Metal / carbide heterojunction thin film material, preparation method, load and application

Abstract

The invention discloses a metal / carbide heterojunction thin film material, a preparation method, a load and application, and the thin film material comprises a carbide structure which is obtained by carbonizing a transition metal wafer or a metal block as a substrate under a protection condition; and an interface only containing a single metal / carbide heterojunction is formed at the adjacent position of the first metal coating and the second metal coating. The method is simple in scheme and good in controllability, the obtained product is not prone to being interfered by impurity elements, the catalytic effect can be efficiently achieved through a simple interface structure, and the method has extremely high popularization and application performance.

Description

Technical Field

[0001] The present invention relates to catalytic technology, in particular to a metal / carbide heterojunction thin film material, a preparation method, a load and an application thereof. Background Art

[0002] Transition metal carbides often have catalytic properties similar to those of precious metals such as platinum, thus attracting more and more attention in the field of energy catalysis, and showing potential as a substitute for precious metal materials in many specific application scenarios. On this basis, loading a second metal component can effectively adjust the electronic properties of transition metal carbides to create a catalytic system with more outstanding performance. For example, Martin's research group has made a series of research progress in related systems in recent years, and found that the Au / α-MoC catalyst bonded to the surface of α-MoC in the form of atomic clusters has extremely good catalytic activity in low-temperature water vapor shift reactions. In the Pt / α-MoC system, it was found that the interface between the precious metal Pt and the substrate α-MoC is a site for low-temperature adsorption and activation of water molecules.

[0003] The preparation methods of carbide-loaded metal material systems include the one-pot method and the impregnation method. The one-pot method is to directly carry out carbonization after adjusting the ratio of all precursors. The carbonization process can use low-carbon alkanes, olefins and other gases. If the precursor is rich in carbon components, an inert atmosphere can also be used for carbonization. The metal / carbide material obtained by this method usually contains a large amount of carbon deposits. The metal component may be dispersed on the surface of the transition metal carbide or on the surface of the carbon deposit. Its structure is complex and uncontrollable. The impregnation method considers the transition metal carbide as a catalyst carrier, impregnates the metal component precursor salt on it, and then decomposes the precursor salt through high-temperature heating treatment to form a strong interaction between the metal and the carbide to ensure the dispersion of the metal component. In order to ensure the high dispersion of the metal component, this method has to control the loading amount of the metal component within a relatively low range, which greatly limits the yield of the metal / carbide heterojunction catalytic material.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The purpose of the present invention is to provide a metal / carbide heterojunction thin film material, a preparation method, a load and an application. The implementation scheme is simple and the controllability is good. The obtained product is not easily interfered by impurity elements, and the catalytic effect can be efficiently achieved through a simple interface structure, which has extremely high promotion and applicability.

[0006] To achieve the above purpose, the embodiment of the present invention provides a metal / carbide heterojunction thin film material, including a carbide structure obtained by carbonizing a transition metal crystal or a metal material as a substrate under protective conditions; a second metal coating formed on the carbide structure; and a metal / carbide heterojunction interface containing only a single structure is formed at the adjacent positions of the two. The protective conditions are measures to isolate air, oxygen, water and other impurities under protective measures such as high vacuum and protective atmosphere.

[0007] In one or more embodiments of the present invention, the transition metal crystal is selected from transition metal single crystals and transition metal polycrystals.

[0008] In one or more embodiments of the present invention, the raw material of the transition metal crystal is selected from molybdenum polycrystal and tungsten polycrystal.

[0009] In one or more embodiments of the present invention, the second metal is selected from copper, nickel, gold, and platinum.

[0010] In one or more embodiments of the present invention, the raw material of the metal material is selected from: Mo or W.

[0011] In one or more embodiments of the present invention, the metal / carbide heterojunction thin film material includes a carbide structure obtained by carbonizing a transition metal crystal with a planar interface or a metal material with a polished interface as a substrate under protective conditions; a second metal coating is formed on the carbide structure; and the adjacent positions of the two form a single metal / carbide heterojunction interface.

[0012] In one or more embodiments of the present invention, the polishing interface satisfies: Ra0.4-Ra0.8.

[0013] In one or more embodiments of the present invention, the planar interface of the transition metal crystal satisfies: Ra4-Ra8.

[0014] In one or more embodiments of the present invention, the second metal coating layer is a sub-molecular monolayer structure, a one-molecular monolayer structure, a two-molecular monolayer structure, or a thin layer structure with a nanometer-scale thickness.

[0015] In one or more embodiments of the present invention, the carbide structure has a layer thickness of the order of hundreds of nanometers, that is, a thickness range of no more than 1 micrometer.

[0016] In one or more embodiments of the present invention, the method for preparing a metal / carbide heterojunction thin film material comprises the following steps: preparing a substrate material, -9mbar background), an appropriate amount of gaseous carbon source (partial pressure of the gaseous carbon source is 1 mbar), carbonization is carried out at a carbonization temperature, and then ultra-high vacuum annealing is carried out to completely eliminate the surface carbon residue to obtain a clean carbide film; a second metal coating is formed on the surface of the carbide film.

[0017] Preferably, the ultra-high vacuum annealing conditions are: 10 -9 mbar, annealing temperature 1100K.

[0018] In one or more embodiments of the present invention, the gaseous carbon source is selected from alkanes, alkenes, and alkynes not higher than C3.

[0019] In one or more embodiments of the present invention, a support includes a carrier and the aforementioned metal / carbide heterojunction thin film material.

[0020] In one or more embodiments of the present invention, the aforementioned metal / carbide heterojunction thin film material or the aforementioned support is used in catalyst technology.

[0021] It is well known that transition metal carbide materials themselves are easily contaminated by water and oxygen, which can change their surface or shallow surface components and structures. If the catalytic performance of the material is improved by increasing the complexity of the components, the complex and changeable structure of the surface interface makes it increasingly difficult to study its relationship with the catalytic performance of the material.

[0022] In view of the limitations of current research in this field, the present invention uses ultra-high vacuum interconnection technology, and can use vacuum chambers, near ambient pressure X-ray photoelectron spectroscopy systems (NAP-XPS), X-ray photoelectron spectrometers (X-ray Photoelectron Spectroscopy, XPS), scanning Auger electron spectrometers (ScanningAuger Electron Spectrometry, Scanning-AES), etc., without being exposed to air at all. A relatively flat transition metal wafer or polished metal block can be used as a substrate, and a carbonization process with controllable variables such as atmosphere and temperature is first performed. On this basis, a second metal component is further evaporated by physical vapor deposition, etc., to prepare a series of metal / carbide heterojunction thin film materials. XPS characterization can prove that the metal / carbide heterojunction film prepared by this method does not contain oxide impurities, and AES imaging can show that the film is uniform and flat at the micrometer scale. The resulting heterojunction thin film material is suitable for a variety of application scenarios such as catalytic mechanism research.

[0023] Compared with the prior art, the metal / carbide heterojunction thin film material, preparation method, load and application according to the embodiment of the present invention have the following advantages: ① A close contact between the metal and the carbide is achieved to avoid interference from components such as carbon deposits and oxides. The material contains only a single metal / carbide heterojunction interface, and there is no metal / carbon deposit and / or metal / oxide interface; ② The metal / carbide heterojunction thin film can be guaranteed to be uniform and flat at the micron size. Compared with the metal / carbide catalyst prepared by the current common method, the heterojunction thin film prepared by this method is much larger in size, and the thickness of the metal component thin film can be controlled to be about the thickness of an atomic monolayer. It has good control over the structure of the interface, has better atomic utilization efficiency for the material, and is conducive to achieving the highest catalytic efficiency per unit volume or unit mass, thereby reducing the loading amount of the catalytic substance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The growth mode calibration of Au on a molybdenum carbide film according to one embodiment of the present invention: (a) the trend of the ratio of Au 4f to Mo 3d with evaporation time, (b) the Au4f spectra obtained by testing at different evaporation times;

[0025] Figure 2 The following are the AES spectrum collection results of different regions after a single layer of Au is evaporated on the surface of molybdenum carbide according to one embodiment of the present invention: a is the EBSD data of the Au / MoC heterojunction, from which it can be seen that the crystal domain of MoC is about tens of microns; b is the AES spectrum collected on different crystal domains, and the peaks at different kinetic energy positions in the curve are the AES peaks of the four elements Au, Mo, C, and O; c is a table showing the content of each element that can be semi-quantitatively calculated based on the AES peak intensity of different elements;

[0026] Figure 3 The growth mode calibration of copper on the surface of molybdenum carbide film according to one embodiment of the present invention: (a) Cu 4f spectra obtained by testing at different evaporation times, (b) the trend of the ratio of Cu 4f to Mo 3d with evaporation time;

[0027] Figure 4 The growth mode calibration of nickel on the surface of molybdenum carbide film according to one embodiment of the present invention: (a) the trend of the ratio of Ni 4f to Mo 3d with evaporation time, and (b) the Ni 4f spectrum obtained by testing at different evaporation times. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0029] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0030] The method for preparing carbide films involved in the patent of the present invention mainly uses transition metal single crystals, polycrystalline sheets and polished polycrystalline blocks as substrate materials, and low-carbon alkanes, alkenes or alkynes as carbon sources. For example, in the vacuum chamber of the NAP-XPS equipment, about 1 mbar of ethylene gas is introduced, and the sample temperature is maintained at above 800K for carbonization. There may be a small amount of graphite carbon residue on the surface after carbonization, and the graphite carbon can be completely eliminated by the subsequent ultra-high vacuum annealing to obtain a clean carbide film. The entire process can be tracked in situ by NAP-XPS to ensure that the generated surface carbon is completely eliminated during the subsequent vacuum annealing process. Subsequently, the second metal component is evaporated on the surface of the above-mentioned transition metal carbide film by physical vapor deposition.

[0031] Example 1

[0032] The gold / molybdenum carbide heterojunction film of this embodiment is used in the vacuum chamber of the NAP-XPS equipment (the basic vacuum of the system is 10 -9 mbar background), ethylene gas of about 1 mbar was introduced, and the temperature of molybdenum multi-crystalline wafer (10*10*1mm, plane meets Ra6) was kept at 800K for carbonization for 10 minutes. A small amount of graphite carbon may remain on the surface after carbonization, which can be removed by subsequent ultra-high vacuum annealing (10 -9 mbar, 1100K, annealing time 10min) to completely eliminate the carbon dioxide, thus obtaining a clean carbide film with a thickness of 0.5 microns. The entire process can be tracked in situ by NAP-XPS to ensure that the generated surface carbon is completely eliminated during the subsequent vacuum annealing process. Subsequently, gold is evaporated at room temperature on the surface of the prepared molybdenum carbide film. Figure 1 As shown in the figure, the samples represented by each point were sequentially evaporated with gold for 5 minutes, and then tested by XPS to obtain the peak area ratio of Au 4f to Mo 3d. A curve of the ratio changing with the evaporation time is drawn, as shown in Figure 1 (a). It can be seen that the curve can be divided into two straight lines and two inflection points. The first inflection point appears at 27 minutes, and the second inflection point appears at 54 minutes. The slope of the second straight line is greater than that of the first straight line. After 55 minutes, the slope of the curve tends to be gentle. Based on this, combined with the classic criterion of film growth mode, we believe that at room temperature, Au first grows layer by layer on the surface of the molybdenum carbide film to two molecular monolayers, and then begins the island growth mode. Schematic diagram of the Au film growth mode, all marked in Figure 1 Near the corresponding stage in (a).

[0033] The prepared Au / MoC heterojunction film was then transferred to the AES equipment for characterization via a vacuum interconnection pipeline. The results showed that the surface of a monolayer of Au / MoC heterojunction film was uniform and flat, which also verified the correctness of the XPS calibration curve for the Au film growth mode. Using the AES point sampling and spectrum measurement function, AES point sampling tests were performed on different areas in different domains, and the results were as follows: Figure 2 It can be seen that the contents of Au, C, and Mo measured in the AES spectra of different domains and different morphological features are basically consistent.

[0034] Example 2

[0035] The preparation method of the copper / molybdenum carbide heterojunction film of this embodiment is basically the same as that of embodiment 1, and only the corresponding raw materials need to be replaced, such as replacing gold with copper during evaporation. The results show that the second metal component can complete the spreading of the first molecular monolayer on the surface in a layer-by-layer growth mode, and a uniform and flat metal / carbide heterojunction film material with a micron size can be formed. Figure 3 shown.

[0036] Example 3

[0037] The nickel / molybdenum carbide heterojunction film of this embodiment is prepared in the same manner as in Example 1, except that the corresponding raw materials need only be replaced, such as replacing gold with copper during evaporation. The results show that the second metal component can complete the spreading of the first molecular monolayer on the surface in a layer-by-layer growth mode, and can form a uniform and flat metal / carbide heterojunction film material at the micron level. Figure 4 shown.

[0038] Example 4

[0039] The difference between the nickel / tungsten carbide heterojunction film of this embodiment and that of embodiment 1 is that the substrate uses a tungsten metal block (10*10*1mm, surface polishing Ra0.8), thereby obtaining a clean carbide film with a thickness of 0.5 microns. The sample results show that the second metal component can complete the spreading of the first molecular monolayer on the surface in a layer-by-layer growth mode, and can form a uniform and flat metal / carbide heterojunction film material at the micron level.

[0040] Example 5

[0041] The difference between the nickel / molybdenum carbide heterojunction film of this embodiment and that of embodiment 1 is that the substrate uses a molybdenum metal block (10*10*1mm, surface polishing Ra0.4), thereby obtaining a clean carbide film with a thickness of 0.5 microns. The sample results show that the second metal component can complete the spreading of the first molecular monolayer on the surface in a layer-by-layer growth mode, and can form a uniform and flat metal / carbide heterojunction film material at the micron level.

[0042] Example 6

[0043] The difference between the nickel / tungsten carbide heterojunction film of this embodiment and the embodiment 1 is that the substrate uses a tungsten single crystal (10*10*1mm, the plane meets Ra4), so as to obtain a clean carbide film with a thickness of 0.5 microns. The sample results show that the second metal component can complete the spreading of the first molecular monolayer on the surface in a layer-by-layer growth mode, forming a uniform and flat metal / carbide heterojunction film material at the micron level.

[0044] Example 7

[0045] The difference between the nickel / tungsten carbide heterojunction film of this embodiment and the embodiment 1 is that the substrate uses a tungsten polycrystalline wafer (10*10*1mm, the plane meets Ra8), so as to obtain a clean carbide film with a thickness of 0.5 microns. The sample results show that the second metal component can complete the spreading of the first molecular monolayer on the surface in a layer-by-layer growth mode, and can form a uniform and flat metal / carbide heterojunction film material at the micron level.

[0046] Example 8

[0047] The difference between the nickel / molybdenum carbide heterojunction film of this embodiment and that of embodiment 1 is that ethane gas of about 1 mbar is introduced to obtain a substantially clean (substantially clean means that the surface area with residual impurities is not more than 0.3%, the same below) 0.6 micron thick carbide film. The sample results show that the second metal component can complete the formation of the surface thin layer structure in a layer-by-layer growth mode (this may be affected by factors such as carbon deposition, which limits the spread of the first molecular monolayer, the same below), and overall a uniform and flat metal / carbide heterojunction film material at the micron level can still be formed.

[0048] Example 9

[0049] The difference between the nickel / molybdenum carbide heterojunction film of this embodiment and that of embodiment 1 is that propylene gas of about 1 mbar is introduced to obtain a substantially clean carbide film with a thickness of 0.67 micrometers. The sample results show that the second metal component can complete the formation of the surface thin layer structure in a layer-by-layer growth mode, and overall a uniform and flat metal / carbide heterojunction film material with a micrometer size can still be formed.

[0050] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A metal / carbide heterojunction thin film material, Including carbide structures obtained by carbonizing transition metal crystals or metal materials as substrates under protective conditions; A second metal coating is formed on the carbide structure, and a heterojunction interface containing only a single metal / carbide is formed at the adjacent positions of the two.

2. The metal / carbide heterojunction thin film material according to claim 1, It is characterized in that The transition metal crystal is selected from transition metal single crystal and transition metal polycrystal.

3. The metal / carbide heterojunction thin film material according to claim 2, It is characterized in that The raw material of the transition metal crystal is selected from molybdenum polycrystal and tungsten polycrystal.

4. The metal / carbide heterojunction thin film material according to claim 1, It is characterized in that The second metal is selected from copper, nickel, gold and platinum.

5. The metal / carbide heterojunction thin film material according to claim 1, It is characterized in that The raw material of the metal material is selected from: Mo or W.

6. The metal / carbide heterojunction thin film material according to claim 1, It is characterized in that The metal / carbide heterojunction thin film material comprises a carbide structure obtained by carbonizing a transition metal crystal with a planar interface or a metal material with a polished interface as a substrate under protective conditions; A second metal coating is formed on the carbide structure, and a heterojunction interface containing only a single metal / carbide is formed at the adjacent positions of the two.

7. The metal / carbide heterojunction thin film material according to claim 1, It is characterized in that The second metal coating layer is a submolecular monolayer structure, a one-molecule monolayer structure, a two-molecule monolayer structure or a thin layer structure with a nanometer-level thickness.

8. The method for preparing the metal / carbide heterojunction thin film material according to any one of claims 1 to 7, comprising the following steps: Prepare a substrate material, introduce an appropriate amount of gaseous carbon source under oxygen-free conditions, carbonize at a carbonization temperature, and then perform ultra-high vacuum annealing to completely eliminate surface carbon residues to obtain a clean carbide film; A second metal coating is formed on the surface of the carbide film.

9. A support, comprising a carrier and the metal / carbide heterojunction thin film material according to any one of claims 1 to 7.

10. Use of the metal / carbide heterojunction thin film material according to any one of claims 1 to 7 or the support according to claim 9 in catalyst technology.

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