CN115231610B

CN115231610B - Two-dimensional nano sheet and preparation method thereof

Info

Publication number: CN115231610B
Application number: CN202210934672.4A
Authority: CN
Inventors: 耿凤霞; 嵇锦鹏; 蒋坤
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2022-08-04
Filing date: 2022-08-04
Publication date: 2023-06-06
Anticipated expiration: 2042-08-04
Also published as: CN115231610A

Abstract

The invention discloses a preparation method of a two-dimensional nano sheet, which comprises the steps of carrying out calendaring treatment on non-van der Waals layered crystal particles, and then mechanically stripping to obtain the two-dimensional nano sheet. Mechanical delamination, commonly known as the scotch tape method, is only possible with tape (sometimes with the aid of an interposer) when the interlayer interactions of the bulk material are dominated by weak van der waals forces; however, many functional materials with layered stacked crystal structures have significant electron density overlap between layers, which form non-van der waals structures that cannot be peeled directly using tape. The invention uses calendaring pretreatment and combines mechanical stripping to successfully obtain few layers or even single layers of various non-Van der Waals layered crystal materials for the first time, and can observe novel physical phenomena in stripped two-dimensional crystals.

Description

Two-dimensional nano sheet and preparation method thereof

Technical Field

The invention belongs to the nano technology, and particularly relates to a two-dimensional nano sheet and a preparation method thereof.

Background

Two-dimensional materials have been of great interest in recent years, having a thickness of a few atomic layers, even a single atomic layer. Limiting the thickness to sub-nanometer scale will impart a number of dimensional-dependent new foreign body physical properties and applications to the material (Novoselov, k.s.; geim, a.k.; morozov, s.v.; jiang, d.; zhang, y.; dubonos, s.v.; grisorieva, i.v.; firsov, a.a. Electric Field Effect in Atomically Thin Carbon Films).Science 2004, 306, 666−669. Tan, C.; Cao, X.; Wu, X.; He, Q.; Yang, J.; Zhang, X.; Chen, J.; Zhao, W.; Han, S.; Nam, G.-H.; Sindoro, M.; Zhang, H. Recent Advances in Ultrathin Two-Dimensional Nanomaterials. Chem. Rev.2017, 117, 6225−6331.Butler, S. Z.; Hollen, S. M.; Cao, L.; Cui, Y.; Gupta, J. A.; Gutierrez, H. R.; Heinz, T. F.; Hong, S. S.; Huang, J.; Ismach, A. F.; Johnston-Halperin, E.; Kuno, m.; Plashnitsa, V. V.; Robinson, R. D.; Ruoff, R. S.; Salahuddin, S.; Shan, J.; Shi, L.; Spencer, M. G.; Terrones, M.; et al. Progress, Challenges, and Opportunities in Two Dimensional Materials beyond Graphene. ACS Nano2013, 7, 2898−2926.Zhou, J.; Lin, J.; Huang, X.; Zhou, Y.; Chen, Y.; Xia, J.; Wang, H.; Xie, Y.; Yu, H.; Lei, J.; Wu, D.; Liu, F.; Fu, Q.; Zeng, Q.; Hsu, C.-H.; Yang, C.; Lu, L.; Yu, T.; Shen, Z.; Lin, H.; Yakobson, B.; Liu, Q.; Suenaga, K.; Liu, G.; Liu, Z. A Library of Atomically Thin Metal Chalcogenides. Nature 2018, 556, 355-361.). Mechanical delamination, also commonly referred to as the scotch tape method, because no chemical reaction is involved in the process, is considered to be the best method to obtain a high quality two-dimensional material and preserve its intrinsic structure and properties. Introduction of an auxiliary interposer (e.g. Au, al ₂ O ₃ Etc.) can be used to enhance the adhesion of the substrate to the target crystal and increase the contact area, thereby peeling off the large-sized nanoflakes. However, the method needs to select different intermediate materials for different stripping objects, and particularly, the intermediate materials need to be removed by a complex method after stripping, and the introduced impurities can greatly limit the intrinsic properties of the two-dimensional material. Furthermore, mechanical delamination (Deng, y.; yu, y.; song, y.; zhang, j.; wang, n.; sun, z.; yi, y.; wu, s.; zhu, j.; zhu.; wang, j.; wang, y.; y. Gate-rotatable roll-Temperature Ferromagnetism in Two-Dimensional Fe) is possible using tape (sometimes with the aid of an interposer) only if the interlayer interactions in the bulk material are dominated by weak van der waals (vdW) forces ₃ GeTe ₂ . Nature 2018, 563, 94-99). After the first successful mechanical exfoliation of graphene, single-layer structures of layered materials such as hexagonal boron nitride (h-BN), transition Metal Dihalides (TMD), metal Organic Frameworks (MOFs), black Phosphorus (BP) have also been reported successively. Notably, there are many functional materials with layered stacked crystal structures, but there is significant electron density overlap from layer to layer. For example, some metal oxides may be considered stacks of rigid layers, where each layer is connected by edges or corners anda metal-oxygen polyhedron extending in a two-dimensional manner. Adjacent layers in these structures typically have a metallic or electrostatic attraction between them, known as non-van der waals (non-vdW) structures, with interactions between the layers being significantly higher than in van der waals layered structures. These materials cannot be mechanically peeled directly into a single layer or few layers due to the strong electronic coupling between adjacent layers. Mechanically exfoliated laminae of such non-van der waals materials are interesting and important from the standpoint of structure-performance relationships and potential applications of new two-dimensional analogs. Therefore, it is highly desirable to develop a method of mechanically exfoliating non-van der Waals layered structures.

Disclosure of Invention

The method of the invention comprises a simple calendering pretreatment followed by mechanical stripping using transparent adhesive tape to obtain a thin layer; successful exfoliation of a variety of materials including metals (Bi, sb), semiconductive metal oxides and chalcogenides (SnO, V) ₂ O ₅ 、Bi ₂ O ₂ Se) and superconducting compound (KV) ₃ Sb ₅ ). Electron density theoretical calculations verify that there is a strong electron coupling between these structural layers and that the exfoliation energy is typically several times higher than that of graphite, which naturally makes conventional exfoliation of these materials difficult or even impossible.

The invention adopts the following technical scheme:

the preparation method of the two-dimensional nano sheet comprises the steps of calendaring crystal particles, and then mechanically stripping to obtain the two-dimensional nano sheet; preferably, the crystal particles are tiled and then subjected to calendaring treatment, and then mechanically peeled off to obtain the two-dimensional nano-sheets.

In the present invention, the crystal particles are crystal particles of a non-van der Waals layered structure such as metal particles, semiconductor metal oxide particles, chalcogenide particles, superconducting compound particles, etc., and as examples, the crystal particles are metal (Bi, sb), semiconductor metal oxide, and chalcogenide (SnO, V) ₂ O ₅ 、Bi ₂ O ₂ Se) and superconducting compound (KV) ₃ Sb ₅ ) Crystal particles; preferably, the crystal particles have a particle size of from micrometer to millimeter scale, such as from 1 μm to 5mm, preferably 1 to more500 μm, and further 10 to 200 μm.

In the invention, rolling treatment is carried out by adopting rollers or rods, and the rolling load is preferably 0.5-10 Kg, and the speed is 10-300 mm/min. For the crystal with the Van der Waals structure, such as graphite, two-dimensional nano sheets can be obtained through conventional mechanical stripping, but for the crystal particles with the non-Van der Waals structure with strong interaction between layers, the two-dimensional nano sheets cannot be obtained through conventional mechanical stripping, the invention creatively proposes that the conventional mechanical stripping is carried out after the extrusion to obtain the two-dimensional nano sheets, and the thickness of the two-dimensional nano sheets is 0.1 nm-50 nm, particularly 0.1 nm-30 nm, particularly 0.3 nm-10 nm, more importantly 0.5 nm-5 nm.

In the invention, mechanical stripping is tape stripping, the particles are stuck by the tape, folded in half, pressed and then torn, a thin layer material is stuck on the tape, the method is specifically operated as a conventional technology, graphite stripping is carried out by using the method in the prior art, but the non-van der Waals layered structure crystals cannot be thinned or nanoscale sheets are obtained by directly adopting the tape stripping, and single-layer or less-layer two-dimensional nano sheets cannot be obtained.

In the present invention, calendering is unidirectional calendering, which is conventionally understood, for example, in that the direction of travel of the roller against the crystal particles is unidirectional, rather than back and forth against the crystal particles.

As an example, crystal particles are tiled on a bottom plate of an electric calendaring roller device, and then one-way single-wheel calendaring is performed to obtain calendared particles; and then sticking and calendaring particles by using a transparent adhesive tape, and then stripping to obtain a thin layer, namely the product two-dimensional nano sheet disclosed by the invention, wherein the two-dimensional nano sheet assembly material such as a superconducting material, an optical material, an electrode material, a heat conducting material, an electric conducting material and the like can be prepared.

The invention uses calendaring pretreatment and then transparent adhesive tape stripping, which successfully obtains few layers or even single layers of several materials for the first time, and can observe exciting new phenomena in the stripped two-dimensional material. Antimony metal becomes a semiconductor with a bandgap of 2.01 eV; the light absorption range of semiconductor SnO can be controlled from the Infrared (IR) to the ultraviolet, with the band gap being controlled from 0.60 eV for the bulk to 3 for the monolayer.65 eV (eV). In addition, KV ₃ Sb ₅ A foil is a very promising two-dimensional superconducting material. Thus, the novel results of the present invention provide a general approach to mechanical cleavage of non-van der Waals layered materials and provide a variety of novel 2D materials.

Drawings

FIG. 1 (a) is a graph showing the release energy (meV A) for a non-Van der Waals layered material studied in the present invention ^-2 ) The method comprises the steps of carrying out a first treatment on the surface of the Values for graphite are also listed for reference. The exfoliation energy of non-van der Waals layered structures is typically 1.3-3.6 times that of graphite (which is in the vdW force range). According to the reference (Nano lett. 2018, 182759-2765), the stripping energy is calculated as the difference in ground state energy between the bulk material (per atomic layer) and the individual bias layers. (b) A contour plot of charge density differences for the calculated representative structure of the inventive material, showing strong interlayer coupling; the red and blue isosurfaces represent electron accumulation and depletion, respectively. (c) For the corresponding AFM images, these materials are shown as single or few layers.

Fig. 2 is a theoretical stability prediction of exfoliated monolayer SnO. Side and top views of (a) SnO. (b) A calculated contour plot of the charge density difference of the SnO crystal structure shows a decrease in interlayer electron density and an attenuation in interlayer interaction; the red and blue regions represent electron accumulation and depletion, respectively. (c) harmonic phonon dispersion spectra of single-layer SnO. (d) The temperature (upper left corner) and total energy (lower left corner) changes with trace time were obtained from molecular dynamics simulations of single layer SnO at 300 and 600K; right figure: corresponding snapshot at the end of molecular dynamics simulation. (e) The method of climbing elastic band (CI-NEB) calculated by density functional calculates O on SnO layer ₂ The minimum energy path of dissociation. Insert: representative CI-NEB configurations along the pathway include an initial state of stable adsorption of molecular oxygen, a transitional state, and a final state of free atomic oxygen. Calculated O ₂ The dissociation potential barrier was 0.58. 0.58 eV, indicating that the SnO flake has a high affinity for O under normal conditions ₂ The attack has good stability.

FIG. 3 is a representation of the crystal structure before and after calendering. (a) XRD pattern of SnO crystals and (b) raman spectrum. The rolled SnO crystals are denoted as M-SnO. SEM images of SnO crystals (c) before and (d) after the calendering process. The inset in each figure shows a schematic view of the stacking plane. (e) measuring the lateral force on the SnO by AFM. Insert: schematic of the experiment. (f) cross-sectional STEM images of SnO and M-SnO crystals.

Fig. 4 is a feature of SnO flakes of different thickness. (a) Typical optical microscopy images of a peeled SnO layer on a glass substrate. (b-f) representative AFM images of SnO flakes having a thickness of 1-5 layers. (g) high resolution TEM images of SnO flakes. (h) The raman spectrum of single-layer SnO was compared to bulk SnO and to raman spectra after exposure to air for 3 months and additional heating to 200 ℃ in air; laser wavelength: 532 nm.

FIG. 5 shows the Raman spectrum of (a) SnO flakes; insert: optical image of nanoplatelets. (b) A is that _1g And (c) E _g Is 15×15 μm ² Raman intensity mapping plot collected over area with a step size of 500 nm. The result shows that the thickness uniformity is high, and the local bonding structure is good.

FIG. 6 is Si/SiO ₂ AFM images of SnO flakes on a substrate after 3 months of exposure to ambient air and additional heating in air at 200 ℃.

Fig. 7 is a comparison of physical properties of single-layer SnO flakes and SnO blocks. (a) Band structure, (b) by drawing (Ahv) ^1/2 The band gap was experimentally estimated in relation to hv, and experimental and fitting values were plotted as solid and dashed lines, respectively. Band gap modulation covers the entire spectral range from infrared to ultraviolet. Experimental estimation of (c) the energy band structure of antimony and (d) the band gap. When thinned to a monolayer, the metal bulk material converts to a semiconductor with a bandgap of 2.01 eV. (e) The band gap modulation range from bulk to single layer SnO and Sb is compared to other reported two-dimensional semiconductors.

Fig. 8 is (a) analysis of optical transmittance and (b) absorbance of SnO nanoplatelets by ultraviolet-visible (UV-Vis) absorption. Collecting spectra on a single sheet deposited on a transparent quartz plate substrate by using an ultraviolet-visible spectrometer, wherein the radius of a laser spot is 2 mu m; illustration (a): optical photographs of individual flakes and bulk SnO crystals. Arrows indicate thickness increases. (c) a plot of bandgap versus thickness.

Fig. 9 shows the characteristics of Bi material. (a-b) representative SEM images and (c) X-ray diffraction patterns. Bismuth powder was purchased from ala Ding Shiye limited. The lateral dimension of the crystallites is about 50 μm.

Fig. 10 is a characteristic of Sb material. (a-b) representative SEM images and (c) X-ray diffraction patterns. Sb powder was purchased from ala Ding Shiye limited. The lateral dimensions of the crystallites are about 60-80 μm.

FIG. 11 is V ₂ O ₅ Characteristics of the material. (a-b) representative SEM images at different magnifications and (c) X-ray diffraction patterns. Vanadium pentoxide powder was purchased from ala Ding Shiye limited. The lateral dimension of the crystallites is about 150 μm.

FIG. 12 is Bi ₂ O ₂ Characterization of Se material. (a-b) representative SEM images at different magnifications and (c) X-ray diffraction patterns. Bi (Bi) ₂ O ₂ Se powder was purchased from ala Ding Shiye limited. The lateral dimension of the crystallites is about 50 μm.

FIG. 13 shows single crystal KV ₃ Sb ₅ Characteristics of the material. (a-b) representative SEM images at different magnifications. (c) X-ray diffraction pattern.

FIG. 14 is (a) Si/SiO ₂ AFM image of Sb nanoplatelets on a substrate; from left to right: a freshly peeled sheet, a sheet after 3 months of exposure to air, and a sheet after an additional 10 minutes of heating in air at 200 ℃, and (b) a corresponding raman spectrum. No significant changes were observed in sheet morphology, thickness or spectral characteristics, indicating good O resistance ₂ Stability.

FIG. 15 is (a) Si/SiO ₂ AFM image of Bi nanoplates on a substrate; from left to right: a freshly peeled sheet, a sheet after 3 months of exposure to air, and a sheet after an additional 10 minutes of heating in air at 150 ℃ and 200 ℃, and (b) a corresponding raman spectrum. No significant changes in nanoplatelet morphology, thickness, or spectral characteristics were observed at temperatures up to 150 ℃, indicating Bi nanoplateletsHas good O resistance ₂ Stability.

FIG. 16 is (a) Si/SiO ₂ Bi on substrate ₂ O ₂ AFM image of Se flakes; from left to right: a freshly exfoliated flake, a flake exposed to air for 3 months, and a flake heated in air at 200 ℃ for 10 minutes, and (b) a corresponding raman spectrum. No significant changes in flake morphology, thickness or spectral characteristics were observed, indicating good O resistance of Bi nanoplatelets ₂ Stability. .

FIG. 17 is a KV less than 2. 2 nm (one or two layers) thick ₃ Sb ₅ Is a representative AFM image of (c).

Fig. 18 is an optical microscopic representative image (taken in transmission mode) of a SnO piece directly tape-released on a slide substrate, showing that these layered crystals are still thick and opaque.

Detailed Description

The exfoliation energy of non-van der Waals layered structures is typically several times higher than that of graphite (fig. 1 a), which naturally makes exfoliation of these materials difficult. The method of the present invention comprises a simple calendering pretreatment followed by mechanical stripping using transparent adhesive tape to obtain a thin layer, successfully stripping a variety of materials including metals (Bi, sb), semiconductor metal oxides and chalcogenides (SnO, V) ₂ O ₅ 、Bi ₂ O ₂ Se) and superconducting compound (KV) ₃ Sb ₅ ) Electron density calculations verify that there is a strong electron coupling between these structural layers (fig. 1 b-c). The invention uses calendaring pretreatment and then transparent adhesive tape stripping, which successfully obtains few layers or even single-layer structures of various materials for the first time, and can observe exciting new phenomena in the stripped 2D material. Antimony metal becomes a semiconductor with a bandgap of 2.01 eV; the light absorption range of semiconductor SnO can be tuned from the Infrared (IR) to the ultraviolet region, with a band gap from 0.60 eV for the bulk to 3.65 eV for the monolayer. In addition, thin KV ₃ Sb ₅ Is a potential two-dimensional superconductor. Thus, the novel results of the present invention provide a general approach to mechanical delamination of non-van der Waals layered materials and provide a variety of novel 2D materials.

SnCl ₂ •2H ₂ O (AR, 98%) and NaOH (AR, 96%) were purchased from national pharmaceutical group chemical company limited. V (V) ₂ O ₅ (metal base, 99.99%), bi (metal base, 99.99%) and Sb (metal base, 99.99%) crystals were purchased from ala Ding Shiye limited (Shanghai, china). Bi (Bi) ₂ O ₂ Se (metal base, 99.99%) was purchased from Nanjing Mi Mu scientific, inc. (Co., ltd.). All reagents were not purified. Scotch tape was purchased from meganew energy, inc. Heat release tape (single sided, heat release temperature 120 ℃) was purchased from Jiangsu Xianfeng nanomaterials science and technology Co. Polydimethylsiloxane films (0.5. 0.5 mm thick) were purchased from loma aitermer commercial limited. Si/SiO ₂ Substrate (SiO) ₂ Thickness: 300 nm) is provided by the mirror department instrument technology limited company in beijing.

And (5) testing materials. The crystal structure of the samples was studied using a powder X-ray diffraction system (XRD, X' Pert-Pro MPD) equipped with a Cu/kα1 target (λ=1.5418 a). The morphology of the samples was studied by scanning electron microscopy (SEM, hitachi SU 8010). The surface chemistry of the Al/ka target test sample was tested under ultra-high vacuum conditions using an X-ray photoelectron spectrometer (XPS) on an Escalab 250Xi X-ray photoelectron spectrometer (Thermo Fisher Scientific inc.) with a standard deviation of binding energy of 0.1 eV. Atomic force microscopy (AFM; bruker Instruments Dimension ion) is used to characterize the lateral dimensions and thickness of a wafer on a silicon substrate. High resolution transmission electron microscopy (HR-TEM) was performed using a FEI Tecnai G2F 20S-TWIN TMP equipped with a field emission gun operating at an accelerating voltage of 200 kV. Mechanically stripped flakes were transferred directly onto copper grids, atomic images were acquired using a Themis aberration corrected scanning transmission electron microscope (STEM, HF 5000), and samples were prepared by Focused Ion Beam (FIB) in which high current gallium ion beam was used to strip surface atoms to complete micro-nano surface topography processing. Ultraviolet-visible near infrared transmission spectra of the release sheet on a transparent quartz slide were recorded on 20/30 PV, and a differential spectrophotometer at ambient temperature (Craic Technologies inc.) from which band gap values were calculated using a Tauc chart, measuring wavelength rangesFor 350-2000 nm, raman spectra were collected at 532 nm laser excitation (power: 1 mW) using a confocal Raman spectrometer (WITec Alpha 300R) equipped with a UHTS 300 spectrometer (600 lines per millimeter of grating) and a CCD detector (DU 401A-BV-352), with a spot radius of 2 μm. Focusing the laser beam and collecting the raman signal using a 100 x objective, transferring the lift-off foil to Si/SiO ₂ And on the substrate.

Synthesis example

And (3) preparing SnO crystal particles. In a typical process, 0.02 mol (4.50 g) of SnCl is stirred ₂ •2H ₂ O was dissolved in 70 mL ultrapure water, and then NaOH was added until the pH of the mixture reached 9. After stirring for a further 30 minutes, the mixture was transferred to a 100 mL polytetrafluoroethylene lined autoclave, sealed and heated at 150 ℃ for 15 hours. Then allowed to cool to room temperature. The product was collected by centrifuging the mixture, alternately washed 3 times with distilled water and absolute ethanol, and then dried overnight in vacuo to give blue-black SnO crystals.

Single crystal KV is prepared by flux method ₃ Sb ₅ In the form of KSb ₂ The alloy grows as a fluxing agent. K. V, sb element and KSb ₂ The precursors were sealed in tantalum crucibles at a molar ratio of 1:3:14:10, then in high vacuum quartz ampoules. The ampoule was heated to 1273K for 20 hours and then cooled to 773K. Single crystals having a lateral dimension of about 1000 μm and a silver luster were separated from the flux by centrifugation.

The invention is prepared by calendering crystal particles first, then mechanically stripping the particles by transparent adhesive tape, and transferring the particles onto a target substrate by using the prior art all-dry method technology. By way of example, the present invention rolls the crystal particles after they are tiled on a surface, i.e. applying shear forces to the crystals, the rolling being in only one direction (not back and forth), resulting in continuous and unidirectional rolling with a roller or bar load of 0.5-10 kg and a speed of 10-500 mm/min. And then according to conventional methods: peeling the rolled crystal particles by using a transparent adhesive tape to obtain a thin layer (namely, the two-dimensional nano-sheet of the product), separating the thin layer from the transparent adhesive tape by using a heat release adhesive tape, transferring the thin layer onto a polydimethylsiloxane film by heating release, and further pressing the adhesive tape vertically on a target substrate to transfer the peeled thin layer onto various substrates such as glass, silicon or silicon/silicon dioxide; the transfer step using a heat release tape and/or a polydimethylsiloxane film may also be omitted. In the invention, the specific tiling method is a conventional technology, is not limited, and does not affect the realization of the technical effect of the invention.

Example 1

Sandwiching the crystal particles between two papers, and then rolling a plastic rod on the surface in a one-way by hand pressure to obtain calendared particles; conventional classical tape stripping methods were then used, namely: the transparent adhesive tape is adhered with the rolled particles, and is split to form stripping after being folded and pressed, so that the thin layer material, namely the two-dimensional nano sheet of the product is obtained. Then baked at 100deg.C for 5 seconds (to facilitate retention of the transverse dimension of the sheet), and then separated from the transparent adhesive tape using a heat release tape, and then released at 150deg.C to transfer the sheet to a different substrate as required for testing.

The crystal particles are respectively metal Bi, metal Sb and semiconductor metal oxide SnO, V ₂ O ₅ 、Bi ₂ O ₂ Se, superconducting compound KV ₃ Sb ₅ 。

Example two SnO two-dimensional nanoplatelets performance characterization.

The crystal structure of SnO belongs to the space group of P4/nmm, has a tetragonal unit cell structure, and the atoms Sn and O are Sn _1/2 −O−Sn _1/2 Sequence edge [001]The crystal directions are alternately arranged to form a layered sequence (fig. 2 a). Each O atom coordinates with four surface metal Sn atoms to form Sn ₄ O tetrahedra. Thus, lone pair electrons consisting of Sn 5s orbitals are directed toward the interlayer spacing, and therefore there is a strong dipole-dipole interaction between adjacent SnO layers. The differential charge density map of the structure shows a high electron density between the layers, indicating the presence of strong inter-layer interactions (fig. 2 b). Due to having 48.4 meV A ^-2 Is not possible by existing machinery, is quantified by the difference in ground state energy between bulk material and monolayer, which is prior artThe peeling produced a single layer sheet. The present invention strips a monolayer of SnO flakes from SnO crystal particles, the nanoflakes having an unusual metallic coating structure in which two atomic layers of Sn sandwich an atomic layer of O. The crystallographic thickness of the SnO monolayer was 0.38 nm. The calculated single layer SnO phonon spectrum shows that all phonon branches of the whole Brillouin zone are positive, no virtual frequency exists (fig. 2 c), indicating the structural stability of the 2D SnO flake in the ground state. The stability of such monolayer nanoplatelets to environmental or oxidative environments and temperatures has been further investigated as this is critical to basic research and technical applications. Theoretical estimation of oxidation potential barrier by climbing elastic band method calculated by DFT shows that SnO flake has stability and can resist O ₂ Attack (fig. 2 e). Molecular dynamics simulation at temperatures 300 and 600K showed no significant structural dissociation (fig. 2 d), indicating that the SnO exfoliate sheet has higher thermal stability. These findings strongly suggest that a monolayer of 2D SnO is stable once separated from the bulk crystalline stack.

The invention prepares SnO crystal particles by the hydrothermal reaction of stannous chloride dihydrate and sodium hydroxide (see synthesis examples for detailed information). The X-ray diffraction pattern (XRD) of the crystal after hydrothermal reaction shows diffraction peaks that can be indexed to tetragonal unit cells with lattice parameters: a=b= 3.8016 (4) a, c= 4.8441 (5) a (fig. 3 a), indicating that pure phase SnO is formed under these conditions. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Sn and O elements with Sn/O ratios approaching 1. The high resolution Sn 3d spectrum shows two distinct peaks at 486.1 and 494.5 eV, corresponding to Sn, respectively ²⁺ Sn 3d of (2) _5/2 And Sn 3d _3/2 Core energy level. The valence state also corresponds to the blue-black color of the crystal (see fig. 3a for an inset). Raman spectral display E of the original crystal _g At 112 cm ^-1 Where A is _1g Peak at 210 cm ^-1 Here, this is characteristic of SnO structure (fig. 3 b). Scanning Electron Microscopy (SEM) showed that SnO crystals had a lateral dimension of 100 μm and a thickness of about 10 μm (fig. 3 c). The platelet shape may be related to an inherent anisotropic layered structure, the thickness of which is related to the stacking of the platelets. Simple calendaring of these crystals can cause SnO crystals to bindThe structural change is called M-SnO. Morphology characterization of SEM showed planar sliding (fig. 3 d), a new diffraction peak was observed in the low angle region of XRD pattern, indicating a slight increase in interlayer spacing from 4.844 a to 4.949 a (fig. 3 a). Fig. 3e is an in situ AFM. Fig. 3f Scanning Transmission Electron Microscopy (STEM) shows the repulsion between adjacent layers and increases the repeat distance along the stacking direction. No vacancies were observed at the Sn sites. The in-plane Sn-Sn distance varied slightly from 2.684 a to 2.715 a, consistent with XRD results. In-plane Raman vibration mode E after calendering _g Is significantly reduced (fig. 3 b).

In the method disclosed by the invention, after calendaring treatment, the crystals can be peeled and layered into single SnO slices by using a conventional transparent adhesive tape method; the optical microscope image of the exfoliated SnO flakes transferred onto a transparent glass substrate was shown to have high transparency (fig. 4 a). The number of layers was verified by AFM as shown in FIGS. 4 b-f. The minimum thickness of the two-dimensional SnO flake measured by AFM is 0.8nm, and the thickness of the SnO monolayer is 0.38 nm based on its crystal structure, with the measured 0.8nm height not corresponding to two or more layers but rather to a monolayer SnO, considering the interfacial "inactive layers" of 0.1-0.6nm that are typically present between the release sheet and the substrate. Layers of different thicknesses, specifically 1.3, 1.8, 2.4 and 2.9 nm, were measured, the thickness increasing in steps of about 0.5 nm, the ideal step size being the crystallization repetition distance (0.48 nm) of the adjacent layers, as shown in the inset of fig. 4c, exactly matching the experimentally measured step size values, and therefore the flakes corresponding to

layers

2, 3, 4 and 5. The release sheet of the present invention is micron sized, the single layer sheet is 2-6 μm in size, and the 5 layer sheet is increased in size to about 15 μm (fig. 4 b-i), which can satisfy basic research applications for intrinsic material properties and certain devices. High resolution Transmission Electron Microscopy (TEM) shows crossed lattice fringes at a spacing of 2.7 a, corresponding to the lattice fringe spacing of the (110) plane (fig. 4 g). Careful examination of the image did not reveal significant defects, indicating that excessive metal vacancy defects were not generated during the calendaring process. In Raman spectroscopy, in-plane vibration mode E _g The strength of (a) decreases rapidly with decreasing sample thickness and is hardly detectable for a single layer (fig. 4 h), a _1g The peak appears red shifted (4 cm) ^-1 ) As the number of layers decreases, the vibration modes in the layered structure soften. E on a single sheet _g And A _1g The raman intensity mapping of the modes further demonstrates the high uniformity of thickness and local bonding structure (fig. 5). Notably, no SnO was observed even after exposing the sample to air for more than 3 months and additionally heating to 200 ℃ ₂ This demonstrates the structural stability of the exfoliated SnO flakes under ambient conditions. AFM studies confirmed that the morphology and thickness of the flakes remained intact (fig. 6).

After the bulk SnO crystals are exfoliated, the physical properties of the bulk SnO crystals are significantly changed. Theoretical predictions showed a significant increase in band gap from 0.64 eV for bulk SnO to 3.95 eV for single layer (fig. 7 a). Experimentally, the absorption spectrum of SnO flakes shows the shape characteristics of semiconductors with distinct absorption edges (fig. 8), consistent with theoretical estimates. As the thickness of the nanoplatelets decreases, the bandgap of the SnO flakes increases continuously (fig. 7 b), the bandgap modulation spans the entire spectral range from infrared to ultraviolet, this very broad absorption window being the maximum absorption window of the 2D semiconductor reported so far (fig. 7 e).

Using an optical microscope attachment on the instrument, the appropriate sample location is selected based on the contrast difference between the substrate and the delamination plate. The original bulk crystals are black in color due to opacity, as compared to the high clarity of the peeled flakes. Thinner flakes exhibit higher transparency. Based on (alpha hv) ^1/2 Tauc graph with hv, whereinαRepresenting the light absorption coefficient of the light,his the planck constant of the sample,νis the incident photon frequency, and the optical band gap value is extracted by extrapolating the fit line to the intercept (α=0).

Example three physical properties of other material sheets obtained by the present invention.

The invention is applicable to various materials including metals (Bi, sb), semiconductor metal oxides and chalcogenides (SnO, V) ₂ O ₅ 、Bi ₂ O ₂ Se) and superconducting compound (KV) ₃ Sb ₅ ) The method comprises the steps of carrying out a first treatment on the surface of the Interlayer interactions and corresponding AFM images as shown in the figure1b and c. Specifically, metallic antimony (Sb) is a three-dimensional pseudo-lamellar crystal, belonging toR3-mh space group having triangular and hexagonal lattices. The crystal can be considered as an ABCABC stack of curved honeycomb arrangement of antimony atoms. Notably, the minimum interlayer spacing is only 0.23 nm, which means that the interlayer interactions are primarily chemical interactions (structure and density diagram in fig. 1 b), which makes direct mechanical delamination difficult to achieve. Using the method of the present invention, a 1.2. 1.2 nm thick monolayer of Sb can be obtained. Fig. 9-13 present characterization details of antimony and other exemplary materials. From these materials (including Bi, sb and Bi ₂ O ₂ Se), the nanoplatelets peeled off, exhibit stability against oxidation for a long period of time even if additionally heated in air (fig. 14-16). Importantly, metallic antimony was converted to a wide bandgap semiconductor (2.01 eV) when thinned to a monolayer of 1.2 a nm a (fig. 7c, d). The broad modulation of the physical properties that the invention achieves in relation to thickness may be related to strong electronic coupling in the interlayer region. In non-van der waals structures, as the number of layers decreases, strong interlayer interactions can cause subtle changes in the lattice structure, which in addition to dimensional effects, also affect the physical properties of the exfoliated platelets, and the unique thickness-property relationships observed in these materials further highlight the importance of extending 2D platelets to non-van der waals materials.

KV ₃ Sb ₅ Is a member of the recently discovered quasi-two-dimensional Kagome metal family of the general formula AV ₃ Sb ₅ (a: K, rb, cs). The material belongs to the P6/mmm space group, and all layers are connected through chemical bonds between A and V. The Kagome lattice of transition metal atoms is considered an excitation platform for studying a range of electron-related phenomena, including charge density waves, extraordinary hall effects, and superconductivity, and produces surprising results. Compared to bulk materials, 2D structures have several advantages: the two-dimensional geometry will enhance quantum fluctuations and dependencies and can also promote charge modulation by carrier doping, all of which can alter superconductivity and charge density waves. For example, for CsV ₃ Sb ₅ For a sheet of thickness 60 nm, the superconducting transition temperature Tc increases from about 2.5K for the bulk to 4.28K, however, whenThe opposite behavior was observed when the sample was further thinned to 4.8 nm, i.e. Tc was reduced to 0.76K. The change trend of the charge density wave transition temperature with the thickness is opposite. With the reactivity of the surface a layer, a recent work reported hole doping by natural oxidation of the Cs layer by simply exposing the Cs layer to air for several minutes. For sheets having a thickness less than 82 a nm a,T _c significantly jump to about 4.7K. KV (kilovolt) ₃ Sb ₅ The Tc of the bulk is lower, 0.93K, and since valence electrons on Cs are easily lost, K-related materials may be a better platform for more effectively adjusting carrier concentration. Thin KV ₃ Sb ₅ The abnormal hall conductivity of the crystal (thickness of about 105 a nm a) is as high as 15507 ohm ^-1 cm ^-1 . Regarding the peeling of such materials, it has been reported that CsV cannot be applied using conventional, conventional scotch tape methods ₃ Sb ₅ The crystal is thinned to the nanometer scale (below 100 nm) due to chemical interactions between Sb and Cs layers; k is smaller in size than Cs, which means KV ₃ Sb ₅ The bonding interactions are stronger, making its exfoliation more difficult. Unexpectedly, KV with thickness of 2-5 nm is obtained by combining calendaring of the invention with conventional tape stripping ₃ Sb ₅ Flakes, corresponding to 2-5 layers (fig. 1c and 17). The flakes of 5.4 nm had a fairly smooth surface, KV, even when exposed to air for at least 10 minutes at ambient conditions ₃ Sb ₅ Successful exfoliation to single or few layers would provide new opportunities for investigation of unconventional superconductivity and interactions with charge density waves in the two-dimensional Kagome lattice.

Application examples

Spreading the crystal particles on a bottom plate of an electric rolling roller (HZ-2403), and rolling by a single unidirectional wheel at 200 mm/min to obtain rolled particles; and sticking the rolled particles by using a transparent adhesive tape, folding and pressing, tearing to form stripping, and obtaining the thin-layer material, namely the two-dimensional nano sheet of the product. The crystal particles are respectively metal Bi, metal Sb and semiconductor metal oxide SnO, V ₂ O ₅ 、Bi ₂ O ₂ Se, superconducting compound KV ₃ Sb ₅ The two-dimensional nano-sheet obtained is similar to the embodiment,including single or few release sheets, the lateral dimensions may also be up to 15 μm. The method disclosed by the invention has universality on various crystal particles, can be prepared by utilizing industrial equipment, and provides a foundation for industrialization.

In summary, the present invention proposes a general solution for mechanical exfoliation of various crystalline structures with non-van der Waals interlayer forces, including metals (Bi, sb), semiconducting metal oxides and chalcogenides (SnO, V) ₂ O ₅ 、Bi ₂ O ₂ Se) and superconducting compound (KV) ₃ Sb ₅ ). Mechanical stripping was successfully achieved by simple calendaring. New 2D sheets from non-van der waals structures show significantly better, distinguishing physical properties from crystalline bulk; the band gap can be tuned from 0.60 Ev (IR) for bulk SnO to 3.65 eV (UV) for single layer; the transition of bulk Sb to a monolayer occurs a metal-semiconductor (2.01 eV bandgap) transition. Single and few layer KV obtained in this work ₃ Sb ₅ Is an exciting product of 2D superconductors. The invention provides a method for mechanically stripping a non-van der Waals layered structure into a high-quality 2D analogue for the first time, and opens the door for easy preparation of new material families with potential applications.

Comparative example

Conventional tape stripping methods were used: and directly adhering SnO crystal particles (not calendaring) by using a transparent adhesive tape, and tearing after folding and pressing to form stripping to obtain a stripping product. Fig. 18 is an optical microscopic image example of tape-peeled SnO pieces on a glass slide substrate collected in transmission mode, showing that these layered crystals are still thick and opaque, with a thickness on the order of microns, indicating that conventional tape-peeling does not yield two-dimensional sheets, but rather flakes with a thickness on the order of nanometers.

Metals (Bi, sb), V ₂ O ₅ 、Bi ₂ O ₂ Se, superconducting compound (KV) ₃ Sb ₅ ) Sheets with a thickness of less than 0.2 μm cannot be obtained using conventional classical tape stripping methods.

Two-dimensional (2D) materials at single layer thicknesses have many new properties and thickness dependencies. Layered structure machineExfoliation is the most efficient method to obtain ultra-thin sheets, but this method is limited to materials where the interlayer interactions are controlled by weak van der waals forces, and is not applicable to materials with non-van der waals structures. The invention discloses a general method for mechanically stripping non-Van der Waals structures to obtain various novel two-dimensional materials, including metals (Bi, sb), semiconductor metal oxides and chalcogenide compounds (SnO, V) ₂ O ₅ 、Bi ₂ O ₂ Se) and superconducting compound (KV) ₃ Sb ₅ ). The method of the present invention involves calendering the raw material and then mechanically stripping the slid-on structure using typical scotch tape methods to give a stable single or multiple layer material with exciting new physical properties. For example, the band gap of metals and semiconductors is modulated in a wide range depending on the number of layers (Sb is 0 to 2.01 ev, sno is 0.60 eV (IR) to 3.65 eV (UV)). Several layers of KV are also obtained ₃ Sb ₅ Is an exciting material for researching the unconventional superconductivity. The novel method for directly and mechanically stripping the non-Van der Waals layered material greatly widens the usability of the 2D material so as to explore the unique physical characteristics and practical application thereof.

Claims

1. A preparation method of a two-dimensional nano sheet is characterized in that crystal particles are rolled, and then mechanically peeled off to obtain the two-dimensional nano sheet; the crystal grain is Bi, sb, snO, V ₂ O ₅ 、Bi ₂ O ₂ Se、KV ₃ Sb ₅ Crystal particles; and the rolling time delay is carried out, the rolling load is 0.5-10 Kg, and the speed is 10-300 mm/min.

2. The method of claim 1, wherein the crystal particles have a particle size of micrometer to millimeter scale.

3. The method for producing a two-dimensional nanosheet according to claim 2, wherein the crystal particles have a particle size of 1 μm to 5mm.

4. The method for preparing the two-dimensional nano-sheet according to claim 1, wherein the crystal particles are tiled and then subjected to calendaring treatment, and then the two-dimensional nano-sheet is obtained by mechanical peeling.

5. The method for preparing two-dimensional nano-sheets according to claim 1, wherein rolling treatment is performed by using rollers or bars; the mechanical peeling is tape peeling.

6. The two-dimensional nanoplatelets prepared by the method of preparing two-dimensional nanoplatelets according to claim 1.

7. The two-dimensional nanosheets of claim 6, wherein the thickness of the two-dimensional nanosheets is between 0.1nm and 50nm.

8. Use of the two-dimensional nanoplatelets of claim 6 for the preparation of two-dimensional nanoplatelet assembly materials.