CN112109411A

CN112109411A - Method for preparing layered metal chalcogenide

Info

Publication number: CN112109411A
Application number: CN201910529797.7A
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: CN112109411B

Abstract

The present invention provides a method for preparing a layered metal chalcogenide comprising the steps of: (1) forming a first metal layer on a substrate, 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; (2) mechanically cleaving the metal chalcogenide with a tape, attaching the metal chalcogenide on the tape to the second metal layer in the step (1), and performing a heat treatment; (3) after the heat treatment is completed, the tape is peeled off from the substrate after cooling to room temperature, thereby producing a layered metal chalcogenide on the substrate. The method can prepare large-area single-layer and thin-layer TMDCs materials. Meanwhile, the method has the advantages of few steps, simplicity, easy realization and high preparation efficiency.

Description

Method for preparing layered metal chalcogenide

Technical Field

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

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), and liquid phase lift-off, the two-dimensional materials prepared by mechanical cleaving methods are still currently recognized as high quality samples. Taking graphene as an example, almost all of the intrinsic physical properties of graphene have been observed and tested on mechanically cleaved samples. 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.

CVD processes can produce large area layered metal chalcogenides, such as MoS₂、WS₂、WSe₂And the like, quartz, silicon wafers, sapphire and the like are commonly used growth substrates at present. The sample prepared by the method has more defects and more crystal domainsIt is difficult to directly reflect the intrinsic properties of the material. Meanwhile, the CVD preparation period is long, the energy consumption is high, and the device processing at the later stage also involves a complex transfer process.

The MBE method can prepare high-quality two-dimensional TMDCs samples, but has high equipment cost, long preparation period, and small sample size. These disadvantages limit their application in research and industrialization.

The prior art is difficult to prepare large-area high-quality TMDCs samples, which limits some experimental measurements requiring higher requirements on the samples, such as research on infrared spectroscopy. The size of a TMDCs sample which is conventionally cleaved is too small and is far smaller than the size of a light spot, but the TMDCs system grown by the common CVD has more defects, and a plurality of impurities are introduced in the transfer process, so that a better measurement result is difficult to obtain. Therefore, the method for efficiently preparing the large-area TMDCs material is of great significance to basic scientific research and application of future materials.

Disclosure of Invention

Aiming at the defects of the preparation methods of the two-dimensional TMDCs materials, the invention provides a method for efficiently preparing large-area single-layer and thin-layer TMDCs materials, and provides powerful material guarantee for exploring the intrinsic physical properties of the materials.

In the present invention, MoS is used₂For example, the thickness of a monolayer means the thickness of two layers of S atoms sandwiching a layer of Mo atoms, and the thickness of a thin layer means the thickness of less than 5 monolayers.

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

The present invention provides a method for preparing a layered metal chalcogenide comprising the steps of:

(1) forming a first metal layer on a substrate, 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;

(2) mechanically cleaving the metal chalcogenide with a tape, attaching the metal chalcogenide on the tape to the second metal layer in the step (1), and performing a heat treatment;

(3) after the heat treatment is completed, the tape is peeled off from the substrate after cooling to room temperature, thereby producing a layered metal chalcogenide on the substrate.

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.

In the method of the present invention, since the heat treatment is performed in an atmospheric environment, a small amount of gas molecules are inevitably adsorbed on the surfaces of the substrate and the TMDCs, and the distance of interaction between the TMDCs and the substrate is further reduced by cooling the gas molecules during the cooling process, thereby enhancing van der waals interaction between the TMDCs and the substrate.

Preferably, the method of the present invention further comprises a step of performing oxygen plasma cleaning on the substrate before performing the step (1). 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 forming a first metal layer on a substrate 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 method 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 (2) is performed at a temperature of 50 to 140 ℃ for 10 to 30 seconds.

The invention has the beneficial effects that:

the method can prepare large-area single-layer and thin-layer TMDCs materials. Meanwhile, the method has the advantages of few steps, simplicity, easy realization and high preparation efficiency. Compared with the conventional mechanical cleavage method, the size of the layered TMDCs is increased from a few micrometers to millimeter to centimeter magnitude, the area is increased by five to six magnitude, and the size of the sample is mainly determined by the size of the bulk crystal. The test result of the Raman spectrum shows that the sample prepared by the 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 the preparation procedure of example 1 of the present invention;

FIG. 2 shows a conventional cleavage method and a single layer of the metal chalcogenide MoS obtained in example 1 of the present invention₂Optical microscope photo contrast;

FIG. 3 shows a conventional mechanical cleaving process and the single layer MoS produced in example 1 of the present invention₂A Raman spectrum contrast map;

FIG. 4 is a single layer metal chalcogenide prepared according to example 1 of the present inventionCompound MoS₂The photograph of (a);

FIG. 5 shows the single-layer metal chalcogenide MoS obtained in comparative example 1₂The optical microscope photograph of (1);

FIG. 6 shows the single-layer metal chalcogenide MoS obtained 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) 2cm multiplied by 2cm silicon dioxide-silicon substrate material is cleaned by oxygen plasma in a plasma generator with model number TS-PL02 from Dongxin Gaokou Automation equipment Limited company in Shenzhen, for 2 minutes, to remove environmental adsorption impurities, wherein the gas flow is 20sccm, and the power is 100W.

(2) Depositing metal on a silicon dioxide-silicon substrate in a purchased Beijing micro-nano vacuum metal evaporation system, wherein a 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.

(3) 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.

(4) The adhesive tape-MoS prepared in the step (3) is used₂Removing the substrate material from the hot plate, cooling naturally in air to room temperature for about 10 seconds, and then rapidly removing the adhesive tape to complete the cleavage, thereby obtaining a large area of single-layer MoS on the substrate surface₂。

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

(a) in SiO₂Evaporating 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;

(b) the substrate is coated with a first metal layer and a second metal layer by evaporation;

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

(d) heating for about 10 seconds, removing from the hot plate, naturally cooling to room temperature, and removing the adhesive tape to obtain large-area single-layer metal chalcogenide MoS₂。

FIG. 2 shows a general cleavage method and a single layer of metal chalcogenide MoS obtained in this example₂Optical microscope photo contrast; (a) cleavage to SiO by conventional methods₂Single layer MoS on a/Si substrate₂(ii) a (b) Single layer metal chalcogenide MoS prepared in this example₂(ii) a Single-layer MoS obtained by two methods₂The dimensions are indicated in the figures.

FIG. 3 shows a general mechanical cleaving process and the single layer MoS produced in this example₂Raman spectrum contrast chart. FIG. 3 shows the MoS cleaved by the two methods₂No significant difference in peak position was observed, and the single-layer MoS was obtained in this example₂The two characteristic peaks are respectively positioned at 385 and 403 wave numbers, and the single-layer MoS is more easily cleaved than the single-layer MoS obtained by the conventional method₂The shift to lower wavenumbers is 1 wavenumber with little apparent difference. In fig. 3, the characteristic peak of 521 wave numbers is a signal of the Si substrate.

FIG. 4 shows a single-layer metal chalcogenide MoS obtained in the present example₂The photograph of (2). Figure 4 shows the size distribution of the monolayer samples produced by the method of the invention between 100 microns and 5 mm.

Example 2

(1) The 2cm multiplied by 2cm sapphire substrate material is cleaned by oxygen plasma for 5 minutes in a plasma generator which is purchased from Dongxin Kogaku Automation equipment Co., Ltd, Shenzhen, and has the model number of TS-PL02, the environmental adsorption impurities are removed, the gas flow is 50sccm, and the power is 50W.

(2) Depositing metal on the sapphire substrate in a purchased Beijing micro-nano vacuum metal evaporation system, wherein a 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.

(3) 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.

(4) The adhesive tape-MoS prepared in the step (3) is used₂The substrate material is taken off the hot plate, naturally cooled to room temperature in the air for about 5 seconds, and then rapidly stripped to finish cleavage, so that a large-area single-layer MoS can be obtained on the substrate surface₂。

It was found by optical microscopy that the size of the monolayer samples was distributed between 100 microns and 5 mm, with the largest dimension depending on the bulk crystal size.

Example 3

(1) 2cm multiplied by 2cm silicon dioxide-silicon substrate material is cleaned by oxygen plasma in a plasma generator with model number TS-PL02 from Dongxin Gaokou Automation equipment Limited company in Shenzhen, and environmental adsorption impurities are removed, wherein the gas flow is 30sccm, and the power is 80W.

(2) Depositing metal on the silicon dioxide-silicon substrate in a purchased Beijing micro-nano vacuum metal evaporation system, wherein a 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.

(3) 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.

(4) And (4) taking the adhesive tape-FeSe-substrate material prepared in the step (3) 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 single-layer FeSe on the surface of the substrate.

Example 4

(1) 2cm multiplied by 2cm silicon dioxide-silicon substrate material is cleaned by oxygen plasma in a plasma generator with model number TS-PL02 from Dongxin Gaokou Automation equipment Limited company in Shenzhen, for 2 minutes, to remove environmental adsorption impurities, wherein the gas flow is 30sccm, and the power is 80W.

(2) Depositing metal on a silicon dioxide-silicon substrate in a purchased Beijing micro-nano vacuum metal evaporation system, wherein a 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.

(3) 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

(1) 2cm multiplied by 2cm silicon dioxide-silicon substrate material is cleaned by oxygen plasma in a plasma generator with model number TS-PL02 from Dongxin Gaokou Automation equipment Limited company in Shenzhen, for 2 minutes, to remove environmental adsorption impurities, wherein the gas flow is 50sccm, and the power is 50W.

(2) Depositing metal on a silicon dioxide-silicon substrate in a purchased Beijing micro-nano vacuum metal evaporation system, wherein a 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.

(3) 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.

(4) The adhesive tape-WSe prepared in the step (3)₂Removing the substrate material from the hot plate, cooling naturally in air to room temperature for about 10 seconds, and then rapidly removing the tape to complete cleavage, thereby obtaining a large area of single layer WSe on the substrate surface₂。

Example 6

Example 7

(3) 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

(3) Mechanical cleaving of WTE 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 30 seconds.

(4) The adhesive tape-WTE prepared in the step (3) is used₂The base 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 debondingThen, a large area of single-layer WTE can be obtained on the surface of the substrate₂。

Comparative example 1

(2) 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).

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

FIG. 5 shows the single-layer metal chalcogenide MoS obtained in comparative example 1₂The optical microscope photograph of (1). FIG. 5 shows a single layer 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

(2) Depositing metal on the silicon dioxide-silicon substrate in a purchased Beijing micro-nano vacuum metal evaporation system, wherein the first metal layer is formed by Ti and is deposited by 2 nanometers, and taking out the substrate after the deposition is finished.

(4) The adhesive tape-MoS prepared in the step (3) is used₂-a substrateThe material was removed from the hot plate, allowed to cool naturally in air to room temperature for about 10 seconds, and then the tape was quickly removed to complete the cleavage.

FIG. 6 shows the single-layer metal chalcogenide MoS obtained in comparative example 2₂The optical microscope photograph of (1). FIG. 6 shows a single layer 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 layered metal chalcogenide comprising the steps of:

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

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 forming a first metal layer on a substrate 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 ℃^-5The reaction was carried out under a vacuum atmosphere of Torr.

5. 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.

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

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

8. The method as claimed in claim 1, wherein the heat treatment in the step (2) is carried out at a temperature of 50-140 ℃ for 10-30 s.