A method and device for controlling the strain effect of a gold-silver nanometer thin film alloy

Abstract

The present invention discloses a method and a device for controlling the strain effect of a gold-silver nanometer thin film alloy. By using first-principles calculations based on density functional theory, the invention for the first time discovers a method for regulating the surface strain direction of a material in a gold-silver system by varying the doping positions of gold atoms in a silver thin film. Surface strain of a material is an effective means for improving the performance of the material. The invention provides a new direction for improving the performance of noble metal alloys such as gold and silver, and also provides a new idea for the research on strain engineering of other alloying systems.

Description

Technical Field

[0001] The present invention relates to the technical field of computational materials chemistry, and particularly relates to a method and device for controlling the strain effect of gold-silver nanothin film alloys. Background Art

[0002] Strain engineering is an effective method for regulating the physical properties of materials. Since the energy levels around the Fermi level are very sensitive to the neighboring atoms of the orbital coupling / interaction in the crystal and the degree of orbital interaction depends on the strain magnitude. This method has a significant impact on the electronic structure, thermoelectric properties, and optical properties of materials. Common methods introduced by strain engineering include intrinsic thermal vibration, atomic doping and adsorption, substrate deformation, pre-stretching the substrate, epitaxial growth, thermal expansion mismatch, substrate topography change, pressing bubbles, and tip indentation, etc. Among them, the atomic doping method can directly modify the material itself to avoid the material substrate and then regulate the performance, which is an efficient and promising means.

[0003] Precious metals such as gold and silver are called noble metals. However, in the state of the surface or nanoparticles, due to the existence of atoms with insufficient coordination, it induces that nanoscale Au and Ag may have strange properties different from those of the bulk. Both of them have extensive applications in the fields of nanophotonics, energy harvesting, molecular detection, biomedical treatment, and catalysis, etc. And due to the special synergistic effect between gold and silver in the gold-silver nanoalloy, it has properties completely different from those of nano-gold or nano-silver, and also has extensive research in multiple research fields. Among them, the regulation of the catalytic performance of AgAu nanoalloy by strain engineering is one of the hot research directions. Through the construction of lattice stretching, the electrochemical oxidation performance of AgAu alloy nanomaterials for biomass-derived alcohols including ethanol, ethylene glycol, and glycerol can be greatly improved.

[0004] However, at present, the influence of strain engineering on materials is mostly one-way, that is, only lattice compression or stretching can be achieved, and the same material will exhibit different properties under different strain degrees. Therefore, it is very necessary to find a method that can adjust the surface strain of materials in multiple directions, which will be very helpful for regulating the properties of materials, especially for improving the catalytic performance of noble metal nanoalloys such as AuAg. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for controlling the strain effect of gold-silver nanothin film alloys to overcome the deficiencies in the prior art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present application discloses a method for controlling the strain effect of gold-silver nanothin film alloys, including the following steps:

[0008] S1. Cut out the Ag(111) thin film from the Ag unit cell, fix the Z-axis of the system, and only allow relaxation in the XY plane. Select different numbers of atomic layers of the Ag(111) thin film, perform self-consistent calculations on the surface energy of Ag(111), obtain the relationship between the surface energy and the number of atomic layers of the Ag(111) thin film, and determine the minimum number of atomic layers of the Ag(111) thin film.

[0009] S2. According to the minimum number of atomic layers of the thin film determined in step S1, model the Ag(111) thin film, perform geometric optimization on the structure of the modeled Ag(111) thin film to obtain the most energy-stable structure, and record the atomic positions, bond lengths, total energy of the system, and total volume of the system of the Ag(111) thin film under this structure.

[0010] S3. Substitute and dope Au atoms in the most energy-stable structure obtained in step S2. According to the doping positions of the Au atoms, obtain different doped structure systems; perform geometric optimization on the doped structure systems to obtain the most stable structures of the doped structure systems, and record the total energy of the system and the total volume of the system under the most stable structures of the doped structure systems.

[0011] S4. Compare the most energy-stable structure in step S2 with the most stable structure of the doped structure system in step S3. According to the total energy of the system and the numerical value of the surface strain of the thin film calculated by subtracting the modulus of the z vector in the total volume and lattice constant of the system, construct the relationship between the atomic doping position and the total energy & surface strain of the system.

[0012] Preferably, a vacuum layer is provided between the atomic layers of the Ag(111) thin film in step S1.

[0013] Preferably, when selecting different numbers of atomic layers of the Ag(111) thin film in step S1 and performing self-consistent calculations on the surface energy of Ag(111), the specific operations are as follows: successively select the numbers of atomic layers of the Ag(111) thin film to be 3 layers, 5 layers, 7 layers, 9 layers, 11 layers, and 13 layers, and calculate the surface energy of Ag(111).

[0014] Preferably, the operations for obtaining the most energy-stable structure in step S2 are as follows: use the quasi-Newton algorithm to perform geometric optimization calculations on the structure of the modeled Ag(111) thin film, and then perform self-consistent calculations after the geometric optimization calculations to obtain the most energy-stable structure; the key parameters for the geometric optimization are: the K point is 13×13×1, the cutoff energy is 1080 eV, and the energy convergence accuracy is 10 -7 eV.

[0015] Preferably, in step S3, according to the doping positions of Au atoms, different doping structure systems are obtained as follows: doping Au atoms by substitution in the intermediate layer of the structure with the lowest energy obtained in step S2 to obtain a Core doping structure system; doping Au atoms by substitution on the upper and lower surfaces of the structure with the lowest energy obtained in step S2 to obtain a Surface doping structure system.

[0016] Preferably, the vacuum layer is

[0017] The present invention also discloses a device for controlling the strain effect of a gold-silver nanometer thin film alloy, including a memory and one or more processors. An executable code is stored in the memory. When the one or more processors execute the executable code, it is used to implement the method for controlling the strain effect of a gold-silver nanometer thin film alloy as described above.

[0018] The present invention also discloses a computer-readable storage medium, on which a program is stored. When the program is executed by a processor, it implements the method for controlling the strain effect of a gold-silver nanometer thin film alloy as described above.

[0019] Advantages of the present invention:

[0020] 1. For the first time, the present method realizes positive and negative surface strains in a material with a constant elemental composition, solving the research status that the strain engineering for regulating the performance of AuAg nanoalloy thin films must rely on a substrate. By doping elements in the thin film, the physical properties of the thin film material are controlled.

[0021] 2. The present invention solves the research status that strain engineering realized by element doping can only construct strain in a single direction; by controlling the relative positions of doped atoms in the nanometer thin film, positive or negative surface strains are realized, and then the performance of the thin film material is regulated from different directions; this method provides a completely new material design idea computationally and has a good guiding effect on the experimental design of new material research and development.

[0022] The features and advantages of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings. Description of the Drawings

[0023] Figure 1 Schematic diagram of controlling the surface strain of a material by changing the atomic doping position;

[0024] Figure 2 Schematic diagram of the surface energy calculation model of an Ag(111) thin film;

[0025] Figure 3 Schematic diagram of the atomic substitution doping calculation model of an AgAu alloy thin film;

[0026] Figure 4It is a result diagram of the atomic doping positions of the seven-layer AgAu alloy thin film and the relative surface strain of the thin film;

[0027] Figure 5 It is a schematic structural diagram of a device for controlling the strain effect of a silver-gold nanometer thin film alloy according to the present invention. Detailed implementation manners

[0028] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0029] An embodiment of the present invention provides a method for controlling the strain effect of a silver-gold nanometer thin film alloy, which specifically includes the following operations:

[0030] (1) Using the xcrysden software, cut out the Ag(111) plane from the Au crystal. Using the open-source first-principles calculation software QuantumESPRESSO (QE) based on the density functional theory (DFT) method, starting from a thin film of three atomic layers, calculate its surface energy. Calculate the surface energy using the following formula:

[0031]

[0032] E slab (N) represents the total energy of the surface slab, N represents the total number of atoms in the slab, and ΔE refers to the energy increment determined by Determined energy increment.

[0033] For the calculation parameter exchange correlation energy, the PBE functional of the generalized gradient approximation (GGA) is adopted, and the energy convergence accuracy is set to 10 -7 eV, and the force convergence accuracy is After the convergence test, the K point (K_POINTS) is set to 5×5×1, the cut-off energy is 1080 eV, the Z axis of the fixed system is fixed, only relaxation in the XY plane is allowed, and at the same time, a vacuum layer of is added in the Z-axis direction. Table 1 shows the relationship between the obtained surface energy and the number of atomic layers.

[0034] Table 1 Calculation results of the surface energy of different atomic layers of Ag(111)

[0035] Number of atomic layers 3 5 7 9 11 13 Surface energy (J / m2) 0.82 1.51 1.49 1.45 1.49 1.48

[0036] As can be seen from Table 1, with the increase in the number of atomic layers, the surface energy of the Ag(111) surface shows convergence. When the number of atomic layers in the slab exceeds 5 layers, the surface energy tends to be stable. Therefore, using an Ag(111) surface composed of 5 or more atomic layers is sufficient to distinguish the differences between the bulk and the thin film, making the surfaces at both ends of the two adjacent systems independent of each other and not affected by each other, forming a stable surface structure.

[0037] (2) Using the Quantum ESPRESS software and combining the surface energy calculation results, a model of the Ag(111) thin film was built. The system has 7 layers, and the system structure is as Figure 2 shown (a 2×2×1 supercell in the figure). A total of 28 atoms were calculated for the smallest unit, 4 atoms per layer. The quasi-Newton method was used to perform geometric optimization on the system. To improve the calculation accuracy, the K_POINTS was increased to 13×13×1 compared with step (1), and other parameters such as the cutoff energy and the convergence accuracy of energy and force remained unchanged.

[0038] (3) Using the Quantum ESPRESSO software, based on the geometrically optimized structure obtained in step (2), some atoms were replaced and doped. The doping sites are as Figure 3 shown. The naming method is based on the atomic layer number where the doped atom is located. Doping two atoms in the central layer is named 44Layer, and when the atoms segregate to the upper and lower surfaces, it is named 17Layer. 26Layer means doping one Au atom in each of the upper and lower sub-surface layers respectively. The quasi-Newton method was used for geometric optimization. To ensure the comparability of the results, all calculation parameters were the same as those in step (2). The calculated results are as Figure 4 shown.

[0039] (4) Compare the results in steps (2) and (3). From the perspective of surface strain, for the doping elements from the outermost layer (11Layer and 17Layer) to the inner layer (44Layer), the overall trend of the surface strain curve of the system is a fluctuating increase, and the maximum strain value appears in 44Layer. The strain amplitude is 0.1048% compared to the Pure system, and the minimum is in 11Layer with a strain amplitude of -0.2023%. Because the system is symmetric up and down, the influence of doping on the surface strain at different layers in the same relative position is small. The surface strain amplitudes of 11Layer (-0.2023%) and 17Layer (-0.1768%) are quite similar, and the same is true for 22Layer (-0.07448%) and 26Layer (-0.06817%), 33Layer (-0.008975%) and 35Layer (-0.01745%). Compared with the Pure system, only the surface strain amplitude of 44Layer is greater than that of Pure, and the rest of the systems are smaller than the Pure system, and the difference in the surface strain amplitudes between the two can reach 0.2815%. Figure 1 It is a schematic diagram of the "abnormal" phenomenon of the intrinsic strain of the AgAu thin film, showing that when Au atoms are doped at different sites, the strain of the surface lattice of the Ag thin film in different positive and negative directions can be controlled.

[0040] In this invention, first-principles calculations based on density functional theory are used to perform high-throughput calculations on binary gold-silver nanoalloy thin films. For the first time, it is invented that in the gold-silver system, a method of controlling the surfaces of materials in different positive and negative directions by controlling the different positions of Au atom doping in the Ag thin film. Surface strain of materials is an effective means to improve material properties. This invention provides ideas for improving the properties of precious metal alloys such as Au and Ag, and also provides a new direction for the research of strain engineering in other alloying systems, and has certain guiding significance for guiding the design of future experiments using first-principles calculations.

[0041] An embodiment of the device for controlling the strain effect of the gold-silver nano thin film alloy in this invention can be applied to any device with data processing capabilities, and such a device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented by software, or by hardware or a combination of software and hardware. Taking software implementation as an example, as a logically meaningful device, it is formed by the processor of any device with data processing capabilities reading the corresponding computer program instructions in the non-volatile memory into the memory for operation. From the hardware level, as Figure 5 shown, it is a hardware structure diagram of any device with data processing capabilities where the device for controlling the strain effect of the gold-silver nano thin film alloy in this invention is located. Except for Figure 5In addition to the processor, memory, network interface, and non-volatile memory shown, any device with data processing capabilities where the device in the embodiment is located can usually also include other hardware according to the actual functions of the device with data processing capabilities. Details thereof will not be elaborated herein. The implementation processes of the functions and roles of each unit in the above device can be specifically referred to the implementation processes of the corresponding steps in the above method, which will not be elaborated herein.

[0042] For the device embodiment, since it basically corresponds to the method embodiment, the relevant parts can be referred to the partial description of the method embodiment. The device embodiments described above are only illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the present invention. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0043] The embodiment of the present invention also provides a computer-readable storage medium, on which a program is stored. When the program is executed by a processor, it implements a device for controlling the strain effect of a gold-silver nanometer thin film alloy in the above embodiment.

[0044] The computer-readable storage medium can be an internal storage unit of any device with data processing capabilities described in any of the foregoing embodiments, such as a hard disk or a memory. The computer-readable storage medium can also be an external storage device of any device with data processing capabilities, such as a plug-in hard disk, a SmartMedia Card (SMC), an SD card, a Flash Card, etc. equipped on the device. Further, the computer-readable storage medium can also include both the internal storage unit and the external storage device of any device with data processing capabilities. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and can also be used to temporarily store the data that has been output or will be output.

[0045] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling the strain effect of a gold-silver nanometer thin film alloy, characterized in that, It includes the following steps: S1. Cut out an Ag(111) thin film from an Ag unit cell, fix the Z-axis of the system, and only allow relaxation in the XY plane. Select different numbers of atomic layers of the Ag(111) thin film, perform self-consistent calculations on the surface energy of Ag(111), obtain the relationship between the surface energy and the number of atomic layers of the Ag(111) thin film, and determine the minimum number of atomic layers of the Ag(111) thin film; S2. According to the minimum number of atomic layers of the thin film determined in step S1, model the Ag(111) thin film, perform geometric optimization on the structure of the modeled Ag(111) thin film, obtain the most energy-stable structure, and record the atomic positions, bond lengths, total energy of the system, and total volume of the system of the Ag(111) thin film under this structure; S3. Substitute and dope Au atoms in the most energy-stable structure obtained in step S2. According to the doping positions of the Au atoms, obtain different doped structure systems; perform geometric optimization on the doped structure systems to obtain the most stable structures of the doped structure systems, and record the total energy of the system and the total volume of the system under the most stable structures of the doped structure systems; S4. Compare the most energy-stable structure in step S2 with the most stable structures of the doped structure systems in step S3. According to the total energy of the system and the numerical value of the surface strain of the thin film calculated by taking the difference between the total volume of the system and the modulus of the z vector in the lattice constant, construct the relationship between the atomic doping positions and the total energy & surface strain of the system.

2. The method for controlling the strain effect of the gold-silver nanometer thin film alloy according to claim 1, wherein: A vacuum layer is provided between the atomic layers of the Ag(111) thin film in step S1.

3. A method for controlling the strain effect of a gold-silver nanometer thin film alloy as described in claim 1, characterized in that: In step S1, when selecting different numbers of atomic layers of the Ag(111) thin film and performing self-consistent calculations on the surface energy of Ag(111), the specific operations are as follows: sequentially select the numbers of atomic layers of the Ag(111) thin film to be 3 layers, 5 layers, 7 layers, 9 layers, 11 layers, and 13 layers, and calculate the surface energy of Ag(111).

4. A method for controlling the strain effect of a gold-silver nanometer thin film alloy as claimed in claim 1, characterized in that, The operation of obtaining the most stable structure in step S2 is as follows: The modeled Ag(111) thin film structure is subjected to geometric optimization calculations using the quasi-Newton algorithm. After the geometric optimization calculations, self-consistent calculations are performed to obtain the most stable structure. The key parameters for the geometric optimization are: the k-point is 13×13×1, the cut-off energy is 1080 eV, and the energy convergence accuracy is 10 -7 eV.

5. A method for controlling the strain effect of a gold-silver nanometer thin film alloy as described in claim 1, characterized in that, In step S3, when obtaining different doped structure systems according to the doping positions of the Au atoms, the specific operations are as follows: substitute and dope Au atoms in the middle layer of the most energy-stable structure obtained in step S2 to obtain a Core doped structure system; substitute and dope Au atoms on the upper and lower surfaces of the most energy-stable structure obtained in step S2 to obtain a Surface doped structure system.

6. A method for controlling the strain effect of a gold-silver nanometer thin film alloy according to claim 2, characterized in that, The vacuum layer is 17.5 Å.

7. A device for controlling the strain effect of a gold-silver nanometer thin film alloy, characterized in that: It includes a memory and one or more processors. Executable code is stored in the memory. When the one or more processors execute the executable code, it is used to implement a method for controlling the strain effect of a gold-silver nanometer thin film alloy according to any one of claims 1-6.

8. A computer-readable storage medium, characterized in that: A program is stored thereon. When the program is executed by a processor, it implements a method for controlling the strain effect of a gold-silver nanometer thin film alloy according to any one of claims 1-6.

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