阅读说明：本技术 独立单原子厚金属膜及其制备方法与应用 (Independent monoatomic thick metal film and preparation method and application thereof ) 是由 刘玉 杨晓琴 它光辉 萨米乌拉赫 安丽莎 施启涛 马克如姆里 于 2020-12-23 设计创作，主要内容包括：本发明涉及一种独立单原子厚金属膜及其制备方法与应用。本发明采用透射电子显微镜原位制备,包括以下步骤：(1)将金属源和二维材料在真空条件下,在100-300℃进行热处理；(2)将热处理后的样品转移至透射电子显微镜中；(3)在样品上选择有大片干净单层二维材料和富集单一金属元素的区域作为成膜区域,不断调整电子束参数辐照该区域,得到独立单原子厚金属膜。本发明在透射电子显微镜中实现了独立单原子厚金属膜的制备。该方法利用电子束的辐照作用,根据不同电子束参数与金属原子间相互作用规律,可实时原位调节参数以实现单原子厚金属膜的形成。该方法材料简单、步骤少、耗时短,具有成本低、最终产物杂质少等优点。(The invention relates to an independent monoatomic thick metal film and a preparation method and application thereof. The invention adopts the in-situ preparation of a transmission electron microscope, and comprises the following steps: (1) carrying out heat treatment on a metal source and a two-dimensional material at the temperature of 100-300 ℃ under the vacuum condition; (2) transferring the heat-treated sample to a transmission electron microscope; (3) and selecting a large area with clean single-layer two-dimensional materials and enriched single metal elements on the sample as a film forming area, and continuously adjusting electron beam parameters to irradiate the area to obtain the independent single-atom thick metal film. The invention realizes the preparation of the independent single-atom thick metal film in the transmission electron microscope. The method utilizes the irradiation of electron beams, and can adjust parameters in situ in real time according to the interaction rule between different electron beam parameters and metal atoms so as to realize the formation of the monoatomic thick metal film. The method has the advantages of simple materials, fewer steps, short time consumption, low cost, fewer impurities in the final product and the like.)

1. A preparation method of an independent single-atom thick metal film is characterized in that the film is prepared in situ by adopting a transmission electron microscope, and comprises the following steps:

(1) carrying out heat treatment on a metal source and a two-dimensional material at the temperature of 100-300 ℃ under the vacuum condition;

(2) transferring the heat-treated sample to a transmission electron microscope;

(3) and selecting a large area with clean single-layer two-dimensional materials and enriched single metal elements on the sample as a film forming area, and continuously adjusting electron beam parameters to irradiate the area to obtain the independent single-atom thick metal film.

2. The method according to claim 1, wherein the two-dimensional material is graphene.

3. The method according to claim 1, wherein the metal source in step (1) is a metal element or a metal acetylacetone compound.

4. The method according to claim 3, wherein the elemental metal is gold, silver, copper, chromium, indium, cobalt, vanadium, manganese, gallium, magnesium, aluminum, calcium, nickel, iron, or zinc.

5. The method according to claim 1, wherein the degree of vacuum in the step (1) is 10^-6-10^-5mbar。

6. The preparation method according to claim 1, wherein in the step (2), if the surface of the sample after the heat treatment is amorphous, the surface is cleaned by irradiating the sample with an electron beam for 1 to 5min according to the thickness of the amorphous layer.

7. The method of claim 1, wherein the electron beam parameters in step (3) include: voltage: 60 or 80 kV; electron beam current: 1.0-2.0 nA; electron beam dose: 10⁵-10⁷A/m²(ii) a Duration of electron beam irradiation: 0.5-5 min.

8. A free-standing monoatomic thick metal film produced by the production method according to any one of claims 1 to 7.

9. The free-standing monatomic thick metal film of claim 8, wherein the free-standing monatomic thick metal film is a single-atom thick metal film formed in a two-dimensional material pore without a substrate support.

10. Use of the free standing monatomic thick metal film of claim 8 in catalysis or gas sensing.

Technical Field

The invention relates to the technical field of metal materials, in particular to an independent monoatomic thick metal film and a preparation method and application thereof.

Background

The independent two-dimensional metal film with single atom thickness refers to a two-dimensional metal film with only one layer of atoms, is not a two-dimensional metal film with a plurality of atoms or an ultrathin two-dimensional metal film, and simultaneously excludes a metal film with a single-layer two-dimensional structure formed on a substrate (the substrate can play a stabilizing role). The exciting new properties and potential application prospects (including catalysis, gas sensing, etc.) of such two-dimensional materials with metal bonding attract a plurality of researchers. Compared to covalent two-dimensional materials, metal bonding is more prone to close-packed structures than to layered structures, and therefore, free-standing monatomic materials with metal bonding are still largely elusive.

In on K, Si (111) substrate and Hf and Bi on Ir (111) substrate on metal two-dimensional material substrate capable of forming two-dimensional structure on base reported so far₂Te₃(111) Sn on the substrate, Rh on the polyvinylpyrrolidone, and Ga on a different substrate. The related reports of the independent single-atom thick two-dimensional metal film are less, most of the reports are theoretical prediction researches, and experiments prove that the number of the independent single-atom thick metal films is less. Although it has been reported that two-dimensional structures of certain elements are obtained, they must be assisted by a substrate without which their free-standing junctions cannot be formedAnd (5) forming. For example, studies have demonstrated the presence of a stannylene material that can be formed on a substrate material and independently to a thickness of several atomic layers, but the presence of stannylene at an independent monoatomic thickness has not been found. Studies have shown that hexagonal lattice structures do not readily form an independent structure when laterally supported as an independent structure. Instead, we have found that atoms in small pores form ordered, reproducible planar clusters.

To date, there is only direct evidence that free standing, single atom thick two-dimensional (2D) element films are limited to the use of two-dimensional material pores to support such two-dimensional films, i.e., the two-dimensional films are suspended in the two-dimensional material pores. Before electron beam irradiation, however, the metal elements in the sample are usually adsorbed in the amorphous region or form carbon-metal bonds with single atoms into the two-dimensional material or only cover the surface of the two-dimensional material, and do not automatically enter the holes of the two-dimensional material to form a metal film, which is driven by electron beam irradiation under appropriate conditions. Clean two-dimensional material, enriched metal elements, and suitable electron beam parameters are therefore critical conditions necessary to form a free-standing single-atom thick metal film. The former two are easy to realize, and the latter is still in the exploration stage, which is a research hotspot of researchers. The activity of metal atoms under electron beam irradiation varies with different types of metal elements and different electron beam conditions (including voltage, electron beam dose, exposure time, electron beam current, etc.). When the electron beam current is larger and the dosage is higher, lighter metal elements (such as Mg and Al) are likely to be bombed out of the sample and cannot enter the holes of the two-dimensional material, so that a metal film is further formed; when the electron beam energy is low, metal atoms cannot obtain a sufficient driving force, and do not migrate long distance or form a carbon-metal bond to form a metal film even with a long exposure time. In addition, the metal atoms entering the pores of the two-dimensional material under the irradiation of the electron beam generally begin to exist in cluster form, and after the irradiation for different time periods, some metal clusters can form a film in a short time (tens of seconds or tens of seconds), and some metal clusters require several minutes. However, even if the above-described various electron beam parameters are satisfied, not all the metal elements can form a metal film of independent monoatomic thickness. 91 of the 118 elements of the periodic table are metals, and only a few of them can be formed on a substrate support at present, while the independent self-supporting metal film is almost absent. Therefore, the ability to experimentally prepare and verify a free-standing single atom thick metal film is an important issue that needs to be addressed.

Patent CN201310535381.9 deposits a single atom thick metal film on a flexible coiled conductive substrate by electrodeposition, however, the metal film is not self-supporting and independent and needs substrate support.

Disclosure of Invention

In order to solve the technical problems, the metal source and the graphene which are subjected to vacuum heat treatment in advance are placed in a TEM, electron beams with certain parameters are used for irradiation, the activity behavior of metal atoms is regulated and controlled, and finally the preparation of the single-atom thick metal film is realized.

The first purpose of the invention is to provide a preparation method of an independent single-atom thick metal film, which adopts a transmission electron microscope to prepare in situ and comprises the following steps:

(1) carrying out heat treatment on a metal source and a two-dimensional material at the temperature of 100-300 ℃ under the vacuum condition;

(2) transferring the heat-treated sample to a transmission electron microscope;

(3) and selecting a large area with clean single-layer two-dimensional materials and enriched single metal elements on the sample as a film forming area, and continuously adjusting electron beam parameters to irradiate the area to obtain the independent single-atom thick metal film.

Further, the two-dimensional material in step (1) is ensured to be clean and free of contamination. The container adopts a quartz tube, the quartz tube is sequentially cleaned by acetone, ethanol and deionized water before use, and then is dried by nitrogen; two-dimensional materials are examined in transmission electron microscopy in advance.

Further, the two-dimensional material is graphene.

Further, the metal source in the step (1) is a metal simple substance or a metal acetylacetone compound.

Further, the metal simple substance is a metal that can form a single-atom thick metal film, and includes, but is not limited to, gold (Au), silver (Ag), copper (Cu), chromium (Cd), indium (In), cobalt (Co), vanadium (V), manganese (Mn), gallium (Ga), magnesium (Mg), aluminum (Al), calcium (Ca), nickel (Ni), iron (Fe), and zinc (Zn).

Further, the vacuum degree in the step (1) is 10^-6-10^-5mbar; preferably 10^-6mbar。

Further, in the step (1), the heat treatment temperature after the tube sealing is 100-300 ℃ according to the different melting points of the metal sources.

Further, if the surface of the sample subjected to the heat treatment in the step (2) is amorphous, the surface is cleaned by irradiating the sample with an electron beam for 1-5min according to the thickness of the amorphous layer.

Furthermore, when the film forming region is selected in the step (3), the region is tested to be rich in only a single metal element except carbon and oxygen elements by a large-area energy spectrum in advance, and is not polluted by any other metal element impurities.

Further, the electron beam parameters in step (3) include: voltage: 60 or 80 kV; electron beam current: 1.0-2.0 nA; electron beam dose: 10⁵-10⁷A/m²(ii) a Duration of electron beam irradiation: 0.5-5 min.

The parameters are determined according to the activity characteristics and the irradiation resistance degree of different metal elements under electron beam irradiation.

It is another object of the present invention to provide a free-standing monoatomic thick metal film produced by the above production method.

Further, the independent monoatomic thick metal film is a metal film which is not supported by a substrate and is formed in the graphene hole in a thickness of only one layer of atom.

The third purpose of the invention is to provide the application of the independent monoatomic thick metal film in catalysis or gas sensing.

By the scheme, the invention at least has the following advantages:

the invention realizes the preparation of the independent single-atom thick metal film in the transmission electron microscope. The method utilizes the irradiation of electron beams, and can adjust parameters in situ in real time according to the interaction rule between different electron beam parameters and metal atoms so as to realize the formation of the monoatomic thick metal film. The method has the advantages of simple materials, fewer steps, short time consumption, low cost, fewer impurities in the final product and the like.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following description is made with reference to the preferred embodiments of the present invention and the accompanying detailed drawings.

Drawings

FIG. 1 is a schematic diagram of a process for forming a free-standing monatomic thick metal film;

FIG. 2 is a graph of experimental proof of a free-standing monatomic thick calcium film in example 1;

fig. 3 is a transmission electron micrograph characterization of a two-dimensional single atom thick metallic Cr film between graphene and CrO Nanoparticles (NPs), (a) high resolution transmission electron micrograph of CrO nanoparticles and Cr thin film suspended in graphene; the top right inset image is a scanning transmission micrograph corresponding to a high resolution transmission image; (b, c) local Electron Energy Loss Spectra (EELS) spectra obtained from CrO nanoparticles and two-dimensional Cr films, respectively; (d, e) image simulation and baseball model of the structure in the TEM image; the inset highlights the atomic spacing of the square cells; (f) normalized intensity distribution relative to graphene; scale 2 nm.

Detailed Description

The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Example 1:

the embodiment provides a preparation method of an independent monoatomic thick calcium film, which comprises the following steps:

(1) calcium acetylacetonate powder and graphene (transferred to a micro-grid and previously examined in a TEM) were placed in a quartz tube and evacuated to 10 deg.C^-6After mbar, the tube mouth was sealed and the quartz tube was then placed in a tube furnace for heat treatment at 200 ℃ for 12 h.

(2) And (3) placing the micro-grid (with the deposited Ca) subjected to the heat treatment into a transmission electron microscope, and irradiating the micro-grid for 1-5 minutes by using electron beams to clean the surface according to the amorphous amount of the surface of the sample.

(3) Selecting a region with large clean single-layer graphene and enriched Ca element, and continuously adjusting electron beam parameters to irradiate the region to form an independent monoatomic thick calcium film. The electron beam parameters used were: voltage: 80 kV; ② electron beam current is 1.1nA-1.2 nA; (iii) electron beam dose: 10⁵-10⁷A/m²(ii) a Duration of electron beam irradiation: 0.5-2 min. These parameters vary depending on the degree of amorphousness in the sample, the degree of aggregation of metal atoms, the size of the metal film, etc., and are in a range.

When a film forming area is selected, a large-area energy spectrum test is carried out in advance to test that the area is only rich in Ca element except carbon and oxygen element and is not polluted by any other impurities. The probability of forming a metal film in two types of characteristic areas is high, namely Ca atoms are enriched around the graphene holes, and the Ca atoms migrate into the holes under the irradiation of electron beams so as to form a film; and secondly, some Ca atoms are already in the holes of the graphene but in the atomic group state, and are irradiated by electron beams with proper parameters to form a film.

Fig. 1 is a schematic diagram of a film forming process of the preparation method, and the graphene pores, the metal atom calcium Ca, the electron beam irradiation mode, the metal film synthesis region and the like are labeled in detail in the diagram. And (3) the interaction between the metal atoms deposited on the graphene in advance and incident electrons is carried out, the parameters of the electron beams are adjusted, and the metal atoms migrate to the pores of the graphene and form a single-atom thick metal film.

FIG. 2 is a graph of experimental results of the prepared independent monatomic thick metallic calcium film. FIGS. 2a and 2b are photomicrographs of the TEM and STEM modes, respectively, of the region where the calcium metal film is located; FIG. 2c is an enlargement of the box area (test area) in FIG. 2 b; FIGS. 2d and 2e are high resolution electron micrographs of the calcium metal film tested; FIG. 2f is a Fourier transform of calcium film and graphene with calcium film diffraction information subtracted; fig. 2g is a high-resolution image of fig. 2f after inverse fourier transform, which clearly shows that the calcium film independently grows in the graphene pores, and no graphene support is located below; fig. 2h shows the Electron Energy Loss Spectrum (EELS) of this calcium film, and this metal film was identified as a calcium film.

Example 2:

the embodiment provides a preparation method of an independent monoatomic thick chromium film, which comprises the following steps:

(1) placing the metal chromium powder and graphene (transferred to a micro-grid and examined in a TEM in advance) in a quartz tube, vacuumizing to 10-6mbar, sealing the tube opening, and then placing the quartz tube in a tube furnace for heat treatment at 250 ℃ for 12 h.

(2) And (3) placing the micro-grid (with Cr deposited) subjected to heat treatment into a transmission electron microscope, and irradiating by using electron beams for 1-5 minutes to clean the surface according to the amorphous thickness of the surface of the sample.

(3) Selecting a region with large clean single-layer graphene and enriched Cr elements, and continuously adjusting electron beam parameters to irradiate the region to form an independent monoatomic thick chromium film. The electron beam parameters used were: voltage: 80 kV; ② electron beam current is 1.2nA-1.5 nA; (iii) electron beam dose: 10⁶-10⁷A/m²(ii) a Duration of electron beam irradiation: 4-5 min. These parameters vary depending on the degree of amorphousness in the sample, the degree of aggregation of metal atoms, the size of the metal film, etc., and are in a range.

When a film forming area is selected, a large-area energy spectrum test is carried out in advance to test that the area is only rich in Cr except carbon and oxygen and is not polluted by any other impurities. The probability of forming a metal film in two types of characteristic areas is high, firstly, Cr atoms are enriched at the periphery of a graphene hole and migrate to the hole under the irradiation of an electron beam so as to form a film; and secondly, some Cr atoms are already in the holes of the graphene but in a radical state, and a film is formed by electron beam irradiation with proper parameters.

Fig. 3 is an experimental demonstration of this one-atom thick chromium metal film prepared.

Fig. 3 shows transmission electron microscopy characterization of a two-dimensional single-atom thick metallic Cr film between graphene and CrO Nanoparticles (NPs). Figure (a) shows a high resolution transmission electron micrograph of CrO nanoparticles and Cr thin film suspended in graphene pores. Local Electron Energy Loss Spectroscopy (EELS) spectra were collected from CrO nanoparticles (red spectrum) and two-dimensional Cr film (blue spectrum), respectively, and the results showed that only two-dimensional films of Cr metal element were indeed generated. To verify this result, an image simulation of the structure in the transmission electron microscope image was performed and a baseball model was created (d, e).

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.