阅读说明：本技术 一种二维非范德瓦尔斯晶体及其制备方法 (Two-dimensional non-van der waals crystal and preparation method thereof ) 是由 黄青松 于 2021-09-14 设计创作，主要内容包括：本发明提供了一种二维非范德瓦尔斯晶体及其制备方法。该非二维非范德瓦尔斯晶体表面具有摩尔超晶格结构,所述摩尔超晶格结构具有由晶体学周期原子排列成六边形或近似六边形组合叠加而成的摩尔超晶格周期图案。本发明首次在二维非范德瓦耳斯晶体材料——二氧化钼表面制备摩尔超晶格结构的制备工艺。在其表面制备出不同扭转扭转错位角度的摩尔超晶格结构。二维非范德瓦尔斯晶体表面具有摩尔超晶格结构；其可以改变二维非范德瓦尔斯晶体表面的润湿性。(The invention provides a two-dimensional non-van der Waals crystal and a preparation method thereof. The non-two-dimensional non-van der waals crystal surface has a molar superlattice structure having a molar superlattice period pattern formed by stacking combinations of periodic atoms arranged in a hexagonal shape or an approximately hexagonal shape. The invention provides a preparation process for preparing a molar superlattice structure on the surface of a two-dimensional non-van der Waals crystal material, namely molybdenum dioxide. Preparing molar superlattice structures with different torsion and torsion dislocation angles on the surfaces of the materials. The two-dimensional non-van der waals crystal surface has a molar superlattice structure; which can alter the wettability of two-dimensional non-van der waals crystal surfaces.)

1. A two-dimensional non-van der Waals crystal, wherein the surface of the two-dimensional non-van der Waals crystal has a molar superlattice structure, and the molar superlattice structure has a molar superlattice period pattern formed by stacking combinations of periodic atoms arranged in a hexagonal shape or an approximately hexagonal shape.

2. A two-dimensional non-van der waals crystal according to claim 1, wherein the geometry of the superimposed two monolayers of the molar superlattice structure is the same; and/or the molar superlattice structure has a twist angle of 0 degrees to ± 30 degrees.

3. The method of preparing a two-dimensional non-van der waals crystal of claim 1 or 2, wherein the two-dimensional non-van der waals crystal is molybdenum dioxide; the preparation method comprises the following steps:

(1) placing the molybdenum trioxide nano strip in a closed reaction container with inert atmosphere inside;

(2) heating the closed reaction container to a set temperature; enabling sulfur vapor to exist in the closed reaction container in the temperature rising process;

(3) heating to a set temperature and then preserving heat for a certain time;

(4) and cooling to room temperature after heat preservation to obtain the molybdenum dioxide crystal with the surface having the molar superlattice structure.

4. The production method according to claim 3, wherein the set temperature is not less than 400 ℃.

5. The production method according to claim 3, wherein the sulfur vapor is produced by introducing a sulfur-containing gas; and/or the sulfur vapor is generated by sublimation of a sulfur-containing compound placed in a closed reaction vessel.

6. The method according to claim 5, wherein the mass ratio of the total amount of all sulfur vapor present in the closed reaction vessel to the molybdenum trioxide nanoribbons is not more than 1: 9.

7. the production method according to claim 5, wherein the sulfur-containing gas is a mixed gas of a carrier gas and sulfur vapor, and the carrier gas is an inert gas or nitrogen.

8. The method according to claim 5, wherein the sulfur-containing gas is introduced at a flow rate of 10 to 500 sccm; and/or the pressure of the closed reaction container is 10 KPa-1.5 atm.

9. The method according to claim 5, wherein when the sulfur vapor is generated by a sulfur compound contained in the closed reaction vessel, the sulfur vapor is not generated any more by rapidly cooling the temperature of the region where the sulfur compound is contained from 200 ℃ by lowering the temperature of the region where the sulfur compound is contained.

10. The production method according to claim 5, wherein the pressure of the sulfur vapor present in the closed reaction vessel is not less than 1 kPa.

Technical Field

The invention relates to the field of chemical preparation, in particular to a preparation method of a molar superlattice surface constructed on a two-dimensional non-van der waals crystal.

Background

"Moire Pattern", Chinese is generally translated into Moire striped Moir patterns that are layered superlattice structures formed by coupling two or more layers of periodic lattice structures. The physical properties of the material, such as energy band, are modulated by the molar period of the superlattice in addition to the period of the original lattice structure. The molar superlattice structure can be observed by using surface testing techniques such as spherical aberration correction transmission microscope (ACTEM), Scanning Tunneling Microscope (STM) and angle-resolved photoelectric emission spectroscopy (ARPES) to observe the surface molar stripes of the material.

In recent years, a twisted magic angle twisted stacked structure mainly composed of two-dimensional van der waals crystals such as graphene has a novel extrinsic effect, such as a characteristic of superconductivity. The torsion angles of the two layers are modulated to enable the relative torsion angle to reach about 1.1 degrees, the material has a miraculous extrinsic property, the angle is adjusted only through the two layers of layered two-dimensional materials with atom thicknesses, the two layers are coupled to form a specific molar superlattice structure, and the material can have a new property means and has important significance in new material research. The twisting means is further expanded to graphene and hexagonal boron nitride (h-BN) systems, graphene-transition metal chalcogenide and the like, and two-dimensional chalcogenide-two-dimensional chalcogenide, MXEene-MXene and mutual superposition coupling between the Van der Waals crystals. Most of the formed mole superlattices have obvious regulation effect on physical characteristics such as band structure, superconductivity, optics and the like. And (6) twisting. Twist-twist torsion although the molar superlattice structure has many magical properties and application prospects, the modulation of the magic angle is difficult to realize in experiments; our method provides a new idea in the laboratory for realizing the in-situ modulation of the magic angle.

The molar superlattice structure torsion has wide potential application in the field of condensed state physics, such as optics, crystallography, electronics and the like, and is concerned by extensive researchers. However, the preparation of molar superlattice structures has so far been limited to two-dimensional van der Waals (van der Waals) crystals. Despite the many studies and theoretical calculations on the molar superlattice structure in recent years, how to controllably achieve the molar superlattice structure on two-dimensional van der waals crystals and non-van der waals crystals remains a challenging problem.

Disclosure of Invention

In view of the above technical problems, it is an object of the present invention to provide a two-dimensional non-van der waals crystal having a molar superlattice structure and a method for preparing the same. The two-dimensional non-van der Waals crystal surface obtained by the method can form a molar superlattice structure, and the preparation method is easy to operate and strong in controllability.

The technical scheme of the invention is as follows:

a two-dimensional non-van der Waals crystal having a molar superlattice structure on a surface thereof, the molar superlattice structure having a molar superlattice period pattern in which periodic atoms of crystallography are arranged in a hexagonal or approximately hexagonal combination and are stacked.

Wherein the superimposed two monolayers of the molar superlattice structure have the same geometry; and/or the molar superlattice structure has a twist angle of 0 degrees to ± 30 degrees.

In the above method for producing a two-dimensional non-van der waals crystal, the two-dimensional non-van der waals crystal is molybdenum dioxide; the preparation method comprises the following steps:

(1) placing the molybdenum trioxide nano strip in a closed reaction container with inert atmosphere inside;

(2) heating the closed reaction container to a set temperature; enabling sulfur vapor to exist in the closed reaction container in the temperature rising process;

(3) heating to a set temperature and then preserving heat for a certain time;

(4) and cooling to room temperature after heat preservation to obtain the molybdenum dioxide crystal with the surface having the molar superlattice structure.

Wherein the set temperature is not less than 400 ℃.

Wherein the sulfur vapor is realized by introducing sulfur-containing gas; and/or the sulfur vapor is generated by sublimation of a sulfur-containing compound placed in a closed reaction vessel.

Wherein the mass ratio of the total amount of all sulfur vapor existing in the closed reaction vessel to the molybdenum trioxide nano-strips is not more than 1: 9.

the sulfur-containing gas is a mixed gas of a carrier gas and sulfur vapor, and the carrier gas is an inert gas or nitrogen.

Wherein the introduction rate of the sulfur-containing gas is 10-500 sccm; and/or the pressure of the closed reaction container is 10 KPa-1.5 atm.

Wherein, when the sulfur vapor is generated by the sulfur-containing compound placed in the closed reaction vessel, the sulfur vapor is not generated any more by a method of rapidly cooling the temperature of the region where the sulfur-containing compound is placed from 200 ℃.

Wherein the pressure of the sulfur vapor present in the closed reaction vessel is not less than 1 kPa.

The invention has the beneficial effects that:

(1) the invention provides a preparation process for preparing a molar superlattice structure on the surface of a two-dimensional non-van der Waals crystal material, namely molybdenum dioxide. Preparing molar superlattice structures with different torsion and torsion dislocation angles on the surfaces of the materials. The two-dimensional non-van der waals crystal surface has a molar superlattice structure; which can alter the wettability of two-dimensional non-van der waals crystal surfaces;

(2) the preparation method has strong operability, can be used for research in a laboratory, and can also be used for industrial large-scale preparation.

Drawings

FIG. 1 is a transmission electron microscope (STEM) view of the spherical aberration of a molybdenum dioxide crystal prepared in example 1;

FIG. 2 is a cross-correlation image obtained by Fourier inverse Fourier transforming the block portion of FIG. 1;

FIG. 3 is a simulation plot of a Moire superlattice structure pattern stacked at a twist angle calculated by simulation;

FIG. 4 is an X-ray diffraction pattern (XRD) chart of the molybdenum dioxide crystal obtained in example 1.

Fig. 5 is a Scanning Electron Microscope (SEM) image of molybdenum trioxide.

Fig. 6-7 are SEM images of MoO2 at various stages during the preparation of example 1.

FIG. 8 is a schematic representation of contact angle measurements of commercial nano-molybdenum dioxide and example one-obtained No. 1 MoO 2.

FIG. 9 is a transmission electron microscope (STEM) spherical aberration map of the molybdenum dioxide crystal prepared in example 2;

FIG. 10 is an SEM image of MoO2 obtained in example 2;

FIG. 11 is an XRD plot of MoO2 obtained in example 2;

fig. 12 is a STEM image and a simulated image of the molybdenum dioxide crystal prepared in example 3.

Detailed Description

The invention provides a two-dimensional non-van der Waals crystal, the surface of which has a molar superlattice structure, and the molar superlattice structure has a molar superlattice periodic pattern formed by stacking combinations of periodic atoms arranged into hexagons or approximate hexagons. This molar superlattice structure consists of a stack of two monolayers twisted at an angle to each other to form a molar superlattice periodic pattern.

In one embodiment, the geometry of the superimposed two monolayers of the molar superlattice structure is the same; and/or the molar superlattice structure has a twist angle of 0 degrees to ± 30 degrees.

In one embodiment, the two-dimensional non-van der waals crystal is molybdenum dioxide; the preparation method of the molybdenum dioxide with the surface having the molar lattice structure comprises the following steps:

(1) placing the molybdenum trioxide nano strip in a closed reaction container with inert atmosphere inside; the closed reaction vessel should be capable of heating, have channels for gas to pass through, and preferably be capable of zone heating, and each zone can be independently controlled in temperature and heating rate;

(2) heating the closed reaction container to a set temperature; enabling sulfur vapor to exist in the closed reaction container in the temperature rising process; sulfur vapor can be present in the whole closed reaction vessel in the whole temperature rising process; or sulfur vapor can exist in the whole closed reaction vessel in the partial process of temperature rise;

(3) heating to a set temperature and then preserving heat for a certain time; sulfur vapor exists in at least one part of the heat preservation process in the heat preservation process; the heat preservation time is longer than 10 minutes;

(4) and cooling to room temperature after heat preservation to obtain the molybdenum dioxide crystal with the surface having the molar superlattice structure. The cooling rate in this step is not limited; rapid cooling is preferred to avoid further conversion of molybdenum dioxide to molybdenum disulfide.

In one embodiment, the set temperature is not less than 400 ℃.

In one embodiment, the sulfur vapor is achieved by passing a sulfur-containing gas; and/or the sulfur vapor is generated by sublimation of a sulfur-containing compound placed in a closed reaction vessel. That is, the sulfur vapor present in the closed reaction vessel may be externally supplied, and in this case, the sulfur-containing gas is introduced through a gas passage, and generally, the temperature of the sulfur-containing gas should be higher than 200 ℃. Alternatively, the sulfur vapor may be generated inside a closed reaction vessel, and the sulfur vapor may be generated by heating the sulfur-containing compound previously placed in the closed reaction vessel to a temperature of not lower than 200 ℃. In the production method of the present invention, the sulfur vapor mainly plays a role of reduction, and reduces molybdenum trioxide to molybdenum dioxide, thereby forming a molar superlattice surface on the molybdenum dioxide surface.

In one embodiment, the mass ratio of the total amount of all sulfur vapors present in the closed reaction vessel to the molybdenum trioxide nanoribbons is no more than 1: 9. in the presence of sulfur vapor, molybdenum dioxide is further reduced to molybdenum disulfide. Since the molar superlattice structure is present only in the molybdenum dioxide structure, the total amount of sulfur vapor present and the time of presence need to be controlled in order to form molybdenum dioxide having a molar superlattice structure.

In one embodiment, the sulfur-containing gas is a mixed gas of a carrier gas and sulfur vapor, and the carrier gas is an inert gas or nitrogen. It should be noted that when the technical scheme of carrying sulfur vapor by carrier gas is adopted, the technical scheme of firstly introducing carrier gas, then introducing sulfur-containing gas and then introducing carrier gas can be adopted, so that the pressure and inert atmosphere in the closed reaction container can be ensured.

Further, the introduction rate of the sulfur-containing gas is 10-500 sccm; and/or the pressure of the closed reaction container is 10 KPa-1.5 atm. In general, the lower the rate of introduction of the sulfur-containing gas, the better.

In one embodiment, when the sulfur vapor is generated by a sulfur-containing compound placed in a closed reaction vessel, the sulfur vapor is no longer generated by a method of rapidly cooling the temperature of the region where the sulfur-containing compound is placed from 200 ℃. The sulfur-containing compound can be one or a mixture of sulfur simple substance, sulfide or disulfide.

In one embodiment, the pressure of the sulfur vapor present in the closed reaction vessel is not less than 1 kPa. Since sulfur vapor functions as a reducing agent in the conversion of molybdenum trioxide to molybdenum dioxide, the pressure of sulfur vapor is set to not less than 1 kPa, and the more uniform the distribution of sulfur vapor, the better.

The following is further illustrated by specific examples.

Example 1

A preparation method of molybdenum dioxide with a molar superlattice structure surface comprises the following specific steps:

(1) placing the molybdenum trioxide nano-strips and the sulfur-containing compound in a closed reaction container with inert atmosphere inside; the molybdenum trioxide nanoribbons in this step can be prepared by the preparation method disclosed in patent 2016110716708. The molybdenum trioxide strip and the sulfur-containing compound are respectively placed in different temperature zones of the closed reaction vessel.

(2) Heating the closed reaction container to 500 ℃; enabling sulfur vapor to exist in the closed reaction container in the temperature rising process; of course, the temperature range in which the sulfur compound is allowed to stand may be controlled to 200 ℃ or higher from the viewpoint of energy saving. As the temperature increases, the sulfur in the sulfur-containing compound gradually sublimes to form sulfur vapor, which can diffuse with the carrier gas to the area where the molybdenum trioxide is placed.

(3) Heating to a set temperature and then preserving heat for a certain time; the incubation time was 30 minutes. The temperature rise time was 100 minutes.

(4) And cooling to room temperature after heat preservation to obtain the molybdenum dioxide crystal with the surface having the molar superlattice structure. After the completion of the heat-retaining, the temperature of the temperature zone in which the sulfur-containing compound is placed should be rapidly lowered so that sulfur vapor is not generated.

The atomic arrangement of the sample surface can be directly observed by a spherical aberration correction transmission electron microscope (STEM), and regular white dots in the image correspond to the atomic arrangement of the sample surface. Referring to fig. 1, fig. 1 is a transmission electron microscope (STEM) view of the spherical aberration of the molybdenum dioxide crystal prepared in this example. On the surface of the molybdenum dioxide crystal prepared in this example, the atoms of molybdenum dioxide constitute a periodic pattern of small circles, a molar superlattice structure (boxed portion in fig. 1). In fact, not all atoms in the molar superlattice structure are in the same plane, but are stacked together at a certain twist angle by the twist-twist coupling of the upper and lower layers. The periodic pattern of the molar superlattice structure depends on the torsion angle between the upper layer and the lower layer, and the molar superlattice structure pattern is further subjected to fitting calculation (the specific fitting calculation method is described in detail below). The periodic diameter of each pattern was about 0.7 nm as measured by magnification, and the twist angle of the molar superlattice structure of the molybdenum dioxide surface of this example was about 28 °.

It is known that the basic constituent structure of a molar superlattice structure is a hexagonal atomic arrangement with a central point, and the periodic relationship of a molar superlattice structure of the hexagonal type can be well described by the rayleigh formula: