CN114428180B - Preparation method of STEM sample of two-dimensional nanomaterial - Google Patents
Preparation method of STEM sample of two-dimensional nanomaterial Download PDFInfo
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- 239000002086 nanomaterial Substances 0.000 title claims abstract description 91
- 238000002360 preparation method Methods 0.000 title claims abstract description 35
- 238000001704 evaporation Methods 0.000 claims abstract description 88
- 230000008020 evaporation Effects 0.000 claims abstract description 69
- 239000011241 protective layer Substances 0.000 claims abstract description 53
- XMWRBQBLMFGWIX-UHFFFAOYSA-N C60 fullerene Chemical compound C12=C3C(C4=C56)=C7C8=C5C5=C9C%10=C6C6=C4C1=C1C4=C6C6=C%10C%10=C9C9=C%11C5=C8C5=C8C7=C3C3=C7C2=C1C1=C2C4=C6C4=C%10C6=C9C9=C%11C5=C5C8=C3C3=C7C1=C1C2=C4C6=C2C9=C5C3=C12 XMWRBQBLMFGWIX-UHFFFAOYSA-N 0.000 claims abstract description 26
- 238000010884 ion-beam technique Methods 0.000 claims abstract description 26
- 238000011065 in-situ storage Methods 0.000 claims abstract description 23
- 238000000034 method Methods 0.000 claims abstract description 19
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 19
- 238000000151 deposition Methods 0.000 claims abstract description 7
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 7
- 238000005070 sampling Methods 0.000 claims abstract description 7
- 238000000313 electron-beam-induced deposition Methods 0.000 claims abstract description 5
- 238000001888 ion beam-induced deposition Methods 0.000 claims abstract description 5
- 239000010410 layer Substances 0.000 claims description 46
- 229910052751 metal Inorganic materials 0.000 claims description 31
- 239000002184 metal Substances 0.000 claims description 30
- 229910052755 nonmetal Inorganic materials 0.000 claims description 29
- 238000007747 plating Methods 0.000 claims description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 6
- 229910052711 selenium Inorganic materials 0.000 claims description 6
- 239000011669 selenium Substances 0.000 claims description 6
- 229910052714 tellurium Inorganic materials 0.000 claims description 6
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 claims description 6
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims description 5
- FAWGZAFXDJGWBB-UHFFFAOYSA-N antimony(3+) Chemical compound [Sb+3] FAWGZAFXDJGWBB-UHFFFAOYSA-N 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 5
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 239000010949 copper Substances 0.000 claims description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 3
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 3
- 229910052797 bismuth Inorganic materials 0.000 claims description 3
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 229910052732 germanium Inorganic materials 0.000 claims description 3
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 3
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical group [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 3
- 229910052737 gold Inorganic materials 0.000 claims description 3
- 239000010931 gold Substances 0.000 claims description 3
- 125000003748 selenium group Chemical group *[Se]* 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 239000010703 silicon Substances 0.000 claims description 3
- 229910052709 silver Inorganic materials 0.000 claims description 3
- 239000004332 silver Substances 0.000 claims description 3
- 229910052725 zinc Inorganic materials 0.000 claims description 3
- 239000011701 zinc Substances 0.000 claims description 3
- 229910003472 fullerene Inorganic materials 0.000 abstract description 20
- 238000012512 characterization method Methods 0.000 abstract description 6
- 239000010408 film Substances 0.000 description 80
- OOEISWVDKCZSMS-UHFFFAOYSA-N bis(tellanylidene)vanadium Chemical compound [Te]=[V]=[Te] OOEISWVDKCZSMS-UHFFFAOYSA-N 0.000 description 23
- 238000007740 vapor deposition Methods 0.000 description 10
- 239000000463 material Substances 0.000 description 9
- 229910052787 antimony Inorganic materials 0.000 description 8
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 8
- 238000002207 thermal evaporation Methods 0.000 description 6
- 238000005520 cutting process Methods 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 238000001338 self-assembly Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000010409 thin film Substances 0.000 description 5
- 239000003344 environmental pollutant Substances 0.000 description 4
- 231100000719 pollutant Toxicity 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 229910021389 graphene Inorganic materials 0.000 description 3
- 238000001451 molecular beam epitaxy Methods 0.000 description 3
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 3
- 229910010271 silicon carbide Inorganic materials 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000000851 scanning transmission electron micrograph Methods 0.000 description 2
- 239000002356 single layer Substances 0.000 description 2
- 238000007738 vacuum evaporation Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- XSOKHXFFCGXDJZ-UHFFFAOYSA-N telluride(2-) Chemical compound [Te-2] XSOKHXFFCGXDJZ-UHFFFAOYSA-N 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
- G01Q30/00—Auxiliary means serving to assist or improve the scanning probe techniques or apparatus, e.g. display or data processing devices
- G01Q30/20—Sample handling devices or methods
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
- Radiology & Medical Imaging (AREA)
- Physical Vapour Deposition (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
- Sampling And Sample Adjustment (AREA)
Abstract
The invention discloses a preparation method of STEM samples of two-dimensional nano materials, which comprises the steps of carrying out in-situ evaporation of a first protective layer on the prepared two-dimensional nano materials in a vacuum environment; evaporating a second protective layer on the two-dimensional nano material on which the first protective layer is evaporated in situ in a vacuum environment; taking out the two-dimensional nano material evaporating the two protective layers from the vacuum environment, depositing a platinum film by means of electron beam and ion beam induced deposition, sampling by adopting a focused ion beam to obtain a sample sheet, and thinning the sample sheet by adopting the focused ion beam until the contrast of the sample sheet becomes white in a Scanning Electron Microscope (SEM), thus obtaining a STEM sample of the two-dimensional nano material. The invention uses vacuum in-situ evaporation of fullerene (C) 60 ) The method solves the problems that a STEM sample is polluted and a characterization structure is damaged in subsequent sampling caused by exposing the STEM sample prepared by the two-dimensional nano material to atmosphere.
Description
Technical Field
The invention relates to the technical field of scanning electron microscope sample preparation, in particular to a preparation method of a STEM sample of a two-dimensional nanomaterial.
Background
In recent years, two-dimensional nanomaterials have received a lot of attention, and because of the fact that they have only one or a few atomic layers in a certain dimension, the generated confinement effect makes them have singular properties different from three-dimensional materials. These novel properties are often determined by the structure of the novel materials, so that the novel materials have great significance for the high-precision characterization of the structure and the research of the related fields. In the atomic scale structure characterization technology, transmission Electron Microscope (TEM) and Scanning Transmission Electron Microscope (STEM) technologies can perform characterization measurement on the atomic scale of a sample structure from different directions, so that the method is an important technical means for researching the current two-dimensional material structure and related phase change process.
In the aspect of two-dimensional nanomaterial preparation technology, molecular Beam Epitaxy (MBE) is a very important and commonly used means for preparing two-dimensional nanomaterial, particularly, the high controllability of the thickness and the layer number of the two-dimensional nanomaterial and the high clean growth environment can effectively prepare a single-layer or less-layer two-dimensional material with high quality and a heterostructure of the single-layer or less-layer two-dimensional material. More importantly, the highly controllable growth condition provides necessary conditions for the growth of two-dimensional nano materials with different phase structures and chemical sensitivity. In recent years, a large number of novel two-dimensional nanomaterials have been prepared by using the MBE method. Because the environment of MBE for growing the two-dimensional nano material is a high vacuum environment, the preparation of STEM samples at present mostly needs to be subjected to the process of exposing the two-dimensional nano material to the atmosphere, but most of the two-dimensional nano materials react with gas molecules in the air or are polluted by other substances after being exposed to the atmosphere, so that it is difficult to prepare high-quality STEM samples on the premise of maintaining the structural properties of the two-dimensional nano materials. Moreover, most of the means for preparing STEM samples today use Focused Ion Beam (FIB) cutting, and two-dimensional nanomaterials usually have only a few atomic layers, which are relatively fragile and easily damaged by ion beams during sample preparation, so that it is difficult to prepare STEM samples with high quality. The precondition of obtaining clear atomic structure images in STEM measurement is to prepare high-quality STEM samples, so that a protective layer which can be prepared in situ and protect samples from atmospheric pollution and ion beam damage in STEM sample preparation has important value for two-dimensional nanomaterial structural characterization and related research.
Disclosure of Invention
The invention provides a preparation method of a STEM sample of a two-dimensional nanomaterial. The method for in-situ evaporation of the protective layer in high vacuum is utilized, and the problems that the STEM sample is polluted due to the fact that the STEM sample is prepared from the two-dimensional nano material prepared in a vacuum environment and the STEM sample structure of the two-dimensional nano material is damaged due to Focused Ion Beam (FIB) cutting sampling are solved.
In order to solve the technical problems, the invention specifically provides the following technical scheme:
a preparation method of a STEM sample of a two-dimensional nanomaterial comprises the following steps:
(1) Evaporating a first protective layer: evaporating a first protective layer on the prepared two-dimensional nano material in situ in a vacuum environment;
(2) Evaporating a second protective layer: evaporating a second protective layer on the two-dimensional nano material on which the first protective layer is evaporated in situ in a vacuum environment;
(3) Preparation of STEM samples: taking out the two-dimensional nano material of the vapor plating two-layer protection layer from the vacuum environment, depositing a platinum film on the two-dimensional nano material of the vapor plating two-layer protection layer by means of electron beam and ion beam induced deposition, then sampling the two-dimensional nano material of the vapor plating two-layer protection layer deposited with the platinum film by adopting a focused ion beam to obtain a sample sheet, and thinning the sample sheet by adopting the focused ion beam until the lining degree of the sample sheet is whitened in a Scanning Electron Microscope (SEM), thus obtaining a STEM sample of the two-dimensional nano material.
As a preferred embodiment of the present invention, the two-dimensional nanomaterial is a two-dimensional nanomaterial prepared in a vacuum environment.
As a preferable mode of the invention, the vacuum degree of the vacuum environment is 10 -10 -10 -7 mbar。
In a preferred embodiment of the present invention, the first protective layer and the second protective layer are evaporated by resistive heating.
In a preferred embodiment of the present invention, in step (1), the protective layer of the first layer is fullerene (C 60 ) Film, C 60 The thickness of the film is 2nm-10nm.
As a preferable mode of the invention, in the step (1), C 60 Inert molecules are used as evaporation sources, the evaporation temperature is 340-370 ℃, and the evaporation rate is 0.2nm/mins-1nm/mins.
In the step (2), the second protective layer is a metal film or a non-metal film, and the thickness of the metal film or the non-metal film is 40nm or more.
As a preferable scheme of the invention, the metal in the metal film is gold element or silver element or copper element or zinc element or antimony element or tin element or aluminum element or tin element or lead element or antimony element or bismuth element, and the nonmetal in the nonmetal film is selenium element and tellurium element or carbon element or silicon element or germanium element.
In the step (2), the metal or nonmetal is used as an evaporation source, the evaporation temperature is 120-1500 ℃, and the evaporation rate is 0.5-5 nm/min.
Compared with the prior art, the invention has the following beneficial effects:
(1) The method for in-situ evaporation of the fullerene protective layer in vacuum can not only enable the two-dimensional nano material to be characterized to be deposited on the protective layer in situ immediately after the preparation, but also isolate pollutants in the operation after the preparation, and protect the two-dimensional nano material to the greatest extent. And because of C 60 The nano-material has good chemical stability, can not react with the grown two-dimensional nano-material, and can keep the intrinsic structure and property of the two-dimensional nano-material. At the same time, C 60 The self-assembly forms a film with regular arrangement, better insulates the atmosphere and pollutants, and helps to obtain atomic structure images of the two-dimensional nano material with higher quality and a cleaner and sharper interface.
(2) The second protective layer is a metal film or a non-metal protective layer, has stronger ion beam bombardment resistance, and can reduce the damage of focused ion beams to samples in the preparation process of STEM measurement samples, thereby realizing the preparation of high-quality STEM samples.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It will be apparent to those of ordinary skill in the art that the drawings in the following description are exemplary only and that other implementations can be obtained from the extensions of the drawings provided without inventive effort.
FIG. 1 is a flowchart of a preparation method of STEM samples of two-dimensional nanomaterial provided by an embodiment of the present invention;
FIG. 2 shows a vapor deposition of C on a grown bilayer vanadium ditelluride surface according to an embodiment of the present invention 60 Schematic representation of the film;
FIG. 3 shows an embodiment of the invention in vapor deposition of C 60 Schematic diagram of evaporating metallic antimony film on the surface of double-layer vanadium ditelluride of the film;
FIG. 4 is a block diagram of an overall cross section of a STEM sample of a double-layer vanadium ditelluride provided by an embodiment of the invention;
fig. 5 is a sectional STEM image of a STEM sample of a double-layered vanadium ditelluride provided in an embodiment of the present invention.
Description of the reference numerals
1、C 60 Evaporation source 2, metal antimony evaporation source 3 and silicon carbide substrate covered by double-layer graphene
4. Double-layer vanadium ditelluride 5, C 60 Film 6, metallic antimony film
Detailed Description
The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to fig. 1 to 5 of the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, according to the preparation method of STEM samples of two-dimensional nanomaterial, fullerene (C 60 ) A protective layer formed on the fullerene (C 60 ) On the basis of the protective layer, a compact metal film or nonmetal film protective layer is evaporated again, so that the problem that a STEM sample is polluted due to the fact that a STEM sample prepared by vacuum preparation of a two-dimensional nano material is exposed to the atmosphere and the problem that a STEM sample structure of the two-dimensional nano material is damaged by Focused Ion Beam (FIB) cutting sampling is solved. By in-situ evaporation of fullerenes (C) in vacuum 60 ) The method for protecting the layer can not only enable the two-dimensional nano material to be characterized to be deposited in situ immediately after being prepared, but also isolate pollutants in the operation after the preparation, and protect the two-dimensional nano material to the greatest extent. And because of fullerene (C) 60 ) The nano-material has good chemical stability, can not react with the grown two-dimensional nano-material, and can keep the intrinsic structure and property of the two-dimensional nano-material. At the same time, fullerene (C 60 ) The self-assembly forms a film with regular arrangement, better insulates the atmosphere and pollutants, and helps to obtain atomic structure images of the two-dimensional nano material with higher quality and a cleaner and sharper interface. The second metal film or nonmetal protective layer has stronger ion beam bombardment resistance, and can reduce the damage of focused ion beams to the sample in the preparation process of STEM measurement samples, thereby realizing the preparation of high-quality STEM samples.
The method specifically comprises the following steps:
(1) Evaporating a first protective layer: evaporating a first protective layer on the prepared two-dimensional nano material in situ in a vacuum environment;
(2) Evaporating a second protective layer: evaporating a second protective layer on the two-dimensional nano material on which the first protective layer is evaporated in situ in a vacuum environment;
(3) Preparation of STEM samples: taking out the two-dimensional nano material of the vapor plating two-layer protection layer from the vacuum environment, depositing a platinum film on the two-dimensional nano material of the vapor plating two-layer protection layer by means of electron beam and ion beam induced deposition, then sampling the two-dimensional nano material of the vapor plating two-layer protection layer deposited with the platinum film by adopting a focused ion beam to obtain a sample sheet, and thinning the sample sheet by adopting the focused ion beam until the lining degree of the sample sheet is whitened in a Scanning Electron Microscope (SEM), thus obtaining a STEM sample of the two-dimensional nano material.
Further, in the preparation method of the STEM sample of the two-dimensional nanomaterial, the two-dimensional nanomaterial is prepared in a vacuum environment.
Further, in the preparation method of the STEM sample of the two-dimensional nanomaterial, the vacuum degree of the vacuum environment is 10 -10 mbar-10 -7 mbar. The vacuum degree condition can not only meet the vacuum degree required by the preparation of the two-dimensional nano material in the vacuum environment, but also carry out the vapor deposition of the first protective layer and the second protective layer in the vacuum environment.
In the preparation method of the STEM sample of the two-dimensional nano material, the evaporation mode of the first protective layer and the second protective layer is resistance heating evaporation. Resistance heating evaporation is a conventional way of vacuum evaporation, and can adapt to vacuum evaporation of various elements. Fullerene (C) in the first protective layer 60 ) The inert molecule is an evaporation source, the second protective layer can be selected from one of multiple metal elements or nonmetal elements, and is suitable for fullerene (C 60 ) Inert, metallic and nonmetallic elements are evaporated in vacuum, and a resistance heating evaporation mode is selected.
Further, in the preparation method of STEM sample of two-dimensional nanomaterial, in the step (1), the protective layer of the first layer is fullerene (C 60 ) Film, C 60 The thickness of the film is 2nm-10nm. Using C 60 As an in-situ first protective layer, due to C 60 The nano-material has good chemical stability, can not react with the grown two-dimensional nano-material, and can keep the intrinsic property of the two-dimensional nano-materialStructure and properties. Also, C 60 The self-assembly forms a dense film with regular arrangement, can effectively isolate impurity molecules in air, and protects the structure and the property of the surface/interface of the prepared material in the STEM sample preparation processing process of the material, thereby obtaining an intrinsic atomic structure image of the sample in STEM measurement. C (C) 60 The thickness of the film is 2nm-10nm, and the thickness range is the optimal C 60 Film thickness range. If C 60 The thickness of the film exceeds 10nm, namely the thickness of the fullerene film formed by self-assembly of fullerene molecules exceeds 10nm by an evaporation method, and the strength of the fullerene film with the thickness cannot meet the requirement of protecting the two-dimensional nano material. If C 60 The thickness of the film is less than 2nm, and the film passes through C when the second protective layer is evaporated 60 The film reacts with the internally protected two-dimensional nanomaterial.
Further, in the preparation method of STEM sample of two-dimensional nanomaterial, in step (1), C 60 Inert molecules are used as evaporation sources, the evaporation temperature is 340-370 ℃, and the evaporation rate is 0.2nm/mins-1nm/mins. Fullerene C 60 Inert molecules as evaporation source due to fullerene C 60 Inert molecules can not react with the grown two-dimensional nano material, and the intrinsic structure and the intrinsic property of the two-dimensional nano material can be maintained. Therefore, fullerene (C) 60 ) Inert molecules are used as evaporation sources. The vapor deposition temperature is 340-370 ℃, the vapor deposition temperature is lower than 340 ℃, and the fullerene (C 60 ) Inert molecules cannot evaporate, the temperature exceeds 370 ℃, the beam current is too high, and fullerene (C 60 ) Film uniformity is deteriorated. The evaporation rate is 0.2 nm/min-1 nm/min, and multiple experiments show that when the evaporation rate is in the rate range, C is evaporated 60 The film arrangement will be more regular and the uniformity will be higher. Too small a rate will result in too long vapor deposition time and too large a rate will result in C 60 The uniformity of the film is reduced.
In the step (2), the second protective layer is a metal film or a non-metal film, and the thickness of the metal film or the non-metal film is 40nm or more. Evaporating the second protective layer due to fullerene (C 60 ) The thin film is formed by self-assembly, the structure of the thin film is relatively fragile, and when a STEM sample is manufactured by using a focused ion beam, the two-dimensional nano material can not be well protected, so that a second protective layer with relatively thicker, denser and stronger second layer and higher ion beam bombardment resistance is required to be deposited. The metal in the metal film is gold element or silver element or copper element or zinc element or antimony element or tin element or aluminum element or tin element or lead element or antimony element or bismuth element, and the nonmetal in the nonmetal film is selenium element and tellurium element or carbon element or silicon element or germanium element. Because these metal or nonmetal films are easily crystallized and easily prepared, and can be closely covered with fullerene (C 60 ) The surface of the film. The thickness of the metal film or the nonmetal film is more than or equal to 40nm. To make the metal film or nonmetal film have enough thickness for C 60 The film provides protection against ion beam bombardment, and the metal film or the nonmetal film with the thinnest thickness of more than or equal to 40nm can resist C after multiple experiments 60 The film provides protection against ion beam bombardment.
Further, in the preparation method of the STEM sample of the two-dimensional nano material, the metal or nonmetal is used as an evaporation source, the evaporation temperature is 120-1500 ℃, and the evaporation rate is 0.5 nm/min-5 nm/min. For various metals or nonmetal as evaporation source, the evaporation temperature is 120-1500deg.C, and the selected metal or nonmetal evaporation source can be used for evaporation and deposition to the evaporated fullerene (C 60 ) On top of the film. The evaporation rate is 0.5 nm/min-5 nm/min, and the time for reaching the thickness of 40nm of the required metal film or nonmetal film is ensured not to be too long by selecting the evaporation rate, and the uniformity of the evaporation of the metal film or nonmetal film is ensured.
Example 1
In this embodiment, the two-dimensional nanomaterial is a bilayer vanadium ditelluride.
Step one, as shown in FIGS. 1 and 2, the preparation is carried out in advance directly in situ in vacuum without transferring or exposing the atmosphereC is carried out on the surface of the double-layer vanadium ditelluride nano material 60 Vapor deposition of film C 60 The evaporation mode of (2) is resistance type thermal evaporation, the evaporation temperature is 370 ℃, the evaporation rate is about 1nm/min, and C is obtained after evaporation is completed 60 The film thickness was 10nm.
Step two, as shown in FIG. 3, the vapor deposition of C is performed in a vacuum environment 60 The double-layer vanadium ditelluride of the film is used for in-situ evaporation of the metal antimony film, the evaporation mode of the antimony source is resistance type thermal evaporation, the evaporation temperature is 390 ℃, the evaporation rate is about 1nm/min, and the thickness of the metal antimony film obtained after the evaporation is finished is 50nm.
And thirdly, preparing a double-layer vanadium ditelluride STEM sample with an in-situ growth protective layer by using the double-layer vanadium ditelluride material with the evaporated protective layer and adopting a focusing ion beam lift-out method. The specific steps are that firstly, a Pt film is deposited on the surface of a sample on which a protective layer is evaporated by an electron beam and ion beam induced deposition mode, further protection is provided for the sample, and the deposited area is 10um multiplied by 2um. A focused ion beam was then used to etch a stepped trench to a depth of approximately 2um on both the upper and lower sides of the Pt thin film protection region. Then, the sample slice is cut off at the bottom, the left side and the half right side of the unetched Pt film protection area in a U-shaped cutting mode, so that the sample slice is cantilever-mounted on the substrate. And then connecting the mechanical arm with the sample slice by means of Pt deposition, cutting off the connection place of the sample slice and the substrate, lifting the sample by using the mechanical arm, and adhering the sample slice on the copper semi-ring by means of Pt deposition. And finally, thinning the sample sheet again by utilizing the focused ion beam until the contrast of the sample becomes white in a Scanning Electron Microscope (SEM), thus completing the preparation of the double-layer vanadium ditelluride STEM sample.
And carrying out section STEM characterization on the prepared double-layer vanadium ditelluride STEM sample so as to test the quality of the prepared STEM sample and measure the atomic structure of the double-layer vanadium ditelluride sample.
As shown in FIG. 3, in the large-scale sectional STEM image, we can clearly distinguish 50nm metal antimony film/10 nmC 60 Thin film/bilayer vanadium ditelluride/bilayer graphene-coated silicon carbide substrateA vertical distribution structure.
Downscaling, as shown in FIG. 4, a regular distribution of C is seen in the higher resolution high angle annular dark field image (HAADF) and bright field image (BF) 60 Film, clear C 60 Film/vanadium ditelluride interface, double-layered vanadium ditelluride atomic structure and C 60 Vertical distribution atomic structure of thin film/double layer vanadium ditelluride/double layer graphene covered silicon carbide substrate. Description C 60 The film effectively maintains the intrinsic structure and the property of the double-layer vanadium telluride, isolates the oxidation and pollution of the subsequent exposure atmosphere, and meanwhile, the metallic antimony film can also effectively avoid the damage of the focused ion beam to the sample, which shows that the embodiment realizes the acquisition of high-quality STEM samples.
Example 2
In this embodiment, the two-dimensional nanomaterial is a bilayer vanadium ditelluride. The same technical features as those in embodiment 1 in this embodiment are not described in detail.
Step one, as shown in fig. 1 and 2, the method directly performs C on the surface of the double-layer vanadium ditelluride nano material prepared in advance in situ without transferring or exposing the atmosphere in ultra-high vacuum 60 Vapor deposition of film C 60 The evaporation mode of (2) is resistance type thermal evaporation, the evaporation temperature is 360 ℃, the evaporation rate is about 0.6nm/min, and C is obtained after evaporation is completed 60 The film thickness was 7nm.
Step two, evaporating C in vacuum environment 60 The double-layer vanadium ditelluride of the film is used for in-situ evaporation of a nonmetallic selenium film, the evaporation mode of a selenium source is resistance type thermal evaporation, the evaporation temperature is 130 ℃, the evaporation rate is about 2.5nm/min, and the thickness of the nonmetallic selenium film obtained after the evaporation is completed is 60nm.
Example 3
In this embodiment, the two-dimensional nanomaterial is a bilayer vanadium ditelluride. In this embodiment, the same technical features as those in embodiment 1 and embodiment 2 are not described in detail.
Step one, as shown in fig. 1 and 2, the method directly performs C on the surface of the double-layer vanadium ditelluride nano material prepared in advance in situ without transferring or exposing the atmosphere in ultra-high vacuum 60 Vapor deposition of film C 60 The evaporation mode of (2) is resistance type thermal evaporation, the evaporation temperature is 340 ℃, the evaporation rate is about 0.2nm/min, and C is obtained after evaporation is completed 60 The film thickness was 4nm.
Step two, evaporating C in vacuum environment 60 The double-layer vanadium ditelluride of the film is used for in-situ evaporation of a non-metal tellurium film, the tellurium source is evaporated by resistance type thermal evaporation, the evaporation temperature is 250 ℃, the evaporation rate is about 1.5nm/min, and the thickness of the obtained non-metal tellurium film after the evaporation is finished is 50nm.
The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application, the scope of which is defined by the claims. Various modifications and equivalent arrangements may be made to the present application by those skilled in the art, which modifications and equivalents are also considered to be within the scope of the present application.
Claims (7)
1. The preparation method of the STEM sample of the two-dimensional nanomaterial is characterized by comprising the following steps of:
(1) Evaporating a first protective layer: evaporating a first protective layer on the prepared two-dimensional nano material in situ in a vacuum environment;
wherein the protective layer of the first layer is fullerene C 60 Film of fullerene C 60 The thickness of the film is 2nm-10 nm;
the fullerene C 60 Film C 60 Inert molecules are used as evaporation sources, the evaporation temperature is 340-370 ℃, and the evaporation rate is 0.2nm/mins-1 nm/mins;
(2) Evaporating a second protective layer: evaporating a second protective layer on the two-dimensional nano material on which the first protective layer is evaporated in situ in a vacuum environment;
wherein the second protective layer tightly covers the fullerene C 60 The surface of the film has higher ion beam bombardment resistance;
(3) Preparation of STEM samples: taking out the two-dimensional nano material of the vapor plating two-layer protection layer from the vacuum environment, depositing a platinum film on the two-dimensional nano material of the vapor plating two-layer protection layer by means of electron beam and ion beam induced deposition, then sampling the two-dimensional nano material of the vapor plating two-layer protection layer deposited with the platinum film by adopting a focused ion beam to obtain a sample sheet, and thinning the sample sheet by adopting the focused ion beam until the contrast of the sample sheet is whitened in a scanning electron microscope SEM to obtain a STEM sample of the two-dimensional nano material.
2. The method for preparing STEM samples of two-dimensional nanomaterial of claim 1, wherein the steps of: the two-dimensional nanomaterial is a two-dimensional nanomaterial prepared in a vacuum environment.
3. A method for preparing STEM samples of two-dimensional nanomaterial according to any of claims 1 or 2, characterized in that: the vacuum degree of the vacuum environment is 10 -10 mbar -10 -7 mbar。
4. The method for preparing STEM samples of two-dimensional nanomaterial according to claim 1, characterized in that: the evaporation mode of the first protective layer and the second protective layer is resistance heating evaporation.
5. The method for preparing STEM samples of two-dimensional nanomaterial according to claim 1, characterized in that: in the step (2), the second protective layer is a metal film or a non-metal film, and the thickness of the metal film or the non-metal film is 40-nm.
6. The method for preparing STEM samples of two-dimensional nanomaterial according to claim 5, characterized in that: the metal in the metal film is gold element or silver element or copper element or zinc element or aluminum element or tin element or lead element or antimony element or bismuth element, and the nonmetal in the nonmetal film is selenium element or tellurium element or carbon element or silicon element or germanium element.
7. The method for preparing STEM samples of two-dimensional nanomaterial according to claim 6, characterized in that: in the step (2), the metal or nonmetal is used as an evaporation source, the evaporation temperature is 120-1500 ℃, and the evaporation rate is 0.5-5 nm/min.
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