1. A method for thinning the thickness of a tellurium nanosheet is characterized by comprising the following steps: and soaking the tellurium nanosheets in a weak oxidizing solution, taking out and drying to obtain the tellurium nanosheets with reduced thickness.

2. The method of claim 1, wherein the weakly oxidizing solution is water, a hydrogen peroxide solution, or an acetic acid solution.

3. The method according to claim 2, wherein the tellurium nanosheets are soaked in water for 30-60 hours.

4. The method according to claim 2, wherein the concentration of the hydrogen peroxide solution is 0.01-5 wt%, and the soaking time of the tellurium nanosheets in the hydrogen peroxide solution is 10-60 s.

5. The method according to claim 2, wherein the pH of the acetic acid solution is 5-6.5, and the soaking time of the tellurium nanosheets in the acetic acid solution is 10-60 s.

6. The method of claim 2, wherein the weakly oxidizing solution is hydrogen peroxide solution or acetic acid solution, and further comprising the step of washing with water before drying.

Background

Moore's law has pushed the silicon electronics industry toward smaller and faster transistors for more than half a century. However, the size of the silicon-based CMOS process is approaching the mole limit, and the power consumption problem caused by the reduction of the size is becoming more serious, and the semiconductor industry is urgently looking for new materials and devices with new principles to further enhance the next-generation information processing technology. The two-dimensional material has the advantages of high mobility, adjustable band gap, large specific surface area, atom level thickness and the like, can avoid the problems of transistor performance degradation and power consumption increase caused by short channel effect, and is an important material in the development and planning of the semiconductor industry in the future. The two-dimensional materials synthesized at present are mainly n-type semiconductors (such as MoS)₂、WS₂Etc.), the predominant carrier is an electron. Although there are bipolar semiconductors in which both electrons and holes can conduct (e.g. MoTe)₂、WSe₂Etc.), but the large carrier concentration difference of electrons and holes limits their practical applications. Black Phosphorus (BP) which is excellent in p-type semiconductor properties has once led to extensive research, but the air instability of BP has also greatly limited its development. The lateral size of tellurium (Te) nano-sheets can reach 100 mu m, the thickness can be adjusted from a single atomic layer to dozens of nanometers, the tellurium (Te) nano-sheets have stable p-type semiconductor characteristics and good air stability, and the hole mobility can reach 700cm²V^-1s^-1However, the tellurium nanosheet currently reported existsThe thickness is large, the field effect switch ratio is small, and the like. Wu et al found that the field-effect mobility of the tellurium nanosheets has a direct dependence on the thickness thereof, and the field-effect on-off ratio thereof can reach a maximum value as the thickness of the nanosheets is reduced (Nano Energy 57(2019) 480-491). Therefore, the development of a mild method capable of realizing controllable thickness reduction of the tellurium nanosheets is of great importance for effectively regulating and controlling the carrier concentration of the tellurium nanosheets and other electrical performance indexes.

Wu et al synthesized two-dimensional tellurium nanosheets by a hydrothermal method, developed a solution thinning method, and placed the grown sample in acetone, and adjusted the pH of the solution by sodium hydroxide to achieve thinning of the nanosheets (Nat Electron 1, 228-. However, the method has poor effect of thinning the sample and complex operation method. Javey et al obtained a tellurium nano-film with a controlled thickness by low temperature thermal evaporation, but when a very thin nano-film (8nm) was evaporated, the influence of impurities, crystal quality and surface roughness became large (Nat. Nanotechnol.15, 53-58 (2020)). The methods generally have the defects of complex process, large damage to the surface appearance of the sample and the like.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a method for thinning the thickness of a tellurium nanosheet, which thins the tellurium nanosheet by using a weak oxidizing solution to realize the accurate regulation and control of the thickness of the tellurium nanosheet.

In order to achieve the purpose, the invention provides the following technical scheme:

the invention provides a method for thinning a tellurium nanosheet, which comprises the following steps: and soaking the tellurium nanosheets in a weak oxidizing solution, taking out and drying to obtain the tellurium nanosheets with reduced thickness.

Further, the tellurium nanosheets are sheet-shaped tellurium obtained by a hydrothermal method or a chemical vapor deposition method.

Further, before the tellurium nanosheets prepared by the hydrothermal method are soaked in the weak oxidizing solution, the tellurium nanosheets are placed on a target substrate, and then the target substrate is transferred to the weak oxidizing solution to be soaked.

Still further, the target substrate is a silicon wafer, a sapphire substrate, glass, or mica.

Further, the weak oxidizing solution is water, a hydrogen peroxide solution or an acetic acid solution.

Further, the soaking time of the tellurium nanosheets in water is 30-60 h.

Further, the concentration of the hydrogen peroxide solution is 0.01-5 wt%, and the soaking time of the tellurium nanosheets in the hydrogen peroxide solution is 10-60 s.

Further, the pH value of the acetic acid solution is 5-6.5, and the soaking time of the tellurium nanosheets in the acetic acid solution is 10-60 s.

Further, when the weak oxidizing solution is hydrogen peroxide solution or acetic acid solution, the method further comprises a step of washing with water before drying.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, the tellurium nanosheets are thinned by utilizing the mild oxidation reaction between the weak oxidizing solution and the surfaces of the tellurium nanosheets, and the precise regulation and control of the thickness of the tellurium nanosheets can be realized by changing the type and the soaking time of the weak oxidizing solution.

The method provided by the invention is adopted to thin the tellurium nanosheets, the advantages of the p-type tellurium nanosheets can be fully exerted, and the thickness of the tellurium nanosheets is positively correlated with the carrier mobility and negatively correlated with the field effect on-off ratio within a certain thickness range (5nm to 100 nm). Along with the reduction of the thickness of the nanosheet, the carrier mobility is continuously reduced, but the field effect switching ratio is continuously increased, so that the requirements of different devices on the material performance can be met. The electronic and photoelectric devices based on the tellurium nanosheets can be constructed in a mode of electron beam exposure and vacuum evaporation of electrode materials, and are good in compatibility with the traditional semiconductor processing technology.

The method can realize effective regulation and control of the thickness and the carrier concentration of the tellurium nanosheets with p-type semiconductor characteristics, and has a promoting significance for development of two-dimensional semiconductor devices.

The method provided by the invention is simple to operate, can realize multiple regulation and control of the thickness of the tellurium nanosheets, the carrier concentration and the field effect on-off ratio, and provides support for the two-dimensional p-type semiconductor material which is stable in development performance and meets the multi-scene requirements.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

Fig. 1a is a pseudocolor light mirror image of a tellurium nanosheet prepared by hydrothermal method in step (1) of example 1, and fig. 1b is a pseudocolor light mirror image of a thinned tellurium nanosheet obtained in step (2) of example 1;

FIG. 2a, 2b, 2c, 2d, 2e, 2f are AFM profile characterization diagrams of the Te nanoplates with thicknesses of 66nm, 19.4nm, 14.1nm, 9.9nm, 7nm, 4nm prepared in example 1,

fig. 3a, 3b, 3c, 3d, 3e, 3f are the original average height map of the tellurium nanosheets along the white straight line in fig. 2a, 2b, 2c, 2d, 2e, 2f and typical height measurements after soaking in deionized water for 30h, 35h, 40h, 50h and 55h, respectively;

FIGS. 4a and 4b are AFM morphology characterization graphs of the tellurium nanosheets prepared in example 2 before and after being soaked in 0.5 wt% hydrogen peroxide solution for 10s, respectively, and FIG. 4c is a height graph of the tellurium nanosheets before and after being soaked along a white straight line in the graphs of FIGS. 4a and 4 b;

FIGS. 5a and 5b are AFM topography characterization diagrams before and after soaking the tellurium nanosheets prepared in example 3 in an acetic acid solution with a pH of 6 for 20s, respectively, and FIG. 5c is a height diagram of the tellurium nanosheets before and after soaking along the white straight lines in the two diagrams of FIGS. 5a and 5 b;

FIGS. 6a and 6b are AFM morphology characterization graphs of the tellurium nanosheets prepared in comparative example 1 before and after being soaked in 10 wt% hydrogen peroxide solution for 10s, respectively;

FIGS. 7a and 7b are AFM morphology characterization graphs of the tellurium nanosheets prepared in comparative example 2 before and after being soaked in an acetic acid solution with a pH of 3.5 for 20s, respectively;

fig. 8 is a graph of the transfer characteristics of a field effect transistor based on tellurium nanoplates with thicknesses of 25nm and 10nm prepared in example 1 and 7nm prepared in example 2, where a is a graph of the transfer characteristics of a field effect transistor based on 25nm thick tellurium nanoplates, b is a graph of the transfer characteristics of a field effect transistor based on 10nm thick tellurium nanoplates, and c is a graph of the transfer characteristics of a field effect transistor based on 7nm thick tellurium nanoplates.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

Example 1

(1) Preparing a tellurium nanosheet by a hydrothermal method: the reaction principle is that sodium tellurite is used as a raw material, ammonia water provides alkaline conditions for reaction, hydrazine hydrate is used for reducing the sodium tellurite, a mirror blocking ligand (PVP) is used for agglomerating tellurium nano particles, and the yield and the size of tellurium nano sheets are controlled by controlling the addition amount of the PVP. The specific operation is that the molar ratio of the raw materials is 2: weighing 0.1165g of sodium tellurite and 6.4g of PVP (polyvinyl pyrrolidone) and dissolving in 25ml of deionized water, stirring uniformly, respectively adding 2.5ml of ammonia water and 1.5ml of hydrazine hydrate solution, stirring uniformly to obtain a mixed solution with a pH value of 9, pouring the mixed solution into a 50ml reaction kettle, reacting at 180 ℃ for 10 hours, and quenching the reaction kettle by flowing cold water after the reaction is finished to obtain a tellurium nanosheet stock solution; centrifuging 3mL of reaction stock solution for 3 times by using deionized water to obtain uniformly dispersed tellurium nanosheets in an aqueous solution, transferring the tellurium nanosheets onto an insulating silicon substrate by using a pulling and fishing method, naturally airing, and drying for 20min at 100 ℃, wherein the thickness of the obtained tellurium nanosheets is 50-100nm, and when preparing the tellurium nanosheets by using a hydrothermal method, the tellurium nanosheets with the same thickness are difficult to fixedly grow under the same condition, and the obtained thickness is an interval value range, so that a sampling and comparison method is selected when carrying out statistical analysis;

(2) slowly thinning the tellurium nanosheets: and (2) immersing the tellurium nanosheets on the insulating silicon substrate obtained in the step (1) into a beaker filled with deionized water, standing for 50h, taking out, and drying by blowing with nitrogen gas to obtain single-layer to 25nm thin-layer tellurium nanosheets. The thickness of the nano-sheets is measured in a statistical distribution mode, and the tellurium nano-sheet thinning process is performed on all tellurium nano-sheet samples in a solution, so that the thickness change of a certain nano-sheet after standing in deionized water for a specific time is not counted independently.

FIG. 1a is a pseudocolor light mirror image of a typical tellurium nanosheet prepared by a hydrothermal method, and FIG. 1b is a pseudocolor light mirror image of the tellurium nanosheet after being soaked in deionized water for 50 h. In both figures, the brighter the color, the thicker the tellurium nanosheets. The color of the tellurium nanosheet just grown is white, the color of the tellurium nanosheet after thinning is purple, but the crystallinity is good, which indicates that the sample is not damaged.

2a, 2b, 2c, 2d, 2e, 2f are AFM morphology characterization of tellurium nanosheets with thicknesses of 66nm, 19.4nm, 14.1nm, 9.9nm, 7nm, 4nm respectively, from each AFM figure, it can be clearly seen that the tellurium nanosheets only have a thickness change, and the overall crystallinity is good;

fig. 3a, 3b, 3c, 3d, 3e, and 3f are the original average height maps of the tellurium nanosheets corresponding to 2a, 2b, 2c, 2d, 2e, and 2f in fig. 2, respectively, and typical height measurements after soaking in deionized water for different periods of time (30h, 35h, 40h, 50h, and 55 h). The average thickness of the sample before thinning is 66nm, and thin-layer tellurium nanosheets with thicknesses of 19.4nm, 14.1nm, 9.9nm, 7nm and 4nm are obtained in the embodiment after soaking in deionized water for 30h, 35h, 40h, 50h and 55h respectively.

Example 2

(1) The preparation method of the tellurium nanosheets is the same as the step (1) of the example 1, and the difference is that the specific operation is as follows according to the molar ratio of 2: weighing 0.1165g of sodium tellurite and 6.4g of PVP, dissolving in 25ml of deionized water, stirring uniformly, adding 2.5ml of ammonia water and 4ml of hydrazine hydrate solution respectively, stirring uniformly, pouring the mixed solution into a 50ml reaction kettle, reacting for 5 hours at 180 ℃, and quenching the reaction kettle by flowing cold water after the reaction is finished to obtain a tellurium nanosheet stock solution; centrifuging 3mL of reaction stock solution by using deionized water for 3 times to obtain uniformly dispersed tellurium nanosheets in the aqueous solution, transferring the tellurium nanosheets onto an insulating silicon substrate by using a pulling and fishing method, naturally airing, and drying at 100 ℃ for 20min to obtain the tellurium nanosheets with the thickness of 30-50 nm.

(2) Slowly thinning the tellurium nanosheets: and (2) immersing the tellurium nanosheets on the insulating silicon substrate obtained in the step (1) into a hydrogen peroxide solution with the concentration of 0.5 wt%, wherein the immersion time is 10 s. And (3) soaking the tellurium nanosheets in a hydrogen peroxide solution for 10s, quickly taking out, cleaning with a large amount of deionized water, and blow-drying with nitrogen to obtain single-layer to 25nm thin-layer tellurium nanosheets.

In order to better compare the morphology change of the tellurium nanosheets before and after soaking in 0.5 wt% hydrogen peroxide solution, the same one-piece tellurium nanosheet is selected for comparison. FIGS. 4a and 4b are AFM morphology representations of samples before and after being soaked in 0.5 wt% hydrogen peroxide solution for 10s, respectively, and it can be seen that the surface morphology of the tellurium nanosheet has no obvious change and the crystallinity is good. FIG. 4c is a height view of the sample along the white straight line in the two graphs 4a and 4b before and after thinning, and it can be seen that the thickness of the tellurium nanosheet before thinning is 39.2nm and the thickness is increased by 0.5 wt% of H₂O₂After the solution was thinned, the thickness was reduced to 24.7 nm.

Example 3

(1) The preparation method of the tellurium nanosheets is the same as the step (1) of the example 2;

(2) slowly thinning the tellurium nanosheets: and (2) immersing the tellurium nanosheets on the insulating silicon substrate obtained in the step (1) into an acetic acid solution with the pH of 6 for 20 s. And (3) soaking the tellurium nanosheets in an acetic acid solution for 20s, then quickly taking out, washing with a large amount of deionized water, and blow-drying with nitrogen to obtain single-layer to 25nm thin-layer tellurium nanosheets.

In order to better compare the morphology change of the tellurium nanosheets before and after soaking in an acetic acid solution with the pH value of 6, the same tellurium nanosheet is selected for comparison. FIGS. 5a and 5b are AFM morphology representations of samples before and after soaking in an acetic acid solution with pH of 6 for 20s, respectively, and it can be seen that the morphology is not significantly changed before and after thinning of the tellurium nanosheets, and the thickness is significantly changed. FIG. 5c is a height view of the sample along the white straight line in the two diagrams 5a and 5b before and after thinning, and it can be seen that the thickness of the tellurium nanosheet before thinning is 30.5nm, and the thickness is reduced to 22.6nm after thinning by the acetic acid solution with pH of 6.

Example 4

(1) Preparing a tellurium nanosheet by a chemical vapor deposition method: 0.2g of tellurium oxide (TeO) is taken₂) Is a precursor and is placed in Al positioned in the central area of the normal-pressure tube furnace₂O₃In the crucible, mica was placed downstream as a collection substrate. Prior to the growth process, the tube was evacuated and flushed with high purity argon (500sccm) for 5min to eliminate oxygen residues. Subsequently, with Ar/H₂Heating the central region to 700 ℃ by mixed carrier gas, growing for 1h, and naturally cooling to obtain triangular tellurium nanosheets with thickThe degree is 30 nm;

(2) slowly thinning the tellurium nanosheets: and (2) placing the tellurium nanosheets obtained in the step (1) in a hydrogen peroxide solution with the concentration of 0.1 wt%, soaking for 30s, quickly washing the sample with a large amount of clear water, and drying by blowing with nitrogen gas to obtain single-layer to 10nm thin-layer tellurium nanosheets.

AFM morphology characterization is carried out on the tellurium nanosheets before and after thinning, the same results are obtained that the surface morphologies of the tellurium nanosheets before and after thinning are not obviously changed, and the crystallinity of the thinned tellurium nanosheets is good.

Comparative example 1

The difference from example 2 is that the concentration of the hydrogen peroxide solution in step (2) was replaced with 10 wt% and the soaking time was 10 seconds.

FIG. 6 is a comparison of AFM morphologies of the same sample before and after soaking in a 10 wt% hydrogen peroxide solution, which shows that the morphology of the tellurium nanosheets is destroyed, and thus the concentration is not suitable for thinning the tellurium nanosheets.

Comparative example 2

The difference from example 3 is that the pH of the aqueous acetic acid solution in step (2) was set to 3.5 and the soaking time was 20 seconds.

Fig. 7 is a comparison of SEM morphologies of the same sample before and after soaking in an acetic acid solution having a pH of 3.5, and it can be seen that the morphology of the tellurium nanosheets has also been destroyed at this time, so that it is not suitable for thinning the tellurium nanosheets when the pH of the acetic acid is too low.

In the comparative examples 1 and 2, the morphology of the finally obtained tellurium nanosheet is damaged due to the fact that the concentration of the weak zinc oxide solution is too high. When the concentration of the hydrogen peroxide solution is less than 0.01 wt% or the pH of the acetic acid is greater than 6.5, the thinning effect is similar to that of deionized water, and the description is omitted here.

The tellurium nanosheets with the thicknesses of 25nm and 10nm prepared in the embodiment 1 and 7nm prepared in the embodiment 2 are selected to prepare the field effect transistor, the transfer characteristics of the field effect transistor are tested, the obtained transfer characteristic curve graph is shown in fig. 8, and as can be seen from fig. 8, the transfer characteristic curve of the field effect transistor constructed by the tellurium nanosheets with the thicknesses of 25nm, 10nm and 7nm has obvious p-type semiconductor characteristics, and most carriers of the field effect transistor are holes.The hole mobility corresponding to the three thicknesses is 162cm²s^-1V^-1，52cm²s^-1V^-1，28.2cm²s^-1V^-1. The field effect switching ratio is respectively: 2.2, 5X 10¹，7×10². When the thickness of the tellurium nanosheets is 25nm, the electrical properties of the tellurium nanosheets are close to the bulk properties, the mobility and the field effect on-off ratio do not change by orders of magnitude along with the increase of the thickness, but the hole mobility of the tellurium nanosheets is in a descending trend along with the reduction of the thickness of the tellurium nanosheets, but is still superior to most two-dimensional p-type semiconductors; meanwhile, as the thickness is reduced, the gate voltage regulation capability of the tellurium nanosheet field effect transistor is improved, and the field effect switching ratio is in an increasing trend. But when the thickness is further reduced to a monolayer, the electrical properties of the tellurium nanosheets become very poor and even non-conductive due to excessive surface defects of the nanosheets, and thus no longer provide the properties of a thinner sample.

The above description is only for the preferred embodiment of the present invention, and the protection scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical scope of the present invention, the technical solution and the inventive concept of the present invention equivalent or change within the technical scope of the present invention.