Method for enhancing second harmonic of graphene and graphene structure

Abstract

The embodiment of the invention provides a method for enhancing graphene second harmonics. The method comprises the following steps: forming a graphene thin layer on a substrate with an electrode structure and a groove structure; and applying a bias voltage between the substrate and an electrode structure in contact with the graphene thin layer so as to enhance the second harmonic of the graphene thin layer at the suspended edge at the groove structure region. According to the method for enhancing the second harmonic of the graphene provided by the embodiment of the invention, the strain of the suspended edge graphene is controlled through the electric field, and the strength of the second harmonic of the graphene can be efficiently and remarkably improved. The embodiment of the invention also provides a graphene structure.

Description

Technical Field

[0001] The present application belongs to the technical field of optical materials, and in particular relates to a method for enhancing the second harmonic of graphene and a graphene structure. Background Art

[0002] In the field of modern materials science and optoelectronics, graphene has become the focus of research due to its unique two-dimensional atomic structure and excellent electrical and optical properties. Graphene has extremely high carrier mobility, excellent optical transparency and good mechanical flexibility, which make it show great application potential in many fields, such as high-speed electronic devices, photodetectors, light-emitting diodes, etc.

[0003] Second harmonic generation (SHG) is an important nonlinear optical process that can convert fundamental frequency light into light with twice its frequency. It has a wide range of applications in optical communications, laser technology, bioimaging and other fields. However, due to the low second-order nonlinear optical coefficient of graphene itself, its second harmonic signal is relatively weak, which limits its further expansion in practical applications. Therefore, how to effectively enhance the second harmonic signal of graphene has become a key issue that needs to be solved in this field. Summary of the invention

[0004] In view of the problems existing in the above-mentioned related technologies, the present invention provides a method for enhancing the second harmonic of graphene and a graphene structure, which can efficiently and significantly improve the intensity of the second harmonic of graphene by controlling the electric field of the suspended edge graphene strain.

[0005] In a first aspect, an embodiment of the present application provides a method for enhancing the second harmonic of graphene, comprising the following steps:

[0006] forming a graphene thin layer on a substrate having an electrode structure and a groove structure; and

[0007] A bias voltage is applied between the substrate and an electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge at the groove structure region.

[0008] Furthermore, the substrate is SiO 2 / Si substrate, wherein a bias voltage is applied between the substrate and an electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region, comprising:

[0009] A bias voltage is applied between the Si layer of the substrate and the electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region.

[0010] Furthermore, the bias voltage is between -30 volts and 30 volts.

[0011] Further, after forming the graphene thin layer on the substrate having the electrode structure and the groove structure, the method further comprises:

[0012] Ultrafast laser pulses are used to excite the second harmonic of the graphene thin layer at the suspended edge at the groove structure region.

[0013] Furthermore, the cross-sectional shape of the hole formed by the groove structure of the substrate is circular, triangular, square or Hall pattern, the length or width of the hole is between 1 and 40 μm, and the depth of the hole is between 1 and 10 μm.

[0014] Furthermore, the step of forming a graphene thin layer on a substrate having an electrode structure and a groove structure comprises:

[0015] Preparing the graphene thin layer on a substrate;

[0016] The graphene thin layer is transferred to the substrate having the electrode structure and the groove structure.

[0017] Furthermore, the step of transferring the graphene thin layer to the substrate having the electrode structure and the groove structure comprises:

[0018] forming a PMMA / graphene composite structure on the substrate having the graphene thin layer formed thereon;

[0019] Peeling the PMMA / graphene composite structure off the substrate and transferring it to a substrate having the electrode structure and the groove structure; and

[0020] Remove the PMMA layer.

[0021] Furthermore, before peeling the PMMA / graphene composite structure from the substrate and transferring it to the substrate having the electrode structure and the groove structure, the method further includes:

[0022] Etching the groove structure on the surface of the substrate; and

[0023] An electrode structure is fabricated around the trench structure.

[0024] Furthermore, the substrate is made of SiO 2 / Si、AlO 3 Or made of Si.

[0025] In a second aspect, an embodiment of the present application provides a graphene structure, wherein the graphene structure is made by any of the methods described above.

[0026] In the method for enhancing the second harmonic of graphene provided in the embodiment of the present application, when a graphene thin layer is formed on a substrate having an electrode structure and a groove structure, and ensuring that the graphene thin layer is in full contact with the electrode structure of the substrate, a bias voltage is applied between the substrate and the electrode structure in contact with the graphene thin layer to enhance the strain stretching degree of the graphene in the suspended edge region, so as to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region, thereby improving the generation efficiency of the second harmonic. Therefore, the method for enhancing the second harmonic of graphene provided in the embodiment of the present application can efficiently and significantly enhance the intensity of the second harmonic of graphene by controlling the electric field of the graphene strain at the suspended edge. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0028] Figure 1 A schematic diagram of a flow chart of a method for enhancing the second harmonic of graphene provided in an embodiment of the present application;

[0029] Figure 2 A schematic diagram of the actual operation process of transferring a graphene thin layer onto a substrate involved in the method for enhancing the second harmonic of graphene provided in an embodiment of the present application;

[0030] Figure 3 A schematic diagram of the actual application status and effect of the method for enhancing the second harmonic of graphene provided in Example 1 of the present application;

[0031] Figure 4 A schematic diagram of the actual application status and effects of the method for enhancing the second harmonic of graphene provided in Example 2 of the present application.

[0032] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0035] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, the singular forms of "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0036] See also Figure 1 , the embodiment of the present application proposes a method for enhancing the second harmonic of graphene, comprising the following steps:

[0037] S101: forming a graphene thin layer on a substrate having an electrode structure and a groove structure; and

[0038] S102: applying a bias voltage between the substrate and an electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region.

[0039] Specifically, when a graphene thin layer is formed on a substrate having an electrode structure and a groove structure, and ensuring that the graphene thin layer is in full contact with the electrode structure of the substrate, a bias voltage is applied between the substrate and the electrode structure in contact with the graphene thin layer to enhance the strain stretching degree of the graphene in the suspended edge region, so as to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region, thereby improving the generation efficiency of the second harmonic. Therefore, the method for enhancing the second harmonic of graphene provided in the embodiment of the present application can efficiently and significantly enhance the intensity of the second harmonic of graphene by controlling the electric field of the graphene strain at the suspended edge.

[0040] Further, in some embodiments of the present application, the substrate is a SiO2 / Si substrate, and a bias voltage is applied between the substrate and an electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region, comprising:

[0041] A bias voltage is applied between the Si layer of the substrate and the electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region.

[0042] As described above, when a graphene thin layer is formed on a substrate having an electrode structure and a groove structure, and ensuring that the graphene thin layer is in full contact with the electrode structure of the substrate, a bias voltage is applied between the Si layer of the substrate and the electrode structure in contact with the graphene thin layer to enhance the strain stretching degree of the graphene in the suspended edge region, so as to enhance the second harmonic of the graphene thin layer at the suspended edge in the groove structure region, thereby improving the efficiency of second harmonic generation. Therefore, the method for enhancing the second harmonic of graphene provided in the embodiment of the present application can efficiently and significantly enhance the intensity of the second harmonic of graphene by controlling the electric field of the graphene strain at the suspended edge.

[0043] Furthermore, in some embodiments of the present application, the bias voltage is between -30 volts and 30 volts, thereby ensuring that the strain stretching degree of the graphene in the suspended edge region changes, thereby enhancing the second harmonic of the graphene thin layer at the suspended edge in the groove structure region. The specific value of the bias voltage is selected according to actual conditions and is not limited here.

[0044] Furthermore, in some embodiments of the present application, after forming the graphene thin layer on the substrate having the electrode structure and the groove structure, the method further includes:

[0045] Ultrafast laser pulses are used to excite the second harmonic of the graphene thin layer at the suspended edge at the groove structure region.

[0046] Specifically, by applying a bias voltage and using ultrafast laser pulse excitation, the enhancement of the second harmonic of graphene is achieved. This step has strict requirements on the voltage, laser parameters and excitation mode, and is the core link for enhancing the second harmonic. For example, a bias voltage is applied to both ends of the electrode structure in contact with graphene and the Si layer of the substrate 2, and the voltage is maintained within plus or minus 30V. By precisely controlling the bias voltage, the strain stretching degree of graphene in the suspended edge region is enhanced, thereby improving the efficiency of second harmonic generation. At the same time, a picosecond or femtosecond infrared laser is used as an ultrafast laser source, and its infrared wavelength can be flexibly adjusted between 800-2000nm to excite the transferred graphene for second harmonic. Different laser parameters interact with graphene in different ways, and reasonable selection of parameters helps to achieve efficient enhancement of second harmonics.

[0047] Furthermore, in some embodiments of the present application, the cross-sectional shape of the hole formed by the groove structure of the substrate is circular, triangular, square or Hall pattern. The cross-sectional shape of the hole formed by the groove structure of the substrate will change the stress distribution and electron transmission characteristics of the graphene, thereby having a certain influence on the enhancement effect of the second harmonic of the suspended edge of the graphene.

[0048] Of course, the cross-sectional shape of the hole formed by the groove structure of the substrate may be other shapes, which are not limited here.

[0049] Further, in some embodiments of the present application, the length or width of the hole is between 1 and 40 μm, and the depth of the hole is between 1 and 10 μm. The hole size formed by the groove structure of the substrate will change the stress distribution and electron transmission characteristics of the graphene, thereby having a certain impact on the enhancement effect of the second harmonic of the graphene at the suspended edge. The specific size of the hole is selected according to actual conditions and is not limited here.

[0050] Further, in some embodiments of the present application, the step of forming a graphene thin layer on a substrate having an electrode structure and a groove structure comprises:

[0051] Preparing the graphene thin layer on a substrate;

[0052] The graphene thin layer is transferred to the substrate having the electrode structure and the groove structure.

[0053] Specifically, for example, a thin layer of graphene sample can be obtained on a substrate by mechanical stripping or chemical vapor deposition, and the number of layers of the sample can be controlled between a single layer and dozens of layers according to actual needs. Afterwards, the graphene thin layer is transferred to a substrate with an electrode structure and a groove structure prepared in advance, thereby preparing for the subsequent strengthening of the second harmonic of the graphene thin layer. This process needs to ensure that the graphene is well electrically connected to the substrate and the electrode structure, creating favorable conditions for subsequent electric field modulation.

[0054] Further, refer to Figure 2 In some embodiments of the present application, the step of transferring the graphene thin layer to the substrate having the electrode structure and the groove structure comprises:

[0055] forming a PMMA / graphene composite structure on the substrate having the graphene thin layer formed thereon;

[0056] Peeling the PMMA / graphene composite structure off the substrate and transferring it to a substrate having the electrode structure and the groove structure; and

[0057] Remove the PMMA layer.

[0058] Specifically, PMMA (Polymethyl Methacrylate) film is a polymer film with high transparency, good mechanical strength, strong weather resistance, etc., and polystyrene film is a film material made of polymer material polystyrene (PS) with good light transmittance and mechanical properties. PMMA spin coating technology is used to form a PMMA / graphene composite structure on the substrate surface, and the composite structure is completely peeled off from the substrate using wet transfer technology, and accurately transferred to a pre-prepared substrate with an electrode structure and a groove structure or holes (such as SiO 2 / Si) surface, and then remove PMMA, so as to transfer the graphene thin layer to a substrate with an electrode structure and a groove structure prepared in advance, so as to prepare for the subsequent enhancement of the second harmonic of the graphene thin layer.

[0059] Furthermore, in some embodiments of the present application, before peeling the PMMA / graphene composite structure from the substrate and transferring it to the substrate having the electrode structure and the groove structure, the method further includes:

[0060] Etching the groove structure on the surface of the substrate; and

[0061] An electrode structure is fabricated around the trench structure.

[0062] Specifically, the electrode structure on the substrate is designed to make full contact with the graphene thin layer above, while the groove structure or hole structure is designed to allow the graphene wave layer to be suspended in the air. When an electric field is applied, the strain stretching degree of the graphene in the suspended edge area can be enhanced to enhance the second harmonic of the graphene thin layer at the suspended edge in the groove structure area, thereby improving the efficiency of second harmonic generation.

[0063] Furthermore, the substrate is made of SiO 2 / Si、AlO 3 Or Si, the material of the substrate will have different effects on the interaction between graphene and the substrate due to its own characteristics, and the specific material of the substrate is selected according to the actual situation.

[0064] In the following, refer to Figure 3 and Figure 4 Embodiment 1 to Embodiment 2 describe in detail the method for enhancing the second harmonic of graphene provided by the embodiments of the present application according to different situations:

[0065] Embodiment 1

[0066] Reference Figure 3 In the first embodiment, a SiO2 with a size of 20×20 mm is selected. 2 / Si substrate, placed in acetone, ethanol and deionized water in turn, ultrasonically cleaned for 15 minutes each to completely remove organic pollutants on the surface. Subsequently, the substrate surface was blown dry with nitrogen, and then placed in a plasma cleaner for 5 minutes of plasma cleaning in an oxygen atmosphere to further remove residual impurities and ensure that the substrate surface is clean. On the surface of the pretreated substrate, use a glue spreader to spin-coat photoresist at a speed of 4000rpm for 30 seconds to make the photoresist evenly covered with a thickness of about 1μm. The substrate is then baked on a hot plate at 115℃ for 5 minutes to remove the solvent in the photoresist. Using professional photolithography design software, a pattern containing only one circular hole with a diameter of 4μm is designed. Using high-precision photolithography equipment at 200mJ / cm 2 The pattern is accurately exposed to the photoresist with an exposure dose of 100 and an exposure time of 4 seconds. The exposed substrate is placed in a developer and developed for 60 seconds. During the development, the exposed part of the photoresist is gently shaken to remove the exposed part and form a photoresist mask. After that, it is rinsed with deionized water for 3 times, each time for 30 seconds, and then dried with nitrogen. Plasma etching technology is used to SF 6 and O 2 The mixed gas is an etching gas, the etching power is 100W, and the etching is performed for 5 minutes to form a single circular hole with a depth of 1μm on the substrate. The substrate is then soaked in a stripper for 10 minutes to remove the remaining photoresist, and rinsed with deionized water for 5 times, each for 30 seconds, and finally dried with nitrogen to obtain a substrate with a single circular hole structure.

[0067] The photoresist was then evenly coated at 4000 rpm for 30 seconds using a photoresist spreader. The substrate was then baked on a 115°C hot plate for 5 minutes to remove the solvent from the photoresist. The electrode pattern was designed to match the circular hole and the subsequent graphene position using professional photolithography software. The photoresist was then evenly coated at 200 mJ / cm 2 The electrode pattern is accurately exposed to the photoresist with an exposure dose of 100 nanometers and an exposure time of 4 seconds. The exposed substrate is placed in a developer and developed for 60 seconds. During the development, it is gently shaken to remove the exposed part of the photoresist and form a photoresist mask. After that, it is rinsed with deionized water three times, each for 30 seconds, and then blown dry with nitrogen. On the surface of the substrate with a single circular hole structure, an electron beam evaporation device is used to first evaporate a layer of chromium (Cr) with a thickness of about 5 nanometers as an adhesion layer, and then evaporate a layer of gold (Au) with a thickness of about 20 nanometers to form the prototype of the metal electrode structure.

[0068] The graphene flakes were peeled off from high-quality graphite crystals by mechanical exfoliation with adhesive tape and transferred to clean Si / SiO 2Substrate. Use an optical microscope to preliminarily screen out large and complete flakes, and then use a Raman spectrometer to determine the number of layers based on the G peak and 2D peak information, and finally obtain three-layer graphene. Spin a layer of polymethyl methacrylate (PMMA) on the surface of the obtained three-layer graphene, spin coating at a speed of 1500rpm for 60 seconds, so that PMMA is evenly covered on the graphene surface with a thickness of about 300 nanometers. Place the graphene sample with PMMA spin-coated on a hot plate and heat at 100℃ for 10 minutes to solidify PMMA. Use a micro alignment system to transfer PMMA / graphene. Fix the substrate with a single circular hole structure and prepared electrodes on the stage of the micro alignment system, adjust the focus of the microscope, and clearly observe the electrodes and hole structures on the substrate. At the same time, the substrate with PMMA / graphene is also placed on another platform of the micro alignment system, and the position of graphene is observed through a microscope. Use the high-precision mobile platform of the micro alignment system to accurately adjust the position of PMMA / graphene so that it is accurately aligned with the holes and electrodes on the substrate for transfer. Finally, the sample was immersed in an acetone solution to dissolve and remove PMMA, obtaining a three-layer graphene sample located on a single circular hole and in good contact with the electrode.

[0069] Turn on the picosecond infrared laser, set the output wavelength to 1064nm, the pulse width to 100fs, and the repetition frequency to 80MHz. The light beam is sequentially focused by the beam expander, collimator, and focusing lens into a spot with a diameter of about 1μm, and precisely focused on the edge of a single circular hole in the suspended three-layer graphene. Place the substrate with the sample on a high-precision three-dimensional mobile platform, and adjust the position through a high-power optical microscope to ensure that the laser focus point accurately falls on the three-layer graphene at the edge of the hole. Turn on the high-sensitivity spectrum analyzer to monitor the second harmonic signal in real time.

[0070] Apply a bias voltage (for example, set to 10V, which can be adjusted later according to optimization requirements) to both ends of the electrode structure in contact with graphene and the Si layer of the substrate, turn on the picosecond infrared laser again, keep other parameters unchanged, and excite the second harmonic signal in the same scanning path and method. Monitor the second harmonic signal in real time, compare the second harmonic signal intensity before and after electric field modulation, and find that the signal intensity is improved after electric field modulation.

[0071] Refer again Figure 3 ,exist Figure 3In the figure, Figure a is a schematic diagram of the electrically driven SHG enhancement of graphene at the groove edge compared to the SHG of graphene on the substrate, wherein the SHG at the groove edge is induced by an excitation laser. Figure b is an inclined scanning electron microscope (SEM) image of graphene deposited on a substrate having a predefined microgroove structure and a contact metal electrode structure. Figures cd are the changes in SHG intensity measured at the substrate (see Figure c) and the groove edge (see Figure d) corresponding to the positions of the gray and white dots in Figure b, which show the comparison of the SHG response before and after applying a voltage of V=15V. By comparing Figures c and d, it is found that the second harmonic of the graphene thin layer at the suspended edge in the substrate groove structure region is enhanced. Therefore, the method for enhancing the second harmonic of graphene provided in the embodiment of the present application can efficiently and significantly improve the intensity of the second harmonic of graphene by controlling the electric field of the graphene strain at the suspended edge.

[0072] Embodiment 2

[0073] Reference Figure 4 In the second embodiment, 15×15 mm SiO 2 / Si substrate, which provides a solid foundation for subsequent complex experimental steps with its extensive experience in semiconductor applications and excellent flatness and stability. Using professional lithography design software, a groove pattern with a width of 4μm and a length of 20μm was designed.

[0074] For SiO 2 The Si substrate was cleaned and pretreated in a standard manner. It was ultrasonically cleaned in acetone, ethanol and deionized water for 15 minutes each, dried with nitrogen, and then cleaned in an oxygen atmosphere plasma cleaner for 5 minutes to completely remove surface impurities and contaminants. On the clean substrate surface, photoresist was evenly spin-coated at 3000 rpm for 30 seconds using a photoresist spreader to make the photoresist thickness about 1 μm. The photolithography equipment was used to apply 200 mJ / cm 2 The exposure dose and exposure time of 5 seconds are used to accurately expose the groove pattern to the photoresist, and then the substrate is placed in the developer and developed for 60 seconds. During the development, the exposed part of the photoresist is gently shaken to remove the exposed part and form a photoresist mask. Reactive ion etching technology is used to CF 4 and O 3 The mixed gas (volume ratio is 8:2) is used as the etching gas, the etching power is 120W, the etching time is 8 minutes, and the SiO 2 / Si substrate was etched to form a groove structure with a depth of 5 μm, and finally the substrate was soaked in a stripper for 10 minutes to remove the remaining photoresist, and then rinsed with deionized water for 5 times, each time for 30 seconds, and dried with nitrogen to obtain a substrate with a specific groove structure.

[0075] Electrodes are prepared on a substrate with a groove structure. Using an electron beam evaporation device, a layer of chromium (Cr) with a thickness of about 5 nanometers is first evaporated as an adhesion layer, and the evaporation rate is controlled at 0.5 angstroms per second; then a layer of gold (Au) with a thickness of about 20 nanometers is evaporated at an evaporation rate of 1 angstrom per second. The photoresist is spin-coated again using a coater, and a photoresist mask with an electrode pattern is formed after exposure and development. The unprotected metal is removed by wet etching, and finally the photoresist is removed with a stripper to complete the electrode preparation.

[0076] Graphene flakes were peeled off from high-quality graphite crystals by mechanical exfoliation. Polymethyl methacrylate (PMMA) was spin-coated on the exfoliated graphene flakes at 1500 rpm for 60 seconds to a PMMA thickness of about 300 nm, and then heated on a 100°C hot plate for 10 minutes to cure. The substrate with PMMA / graphene was immersed in a hydrofluoric acid solution to separate the graphene from the original substrate, and then transferred to deionized water for rinsing. Using a micromanipulation device, PMMA / graphene was transferred to a substrate with electrodes and groove structures, and the position was observed and adjusted under an optical microscope to ensure that the graphene was located above the groove structure. Finally, the sample was immersed in an acetone solution to dissolve and remove PMMA, and optical microscopy and Raman spectroscopy were used to characterize and select a few layers of complete and uniform graphene, which was located on the suspended groove array.

[0077] A picosecond infrared laser with an output wavelength of 1064nm, a pulse width of 100fs, and a repetition frequency of 80MHz was selected. The substrate with the suspended graphene sample was placed on a high-precision three-dimensional mobile platform, and the sample position was accurately adjusted through a microscope so that the laser focus point accurately fell on the graphene at the edge of the groove. A bias voltage was applied to both ends of the electrode in contact with the graphene and the Si layer of the substrate, for example, it was first set to 10V, and the graphene in the suspended area was stretched by the electric field, so that the graphene strain was enhanced, thereby enhancing the second harmonic of the graphene. At the same time, a spectrum analyzer was used to monitor the intensity and spectral distribution of the second harmonic signal in real time. After many experiments, it was found that compared with the case when no electric field was applied, the second harmonic signal intensity was improved, and the spectral characteristics also changed significantly, such as the narrowing of the spectral bandwidth and the increase of the peak intensity.

[0078] Refer again Figure 4 , Figure 4 A schematic diagram of the implementation process and effect of electrically driven second harmonic generation enhancement in few-layer graphene at the overlapping edge of double holes provided in the embodiment of the present application. Figure 4In the figure, Figure a is a cross-sectional schematic diagram of an electrically driven SHG enhanced graphene device. Figure b is a surface scanning electron microscope (SEM) image of the graphene device in Figure a. Figure c is the SHG mapping image of Figure b, which compares the spatial distribution of the SHG signal before and after electrical driving, and the SHG intensity along the line profile spanning two adjacent holes, highlighting the modulation effect. Figure d is the simulated shear strain in the FLG suspended above two holes under applied voltages of 0V and 15V. Figure e is an idealized model prediction, which shows how the electric field effectively modulates the shear stress in the graphene bridging region between two circular holes assuming that the substrate is smooth and the graphene edges are fixed. From Figure 4 It can be seen that, compared with the case where no electric field is applied, after the electric field is applied, the second harmonic signal intensity of the suspended edge region of the graphene is improved, and the spectral characteristics also change significantly, such as the narrowing of the spectral bandwidth and the increase of the peak intensity. Therefore, the method for enhancing the second harmonic of graphene provided in the embodiment of the present application can efficiently and significantly improve the intensity of the second harmonic of graphene by controlling the electric field of the suspended edge graphene strain.

[0079] In addition, the embodiment of the present application also provides a graphene structure, which is made by any of the methods described above. The specific preparation method of the graphene structure refers to the above embodiment. Since the specific preparation method of the graphene structure adopts all the technical solutions of all the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here one by one.

[0080] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for enhancing the second harmonic of graphene, characterized in that: The following steps are involved: forming a graphene thin layer on a substrate having an electrode structure and a groove structure; and A bias voltage is applied between the substrate and an electrode structure in contact with the graphene thin layer to enhance the second harmonic of the suspended edge graphene thin layer located in the groove structure region.

2. The method according to claim 1, characterized in that The substrate is a SiO2 / Si substrate, and a bias voltage is applied between the substrate and an electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region, comprising: A bias voltage is applied between the Si layer of the substrate and the electrode structure in contact with the graphene thin layer to enhance the second harmonic of the graphene thin layer at the suspended edge located in the groove structure region.

3. The method according to claim 2, characterized in that The bias voltage is between -30V and 30V.

4. The method according to any one of claims 1 to 3, characterized in that After forming the graphene thin layer on the substrate having the electrode structure and the groove structure, the method further includes: Ultrafast laser pulses are used to excite the second harmonic of the graphene thin layer at the suspended edge at the groove structure region.

5. The method according to claim 1, characterized in that The cross-sectional shape of the hole formed by the groove structure of the substrate is circular, triangular, square or Hall pattern, the length or width of the hole is between 1 and 40 μm, and the depth of the hole is between 1 and 10 μm.

6. The method according to claim 1, characterized in that The step of forming a graphene thin layer on a substrate having an electrode structure and a groove structure comprises: Preparing the graphene thin layer on a substrate; The graphene thin layer is transferred to the substrate having the electrode structure and the groove structure.

7. The method according to claim 6, characterized in that The step of transferring the graphene thin layer to the substrate having the electrode structure and the groove structure comprises: forming a PMMA / graphene composite structure on the substrate having the graphene thin layer formed thereon; Peeling the PMMA / graphene composite structure off the substrate and transferring it to a substrate having the electrode structure and the groove structure; and Remove the PMMA layer.

8. The method according to claim 7, characterized in that Before peeling the PMMA / graphene composite structure from the substrate and transferring it to the substrate having the electrode structure and the groove structure, the method further includes: Etching the groove structure on the surface of the substrate; and An electrode structure is fabricated around the trench structure.

9. The method according to any one of claims 6 to 8, characterized in that The substrate is made of SiO2 / Si, AlO3 or Si.

10. A graphene structure, characterized in that: The graphene structure is made by the method according to any one of claims 1 to 9.

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