JP2007246326A - Composite structure, its producing method, and thermoelectric conversion element using the composite structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite structure having, as a base unit, a cage-like structure which is required when a compound bonded into a cage-like conformation is applied to a device, and to provide a thermoelectric conversion element using the same. <P>SOLUTION: A cage-like compound is formed on a base material as the composite structure by an aerosol deposition method utilizing an ordinary temperature shock compaction phenomenon. The thermoelectric conversion element 10 is constituted by using the composite structure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a composite structure, a thermoelectric conversion element, and a method for producing the same, having a saddle-like structure as a basic unit required when a compound bonded in a saddle-like form is applied to a device.

  Currently, electronic devices are made using III-V compound semiconductors such as silicon, germanium, and gallium-arsenic, and II-VI compound semiconductors such as arsenic sulfide. Conventionally, improvement in performance of elements using these has been progressed by microfabrication technology.

  However, as the microfabrication technology is approaching its limit, performance improvement due to miniaturization cannot be expected so much, and expectation for improvement of characteristics of materials constituting the element is increasing. In order to further develop the electronics field, it is necessary to develop a new material having physical properties significantly different from those of conventional electronic materials. As such a new material, development of a compound in which a basic structure in which atoms are arranged in a cage shape by an ionic bond or a covalent bond forms a higher-order structure with the same bond is progressing.

  The semiconductor clathrate is composed of a cage structure made of Si and Ge. A clathrate compound is a material that has a significant difference in bonding mode between elements constituting the substance from conventional substances, and is a rod-like substance that can have another element in the clathrate structure. It is conceivable that the basic physical properties are dramatically improved.

  In addition, clathrate compounds have a structure that is significantly different from conventional silicon crystals, etc., and can be used as insulators, semiconductors with various band gaps, and as metals and superconductors by changing the metal contained. From this point of view, development of the applied technology is desired. Application to optical devices is also conceivable.

  As a specific application, application of semiconductor clathrate from high thermoelectric power to energy devices such as thermoelectric conversion elements has been studied. Thermoelectric conversion elements using the Seebeck effect can convert thermal energy into electrical energy. Utilizing this property, it is possible to convert exhaust heat exhausted from industrial / consumer processes and mobile objects into effective electric power, and thermoelectric conversion elements are attracting attention as energy-saving technologies in consideration of environmental problems.

  Oxide soot-like compounds are attracting attention because they can be applied to many fields of application because they are stable in the use environment and their constituent elements are inexpensive. The soot-like oxide 12CaO · 7Al2O3 can contain oxygen radicals and electrons in the soot, and its electrical and optical properties can be freely controlled, so that it can be expected to be applied in various fields. In particular, it can be expected to be applied to cold electron emission guns that extract electrons to the outside at room temperature, infrared detection elements that use electron light absorption, and reducing reagents that use electron chemical reactivity.

  As described above, when the useful properties of the cage structure compound are applied to an electronic device, it is extremely important to develop a thin film formation technique for the cage structure compound. However, with conventional film forming methods such as sputtering and vacuum deposition, film formation is difficult due to the complexity of the structure. This is because alkali metal / alkaline earth metal elements, which are encapsulated atoms in semiconductor clathrate, are very reactive and difficult to handle, and Ba elements etc. are more likely to evaporate than Ge etc. It is a cause.

  For this reason, it is difficult to form a film while maintaining the clathrate structure by the conventional vacuum deposition method or molecular beam epitaxy (MBE) method, and examples of producing thin film samples necessary for the formation of electronic devices have been reported so far. It wasn't.

  Here, Patent Document 1 discloses a method of forming a clathrate compound thin film. The deposition method consists of a complicated process in which an alkali metal vapor deposition film is formed on a group IV element substrate, an amorphous semiconductor film made of the same material as the substrate is formed thereon, and then the substrate is heated. Since the substrate is limited, applicable devices are limited.

JP-A-11-343110

  Therefore, the present invention has been made in view of the above-mentioned problems of the prior art, and a first object is to form a thin film of a cage-like structure compound on the surface of a substrate, which can be considered for many application devices in the future. It is to provide a composite structure.

  The second object of the present invention is to provide a method for producing a thin film composite structure of cage-like structure compounds.

  Furthermore, the third object of the present invention is to provide an excellent thermoelectric conversion element that can be used for general uses such as waste heat power generation.

  In order to achieve the above object, in the present invention, a composite of compounds formed on the surface of a substrate and having a basic structure in which atoms are arranged in a cage by ionic bonds or covalent bonds forms a higher order structure by the same bond. The composite structure is polycrystalline, the crystals constituting the composite structure are substantially free of crystal orientation, and a grain boundary layer composed of a glass layer is substantially formed at the interface between the crystals. It is characterized by not existing.

  Here, the composite structure preferably has an average particle size of 100 nm or less. The compound is preferably a semiconductor clathrate.

  The semiconductor clathrate includes a clathrate lattice mainly composed of atoms of Group IVB elements of the periodic table, and a periodic table IA group, IIA having a mass larger than that of the constituent atoms of the clathrate lattice contained in the lattice gap of the clathrate lattice. It is preferable that it is at least one doping atom selected from the group III, IIIA, IB, IIB, and IIIB atoms.

  Alternatively, the semiconductor clathrate includes a clathrate lattice mainly composed of atoms of group IVB of the periodic table, and a group IA of the periodic table having a mass larger than the constituent atoms of the clathrate lattice contained in the lattice gap of the clathrate lattice. A periodic table VA, VIA substituted with at least one doping atom of group IIA, group IIIA, group IB, group IIB, group IIIB and at least part of the atoms constituting the clathrate lattice It is preferably a clathrate compound mainly composed of at least one kind of substituent atom among atoms of group VIIA, group VB, group VIB, group VIB, group VIIB, and group VIII.

  Here, the group IVB element of the periodic table is, for example, Si or Ge.

  The semiconductor clathrate is Ge-based, BaGe-based, BaAuGe-based, BaAuGaGe-based, BaPtGe-based, BaPdGe-based, BaPdGaGe-based, BaCuGaGe-based, BaAgGaGe-based, Si-based, BaSi-based, BaAuSiSi-based, BaPtSi-based, A clathrate compound of at least one system selected from the group consisting of BaPdSi, BaPdGaSi, BaPtGaSi, BaCuGaSi, and BaAgGaSi is preferable.

  Preferably, the compound is an oxide cage. For example, the oxide cage material is based on 12CaO · 7Al2O3. Alternatively, the compound is preferably an electride compound.

  Here, the composite structure is formed into a thin film by a normal temperature impact solidification phenomenon. The composite structure is preferably formed by an aerosol deposition method.

  Here, the said composite structure is used for a thermoelectric conversion element, for example. The thermoelectric conversion element includes a plurality of thermoelectric films made of p-type thin film semiconductor clathrate and a plurality of n-type thin film semiconductor clathrate between substrates disposed opposite to each other in the vertical direction. Thermoelectric films are arranged alternately, the lower ends of a pair of adjacent thermoelectric films are intermittently connected by thin film electrodes, and the upper ends of other thermoelectric films adjacent to each other are intermittently thin film electrodes A plurality of electrodes are connected so that all the thermoelectric films are connected in series by alternately connecting the ends of the adjacent p-type thermoelectric films and the ends of the n-type thermoelectric films. It is preferable to be connected by a thin film.

  The composite structure is formed on a substrate made of glass or plastic, for example.

  The present invention is based on the finding that it is effective to apply a normal temperature impact solidification phenomenon in order to form a cage structure compound, particularly a clathrate compound and an oxide cage material on an arbitrary substrate with good controllability. It has been made.

  As described above, the composite structure of the present invention is a compound that is formed on the surface of a substrate and has a basic structure in which atoms are arranged in a cage by ionic bonds or covalent bonds to form a higher order structure by the same bond. It is a composite structure, the structure is polycrystalline, crystals constituting the structure are substantially free of crystal orientation, and a grain boundary layer composed of a glass layer is substantially formed at the interface between the crystals. It does not exist.

  By adopting such a structure, it becomes possible to form a cage-like substance as a thin film on an arbitrary substrate such as glass or plastic.

  Further, it has been found that a normal temperature impact solidification phenomenon, in particular, an aerosol deposition method is effective for forming this structure.

  In addition, the composite structure of the present invention can form a strongly bonded thin film when the average particle size is 100 nm or less.

  Further, the cage compound forming the composite structure of the present invention is a semiconductor clathrate. This semiconductor clathrate includes a clathrate lattice mainly composed of atoms of group IVB elements of the periodic table such as Si or Ge, and a periodic rule having a mass larger than that of the constituent atoms of the clathrate lattice contained in the lattice gap of the clathrate lattice. Table: Periodic table substituted with at least one doping atom of group IA, group IIA, group IIIA, group IB, group IIB, group IIIB and at least part of the atoms constituting the clathrate lattice A composite structure characterized in that it is a clathrate compound mainly composed of at least one substitution atom among atoms of group VA, group VIA, group VIIA, group VB, group VIB, group VIIB, group VIII. .

  Specifically, the semiconductor clathrate is Ge-based, BaGe-based, BaAuGe-based, BaAuGaGe-based, BaPtGe-based, BaPdGe-based, BaPdGaGe-based, BaCuGaGe-based, BaAgGaGe-based, Si-based, BaSi-based, BaAuSiSi-based, BaPtSi-based. BaPdSi-based, BaPdGaSi-based, BaPtGaSi-based, BaCuGaSi-based, and BaAgGaSi-based clathrate compounds.

  Since these clathrate compounds have high thermoelectric power, they are suitable for application in the field of electronic devices such as thermoelectric conversion elements.

  In addition, the cage compound forming the composite structure of the present invention is an oxide cage material. Specifically, this oxide cage material is based on 12CaO · 7Al2O3, and can be made into an electride compound by confining electrons in the cage structure. The electride compound is suitable for application to the field of electronic devices such as electron sources and semiconductors.

  Moreover, the method for producing a composite structure of the present invention is characterized in that a film is formed by a normal temperature impact solidification phenomenon. By using a normal temperature impact solidification phenomenon, a cage structure compound can be formed on an arbitrary substrate at room temperature. Among the film forming methods based on the normal temperature impact solidification phenomenon, the aerosol deposition method is suitable as a method for producing a cage structure compound.

  Furthermore, the present invention is characterized in that a cage structure compound, particularly a composite structure of a semiconductor clathrate is used for a thermoelectric conversion element. The thermoelectric conversion element of the present invention has an advantage that it has higher conversion efficiency than a thermoelectric conversion element using a conventional material and can be formed on an arbitrary base material or substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the composite structure by which the thin film of the cage-like structure compound which can consider many application devices in the future was formed on the surface of the base material can be provided. Moreover, the manufacturing method of the thin film composite structure of a cage-like structure compound can be provided. Furthermore, it is possible to provide an excellent thermoelectric conversion element that can be used for general uses such as waste heat power generation.

  Embodiments of the present invention will be described with reference to the drawings.

<Manufacture of composite structure of semiconductor clathrate Ba6Ge25>
First, a semiconductor clathrate was synthesized from Ba and Ge. A CO2 laser heating method was used for the synthesis. Since the oxide film was already formed on the surface of the purchased Ba and Ge, the oxide film was first removed. In order to prevent oxidation of Ba, the surface was shaved with a cutter in an Ar atmosphere glove box to remove the oxide film. The Ge oxide film was removed in a draft using hydrofluoric acid (HF: HNO3 = 1: 4). In order to prevent oxidation of Ba, weighing work was performed in an Ar atmosphere glove box. After weighing Ge, Ba and Ge were placed on a water-cooled Cu dish of a CO2 laser heating device. This is because Ba, which has a high absorption of CO2 laser, is placed on a Cu plate so that Ge, which has low absorption, is on the bottom, and the dissolved Ba is soaked into Ge. These operations were also performed in an Ar atmosphere glove box.

  The CO2 laser heating device was evacuated to about 5 × 10 −3 Pa using a turbo molecular pump, and then the Ar was replaced and the heating process was performed in a pressurized state of gauge pressure +0.01 MPa. This has the meaning of preventing oxygen in the atmosphere from entering the chamber by applying pressure.

  Next, Ba and Ge were heated and exploded by using a 250 W CO2 laser. In order to eliminate unreacted samples, heating was continued for 10 minutes after the reaction. After 10 minutes, the heating was stopped and the solution was rapidly solidified by a water-cooled Cu dish. By this step, a clathrate structure is formed. This is because the clathrate structure is a non-equilibrium phase and the synthesis work must be performed in a non-equilibrium state.

  Since the CO2 laser has limitations on the output and beam spot and the entire sample cannot be heated uniformly, there may be an unreacted sample in the synthesized clathrate compound semiconductor sample. Therefore, after heating with a CO2 laser, it was reheated, remelted and rapidly solidified using an arc furnace. At this time, the gauge pressure in the arc furnace was -0.02 MPa, and the arc current was 20 mA.

  The synthesized semiconductor clathrate Ba6Ge25 compound was coarsely pulverized with a mortar and then pulverized with a ball mill to form fine particles. The ball mill conditions are 200 rpm and 15 minutes.

  A thin film was formed by aerosol deposition (AD) method using room temperature impact solidification phenomenon using micronized particles. In the AD method, a compact is formed on a substrate by applying a mechanical impact force to a fine particle brittle material and crushing and bonding the material. A glass substrate is used, the carrier gas is oxygen, the incident angle between the nozzle and the substrate is 10 degrees, the gas flow rate is 12 liters / minute, the distance between the nozzle substrates is 5 mm, the deposition rate is 0.8 μm / min, and the vibration frequency of the vibrator Was 250 rpm and the film was formed at room temperature.

  FIG. 1 shows a photograph of the semiconductor clathrate Ba6Ge25 compound produced in this example. (1) is an appearance photograph of a semiconductor clathrate Ba6Ge25 compound thin film produced by the AD method. It can be seen that a thin film is uniformly formed on the glass substrate. (2) is a micrograph of a semiconductor clathrate Ba6Ge25 compound thin film produced by the AD method. It can be seen that a continuous film can be formed by the AD method. (3) is a scanning electron micrograph of fine particles of a semiconductor clathrate Ba6Ge25 compound formed by a ball mill. Micron-level fine particles are formed. The thin film of the semiconductor clathrate Ba6Ge25 compound as shown in (1) and (2) could be formed by colliding, crushing and solidifying the fine particles shown in (3) on the glass substrate by AD method. . The film thickness was about 2 microns.

  FIG. 2 shows X-ray diffraction profiles of the fine particles after ball milling and the produced thin film. (1) is a clathrate fine particle, and (2) is a diffraction profile of a thin film formed by the AD method. Although the half width of the profile of the thin film formed by the AD method is widened, it was confirmed that the produced thin film was formed while maintaining the clathrate structure because the peak positions almost coincided.

  FIG. 3 shows a transmitted light spectrum of a clathrate thin film formed by the AD method. (1) shows the transmitted light spectrum of the clathrate thin film formed by the AD method, and (2) shows the transmitted light spectrum (document value) of the Ge thin film. The absorption edge of the clathrate thin film is shifted to a wavelength lower than that of the Ge thin film, which indicates that the band structure change due to the clathrate structure can be observed in the AD film.

  The above results show that fine particles of semiconductor clathrate can be formed as a thin film by the AD method using room temperature impact solidification, which is the first example of thinning of a semiconductor clathrate at room temperature. This result is a major advancement that enables the application of semiconductor clathrate to electronics and the like.

  In the above description, the case where the composition of the semiconductor clathrate is Ba6Ge25 has been described. However, the composition is not limited to this composition. For example, a composition in which one or more kinds of Au, Pt, Pd, Ag, and Ga are added may be used. . Alternatively, the clarate of Ge alone may be used. In addition to Ge-based materials, Si-based materials are also useful semiconductor clathrate materials.

<Manufacture of composite structure of oxide cage material 12CaO ・ 7Al2O3>
The raw material powder in which 12: 7 equivalent of calcium carbonate and γ-alumina was mixed was sintered at 1300 ° C. for 2 hours in 1 atmosphere of oxygen to obtain 12CaO · 7Al2O3 compound. The synthesized 12CaO · 7Al2O3 compound was pulverized by a ball mill into fine particles.

  A thin film was formed by aerosol deposition (AD) method using room temperature impact solidification phenomenon using micronized particles. In the AD method, a compact is formed on a substrate by applying a mechanical impact force to a fine particle brittle material and crushing and bonding the material. A glass substrate is used, the carrier gas is oxygen, the incident angle between the nozzle and the substrate is 30 degrees, the gas flow rate is 12 liters / minute, the distance between the nozzle substrates is 5 mm, the deposition rate is 0.3 μm / min, and the vibration frequency of the vibrator Was 250 rpm and the film was formed at room temperature.

  As in Example 1, it was confirmed by X-ray diffraction measurement that the structure of the cage-like oxide 12CaO · 7Al2O3 compound was maintained in the thin film.

  Next, the influence of the average particle diameter of the structure will be described based on examples.

  A semiconductor clathrate Ba6Ge25 was synthesized in the same procedure as in Example 1, and a film was formed by the AD method using finely pulverized fine particles in a mortar. A glass substrate is used, the carrier gas is oxygen, the incident angle between the nozzle and the substrate is 0 degree, the gas flow rate is 12 liters / minute, the distance between the nozzle substrates is 5 mm, the deposition rate is 0.5 μm / min, and the vibration frequency of the vibrator Was 200 rpm and the film was formed at room temperature.

  FIG. 4 shows a photograph of the semiconductor clathrate Ba6Ge25 compound produced in this example. (1) is an appearance photograph of a semiconductor clathrate Ba6Ge25 compound thin film produced by the AD method. Although a thin film is formed on the glass substrate, it can be seen that there is a large distribution in film thickness, and the central part is thin. (2) is a micrograph of a semiconductor clathrate Ba6Ge25 compound thin film produced by the AD method. A non-uniform film is formed. At this time, the average particle size of the clathrate structure was 150 nm. On the other hand, in the uniform film structure of Example 1, the average particle diameter is 50 nm, and the average particle diameter of the structure is important in forming a uniform and dense structure.

  FIG. 5 shows one embodiment of a thermoelectric conversion element constituted by using a thermoelectric material of a semiconductor clathrate compound according to the present invention.

  The thermoelectric conversion element 10 of this embodiment includes a plurality of thermoelectric films 13 made of a p-type thin-film semiconductor clathrate, n-type, between insulating substrates 11 and 12 that are spaced apart from each other and disposed opposite to each other. A plurality of thermoelectric films 14 made of a thin-film semiconductor clathrate are alternately arranged, and lower ends of a pair of adjacent thermoelectric films 13 and 14 are intermittently connected by a thin film electrode 15 and adjacent to each other. The upper ends of the other thermoelectric films 13 and 14 are intermittently connected to each other by the thin film electrode 16 and at the same time, the end of the adjacent p-type thermoelectric film 13 and the end of the n-type thermoelectric film 14 are staggered. Are connected by a plurality of electrode thin films 15 and 16 so that all thermoelectric films are connected in series. Further, of the plurality of thermoelectric films 13 and 14 between the upper and lower substrates, the connection part 17 is joined to the thermoelectric film 13 at one end, and the connection part 18 is joined to the thermoelectric film 14 at the other end. It is configured.

  As the substrates 11 and 12, transparent resin substrates are used, but resin sheets may be used. As a semiconductor clathrate, a BaAuGe clathrate was used as a raw material powder, and a film was formed by the AD method described in Example 1. A Ti / AuTi film was formed on the thin film electrode by sputtering. Electric power can be generated by adding a temperature difference of 100 degrees above and below the substrates 11 and 12. By using the present invention, it is possible to manufacture a sheet-like heat conversion element.

It is the photograph of the semiconductor clathrate Ba6Ge25 compound of 1st Example produced by this invention, (1) is an external appearance electron micrograph of a composite structure, (2) is an electron micrograph of a composite structure, (3) is It is a scanning electron micrograph of fine particles. It is a figure which shows the X-ray-diffraction profile of the semiconductor clathrate Ba6Ge25 compound of the 1st Example produced by this invention. It is a figure which shows the transmittance | permeability spectrum of the semiconductor clathrate Ba6Ge25 compound of the 1st Example produced by this invention. It is a photograph of the 3rd Example of the semiconductor clathrate Ba6Ge25 compound produced by this invention, (1) is an external appearance electron micrograph of a composite structure, (2) is an electron micrograph of a composite structure. It is a figure which shows the cross-section of the thermoelectric conversion element which is the 4th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Thermoelectric conversion element 11, 12 Board | substrate 13 Thermoelectric film which consists of p-type thin film-like semiconductor clathrate 14 Thermoelectric film which consists of n-type thin-film-like semiconductor clathrate 15, 16 Thin film electrodes 17, 18 Connection part

Claims (17)

A compound structure formed on a substrate surface and having a basic structure in which atoms are arranged in a cage shape by ionic bonds or covalent bonds to form a higher order structure by the same bond,
The composite structure is polycrystalline, the crystals constituting the composite structure have substantially no crystal orientation, and there is substantially no grain boundary layer composed of a glass layer at the interface between the crystals. And a composite structure.   The composite structure according to claim 1, wherein the composite structure has an average particle diameter of 100 nm or less.   The composite structure according to claim 1, wherein the compound is a semiconductor clathrate.   The semiconductor clathrate includes a clathrate lattice mainly composed of atoms of group IVB elements of the periodic table, and a periodic table IA group, IIA having a mass larger than that of the constituent atoms of the clathrate lattice contained in the lattice gap of the clathrate lattice 4. The composite structure according to claim 3, wherein the composite structure is at least one doping atom selected from the group consisting of Group III, Group IIIA, Group IB, Group IIB, and Group IIIB.   The semiconductor clathrate includes a clathrate lattice mainly composed of atoms of group IVB elements of the periodic table, and a periodic table IA group having a mass larger than the constituent atoms of the clathrate lattice contained in the lattice gap of the clathrate lattice, IIA Group VA, VIA, Periodic Table VA, Group IIIA, Group IB, Group IIB, Group IIIB, at least one doping atom substituted with at least a part of the atoms constituting the clathrate lattice, 4. The composite structure according to claim 3, which is a clathrate compound mainly composed of at least one substituent atom among atoms of Group VIIA, Group VB, Group VIB, Group VIIB, and Group VIII.   The composite structure according to claim 4 or 5, wherein the group IVB element of the periodic table is Si or Ge.   The semiconductor clathrate is Ge-based, BaGe-based, BaAuGe-based, BaAuGaGe-based, BaPtGe-based, BaPdGe-based, BaPdGaGe-based, BaCuGaGe-based, BaAgGaGe-based, Si-based, BaSi-based, BaAuSi-based, BaAuGaSi-based, BaPdSi-based, BaPdSi-based, The composite structure according to claim 3, which is a clathrate compound of at least one system selected from the group consisting of: BaPdGaSi, BaPtGaSi, BaCuGaSi, and BaAgGaSi.   The composite structure according to claim 1, wherein the compound is an oxide cage material.   9. The composite structure according to claim 8, wherein the oxide soot-like substance is based on 12CaO.7Al2O3.   The composite structure according to claim 1, wherein the compound is an electride compound.   The composite structure according to claim 1, wherein the composite structure is formed into a thin film by a normal temperature impact solidification phenomenon.   The composite structure according to claim 11, wherein the composite structure is formed by an aerosol deposition method.   A thermoelectric conversion element using the composite structure according to claim 1. A plurality of thermoelectric films made of p-type thin-film semiconductor clathrate and a plurality of thermoelectric films made of n-type thin-film semiconductor clathrate are alternately arranged between substrates that are opposed to each other in the vertical direction. And
The lower end portions of a set of adjacent thermoelectric films are intermittently connected by thin film electrodes, and the upper end portions of other thermoelectric films adjacent to each other are intermittently connected by thin film electrodes,
The ends of the adjacent p-type thermoelectric films and the ends of the n-type thermoelectric films are alternately connected, so that all the thermoelectric films are connected by a plurality of electrode thin films so that they are connected in series. It is comprised, The thermoelectric conversion element of Claim 13 characterized by the above-mentioned.   The composite structure according to claim 1, wherein the composite structure is formed on a substrate made of glass or plastic.   A method for producing a composite structure, comprising forming a cage structure compound on a substrate by an aerosol deposition method using a normal temperature impact solidification phenomenon. The method according to claim 16, wherein by the aerosol deposition method, the fine brittle material is loaded with a mechanical impact force and pulverized and bonded to form the cage structure compound as a molded body on the substrate. The manufacturing method of the composite structure of description.