Epitaxial preparation method and application of two-dimensional sliding ferroelectric / iron valley heterojunction
The preparation of two-dimensional slip ferroelectric SnSe2 semiconductor and SnSe2/SnSe ferroelectric/ferroval heterojunctions through low-temperature annealing and in-situ epitaxial methods has solved the problem of regulating and obtaining these materials in the prior art, and achieved the growth of large-area heterostructures and the regulation of ferroelectric properties, with wide application prospects.
Patent Information
- Application Number
- CN202510378199.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2025-06-20
AI Technical Summary
The prior art is difficult to effectively regulate and obtain two-dimensional skid ferroelectric SnSe2 semiconductor and SnSe2/SnSe ferroelectric/ferroval heterojunction, and the layer stacking method of vdW heterostructure is difficult to control.
By annealing SnSe single crystal at low temperature, two-dimensional slip ferroelectric SnSe2 semiconductor and SnSe2/SnSe ferroelectric/ferroval heterojunction were prepared by in-situ epitaxial method. The growth conditions were optimized including annealing temperature and time, and the interface characteristics were regulated through in-situ Raman spectroscopy and surface morphology.
The optimized annealing conditions for the large-area vdW epitaxial growth of SnSe2/SnSe heterostructure were achieved, and atomic sharp interfaces and specific orientations were obtained, with the application prospects of ferroelectricity and valley electronics.
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Figure CN120174478A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the in-situ epitaxial growth technology of two-dimensional materials, and particularly to a preparation method and application of two-dimensional sliding ferroelectric SnSe2 semiconductors and SnSe2 / SnSe ferroelectric / ferrovalley heterojunctions. Background Art
[0002] Van der Waals (vdW) heterostructures can exhibit unique condensed matter effects through the vertical integration of two-dimensional (2D) materials. The two-dimensional vdW layered SnSe semiconductor has a high light absorption coefficient, photoelectric effect, in-plane anisotropy, ferrovalley property, in-plane ferroelectricity, etc., and is suitable for photodetectors and photovoltaic applications. SnSe2 with the same elemental composition has a trigonal or hexagonal structure, has good thermoelectric, electrochemical, and excellent optoelectronic properties, and theoretically SnSe2 has sliding ferroelectricity. If SnSe with ferrovalley property and SnSe2 with sliding ferroelectricity are stacked to form a heterojunction, its applications in optoelectronics, thermoelectrics, ferroelectrics, and valley electronics can be effectively regulated. However, due to the multiple configurations of SnSe2 and the difficulty in regulating its layer stacking method, it is relatively difficult to obtain the ferroelectric SnSe2 phase, and there are currently no experimental reports on the regulation and application of its sliding ferroelectricity.
[0003] Generally speaking, constructing vdW heterostructures mainly relies on two methods: top-down stacking and bottom-up growth. The top-down method relies on exfoliating layered materials, which is applicable to a variety of 2D materials, but has limitations in production capacity and scalability. The bottom-up method mainly relies on chemical vapor deposition, but faces problems such as harsh growth conditions and limited selection of 2D materials. At present, although progress has been made in the synthesis of vdW superlattices and heterostructures, obtaining large-area heterostructures with specific orientations still poses a challenge; the in-situ epitaxial formation of vdW heterostructures is an effective strategy to address this challenge. Summary of the Invention
[0004] In view of this, the purpose of the present invention is to provide a method for preparing two-dimensional sliding ferroelectric SnSe2 semiconductors and SnSe2 / SnSe ferroelectric / ferrovalley heterojunctions by annealing SnSe single crystals at low temperature, and to reveal the optimized growth conditions including annealing temperature and time through in-situ Raman spectroscopy and surface morphology analysis, study its interface regulation characteristics through aberration-corrected electron microscopy, and characterize its ferroelectric properties through piezoresponse force microscopy. The invention discloses a method for preparing two-dimensional sliding ferroelectric SnSe2 semiconductors and SnSe2 / SnSe ferroelectric / ferrovalley heterojunctions by in-situ epitaxy, which helps to promote the application of this material in the development of next-generation valley electronic devices, optical anisotropic devices, and new memory-computation integrated devices.
[0005] The technical solution to achieve the purpose of the present invention is as follows: An epitaxial preparation method for a two-dimensional sliding ferroelectric / ferrotropic heterojunction, comprising the following steps: Step 1: Use the tape peeling method to peel the bulk SnSe material to obtain a thin SnSe sample; Step 2: Place the thin sample in Step 1 in the middle temperature zone of a three-temperature zone tube furnace; Step 3: After evacuating the tube furnace in Step 2, introduce oxygen; Step 4: Set the annealing temperature and time, and anneal the sample; Step 5: Take out the sample annealed in Step 4, and use the mechanical peeling method to obtain SnSe2 epitaxially grown from SnSe; Step 6: Characterize the ferroelectric properties of the SnSe2 sample prepared in Step 5; Step 7: Characterize the ferrotropic properties of the SnSe2 sample prepared in Step 5.
[0006] Further, Step 1 specifically includes: placing the bulk SnSe material on a 3M transparent tape, using the tape peeling method, folding and pasting the tape multiple times, gradually thinning the SnSe bulk into thin flakes of different thicknesses, and using tweezers to pick up the flat-surfaced thin sample and place it on a circular iron sheet.
[0007] Further, Step 2 is specifically as follows: A1: Place the SnSe thin flakes on the iron sheet together on the crucible lid, invert the crucible, and close the crucible and the crucible lid; A2: Select a clean quartz furnace tube and a heat insulation plug, and push the entire crucible in A1 into the middle temperature zone of the three-temperature zone tube furnace; A3: Ensure that the entire crucible in A2 is placed horizontally to prevent tilting and collapse, and at the same time seal the openings at both ends of the furnace tube.
[0008] Further, Step 3 specifically includes: B1: The pumping rate of the vacuum pump is 2.2 L / S, and the vacuum degree is 4 - 5×10-1 Pa; B2: Connect the ventilation pipeline and introduce oxygen with a purity of 99.9%; B3: Observe the vacuum gauge on the sealing flange on one side of the furnace tube. When the reading shows 0.01 MPa, close the ventilation valve to ensure that the whole is in a sealed state.
[0009] Further, Step 4 specifically includes: C1: Set the temperature to rise from room temperature to 400 - 500 °C, and the heating time is 1 - 1.5 hours, so the heating rate is 5 °C / min; C2: Set the holding time to 1 - 2 hours, and the temperature control accuracy is ±1 °C; C3: After the heat preservation is completed, cool the sample from the heat preservation temperature to 200 - 150 °C, and set the cooling time to 1 - 1.5 hours; C4: After reaching 200 - 150 °C, allow the sample to cool naturally to room temperature.
[0010] Furthermore, step 5 specifically includes: D1: Place the taken-out annealed sample on a 3M blue film tape (Silicone-Free Adhesive Plastic Films, UST), fold it once and then remove the annealed thin sheet. The epitaxial sample SnSe2 on the surface of the thin sheet remains on the tape; D2: Use a PDMS tape (polydimethylsiloxane, Gel-Pak) to stick it to an obvious and concentrated position of the blue tape material, and press it flat with a flat glass slide or the back end of tweezers so that the sample can adhere to the PDMS tape; D3: Use tweezers to remove the PDMS in D2, stick the back side to a clean glass slide, place it on the left operation table of the microscope, and place a clean silicon wafer (conductive) on the right operation table; D4: Align the focus, find the sample on the PDMS, transfer it to the silicon wafer, and after standing for 5 - 10 minutes, slowly peel off the PDMS so that SnSe2 remains on the silicon wafer.
[0011] Furthermore, step 6 is specifically: The SnSe2 sample on the silicon wafer is pasted on a round iron sheet with conductive carbon paste and silver paste is dotted at the adhesion point, and then placed in a piezoresponse force microscope (PFM) to characterize the ferroelectric characteristics of the sample.
[0012] Furthermore, step 7 is specifically: Use a PDMS tape to transfer the SnSe2 sample on the silicon wafer to a transparent glass substrate, place it in a Fourier transform infrared spectrometer (FTIR), and use polarization transmission technology to characterize the iron valley characteristics of the sample.
[0013] A two-dimensional SnSe2 material obtained by the method based on the above.
[0014] An application of the above two-dimensional SnSe2 material in the field of ferroelectricity.
[0015] The beneficial effects of the present invention: Through the study of the spontaneous formation of SnSe2 on the SnSe surface, the optimized annealing conditions for the large-area vdW epitaxial growth of the SnSe2 / SnSe heterostructure were obtained: annealing temperature ~670 K, holding time 60 min. HAADF-STEM results along two directions showed that the in-situ vdW epitaxially grown SnSe2 / SnSe heterostructure has an atomically sharp interface and a specific orientation. Further analysis of the epitaxial relationship indicated that there are some lattice mismatches during the epitaxial growth of SnSe2 on SnSe. Given the good flexible properties of SnSe2, strain or stress can be relaxed by forming regularly spaced "cracks" or "folds", thus forming a large-area continuous and flat SnSe2 / SnSe vertical heterostructure. It was found by piezoresponse force microscopy characterization that the epitaxially grown two-dimensional SnSe2 semiconductor has the theoretically predicted ferroelectricity, fully demonstrating the unique advantages of this method in regulating the structure and ferroelectricity of two-dimensional sliding ferroelectric SnSe2 semiconductors.
[0016] In addition, based on this structure, the inherently valley polarization effect in anisotropic SnSe naturally constructs an adjustable band alignment covering type-II and type-III, indicating that the SnSe2 / SnSe heterostructure with SnSe2 as a flexible substrate has good application prospects in valley (opto)electronics. As is well known, due to the internal built-in electric field between the SnSe2 / SnSe interfaces, the type-II band alignment can promote the spatial separation of photo-generated electron-hole pairs and has good application prospects in polarization-dependent two-color light detection, especially in photovoltaics with low intrinsic thermal effects. For the type-III band alignment, by adjusting the degeneracy between the intrinsic p-SnSe and n-SnSe2, similar to Esaki diodes, it has advantages for the development of tunnel field-effect transistors and wide-wavelength detectors. At the same time, this polarization-controllable band alignment between type-II and type-III in the vdW heterojunction is gate-tunable, which will be beneficial for achieving positive and negative photoconductivity under polarized line light and achieving a wider light response than single SnSe or SnSe2 through gate control. Simultaneous broadband image sensing and convolutional processing were obtained, improving the recognition accuracy of multi-band images compared with traditional single-band-based convolutional neural networks. As another hot topic outlook, if the intrinsic spontaneous charge polarization (or in-plane ferroelectricity) along the AC direction in orthorhombic layered SnSe is considered, more interesting physical properties such as the anomalous valley-Hall effect of photo-generated carriers can be expected under the action of the in-plane polarization field. Brief Description of the Drawings
[0017] Figure 1 Schematic diagram of the sample annealing method in step 2 of the preparation method of the present invention; Figure 2Schematic diagram of the set oxygen content, annealing temperature and time, and the corresponding epitaxial sample composition mentioned in steps 3 and 4 of the preparation method of the present invention; Figure 3 Cross-sectional transmission electron microscope image of the heterojunction grown epitaxially in the embodiment of the present invention; Figure 4 Selected electron diffraction images corresponding to SnSe and SnSe2 / SnSe respectively in the embodiment of the present invention; Figure 5 Ferroelectric property of the SnSe2 / SnSe heterojunction in the embodiment of the present invention: Schematic diagram of the test results of piezoresponse force microscopy (PFM); Figure 6 Ferrotropic property of the SnSe2 / SnSe heterojunction in the embodiment of the present invention: Schematic diagram of the test results of polarization transmission spectrum; Detailed implementation manners
[0018] The present invention will be described in detail below in conjunction with specific embodiments and the accompanying drawings.
[0019] Embodiment: Preparation of two-dimensional sliding ferroelectric SnSe2 semiconductor and SnSe2 / SnSe ferroelectric / ferrotropic heterojunction, including the following steps: Step 1: Place the bulk SnSe material on a 3M transparent tape. Using the tape peeling method, after folding and pasting the tape multiple times, the SnSe bulk is gradually thinned into thin flakes of different thicknesses. Use tweezers to pick up the relatively flat surface flake sample and place it on a circular iron sheet.
[0020] Step 2: Place the flake sample in step 1 in the middle temperature zone of a three-temperature zone tube furnace (as Figure 1 shown), and the specific steps include: A1: Place the SnSe flake on the iron sheet together on the crucible lid ( Figure 2 a), and invert the crucible, closing the crucible and the crucible lid; A2: Select a clean quartz furnace tube and a heat insulation plug, and push the whole crucible in A1 into the middle temperature zone of the three-temperature zone tube furnace; A3: Ensure that the whole crucible in A2 is placed horizontally to prevent tilting and collapse, and at the same time seal the openings at both ends of the furnace tube.
[0021] Step 3: Perform vacuum treatment on step 2 and introduce oxygen. The specific steps include B1: The pumping rate of the vacuum pump is 2.2 L / S, and the vacuum degree is 4 - 5×10-1 Pa ( Figure 2 b); B2: Connect the ventilation pipeline and input oxygen (CAS-7782-44-7, 3N, 99.9%); B3: Observe the vacuum gauge on the sealing flange on one side of the furnace tube. When the reading shows 0.01 MPa, close the ventilation valve to ensure the overall sealed state.
[0022] Step 4: Set the annealing temperature and time, and perform annealing treatment on the sample; C1: Set the temperature to rise from 25 °C to 400 °C, with a heating time of 75 min, then the heating rate is 5 °C / min; C2: Set the holding time to 60 min, with a temperature control accuracy of ±1 °C; C3: After the holding is completed, cool the sample from 400 °C to 200 °C, and set the cooling time to 60 min; C4: After reaching 200 °C, let the sample cool naturally to room temperature.
[0023] Step 5: Take out the sample annealed in Step 4, and adopt the mechanical exfoliation method to obtain SnSe2 epitaxially grown from SnSe; ( Figure 2 c) The Raman spectroscopy characterization results show that SnSe2 / SnSe thin films with vertical heterostructures are grown ( Figure 2 d), specifically including: D1: Place the taken-out annealed sample on a 3M blue film tape (Silicone-Free Adhesive Plastic Films, UST), fold it once and then remove the annealed thin sheet. The epitaxial sample SnSe2 on the surface of the thin sheet remains on the tape; D2: Use a PDMS tape (polydimethylsiloxane, Gel-Pak) to stick to the position on the 3M blue tape material where it is obvious and there is a large amount. Press it flat with a flat glass slide or the back end of forceps, so that the sample can adhere to the PDMS tape; D3: Use forceps to remove the PDMS in D2, stick the back side to a clean glass slide, place it on the left operation table of the microscope, and place a clean silicon wafer (conductive) on the right operation table; D4: Align the focus, find the appropriate sample on the PDMS, transfer it to the silicon wafer, let it stand for a period of time, and then slowly peel off the PDMS, so that SnSe2 remains on the silicon wafer.
[0024] Step 6: The SnSe2 sample on the silicon wafer in Step 5 is prepared by a focused ion beam microscope (FIB), and transmission electron microscopy observation is carried out to obtain the high-angle annular dark field image of the cross section ( Figure 3 a,b) and the energy spectrum diagrams of Se element ( Figure 3 c,d) and Sn element ( Figure 3 e,f). At the same time, selected area electron diffraction is performed on this FIB sample, and the electron diffraction images of the
[110] crystal orientation in different regions of SnSe and SnSe2 / SnSe can be seen respectively ( Figure 4Electron diffraction images of the
[100] crystal orientation for (a, b) Figure 4 (c, d).
[0025] Step 7: The SnSe2 sample on the silicon wafer in Step 5 is attached to a circular iron sheet using carbon paste (conductive), and silver paste is dotted at the adhesion point. Then it is placed in the PFM to characterize the ferroelectric signal of the sample. Figure 5 Figures (a) and (b) are the amplitude map and phase map respectively.
[0026] Step 8: The SnSe2 sample on the silicon wafer in Step 5 is transferred to a transparent glass substrate using PDMS tape and then placed in a Fourier transform infrared spectrometer (FTIR). The valley polarization characteristics of the sample are characterized using polarization transmission technology. Figure 6 Figure (a) is the polarization transmission spectrum of the SnSe2 / SnSe heterojunction, showing two bandgaps in different directions. The inset shows the corresponding tauc curve, indicating the ferro-valley characteristics of this heterojunction. Figure 6 Figure (b) shows the relationship between this ferro-valley characteristic and the SnSe2 / SnSe stacking structure.
[0027] The ferroelectric / ferro-valley characteristics demonstrated in Steps 7 and 8 fully illustrate the unique advantages of this method in regulating two-dimensional sliding ferroelectric SnSe2 semiconductor structures, ferroelectricity, and in valley (opto)electronics. This invention contributes to the application of this material in the development of next-generation valley electronic devices, optical anisotropic devices, and new memory-computation integrated devices.
Claims
1. A method for epitaxially preparing a two-dimensional slip ferroelectric / iron valley heterojunction, characterized in that: The following steps are involved: Step 1: Use the tape stripping method to strip the bulk SnSe material to obtain a thin SnSe sample; Step 2: Place the thin slice sample in step 1 in the middle temperature zone of the three-temperature zone tube furnace; Step 3: After the tube furnace in step 2 is vacuumized, oxygen is introduced; Step 4: Set the annealing temperature and time to anneal the sample; Step 5: Take out the sample after annealing in step 4, and use mechanical stripping method to obtain SnSe2 generated by SnSe epitaxy; Step 6: characterizing the ferroelectric properties of the SnSe2 sample prepared in step 5; Step 7: Characterize the iron valley properties of the SnSe2 sample prepared in Step 5.
2. The epitaxial preparation method according to claim 1, characterized in that: The step 1 specifically includes: placing the bulk SnSe material on a 3M transparent tape, using the tape stripping method, folding the tape in half multiple times and pasting it, gradually thinning the SnSe bulk into slices of different thicknesses, and using tweezers to take out the slice sample with a flat surface and place it on a round iron sheet.
3. The epitaxial preparation method according to claim 1, characterized in that: The step 2 is specifically as follows: A1: Place the SnSe sheet on the iron sheet on the crucible cover, turn the crucible upside down, and close the crucible and the crucible cover; A2: Select a clean quartz furnace tube and insulation plug, and push the crucible in A1 into the middle temperature zone of the three-temperature zone tubular furnace; A3: Ensure that the crucible in A2 is placed horizontally as a whole to prevent it from tilting and collapsing, and seal the openings at both ends of the furnace tube.
4. The epitaxial preparation method according to claim 1, characterized in that: The step 3 specifically includes: B1: The vacuum pump has a pumping rate of 2.2 L / S and a vacuum degree of 4 ~ 5×10-1 Pa; B2: Connect the ventilation pipe and introduce oxygen with a purity of 99.9%; B3: Observe the vacuum gauge on the sealing flange on one side of the furnace tube. When the reading shows 0.01 MPa, close the ventilation valve to ensure that the whole is in a sealed state.
5. The epitaxial preparation method according to claim 1, characterized in that: The step 4 specifically includes: C1: Set the temperature from room temperature to 400-500℃, the heating time is 1-1.5 hours, and the heating rate is 5℃ / min; C2: Set the insulation time to 1-2 hours, and the temperature control accuracy to ±1°C; C3: After the insulation is completed, the sample is cooled from the insulation temperature to 200-150°C, and the cooling time is set to 1-1.5 hours; C4: After reaching 200-150°C, the sample is allowed to cool naturally to room temperature.
6. The epitaxial preparation method according to claim 1, characterized in that: The step 5 specifically includes: D1: Place the taken out annealed sample on a 3M blue film tape UST, fold it in half once and remove the annealed slice, leaving the epitaxial sample SnSe2 on the slice surface on the tape; D2: Use PDMS tape to stick to the obvious and concentrated position of the material on the blue film tape, and press it flat with a flat glass sheet or the back end of tweezers to make the sample adhere to the PDMS glue; D3: Use tweezers to remove the PDMS in D2, stick the back side to a clean glass sheet, and place it on the left operating table of the microscope. Place a clean silicon wafer (conductive) on the right operating table. D4: Align the focus, find the sample on the PDMS, transfer it to the silicon wafer, let it stand for 5-10 minutes, then slowly peel off the PDMS to leave SnSe2 on the silicon wafer.
7. The epitaxial preparation method according to claim 1, characterized in that: The step 6 is specifically as follows: the SnSe2 sample on the silicon wafer is attached to the round iron sheet by using conductive carbon adhesive and silver paste is applied at the adhesion point, and the sample is placed in a piezoelectric force microscope to characterize the ferroelectric characteristics of the sample.
8. The epitaxial preparation method according to claim 1, characterized in that: The step 7 is specifically as follows: using PDMS tape to transfer the SnSe2 sample on the silicon wafer to a transparent glass substrate, placing it in a Fourier transform infrared spectrometer, and using polarization transmission technology to characterize the iron valley characteristics of the sample.
9. A two-dimensional SnSe2 material obtained by the method according to any one of claims 1 to 6.
10. Use of the material according to claim 9 in the ferroelectric field.