Two-dimensional heterojunction clean transfer technology based on Van der Waals auxiliary layer

Abstract

The invention provides a two-dimensional heterojunction clean transfer technology based on a Van der Waals auxiliary layer. The specific method comprises the following steps: preparing micro-dome type PVC (PVC-MDP) on a glass slide, picking up an h-BN auxiliary layer by using the PVC-MDP, then picking up an h-BN / two-dimensional heterojunction by using the PVC-MDP, then releasing the h-BN / two-dimensional heterojunction to a target substrate, and finally removing the h-BN auxiliary layer. In the method, the direct contact between the polymer and the target heterojunction is avoided by introducing the h-BN auxiliary layer, so that the polymer pollution is avoided from the source, and the two-dimensional heterojunction transfer of the atomic-scale clean surface is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material transfer, and more specifically, relates to a two-dimensional heterojunction clean transfer technology based on a van der Waals auxiliary layer. Background Art

[0002] Two-dimensional materials exhibit excellent electrical and optical properties due to the quantum confinement effect, and have broad application prospects in the fields of high-end electronics and optoelectronic devices. Since there are no dangling bonds on the surface of two-dimensional materials, two-dimensional heterojunctions can be directly constructed by stacking them layer by layer without considering lattice matching. This feature gives two-dimensional heterojunctions greater freedom in construction than traditional three-dimensional heterojunctions, and has gradually become a research hotspot in the field of optoelectronic science.

[0003] At present, the mainstream method for constructing two-dimensional heterojunctions is to stack two-dimensional materials using a pick-up and release technique with a polymer support layer, which is the so-called two-dimensional material transfer technology. Polymer-assisted two-dimensional material transfer technology can be roughly divided into two categories: wet transfer (direct contact between the material and the liquid) and dry transfer (the surface of the material remains dry during the entire transfer process). Compared with wet transfer, dry transfer avoids the potential impact of liquid on material properties. However, even with dry transfer, direct contact between the polymer and the material will inevitably leave polymer residues on the surface of the two-dimensional material. These residues will not only reduce the optoelectronic properties of the material itself, but also increase the surface roughness of the two-dimensional material, thereby greatly affecting the success rate of preparing two-dimensional heterojunctions with atomically clean interfaces. Therefore, in order to further promote the research and application development of two-dimensional heterojunction optoelectronic devices, a pollution-free clean transfer technology is urgently needed. Summary of the invention

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

[0005] In order to solve the above technical problems, the technical solution provided by the present invention comprises the following steps:

[0006] S1: Prepare microdome-shaped polymer (MDP) using polydimethylsiloxane (PDMS), pour PDMS base and curing agent into a plastic beaker at a mass ratio of 10:1, stir the mixture thoroughly and pour it into a plastic culture dish, then put it into a vacuum dryer for degassing to obtain a bubble-free liquid PDMS mixture (hereinafter referred to as liquid PMDS);

[0007] S2: the liquid PMDS in step S1 is divided into two parts, one of which is cured at 60° C. for 6 to 8 hours to obtain solid PDMS (hereinafter referred to as solid PDMS);

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

[0009] S4: Use a toothpick, tweezers and a tungsten needle (needle tip diameter is about 5 μm) to drop another portion of liquid PMDS in step S2 on the center of the solid PDMS block, and cure it at 150°C for 2-3 min to obtain a PDMS-MDP with a dome diameter of about 30 μm;

[0010] S5: Double-sided tape is attached around the solid PDMS square, and then a polyvinyl chloride (PVC) film is used as an adhesive layer to tightly adhere to the PDMS-MDP to form a PVC-MDP;

[0011] S6: Use mechanical exfoliation to exfoliate the van der Waals auxiliary layer (h-BN nanosheets) and the target heterojunction material (MoS2 and WSe2 nanosheets) from the bulk crystal onto Si / SiO2 substrate 1, substrate 2, and substrate 3, respectively;

[0012] S7: using the PVC-MDP in step S5 to sequentially pick up the h-BN, MoS2 and WSe2 nanosheets on Si / SiO2 substrates 1, 2 and 3 at 50-70°C, and then slowly release the h-BN / MoS2 / WSe2 to the target substrate at 100-150°C;

[0013] S8: Use 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.

[0014] Preferably, the mass ratio of the PDMS base and the 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 size of the solid PDMS block in step S3 is 1 cm×1 cm.

[0018] Preferably, the dripping tools of the liquid PMDS in step S4 are toothpicks, tweezers and tungsten needles, respectively, and the curing temperature of the liquid PMDS is 150° C., and the curing time is 2 to 3 minutes.

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

[0020] Preferably, the tool used for obtaining the nanosheets by the mechanical exfoliation method in step S6 is a blue film tape, the van der Waals auxiliary layer is h-BN, the exfoliation temperature is 70-90° C., 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-up speed is greater than 30 μm / s; the temperature at which the PVC-MDP releases the nanosheets is 100-150°C, and the releasing speed is less than 3 μm / s.

[0022] Preferably, when the PVC-MDP slides to remove the h-BN auxiliary layer in step S8, it only contacts the h-BN area at the bottom where there is no MoS2 / WSe2, and the sliding operation temperature is 100°C and the speed is 10 μm / s.

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

[0024] The present invention provides a two-dimensional heterojunction clean transfer technology based on a van der Waals auxiliary layer. The specific method is: prepare PVC-MDP on a glass slide; pick up the h-BN auxiliary layer with PVC-MDP; pick up the h-BN / two-dimensional heterojunction with PVC-MDP; release the h-BN / two-dimensional heterojunction to the target substrate; remove the h-BN auxiliary layer. The method has the following advantages: 1) using reusable micro-dome polymers instead of disposable traditional planar polymers can greatly improve the transfer efficiency and realize the transfer of two-dimensional materials in micro-areas; 2) the presence of the h-BN auxiliary layer avoids direct contact between the polymer and the target heterojunction, thereby avoiding polymer contamination at the source; 3) using micro-dome polymers instead of traditional planar polymers can achieve more complex sliding transfer operations, thereby removing the h-BN auxiliary layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 A schematic diagram of the process for preparing the PVC-MDP;

[0027] Figure 2 The clean transfer technology flow chart of 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 MoS2 / WSe2 heterojunction. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways 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 only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0032] Example 1

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

[0034] S1: Prepare microdome-shaped polymer (MDP) using polydimethylsiloxane (PDMS), pour PDMS base and curing agent into a plastic beaker at a mass ratio of 10:1, stir the mixture thoroughly and pour it into a plastic culture dish, then put it into a vacuum dryer for degassing to obtain a bubble-free liquid PDMS mixture (hereinafter referred to as liquid PMDS);

[0035] S2: the liquid PMDS in step S1 is divided into two parts, one of which is cured at 60° C. for 6 to 8 hours to obtain solid PDMS (hereinafter referred to as solid PDMS);

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

[0037] S4: Use a toothpick, tweezers and a tungsten needle (needle tip diameter is about 5 μm) to drop another portion of liquid PMDS in step S2 on the center of the solid PDMS block, and cure it at 150°C for 2-3 min to obtain a PDMS-MDP with a dome diameter of about 30 μm;

[0038] S5: Double-sided tape is attached around the solid PDMS square, and then a polyvinyl chloride (PVC) film is used as an adhesive layer to tightly adhere to the PDMS-MDP to form a PVC-MDP;

[0039] S6: Mechanical exfoliation is used to exfoliate the van der Waals auxiliary layer (h-BN nanosheets) and the target heterojunction material (MoS2 and WSe2 nanosheets) from the bulk crystal onto Si / SiO2 substrate 1, substrate 2, and substrate 3, respectively.

[0040] S7: using the PVC-MDP in step S5 to sequentially pick up the h-BN, MoS2 and WSe2 nanosheets on Si / SiO2 substrates 1, 2 and 3 at 50-70°C, and then slowly release the h-BN / MoS2 / WSe2 to the target substrate at 100-150°C;

[0041] S8: Use 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.

[0042] Figure 1 Schematic diagram of the process for the preparation of PVC-MDP. Figure 1 In the ac, liquid PMDS was dropped in the center of the solid PDMS block using a toothpick, tweezers and tungsten needle in turn, and cured at 150°C for 2-3 minutes to obtain a PDMS-MDP with a dome diameter of about 30 μm; then double-sided tape was attached around the solid PDMS block, and a PVC film was used as an adhesive layer to tightly adhere to the PDMS-MDP to form a PVC-MDP ( Figure 1 d).

[0043] Figure 2 Flow chart of clean transfer of MoS2 / WSe2 heterojunction in Example 1. Figure 2 It can be seen that the realization of clean transfer of MoS2 / WSe2 heterojunction mainly includes the following steps: pick up the h-BN auxiliary layer with PVC-MDP ( Figure 2 i, ii); Pick up h-BN / MoS2 with PVC-MDP ( Figure 2 iii,iv); Pick up h-BN / MoS2 / WSe2 with PVC-MDP ( Figure 2 v, vi); release h-BN / MoS2 / WSe2 to the target substrate ( Figure 2 vii, viiii); remove the h-BN auxiliary layer using PVC-MDP ( Figure 2 ix,x).

[0044] Figure 3 This is an optical microscope image of a MoS2 / WSe2 heterojunction transferred to a Si / SiO2 substrate using the method in Example 1. Figure 3 It can be seen that the surface of the MoS2 / WSe2 heterojunction transferred by the method of the present invention is clean and flat.

[0045] Figure 4 for Figure 3 Atomic force microscope image of MoS2 / WSe2 heterojunction. Figure 4It can be further proved that the MoS2 / WSe2 heterojunction transferred by the method of the present invention has an atomically clean surface with a root mean square roughness of only 1.1 nm (solid line box area).

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

[0047] In summary, the present invention provides a two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer. The specific method is: prepare PVC-MDP on a glass slide; pick up the h-BN auxiliary layer with PVC-MDP; pick up the h-BN / two-dimensional heterojunction with PVC-MDP; release the h-BN / two-dimensional heterojunction to the target substrate; remove the h-BN auxiliary layer. Among them, the introduction of the h-BN auxiliary layer avoids direct contact between the polymer and the target heterojunction, thereby avoiding polymer contamination at the source. The two-dimensional heterojunction transferred by the transfer method of the present application has 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 methods of the present invention. Any modifications, equivalent substitutions and improvements within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer, characterized in that: The method comprises the following steps: S1: Prepare microdome-shaped polymer (MDP) using polydimethylsiloxane (PDMS), pour PDMS base and curing agent into a plastic beaker at a mass ratio of 10:1, stir the mixture thoroughly and pour it into a plastic culture dish, then put it into a vacuum dryer for degassing to obtain a bubble-free liquid PDMS mixture (hereinafter referred to as liquid PMDS); S2: the liquid PMDS in step S1 is divided into two parts, one of which is cured at 60° C. for 6 to 8 hours to obtain solid PDMS (hereinafter referred to as solid PDMS); S3: Take a 1 cm × 1 cm square from the solid PDMS in step S2 and place it on a glass slide; S4: Use a toothpick, tweezers and a tungsten needle (needle tip diameter is about 5 μm) to drop another portion of liquid PMDS in step S2 on the center of the solid PDMS block, and cure it at 150°C for 2-3 min to obtain a PDMS-MDP with a dome diameter of about 30 μm; S5: Double-sided tape is attached around the solid PDMS square, and then a polyvinyl chloride (PVC) film is used as an adhesive layer to tightly adhere to the PDMS-MDP to form a PVC-MDP; S6: Use mechanical exfoliation to exfoliate the van der Waals auxiliary layer (h-BN nanosheets) and the target heterojunction material (MoS2 and WSe2 nanosheets) from the bulk crystal onto Si / SiO2 substrate 1, substrate 2, and substrate 3, respectively; S7: using the PVC-MDP in step S5 to sequentially pick up the h-BN, MoS2 and WSe2 nanosheets on Si / SiO2 substrates 1, 2 and 3 at 50-70°C, and then slowly release the h-BN / MoS2 / WSe2 to the target substrate at 100-150°C; S8: Use 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.

2. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: The mass ratio of the PDMS base and the curing agent in step S1 is 10:

1.

3. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: The vacuum degree of the liquid PDMS degassing treatment in step S1 is 0.1 Pa, and the time is 3 to 5 hours.

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

5. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: The size of the solid PDMS block in step S3 is 1 cm×1 cm.

6. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: The tools for dripping the liquid PMDS in step S4 are toothpicks, tweezers and tungsten needles, respectively. The curing temperature of the liquid PMDS is 150° C., and the curing time is 2 to 3 minutes.

7. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: The adhesion layer of the PDMS-MDP in step S5 is a PVC film.

8. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: The tool used for obtaining the nanosheets by the mechanical exfoliation method in step S6 is a blue film tape, the van der Waals auxiliary layer is h-BN, the exfoliation temperature is 70-90° C., and the heating time is 1-2 min.

9. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: In step S7, the temperature at which the PVC-MDP picks up the nanosheets is 50-70°C, and the picking-up speed is greater than 30 μm / s; the temperature at which the PVC-MDP releases the nanosheets is 100-150°C, and the releasing speed is less than 3 μm / s.

10. The two-dimensional heterojunction clean transfer technology based on van der Waals auxiliary layer according to claim 1, characterized in that: When the PVC-MDP in step S18 slides to remove the h-BN auxiliary layer, it only contacts the h-BN area at the bottom without MoS2 / WSe2, and the sliding operation temperature is 100°C and the speed is 10 μm / s.

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