A method for controllable selenization of different tellurium atomic layers in a single-layer VTe2 sandwich structure

Abstract

This invention provides a method for controllably selenizing different tellurium atom layers in a monolayer VTe2 sandwich structure, which mainly includes: (1) preparing a monolayer VTe2 on a graphene substrate using molecular beam epitaxy at three temperatures; (2) evaporating and depositing selenium atoms with a purity of 99.999% onto the surface of the monolayer VTe2 under vacuum, while maintaining the monolayer VTe2 and the graphene substrate at a preset reaction temperature, so that the deposited selenium atoms interact with the monolayer VTe2 and diffuse sufficiently, thereby controllably generating either the two-dimensional ordered selenization product VTeSe or VSe2 of a Janus structure vanadium chalcogenide. This invention is conceptually sound and can grow a novel Janus structure vanadium chalcogenide compound or controllably selenize to obtain VSe2.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to a method for controllably selenizing different tellurium atom layers in a single-layer VTe2 sandwich structure. Background Technology

[0002] Since the discovery of graphene, two-dimensional materials with various properties have attracted increasing attention in novel electronic, optical, spintronic, and valleytronic devices. As an important derivative of two-dimensional materials, Janus-structured two-dimensional materials, such as Janus-structured transition metal chalcogenides, exhibit novel properties due to their broken mirror symmetry, such as the Rashba effect and piezoelectric polarization. These properties offer great promise for their application in sensors and other electromechanical devices. However, due to the poor air stability of these materials and the high requirements of atomic-level fabrication techniques, research on introducing Janus structures into transition metal dichalcogenides with electronic correlation properties and observing their charge density wave states remains scarce, with only a few theoretical predictions to date. Therefore, realizing the construction of two-dimensional materials at the atomic scale and controlling the in-plane and out-of-plane symmetry of two-dimensional materials is crucial for preparing special Janus-structured transition metal chalcogenides, and can also enable the construction of abundant heterostructures at the atomic scale. Summary of the Invention

[0003] To address the technical problems existing in the background art mentioned above, this invention proposes a method for controllable selenization of different tellurium atom layers in a single-layer VTe2 sandwich structure. The method is well-conceived and can control the reaction conditions relatively precisely to obtain a two-dimensional ordered periodic structure of Janus structure vanadium chalcogenides or to controllably selenize VSe2, providing a foundation for subsequent microscopic research and macroscopic applications.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for controllably selenizing different tellurium atom layers in a single-layer VTe2 sandwich structure, which mainly includes the following steps:

[0005] (1) A monolayer of VTe2 was prepared on a graphene substrate by a three-temperature molecular beam epitaxy method;

[0006] (2) In a vacuum environment, selenium atoms with a purity of 99.999% are evaporated and deposited onto the surface of a monolayer VTe2. At the same time, the monolayer VTe2 and the graphene substrate are kept at a preset reaction temperature so that the deposited selenium atoms interact with the monolayer VTe2 and diffuse fully, thereby controllably generating either VTeSe or VSe2, two-dimensional ordered selenide products of Janus structure vanadium chalcogenide.

[0007] The method for controllably selenizing different tellurium atom layers in a single-layer VTe2 sandwich structure, wherein the graphene substrate can be obtained by annealing highly oriented pyrolytic graphite at 600℃~1000℃ for 1 hour.

[0008] The method for controlling the selenization of different tellurium atom layers in the monolayer VTe2 sandwich structure, wherein: the graphene substrate can also be obtained by annealing silicon carbide material with a purity of 99.999% at 1300℃~1400℃ for 1 hour.

[0009] The method for controllably selenizing different tellurium atom layers in a single-layer VTe2 sandwich structure, wherein the specific process of step (1) is as follows:

[0010] (1.1) A clean and flat graphene substrate is obtained in a vacuum cavity;

[0011] (1.2) On a clean and flat graphene substrate, tellurium atoms are deposited on the graphene substrate surface using a thermal resistance evaporation source, while vanadium atoms are deposited on the graphene substrate surface using an electron beam thermal evaporation source. The graphene substrate is kept at 200℃~250℃ to allow the tellurium and vanadium atoms to fully combine with each other. The growth time lasts for 30~60 minutes, and finally a two-dimensional ordered monolayer VTe2 is formed on the graphene substrate surface.

[0012] The method for controllable selenization of different tellurium atom layers in a single-layer VTe2 sandwich structure, wherein: in step (2), the single-layer VTe2 and the graphene substrate are reacted at a preset reaction temperature of 250°C to obtain Janus structure vanadium chalcogenide VTeSe, and at a preset reaction temperature of 300°C to obtain VSe2.

[0013] The method for controllable selenization of different tellurium atom layers in a single-layer VTe2 sandwich structure, wherein: the atomic structure and charge density wave superperiod of the single-layer VTe2, selenization products VTeSe and VSe2 in step (2) can be characterized by scanning tunneling microscopy, and the atomic arrangement structure between different layers can be characterized by scanning transmission electron microscopy.

[0014] By adopting the above technical solution, the present invention has the following beneficial effects:

[0015] The method for controllably selenizing different tellurium atom layers in a monolayer VTe2 sandwich structure is well-conceived and can grow a novel Janus-structured vanadium chalcogenide or controllably selenize to obtain VSe2. In particular, high-purity selenium atoms are evaporated and deposited onto a monolayer VTe2 using molecular beam epitaxy, while the monolayer VTe2 is maintained at different preset temperatures. This allows for the controllable selenization of different tellurium atom layers in the monolayer VTe2 sandwich structure, facilitating the further generation of a novel Janus-structured vanadium chalcogenide. This novel Janus-structured vanadium chalcogenide exhibits electron-correlated charge density waves, thus possessing significant value in the study of strong electron correlation characteristics.

[0016] The main advantage of this invention lies in its ability to grow Janus structures. Prior to this, there were very few examples of atomically controlled growth and observation of such Janus structures, representing a gap in the field. The Janus structure and VSe2 are two products of selenization. This invention allows for precise control of the reaction conditions, yielding only the desired Janus structure or VSe2. The Janus structure is grown primarily because it possesses some novel properties (as described in the background information), making it promising for applications in sensors and other electromechanical devices.

[0017] The main advantages of this invention are the controllability of the product, allowing for the selection of either Janus-like structures or VSe2, and the high quality and cleanliness of the product, which can be characterized using precision techniques such as scanning tunneling microscopy and scanning transmission microscopy. Furthermore, Janus-structured materials are relatively novel, and this invention enables their controllable preparation, providing a foundation for subsequent microscopic research and macroscopic applications. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram illustrating the preparation process of VTe2 in the method for controllable selenization of different tellurium atom layers in the VTe2 sandwich structure of the present invention.

[0020] Figure 2This is a scanning tunneling microscope image of a large-area monolayer VTe2 two-dimensional material prepared on the surface of graphene in the method of controllable selenization of different tellurium atomic layers in the VTe2 sandwich structure of the present invention, at a low temperature of -269℃. The image also shows the charge density wave superperiod of the monolayer 1T phase VTe2 and the period display diagram after fast Fourier transform.

[0021] Figure 3 This is a schematic diagram illustrating the preparation process of the Janus structure VTeSe by controllably selenizing the surface tellurium atoms of monolayer VTe2 to obtain different tellurium atom layers in the sandwich structure of monolayer VTe2 according to the present invention.

[0022] Figure 4 The image shows a Janus structure VTeSe obtained by controllably selenizing the surface tellurium atoms of monolayer VTe2 in the method of controllable selenization of different tellurium atom layers in the sandwich structure of the present invention at a low temperature of -269℃. The image also shows the charge density wave superperiod of monolayer 1T phase VTeSe and the period display diagram after fast Fourier transform.

[0023] Figure 5 This is a scanning transmission electron microscope cross-sectional image at room temperature after the controllable selenization of the surface tellurium atoms of monolayer VTe2 to obtain a Janus-like VTeSe structure, in the method of controllable selenization of different tellurium atom layers in the VTe2 sandwich structure of the present invention; wherein, Figure 5 The right figure shows the spatial imaging of the electron energy loss spectrum of a single-layer VTeSe cross section, which clearly shows that the spatial positions of the three elements (selenium, vanadium, and tellurium) form a sandwich structure, proving the formation of a single-layer Janus structure VTeSe.

[0024] Figure 6 This is a schematic diagram illustrating the preparation process of VSe2 obtained by controllably selenizing two tellurium layers of monolayer VTe2 in the method of controllably selenizing different tellurium atom layers in the sandwich structure of monolayer VTe2 of the present invention.

[0025] Figure 7 The image is a scanning tunneling microscope image at -269℃ after the two tellurium atoms of the monolayer VTe2 are controllably selenized to obtain VSe2 in the method of controllable selenization of different tellurium atom layers in the sandwich structure of the present invention. The charge density wave superperiod of the monolayer 1T phase VSe2 is marked, as well as the period display diagram after fast Fourier transform.

[0026] Figure 8 This is a schematic diagram illustrating the preparation process of VSe2 obtained by controllably selenizing the bottom tellurium atom of a monolayer VTeSe in the method of controllably selenizing different tellurium atom layers in the sandwich structure of VTe2 of the present invention.

[0027] Figure 9 The image shows a scanning tunneling microscope image at -269°C obtained by controlling the bottom tellurium atom of a monolayer VTeSe in the method of controlling the selenization of different tellurium atom layers in the sandwich structure of VTeSe monolayer of the present invention after controlling the selenization of the bottom tellurium atom of a monolayer VTeSe. The image also shows the charge density wave superperiod of the monolayer 1T phase VTeSe and the period display diagram after fast Fourier transform. Detailed Implementation

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The present invention will be further explained below with reference to specific embodiments.

[0030] This embodiment provides a method for controllably selenizing different tellurium atom layers in a single-layer VTe2 sandwich structure, which mainly includes the following steps:

[0031] (1) A monolayer of VTe2 was prepared on a graphene substrate by a three-temperature molecular beam epitaxy method;

[0032] Molecular beam epitaxy (MBE) in step (1) above is an advanced bottom-up thin film fabrication technique designed to meet the ever-increasing demands for precision in thin film growth. Furthermore, MBE was first applied in the production of gallium arsenide thin films. The basic principle of MBE is to place various components of the material in independent evaporation sources under ultra-high vacuum conditions. These evaporation sources are heated to generate beams of each component, which are then deposited on a temperature-controlled substrate. These deposited components interact and react chemically on the substrate surface, enabling thin film growth even at the atomic level. Adjusting the beam size allows for precise control of the thin film growth rate, thereby achieving layer-by-layer growth on the substrate. Compared to traditional thermal vacuum evaporation deposition and chemical vapor deposition (CVD) methods, MBE allows for more precise control of the growth process, resulting in higher-quality thin films, and also enables the construction of structures and doping modes that are difficult to achieve using traditional methods.

[0033] In molecular beam epitaxy (MBE) technology, one of the key pieces of equipment is the molecular beam evaporation source. The MBE source allows for precise control of the beam current for each component, playing a decisive role in achieving a high-quality, controllable growth process. Currently, there are two main types of widely used MBE sources. One is the Knudsen diffusion (K-Cell) evaporation source, whose key components include a crucible, resistance heater, cooling system, temperature measurement system, and controllable baffles. K-Cell evaporation sources are primarily suitable for materials with low melting points, and their operating temperature range is typically between 120°C and 1030°C. The other type is the electron beam (E-Beam) heated evaporation source. This type of evaporation source generates thermionic electrons through a heated filament. These electrons are accelerated by high voltage and focused onto the target material to achieve heating. Electron beam evaporation sources can achieve higher temperatures than traditional heating techniques and are suitable for materials with higher melting points.

[0034] (2) In a vacuum environment, a suitable amount of high-purity selenium atoms are evaporated and deposited onto the surface of a monolayer VTe2, while the monolayer VTe2 and the substrate are kept at a specific preset temperature so that the deposited selenium atoms interact with the monolayer VTe2 and diffuse fully, thereby controllably forming two-dimensional ordered selenide products VTeSe or VSe2 of Janus structure vanadium chalcogenide.

[0035] In step (1) above, a high-quality single-layer VTe2 two-dimensional material is prepared on the surface of multilayer graphene. The clean and flat graphene substrate can be obtained by mechanically cleaving highly oriented pyrolytic graphite (a new type of graphite that has undergone high-temperature treatment of pyrolytic graphite, resulting in properties close to single-crystal graphite) and annealing it at 600℃~1000℃ for 1 hour (below 600℃, degassing is incomplete; above 1000℃, graphene defects may occur; the optimal implementation value in this embodiment is 800℃), or by annealing 99.999% pure silicon carbide at 1300℃~1400℃ (the optimal implementation value in this embodiment is 1350℃) for 1 hour.

[0036] A schematic diagram illustrating the preparation process of the monolayer VTe2 of the present invention is shown below. Figure 1 As shown in the figure, the left portion illustrates the deposition of vanadium and tellurium atoms on the surface of graphene in this invention, while maintaining the substrate at a growth temperature of 230°C. The right portion shows the final VTe2 two-dimensional material grown on the graphene surface.

[0037] The specific process of step (1) above is as follows:

[0038] (1.1) First, a clean and flat graphene substrate is obtained in a vacuum cavity.

[0039] (1.2) Subsequently, on a clean and flat graphene surface, tellurium atoms are deposited onto it using a thermal resistance evaporation source, while vanadium atoms are deposited onto it using an electron beam thermal evaporation source. The substrate temperature is maintained at 200℃~250℃ (the optimal temperature in this embodiment is 230℃) to allow the tellurium and vanadium atoms to fully bond together. The growth time lasts 30~60 minutes (the optimal time in this embodiment is 50 minutes), ultimately forming a large-area two-dimensional ordered monolayer VTe2 on the graphene surface, as shown below. Figure 2 The scanning tunneling microscopy image on the left shows that monolayer VTe2 exhibits a distinct 4×4 charge density wave superperiodic lattice at a low temperature of -269℃. Figure 2 The image on the right, obtained by performing a fast Fourier transform on the image on the left, also shows that its charge density wave is superperiodic, proving that the obtained thin film is a monolayer 1T phase VTe2 two-dimensional material.

[0040] In step (2) above, monolayer VTe2 and graphene substrate are used to obtain Janus structure vanadium chalcogenide VTeSe at a preset reaction temperature of 250℃, and VSe2 is obtained at a preset reaction temperature of 300℃.

[0041] The atomic structure and charge density wave superperiod of monolayer VTe2, selenide products VTeSe and VSe2 in step (2) above can be characterized by scanning tunneling microscopy, and the atomic arrangement structure between different layers can be characterized by scanning transmission electron microscopy.

[0042] A schematic diagram illustrating the preparation process of Janus-structured VTeSe by controllably selenizing the surface tellurium atoms of monolayer VTe2 in this invention is shown below. Figure 3 As shown in the figure, the left portion illustrates the deposition of selenium atoms on the surface of a monolayer VTe2 during the reaction, while maintaining the substrate at a reaction temperature of 250°C for 1 hour. The right portion shows the Janus-structured two-dimensional material VTeSe ultimately grown on the graphene surface.

[0043] like Figure 4 As shown in the scanning tunneling microscope image on the left, monolayer VTeSe exhibits a distinct √13×√13 charge density wave superperiodic lattice at a low temperature of -269℃. Figure 4 The image on the right, which is a fast Fourier transform of the image on the left, also shows that its charge density wave is superperiodic.

[0044] Since there are currently no experimental reports on Janus-structured VTeSe, further verification of the product after controllable selenization is needed. Cross-sectional samples of the product after controllable selenization were obtained using focused ion beam microscopy, followed by characterization using scanning transmission electron microscopy. Figure 5The bright white area on the left represents the product after controlled selenization. The region within the frame was characterized by electron energy loss spectroscopy, and the results are shown in the right figure. It clearly shows that the spatial positions of the three elements (selenium, vanadium, and tellurium) form a sandwich structure, proving the formation of the monolayer Janus structure VTeSe.

[0045] A schematic diagram illustrating the preparation process of VSe2 obtained by controllably selenizing two layers of tellurium atoms in monolayer VTe2 in this invention is shown below. Figure 6 As shown in the figure. The left portion illustrates the deposition of selenium atoms on the surface of a monolayer VTe2 in this invention, while maintaining the substrate at a reaction temperature of 300°C for 1 hour. The right portion illustrates the final two-dimensional material VSe2 grown on the graphene surface.

[0046] like Figure 7 The scanning tunneling microscope image is shown. Figure 6 The monolayer VSe2 obtained by the process exhibits a distinct √3×√7 charge density wave superperiodic lattice at a low temperature of -269℃. The image obtained by fast Fourier transform of the scanning tunneling microscope image shown in the upper right inset also shows its charge density wave superperiodicity, proving that the obtained film is a monolayer 1T phase VSe2 two-dimensional material.

[0047] A schematic diagram illustrating the preparation process of VSe2 obtained by controllably selenizing the bottom tellurium atoms of a monolayer VTeSe in this invention is shown below. Figure 8 As shown in the figure, the left portion illustrates the deposition of selenium atoms on the surface of a monolayer VTeSe during the reaction, while maintaining the substrate at a reaction temperature of 250°C for 1 hour. The right portion shows the final two-dimensional material VSe2 grown on the graphene surface.

[0048] like Figure 9 The scanning tunneling microscope image is shown. Figure 8 The monolayer VSe2 obtained by the process exhibits a distinct √3×√7 charge density wave superperiodic lattice at a low temperature of -269℃. The image obtained by fast Fourier transform of the scanning tunneling microscope image shown in the upper right inset also shows its charge density wave superperiodicity, proving that the obtained film is a monolayer 1T phase VSe2 two-dimensional material.

[0049] This invention is well-conceived and can grow a novel Janus-structured vanadium chalcogenide or controllably selenize it to obtain VSe2.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of controllably selenizing different tellurium atom layers in a monolayer VTe2 sandwich structure, characterized by, The main steps include: (1) A monolayer of VTe2 was prepared on a graphene substrate using the three-temperature molecular beam epitaxy method; the specific process is as follows: (1.1) A clean and flat graphene substrate is obtained in a vacuum cavity; (1.2) On a clean and flat graphene substrate, tellurium atoms are deposited on the graphene substrate surface using a thermal resistance evaporation source, while vanadium atoms are deposited on the graphene substrate surface using an electron beam thermal evaporation source. The graphene substrate is kept at 200℃~250℃ to allow the tellurium and vanadium atoms to fully combine with each other. The growth time lasts for 30~60 minutes, and finally a two-dimensional ordered monolayer VTe2 is formed on the graphene substrate surface. (2) In a vacuum environment, selenium atoms with a purity of 99.999% are evaporated and deposited onto the surface of a monolayer VTe2, while keeping the monolayer VTe2 and the graphene substrate at a preset reaction temperature so that the deposited selenium atoms interact with the monolayer VTe2 and diffuse fully, thereby controllably generating either the two-dimensional ordered selenide product VTeSe or VSe2 of Janus structure vanadium chalcogenide; The graphene substrate was obtained by annealing highly oriented pyrolytic graphite at 600℃~1000℃ for 1 hour. In step (2), a monolayer VTe2 and a graphene substrate are reacted at a preset reaction temperature of 250°C to obtain Janus-structured vanadium chalcogenide VTeSe, and at a preset reaction temperature of 300°C to obtain VSe2.

2. The method of claim 1, wherein the controllable monolayer of seleniumized single-layer VTe2 sandwich structure of different tellurium atom layers is characterized by: The graphene substrate can also be obtained by annealing silicon carbide material with a purity of 99.999% at 1300℃~1400℃ for 1 hour.

3. The method of claim 1, wherein the controllable monolayer of selenium-encapsulated bilayer VTe2 sandwich structure of different tellurium atomic layers is characterized by: The atomic structure and charge density wave superperiod of monolayer VTe2, selenide products VTeSe and VSe2 in step (2) can be characterized by scanning tunneling microscopy, and the atomic arrangement structure between different layers can be characterized by scanning transmission electron microscopy.

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