Patterned graphene second harmonic generation method

Abstract

The embodiment of the invention provides a method for generating second harmonics of patterned graphene. The method comprises the following steps: forming a graphene thin layer on a substrate with a groove structure; and using ultrafast laser pulses to excite graphene second harmonics at the suspended edge at the trench structure region of the substrate and generate patterned second harmonics. According to the patterned graphene second harmonic generation method provided by the embodiment of the invention, the graphene on the suspended edge of the groove structure is excited through the ultrafast laser pulse, so that patterned second harmonic generation can be efficiently and accurately realized. The embodiment of the invention also provides a graphene structure.

Description

Technical Field

[0001] The present application belongs to the field of optical material technology, and in particular relates to a method for generating second harmonics of patterned graphene. 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. The most direct way to modulate SHG in two-dimensional materials is to apply mechanical strain, that is, to apply strain by bending or twisting the substrate, which will change the lattice symmetry of the material, thereby enhancing its second-order polarizability and significantly improving the intensity of the second harmonic. However, strain-induced SHG enhancement is often hindered by problems such as uneven strain distribution, which limits the ability to achieve large-scale patterned SHG enhancement. Therefore, in order to overcome the challenges associated with strain engineering, it is urgent to develop new technologies that can achieve controllable and patterned SHG enhancement. Graphene, with its good electrical, mechanical flexibility and optical properties, stands out among two-dimensional materials and becomes an effective medium for manipulating nonlinear optical phenomena. Summary of the invention

[0004] In view of the problems existing in the above-mentioned related technologies, the present invention provides a method for generating second harmonics of patterned graphene, which can efficiently and accurately generate second harmonics of patterned graphene by exciting the suspended edges of graphene with ultrafast laser pulses.

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

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

[0007] Ultrafast laser pulses are used to excite the second harmonic of the dangling edge graphene at the trench structure region of the substrate and generate patterned second harmonics.

[0008] Furthermore, the step of forming a graphene thin layer on a substrate having a groove structure comprises:

[0009] Preparing the graphene thin layer on a substrate;

[0010] The graphene thin layer is transferred to the substrate having the groove structure.

[0011] Furthermore, the step of transferring the graphene thin layer to the substrate having the groove structure comprises:

[0012] forming a support layer / graphene composite structure on the substrate having the graphene thin layer formed thereon;

[0013] Peeling the support layer / graphene composite structure off the base and transferring it to the substrate having the groove structure; and

[0014] The support layer is removed.

[0015] Furthermore, the support layer is a pyrolytic adhesive tape or PDMS.

[0016] Furthermore, the cross-sectional shape of the holes formed by the groove structure of the substrate is circular, triangular, square or Hall pattern.

[0017] Furthermore, the length or width of the hole formed by the groove structure of the substrate is between 1 and 40 μm, and the depth is between 1 and 10 μm.

[0018] Furthermore, the base or the substrate is made of SiO 2 / Si、AlO 3 Or made of Si.

[0019] Furthermore, the substrate is a wafer-level substrate with a size of 5×5 mm.

[0020] Furthermore, the ultrafast laser pulse is emitted by a picosecond or femtosecond infrared laser, and the infrared wavelength of the ultrafast laser pulse is between 800 and 2000 nm.

[0021] 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.

[0022] In the method for generating the second harmonic of patterned graphene provided in the embodiment of the present application, when a graphene thin layer is formed on a substrate having a groove structure, a graphene suspended sample located on the hole structure is obtained, thereby ensuring that the suspended state of graphene on the substrate hole meets the requirements, creating good conditions for subsequent second harmonic excitation. Then, an ultrafast laser pulse is used to excite the second harmonic generation at the edge of the suspended graphene hole, and the second harmonic is generated along the suspended edge graphene covered on the hole. By controlling the shape of the groove structure of the substrate, the generation of patterned second harmonics can be further achieved. Therefore, the method for generating the second harmonic of patterned graphene provided in the embodiment of the present application, by exciting the suspended edge graphene with an ultrafast laser pulse, can efficiently and accurately achieve the generation of the second harmonic of patterned graphene. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] 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.

[0024] Figure 1 A schematic flow chart of a method for second harmonic generation of patterned graphene provided in an embodiment of the present application;

[0025] Figure 2 A schematic diagram of the preparation process and structural characterization of suspended few-layer graphene on a circular hole array provided in Example 1 of the present application;

[0026] Figure 3 This is a schematic diagram of the process of second harmonic generation in strain-induced graphene near the edge of a circular hole in a substrate provided in Example 1 of the present application.

[0027] Figure 4 A schematic diagram of atomic force microscopy (AFM) characterization of graphene suspended above a circular hole in a substrate provided in Example 1 of the present application;

[0028] Figure 5 A schematic diagram of Raman and second harmonic generation images corresponding to graphene above the hole array provided in Example 1 of the present application;

[0029] Figure 6 A schematic diagram of the second harmonic generation enhancement phenomenon of a single-layer graphene at the edge of a hole provided in Example 2 of the present application;

[0030] Figure 7 A schematic diagram of the second harmonic generation phenomenon induced by strain of ABA-stacked three-layer graphene (3LG) at the edge of a substrate hole provided in Example 3 of the present application;

[0031] Figure 8 Schematic diagram of the second harmonic generation enhancement phenomenon of graphene near the hole of the Hall structure provided in Example 4 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 present application embodiment provides a method for second harmonic generation of patterned graphene, comprising the following steps:

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

[0038] S102: using an ultrafast laser pulse to excite the second harmonic of the suspended edge graphene in the groove structure region of the substrate and generate patterned second harmonic.

[0039] Specifically, when a graphene thin layer is formed on a substrate with a groove structure, a graphene suspended sample located on a hole structure is obtained, thereby ensuring that the suspended state of graphene on the substrate hole meets the requirements, creating good conditions for subsequent second harmonic excitation. Then, an ultrafast laser pulse is used to excite the second harmonic generation at the edge of the suspended graphene hole, and the second harmonic is generated along the graphene at the edge of the hole. By controlling the shape of the groove structure of the substrate, the generation of patterned second harmonics can be further achieved. Therefore, the method for generating second harmonics of patterned graphene provided in the embodiment of the present application can efficiently and accurately achieve the generation of second harmonics of patterned graphene by exciting strained graphene at the suspended edge with an ultrafast laser pulse.

[0040] Further, in some embodiments of the present application, the step of forming a graphene thin layer on a substrate having a groove structure includes:

[0041] Preparing the graphene thin layer on a substrate;

[0042] The graphene thin layer is transferred to the substrate having the groove structure.

[0043] Specifically, for example, a thin-layer graphene sample can be obtained on a substrate by mechanical exfoliation 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 a groove structure prepared in advance, thereby preparing for the subsequent patterned generation of the second harmonic of the graphene thin layer.

[0044] Further, in some embodiments of the present application, the step of transferring the graphene thin layer to the substrate having the groove structure comprises:

[0045] forming a support layer / graphene composite structure on the substrate having the graphene thin layer formed thereon;

[0046] Peeling the support layer / graphene composite structure off the base and transferring it to the substrate having the groove structure; and

[0047] The support layer is removed.

[0048] Specifically, the support layer provides a stable support for the transfer of the low-dimensional material. For example, a support layer / graphene composite structure can be formed on the substrate surface by spin coating technology, and the composite structure can be completely peeled off from the substrate by wet transfer technology and accurately transferred to a pre-prepared substrate (e.g., SiO 2 / Si) surface, and then remove the supporting layer, so as to transfer the graphene thin layer to a substrate with a groove structure prepared in advance, so as to prepare for the subsequent enhancement of the second harmonic of the graphene thin layer.

[0049] Further, in some embodiments of the present application, the support layer is a pyrolytic tape or PDMS.

[0050] Specifically, there are also multiple options for the support layer. Thermal cleavage tape can provide stable support during the graphene transfer process due to its good adhesion and cleavability. PDMS (polydimethylsiloxane) has also become one of the ideal choices for the support layer for cleavage due to its unique physical and chemical properties, such as softness and chemical stability. Thermal decomposition tape or thermal dissociation tape, also known as high-temperature decomposition tape or foaming tape, uses polyester film as a substrate and is coated with a special pressure-sensitive adhesive, such as PMMA (Polymethyl Methacrylate). PMMA film is a polymer film with high transparency, good mechanical strength, and strong weather resistance. Polystyrene film is a film material made of polymer material polystyrene (PS) with good light transmittance and mechanical properties. The thickness of the porous organic film layer is between 100 nanometers and 5 microns, thereby ensuring that the low-dimensional material can be stably transferred to the suspended structure or hole structure. PDMS is a polymer compound with many unique physical and chemical properties, such as hydrophobicity, air permeability, chemical stability, physiological inertness, etc. As mentioned above, the support layer is made of PDMS, and the thickness of the support layer is between 0.4 mm and 3 mm, so that it can provide stable support for the transfer of low-dimensional materials, and then on the basis of ensuring the integrity of the low-dimensional materials or samples, the samples can be efficiently transferred to the suspended structure or hole structure, and a clean suspended sample can be obtained by removing the support layer.

[0051] 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 affecting the generation effect of the second harmonic and the patterned presentation to a certain extent.

[0052] 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.

[0053] Furthermore, in some embodiments of the present application, the length or width of the hole formed by the groove structure of the substrate is between 1 and 40 μm, and the depth is between 1 and 10 μm. The setting of this size range is based on an in-depth study of the properties of graphene materials and the principle of second harmonic generation. The appropriate length and width range helps to optimize the suspended state of graphene on the hole and the interaction effect with the laser. The hole depth can be controlled between 1 and 10 μm. The change in hole depth will affect the interaction strength between graphene and the substrate, and plays an important role in the generation efficiency of the second harmonic and the patterning accuracy.

[0054] Further, in some embodiments of the present application, the base or the substrate is made of SiO 2 / Si、AlO 3 The material of the base or substrate will have different effects on the interaction between graphene and the substrate due to its own characteristics, and the specific material of the base is selected according to the actual situation.

[0055] Furthermore, in some embodiments of the present application, the substrate is a wafer-level substrate with a size of 5×5 mm. That is, the method for generating second harmonics of patterned graphene provided in the embodiments of the present application can be applied to wafer-level devices, thereby achieving stable preparation of second harmonics of patterned graphene, and providing a technical basis for graphene optical applications, development of new optoelectronic devices, and the like.

[0056] Furthermore, in some embodiments of the present application, the ultrafast laser pulse is emitted by a picosecond or femtosecond infrared laser, and the infrared wavelength of the ultrafast laser pulse is between 800 and 2000 nm.

[0057] Specifically, the ultrafast laser source selects a picosecond or femtosecond infrared laser. Picosecond and femtosecond laser pulses have extremely short pulse widths, can provide high-intensity energy in an instant, interact more violently with graphene and have unique time-resolved characteristics, which helps to achieve efficient second harmonic excitation. The infrared wavelength can be adjusted between 800-2000nm. Different infrared wavelengths correspond to different photon energies, and the way they interact with the electronic structure of graphene is also different. By accurately selecting the wavelength, the second harmonic generation efficiency and patterning effect can be optimized.

[0058] For example, in one embodiment of the present application, a 20×20 mm SiO / Si substrate is sequentially placed in acetone, ethanol, and deionized water, and ultrasonically cleaned for 15 minutes to remove organic pollutants on the surface. The substrate surface is blown dry with nitrogen, and then placed in a plasma cleaning machine for plasma cleaning for 5 minutes in an oxygen atmosphere to further remove impurities remaining on the surface and ensure the cleanliness of the substrate surface.

[0059] After pretreatment, SiO 2 On the surface of the Si substrate, a layer of photoresist is spin-coated at 3000 rpm using a coating machine for 30 seconds, so that the photoresist evenly covers the substrate surface with a thickness of about 1 μm. The substrate with the photoresist spin-coated is baked on a hot plate at 115°C for 5 minutes to remove the solvent in the photoresist. Using professional photolithography design software, a pattern containing only one circular hole is designed, and the diameter of the circular hole is set to 4 μm.

[0060] The designed circular hole pattern is accurately exposed to the photoresist through high-precision lithography equipment, with an exposure dose of 200mJ / cm 2 , the exposure time is 4 seconds. Put the exposed substrate into the developer for 60 seconds, shake the substrate gently to make the developer fully contact with the photoresist, remove the photoresist of the exposed part, and form a photoresist mask. Rinse the substrate with deionized water 3 times, 30 seconds each time, remove the residual developer, and then blow dry with nitrogen.

[0061] Using advanced plasma etching technology and photoresist mask as a precise template, SiO 2 / Si substrate is etched. Etching gas is SF 6 and O 2 The mixed gas (volume ratio is 10:1), the etching power is 100W, and the etching time is 5 minutes to form a single circular hole structure with a depth of 1μm. Use a professional debonding agent to soak the substrate in the debonding agent for 10 minutes to remove the remaining photoresist. Rinse the substrate with deionized water 5 times, 30 seconds each time to remove the residual debonding agent, and then blow dry with nitrogen to obtain a substrate with a single specific circular hole structure.

[0062] Using delicate mechanical exfoliation, graphene flakes were carefully peeled off from high-quality graphite crystals using adhesive tape. The exfoliated graphene flakes were transferred to clean Si / SiO 2 On the substrate, the shape and size of graphene were observed by optical microscope, and graphene flakes with larger area and more complete were preliminarily selected. The selected graphene flakes were characterized by Raman spectrometer, and the number of graphene layers was determined according to the position, intensity and half-height width of the G peak and 2D peak in the Raman spectrum, and finally three-layer graphene was obtained.

[0063] Use pyrolytic tape as the support layer and carefully stick the pyrolytic tape on the surface of the three-layer graphene to ensure that the tape is in full contact with the graphene. Use tweezers to pull the pyrolytic tape with the three-layer graphene from the Si / SiO 2 The substrate is gently lifted up and then aligned with the SiO 2 / Si substrate, slowly put it down so that the three-layer graphene covers the circular hole accurately. Heat it at 80℃ for 5 minutes on a hot plate to make the pyrolytic tape fit better with the substrate, and then carefully peel off the pyrolytic tape from the surface of the three-layer graphene to obtain a three-layer graphene sample located on a single circular hole.

[0064] Turn on the picosecond infrared laser and set its output wavelength precisely to 1064nm, pulse width to 100fs, and repetition frequency to 80MHz. The beam output by the laser is expanded, collimated, and focused through a beam expander, collimator, and focusing lens in sequence, so that the beam is focused to a spot with a diameter of about 1μm, which can be accurately focused on the edge of a single circular hole in the suspended three-layer graphene. The substrate with the suspended three-layer graphene sample is firmly placed on a high-precision three-dimensional mobile platform. The sample is observed through a high-power optical microscope, and the position of the three-dimensional mobile platform is precisely adjusted so that the laser focus point accurately falls on the three-layer graphene at the edge of a single circular hole.

[0065] Turn on the high-sensitivity spectrum analyzer to monitor the intensity and spectral distribution of the second harmonic signal in real time and accurately. Adjust the scanning path and power of the laser and conduct multiple experiments. The scanning path adopts a spiral scanning method from the center of the hole edge to the outside, and the scanning range is a circular area with a radius of 5μm with the center of the hole as the center. After multiple experiments and parameter optimization, it was found that when the laser power is 20mW·μm-2 and the scanning speed is 0.1μm / s, a clear and stable second harmonic signal can be obtained.

[0066] Record the second harmonic signal intensity and spectral distribution data at different positions and powers. Analyze the collected data in detail, plot the variation curve of the second harmonic signal intensity with laser power and scanning position, and study the second harmonic generation characteristics of three-layer graphene on a single circular hole, including the intensity, spectral shape, polarization dependence, etc. of the second harmonic signal.

[0067] In the following, refer to Figures 2 to 8 Embodiments 1 to 4 describe in detail the method for generating the patterned second harmonic of graphene provided by the embodiments of the present application according to different situations:

[0068] Embodiment 1

[0069] Reference Figures 2 to 5 In the first embodiment, a SiO 2 / Si substrate. This substrate is widely used in the semiconductor field, has good flatness and stability, and can provide a reliable basis for subsequent experiments. Using professional photolithography design software, the design contains a circular hole (round hole) pattern. The diameter of the circular hole is 4μm, and the center spacing between adjacent holes is 15μm.

[0070] First, SiO 2The SiO2 / Si substrate is cleaned and pretreated in a standard manner to remove impurities and contaminants on the surface. Then, a layer of photoresist is evenly spin-coated on the substrate surface, and the designed hole pattern is exposed to the photoresist through a photolithography device. Next, a developer is used to remove the exposed part of the photoresist to form a photoresist mask. Using plasma etching technology, the SiO2 / SiO2 substrate is etched using the photoresist mask as a template. 2 The Si substrate is etched to form a hole structure with a depth of 5 μm. Finally, a stripper is used to remove the remaining photoresist to obtain a substrate with a specific hole structure.

[0071] PDMS was selected as the support layer. The PDMS prepolymer and curing agent were mixed in a ratio of 10:1, poured into the mold, and cured at 80°C for 2 hours to obtain a PDMS film with a thickness of about 1 mm. The graphene flakes were peeled off from the high-quality graphite crystal by mechanical exfoliation and transferred to a clean SiO2 using PDMS. 2 / Si substrate. Through optical microscopy and Raman spectroscopy characterization, the few-layer graphene suspended hole array film was screened to ensure its integrity and uniformity.

[0072] A picosecond infrared laser was selected, with an output wavelength of 1064nm, a pulse width of 100fs, and a repetition frequency of 80MHz. The beam output by the laser was expanded, collimated, and focused through a series of optical elements so that it was focused on the graphene at the edge of the hole. The substrate with the suspended graphene sample was placed on a high-precision three-dimensional mobile platform, and the sample position was precisely adjusted through a microscope so that the laser focus point fell accurately on the graphene at the edge of the hole. The intensity and spectral distribution of the second harmonic signal were monitored in real time using a spectrometer. The patterned excitation of the second harmonic was achieved by controlling the scanning path and power of the laser. During the experiment, it was found that when the laser power was 15mW·μm-2 and the scanning speed was 0.1μm / s, a clear patterned second harmonic signal could be obtained.

[0073] Refer again Figures 2 to 5 , Figure 2 This is a schematic diagram of the preparation process and structural characterization of suspended few-layer graphene on a circular hole array provided in Example 1 of the present application. Figure 2 Figure a shows a schematic diagram of the complete preparation process, showing in detail the SiO 2 Figure 1 shows a process of preparing a circular hole array on a Si / Si substrate and preparing suspended few-layer graphene on the circular holes using an oxygen plasma-assisted cleavage method. Figure b shows an optical image of the few-layer graphene cleaved on the circular holes. Figure c is a scanning electron microscope (SEM) image of Figure b at an oblique angle, which shows the structural morphology of the circular holes and the suspended few-layer graphene across the hole array area.

[0074] Figure 3The second harmonic generation in the strain-induced graphene near the edge of the substrate hole provided in Example 1 of the present application. Figure 3 In the figure, Figure a is a schematic diagram of a strained few-layer graphene sample placed on a hole array substrate, which shows the process of generating second harmonics (visible light) at the edge of the hole when excited by an ultrafast laser pulse (infrared light). Figure b is a scanning electron microscope (SEM) image of Figure a at an oblique angle, showing the strained graphene on the hole array substrate. Figure c is a side view schematic of the graphene above a single substrate hole, which illustrates the induced strain on the graphene at the edge of the hole (gray gradient area, the inset in Figure c shows a cross-sectional SEM image of the graphene on a single hole.

[0075] Figure 4 This is a schematic diagram of atomic force microscopy (AFM) characterization of graphene suspended above a circular hole provided in Example 1 of the present application. Figure 4 In the figure, Figure a is a 3D AFM image of suspended graphene above a circular hole acquired in contact mode. Due to the local pressure applied by the atomic force microscope probe during the scanning process, the graphene surface presents a distinct concave morphology. Figure b is an AFM cross-sectional image across the center of the suspended graphene.

[0076] Figure 5 The Raman and second harmonic generation images corresponding to the graphene on the hole array provided in Example 1 of the present application are shown in FIG. Figure 5 Figure a is an optical image of graphene on a hole array substrate. Figure b is the 2D peak to G peak intensity ratio (I 2D / I G Figure c is a second harmonic generation mapping image of graphene on a hole array substrate, which highlights the enhanced second harmonic signal due to the irregular strain near the hole edge.

[0077] Depend on Figures 2 to 5 It can be seen that the method for generating the patterned second harmonic of graphene provided in the first embodiment of the present application can efficiently and accurately generate the second harmonic of patterned graphene by exciting the suspended edge graphene with ultrafast laser pulses.

[0078] Embodiment 2

[0079] Reference Figure 6 In the second embodiment, a SiO 2 / Si substrate. Using professional photolithography design software, a pattern containing only one circular hole was designed. The diameter of the circular hole was set to 4μm. 2The Si substrate is subjected to comprehensive and standard cleaning and pretreatment steps to completely remove impurities and contaminants on the surface and ensure the cleanliness of the substrate surface. Subsequently, a layer of photoresist is evenly spin-coated on the substrate surface, and the designed circular hole pattern is accurately exposed to the photoresist through high-precision photolithography equipment. Next, the exposed part of the photoresist is carefully removed using a matching developer to form a photoresist mask.

[0080] Using advanced plasma etching technology and photoresist mask as a precise template, SiO 2 The / Si substrate is etched to form a single circular hole structure with a depth of 1μm. Finally, a professional photoresist is used to remove the remaining photoresist to obtain a substrate with a single specific circular hole structure.

[0081] Pyrolytic tape was used as the support layer. Graphene flakes were carefully peeled off from high-quality graphite crystals using a fine mechanical exfoliation method. After multiple operations and screening, single-layer graphene was finally obtained. The single-layer graphene was fully tested for second harmonic generation to ensure its integrity and uniformity, and a single-layer graphene sample located on a single circular hole was obtained.

[0082] A picosecond infrared laser with excellent performance is selected, with an output wavelength precisely set to 1064nm, a pulse width of 100fs, and a repetition frequency of 80MHz. The laser output beam is expanded, collimated, and focused through a series of optical elements, so that it can be precisely focused on the edge of a single circular hole in the suspended monolayer graphene.

[0083] The substrate with the suspended single-layer graphene sample is firmly placed on a high-precision three-dimensional moving platform, and the sample position is precisely adjusted using a high-power microscope to ensure that the laser focus point falls accurately on the single-layer graphene at the edge of a single circular hole.

[0084] A highly sensitive spectrum analyzer is used to monitor the intensity and spectral distribution of the second harmonic signal in real time and accurately. During the experiment, the scanning path and power of the laser are carefully controlled to achieve accurate excitation of the second harmonic. After many experiments and parameter optimization, it is found that when the laser power is 20mW·μm -2 When the scanning speed is 0.1μm / s, a clear and stable second harmonic signal can be obtained. Through detailed analysis of the signal, the second harmonic generation characteristics of single-layer graphene on a single circular hole are deeply studied.

[0085] Refer again Figure 6 , Figure 6 A schematic diagram of the second harmonic generation enhancement phenomenon of a single-layer graphene at the hole edge provided in an embodiment of the present application. Figure 6Figure a is an optical image of a suspended monolayer graphene above a circular hole. Figure b is a schematic cross-sectional view of a suspended monolayer graphene across a hole. Figure c shows the second harmonic generation of a monolayer graphene in three different regions, namely on the substrate (middle curve), on the hole (lower curve), and at the edge of the hole (upper curve), corresponding to the marked points in Figure a. Figure d is a second harmonic generation mapping of a monolayer graphene in the white area in Figure a. Figure 6 It can be seen that the method for generating the second harmonic of patterned graphene provided in the second embodiment of the present application can efficiently and accurately generate the second harmonic of patterned graphene by exciting the suspended edge of graphene with ultrafast laser pulses.

[0086] Embodiment 3

[0087] Reference Figure 7 In the third embodiment, a SiO 2 / Si substrate. Using professional photolithography design software, a pattern containing only one circular hole was designed, and the diameter of the circular hole was precisely set to 4μm. Before the photolithography operation, the SiO 2 / Si substrates undergo comprehensive and standard cleaning and pretreatment steps. This process includes the use of a variety of chemical reagents and physical methods to thoroughly remove impurities and contaminants on the substrate surface, ensuring that the substrate surface reaches an extremely high level of cleanliness.

[0088] Subsequently, a layer of photoresist is evenly spin-coated on the surface of the substrate. The spin-coating process requires strict control of the rotation speed and time to ensure that the thickness of the photoresist is uniform. The designed circular hole pattern is accurately exposed to the photoresist through high-precision lithography equipment. The accuracy of the lithography equipment directly affects the accuracy and resolution of the hole pattern. Next, the exposed part of the photoresist is carefully removed using a matching developer to form a photoresist mask. The development process requires strict control of time and temperature to ensure that the removal effect of the photoresist meets the requirements. Using advanced plasma etching technology, the photoresist mask is used as a precise template to etch the SiO 2 The 3D / Si substrate is etched to form a single circular hole structure with a depth of 1.5 μm. Plasma etching technology can achieve high-precision etching to ensure that the size and shape of the hole meet the design requirements. Finally, a professional debonding agent is used to remove the remaining photoresist to obtain a substrate with a single specific circular hole structure.

[0089] Pyrolytic tape was used as the support layer. Pyrolytic tape has good adhesion and flexibility, and can provide stable support for graphene during the transfer process. A fine mechanical exfoliation method was used to carefully exfoliate graphene flakes from high-quality graphite crystals. Mechanical exfoliation is a commonly used method for preparing graphene. After multiple operations and screening, three-layer graphene is finally obtained. After obtaining the three-layer graphene, a comprehensive second harmonic test was performed on it. During the test, professional testing equipment and methods were used to evaluate the integrity and uniformity of the three-layer graphene to ensure that its quality met the experimental requirements. A three-layer graphene sample located on a single circular hole was obtained.

[0090] A picosecond infrared laser with excellent performance is selected, and its output wavelength is precisely set to 1064nm, the pulse width is 100fs, and the repetition frequency is 80MHz. Picosecond infrared lasers have the characteristics of short pulse width and high repetition frequency, and can provide high-intensity laser pulses, which are suitable for the excitation of second harmonics. The beam output by the laser is expanded, collimated and focused through a series of carefully configured optical elements. Beam expansion can increase the diameter of the beam, collimation can ensure the parallelism of the beam, and focusing can focus the beam to an extremely small spot size, so that it can be accurately focused on the edge of a single circular hole in the suspended three-layer graphene.

[0091] The substrate with the suspended three-layer graphene sample is stably placed on a high-precision three-dimensional mobile platform. The three-dimensional mobile platform can realize the precise movement of the sample in three directions, and the position of the sample is precisely adjusted through a high-power microscope to ensure that the laser focus point accurately falls on the three-layer graphene at the edge of a single circular hole.

[0092] A highly sensitive spectrum analyzer is used to monitor the intensity and spectral distribution of the second harmonic signal in real time and accurately. The spectrum analyzer can detect slight changes in the second harmonic signal and analyze it in detail. During the experiment, the second harmonic was accurately excited by finely controlling the scanning path and power of the laser. The control of the scanning path can detect the second harmonic signal at different positions, and the control of the power can adjust the intensity of the second harmonic signal. After many experiments and parameter optimization, it was found that when the laser power was 15mW·μm-2 and the scanning speed was 0.1μm / s, a clear and stable second harmonic signal could be obtained.

[0093] Refer again Figure 7 , Figure 7 A schematic diagram of the second harmonic generation phenomenon induced by strain in ABA stacked three-layer graphene (3LG) at the edge of a substrate hole provided in an embodiment of the present application. Figure 7In the figure, Figure a is a simulated surface displacement map of three-layer graphene on a single circular hole under slight surface pressure, where the graphene edge is fixed and the dotted line represents the circular hole area. Figure b is a second harmonic generation mapping map of the ABA-stacked three-layer graphene above the circular hole, which shows that the enhanced second harmonic signal is concentrated around the strained edge of the hole. Figure c is a schematic comparison of the second harmonic generation of the strained three-layer graphene at the hole edge (upper curve) and the three-layer graphene on the substrate (middle curve). No significant second harmonic generation effect was observed in the three-layer graphene on the hole (lower curve). Figure d is a comparison of the second harmonic generation intensity of the strained three-layer graphene at the hole edge (upper curve) and the three-layer graphene on the substrate (lower curve) as a function of power. Figure 7 It can be seen that the method for generating the patterned second harmonic of graphene provided in Example 3 of the present application can efficiently and accurately generate the second harmonic of patterned graphene by exciting the suspended edges of graphene with ultrafast laser pulses.

[0094] Embodiment 4

[0095] Reference Figure 8 In the fourth embodiment of the present application, a SiO 2 / Si substrate. The substrate was ultrasonically cleaned in acetone and ethanol for 15 minutes each to remove oil and organic impurities on the surface, then rinsed with deionized water for several times and dried with nitrogen. The substrate was then placed in a plasma cleaner and treated at 100W for 5 minutes in an oxygen atmosphere to further remove residual contaminants and ensure that the substrate surface reached a very high cleanliness.

[0096] Then, the photoresist is spin-coated and patterned. Use a coating machine to spin-coat the photoresist on the substrate surface, set the speed to 3000rpm, and the time to 30 seconds to form a uniform photoresist layer of about 1μm thick. After spin coating, bake the substrate on a 90℃ hot plate for 5 minutes to enhance the adhesion between the photoresist and the substrate. Use professional photolithography design software to design a pattern containing Hall structure holes, in which the diameter of the key circular hole is precisely set to 4μm, and use high-precision photolithography equipment at 200mJ / cm 2 The pattern is exposed to the photoresist with an exposure dose of and an exposure time of 10 seconds.

[0097] After exposure, the substrate is placed in a developer and developed at 25°C for 60 seconds. Gently shake to ensure uniform development, and remove the exposed part of the photoresist to form a photoresist mask. Then plasma etching technology is used to SF 6 , CHF 4 With O 2The mixed gas is the etching gas, and the etching power is 120W for 15 minutes to form a Hall structure hole with a depth of 1.5μm, ensuring that the hole size and shape meet the design requirements. Finally, the substrate is soaked in a debonding agent for 10 minutes to remove the residual photoresist, and then rinsed with deionized water multiple times and dried with nitrogen to obtain a substrate with a specific Hall structure hole.

[0098] Use pyrolytic tape as the support layer. Carefully stick the pyrolytic tape on the surface of the three-layer graphene to ensure full contact, then use tweezers to lift it up and align it with the SiO2 with the hole in the Hall structure. 2 / Si substrate, slowly lower it so that the three-layer graphene covers the hole accurately. Place the substrate on a hot plate at 80℃ and heat it for 5 minutes. After enhancing the fit, carefully peel off the pyrolytic tape and successfully obtain a three-layer graphene sample located on the hole of the Hall structure.

[0099] Build the laser optical path, turn on the picosecond infrared laser and set the parameters. The light beam passes through the beam expander, collimator and focusing lens in turn, focusing the light beam to a spot with a diameter of about 1μm, and accurately focusing on the edge of the Hall structure hole of the suspended three-layer graphene. Place the substrate with the suspended three-layer graphene sample on a high-precision three-dimensional mobile platform, and accurately adjust the sample position through a high-power microscope so that the laser focus point falls accurately on the target position. Use a high-sensitivity spectrometer to monitor the intensity and spectral distribution of the second harmonic signal in real time and accurately. In the experiment, the scanning path and power of the laser are finely controlled, and the scanning path is based on the Hall structure hole. After many experiments and parameter optimization, it was found that when the laser power is 15mW·μm-2 and the scanning speed is 0.1μm / s, a clear, stable and enhanced second harmonic signal can be obtained.

[0100] Refer again Figure 8 , Figure 8 This is a schematic diagram of the second harmonic generation (SHG) enhancement phenomenon of graphene near the hole of the Hall structure provided in Example 4 of the present application. Figure 8 In Figure 1, Figure a shows optical microscopy images of a single-layer graphene (1LG) and an ABC-stacked three-layer graphene (3LG) placed on the hole of the Hall structure. Figure b shows the Raman mapping of the second harmonic ratio in different regions, showing a significant enhancement in the hole region. Figure c is a mapping of the second harmonic generation, which shows a significant enhancement near the edge of the Hall structure hole. In contrast, neither 1LG nor ABC-stacked 3LG showed obvious second harmonic generation signals in the unstrained region.

[0101] Therefore, Figure 8 It can also be seen that the method for generating the patterned second harmonic of graphene provided in Example 4 of the present application can efficiently and accurately generate the second harmonic of patterned graphene by exciting the suspended edge of graphene with an ultrafast laser pulse.

[0102] 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.

[0103] 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 second harmonic generation of patterned graphene, characterized in that: The following steps are involved: forming a graphene thin layer on a substrate having a groove structure; and Ultrafast laser pulses are used to excite the second harmonic of the dangling edge graphene at the trench structure region of the substrate and generate patterned second harmonics.

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

3. The method according to claim 2, characterized in that The step of transferring the graphene thin layer to the substrate having the groove structure comprises: forming a support layer / graphene composite structure on the substrate having the graphene thin layer formed thereon; Peeling the support layer / graphene composite structure off the base and transferring it to the substrate having the groove structure; and The support layer is removed.

4. The method according to claim 3, characterized in that The support layer is a pyrolytic adhesive tape or PDMS.

5. The method according to claim 1, characterized in that The cross-sectional shape of the holes formed by the groove structure of the substrate is circular, triangular, square or Hall pattern.

6. The method according to claim 5, characterized in that The length or width of the hole formed by the groove structure of the substrate is between 1 and 40 μm, and the depth is between 1 and 10 μm.

7. The method according to claim 2, characterized in that The base or the substrate is made of SiO2 / Si, AlO3 or Si.

8. The method according to claim 7, characterized in that The substrate is a wafer-level substrate with a size of 5×5 mm.

9. The method according to claim 1, characterized in that The ultrafast laser pulse is emitted by a picosecond or femtosecond infrared laser, and the infrared wavelength of the ultrafast laser pulse is between 800 and 2000 nm.

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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