magnesium oxide thin film - Google Patents

Abstract

A method for producing a flat MgO (111) surface by a simple method and a processing plate having a flat MgO (111) surface are provided.
A magnesium oxide thin film 3 is deposited on a substrate 2 using a sintered body of magnesium oxide or a single crystal as a target by laser ablation. In this method, a substrate 2 made of strontium titanate having a (111) plane as a major surface 2a or yttria-stabilized zirconia having a (111) plane as a major surface 2a is used, and a film is formed on the major surface 2a of the substrate 2. Is directly deposited and epitaxially grown to form a flat treatment film 3 made of magnesium oxide having a (111) plane as the surface 3a.
[Selection] Figure 1

Description

  Various aspects and embodiments of the present invention relate to a method for producing a magnesium oxide thin film and a treated plate.

Magnesium oxide (MgO) is a typical oxide insulator having a wide gap like sapphire (Al ₂ O ₃ ). For this reason, MgO may be used as a substrate for thin film growth. When using MgO as the growth substrate, matching of the lattice constant of the MgO substrate with the lattice constant of the growth thin film is considered. As a crystal plane of MgO for growing a thin film, for example, a plane having a plane orientation of (100) may be used (for example, see Non-Patent Document 1). Non-Patent Document 1 describes Fe ₃ O ₄ (100) / MgO (100) / Fe ₃ O ₄ (100) as a configuration that exhibits the TMR effect. The lattice mismatch between MgO and Fe ₃ O ₄ is 1% or less, suggesting that MgO is suitable as a growth substrate for Fe ₃ O ₄ .

On the other hand, as the MgO crystal plane for growing a thin film, for example, a plane having a plane orientation of (111) may be used (for example, see Non-Patent Documents 2 and 3). Non-Patent Document 2 describes that coercivity and remanence are increased by forming a ferromagnetic material having a spinel structure on the MgO (111) surface. Non-Patent Document 3 describes that a (Ba, Sr) TiO ₃ thin film, which is a typical ferroelectric thin film, is formed on the (111) plane or the (100) plane of the MgO substrate. It is described that the characteristics in the high frequency region are better when the (Ba, Sr) TiO ₃ thin film is formed on the (111) plane of the MgO substrate than when it is formed on the (100) plane. Yes.

As described above, the (100) plane and (111) plane of MgO can be applied to various films as a growth substrate. In some cases, the (111) face of MgO has an advantageous effect compared to the (100) face. In Non-Patent Document 4, NiO (111) is formed on yttria-stabilized zirconia (YSZ) having a (111) plane as a main surface, and MgO is grown on the NiO (111). There is a description that a (111) plane of MgO having a root mean square roughness R _RMS of 0.21 to 0.23 nm is obtained. Here, the root mean square roughness R _RMS is synonymous with the root mean square roughness R _q (JIS B0601).

X.W.Li, A. Gupta, Gang Xiao, W. Qian, and V. P. Dravid, Appl. Phys. Lett. 73, 3282 (1998). S.D.Yoon, S.A.Oliver, and C. Vittoria, J. Appl.Phys. 91, 7379 (2002). M. Noda, T. Yamada, K. Seki, T. Kamo, K. Yamashita, H. Funakubo and M. Okuyama: IEEE Trans. On UFFC, 57 (10) (2010) 2221-2227. K. Matsuzaki, H. Hosono, T. Susaki. Layer-by-layer epitaxial growth of polar MgO (111) thin films, PHYSICAL REVIEW B, vol. 82, 3, p. 033408, Jul. 2010.

On the (100) surface of MgO, equal amounts of Mg ^{2+ as} a cation and O ^{2− as an} anion are exposed and are electrostatically stable. On the other hand, the (111) plane of MgO is electrostatically unstable because either the positive ion Mg ^{2+ or the} negative ion O ²⁻ is exposed, and does not exist in nature. That is, the (111) face of MgO has unique chemical and electrical surface characteristics. This characteristic is considered to be more remarkable as the (111) face of MgO becomes flatter. Therefore, if a flat (111) surface of MgO can be obtained, a new device may be created as a substrate to which values other than the control of the growth surface by lattice matching can be added.

Here, the (111) plane of MgO is usually obtained by a method in which an MgO (111) plane is cut out from a single crystal and mechanically polished. However, with such a method, the root mean square roughness _Rq is about 3 nanometers or more, and it is difficult to obtain an electrostatically unstable flat surface of MgO (111). Therefore, MgO (111) has the unique characteristics as described above, but is difficult to employ as a substrate for controlling the growth film on the nanometer order. Further, in the method described in Non-Patent Document 4, since it is necessary to form a NiO film between the substrate and the substrate, it takes time and is not efficient, and the film is thicker than the NiO film. In this technical field, a production method capable of producing a flat MgO (111) surface by a simple method and a processing plate having a flat MgO (111) surface are desired.

A method for producing a magnesium oxide thin film according to one aspect of the present invention is a method of depositing a magnesium oxide thin film on a substrate by using a magnesium oxide sintered body or a single crystal as a target by a laser ablation method. In this method, a treatment film made of magnesium oxide is formed on a substrate. The substrate is made of strontium titanate having a (111) plane as a main surface or yttria-stabilized zirconia having a (111) plane as a main surface. A flat treatment film made of magnesium oxide having the (111) plane as a surface is formed by directly depositing a film on the main surface of the substrate and epitaxially growing the film. The treated film is a film whose film thickness does not exceed 50 nm and whose root mean square roughness Rq of the magnesium oxide (111) surface does not exceed 0.5 nm. The amount of laser energy in the laser ablation method is 50 mJ or more.

In this production method, magnesium oxide having a (111) plane as a surface is directly formed on a (111) plane of a substrate made of strontium titanate (111) or yttria-stabilized zirconia (111). That is, the (111) plane of a substrate made of strontium titanate (111) or yttria-stabilized zirconia (111) is adopted as a growth substrate for MgO, and is deposited by laser ablation and epitaxially grown, so that ( 111) plane can be obtained. By setting the thickness of the treatment film in a range that does not exceed 50 nm, it is possible to realize flatness in a range in which the root mean square roughness Rq of the magnesium oxide (111) surface does not exceed 0.5 nm. Then, the MgO (111) surface can be formed by increasing the energy at the time of film formation as compared with the conventional method.

  In one embodiment, the treatment film may be a film having a thickness of 5 to 20 nm. By setting the thickness of the treatment film to 5 to 20 nm, a flat (111) surface of MgO can be obtained reliably.

Also, the substrate temperature during the deposition of the treatment film may be 600 to 650 ° C.. Furthermore, the oxygen partial pressure during the formation of the treatment film may be 0.5 × 10 ^{−3 to} 2.0 × 10 ⁻³ Pa.

  As described above, according to various aspects and embodiments of the present invention, a flat (111) plane of MgO can be obtained by a simple method.

It is a figure for demonstrating the structure of a process board. It is a figure which shows typically the crystal structure of MgO. It is a figure for demonstrating the main structures of a manufacturing apparatus. It is a XRD diffraction pattern of the process board which concerns on an Example. It is an AFM image of the process film | membrane which concerns on an Example. (A) is a film thickness of 5 nm, (b) is a film thickness of 10 nm, (c) is a film thickness of 20 nm, and (d) is a film thickness of 50 nm. (A) is a figure for demonstrating the characteristic of the process film which concerns on an Example, (b) is a figure for demonstrating the characteristic of the process film which concerns on a comparative example.

  Hereinafter, various embodiments will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

  The configuration of the processing plate according to this embodiment will be described. FIG. 1 is a diagram for explaining the configuration of the processing plate 1. The processing plate 1 includes a substrate 2 and a processing film 3.

The substrate 2 is a plate-like material formed of an inorganic material, and is preferably a crystal or an amorphous structure formed of one or more types such as strontium titanate or yttria-stabilized zirconia. The preferred crystal structure of the substrate 2 has a 3-fold symmetry or a 6-fold symmetry with respect to the direction along the normal line of the main surface 2a. As the substrate 2, for example, strontium titanate (SrTiO ₃ ) having a (111) plane as a surface, yttria stabilized zirconia (YSZ) having a (111) plane as a surface, or the like is used.

SrTiO ₃ is also called titanium (IV) strontium trioxide, is a complex oxide, and has a perovskite crystal structure. Further, impurities such as SrTiO ₃ constituting the substrate 2 may be doped. When a voltage is applied to the substrate 2 doped with impurities, a current flows through the substrate 2, so that the substrate 2 is heated by resistance heat generation. Therefore, the temperature of the treatment film 3 can be controlled by controlling the voltage applied to the substrate 2. That is, the treatment film 3 can be easily heated. For example, niobium (Nb) is used as the impurity. The doping amount of Nb as an impurity is, for example, 0.01 to 0.5 weight percent. The substrate 2 has, for example, a main surface 2a whose plane orientation is (111).

  The treatment film 3 is directly formed on the main surface 2 a of the substrate 2. That is, the back surface of the treatment film 3 and the main surface 2a of the substrate 2 are joined. The treatment film 3 has a surface 3a made of magnesium oxide with the (111) plane as the surface. The thickness (film thickness) of the treatment film 3 is, for example, 0.5 to 100 nm. Note that the thickness of the treatment film 3 may not exceed 50 nm. Further, the thickness of the treatment film 3 may be 5 to 20 nm or 7 to 15 nm.

Here, the general crystal structure of MgO will be described. FIG. 2 is a diagram schematically showing the crystal structure of MgO. MgO has a cubic sodium chloride type crystal structure, and the surface orientation of the naturally occurring MgO is (100). The (100) plane of MgO flattened on the atomic scale is a plane where Mg ²⁺ which is a cation and O ²⁻ which is an anion are exposed in equal amounts, and is stable because it is electrically neutral. This is a serious aspect.

On the other hand, the treatment film 3 according to the present embodiment has a surface 3a made of a crystal plane CF whose plane orientation is (111). In the crystal plane CF, a surface in which only Mg ²⁺ that is a cation is exposed or a surface in which only O ²⁻ that is an anion is exposed is exposed. For this reason, the crystal plane CF is electrically positively or negatively charged and is an electrostatically unstable surface. Such a crystal plane CF has unique chemical and electrical surface characteristics. For example, the crystal plane CF has strong basicity, electron supply ability, or catalytic ability. A specific example of the catalytic ability is the ability to adsorb or reduce carbon dioxide (CO ₂ ).

The surface 3a of the treatment film 3 is flattened on an atomic scale. “Flat on the atomic scale” is not limited to the case where the crystal plane is completely flat. When a crystal plane flattened at the atomic level is actually created, the crystal surface is slightly inclined when viewed at the atomic level. At this time, a step structure corresponding to an atomic layer is formed on the surface of the crystal. Such a case is also included when the crystal plane is “atomic scale flat”. Specifically, the root mean square roughness R _q of the surface 3a of the treatment film 3 is a range of, for example not exceeding 1.0 nm. Further, the root mean square roughness R _q may be in a range not exceeding 0.5 nm. R _q is calculated, for example, by scanning an area having one side of 1 to 2 μm by using an atomic force microscope.

  Next, the manufacturing method of the processing board 1 is demonstrated. For manufacturing the processing plate 1, for example, a laser ablation method can be used. According to the laser ablation method, the processing plate 1 can be manufactured under relatively wide film forming conditions.

  FIG. 3 is a diagram for explaining the configuration of the manufacturing apparatus 10. The manufacturing apparatus 10 includes a chamber 11, a substrate 2, and a target 12.

  The chamber 11 defines a processing space 11a for accommodating the substrate 2 and the target 12 therein. The substrate 2 is disposed, for example, above the processing space 11a. The target 12 is disposed below the processing space 11a. In other words, the target 12 is arranged away from the substrate 2 in a vertically downward direction with respect to the substrate 2. The distance between the target 12 and the substrate 2 is arbitrary and may be appropriately selected according to the scale of the manufacturing apparatus 10. The target 12 is a raw material for the treatment film 3 formed on the main surface 2 a of the substrate 2.

  A window 13 configured to be optically transparent is provided on a side wall of the chamber 11. The laser light source 15 is disposed outside the chamber 11 and generates a laser beam L that is applied to the target 12. The laser light source 15 emits laser light L to the target 12 through the window 13.

  An exhaust device 14 is connected to the chamber 11. The exhaust device 14 depressurizes the processing space 11 a in the chamber 11. The exhaust device 14 is a predetermined vacuum pump. For example, a turbo molecular pump or an oil diffusion pump can be used. Thus, the chamber 11 is configured to be evacuated. Further, a gas introduction device 18 is connected to the chamber 11. The gas introduction device 18 includes a gas source 19 and a valve 20, and introduces a predetermined gas into the processing space 11 a of the chamber 11.

  A heating device 16 is arranged in the processing space 11a. The heating device 16 includes a lamp light source 17. The light from the lamp light source 17 is condensed on the substrate 2 and can heat the substrate to a predetermined temperature.

Then, the process which manufactures the process board 1 is demonstrated. First, the substrate 2 and the target 12 are placed in the chamber 11. In addition, the case where SrTiO ₃ or YSZ is used as an example of the material of the substrate 2 and the main surface 2a is the (111) surface will be described. Moreover, the case where a MgO sintered compact or a MgO single crystal is used as an example of the target 12 is demonstrated.

After arranging the substrate 2 and the target 12 in the chamber 11, the inside of the chamber 11 is depressurized to about 10 ⁻⁵ to 10 ⁻⁷ Pa. Subsequently, oxygen gas is injected from the outside using the gas introduction device 18, and the oxygen partial pressure is set to about 10 ⁻² to 10 ⁻⁵ Pa, for example. The oxygen partial pressure may be 0.5 × 10 ^{−3 to} 2.0 × 10 ⁻³ Pa. Next, the lamp light is condensed on the substrate 2 from the lamp light source 17 and the substrate 2 is heated to a predetermined substrate temperature. The predetermined substrate temperature is, for example, 400 to 700 ° C. The predetermined substrate temperature may be 600 to 650 ° C.

  Next, the laser beam L is irradiated into the chamber 11 from the window 13 of the chamber 11. This laser beam L is a pulse laser beam, has a high energy density, and is irradiated onto the target 12. For example, the laser beam L is a KrF excimer laser (krypton fluoride excimer laser) having a wavelength of 248 nm. The total energy (laser energy amount) of the laser light L introduced into the chamber 11 is 50 mJ or more. Further, the total energy of the laser light L may be 50 to 150 mJ. When the laser beam L is irradiated to the surface 12a of the target 12, the MgO present on the surface 12a of the target 12 is peeled off. The peeled MgO is deposited on the main surface 2a of the substrate 2 and epitaxially grows. Thereby, the treatment film 3 is formed.

As described above, the treatment film 3 is directly deposited on the (111) face of SrTiO ₃ or the (111) face of YSZ and epitaxially grown, whereby the treatment film 3 having the (111) face is formed and the treatment plate 1 is manufactured. When the film is formed by the laser ablation method, the energy at the time of film formation is larger than that when the film is formed by the molecular beam epitaxy method or the like. It is considered that the large energy during film formation contributes to the formation of the MgO (111) surface.

  In addition, embodiment mentioned above shows an example of the processing board and preparation method which concern on this invention. The processing plate and the production method according to the present invention are not limited to the above-described embodiments. In the range which does not change the summary described in the claims, the processing plate and the creation method according to the above-described embodiment may be modified or applied to others.

For example, in the above-described embodiment, the substrate 2 doped with impurities has been described as an example, but the present invention is not limited to this. As the substrate 2, SrTiO ₃ or the like not doped with impurities may be used.

  Moreover, although embodiment mentioned above demonstrated to the example the method of heating the board | substrate 2 with the light from the lamp light source 17 in the manufacturing process of the process board 1, it is not limited to this. Various methods can be used for heating the substrate 2. For example, instead of the light from the lamp light source 17, an infrared laser may be used.

  Hereinafter, examples and comparative examples implemented by the present inventors will be described in order to explain the above effects.

(Example)
The processing board which concerns on an Example was created using the manufacturing apparatus 10 shown in FIG. As an example, a treatment film made of MgO having a (111) plane as a surface was formed on the main surface of the substrate. The specific configuration and production conditions of the manufacturing apparatus 10 are as follows.
Target: MgO single crystal target substrate: SrTiO ₃ having (111) plane doped with Nb on the surface (Nb doping amount is 0.5 weight percent)
Laser light source: Excimer laser COMPexPro201 manufactured by Coherent
Laser wavelength: 248 nm
Laser energy: 100mJ
Laser pulse frequency: 10 Hz
(Comparative example)
The processing board which concerns on a comparative example was created using the manufacturing apparatus 10 shown in FIG. A treatment film made of MgO having the (100) plane as the surface was formed on the main surface of the substrate. The specific configuration and production conditions of the manufacturing apparatus 10 are the same as in the embodiment except for the substrate.
Substrate: SrTiO ₃ having a (100) plane doped with Nb on the surface (the doping amount of Nb is 0.5 weight percent)

(Structural evaluation)
The structure of the treatment film 3 according to the example was evaluated. FIG. 4 shows an X-ray diffraction pattern of the processing plate according to the example. In FIG. 4, a graph G1 is a pattern of a processing plate formed when the substrate temperature is 400 ° C., a graph G2 is a pattern of a processing plate formed when the substrate temperature is 500 ° C., and a graph G3 is a substrate. The pattern of the processing plate formed when the temperature of the substrate is 600 ° C., and the graph G4 is the pattern of the processing plate formed when the temperature of the substrate is 700 ° C. Further, the treatment films of these treatment plates were formed in an environment where the oxygen partial pressure was 1 × 10 ⁻³ Pa. As shown in the graphs G1 to G4, it was confirmed that peaks appeared at the location D1 indicating the (111) plane of MgO and the location D2 indicating the (222) plane under any temperature condition. As a result, it was confirmed that a treatment film made of MgO having the (111) plane as a surface was formed when the temperature of the substrate was in the range of 400 to 700 ° C. It was also confirmed that a treatment film made of MgO having the (111) plane as the surface was formed when the laser energy amount was 100 mJ. Considering that the high energy during the film formation contributes to the formation of the MgO (111) surface, if the laser energy amount is at least 100 mJ or more, MgO having the (111) surface as the surface is formed. It can be said that it was suggested.

(Surface observation results)
The surface of the treatment film of the treatment plate 1 according to the example was observed using an atomic force microscope. As a sample of the example to be observed, the substrate temperature at the time of forming the treatment film was 600 to 650 ° C., and the oxygen partial pressure was 1.5 × 10 ⁻³ Pa. As an atomic force microscope, an SPI3800N probe station manufactured by SII Nanotechnology Inc. was used. As measurement conditions, 2 micrometer squares of the sample surface were observed in the atmosphere. The results are shown in FIG. FIG. 5A is an AFM image with a processing film thickness of 5 nm, (b) an AFM image with a film thickness of 10 nm, (c) an AFM image with a film thickness of 20 nm, and (d). Is an AFM image with a film thickness of 50 nm. In FIG. 5A, the blackest part displays 0.81 nm, and the whitest part displays 1.36 nm. In FIG. 5B, the blackest part displays 0.00 nm, and the whitest part displays 1.89 nm. In FIG. 5C, the blackest portion displays 0.00 nm, and the whitest portion displays 2.98 nm. In FIG. 5D, the blackest part displays 0.00 nm and the whitest part displays 13.31 nm. As shown in the AFM images shown in FIGS. 5A to 5C, it was confirmed that the surface of MgO (111) having a film thickness of 5 to 20 nm grew as a film with little unevenness. On the other hand, it was confirmed that the surface of MgO (111) having a film thickness of 50 nm grew as a film having a relatively large number of irregularities. In addition to the measurement of the AFM image, the root mean square roughness _Rq was measured. Mean square when a thickness of 5nm square roughness _{R q} is 0.3037Nm, the root mean square roughness _{R q} when the film thickness 10nm 0.2992nm, the root mean square roughness _{R q} when the thickness of 20 nm 0.4702Nm When the film thickness was 20 nm, the root-mean-square roughness R _q was 1.580 nm. As root mean square measure of roughness R _q result, processing film processing board 1 according to the embodiment, the root mean square roughness R _q to the extent that the film thickness does not exceed 50nm is at 0.5nm or less, flat The surface was confirmed. If the film thickness is 5~20nm specifically, root mean square roughness _{R q} is at 0.5nm or less, it was confirmed that the flat surface.

(Surface property evaluation)
The surface property of the processing board 1 which concerns on an Example, and the processing board which concerns on a comparative example was evaluated. As an adsorbent for adsorption experiments for evaluating the chemical properties (acidic / basic) of the substrate surface, CO ₂ and NH ₃ are most commonly employed. Here, adsorption characteristics and reduction characteristics were evaluated using CO ₂ . In this evaluation, by measuring the gas Atsushi Nobori characteristics of CO _2, adsorption characteristics of the CO _2, i.e. the basic surface were evaluated. Further, the CO 2 gas thermal desorption characteristics were measured to evaluate the CO ₂ reduction characteristics, that is, the degree of chemical activity. Gas thermal desorption characteristics were measured using quadrupole mass spectrometry. Quadrupole mass spectrometry is a method of adding perturbation to ions by passing ions through four electrode tubes to which a high-frequency voltage is applied, and passing only desired ions, and measuring the mass of the passed ions. It is. In this evaluation, a processing plate provided with a processing film having a thickness of 50 nm prepared in a state where the substrate temperature is 650 ° C. was used as an example. Further, as a comparative example, a treatment plate having a treatment film with a thickness of 5 nm and having a surface made of (100) face of MgO prepared in a state where the temperature of the substrate is 650 ° C. was used.

6 (a) shows the CO ₂ and gas Atsushi Nobori characteristics of CO treated sheet according to the embodiment. In FIG. 6A, a graph G5 shows the gas temperature-programmed desorption characteristic of CO ₂ , and a graph G6 shows the gas temperature-programmed desorption characteristic of CO. As shown in the graph G5, it was confirmed that CO ₂ was desorbed from the surface 3a from around 50 ° C. Further, as shown in the graph G6, it was confirmed that CO _{2 on the} surface 3a was reduced from around 50 ° C. to generate CO, and a large amount of CO was produced from around 100 ° C. Therefore, in the CO ₂ reduction method using the treatment film 3, it was confirmed that the CO ₂ reduction proceeds on the surface 3a without irradiating ultraviolet rays or the like. That is, since reduction of carbon dioxide occurred at a relatively low temperature of 50 ° C. to 100 ° C., it was confirmed that the treatment film of the treatment plate according to the example has strong chemical activity.

FIG. 6 (b) shows the gas temperature desorption characteristics of CO ₂ and CO of the treatment plate according to the comparative example. In FIG. 6B, a graph G7 shows the CO ₂ gas temperature programmed desorption characteristic, and a graph G8 shows the CO gas temperature desorption characteristic. As shown in the graph G7, it was confirmed that CO ₂ was desorbed from the surface from around 50 ° C. On the other hand, as shown in the graph G8, the amount of CO generated was almost zero, and it was confirmed that CO was not generated because CO ₂ was not reduced even when the treatment film was heated.

When comparing the G7 graphs G5 and graphs desorption amount of CO ₂ from the processing film according to Example, it was confirmed greater than the amount of released CO ₂ from the processing film according to Comparative Example . Therefore, it was confirmed that the treatment film having the surface made of the (111) face of MgO can adsorb CO ₂ more efficiently than the treatment film having the surface of the (100) face of MgO. That is, it was confirmed that the treatment film of the treatment plate according to the example has a stronger surface basicity than the treatment film of the treatment plate according to the comparative example.

  Conventionally, as a thin film substrate, a MgO substrate having a naturally existing (100) plane as a surface is used. On the other hand, the lattice constant of the (111) plane of MgO is different from the lattice constant of the substrate on which a commercially available triangular lattice is formed. Therefore, the processing plate 1 according to the present embodiment is useful as a new substrate for growing an electronic thin film.

Furthermore, conventionally, when selecting a substrate for thin film growth, the lattice constant matching is mainly emphasized, and the catalytic ability on the substrate surface is not emphasized. On the other hand, the processing plate 1 according to the present embodiment has strong basicity and chemical activity due to polarization in the direction perpendicular to the substrate surface. Therefore, it can have added value as a substrate for crystal growth of a thin film or the like. For example, the processing plate 1 according to the present embodiment may be employed as a substrate for thin film growth by a soft solution process or a substrate for CVD. In addition, after a thin film is formed on the processing plate 1 according to the present embodiment, the electronic state of the thin film can be modulated using the polarization of the processing film of the processing plate 1. The natural growth surface of magnetite Fe ₃ O ₄ described in Non-Patent Document 1 is not the (100) plane but the (111) plane or the (110) plane. For this reason, it is expected that a better quality Fe ₃ O ₄ film can be formed by forming Fe ₃ O ₄ on the processing plate 1 according to the present embodiment. Further, since it is presumed that none of the (111) planes of MgO described in Non-Patent Documents 2 and 3 is flat, by using the flat (111) of MgO of the processing plate 1 according to the present embodiment, It is assumed that the effects described in Patent Documents 2 and 3 become more prominent. That is, the processing plate 1 according to the present embodiment is useful as a ferromagnetic thin film substrate having a spinel structure described in Non-Patent Document 2. Moreover, it can employ | adopt suitably for a device which needs to suppress interface roughness, such as a magnetic tunnel junction, using the flat surface. Furthermore, the processing plate 1 according to the present embodiment is also useful as a substrate for a ferroelectric thin film described in Non-Patent Document 3. Moreover, the film thickness of the dielectric thin film which has a desired characteristic can be reliably made thin using the (111) surface of MgO, and a flat surface. Further, the processing plate 1 can be used for processing having a process of depositing on a substrate while reacting molecules, such as MOCVD.

  Furthermore, noble metals such as platinum and palladium or hybrids of noble metals and oxides are used as catalysts. However, these substances are rare and can be toxic. On the other hand, the processing plate 1 according to the present embodiment uses MgO. MgO is a common substance and has no toxicity. Therefore, the processing plate 1 according to the present embodiment does not have to worry about environmental pollution. Furthermore, since MgO has no toxicity to the living body, the treatment plate 1 according to this embodiment can be used for selective adsorption of acidic molecules in the living body. For example, the processing plate 1 according to the present embodiment can be applied as a so-called biosensor which is a detection element for biomolecules (protein, virus, amino acid). Specifically, the biomolecule can be detected from the change in the electrical conductivity of the treatment plate 1 before and after the adsorption of the biomolecule. Therefore, it can be used as a diagnostic agent or a test agent.

Then, CO ₂ continues to increase by the use of fossil fuels. Since this CO ₂ is extremely chemically stable, it is not easy to modify it to other chemical species under atmospheric pressure and room temperature conditions. For this reason, methods for collecting and confining CO ₂ and using it effectively have been studied. According to the process plate 1 according to the present embodiment, by MgO and (111) and the surface (suction surface), it is possible to adsorb CO ₂ efficiently. Therefore, CO ₂ can be easily stored.

Further, according to the process plate 1 according to the present embodiment, it is possible to reduce CO ₂ in the CO by heating the film after adsorbing the CO ₂ in the treatment film. Thus, easily it is possible to reduce CO _2, it is possible to realize a reaction step in which the CO ₂ as a starting material. Therefore, CO ₂ can be used effectively.

Further, the treatment film of the treatment plate 1 according to the present embodiment is formed on the substrate. For this reason, handling of a processing board can be made easy. Furthermore, it can couple | bond with another member via a board | substrate. In addition, for example, when the substrate is doped with impurities and has conductivity, the temperature of the treatment film can be easily controlled by controlling the voltage applied to the substrate. By controlling the temperature of the treatment film, the adsorption or reduction (desorption) of CO _{2 in} the treatment film can be easily controlled. In addition, for example, when the substrate has a low light transmittance, such as a blackish-colored substrate, the temperature of the substrate may be increased to about 50 ° C. when the substrate is irradiated with sunlight. According to this, adsorption and reduction (desorption) of CO ₂ are performed on the processing plate without artificially injecting energy. Therefore, it is possible to adsorb and store the CO ₂ exhaled at night by the plant using the treatment plate, and to desorb CO ₂ from the treatment plate in the daytime and use it as a raw material for photosynthesis.

  DESCRIPTION OF SYMBOLS 1 ... Processing board, 2 ... Substrate, 3 ... Processing film, 5 ... Processing apparatus, 10 ... Manufacturing apparatus, 11, 21 ... Chamber, 12 ... Target, 13 ... Window, 14 ... Exhaust device, 15 ... Laser light source, 16, 25 ... heating device, 17 ... lamp light source, 18 ... gas introduction device, G1 to G8 ... graph, L ... laser beam.

Claims (4)

In a method of depositing a magnesium oxide thin film on a substrate using a sintered body of magnesium oxide or a single crystal as a target by a laser ablation method,
By using a substrate made of strontium titanate having a (111) plane as a main surface or yttria-stabilized zirconia having a (111) plane as a main surface, a film is directly deposited and epitaxially grown on the main surface of the substrate ( A flat treatment film made of magnesium oxide having a (111) plane as a surface;
The amount of laser energy in the laser ablation method is 50 mJ or more,
The said process film is a film-forming method of the magnesium oxide thin film which is a film | membrane whose film thickness does not exceed 50 nm, and whose root mean square roughness Rq of a magnesium oxide (111) surface does not exceed 0.5 nm.   The method for producing a magnesium oxide thin film according to claim 1, wherein the treatment film is a film having a thickness of 5 to 20 nm. The method for producing a magnesium oxide thin film according to claim 1 or 2 , wherein a substrate temperature at the time of forming the treatment film is 600 to 650 ° C. The method for producing a magnesium oxide thin film according to any one of claims 1 to 3 , wherein an oxygen partial pressure at the time of forming the treatment film is 0.5 x ^{10-3 to} 2.0 x ^10-3 Pa. .