A method of layered material transfer suitable for scanning probe microscopy analysis

Abstract

The application belongs to the technical field of microscopic analysis, and particularly discloses a layered material transfer method suitable for scanning probe microscopic analysis, which comprises the following steps: flatly attaching a PDMS film to the surface of layered material to be transferred on an initial growth substrate to obtain a PDMS film / layered material / initial growth substrate, and then vacuumizing the obtained PDMS film / layered material / initial growth substrate; soaking the obtained PDMS film / layered material / initial growth substrate in deionized water, and then peeling the PDMS film / layered material from the initial growth substrate in the deionized water; picking up the obtained PDMS film / layered material and attaching the PDMS film / layered material to a target substrate to obtain a PDMS film / layered material / target substrate, and then vacuumizing the obtained PDMS film / layered material / target substrate; after heating the obtained PDMS film / layered material / target substrate, peeling the PDMS film while hot to obtain a layered material / target substrate, and realizing the transfer of a single layered material to the target substrate. Meanwhile, the application can also realize the preparation of high-quality layered material homojunctions or heterojunctions at interfaces.

Description

Technical Field

[0001] This invention belongs to the field of microscopic analysis technology, specifically relating to a method for transferring layered materials suitable for scanning probe microscopy. Background Technology

[0002] The discovery of graphene has sparked a surge of research into layered materials. Numerous layered materials, including boron nitride, transition metal chalcogenides, and black phosphorus, possess excellent photoelectric and thermodynamic properties, demonstrating enormous application potential in energy, biology, chemistry, photoelectric conversion, and valley electronics. Furthermore, because these layered materials lack surface suspending bonds and rely on van der Waals forces for interlayer interaction, stacking materials with different numbers of layers, different rotation angles, and different properties does not require consideration of lattice mismatch. Compared to traditional semiconductor materials, constructing van der Waals heterostructures has become simpler and more feasible. Van der Waals homostructures or heterostructures often combine the advantages of the materials themselves, and physical processes such as interlayer interactions and charge transfer often generate new physical properties. Using scanning probe microscopy, a powerful tool for investigating the physical properties of material surfaces or interfaces, researchers have discovered and reported novel physical phenomena such as surface lattice reconstruction, Mohr's excitons, flat bands, and polarization reversal. To further explore the physical properties, intrinsic physical laws, and mechanisms of action of thin-layer or monolayer layered materials and their related heterostructures, it is particularly important to provide high-quality, high-cleanliness samples suitable for research in the field of scanning probe microscopy.

[0003] Currently, chemical vapor deposition (CVD) is a widely used growth method for preparing layered materials and their van der Waals heterostructures, offering advantages such as economy, convenience, efficiency, and high quality. However, the growth process of CVD is typically influenced by various factors. Different layered materials and different growth substrates often require significantly different growth temperatures, times, and operating procedures, necessitating extensive exploration of growth conditions. This is especially true for the growth of van der Waals homostructures or heterostructures, greatly limiting the exploration of layered materials and their heterostructures. Furthermore, in practical applications, it is usually necessary to transfer layered materials to specific substrates according to specific application requirements and experimental objectives. Currently, wet transfer and dry transfer are two common methods for transferring layered materials to target substrates. Both methods have their own drawbacks. For wet transfer, polymers such as polymethyl methacrylate (PMMA) are typically used, and strong acids, strong bases, or organic solvents are used to separate the substrate, followed by removal through methods such as immersion in organic solvents like acetone and annealing. It goes without saying that this process introduces many impurities, especially a large amount of PMMA residue on the surface, which greatly affects the quality of the prepared samples. Particularly for scanning tunneling microscopy, samples prepared using this method are often difficult to characterize. As for dry transfer, polydimethylsiloxane (PDMS) is typically used, utilizing its adhesiveness to directly peel off the layered material. However, this method obviously suffers from problems such as small transfer volume of layered material, low efficiency, and easy surface damage.

[0004] Based on the above analysis, there is an urgent need for an improved transfer technology to achieve large-scale, high-efficiency transfer of layered materials, without being limited by the size and number of layers, while maintaining the high integrity and cleanliness of the materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the difficulty of applying layered materials and their van der Waals heterostructures or homostructures transferred using traditional wet or dry transfer techniques to the field of scanning probe microscopy. This invention provides a layered material transfer method suitable for scanning probe microscopy analysis. Based on the difference in water wettability between the grown sample and the substrate, layered materials prepared by chemical vapor deposition (CVD) are transferred using a water immersion method. A PDMS film is bonded to the material, and the grown layered material is efficiently and extensively transferred to the target substrate in a smooth, clean, and uniform manner through thorough water immersion. Furthermore, flat, complete van der Waals homostructures or heterostructures with high interface cleanliness are stacked and transferred. This provides high-quality samples for the field of scanning probe microscopy, thus providing a strong technical guarantee for exploring the surface or interface properties of materials or heterostructures and elucidating the mechanisms of microscopic particle interactions.

[0006] To achieve the above objectives, one of the technical solutions of the present invention is: a method for transferring layered materials suitable for scanning probe microscopy analysis, comprising the following steps:

[0007] (1) The PDMS film is flatly attached to the surface of the layered material to be transferred on the initial growth substrate to obtain PDMS film / layered material / initial growth substrate, and then the substrate is evacuated.

[0008] (2) Immerse the PDMS film / layered material / initial growth substrate obtained in step (1) in deionized water, and then peel the PDMS film / layered material from the initial growth substrate in deionized water.

[0009] (3) The outer surface of the PDMS thin film / layered material obtained in step (2) is attached to the target substrate to obtain the PDMS thin film / layered material / target substrate, and then the substrate is evacuated.

[0010] (4) After heating the PDMS film / layered material / target substrate obtained in step (3), peel off the PDMS film while it is hot to obtain the layered material / target substrate, thereby realizing the transfer of a single layered material to the target substrate.

[0011] The purpose of vacuuming in steps (1) and (3) is to remove the gas between the PDMS film and the substrate, so that they adhere more tightly.

[0012] In a preferred embodiment of the present invention, the layered material to be transferred in step (1) is prepared by chemical vapor deposition, and the initial growth substrate includes, but is not limited to, SiO2 / Si, sapphire, mica, SiC, GaN, etc.

[0013] In a preferred embodiment of the present invention, the layered material to be transferred in step (1) includes, but is not limited to, MoS2, MoSe2, WS2, WSe2, ReS2, etc., and is not limited to the original number of layers and size of the material growth, and also includes the grown transverse heterojunction or vertical heterojunction.

[0014] In a preferred embodiment of the present invention, the PDMS film in step (1) is a high molecular polymer polydimethylsiloxane with a thickness of 300-500 μm.

[0015] In a preferred embodiment of the present invention, the vacuuming time in steps (1) and (3) is 10-15 min.

[0016] In a preferred embodiment of the present invention, the soaking time in deionized water in step (2) needs to be 30-60 minutes.

[0017] In a preferred embodiment of the present invention, the target substrate in step (3) includes various single crystals such as SiO2 / Si, Si sheets, highly oriented pyrolytic graphene (HOPG), single crystal Au, single crystal Ag, or flat metals such as sapphire, SiC, and GaN deposited on SiO2 / Si. For scanning tunneling microscopes, a flat substrate with strong conductivity is usually preferred.

[0018] In a preferred embodiment of the present invention, the preferred range for the heating table temperature setting in step (4) is 40-50°C, and the preferred range for the heating time is 15-20 min.

[0019] To achieve the above objectives, the second technical solution of the present invention is: the application of a layered material transfer method suitable for scanning probe microanalysis in the preparation of layered material homojunctions or heterojunctions / target substrate structures.

[0020] In a preferred embodiment of the present invention, the method for preparing the layered material homojunction or heterojunction / target substrate structure includes the following steps:

[0021] (1) The PDMS film is flatly attached to the surface of the layered material to be transferred on the initial growth substrate to obtain PDMS film / layered material / initial growth substrate, and then the substrate is evacuated.

[0022] (2) Immerse the PDMS film / layered material / initial growth substrate obtained in step (1) in deionized water, and then peel the PDMS film / layered material from the initial growth substrate in deionized water.

[0023] (3) Replace the PDMS film in step (1) with the PDMS film / layered material obtained in step (2), and repeat steps (1) and (2) to obtain the PDMS film / multilayer layered material structure.

[0024] (4) The outer surface of the PDMS thin film / multilayer material obtained in step (3) is attached to the target substrate to obtain the PDMS thin film / multilayer material / target substrate, and then the substrate is evacuated.

[0025] (5) After heating the PDMS film / multilayer layered material / target substrate obtained in step (4), the PDMS film is peeled off while it is hot to obtain a homojunction or heterojunction of layered material / target substrate structure, thereby realizing the transfer of multilayer layered material to the target substrate.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The method of the present invention can achieve planar transfer of large areas or even wafer-level dimensions;

[0028] 2. The layered material transferred by the method of the present invention is not limited by its growth thickness and size;

[0029] 3. The method of the present invention transfers layered materials with fewer air bubbles on the surface, resulting in high flatness, integrity, and minimal surface residue, making it suitable for research in the field of scanning probe microscopy.

[0030] 4. This invention can realize the preparation of high-quality layered material homojunctions or heterojunctions, providing strong technical support for the exploration of their physical properties. Attached Figure Description

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] Figure 1 This is a schematic diagram of the sample immersed in deionized water.

[0033] Wherein: a-glass slide; b-grown substrate; c-grown layered material; d-PMDS thin film; e-culture dish; f-deionized water;

[0034] Figure 2 The images show optical micrographs and Raman spectra of a monolayer WS2 crystal grown on sapphire and transferred to a SiO2 / Si substrate, as shown in Example 1. a is the optical micrograph, and b is the Raman spectra.

[0035] Figure 3 The images shown are optical micrographs, scanning tunneling micrographs, and atomic resolution images of the MoSe2 monolayer crystal grown on sapphire and transferred to a highly oriented pyrolytic graphene (HOPG) substrate in Example 2. a is an optical micrograph, b is a scanning tunneling micrograph of the MoSe2 morphology, and c is an atomic resolution image.

[0036] Figure 4 The images shown are optical micrographs of the monolayer MoS2 grown on the SiO2 / Si substrate in Example 3 transferred to the HOPG substrate, and the morphology and moiré pattern of the MoS2 point defects characterized by scanning tunneling microscopy. a is an optical micrograph, b is a morphology of the MoS2 point defects characterized by scanning tunneling microscopy, and c is a moiré pattern.

[0037] Figure 5 Scanning tunneling microscope image of the MoS2 homojunction prepared in Example 4. Detailed Implementation

[0038] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0039] A method for transferring layered materials suitable for scanning probe microscopy includes the following steps:

[0040] (1) The PDMS film is flatly attached to the surface of the layered material to be transferred on the initial growth substrate to obtain PDMS film / layered material / initial growth substrate, and then the substrate is evacuated.

[0041] (2) Immerse the PDMS film / layered material / initial growth substrate obtained in step (1) in deionized water, and then peel the PDMS film / layered material from the initial growth substrate in deionized water.

[0042] (3) The outer surface of the PDMS thin film / layered material obtained in step (2) is attached to the target substrate to obtain the PDMS thin film / layered material / target substrate, and then the substrate is evacuated.

[0043] (4) After heating the PDMS film / layered material / target substrate obtained in step (3), peel off the PDMS film while it is hot to obtain the layered material / target substrate, thereby realizing the transfer of a single layered material to the target substrate.

[0044] The layered material to be transferred in step (1) is prepared by chemical vapor deposition. The initial growth substrate includes, but is not limited to, SiO2 / Si, sapphire, mica, SiC, GaN, etc.

[0045] The layered material to be transferred in step (1) includes, but is not limited to, MoS2, MoSe2, WS2, WSe2, ReS2, etc., and is not limited to the original number of layers and size of the material growth, and also includes the grown lateral heterojunction or vertical heterojunction.

[0046] The PDMS film in step (1) is a high molecular polymer polydimethylsiloxane with a thickness of 300-500 μm.

[0047] The vacuuming time in steps (1) and (3) is 10-15 minutes.

[0048] The soaking time in deionized water in step (2) needs to be 30-60 minutes.

[0049] The target substrate in step (3) includes various single crystals such as SiO2 / Si, Si sheets, highly oriented pyrolytic graphene (HOPG), Au, Ag, or flat metals such as sapphire, SiC, and GaN deposited on SiO2 / Si. For scanning tunneling microscopes, a flat substrate with strong conductivity is usually preferred.

[0050] The preferred range for the heating table temperature setting in step (4) is 40-50℃, and the preferred range for the heating time is 15-20min.

[0051] Application of a layered material transfer method suitable for scanning probe microscopy in the preparation of layered material homojunctions or heterojunctions / target substrate structures.

[0052] The method for fabricating the layered material homojunction or heterojunction / target substrate structure includes the following steps:

[0053] (1) The PDMS film is flatly attached to the surface of the layered material to be transferred on the initial growth substrate to obtain PDMS film / layered material / initial growth substrate, and then the substrate is evacuated.

[0054] (2) Immerse the PDMS film / layered material / initial growth substrate obtained in step (1) in deionized water, and then peel the PDMS film / layered material from the initial growth substrate in deionized water.

[0055] (3) Replace the PDMS film in step (1) with the PDMS film / layered material obtained in step (2), and repeat steps (1) and (2) to obtain the PDMS film / multilayer layered material structure.

[0056] (4) The outer surface of the PDMS thin film / multilayer material obtained in step (3) is attached to the target substrate to obtain the PDMS thin film / multilayer material / target substrate, and then the substrate is evacuated.

[0057] (5) After heating the PDMS film / multilayer material / target substrate obtained in step (4), peel off the PDMS film while it is hot to obtain a stacked layered homojunction or heterojunction / target substrate structure, thereby realizing the transfer of multilayer material to the target substrate.

[0058] Example 1

[0059] Using a monolayer WS2 crystal grown on sapphire as the target sample, this invention achieves complete and high-quality transfer of the monolayer WS2 to a SiO2 / Si substrate. The specific steps are as follows: First, the sapphire crystal with WS2 grown on it is fixed to a glass slide using double-sided adhesive tape. Then, a PDMS film of appropriate size is cut (adjusted according to the size of the target substrate; here, the size is approximately 8mm × 6mm) and attached to the WS2 crystal to be transferred on the sapphire, resulting in a PDMS film / WS2 crystal / sapphire structure. Next, the obtained structure is placed in a vacuum chamber, and a mechanical pump is used to evacuate the vacuum for 10 minutes. After evacuation, it is immersed in deionized water for 30 minutes (see schematic diagram). Figure 1(As shown). After completion, the PDMS film / WS2 crystal was directly peeled from the substrate in deionized water to obtain the PDMS film / WS2 crystal. Then, it was lifted from the liquid surface, ensuring the outer surface with WS2 attached was in close contact with the SiO2 / Si substrate, resulting in the PDMS film / WS2 crystal / SiO2 / Si substrate. This was then placed in a vacuum apparatus and evacuated for 10 minutes. Finally, the obtained structure was placed on a heating stage and heated at 40°C for 15 minutes. The PDMS film was then peeled off while still hot, completing the transfer.

[0060] Figure 2 Optical micrographs and Raman spectra of WS2 crystals transferred to a SiO2 / Si substrate. The images show that the transferred WS2 crystal retains a relatively intact and flat triangular structure. The Raman spectrum displays the characteristic Et of the WS2 crystal. 2g Peak and A 1g The peaks are 362.0 cm⁻¹. -1 and 423.2cm -1 This indicates that WS2 still maintains its high monolayer crystal quality after the transfer.

[0061] Example 2

[0062] Using a monolayer MoSe2 crystal grown on sapphire as the target sample, this invention achieves complete and high-quality transfer of monolayer MoSe2 to a highly oriented pyrolytic graphene (HOPG) substrate. The specific steps are as follows: First, the sapphire crystal with MoSe2 grown on it is fixed to a glass slide using double-sided adhesive tape. Then, a PDMS thermally release film of appropriate size is cut (adjusted according to the size of the target substrate; here, the cut size is approximately 6mm × 5mm) and attached to the MoSe2 crystal to be transferred on the sapphire, resulting in a PDMS film / MoSe2 crystal / sapphire structure. Next, the obtained structure is placed in a vacuum chamber, and a mechanical pump is used to evacuate the vacuum for 10 minutes. After evacuation, it is immersed in deionized water for 30 minutes (see schematic diagram). Figure 1 (As shown). The PDMS film was directly peeled off from the substrate in water to obtain a PDMS film / MoSe2 crystal. This was then removed from the liquid surface, ensuring the MoSe2-coated outer surface adhered tightly to the HOPG substrate, resulting in a PDMS film / MoSe2 crystal / HOPG. This was then placed in a vacuum chamber and evacuated for 10 minutes. Finally, the resulting structure was placed on a heating stage and heated at 40°C for 15 minutes. The PDMS thermally released film was then peeled off while still hot, completing the transfer process. Figure 3Optical micrographs, scanning tunneling microscope (STM) images, and atomic resolution images of MoSe2 crystals transferred to HOPG substrates are shown. The images reveal that the MoSe2 transferred to HOPG under the optical microscope retains its initial growth morphology, with a large coverage area, complete morphology, and smooth surface. The obtained STM images show the complete crystal morphology and point defects and grain boundaries generated during the growth process. The obtained atomic resolution images clearly reflect the atomic arrangement of MoSe2, with a lattice period of 3.30 Å.

[0063] Example 3

[0064] Using MoS2 crystals grown on a SiO2 / Si substrate as the target sample, this invention achieves complete and high-quality transfer of monolayer MoS2 to a highly oriented pyrolytic graphene (HOPG) substrate. The specific steps are as follows: First, the SiO2 / Si substrate with grown MoS2 crystals is fixed to a glass slide using double-sided adhesive tape. Then, a PDMS thermally released film of appropriate size is cut (adjusted according to the size of the target substrate; here, the cut size is approximately 5mm × 5mm) and attached to the MoS2 crystal to be transferred on the SiO2 / Si substrate, resulting in a PDMS film / MoS2 crystal / SiO2 / Si substrate. Next, the obtained structure is placed in a vacuum chamber, and a vacuum is drawn using a mechanical pump for 10 minutes. After vacuuming, it is immersed in deionized water for 60 minutes (see schematic diagram). Figure 1 (As shown). The PDMS film was directly peeled off from the substrate in water to obtain a PDMS film / MoS2 crystal. This was then removed from the liquid surface, ensuring the MoS2-coated outer surface adhered tightly to the HOPG substrate, resulting in a PDMS film / MoS2 crystal / HOPG. This was then placed in a vacuum chamber and evacuated for 10 minutes. Finally, the resulting structure was placed on a heating stage and heated at 40°C for 15 minutes. The PDMS thermally released film was then peeled off while still hot, completing the transfer process. Figure 4 Images A and C represent optical micrographs, scanning tunneling microscope (STM) images, and atomic-resolution images of MoS2 crystals transferred to the HOPG substrate, respectively. It can be observed that the MoS2 transferred to the HOPG substrate retains its initial growth morphology under the optical microscope, with a large coverage area, intact triangular shapes, and a smooth surface. The obtained STM images clearly show point defects generated during the growth process. The moiré pattern image between MoS2 and HOPG has a moiré period of 1.18 nm.

[0065] Example 4

[0066] Using a single-layer MoS2 crystal grown on sapphire as the target sample, this invention achieves complete and high-quality multiple stacking of single-layer MoS2 and transfer to a highly oriented pyrolytic graphene (HOPG) substrate to construct a homogeneous MoS2 structure. The specific steps are as follows: First, two sapphire crystals (labeled MoS2 crystal 1 and MoS2 crystal 2) with MoS2 crystals grown on them are fixed to two glass slides using double-sided adhesive. Next, two appropriately sized PDMS films are cut (adjusted according to the size of the target substrate; here, the cut size is approximately 5mm × 5mm). One PDMS film is then attached to the MoS2 crystal 1 to be transferred, grown on sapphire 1, resulting in PDMS film / MoS2 crystal 1 / sapphire 1. The resulting structure is then placed in a vacuum chamber and evacuated using a mechanical pump for 10 minutes. After evacuation, it is immersed in deionized water for 30 minutes (see schematic diagram). Figure 1 (As shown). Next, the PDMS film was directly peeled off from the substrate in water to obtain PDMS film / MoS2 crystal 1. This was then attached to the MoS2 crystal 2 to be transferred, grown on sapphire 2, resulting in PDMS film / MoS2 crystal 1 / MoS2 crystal 2 / sapphire 2. The vacuuming and water immersion process was repeated: the obtained structure was placed in a vacuum chamber and evacuated using a mechanical pump for 10 minutes, then immersed in deionized water for 30 minutes. Subsequently, it was removed from the liquid surface and the surface with the double-layered MoS2 was tightly attached to the HOPG substrate to obtain PDMS film / MoS2 crystal 1 / MoS2 crystal 2 / HOPG, which was then placed in a vacuum device and evacuated for 10 minutes. Finally, the obtained structure was placed on a heating stage and heated at 40 degrees Celsius for 15 minutes. The PDMS thermally released film was then peeled off while hot, completing the transfer. Figure 5 The image shows the molar superlattice structure of the MoS2 homojunction transferred to the HOPG substrate as observed under a scanning tunneling microscope. The superlattice is arranged regularly with a period of 3.81 nm.

[0067] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for transferring a layered material suitable for scanning probe microscopy, characterized by, The method comprises the following steps: (1) a PDMS film is flatly attached to the surface of the layered material to be transferred on the initial growth substrate to obtain a PDMS film / layered material / initial growth substrate, which is then vacuumized; (2) the PDMS film / layered material / initial growth substrate obtained in step (1) is soaked in deionized water, and then the PDMS film / layered material is peeled off from the initial growth substrate in deionized water; (3) the PDMS film / layered material obtained in step (2) is used to replace the PDMS film in step (1), and steps (1) and (2) are repeated to obtain a PDMS film / multilayer layered material structure; (4) the outer surface of the multilayer layered material of the PDMS film / multilayer layered material obtained in step (3) is attached to a target substrate to obtain a PDMS film / multilayer layered material / target substrate, which is then vacuumized; (5) after the PDMS film / multilayer layered material / target substrate obtained in step (4) is heated, the PDMS film is peeled off while hot to obtain a stacked layered homojunction or heterojunction / target substrate structure, and the multilayer layered material is transferred to the target substrate; In the step (1), the layered material to be transferred is prepared by a chemical vapor deposition method, the initial growth substrate comprises SiO2 / Si, sapphire, mica, SiC, GaN, the layered material to be transferred comprises MoS2, MoSe2, WS2, WSe2, ReS2, and also includes a grown lateral heterojunction or vertical heterojunction, the PDMS film is a high molecular polymer polydimethylsiloxane, and the thickness is 300-500 µm; the vacuumization time in the steps (1) and (4) is 10-15 min; the soaking time of the deionized water in the step (2) is 30-60 min; the target substrate in the step (4) comprises SiO2 / Si, a Si sheet, HOPG, a single-crystal Au, a single-crystal Ag, or a flat metal evaporated on SiO2 / Si, sapphire, SiC, GaN; the heating process in the step (5) involves that the temperature of the heating table is set in the range of 40-50 ℃, and the heating time is 15-20 min.

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