CN112110411A

CN112110411A - Method for preparing suspended layered metal chalcogenide

Info

Publication number: CN112110411A
Application number: CN201910529623.0A
Authority: CN
Inventors: 黄元; 罗海兰; 赵林; 周兴江
Original assignee: Institute of Physics of CAS
Current assignee: Institute of Physics of CAS
Priority date: 2019-06-19
Filing date: 2019-06-19
Publication date: 2020-12-22
Anticipated expiration: 2039-06-19
Also published as: CN112110411B

Abstract

The invention provides a method for preparing suspended layered metal chalcogenide, which comprises the following steps: (1) preparing a patterned array of holes on a substrate; (2) forming a first metal layer on a substrate having an array of holes, and then forming a second metal layer on the first metal layer; the first metal layer is formed of Ti, Cr, Zn, Al, Ni, Cu, Fe or an alloy of two or more thereof, and the second metal layer is formed of Au; (3) mechanically cleaving the metal chalcogenide with a tape, attaching the metal chalcogenide on the tape to the second metal layer in the step (2), and performing a heat treatment; (4) after the heat treatment is completed, the substrate is cooled to room temperature, and then the adhesive tape is peeled off from the substrate with the hole array, so that the suspended layered metal chalcogenide is prepared on the substrate with the hole array. The preparation method provided by the invention has the advantages of few steps, simplicity, easiness in implementation and high preparation efficiency.

Description

Method for preparing suspended layered metal chalcogenide

Technical Field

The invention relates to the field of materials. In particular, the present invention relates to a method of preparing suspended layered metal chalcogenides.

Background

There are hundreds of known layered materials, most of which are still under investigation in the first stage, and many important properties still need to be deeply explored. The discovery of graphene raises the hot trend of research on two-dimensional materials, which are the two-dimensional materials discovered at the earliest time and have very many excellent properties, but graphene is difficult to be applied to future flexible semiconductor devices due to the fact that graphene does not have a proper band gap. With molybdenum disulfide (MoS)₂) Molybdenum diselenide (MoSe)₂) Molybdenum ditelluride (MoTe)₂) The typical layered metal chalcogenides (TMDCs) cover important constituent materials in future electronic devices such as semiconductors, semi-metals and superconductors, and the excellent electrical and optical properties of the TMDCs make the materials have important application potential, and thus the TMDCs attract extensive attention and intensive research in the international material and physical communities.

Although there are many methods for preparing two-dimensional materials, including Molecular Beam Epitaxy (MBE), Chemical Vapor Deposition (CVD), liquid phase lift-off, etc., the two-dimensional materials prepared by the mechanical cleavage method are still the currently accepted high quality samples, and in the case of graphene, almost all the intrinsic physical properties of graphene have been observed and tested on the mechanically cleaved samples. In the two-dimensional material prepared by mechanical cleavage, the suspended cleavage sample has the highest quality, and the suspended sample is a rational system for researching the mechanical property, the electrical property and the optical property of the two-dimensional material. For example, suspended graphene exhibits ultra-high electron mobility, suspended single-layer MoS₂Has strong fluorescence. The mechanical cleavage method has disadvantages of small sample size (about ten micrometers or more), low yield, etc., although the sample quality is very high, and it is difficult to find a single-layer sample under a microscope, so that the mechanical cleavage method requires a large investment in labor and time for preparing a two-dimensional material.

Although the sample prepared by the CVD method has a large area, the steps of gluing, transferring and the like are required when the suspended sample is prepared, the pollution and damage are introduced in the processes, and the intrinsic properties of the two-dimensional material cannot be effectively reflected due to the reasons that the density of defects is difficult to control in the growth process and the like.

The MBE method can prepare high-quality two-dimensional suspended TMDCs samples, but the defects of high equipment cost, long preparation period and small sample size limit the application of the TMDCs samples in scientific research and industrialization.

Suspended layered metal chalcogenides have long faced significant processing challenges, and scientists have difficulty in efficiently preparing suspended layered metal chalcogenides, making some important scientific studies difficult to develop. Most of the suspended layered metal chalcogenides have been prepared by cleaving layered materials onto a substrate having an array of pores, but the conventional cleaving method has a very low preparation efficiency and has a high requirement on the size of the array of pores on the substrate.

Therefore, the method for efficiently preparing the suspended layered metal chalcogenide is important for basic scientific research and application of future materials.

Disclosure of Invention

Aiming at the defects of the method for preparing the suspended layered metal chalcogenide, the invention provides a method for efficiently preparing a plurality of suspended single-layer and thin-layer metal chalcogenide (TMDCs) materials with large area by enhancing the van der Waals force interaction force between the metal chalcogenide and the substrate, and provides powerful material guarantee for the aspects of the intrinsic physical properties and the like of the materials.

In the present invention, the term "monolayer" refers to a single atomic or molecular layer; the term "thin layer" refers to an atomic or molecular layer of two to five layers. Correspondingly, the term "thickness of a monolayer" refers to the thickness of a single atomic or molecular layer; the term "thickness of a thin layer" refers to the thickness of an atomic or molecular layer of two to five layers. In MoS₂For example, the thickness of a single layer refers to MoS₂The thickness of the molecule, i.e. the thickness of a layer of Mo atoms sandwiched between two layers of S atoms; the thickness of the thin layer means a thickness of 2 to 5 above-mentioned single layers.

The above object of the present invention is achieved by the following means.

The invention provides a method for preparing suspended layered metal chalcogenide, which comprises the following steps:

(1) preparing a patterned array of holes on a substrate;

(2) forming a first metal layer on a substrate having an array of holes, and then forming a second metal layer on the first metal layer; the first metal layer is formed of Ti, Cr, Zn, Al, Ni, Cu, Fe or an alloy of two or more thereof, and the second metal layer is formed of Au;

(3) mechanically cleaving the metal chalcogenide with a tape, attaching the metal chalcogenide on the tape to the second metal layer in the step (2), and performing a heat treatment;

(4) after the heat treatment is completed, the substrate is cooled to room temperature, and then the adhesive tape is peeled off from the substrate with the hole array, so that the suspended layered metal chalcogenide is prepared on the substrate with the hole array.

In the method of the present invention, mechanical cleavage of the metal chalcogenide by the tape can provide a fresh surface before the metal chalcogenide is attached to the substrate, ensuring that the interface between the metal chalcogenide and gold does not have excessively adsorbed small molecules, thereby reducing the contact distance between the metal chalcogenide and gold and increasing the van der waals interaction strength. In the method of the present invention, the heat treatment can make the TMDCs adhere to the substrate as much as possible.

Preferably, the method of the present invention further comprises a step of performing oxygen plasma cleaning on the substrate having the array of holes before performing the step (2). Cleaning the substrate with an oxygen plasma removes environmentally adsorbed impurities, thereby enhancing van der waals interactions between the TMDCs and the substrate.

Preferably, in the method of the present invention, the oxygen plasma cleaning is performed under the following conditions: the flow rate is 20-50 sccm, the power is 50-100W, and the cleaning time is 2-5 min.

Preferably, in the method of the present invention, the step (1) of preparing the patterned hole array on the substrate is performed by optical exposure and ion etching.

Preferably, in the method of the present invention, the array of wells has a well diameter of 2-10 μm and a well-to-well spacing of 10-20 μm.

Preferably, in the method of the present invention, the step (2) of forming a first metal layer on the substrate having the hole array and then forming a second metal layer on the first metal layer is performed by thermal evaporation or electron beam evaporation at a temperature higher than 10 deg.f^- ⁵The reaction was carried out under a vacuum atmosphere of Torr. In the invention, the first metal layer is evaporated as a transition layer, which can make the second metal layer better adhere to the substrate. The invention can increase the interaction between the TMDCs and the interface of the substrate by forming two metal layers on the substrate.

Preferably, in the method of the present invention, the thickness of the first metal layer is 1 to 5nm, and the thickness of the second metal layer is 2 to 10 nm.

Preferably, in the method of the present invention, the substrate is SiO₂a/Si substrate, a sapphire substrate, a glass substrate or a quartz substrate.

Preferably, in the process of the present invention, the metal chalcogenide is MX₂Wherein M is Mo, W, Sn, Ta, V, Ti, Re, Nb, Pt or Pd, and X is S, Se or Te; or

MX, wherein M is Fe, Ga or Sn and X is S, Se or Te.

Preferably, in the method of the present invention, the heat treatment in the step (3) is performed at a temperature of 50 to 140 ℃ for 10 to 30 seconds.

The invention has the beneficial effects that:

the preparation method can prepare suspended large-area single-layer and thin-layer TMDCs materials. Meanwhile, the preparation method provided by the invention has the advantages of few steps, simplicity, easiness in implementation and high preparation efficiency. Compared with the conventional mechanical cleavage method, the size of the suspended layered TMDCs is increased from several micrometers to millimeter to centimeter magnitude, the area is increased by five to six magnitude orders, and the size of a sample is mainly determined by the size of a bulk crystal. The test result of the Raman spectrum shows that the sample prepared by the preparation method has very high quality, no additional defect is introduced, and the single-layer sample has the same spectral peak position as the sample obtained by the common mechanical cleavage method.

Drawings

Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a schematic diagram of a production process of embodiment 1 of the present invention;

FIG. 2 shows a conventional cleaving process and suspended monolayer metal chalcogenide MoS prepared in accordance with example 1 of the present invention₂Light micrograph comparison. (a) The common method can only be used for processing thicker MoS₂Transferred to the hole array (dotted line), most of the area is free of two-dimensional material; (b) large area single and double layer (dotted) MoS obtained by improved cleaving process₂。

FIG. 3 shows a conventional mechanical cleaving process and suspended single layer MoS made in accordance with example 1 of the present invention₂A Raman spectrum contrast map; it can be seen that the MoS2 characteristic peak produced by the conventional method is weak (a) and the peak of silicon (521 wavenumbers) can be seen, while the raman signal is very strong on the suspended sample (b).

FIG. 4 shows suspended single-, double-and triple-layered metal chalcogenides MoS prepared according to example 1 of the present invention₂The photograph of (a);

FIG. 5 is a graph of suspended single, double and triple layer metal chalcogenides WSe prepared in comparative example 1₂The optical microscope photograph of (1);

FIG. 6 shows the suspended monolayer metal chalcogenide MoS prepared in comparative example 2₂The optical microscope photograph of (1).

Detailed Description

The present invention is described in further detail below with reference to specific embodiments, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.

Example 1

(1) Patterning a 2cm × 2cm silica-silica base material: firstly, spin-coating a layer of photoresist on a substrate, then obtaining an exposed circular pattern by a mask under ultraviolet exposure, and then utilizing a fluorine-containing gas SF in a reactive ion etching system₆As a plasma source, the etching power is 100W, and the etching time is 5 minutes;the resulting array of wells had a diameter of 5 μm and a center-to-center spacing of 15 μm.

(2) The substrate with the array of holes was then cleaned with oxygen plasma in a plasma generator model TS-PL02 from Toxico and high sciences Automation Equipment Inc. of Shenzhen, Inc. for 2 minutes to remove environmentally adsorbed impurities at a flow rate of 20sccm and a power of 100W.

(3) The silicon dioxide-silicon substrate with the hole array is purchased in a metal evaporation system of Beijing micro-nano vacuum at a vacuum degree of about 10^-6Depositing metal by thermal evaporation under the condition of Torr, wherein the first metal layer is formed by Ti and is deposited by 1 nanometer; the second metal layer was formed of Au deposited to a thickness of 2 nm. And taking out the substrate after the deposition is finished.

(4) Mechanical cleaving of MoS with tape₂And (3) obtaining a fresh surface, then quickly attaching the crystal on the adhesive tape to the surface of the base material prepared in the step (2), and heating the adhesive tape on a hot plate at 100 ℃ for 20 seconds.

(5) The adhesive tape-MoS prepared in the step (4) is used₂The substrate material is taken off from the hot plate, naturally cooled to room temperature in the air for about 10 seconds, and then the adhesive tape is rapidly removed to finish cleavage, so that large-area suspended single-layer MoS can be obtained on the surface of the substrate₂。

FIG. 1 is a schematic view of the preparation process of this example;

(a) first, a piece of SiO is prepared₂Spin-coating a layer of photoresist (AZ6130) on a Si substrate at 3000 rpm for 1 min, as shown in FIG. 1 a;

(b) the substrate was exposed using a reticle having a circular array pattern for 10 seconds. Developing and fixing to obtain an exposed circular array pattern, etching an unprotected circular area by using a reactive ion etching method, and then washing away the photoresist by using acetone to obtain a hole array structure, wherein the hole array structure is shown in figure 1 b;

(c) in SiO with an array of holes₂Evaporating a first metal layer on the Si substrate, wherein the first metal layer is formed by Ti; then evaporating a second metal layer, wherein the second metal layer is formed by Au; FIG. 1c shows the first metal layer and the second metal layer after evaporationA substrate having an array of wells;

(d) metal chalcogenide MoS on adhesive tape₂Cleaving to obtain a new surface, then attaching to the second metal layer, and performing heating treatment;

(e) heating for about 10 seconds, taking off the metal chalcogenide alloy from the hot plate, naturally cooling to room temperature, and removing the adhesive tape to obtain large-area suspended monolayer metal chalcogenide MoS₂. The fig. 1e and 1f profiles are schematic side and top views after cleaving.

FIG. 2 shows a conventional cleaving process and the suspended monolayer metal chalcogenide MoS produced in this example₂Optical microscope photo contrast; (a) cleavage to SiO by conventional methods₂Suspended multilayer MoS on Si substrate₂(ii) a (b) The suspended monolayer metal chalcogenide MoS prepared in this example₂(ii) a Single-layer MoS obtained by two methods₂The sample area is indicated in the figure. The ordinary cleaving method is to cleave the metal chalcogenide MoS repeatedly with an adhesive tape₂And then directly attaching to a substrate having an array of holes, and removing the tape to obtain a metal chalcogenide MoS₂. The single-layer yield of the common method is low, a proper area is difficult to find, the single-layer yield of the improved method is high, and the sample size is large.

FIG. 3 is a graph of the single layer MoS obtained on a flat substrate by conventional mechanical cleaving₂And the suspended monolayer MoS prepared in this example₂Raman spectrum contrast chart. The ordinary cleaving method is to cleave the metal chalcogenide MoS repeatedly with an adhesive tape₂And then directly attached to SiO₂Metal chalcogenide MoS with a/Si substrate and subsequent removal of the adhesive tape₂. FIG. 3 shows the MoS cleaved by the two methods₂No significant difference in peak position was observed, and the suspended monolayer MoS prepared in this example was₂Are located at 385 and 403 wavenumbers, respectively, but the intensity of the peaks is significantly higher than that of a single-layer MoS cleaved by a conventional method₂The sample is strong, and the Raman peak of the suspended part does not contain the characteristic peak of Si, so that the intrinsic characteristics of the reaction material can be better. In fig. 3a, the characteristic peak of 521 wavenumbers is the signal of the Si substrate.

FIG. 4 shows the suspended metal chalcogenides MoS with different number of layers obtained in this example₂The photograph of (2). Fig. 4 shows a suspended single to three layer sample area made by the method of the present invention, well suited for performing various spectroscopic studies in different layers.

Example 2

(1) Patterning sapphire substrate base material: firstly, spin-coating a layer of photoresist on a substrate, then obtaining an exposed circular pattern by a mask under ultraviolet exposure, and then utilizing CHF gas containing fluorine in a reactive ion etching system₃As a plasma source, the etching power is 100W, and the etching time is 5 minutes; the resulting array of wells had a well diameter of 2 μm and a well-to-well spacing of 10 μm.

(2) The substrate with the array of holes was then cleaned with oxygen plasma in a plasma generator model TS-PL02 from Toxico and high sciences Automation Equipment Inc. of Shenzhen, removing environmentally adsorbed impurities at a gas flow rate of 50sccm and a power of 50W for 5 minutes.

(3) Sapphire substrate with hole array is purchased in a metal evaporation system of Beijing micro-nano vacuum at a vacuum degree of about 10^-7Depositing metal by thermal evaporation under the condition of Torr, wherein the first metal layer is formed by Ti and is deposited by 1 nanometer; the second metal layer was formed of Au deposited to a thickness of 8 nm. And taking out the substrate after the deposition is finished.

(4) Mechanical cleaving of MoS with tape₂And (3) obtaining a fresh surface, then quickly attaching the crystal on the adhesive tape to the surface of the base material prepared in the step (1), and heating the adhesive tape on a hot plate at 50 ℃ for 30 seconds.

(5) The adhesive tape-MoS prepared in the step (4) is used₂The substrate material is taken off from the hot plate, naturally cooled to room temperature in the air for about 5 seconds, and then the adhesive tape is rapidly removed to finish cleavage, so that large-area suspended single-layer MoS can be obtained on the surface of the substrate₂。

It was observed by optical microscopy that the suspended monolayer samples ranged in size from 100 microns to 5 mm, with the largest dimension depending on the bulk crystal size.

Example 3

(1) Patterning a 2cm x 2cm silica-silicon based base material: firstly, spin-coating a layer of photoresist on a substrate, then obtaining an exposed circular pattern by a mask under ultraviolet exposure, and then utilizing a fluorine-containing gas SF in a reactive ion etching system₆As a plasma source, the etching power is 100W, and the etching time is 5 minutes; the resulting array of wells had a well diameter of 10 μm and a well-to-well spacing of 20 μm.

(2) The substrate with the array of holes was then cleaned with oxygen plasma in a plasma generator model TS-PL02 from Toxico and high sciences Automation Equipment Inc. of Shenzhen, removing environmentally adsorbed impurities at a gas flow rate of 30sccm and a power of 80W for 3 minutes.

(3) The silicon dioxide-silicon substrate with the hole array is purchased in a metal evaporation system of Beijing micro-nano vacuum at a vacuum degree of about 10^-8Depositing metal by thermal evaporation under the condition of Torr, wherein the first metal layer is formed by Ti and is deposited by 5 nanometers; the second metal layer was formed of Au deposited to a thickness of 5 nm. And taking out the substrate after the deposition is finished.

(4) Mechanically cleaving FeSe with an adhesive tape to obtain a fresh surface, immediately attaching the crystals on the adhesive tape to the surface of the base material prepared in step (1), and heating on a hot plate at 100 ℃ for 30 seconds.

(5) And (4) taking the adhesive tape-FeSe-substrate material prepared in the step (4) down from a hot plate, naturally cooling to room temperature in the air for about 20 seconds, and then quickly removing the adhesive tape to finish cleavage, thus obtaining large-area suspended single-layer FeSe on the surface of the substrate.

Example 4

(1) Patterning a 2cm x 2cm silica-silicon based base material: firstly, a layer of photoresist is coated on a substrate in a spin mode, and then the exposed photoresist is obtained under the ultraviolet exposure through a maskCircular pattern, then CHF in a reactive ion etching system using a gas containing fluorine₃As a plasma source, the etching power is 100W, and the etching time is 5 minutes; the resulting array of wells had a well diameter of 10 μm and a well-to-well spacing of 20 μm.

(2) The substrate with the array of holes was then cleaned with oxygen plasma in a plasma generator model TS-PL02 from Toxico and high sciences Automation Equipment Inc. of Shenzhen, Inc. for 2 minutes to remove environmentally adsorbed impurities at a gas flow rate of 30sccm and a power of 80W.

(3) The silicon dioxide-silicon substrate is purchased in a metal evaporation system of Beijing micro-nano vacuum at the vacuum degree of about 10^- ⁶Depositing metal by thermal evaporation under the condition of Torr, wherein the first metal layer is formed by Cr and is deposited by 2 nanometers; the second metal layer was formed of Au deposited to a thickness of 5 nm. And taking out the substrate after the deposition is finished.

(4) Mechanical cleaving of MoS with tape₂And (3) obtaining a fresh surface, then quickly attaching the crystals on the adhesive tape to the surface of the base material prepared in the step (1), and heating the adhesive tape on a hot plate at 130 ℃ for 10 seconds.

Example 5

(2) The substrate with the array of holes was then cleaned with oxygen plasma in a plasma generator model TS-PL02 from Toxico and high sciences Automation Equipment Inc. of Shenzhen, removing environmentally adsorbed impurities at a gas flow rate of 50sccm and a power of 50W for 2 minutes.

(3) The silicon dioxide-silicon substrate is purchased in a metal evaporation system of Beijing micro-nano vacuum at the vacuum degree of about 10^- ⁶Depositing metal by thermal evaporation under the condition of Torr, wherein the first metal layer is formed by Ti and is deposited by 2 nanometers; the second metal layer was formed of Au deposited to a thickness of 5 nm. And taking out the substrate after the deposition is finished.

(4) Mechanical cleaving of WSe with tape₂And (3) obtaining a fresh surface, then quickly attaching the crystal on the adhesive tape to the surface of the base material prepared in the step (1), and heating the adhesive tape on a hot plate at 100 ℃ for 20 seconds.

(5) The adhesive tape-WSe prepared in the step (4) is used₂The substrate material is taken off from the hot plate, naturally cooled to room temperature in the air for about 10 seconds, and then the adhesive tape is rapidly removed to complete cleavage, so that a large-area suspended monolayer WSe can be obtained on the substrate surface₂。

Example 6

(3) The silicon dioxide-silicon substrate is purchased in a metal evaporation system of Beijing micro-nano vacuum at the vacuum degree of about 10^- ⁶Depositing metal by thermal evaporation under the condition of Torr, wherein the first metal layer is formed by Ni and is deposited by 2 nanometers; the second metal layer was formed of Au deposited to a thickness of 5 nm. And taking out the substrate after the deposition is finished.

Example 7

(1) Patterning a 2cm x 2cm silica-silicon based base material: firstly, spin-coating a layer of photoresist on a substrate, then obtaining an exposed circular pattern by a mask under ultraviolet exposure, and then utilizing CHF gas containing fluorine in a reactive ion etching system₃As a plasma source, the etching power is 100W, and the etching time is 5 minutes; the resulting array of wells had a well diameter of 10 μm and a well-to-well spacing of 20 μm.

(3) The silicon dioxide-silicon substrate is purchased in a metal evaporation system of Beijing micro-nano vacuum at the vacuum degree of about 10^- ⁶Depositing a metal, a first metal, by thermal evaporation under Torr conditionsThe layer is formed of Ti deposited at 2 nm; the second metal layer was formed of Au deposited to a thickness of 5 nm. And taking out the substrate after the deposition is finished.

(4) Mechanical cleaving of MoS with tape₂And (3) obtaining a fresh surface, then quickly attaching the crystal on the adhesive tape to the surface of the base material prepared in the step (1), and heating the adhesive tape on a hot plate at 140 ℃ for 30 seconds.

Example 8

(4) Mechanical cleaving of WTE with tape₂Obtaining a fresh surface, and then applying the adhesive tapeThe crystals on (2) were rapidly attached to the surface of the base material prepared in step (1), and heated on a hot plate at 100 ℃ for 30 seconds.

(5) The adhesive tape-WTE prepared in the step (4) is used₂Removing the substrate material from the hot plate, naturally cooling to room temperature in air for about 10 seconds, and rapidly removing the adhesive tape to complete cleavage, thereby obtaining a large-area suspended single-layer WTE on the substrate surface₂。

Comparative example 1

(1) Patterning a 2cm × 2cm silica-silica base material: firstly, spin-coating a layer of photoresist on a substrate, then obtaining an exposed circular pattern by a mask under ultraviolet exposure, and then utilizing a fluorine-containing gas SF in a reactive ion etching system₆As a plasma source, the etching power is 100W, and the etching time is 5 minutes; the resulting array of wells had a diameter of 5 μm and a center-to-center spacing of 15 μm.

(3) Mechanical cleaving of MoS with tape₂Obtaining a fresh surface, and then quickly attaching the crystal on the adhesive tape to the surface of the substrate material prepared in the step (1).

(4) The tape was quickly removed to complete cleavage and observed under a microscope.

FIG. 5 shows the suspended monolayer metal chalcogenide MoS prepared in comparative example 1₂The optical microscope photograph of (1). FIG. 5 shows a suspended monolayer of a metal chalcogenide MoS₂The samples were difficult to find, most of them were thick layers of MoS₂And the yield is very low.

Comparative example 2

(3) The silicon dioxide-silicon substrate is purchased in a metal evaporation system of Beijing micro-nano vacuum at the vacuum degree of about 10^- ⁶Depositing metal by thermal evaporation under the condition of Torr, forming the first metal layer by Ti, depositing 2 nm, and taking out the substrate after the deposition is finished.

(4) Mechanical cleaving of MoS with tape₂And (3) obtaining a fresh surface, then quickly attaching the crystal on the adhesive tape to the surface of the base material prepared in the step (1), and heating the adhesive tape on a hot plate at 100 ℃ for 20 seconds.

(5) The adhesive tape-MoS prepared in the step (4) is used₂The substrate material is removed from the hot plate, allowed to cool naturally in air to room temperature for about 10 seconds, and then rapidly removed to complete the cleavage.

FIG. 6 shows the suspended monolayer metal chalcogenide MoS prepared in comparative example 2₂The optical microscope photograph of (1). FIG. 6 shows a suspended monolayer of a metal chalcogenide MoS₂The yield of the sample was very low and almost no monolayer sample could be found.

As can be seen from a comparison between example 1 and comparative example 1, the yield of the sample after the cleavage was directly performed without depositing the first metal layer and the second metal layer was extremely low, and the yield of the sample after depositing Ti/Au metal (the first metal layer was formed of Ti and the second metal layer was formed of Au) and heating was almost one hundred percent, high in yield, and large in area.

It can be seen from a comparison of example 1 and comparative example 2 that the yield of the sample after cleavage of the deposited metal Ti alone is extremely low, whereas the yield of the sample after deposition of Ti/Au metal (the first metal layer is formed of Ti and the second metal layer is formed of Au) and heat treatment is almost one hundred percent, high, and large in area.

Claims

1. A method of making a suspended layered metal chalcogenide comprising the steps of:

(1) preparing a patterned array of holes on a substrate;

2. The method of claim 1, further comprising the step of performing an oxygen plasma clean of the substrate having the array of holes prior to performing step (2).

3. The method of claim 2, wherein the oxygen plasma cleaning is performed under the following conditions: the flow rate is 20-50 sccm, the power is 50-100W, and the cleaning time is 2-5 min.

4. The method of claim 1, wherein the step (1) of preparing the patterned array of apertures on the substrate is performed by optical exposure and ion etching.

5. The method of claim 1, wherein the array of holes has a hole diameter of 2-10 μm and a hole center-to-center spacing of 10-20 μm.

6. The method of claim 1, wherein the step (2) of forming a first metal layer on a substrate having an array of holes and then forming a second metal layer on the first metal layer is performed by thermal evaporation or electron beam evaporation at a temperature higher than 10 deg^-5The reaction was carried out under a vacuum atmosphere of Torr.

7. The method of claim 1, wherein the first metal layer has a thickness of 1-5nm and the second metal layer has a thickness of 2-10 nm.

8. The method of claim 1, wherein the substrate is SiO₂a/Si substrate, a sapphire substrate, a glass substrate or a quartz substrate.

9. The method of claim 1, wherein the metal chalcogenide is MX₂Wherein M is Mo, W, Sn, Ta, V, Ti, Re, Nb, Pt or Pd, and X is S, Se or Te; or MX, where M is Fe, Ga or Sn and X is S, Se or Te.

10. The method as claimed in claim 1, wherein the heat treatment in the step (3) is carried out at a temperature of 50-140 ℃ for 10-30 s.