Preparation Method and Application of Cu7Te4 Nanosheets

Abstract

The present invention provides a method for preparing Cu7Te4 nanosheets and its application. The preparation method includes: a tellurium source and a copper source are used to prepare the Cu7Te4 nanosheets on a substrate through chemical vapor deposition. The present invention provides a process for epitaxially growing two-dimensional Cu7Te4 nanosheets through chemical vapor deposition, and realizes the growth of two-dimensional Cu7Te4 nanosheets by using the method of chemical vapor deposition. It can form an ideal metal-semiconductor interface with traditional two-dimensional semiconductors, and is expected to solve the contact problems of two-dimensional materials in electronic, optoelectronic devices and spintronic devices.

Description

Technical Field

[0001] The present invention belongs to the field of electronic devices, and relates to a preparation method and application of Cu7Te4 nanosheets. Background Art

[0002] Two-dimensional transition metal chalcogenide (TMDCs) materials have attracted wide attention due to their unique phase structures and excellent physical properties, such as magnetism, valley polarization, superconductivity, charge density wave, topological properties, etc., and thus have potential application prospects in the fields of spintronics and optoelectronics. More interestingly, such two-dimensional materials such as VS2, 1T-MoS2, NbSe2 and TaS2 have excellent electrical conductivity and have been widely used in the fields of supercapacitors, sensing, electrochemistry and catalysis.

[0003] Copper-based chalcogenide, as a member of metallic TMDCs, has been considered a promising candidate material for next-generation green electronic products due to its high electrical conductivity and structural phase transition and other characteristics. Moreover, an ideal interface between metallic copper-based chalcogenide and two-dimensional semiconductor materials can be formed by van der Waals epitaxial growth, and the metal-induced gap states formed in the semiconductor can be suppressed, which is expected to solve the contact problem in constructing electronic and optoelectronic devices based on two-dimensional materials.

[0004] CN111874876B discloses a method for growing copper telluride, copper telluride and its application. After placing a substrate, cuprous iodide and tellurium powder in sequence, a few-layer copper telluride two-dimensional material is grown by chemical vapor deposition, the growth time is 30 min to 1 h, and the growth temperature is 500 °C to 800 °C. The two-dimensional stoichiometric Cu2Te nanosheets prepared by this method have fewer two-dimensional Cu2Te nanosheet layers, uneven thickness, and long preparation time.

[0005] The existing preparation methods for Cu7Te4 materials are mainly hydrothermal method or electrochemical method. The hydrothermal method for preparing Cu7Te4 nanospheres usually uses a fixed template for growth, which is time-consuming, has a low controllability, low purity and crystallinity, and introduces organic solvents to cause material interface pollution. And the Cu7Te4 particles synthesized by the electrochemical deposition method are mixed with a small amount of Cu4Te3 phase and Te phase. The limitations of these two preparation methods are that only nano-sized Cu7Te4 particles or amorphous Cu7Te4 particles can be obtained. And since Cu7Te4 nanosheets belong to non-layered compounds, that is, the atoms between layers and within layers are all connected by covalent bonds, it is difficult to prepare the corresponding two-dimensional thin-layer structure by simple mechanical or liquid-phase exfoliation. In addition, different stoichiometric mixed phases are easily introduced during the growth and preparation of Cu7Te4, such as the existence of CuTe, Cu2Te, Cu4Te3, etc., which will greatly limit the high-quality preparation of two-dimensional non-stoichiometric materials.

[0006] Therefore, how to prepare high-quality two-dimensional Cu7Te4 nanosheets with non-stoichiometric ratio is an important research direction in this field. Summary of the invention

[0007] The object of the present invention is to provide a high-quality two-dimensional Cu7Te4 nanosheet with a non-stoichiometric ratio.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] One of the purposes of the present invention is to provide a method for preparing Cu7Te4 nanosheets, the preparation method comprising:

[0010] The tellurium source and the copper source are deposited by chemical vapor phase to prepare the Cu7Te4 nanosheets on the substrate.

[0011] The present invention provides a method for epitaxially growing two-dimensional Cu7Te4 nanosheets through a chemical vapor deposition process. The growth of two-dimensional Cu7Te4 nanosheets is achieved for the first time by using the chemical vapor deposition method. The prepared nanosheets present triangular and hexagonal shapes.

[0012] As a preferred technical solution of the present invention, the substrate includes any one of mica sheets, highly oriented graphite sheets, sapphire sheets, quartz sheets, silicon sheets or SiO2 (300nm) / Si on which TMDCs have been grown, or a combination of at least two of them, wherein typical but non-limiting examples of the combinations include: a combination of mica sheets and highly oriented graphite sheets, a combination of highly oriented graphite sheets and sapphire sheets, a combination of sapphire sheets and quartz sheets, a combination of quartz sheets and silicon sheets, or a combination of silicon sheets and SiO2 (300nm) / Si on which TMDCs have been grown, etc.

[0013] Preferably, the thickness of the mica sheet is 0.15-0.25 mm, wherein the thickness may be 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, 0.20 mm, 0.21 mm, 0.22 mm, 0.23 mm, 0.24 mm or 0.25 mm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] Preferably, the thickness of the highly oriented graphite sheet is 0.35-0.45 mm, wherein the thickness may be 0.35 mm, 0.36 mm, 0.37 mm, 0.38 mm, 0.39 mm, 0.40 mm, 0.41 mm, 0.42 mm, 0.43 mm, 0.44 mm or 0.45 mm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] Preferably, the thickness of the sapphire wafer is 0.4 to 0.5 mm, and the thickness can be 0.4 mm, 0.41 mm, 0.42 mm, 0.43 mm, 0.44 mm, 0.45 mm, 0.46 mm, 0.47 mm, 0.48 mm, 0.49 mm or 0.5 mm, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] Preferably, the thickness of the quartz wafer is 0.45 to 0.55 mm, and the thickness can be 0.45 mm, 0.46 mm, 0.47 mm, 0.48 mm, 0.49 mm, 0.50 mm, 0.51 mm, 0.52 mm, 0.53 mm, 0.54 mm or 0.55 mm, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] Preferably, the size of the substrate is 0.01 to 4 cm 2 , and the size can be 0.1 cm × 0.1 cm, 0.1 cm × 0.5 cm, 0.1 cm × 1 cm, 0.1 cm × 2 cm, 0.5 cm × 0.5 cm, 0.5 cm × 1 cm, 0.5 cm × 2 cm, 1 cm × 1 cm, 1 cm × 2 cm or 2 cm × 2 cm, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] As a preferred technical solution of the present invention, the substrate is pretreated, and the pretreatment includes cleaning the substrate.

[0019] Preferably, the cleaning solution for the cleaning includes acetone and isopropyl alcohol.

[0020] Preferably, the cleaning is ultrasonic cleaning.

[0021] As a preferred technical solution of the present invention, the chemical vapor deposition is carried out in a two-temperature zone tube furnace.

[0022] Preferably, in the two-temperature zone tube furnace, the tellurium source is placed in the low-temperature region, and the mixture of the copper source and sodium chloride and the substrate are placed in the high-temperature region.

[0023] The reason for mixing the copper source and sodium chloride in the present invention is that the melting point of the copper elemental reaction source is high (~1084 °C), and mixing copper with the molten salt (sodium chloride) can not only reduce the melting point of the precursor and increase the saturated vapor pressure of the copper reaction source, but also effectively provide nucleation sites to form a thin layer of Cu7Te4 nanosheets.

[0024] Preferably, the distance between the tellurium source and the copper source is 55 to 65 cm. The distance can be 55 cm, 56 cm, 57 cm, 58 cm, 59 cm, 60 cm, 61 cm, 62 cm, 63 cm, 64 cm, 65 cm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0025] Preferably, the distance between the copper source and the substrate is 1 to 5 cm. The distance can be 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0026] If the distance between the tellurium source and the copper source and the distance between the copper source and the substrate in the present invention are too large or too small, the tellurium source will evaporate slower or faster, and it cannot react well with the copper source, resulting in the failure to obtain Cu7Te4 nanosheets. If the distance between the copper source and the substrate is too small, the concentration of the reaction source is too high, resulting in the growth of thicker Cu7Te4 nanosheets. If the distance between the copper source and the substrate is too large, the concentration of the reaction source is small, resulting in the growth of smaller-sized Cu7Te4 nanosheets.

[0027] As a preferred technical solution of the present invention, the tellurium source includes any one or a combination of at least two of tellurium powder, tellurium oxide, tellurium chloride, tellurium bromide, or tellurium iodide. Typical but non-limiting examples of the combination include: the combination of tellurium powder and tellurium chloride, the combination of tellurium chloride and tellurium bromide, or the combination of tellurium bromide and tellurium iodide, etc.

[0028] Preferably, the copper source includes any one or a combination of at least two of copper powder, copper oxide, copper chloride, copper bromide, or copper iodide. Typical but non-limiting examples of the combination include: the combination of copper powder and copper chloride, the combination of copper chloride and copper bromide, or the combination of copper bromide and copper iodide, etc.

[0029] Preferably, the mass ratio of the tellurium source, the copper source, and sodium chloride is 18:1:1 to 22:1:1. The mass ratio can be 18:1:1, 19:1:1, 20:1:1, 21:1:1, 22:1:1, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 20:1:1.

[0030] In the present invention, if the mass ratio of tellurium powder, copper powder, and sodium chloride is too large, an excessive amount of tellurium source will deposit and grow tellurium nanowires on mica. If the mass ratio of tellurium powder, copper powder, and sodium chloride is too small, more copper powder particles will deposit on mica, which is not conducive to obtaining two-dimensional Cu7Te4 nanosheets.

[0031] Exemplarily, the mass of the tellurium powder is 0.5 to 1 g. The mass can be 0.5 g, 0.6 g, 0.7 g, 0.8 g, 0.9 g, 1 g, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0032] Exemplarily, the mass of the copper powder is 10 to 100 mg. The mass can be 10 mg, 20 mg, 30 mg, 40 mg, 50 mg, 60 mg, 70 mg, 80 mg, 90 mg, 100 mg, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0033] Exemplarily, the mass of the sodium chloride is 50 to 500 mg. The mass can be 50 mg, 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, 350 mg, 400 mg, 450 mg, 500 mg, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0034] As a preferred technical solution of the present invention, the method of chemical vapor deposition includes: introducing a carrier gas into the two-temperature zone tube furnace for heating.

[0035] Preferably, after pre-treating the two-temperature zone tube furnace, heating is carried out. The pre-treatment includes: evacuating air, cleaning, and filling with an inert gas in sequence for the two-temperature zone tube furnace.

[0036] Preferably, the cleaning includes: cleaning the two-temperature zone tube furnace with argon at a flow rate of 95 to 105 sccm. The flow rate of the argon can be 95 sccm, 96 sccm, 97 sccm, 98 sccm, 99 sccm, 100 sccm, 101 sccm, 102 sccm, 103 sccm, 104 sccm, 105 sccm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0037] Preferably, the inert gas is argon.

[0038] Preferably, the carrier gas includes argon and hydrogen with a gas flow ratio of (18 to 22):1. The gas flow ratio is 18:1, 19:1, 20:1, 21:1, 22:1, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0039] The present invention uses argon and hydrogen as carrier gases. On the one hand, it can transport the tellurium source to the substrate for the synthesis of two-dimensional Cu7Te4 nanosheets. On the other hand, since the reducibility of tellurium in the reaction is extremely weak, adding reducing hydrogen enables the reaction for preparing Cu7Te4 nanosheets to proceed. When the gas flow ratio is small, that is, the concentration of hydrogen is high, it leads to the formation of relatively thick Cu7Te4 nanosheets. When the gas flow ratio is large, that is, the concentration of hydrogen is low, it leads to the formation of Cu7Te4 nanosheets with smaller sizes or even the inability to synthesize Cu7Te4 nanosheets.

[0040] The present invention utilizes carrier gases to transport the tellurium source and copper source through a gas-phase transport reaction to prepare two-dimensional Cu7Te4 nanosheets on a van der Waals substrate.

[0041] As a preferred technical solution of the present invention, the heating includes heating a high-temperature region and a low-temperature region.

[0042] Preferably, the heating rate of the low-temperature region is 20 - 30 °C / min. The heating rate can be 20 °C / min, 21 °C / min, 22 °C / min, 23 °C / min, 24 °C / min, 25 °C / min, 26 °C / min, 27 °C / min, 28 °C / min, 29 °C / min or 30 °C / min, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0043] Preferably, the temperature of the low-temperature region is 500 - 700 °C. The temperature can be 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, 600 °C, 620 °C, 640 °C, 660 °C, 680 °C or 700 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0044] In the present invention, if the temperature of the low-temperature region is too high, a small amount of tellurium nanowires or nanoparticles will be deposited on the mica sheet. If the temperature is too low, no tellurium source participates in the reaction and Cu7Te4 nanosheets cannot be obtained.

[0045] Preferably, the heat preservation time of the low-temperature region is 15 - 25 °C. The heat preservation time can be 15 °C, 16 °C, 17 °C, 18 °C, 19 °C, 20 °C, 21 °C, 22 °C, 23 °C, 24 °C or 25 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0046] As a preferred technical solution of the present invention, the heating rate of the high-temperature region is 20-30 °C / min. The heating rate can be 20 °C / min, 21 °C / min, 22 °C / min, 23 °C / min, 24 °C / min, 25 °C / min, 26 °C / min, 27 °C / min, 28 °C / min, 29 °C / min or 30 °C / min, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0047] Preferably, the temperature of the high-temperature region is 600-800 °C. The temperature can be 600 °C, 620 °C, 640 °C, 660 °C, 680 °C, 700 °C, 720 °C, 740 °C, 760 °C, 780 °C or 800 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0048] In the present invention, if the temperature of the high-temperature region is too high, a large amount of copper source will participate in the reaction, and it is easy to form hexagonal Cu7Te4 nanosheets. If the temperature is too low, the copper source concentration will be too low, and it is easy to form triangular Cu7Te4 nanosheets.

[0049] Preferably, the heat preservation time of the high-temperature region is 15-25 °C. The heat preservation time can be 15 °C, 16 °C, 17 °C, 18 °C, 19 °C, 20 °C, 21 °C, 22 °C, 23 °C, 24 °C or 25 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0050] As a preferred technical solution of the present invention, the preparation method includes:

[0051] Put 0.5-1 g of tellurium powder, 10-100 mg of copper powder, 50-500 mg of sodium chloride and a substrate into a two-temperature zone tube furnace, and prepare the Cu7Te4 nanosheets on the substrate by chemical vapor deposition.

[0052] The second object of the present invention is to provide an application of the preparation method of the Cu7Te4 nanosheets as described in the first object, and the preparation method is applied in the field of electronic devices.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) The present invention proposes a method for preparing high-quality two-dimensional Cu7Te4 nanosheets with non-stoichiometric ratio. For the first time, the growth of two-dimensional Cu7Te4 nanosheets is realized by chemical vapor deposition method, and the prepared nanosheets show triangular and hexagonal shapes;

[0055] (2) The conditions for preparing two-dimensional Cu7Te4 nanosheets in this invention are simple and highly reproducible. By using atomically flat van der Waals materials as the growth substrate and controlling conditions such as the ratio of reaction sources, carrier gas flow rate, temperature, and growth time, the shape, size, and thickness of the Cu7Te4 nanosheets can be regulated. The thinnest thickness of the Cu7Te4 nanosheets in this invention can reach 1.6 nm;

[0056] (3) The two-dimensional Cu7Te4 prepared in this invention has excellent electrical conductivity (with resistance in the ohm level). At a voltage of 0.01 V, the conduction current can reach over 1.3 mA; it can form an ideal metal-semiconductor interface with traditional two-dimensional semiconductors, and is expected to solve the contact problems in electronic, optoelectronic, and spintronic devices based on two-dimensional materials. Description of the Drawings

[0057] Figure 1 It shows the positional relationship of tellurium powder, copper powder, and the substrate placed in the two-zone tube furnace in Example 1 of this invention.

[0058] Figure 2 It is an optical photograph of the triangular Cu7Te4 nanosheets prepared in Example 1 of this invention.

[0059] Figure 3 It is a Raman spectrum of the Cu7Te4 nanosheets prepared in Example 1 of this invention.

[0060] Figure 4 It is a typical Raman vibration of the Cu7Te4 nanosheets prepared in Example 1 of this invention 1 B 2g 、 1 A g and 2 A g It is a graph showing the variation relationship with the thickness of Cu7Te4.

[0061] Figure 5 It is an X-ray photoelectron spectroscopy of the Cu7Te4 nanosheets prepared in Example 1 of this invention.

[0062] Figure 6 It is a comparison graph of the X-ray diffraction pattern (above) of the Cu7Te4 nanosheets prepared in Example 1 of this invention and the corresponding standard PDF card (below).

[0063] Figure 7 It is a high-resolution transmission electron microscopy image of the Cu7Te4 nanosheets prepared in Example 1 of this invention.

[0064] Figure 8 It is an electron diffraction pattern of the Cu7Te4 nanosheets prepared in Example 1 of this invention.

[0065] Figure 9 It is the current-voltage curve graph of the device based on Cu7Te4 nanosheets prepared in Example 1 of the present invention.

[0066] Figure 10 It is the optical photograph of the hexagonal Cu7Te4 nanosheets prepared in Example 2 of the present invention.

[0067] Figure 11 It is the high-angle annular dark-field image of the Cu7Te4 nanosheets prepared in Example 2 of the present invention.

[0068] Figure 12 It is the atomic force picture and the corresponding height profile curve graph of the Cu7Te4 nanosheets prepared in Example 1 and Example 2 of the present invention. Detailed implementation manners

[0069] The technical solution of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0070] Example 1

[0071] This example provides a preparation method for two-dimensional non-stoichiometric Cu7Te4 nanosheets. The preparation method includes:

[0072] Tellurium powder and copper powder are used to prepare the two-dimensional non-stoichiometric Cu7Te4 nanosheets on a substrate through chemical vapor deposition.

[0073] The specific preparation method includes the following steps:

[0074] (1) Cleaning of the substrate. A clean substrate is the key to epitaxial high-quality two-dimensional materials. Ultrasonic cleaning is carried out in an acetone and isopropyl alcohol solution to remove organic residues and impurities on the substrate surface. The substrate is a mica sheet with a thickness of 0.2 mm.

[0075] (2) Weighing of the chemicals. Weigh 0.5 - 1 g of tellurium powder, 10 - 100 mg of copper powder, and 50 - 500 mg of NaCl. The purity of all chemicals is 99.99%, and they are purchased from Alfa Company.

[0076] (3) Put the chemicals weighed in step (2) into a two-zone tube furnace. Place the tellurium powder, copper powder, and substrate in the two-zone tube furnace according to the Figure 1 positions shown. The tellurium powder is placed in the upstream area (low-temperature area), the copper powder and sodium chloride are mixed and placed in the downstream area (high-temperature area), and the substrate is placed close to the copper source. The distance between the tellurium source and the copper source is 60 cm, and the distance between the copper source and the substrate is 3 cm.

[0077] (4) The air in the double-temperature zone tube furnace was pumped out with a mechanical pump and repeatedly purged with 100 sccm of argon, and then the quartz tube was quickly filled with 500 sccm of high-purity argon to atmospheric pressure.

[0078] (5) An oxygen-argon mixture was introduced as the carrier gas (the gas flow ratio of argon to hydrogen was 20:1). The central temperature zone was heated to 600 °C at a heating rate of 25 °C / min in the tellurium source zone, and the central temperature zone was heated to 650 °C at a heating rate of 25 °C / min in the copper source zone. The heating temperature of the substrate was 650 °C, and it was kept warm for 20 minutes. After the reaction ended, the tube furnace was slowly cooled to room temperature.

[0079] The optical photograph of the triangular Cu7Te4 nanosheets prepared in this example is as Figure 2 shown;

[0080] The Raman spectrum of the Cu7Te4 nanosheets prepared in this example is as Figure 3 shown, showing the Raman spectra of Cu7Te4 nanosheets with different thicknesses. The Raman vibration peaks of Cu7Te4 with a thickness of 36 nm are located at 115.9 cm -1 , 133.1 cm -1 and 153.9 cm -1 , corresponding to the 2 B 2g , 1 A g and 2 A g vibration modes of Cu7Te4 nanosheets. The relationship between the thickness and the 2 B 2g , 1 A g and 2 A g Raman shifts was obtained by Gaussian-Lorentz fitting;

[0081] The typical Raman vibrations of the Cu7Te4 nanosheets prepared in this example 1 B 2g , 1 A g and 2 A g as a function of the Cu7Te4 thickness is as Figure 4 shown. The characteristic peaks of Cu7Te4 2 B 2g and 1 A g shift to higher wavenumbers (red shift) with increasing thickness. While the characteristic peak of Cu7Te4 2 A g shifts to lower wavenumbers (blue shift) with increasing thickness;

[0082] The X-ray photoelectron spectrum of the Cu7Te4 nanosheets prepared in this example is as Figure 5 shown. XPS is used to explore the phase composition of the Cu7Te4 nanosheets, including the XPS spectra of the 2p orbit of Cu and the 3d orbit of Te. By peak fitting, two peak positions are obtained at 951.6 eV and 932.1 eV, respectively, corresponding to the 2p 1 / 2 and 2p 3 / 2 orbits of Cu. Peaks at 582.3 eV and 571.7 eV correspond to the 3d 3 / 2 and 2d 5 / 2 orbits of Cu, respectively. The remaining peaks are formed due to the oxidation of the surface of the prepared Cu7Te4 nanosheets;

[0083] The comparison between the X-ray diffraction spectrum (above) of the Cu7Te4 nanosheets prepared in this example and the corresponding standard PDF card (below) is as Figure 6 shown, Figure 6 showing the X-ray diffraction spectrum (upper) of the Cu7Te4 nanosheets and the standard card of JCPDS No. 18-0456 (lower). The strongest diffraction peak is located at 24.7 degrees, belonging to the (002) crystal plane of Cu7Te4. The other three negligible diffraction peaks at 12.2 degrees, 32.8 degrees, and 39.5 degrees correspond to the (100), (210), and (103) crystal planes of Cu7Te4, respectively. The XRD spectrum proves that the epitaxial growth direction of the Cu7Te4 nanosheets is the (001) direction. It can be preliminarily judged that the in-plane growth rate of Cu7Te4 is significantly higher than the out-of-plane growth rate, so it is more inclined to grow large-sized two-dimensional Cu7Te4 nanosheets;

[0084] The high-resolution transmission electron microscopy image of the Cu7Te4 nanosheets prepared in this example is as Figure 7 shown. From the HADDF-STEM image, it can be seen that Te atoms and Te atoms are arranged alternately, corresponding to the Cu7Te4 crystal model (upper left);

[0085] The electron diffraction pattern of the Cu7Te4 nanosheets prepared in this example is as Figure 8 shown, showing the corresponding selected area electron diffraction image of the Cu7Te4 nanosheets. Measured from the selected area electron diffraction image, 0.357 nm, 0.358 nm, and 0.358 nm correspond to the (1-10), (100), and (010) crystal planes, respectively;

[0086] The current-voltage curve of the device based on the Cu7Te4 nanosheets prepared in this example is as Figure 9 shown. From the current-voltage curve, a linear relationship is presented, and at 0.01 V, the resistance can be calculated to be 7.12 Ω.

[0087] Example 2

[0088] In this example, except that the central temperature zone of the copper source region is heated to 650 °C at a heating rate of 25 °C / min and the heating temperature of the substrate is replaced with 780 °C instead of 650 °C, other conditions are the same as those in Example 1. The optical photograph of the hexagonal Cu7Te4 nanosheets prepared in this example is as shown Figure 10 below. Figure 2 and Figure 10 are respectively the optical morphology diagrams of the Cu7Te4 nanosheets obtained at different growth temperatures. Parameters such as the mass ratio of the reaction sources, temperature, time, and carrier gas flow rate usually can affect the morphology and thickness of the samples. Obviously, in the low-temperature region, the Cu7Te4 nanosheets mainly present a triangular shape. While in the high-temperature region, the Cu7Te4 nanosheets mainly present a hexagonal shape. This is due to the different concentration ratios of Te and Cu atoms in the precursor. During the evaporation process, the Cu and Te atoms are affected by the carrier gas flow and form a gradient concentration distribution to the deposition region (lower concentration in the higher temperature region). Therefore, the different ratios of Cu and Te atoms bring different crystal edge terminations, growth rates, and morphological transformations. This shows that different-shaped and -thickness Cu7Te4 nanosheets can be controllably synthesized by controlling the growth temperature of the reaction.

[0089] The high-angle annular dark-field image, the distribution diagrams of copper element and tellurium element of the Cu7Te4 nanosheets prepared in this example are as shown Figure 11 below. From the transmission electron microscope image (a) at a lower magnification, it can be seen that the transferred sample still maintains a complete morphology. The Cu element (b) and Te element (c) are uniformly distributed on the entire Cu7Te4 nanosheet, proving that the synthesized Cu7Te4 nanosheets have a very high crystal quality.

[0090] The atomic force pictures and the corresponding height profile curves of the Cu7Te4 nanosheets prepared in this example and Example 1 are as shown Figure 12 below. From the atomic force image, it can be seen that the thinner ones are triangular in shape, while the thicker ones are hexagonal in shape. From the height profile curve, it can be known that the surface of the nanosheets has atomic-level flatness, and the thickness of the thinnest Cu7Te4 nanosheet is measured to be 1.6 nm. By regulating the reaction temperature, the thickness can be obtained in the range of 1.6 nm to 1 μm.

[0091] Example 3

[0092] In this example, except that the substrate is not cleaned in step (1), other conditions are the same as those in Example 1.

[0093] Example 4

[0094] In this example, except that the distance between the tellurium source and the copper source is replaced by 50 cm, other conditions are the same as those in Example 1.

[0095] Example 5

[0096] In this example, except that the substrate is placed between the copper source and the tellurium source close to the copper source, other conditions are the same as those in Example 1.

[0097] Example 6

[0098] In this example, except that the temperature of the low-temperature region is raised to 650 °C, which is the same as the temperature of the high-temperature region, other conditions are the same as those in Example 1.

[0099] Example 7

[0100] In this example, except that sodium chloride is not used in the downstream region in step (3), other conditions are the same as those in Example 1.

[0101] The thickness and length of the two-dimensional non-stoichiometric Cu7Te4 nanosheets prepared in Examples 1-7 were measured, and the test results are shown in Table 1.

[0102] Among them, the methods for testing the thickness and length are: atomic force microscopy and optical microscopy (or scanning electron microscopy).

[0103] Table 1

[0104]

[0105]

[0106] From the data results of Example 1 and Example 2, it can be seen that at low deposition temperatures, triangular Cu7Te4 nanosheets will be formed, while at high deposition temperatures, hexagonal Cu7Te4 nanosheets will be formed.

[0107] From the data results of Example 3 and Example 1 and Example 2, it can be seen that without cleaning the substrate, the impurities and organic substances on the substrate surface affect nucleation and growth, resulting in epitaxial growth of thick and small Cu7Te4 nanosheets.

[0108] From the data results of Example 4 and Example 1, it can be seen that reducing the distance between the tellurium source and the copper source will lead to a high precursor concentration, and the obtained two-dimensional Cu7Te4 nanosheets will be too thick.

[0109] From the data results of Example 5 and Example 1, it can be seen that placing the position close to the copper source between the copper source and the tellurium source makes it impossible to obtain thin-layer two-dimensional nickel halide.

[0110] From the data results of Example 6 and Example 1, it can be seen that when the temperature in the low-temperature region is raised to 650 °C, a small amount of tellurium nanowires or nanoparticles will be deposited on the mica sheet, and a relatively thick Cu7Te4 nanosheet can be obtained.

[0111] From the data results of Example 7 and Example 1, it can be seen that without using sodium chloride, two-dimensional Cu7Te4 nanosheets cannot be obtained.

[0112] In summary, in the present invention, the two-dimensional non-stoichiometric Cu7Te4 nanosheets are epitaxially grown on a substrate by a chemical vapor deposition method. The obtained two-dimensional Cu7Te4 nanosheets have controllable thickness, flat surface and regular shape. They can form an ideal metal-semiconductor interface with traditional two-dimensional semiconductors, and are expected to solve the contact problem of two-dimensional materials in electronic, optoelectronic devices and spintronic devices.

[0113] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of Cu7Te4 nanosheets, characterized in that, The preparation method includes: Using a tellurium source and a copper source, Cu7Te4 nanosheets with triangular and hexagonal shapes are prepared on a substrate by chemical vapor deposition. The chemical vapor deposition is carried out in a two-zone tube furnace. In the two-zone tube furnace, the tellurium source is placed in the low-temperature zone, and the mixture of the copper source and sodium chloride and the substrate are placed in the high-temperature zone; the temperature of the low-temperature zone is 500 - 700 °C; the temperature of the high-temperature zone is 600 - 800 °C.

2. The preparation method according to claim 1, characterized in that, The substrate includes any one or a combination of at least two of mica sheet, highly oriented graphite sheet, sapphire sheet, quartz sheet, silicon wafer, or SiO2(300nm) / Si on which TMDCs have grown.

3. The preparation method according to claim 2, characterized in that, The thickness of the mica sheet is 0.15 - 0.25 mm.

4. The preparation method according to claim 2, characterized in that, The thickness of the highly oriented graphite sheet is 0.35 - 0.45 mm.

5. The preparation method according to claim 2, wherein The thickness of the sapphire sheet is 0.4 - 0.5 mm.

6. The preparation method according to claim 2, characterized in that, The thickness of the quartz sheet is 0.45 - 0.55 mm.

7. The preparation method according to claim 1, characterized in that, The size of the substrate is 0.01 to 4 cm 2 .

8. The preparation method according to claim 1, wherein The substrate is pretreated, and the pretreatment includes cleaning the substrate.

9. The preparation method according to claim 8, characterized in that, The cleaning solution for the cleaning includes acetone and isopropyl alcohol.

10. The preparation method according to claim 8, characterized in that, The cleaning is ultrasonic cleaning.

11. The preparation method according to claim 1, wherein, The distance between the tellurium source and the copper source is 55 - 65 cm.

12. The preparation method according to claim 1, wherein The distance between the copper source and the substrate is 1 - 5 cm.

13. The preparation method according to claim 1, wherein The tellurium source includes any one or a combination of at least two of tellurium powder, tellurium oxide, tellurium chloride, tellurium bromide, or tellurium iodide.

14. The preparation method according to claim 1, characterized in that, The copper source includes any one or a combination of at least two of copper powder, copper oxide, copper chloride, copper bromide, or copper iodide.

15. The preparation method according to claim 1, characterized in that, The mass ratio of the tellurium source, copper source, and sodium chloride is 18:1:1 - 22:1:

1.

16. The preparation method according to claim 1, characterized in that, The method of chemical vapor deposition includes: heating the two-zone tube furnace by introducing a carrier gas.

17. The preparation method according to claim 1, characterized in that, After the two-zone tube furnace is pretreated, it is heated. The pretreatment includes: evacuating air, cleaning, and filling with an inert gas in sequence for the two-zone tube furnace.

18. The preparation method according to claim 17, wherein The cleaning includes: cleaning the two-zone tube furnace with argon at 95 - 105 sccm.

19. The preparation method according to claim 17, characterized in that, The inert gas is argon.

20. The preparation method according to claim 16, characterized in that, The carrier gas includes argon and hydrogen with a gas flow ratio of (18 - 22):

1.

21. The preparation method according to claim 16, characterized in that, The heating includes heating the low-temperature zone and the high-temperature zone.

22. The preparation method according to claim 1, characterized in that, The heating rate of the low-temperature zone is 20 - 30 °C / min.

23. The preparation method according to claim 1, characterized in that, The holding time of the low-temperature zone is 15 - 25 min.

24. The preparation method according to claim 1, characterized in that, The heating rate of the high-temperature zone is 20 - 30 °C / min.

25. The preparation method according to claim 1, characterized in that, The holding time of the high-temperature zone is 15 - 25 min.

26. The preparation method according to claim 1, characterized in that, The preparation method includes: Placing 0.5 - 1 g of tellurium powder, 10 - 100 mg of copper powder, 50 - 500 mg of sodium chloride, and the substrate in a two-zone tube furnace, and preparing the Cu7Te4 nanosheets on the substrate by chemical vapor deposition.

27. Use of a preparation method of Cu7Te4 nanosheets according to any one of claims 1-26, characterized in that, The preparation method is applied in the field of electronic devices.

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