JP2005279843A - Crystal material including fine wires, method of producing it, and nanowire device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new technique which enables the control of fine wire arrangement in a crystal material. <P>SOLUTION: The crystal material includes a crystalline matrix and the plurality of fine wires each having a composition different from that of the crystalline matrix. The crystalline matrix includes a grain boundary or a hetero-phase interface, and the fine wires extend in a predetermined direction along the grain boundary or the hetero-phase interface. Each fine wire 5 is preferably formed of atoms 4 diffused along dislocations 3 present in a small angle boundary at predetermined intervals. By using the dislocations or the like of the grain boundary to control the fine wire arrangement, the crystal material in which the arrangement of nanowires that are so fine that a quantum effect can be expected, is correctly, e.g. periodically regularly, controlled, is produceable. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a crystal material useful for various devices utilizing a fine wire such as a nanowire and a method for producing the same, and further relates to a nanowire device using the crystal material.

  Dislocations are linear lattice defects with disordered atomic arrangement. Conventionally, the application of dislocation has been limited to improving the strength of the material, but the present inventors have proposed a new device using dislocation inside the crystal in Patent Document 1.

  In Patent Document 1, dislocations 2 are introduced into single crystal 1 (FIG. 11A) at a high density by plastic deformation under predetermined conditions (FIG. 11B), and then dislocations 2 are arranged in a predetermined direction by heat treatment. A crystal material (FIG. 11 (c)) obtained by the above process is disclosed. If dislocations arranged in a predetermined direction at a high density are used for forming nanoholes, nanowires, etc., a new high-functional device can be obtained from this crystalline material.

  Patent Document 1 also discloses a basic technique for forming nanowires. Since there is a strain field around the dislocation, this influence causes segregation of solute elements (Cottrell effect) and the diffusion rate becomes faster than the bulk (pipe diffusion). For this reason, if atoms are diffused from the surface of the crystal material to the inside, the atoms are segregated along the dislocations to form nanowires.

  Note that in this specification, the nanowire means a wire having a diameter of 50 nm or less, preferably 10 nm or less.

International Publication No. 03/089698 Pamphlet

  According to the technology disclosed in Patent Document 1, a crystal material including nanowires arranged in a predetermined direction can be obtained. However, with the technique disclosed in Patent Document 1, it is difficult to regularly arrange nanowires in a crystal material or to form nanowires in a desired position of the crystal material.

  Therefore, the present invention aims to establish a new technique capable of controlling the arrangement of fine lines in a crystal material, thereby providing a new crystal material and a device using this material.

  If dislocations introduced by plastic deformation are used, there is a limit to the fine line arrangement control. The present inventors paid attention to the crystal grain boundary and the heterogeneous interface, and completed the present invention.

  The crystal material of the present invention includes a crystal matrix and a plurality of fine wires having a composition different from that of the crystal matrix, and the crystal matrix includes a crystal grain boundary or a heterophasic interface, along the crystal grain boundary or the heterophasic interface. The plurality of thin wires extend in a predetermined direction.

  According to another aspect of the present invention, as a method suitable for manufacturing the above crystal material, at least two crystals are joined at a small inclination grain boundary, a corresponding grain boundary, or an angle within ± 10 ° from the corresponding grain boundary. A process for producing a crystal matrix including a crystal grain boundary which is a shifted grain boundary, and heating in a state where a material different from the crystal matrix is in contact with the crystal grain boundary has a composition different from that of the crystal matrix. And a step of forming a plurality of fine lines extending in a predetermined direction along a plurality of voids existing at the crystal grain boundary.

  In the present invention, the arrangement of a plurality of fine lines is controlled using a crystal grain boundary or a heterogeneous interface. For example, if a crystal grain boundary is formed at a predetermined position by joining two crystals, a plurality of fine lines can be introduced at that position. As represented by the small-angle grain boundary and the corresponding grain boundary (Σ grain boundary), the atomic arrangement in the crystal grain boundary may have atomic level regularity. In the embodiment of the present invention using this, a plurality of fine lines can be regularly arranged. In at least a preferred embodiment of the present invention, the arrangement of fine nanowires can be accurately controlled to such an extent that a quantum effect can be expected. This excellent controllability is extremely useful for the production of nanowire devices.

  Hereinafter, preferred embodiments of the present invention will be described.

  The crystal material of the present invention only needs to include a structure in which a plurality of fine lines extend along one crystal grain boundary or a heterogeneous interface, and includes a member other than a crystal grain boundary in which no fine lines are formed or a crystal matrix. It does not matter.

  The material of the crystal matrix is not particularly limited, and may be appropriately selected from various ceramics, semiconductors, and metals according to desired characteristics and applications. There is no limitation on the crystal system of the crystal matrix. The crystal matrix may be, for example, alumina, zirconia, barium titanate, silicon carbide, strontium titanate, zinc oxide, silicon, germanium, or gallium nitride.

  The fine wire has a composition different from that of the crystal matrix. That is, the thin line may contain the same atoms as the crystal matrix, but is displayed with a composition formula different from at least the crystal matrix. The thin wire is not particularly limited like the material of the crystal matrix, but may contain a transition metal element and a rare earth element. For example, Ti, Cu, Mn, Fe, Ni, Au, and Ag are included. It is preferable. However, the thin wire may contain a nonmetallic element or may be composed of only a nonmetallic element. The fine line may be a metal or a compound (including a non-stoichiometric compound).

In a preferred embodiment of the present invention, the electrical conductivity of the plurality of fine wires is higher than that of the crystal matrix, and this local conductivity is used in the device. In this case, the electrical conductivity of the plurality of thin wires is preferably 10 ⁻⁶ Ω ⁻¹ cm ⁻¹ or more, more preferably 10 ⁻¹ Ω ⁻¹ cm ⁻¹ or more.

  The crystal grain boundary in the present invention is preferably a low-angle grain boundary, a corresponding grain boundary, or a grain boundary deviated by an angle within ± 10 ° from the corresponding grain boundary, particularly a low-angle grain boundary. The low-angle grain boundary is a grain boundary having an inclination angle (2θ; see FIG. 1) of 15 ° or less. As shown in FIG. 1, dislocations (edge dislocations or dislocations containing edge components) 3 are regularly arranged at a predetermined interval d in a grain boundary having an ideal state or close to it. The crystal grain boundary may be either symmetric or asymmetric, but is preferably a symmetric grain boundary as shown in FIG.

  The distance d between the dislocations 3 can be controlled by the tilt angle 2θ. Increasing the tilt angle 2θ decreases the distance d, and decreasing the tilt angle 2θ increases the distance d.

  As shown in FIG. 2, if the atoms 4 are diffused along the dislocations 3 by heat treatment or the like, the thin wires 5 can be arranged at a predetermined interval d.

  The distance between the thin wires 5 is not particularly limited. However, in order to increase the density of the thin wires, the surface perpendicular to the direction in which the thin wires 5 extend (for example, the surface 6 of the crystal material) is 1 μm or less, for example, 0.5 nm to 1 μm. In the following, it is more preferably 1 nm to 100 nm, particularly 5 nm to 50 nm.

  Fine lines can also be regularly arranged by using corresponding grain boundaries (Σ grain boundaries). The corresponding grain boundary belongs to a large-angle grain boundary having an inclination angle (2θ) of more than 15 °, but, like the small-angle grain boundary, has a regular regular structure at the grain boundary and has a structural unit atomic arrangement having a void structure. . Further, it may be a grain boundary having an angle slightly deviated from the corresponding grain boundary (deviation is within ± 10 °). In this case, a special dislocation called a DSC dislocation is formed in order to compensate for the angular deviation.

  1 and 2 show an example of using a low-inclination grain boundary, so diffusion along a dislocation (edge dislocation or dislocation including an edge component) has been described. The atoms may be diffused along the void structure in the structural unit, and the atoms may be diffused along the void structure and / or DSC dislocation in the structural unit existing at the grain boundary slightly shifted from the corresponding grain boundary. Good. If atoms are diffused along voids represented by these dislocations and void structures, it is possible to arrange a plurality of fine lines in a predetermined direction. In this specification, as terms including the above dislocations and void structures, Use “void”.

  In the present invention, a plurality of fine wires may be introduced at the heterogeneous interface. That is, the materials facing each other through the interface may be different from each other. In this case, a fine line may be formed using misfit dislocations.

  Thus, by utilizing the regularity of the atomic arrangement at the grain boundary, at least a part, preferably all, of the plurality of fine lines can be arranged so as to satisfy the predetermined regularity. The predetermined regularity is not limited to the equidistant arrangement as shown in FIG.

  Note that in the crystal grain boundary, one dislocation may be decomposed to form a partial dislocation. The crystal material of the present invention may contain partial dislocations, and at least a part of the plurality of fine wires may extend along the partial dislocations.

  The edge dislocation 3 has nano-order holes. The diameter of this hole is about several angstroms although it depends on the Burgers vector of the edge dislocation 3. This hole can be enlarged by a) heat-treating at a temperature more than half the melting point of the crystal expressed in absolute temperature, or b) etching performed by immersion in a chemical corrosive solution such as molten KOH.

  The diameter of the fine wire can be adjusted by controlling the hole diameter as described above. The diameter of the thin wire is merely an example, but it may be, for example, 0.1 nm to 1 μm, further 0.2 nm to 50 nm, particularly 0.5 nm to 5 nm.

  In the embodiment using the periodic structure such as the crystal grain boundary described above, the interval between the fine lines can be controlled, and the diameter of the fine lines can also be controlled. If a method described later is used, the crystal grain boundary can be formed at an arbitrary position. If this is utilized, it becomes possible to arrange | position a nano fine wire with the desired regularity in the desired position in a bulk. This is extremely significant in the design of various nanowire devices. The present invention encompasses nanowire devices comprising a crystalline material provided by the present invention.

  The crystal material of the present invention is also useful for a device utilizing the quantum effect of fine wires. Since the conventional quantum wire is formed on the solid surface, the volume fraction is low, and the electronic physical properties are affected by the portion in contact with the solid surface and the exposed portion. On the other hand, in a preferred embodiment of the present invention, the quantum wires are embedded in the crystal at a high density, so that the volume fraction is high, and the interface between the crystal and the quantum wires contributes to the development of electronic properties. If this is utilized, the realization of the quantum wire bundle containing device which has a new function can be expected.

  Although the arrangement control of thin lines has been described above, the present invention can also be applied to the arrangement control of nanoholes in a crystal material into which nanoholes are introduced. Nanoholes have high utility value as molecular sieve membranes.

  That is, the present invention includes a crystal matrix and a plurality of nanoholes present in the crystal matrix, and the crystal matrix includes a crystal grain boundary or a heterophase interface, and a plurality of crystal holes along the crystal grain boundary or heterophase interface. You may implement as a crystalline material characterized by the nanohole extending | stretched to the predetermined direction, and also a nanohole device containing this crystalline material.

  The crystal material having a plurality of nanoholes is formed by joining at least two crystals and forming a crystal grain boundary which is a low-angle grain boundary, a corresponding grain boundary, or a grain boundary shifted by an angle within ± 10 ° from the corresponding grain boundary. It can manufacture by the method including the process of producing the crystal parent | base containing.

  The nanoholes may use voids such as dislocations already described, and the arrangement control thereof may be performed in the same manner as the arrangement control of thin lines already described, and thus description thereof is omitted. All of the above descriptions for thin wires, such as spacing, diameter, etc., also apply to nanoholes.

  The diameter of the nanohole differs depending on the type of void to be formed (dislocation, void structure in the structural unit), so it may be selected using this, but the control of the hole diameter in the dislocation exemplified above (hole diameter Adjustment may be made by applying (enlargement). The preferred diameter of the nanohole is not particularly limited because it is specified by the gas molecules to be transmitted, etc., but is, for example, 0.1 nm or more and 1 μm or less.

  If the arrangement of the nanoholes is controlled by using the present invention, it is possible to realize, for example, higher transparency due to regular transmission positions as compared with the case where the nanoholes are randomly formed.

  The production method of the present invention includes a step of producing a crystal matrix including a crystal grain boundary which is a low-inclination grain boundary, a corresponding grain boundary, or a grain boundary shifted by an angle within ± 10 ° from the corresponding grain boundary. This step is preferably performed by heating in a state where the crystal planes to be bonded are in contact with each other. Although the heating temperature depends on the crystal material, for example, in the case of alumina, the heating temperature is preferably 400 ° C. or higher and the melting point (about 2080 ° C.) or lower. When heating, compressive stress may be applied to the joint surfaces as necessary.

  In order to perform this bonding process satisfactorily and obtain an ideal crystal grain boundary in which the dislocation arrangement is controlled, it is preferable to take some measures. For example, at least two crystals to be bonded may be prepared so as to have a thickness of 0.01 mm or more, preferably 0.1 mm or more in the direction perpendicular to the bonding surface. If it is too thin, micro deformation of the crystal such as warping may hinder crystal bonding. When a minute crystal material is required, the crystal material obtained by carrying out the manufacturing method of the present invention may be cut or polished in a later step, as will be described later.

  The crystal planes to be joined are selected so that the tilt angle is 15 ° or less when forming a small tilt grain boundary. The parallelism is preferably within 3 °. The common rotation axis should be in the low index direction. Furthermore, the crystal planes to be joined should be improved in smoothness in advance, for example, by mechanochemical polishing. The smoothness is preferably 100 nm or less, more preferably 10 nm or less, and particularly preferably 5 nm or less, expressed as Rmax.

  The production method of the present invention further includes a heating step (diffusion step) performed in a state where a material different from the crystal matrix is in contact with the crystal grain boundary. The above-mentioned material for supplying the atoms constituting the thin wire is a liquid phase such as a well-known thin film forming method, for example, a vapor phase film forming method such as a sputtering method or a chemical vapor deposition method, or a plating method on the surface where the grain boundary is exposed. A thin film may be formed by a film formation method (see FIG. 2). However, the present invention is not limited to this, and a previously formed bulk material may be used.

  The heating temperature in this diffusion step may be selected as appropriate, but is preferably 400 to 2000 ° C, for example. The atmosphere during heating is not particularly limited. When the metal is diffused, a reducing atmosphere or an inert atmosphere is preferable, but depending on the type of metal, heating may be performed in an oxidizing atmosphere such as the air. The object to be diffused is preferably a metal as described above, but is not limited thereto. There is no restriction | limiting in the form of diffusion, You may diffuse as not only an atom but ion.

  In the manufacturing method of the present invention, a processing step of processing the crystal base into a predetermined shape may be further performed after the step of manufacturing the crystal base including the crystal grain boundary. In the bonding process for manufacturing the crystal matrix, it is desirable that the crystal to be bonded has a certain size (thickness) in the direction perpendicular to the bonding surface. A processing step of adjusting the size of the crystal matrix by cutting, polishing, or the like may be performed. This processing step may be performed before or after the diffusion step.

  In the above description, the method of forming a thin film on the surface where the crystal grain boundary is exposed to form a thin wire material after the bonding step has been described, but the manufacturing method of the present invention can be implemented without following this. For example, a crystal matrix may be manufactured by previously arranging a predetermined element on the bonding surface of the crystal to be bonded and then bonding the crystal. In this case, the material is arranged before the bonding step, and heating is performed in a state where the material is present on at least one of opposing surfaces (bonding surfaces) in the crystal grain boundary. The material may be arranged on the bonding surface by, for example, depositing a thin metal or the like on the crystal bonding surface, or by applying a solution containing predetermined ions on the bonding surface. In the production method of the present invention, it is only necessary that a thin wire material is disposed in the vicinity of the crystal grain boundary so that the fine wire can be formed by heating, and this state is called a state in which the material is in contact with the crystal grain boundary.

  The method described above is a method suitable for the production of the crystal material of the present invention, but is not limited to the method of producing the crystal material of the present invention by the above method. The crystal material of the present invention may be manufactured using a heterogeneous interface, for example, there is a possibility that it can be manufactured by utilizing abnormal grain growth, recrystallization, and grain growth in the presence of a liquid phase. is there.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, the following Example is only the illustration of preferable embodiment of this invention similarly to the said description in this column.

  First, as shown in FIG. 3, two alumina single crystals are formed such that the [1-100] axis is the common rotation axis, the (11-20) plane is the reference plane, and the angle (2θ) between the [0001] axes is 2 °. Then, diffusion bonding was performed at 1500 ° C. for 10 hours under a load of 0.2 MPa. The single crystal had a thickness in the joining direction of 6 mm and a joining surface of 12 mm × 15 mm. A photograph of the bicrystal obtained by bonding is shown in FIG. When the vicinity of the joint was observed with an optical microscope, pores and the like were not observed, and a good joined state was obtained. The bicrystal thus obtained was cut and polished into a thin film having a diameter of 3 mm and a thickness of 0.1 mm.

Next, a Ti film was formed on the surface of the thin film sample by vapor deposition. The thickness of the Ti film was about 50 nm. Subsequently, heat treatment was performed at 1500 ° C. for 8 hours in a reducing atmosphere of Ar 95% and H ₂ 5%.

  FIG. 5 shows a state in which the periphery of the crystal grain boundary of the crystal material thus obtained is observed with a transmission electron microscope (TEM). FIG. 5 is a TEM bright field image. From FIG. 5, the periodic contrast along the low-inclination grain boundary of alumina can be confirmed.

  FIG. 6 shows the result of line analysis using a scanning transmission electron microscope (STEM) along the direction in which periodic contrast is observed by X-ray energy dispersive spectroscopy (EDS). From FIG. 6, the presence of Ti element can be confirmed at the same interval as the periodic contrast.

  From the above, it was confirmed that Ti was segregated strongly along the dislocations present in the low-angle grain boundaries.

When Ti segregated to dislocations was analyzed by electron energy loss spectroscopy (EELS), the spectrum was consistent with the EELS spectrum of Ti ³⁺ . Ti was segregated as Ti ³⁺ , ie, Ti ₂ O ₃ instead of TiO ₂ .

The conductivity around the crystal grain boundary was measured with a scanning probe microscope (SPM). FIG. 7 shows an outline of SPM used for measurement and measurement conditions. As shown, the applied voltage was 200V. The results are shown in FIG. In insulating alumina, it can be confirmed that Ti segregated to dislocations periodically forms conductive thin wires. As a result of the analysis, the electrical conductivity of the thin wire was about 10 ⁻¹ cm ⁻¹ Ω ⁻¹ .

  Furthermore, when the magnification was slightly increased and observation was performed by TEM, it was confirmed that the contrast at the crystal grain boundary was separated into two in detail, as shown in FIG. 9 which is a dark field image. Therefore, the structure was analyzed using a high-resolution electron microscope (HRTEM). The results are shown in FIG.

  From this HRTEM image, the dislocation contrast of the pair is composed of two partial dislocations having Burgers vectors of b = 1/3 [10-10] and b = 1/3 [01-10]. B = 1/3 [11-20]. 1/3 [11-20] corresponds to the minimum translation vector in the plane direction of the grain boundary. This result shows that the dislocation formed to compensate the tilt angle decomposed into two. The distance between the fine lines can be adjusted by utilizing the decomposition of dislocations.

  According to the present invention, it is possible to introduce a plurality of nanowires into a crystalline material while controlling the arrangement. The present invention makes it possible to introduce fine wires with high density and high orientation into a base material with good controllability, and is useful, for example, in devices using quantum wires. However, the use of the present invention is not limited to the quantum wire, and may be simply the use of conduction of the thin wire, or the electron wave between the thin wires. The characteristic that the thin wire appears is not limited to the electrical characteristic. The present invention has a great utility value in a wide variety of devices.

It is a figure which illustrates arrangement | positioning of the dislocation in the symmetrical low inclination grain boundary contained in one form of the crystal material of this invention. It is sectional drawing which showed the state before and behind diffusing an atom along a dislocation in order to manufacture one form of the crystal material of this invention. It is a perspective view which shows the crystal axis etc. of the alumina bicrystal produced in the Example. It is a photograph of the alumina bicrystal produced in the Example. It is a TEM bright field image of the low-inclination grain boundary of the alumina bicrystal produced in the Example. It is the EDS spectrum measured along the low-angle grain boundary of the alumina bicrystal produced in the Example. It is a figure which shows the outline | summary of the electric current value measurement by SPM implemented about the alumina bicrystal produced in the Example. FIG. 8 is a measurement result of a current value obtained by the measurement schematically shown in FIG. It is a TEM dark field image of the low-inclination grain boundary of the alumina bicrystal produced in the Example measured by higher magnification than FIG. It is a figure which shows the result of having observed the decomposition | disassembly of the dislocation in the alumina bicrystal produced in the Example by HRTEM. It is a figure which shows the conventional crystal material which patent document 1 discloses, and its manufacturing method.

Explanation of symbols

1 single crystal 2, 3 dislocation 4 atom 5 fine wire 6 surface of crystal material

Claims (16)

A crystal matrix, and a plurality of fine wires having a composition different from that of the crystal matrix,
The crystal material, wherein the crystal matrix includes a crystal grain boundary or a heterophase interface, and the plurality of thin wires extend in a predetermined direction along the crystal grain boundary or the heterophase interface.   The crystal material according to claim 1, comprising a crystal grain boundary in which the plurality of thin wires extend.   The crystal material according to claim 2, wherein the crystal grain boundary is a low-inclination grain boundary, a corresponding grain boundary, or a grain boundary shifted from the corresponding grain boundary by an angle within ± 10 °.   The crystal material according to any one of claims 1 to 3, wherein at least some of the plurality of thin wires are arranged so as to satisfy a predetermined regularity.   The crystal material according to any one of claims 1 to 4, wherein an interval between the plurality of thin wires is 1 µm or less on a plane orthogonal to the predetermined direction.   The crystal material according to any one of claims 1 to 5, wherein at least some of the plurality of thin wires extend along partial dislocations in which one dislocation is decomposed.   The crystal material according to any one of claims 1 to 6, wherein a diameter of the plurality of thin wires is 0.1 nm or more and 1 µm or less.   The crystal material according to claim 1, wherein the electrical conductivity of the plurality of thin wires is higher than that of the crystal matrix. The crystal material according to claim 8, wherein the electrical conductivity of the plurality of thin wires is 10 ⁻⁶ Ω ⁻¹ cm ⁻¹ or more.   A nanowire device comprising the crystalline material according to claim 1. Joining at least two crystals to produce a crystal matrix including a crystal grain boundary that is a low-angle grain boundary, a corresponding grain boundary, or a grain boundary that is displaced from the corresponding grain boundary by an angle within ± 10 °;
By heating in a state where a material different from the crystal matrix is in contact with the crystal grain boundary, the crystal grain boundary has a composition different from that of the crystal matrix, and in a predetermined direction along a plurality of voids existing in the crystal grain boundary. Forming a plurality of elongated wires; and
A method for producing a crystalline material comprising:   The method for producing a crystal material according to claim 11, wherein heating is performed in a state where the material is in contact with a surface where the crystal grain boundary is exposed.   The method for producing a crystal material according to claim 11, wherein heating is performed in a state where the material is present on at least one of opposing faces in the crystal grain boundary.   The method for producing a crystal material according to any one of claims 11 to 13, wherein the at least two crystals have a thickness of 0.01 mm or more in a direction perpendicular to a bonding surface.   The method for producing a crystal material according to any one of claims 11 to 14, wherein the at least two crystals have a surface having Rmax of 100 nm or less as a bonding surface.   The method for producing a crystal material according to any one of claims 11 to 15, further comprising a step of processing the crystal matrix into a predetermined shape after the step of manufacturing the crystal matrix including a crystal grain boundary.