A two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layers

Abstract

This invention provides a clean transfer technique for two-dimensional heterojunctions based on a van der Waals auxiliary layer. The specific method involves: fabricating a micro-dome-shaped PVC (PVC-MDP) on a glass slide; using the PVC-MDP to pick up the h-BN auxiliary layer; then using the PVC-MDP to pick up the h-BN / two-dimensional heterojunction; finally, releasing the h-BN / two-dimensional heterojunction to the target substrate; and finally removing the h-BN auxiliary layer. In this method, the introduction of the h-BN auxiliary layer avoids direct contact between the polymer and the target heterojunction, thereby preventing polymer contamination at the source and achieving two-dimensional heterojunction transfer on an atomically clean surface.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material transfer technology, and more specifically, relates to a two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layers. Background Technology

[0002] Two-dimensional materials exhibit excellent electrical and optical properties due to the quantum confinement effect, showing broad application prospects in high-end electronic and optoelectronic devices. Since there are no dangling bonds on the surface of two-dimensional materials, two-dimensional heterostructures can be directly constructed by stacking layers of them without considering lattice matching. This characteristic gives two-dimensional heterostructures greater freedom in construction compared to traditional three-dimensional heterostructures, thus gradually becoming a research hotspot in the field of optoelectronic science.

[0003] Currently, the mainstream method for constructing two-dimensional heterojunctions is to use pick-and-release techniques with polymer support layers to stack two-dimensional materials, also known as two-dimensional material transfer technology. Polymer-assisted two-dimensional material transfer techniques can be broadly classified into wet transfer (direct contact between the material and the liquid) and dry transfer (keeping the material surface dry throughout the transfer process). Compared to wet transfer, dry transfer avoids the potential impact of the liquid on the material's properties. However, even in dry transfer, direct contact between the polymer and the material inevitably leaves polymer residues on the surface of the two-dimensional material. These residues not only reduce the photoelectric properties of the material itself but also increase the surface roughness of the two-dimensional material, thus significantly affecting the success rate of fabricating two-dimensional heterojunctions with atomically clean interfaces. Therefore, to further promote the research and application of two-dimensional heterojunction optoelectronic devices, a pollution-free clean transfer technology is urgently needed. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layers.

[0005] To solve the above-mentioned technical problems, the present invention provides a technical solution with the following steps:

[0006] S1: Micro-dome polymer (MDP) was prepared using polydimethylsiloxane (PDMS). PDMS base agent and curing agent were poured into a plastic beaker at a mass ratio of 10:1. After thorough stirring, the mixture was poured into a plastic petri dish and then placed in a vacuum desiccator for degassing treatment to obtain a bubble-free liquid PDMS mixture (hereinafter referred to as liquid PMDS).

[0007] S2: Divide the liquid PMDS in step S1 into two parts, and cure one part at 60°C for 6-8 hours to obtain solid PDMS (hereinafter referred to as solid PDMS);

[0008] S3: Take a 1cm×1cm cube from the solid PDMS in step S2 and place it on a glass slide;

[0009] S4: Use a toothpick, tweezers, and a tungsten needle (tip diameter about 5μm) to drop another portion of liquid PMDS from step S2 onto the center of the solid PDMS block, and cure at 150℃ for 2-3 minutes to obtain a PDMS-MDP with a dome diameter of about 30μm.

[0010] S5: Apply double-sided tape around the solid PDMS block, and then use polyvinyl chloride (PVC) film as an adhesive layer to tightly bond the PDMS-MDP to form PVC-MDP.

[0011] S6: The van der Waals auxiliary layer (h-BN nanosheets) and the target heterojunction materials (MoS2 and WSe2 nanosheets) were exfoliated from the bulk crystals onto Si / SiO2 substrates 1, 2 and 3 respectively using mechanical exfoliation.

[0012] S7: Using the PVC-MDP from step S5, the h-BN, MoS2 and WSe2 nanosheets on Si / SiO2 substrates 1, 2 and 3 are picked up sequentially at 50-70°C, and then the h-BN / MoS2 / WSe2 is slowly released into the target substrate at 100-150°C.

[0013] S8: Use the PVC-MDP from step S5 to contact the h-BN region at the bottom that does not have MoS2 / WSe2, and perform a sliding operation to remove the h-BN auxiliary layer to obtain a clean MoS2 / WSe2 heterojunction.

[0014] Preferably, the mass ratio of PDMS base agent to curing agent in step S1 is 10:1.

[0015] Preferably, the vacuum degree of the liquid PDMS degassing treatment in step S1 is 0.1 Pa, and the time is 3 to 5 hours.

[0016] Preferably, the curing temperature of the liquid PMDS in step S2 is 60°C, and the curing time is 6 to 8 hours.

[0017] Preferably, the solid PDMS block size in step S3 is 1cm × 1cm.

[0018] Preferably, the tools for dispensing the liquid PMDS in step S4 are, in order, a toothpick, tweezers, and a tungsten needle, and the curing temperature of the liquid PMDS is 150°C, with a curing time of 2 to 3 minutes.

[0019] Preferably, the adhesive layer of the PDMS-MDP in step S5 is a PVC film.

[0020] Preferably, the tool used to obtain nanosheets by mechanical exfoliation in step S6 is blue film tape, the van der Waals auxiliary layer is h-BN, the exfoliation temperature is 70-90℃, and the heating time is 1-2 min.

[0021] Preferably, in step S7, the temperature at which the PVC-MDP picks up the nanosheets is 50–70°C and the picking speed is greater than 30 μm / s; the temperature at which the PVC-MDP releases the nanosheets is 100–150°C and the release speed is less than 3 μm / s.

[0022] Preferably, in step S8, when the PVC-MDP slides to remove the h-BN auxiliary layer, it only contacts the h-BN region at the bottom that does not have MoS2 / WSe2, and the sliding operation temperature is 100°C and the speed is 10 μm / s.

[0023] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0024] This invention provides a clean transfer technique for two-dimensional heterojunctions based on a van der Waals auxiliary layer. The specific method is as follows: PVC-MDP is prepared on a glass slide; the h-BN auxiliary layer is picked up using the PVC-MDP; the h-BN / two-dimensional heterojunction is picked up using the PVC-MDP; the h-BN / two-dimensional heterojunction is released to the target substrate; and the h-BN auxiliary layer is removed. This method has the following advantages: 1) Using a reusable micro-dome polymer instead of a disposable planar polymer can greatly improve transfer efficiency and realize two-dimensional material transfer in micro-regions; 2) The presence of the h-BN auxiliary layer avoids direct contact between the polymer and the target heterojunction, thus avoiding polymer contamination at the source; 3) Using a micro-dome polymer instead of a traditional planar polymer enables more complex sliding transfer operations, thereby removing the h-BN auxiliary layer. Attached image description:

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0026] Figure 1 This is a schematic diagram of the process for preparing the PVC-MDP.

[0027] Figure 2 This is a flowchart of the clean transfer technique for the MoS2 / WSe2 heterojunction in Example 1;

[0028] Figure 3 Optical microscope image of MoS2 / WSe2 heterojunction transferred onto Si / SiO2 substrate;

[0029] Figure 4 for Figure 3 Atomic force microscopy image of the MoS2 / WSe2 heterojunction;

[0030] Figure 5 for Figure 3 Raman spectrum of the MoS2 / WSe2 heterojunction. Detailed implementation method:

[0031] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0032] Example 1

[0033] A two-dimensional heterojunction clean transfer technique based on van der Waals auxiliary layers, the specific transfer method is as follows:

[0034] S1: Micro-dome polymer (MDP) was prepared using polydimethylsiloxane (PDMS). PDMS base agent and curing agent were poured into a plastic beaker at a mass ratio of 10:1. After thorough stirring, the mixture was poured into a plastic petri dish and then placed in a vacuum desiccator for degassing treatment to obtain a bubble-free liquid PDMS mixture (hereinafter referred to as liquid PMDS).

[0035] S2: Divide the liquid PMDS in step S1 into two parts, and cure one part at 60°C for 6-8 hours to obtain solid PDMS (hereinafter referred to as solid PDMS);

[0036] S3: Take a 1cm×1cm cube from the solid PDMS in step S2 and place it on a glass slide;

[0037] S4: Use a toothpick, tweezers, and a tungsten needle (tip diameter about 5μm) to drop another portion of liquid PMDS from step S2 onto the center of the solid PDMS block, and cure at 150℃ for 2-3 minutes to obtain a PDMS-MDP with a dome diameter of about 30μm.

[0038] S5: Apply double-sided tape around the solid PDMS block, and then use polyvinyl chloride (PVC) film as an adhesive layer to tightly bond the PDMS-MDP to form PVC-MDP.

[0039] S6: The van der Waals auxiliary layer (h-BN nanosheets) and the target heterojunction materials (MoS2 and WSe2 nanosheets) were exfoliated from the bulk crystals onto Si / SiO2 substrates 1, 2, and 3 using mechanical exfoliation.

[0040] S7: Using the PVC-MDP from step S5, the h-BN, MoS2 and WSe2 nanosheets on Si / SiO2 substrates 1, 2 and 3 are picked up sequentially at 50-70°C, and then the h-BN / MoS2 / WSe2 is slowly released into the target substrate at 100-150°C.

[0041] S8: Use the PVC-MDP from step S5 to contact the h-BN region at the bottom that does not have MoS2 / WSe2, and perform a sliding operation to remove the h-BN auxiliary layer to obtain a clean MoS2 / WSe2 heterojunction.

[0042] Figure 1 A schematic diagram of the process for preparing PVC-MDP. Figure 1 In the process of preparing a PDMS-MDP, liquid PMDS is dropped sequentially onto the center of a solid PDMS cube using a toothpick, tweezers, and a tungsten needle, and cured at 150°C for 2–3 minutes to obtain a dome-shaped PDMS-MDP with a diameter of approximately 30 μm. Then, double-sided tape is applied around the solid PDMS cube, and a PVC film is used as an adhesive layer to tightly bond the PDMS-MDP, forming a PVC-MDP. Figure 1 d).

[0043] Figure 2 This is a flowchart illustrating the clean transfer of the MoS2 / WSe2 heterojunction in Example 1. From... Figure 2 As can be seen from this, achieving clean transfer of the MoS2 / WSe2 heterojunction mainly includes the following steps: picking up the h-BN auxiliary layer with PVC-MDP ( Figure 2 i,ii); h-BN / MoS2 (i,ii); pick up h-BN / MoS2 with PVC-MDP (i,ii); Figure 2 iii,iv); using PVC-MDP to pick up h-BN / MoS2 / WSe2 ( Figure 2 v,vi); release h-BN / MoS2 / WSe2 to the target substrate (v,vi); Figure 2 vii, viiii); Remove the h-BN auxiliary layer with PVC-MDP ( Figure 2 ix,x).

[0044] Figure 3 Optical microscope image of the transfer of MoS2 / WSe2 heterojunction onto a Si / SiO2 substrate using the method described in Example 1. Figure 3 As can be seen, the surface of the MoS2 / WSe2 heterojunction transferred using the method of the present invention is clean and flat.

[0045] Figure 4 for Figure 3 Atomic force microscopy image of a MoS2 / WSe2 heterojunction. From Figure 4Further evidence shows that the MoS2 / WSe2 heterojunction transferred using the method of this invention has an atomically clean surface with a root mean square roughness of only 1.1 nm (solid box area).

[0046] Figure 5 for Figure 3 Raman spectrum of the MoS2 / WSe2 heterojunction. Figure 5 Typical MoS2 can be observed in the middle. (381.4cm -1 ) and A 1g (405.5cm -1 Raman peak, and typical WSe2 (250.5cm -1 ) and A 1g (257.5cm -1 Raman peaks. This indicates that the MoS2 / WSe2 heterojunction prepared by the transfer technology of this invention has no physical damage such as cracks, wrinkles, or strain.

[0047] In summary, this invention provides a clean transfer technique for two-dimensional heterojunctions based on a van der Waals auxiliary layer. The specific method involves: preparing PVC-MDP on a glass slide; picking up the h-BN auxiliary layer using the PVC-MDP; picking up the h-BN / two-dimensional heterojunction using the PVC-MDP; releasing the h-BN / two-dimensional heterojunction to a target substrate; and removing the h-BN auxiliary layer. The introduction of the h-BN auxiliary layer avoids direct contact between the polymer and the target heterojunction, thus preventing polymer contamination at the source. The two-dimensional heterojunction transferred using this method exhibits an atomically clean surface.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the implementation of the present invention. Any modifications, equivalent substitutions, and improvements within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for clean transfer of van der Waals assisted layer based two-dimensional heterojunctions, comprising: The method comprises the following steps: S1: preparing a micro-dome-shaped polymer MDP using polydimethylsiloxane PDMS, pouring a PDMS base and a curing agent into a plastic beaker at a mass ratio of 10:1, after fully stirring, pouring the mixture into a plastic culture dish, and then placing it into a vacuum dryer for degassing treatment to obtain a bubble-free liquid PDMS mixture; S2: dividing the liquid PMDS in step S1 into two parts, one of which is cured at 60°C for 6-8 hours to obtain a solid PDMS; S3: taking a 1cm×1cm square block from the solid PDMS in step S2 and placing it on a glass slide; S4: sequentially using a toothpick, tweezers and a tungsten needle with a diameter of 5μm to drop the other part of the liquid PMDS in step S2 in the center of the solid PDMS square block, and curing it at 150°C for 2-3min to obtain a PDMS-MDP with a dome diameter of 30μm; S5: attaching double-sided tape around the solid PDMS square block, and then tightly attaching a polyvinyl chloride PVC film as an adhesion layer to the PDMS-MDP to form a PVC-MDP; S6: using a blue film tape mechanical peeling method to peel h-BN, MoS2 and WSe2 nanosheets from bulk crystals onto Si / SiO2 substrates 1, 2 and 3, respectively, wherein h-BN is a van der Waals auxiliary layer, MoS2 and WSe2 are target heterojunction materials, the peeling temperature is 70-90°C, and the heating time is 1-2min; S7: using the PVC-MDP in step S5 to pick up the h-BN, MoS2 and WSe2 nanosheets on the Si / SiO2 substrates 1, 2 and 3 in turn at 50-70°C, the picking speed is greater than 30μm / s, and then slowly releasing the h-BN / MoS2 / WSe2 to the target substrate at 100-150°C, the release speed is less than 3μm / s; S8: using the PVC-MDP in step S5 to contact the h-BN area without MoS2 / WSe2 at the bottom and perform a sliding operation to remove the h-BN auxiliary layer to obtain a clean MoS2 / WSe2 heterojunction, the sliding operation temperature is 100°C, and the speed is 10μm / s.

2. The method of claim 1, wherein the van der Waals assisted layer is selected from the group consisting of graphene, hexagonal boron nitride, and molybdenum disulfide. The mass ratio of the PDMS base and the curing agent in step S1 is 10:

1.

3. The method of claim 1, wherein the van der Waals assisted layer is selected from the group consisting of graphene, hexagonal boron nitride, and molybdenum disulfide. The vacuum degree of the liquid PDMS degassing treatment in step S1 is 0.1Pa, and the time is 3-5h.

4. The van der Waals assisted layer based two-dimensional heterojunction clean transfer method according to claim 1, characterized in that: The liquid PMDS curing temperature in step S2 is 60°C, and the time is 6-8h.

5. The method of claim 1, wherein: The size of the solid PDMS square block in step S3 is 1cm×1cm.

6. The two-dimensional heterojunction clean transfer method based on a van der Waals auxiliary layer according to claim 1, characterized in that: The liquid PMDS dropping tool in step S4 is sequentially a toothpick, tweezers and a tungsten needle with a diameter of 5μm, the liquid PMDS curing temperature is 150°C, and the curing time is 2-3min.

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