A multilayer graphene terahertz metamaterial structure and preparation method thereof

Abstract

A multilayer graphene terahertz metamaterial structure and its preparation method belong to the field of material preparation. The specific scheme is as follows: A multilayer graphene terahertz metamaterial structure includes a graphene layer, a substrate layer, and a gold thin film layer. The graphene layer is disposed on the upper surface of the substrate layer, and the gold thin film layer is disposed on the lower surface of the substrate layer. The graphene layer includes multiple layers of graphene, each of which includes a plurality of graphene periodic structural units. The growth pattern of the graphene in each graphene periodic structural unit is a 'G'-shaped pattern. The multilayer graphene terahertz material of the present invention utilizes the 'G'-shaped structure of graphene to achieve a change in the distribution of electric and magnetic fields on the graphene surface, thereby achieving response to terahertz electromagnetic waves. At the same time, the "sandwich structure" can achieve multiple reflection and absorption of terahertz waves in the composite structure.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation, and in particular relates to a multi-layer graphene terahertz metamaterial structure and a preparation method thereof. Background Art

[0002] In recent years, the emergence of new two-dimensional materials, such as graphene, vanadium dioxide, and Dirac semimetals, has been applied to the design of terahertz absorbers, greatly enriching the types and functions of terahertz absorbers. The most important of these applications is the use of two-dimensional materials to make terahertz absorbers tunable. However, due to the relatively fixed excitation structural units of single or few layers of two-dimensional materials, their excitation tuning range is limited. Furthermore, the preparation and transfer processes of two-dimensional materials are complex, prone to wrinkles and defects, resulting in low electromagnetic absorption efficiency of two-dimensional terahertz materials. This severely restricts the controllability, stability, and bandwidth of two-dimensional terahertz devices and is not conducive to the development and application of terahertz intelligent tuning devices.

[0003] Currently, research on two-dimensional actively tuned terahertz devices focuses primarily on the structural design of two-dimensional metamaterials, the development of two-dimensional heterojunctions, and the performance of two-dimensional phase-change materials. Among these, research on terahertz devices based on single-layer graphene is widespread. By varying the graphene Fermi level to control the material's conductivity, researchers can achieve absorption of terahertz waves at multiple frequencies. However, single-layer graphene terahertz absorbers suffer from low absorption efficiency and a narrow dynamic adjustment range. To address this bottleneck, researchers have proposed increasing the thickness of graphene to improve terahertz wave absorption efficiency. However, the preparation technology for multilayer graphene terahertz materials is still immature. Therefore, developing a method for preparing multilayer graphene terahertz materials is one of the important approaches to addressing the narrow adjustment range of current devices.

[0004] In summary, the existing graphene terahertz metamaterial preparation process has problems such as preparation difficulty and electromagnetic response insensitivity, and still requires in-depth scientific research. Summary of the Invention

[0005] In order to solve the problems of preparing multi-layer graphene terahertz metamaterials and patterned growth of graphene, the present invention provides a multi-layer graphene terahertz metamaterial structure and a preparation method thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A multilayer graphene terahertz metamaterial structure includes a graphene layer, a substrate layer, and a gold film layer. The graphene layer is arranged on the upper surface of the substrate layer, and the gold film layer is arranged on the lower surface of the substrate layer. The graphene layer includes multiple layers of graphene, and the graphene layer includes a plurality of graphene periodic structural units. The growth pattern of the graphene in each graphene periodic structural unit is a 'G'-shaped pattern.

[0008] Furthermore, the substrate layer is a SiO2 substrate, a sapphire substrate, an intrinsic silicon substrate or a polyimide substrate.

[0009] Furthermore, the 'G'-shaped pattern is composed of a first horizontal structure, a 3 / 4 circular structure and a second horizontal structure that are sequentially connected as one body, and the first horizontal structure and the second horizontal structure are parallel to each other.

[0010] Furthermore, the length of each graphene periodic structure unit is 50-100 μm, the length of the first horizontal structure is equal to that of the second horizontal structure w=10-30 μm; the inner diameter R1 of the 3 / 4 circular structure is 5-25 μm, and the outer diameter R2 is 10-30 μm.

[0011] Furthermore, the difference between the outer diameter and the inner diameter of the 3 / 4 circular structure is 5-25 μm.

[0012] Furthermore, the thickness of the graphene layer is 0.001-0.01 μm, the thickness of the substrate layer is 15-150 μm, and the thickness of the gold thin film layer is 0.5-1.5 μm.

[0013] A method for preparing the multilayer graphene terahertz metamaterial comprises the following steps:

[0014] Step 1: Design and optimize the graphene growth pattern using electromagnetic simulation software;

[0015] Step 2: placing the substrate on a mask having a graphene growth pattern, and vacuum evaporating a patterned copper film on the substrate;

[0016] Step 3: Wrap the outer periphery of the copper film with copper foil, leaving a gap between the copper foil and the copper film, and grow patterned multilayer graphene on the copper film using a chemical vapor deposition method;

[0017] Step 4: coating the surface of the multilayer graphene grown on the copper film with glue and then drying it, etching the copper film with an etching solution, and using a substrate to pick up the coated multilayer graphene;

[0018] Step 5: evaporating a gold film on the side of the substrate away from the multilayer graphene to obtain a glue-coated multilayer graphene / substrate / gold film;

[0019] Step 6: Remove the adhesive layer to obtain a multilayer graphene terahertz metamaterial with a multilayer graphene / substrate / gold film structure.

[0020] Furthermore, in step 2, a mask having a graphene growth pattern is printed out of industrial plastic using 3D printing technology.

[0021] Furthermore, in step three, the gap between the copper foil and the copper film is 0.5-3.5 mm.

[0022] Furthermore, in step 4, the glue is a polymethyl methacrylate solution; and the etching solution includes a combination of one or more of a ferric chloride solution, a dilute sulfuric acid solution, or an ammonium persulfate solution.

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

[0024] The present invention develops a multilayer graphene terahertz metamaterial structure and preparation process. Using electromagnetic simulation technology, graphene is patterned and designed to obtain a terahertz absorption material with a "sandwich structure" of graphene / substrate / gold film. Research results show that the multilayer graphene terahertz material of the present invention utilizes the 'G'-type structure of graphene to achieve a change in the distribution of electric and magnetic fields on the graphene surface, thereby achieving a response to terahertz electromagnetic waves. Simultaneously, the "sandwich structure" can be utilized to achieve multiple reflections and absorption of terahertz waves in the composite structure. Therefore, from the calculation results, it can be found that the absorption frequency range of the terahertz metamaterial of the present invention is 1.2THz-3.2THz, and the absorption intensity reaches more than 80%, achieving the design goal of broadband absorption. Therefore, the research method of the present invention has important development and utilization value for the subsequent development and application of terahertz band devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a photo of the copper film with the grid pattern obtained in step 3 of comparative example 1;

[0026] Figure 2 is a graph showing the relationship between the terahertz absorption intensity and frequency of the multilayer graphene terahertz metamaterial obtained in Comparative Example 1;

[0027] Figure 3 This is a Raman spectrum of the patterned multilayer graphene obtained in step 4 of Comparative Example 1;

[0028] Figure 4 is a schematic diagram of the multilayer graphene terahertz metamaterial structure designed in step 1 of Example 1; wherein, E x is the direction of electric field polarization, H y is the magnetic field polarization direction, K z is the incident direction of the terahertz wave;

[0029] Figure 5This is a photograph of the copper film with the 'G'-shaped pattern obtained in step 3 of Example 3;

[0030] Figure 6 is a graph showing the relationship between the terahertz absorption intensity and frequency of the multilayer graphene terahertz metamaterial obtained in step nine of Example 1;

[0031] Figure 7 1 is the electromagnetic field distribution diagram of the multilayer graphene terahertz metamaterial obtained in step nine of Example 1, (a) is the y-axis polarization electric field distribution; (b) is the x-axis polarization electric field distribution. DETAILED DESCRIPTION

[0032] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Specific implementation method 1

[0034] A multilayer graphene terahertz metamaterial structure includes a graphene layer, a substrate layer, and a gold film layer. The graphene layer is arranged on the upper surface of the substrate layer, and the gold film layer is arranged on the lower surface of the substrate layer. The graphene layer includes multiple layers of graphene, and the graphene layer includes a plurality of graphene periodic structural units. The growth pattern of the graphene in each graphene periodic structural unit is a 'G'-shaped pattern.

[0035] Furthermore, the substrate layer is a SiO2 substrate, a sapphire substrate, an intrinsic silicon substrate or a polyimide substrate.

[0036] Furthermore, the 'G'-shaped pattern is composed of a first horizontal structure, a 3 / 4 circular structure and a second horizontal structure that are sequentially connected as one body, and the first horizontal structure and the second horizontal structure are parallel to each other.

[0037] Furthermore, the length p of each graphene periodic structure unit is 50-100 μm, the length of the first horizontal structure is equal to the length of the second horizontal structure w = 10-30 μm; the inner diameter R1 of the 3 / 4 circular structure is 5-25 μm, and the outer diameter R2 is 10-30 μm; the difference between the outer diameter and the inner diameter of the 3 / 4 circular structure is 5-25 μm.

[0038] Furthermore, the thickness h3 of the graphene layer is 0.001-0.01 μm, the thickness of the substrate layer h2 is 15-150 μm, and the thickness h1 of the gold thin film layer is 0.5-1.5 μm. Specific implementation method 2

[0040] A method for preparing a multilayer graphene terahertz metamaterial according to a specific embodiment 1 comprises the following steps:

[0041] 1. Graphene terahertz metamaterial structure design: Graphene patterns are designed and optimized using electromagnetic simulation software. The terahertz electromagnetic response results from the simulation are analyzed to optimize the graphene growth pattern.

[0042] 2. Preparation of a graphene growth pattern mask: Using 3D printing equipment, a mask with a graphene growth pattern is printed out of ABS (industrial plastic), and the mask surface is further smoothed using a chemical polishing method;

[0043] 3. Preparation of patterned copper film: The patterned copper film is prepared by physical vapor deposition. The specific preparation steps are as follows: the substrate is ultrasonically cleaned in acetone, deionized water, anhydrous ethanol, and deionized water in sequence. After removing the substrate, the substrate surface is blown dry with a nitrogen gun. The substrate is placed on a mask with a graphene growth pattern and placed in the deposition area of a vacuum evaporation coater. High-purity copper powder is placed on a heated tungsten boat. The coating chamber is then evacuated to a vacuum. The heating system is turned on to melt the copper powder and generate metal vapor. The patterned copper metal film of different thicknesses is prepared by controlling the on-time of the evaporation switch.

[0044] 4. Preparation of patterned graphene: Patterned graphene was prepared by chemical vapor deposition. The specific preparation steps are as follows: Wrap the patterned copper film with copper foil on the periphery, with a gap of 0.5-3.5 mm between the copper foil and the copper film, and place it in the CVD growth area. H2 / Ar carrier gas is introduced, and the carbon source methane reacts in the reaction zone of the tube furnace to grow multilayer graphene on the copper film. The flow ratio of H2 and Ar is 1:10-3:10, and the methane flow rate is 10 sccm-50 sccm. The temperature of the reaction zone of the tube furnace is 1000℃-1050℃ to obtain a patterned multilayer graphene / copper film / substrate sample.

[0045] 5. Prepare polymethyl methacrylate solution: add polymethyl methacrylate into deionized water and prepare PMMA solution by ultrasonic dispersion;

[0046] 6. Prepare etching solution: the etching solution includes one or more of ferric chloride solution, dilute sulfuric acid and ammonium persulfate solution;

[0047] 7. Transfer of Patterned Multilayer Graphene: The patterned multilayer graphene is transferred using a wet chemical method. A PMMA solution is first spin-coated on the surface of the patterned multilayer graphene, then baked on a hot plate. A second coat of the resin is then performed, and the sample is dried. The spin-coated sample is placed in an etching solution to remove the copper film. The sample is then rinsed and soaked in deionized water, and the PMMA / patterned multilayer graphene is salvaged using a substrate.

[0048] 8. Prepare a gold backplane using a thermal evaporation method: Place PMMA / patterned multilayer graphene / substrate into a gold spraying device, and prepare a gold film on the back of the substrate to obtain a terahertz metamaterial structure of PMMA / patterned multilayer graphene / substrate / gold film;

[0049] 9. Graphene terahertz metamaterial degumming: Soak the PMMA / patterned multilayer graphene / substrate / gold film sample in acetone solution, then take it out and soak it in isopropyl alcohol. After taking out the multilayer graphene / substrate / gold film sample, blow it dry with a nitrogen gun.

[0050] Comparative Example 1

[0051] A method for preparing a multilayer graphene terahertz metamaterial comprises the following steps:

[0052] 1. Patterned graphene design: Graphene terahertz metamaterials were designed using electromagnetic simulation software. The designed graphene "grid" pattern consists of periodic structural units consisting of rectangles with a length of 1000μm and a width of 500μm.

[0053] Among them, the designed "gate-type" pattern is a rectangular structure with a length of 10,000 μm and a width of 500 μm. The interval between periodic structural units is 500 μm, and the thickness of the graphene design is 2-4 atomic layers thick.

[0054] 2. Use 3D printing technology to produce a patterned graphene metamaterial mask, where the printing mask accuracy is 100μm.

[0055] Among them, the 3D printing material is industrial-grade plastic ABS, which can withstand a temperature of 200°C.

[0056] 3. Preparation of patterned copper film: The patterned copper film was prepared by physical vapor deposition: the sapphire substrate was ultrasonically cleaned in acetone, deionized water, anhydrous ethanol, and deionized water for 20 minutes in sequence. After the substrate was taken out, the substrate surface was blown dry with a nitrogen gun. The substrate was placed on a patterned mask and placed in the deposition area of a vacuum evaporation coating apparatus. High-purity copper powder was placed on a heated tungsten boat. The vacuum system was turned on and the coating chamber was evacuated to 1.5×10 -4Pa; turn on the rotating bracket, adjust the evaporation source potentiometer to 30A-40A, preheat the copper powder for 30s-60s, continue adjusting the potentiometer to the target power current, and after stabilization for 30s, turn on the film thickness meter and open the evaporation source baffle, and measure the thickness according to the designed film thickness; after the evaporation is completed, close the evaporation source baffle and the film thickness meter, slowly adjust the potentiometer to 0A, and continue operating the vacuum system for 15-20 minutes, waiting for the temperature of the deposited copper film to cool to room temperature. Turn off the vacuum system and the rotating bracket switch, fill the vacuum chamber with nitrogen to atmospheric pressure, open the vacuum chamber, and remove the substrate to obtain the patterned copper film prepared on the sapphire substrate surface.

[0057] The evaporation current intensity is 90A, and the heating is turned off for 10 minutes after every 15 minutes of evaporation to ensure the flatness of the copper surface.

[0058] 4. Preparation of patterned multilayer graphene: Patterned multilayer graphene was prepared using chemical vapor deposition. The substrate on which the patterned copper film had grown was wrapped with copper foil, ensuring a certain distance between the copper foil and the copper film to prevent adhesion of the copper film to each other during the annealing process. The substrate was placed in a vacuum tube furnace, and an H2 flow rate of 50 sccm and an Ar flow rate of 200 sccm were introduced. The temperature was raised from room temperature to 1050°C over 50 minutes, and annealed for 60 minutes. Then, at 1050°C, a CH4 flow rate of 20 sccm was introduced, and the H2 and Ar flow rates were adjusted to 20 sccm and 500 sccm, respectively, for 10 minutes. After the reaction, the gas flow rates were maintained constant, and the sample was cooled to room temperature in the furnace to obtain a patterned multilayer graphene / copper film / sapphire substrate sample.

[0059] The annealing temperature zone temperature is 1050° C., the H2 flow rate is 50 sccm, the Ar flow rate is 200 sccm, and the annealing time is 60 min; the growth temperature is 1050° C., the growth time is 10 min, the CH4 flow rate is 20 sccm, the H2 flow rate is 20 sccm, and the Ar flow rate is 500 sccm.

[0060] 5. Prepare a polymethyl methacrylate (PMMA) solution: Add PMMA to deionized water to prepare a 4 wt% solution, and disperse under electromagnetic stirring for 5-24 hours to prepare a 4 wt% PMMA solution. Place the solution in a sealed tank and stir under electromagnetic heating for 8 hours at a heating temperature of 110°C.

[0061] 6. Prepare ammonium persulfate solution: Add ammonium persulfate to deionized water and ultrasonically disperse for 20 minutes to prepare a 2 mol / L ammonium persulfate solution.

[0062] 7. Transfer of patterned multilayer graphene: The multilayer graphene film sample grown on the patterned copper film is placed on a spin coater, and PMMA solution is dropped on the sample. The sample is spin-coated at 500 rpm for 10 seconds, 2000 rpm for 90 seconds, and 500 rpm for 10 seconds, respectively. After spin coating, it is placed on a heating table and dried at 150°C for 15 minutes. Then, the second spin coating is performed with the same parameters and then dried. The multilayer graphene after spin coating is placed in a 2 mol / L ammonium persulfate solution and etched for 16 hours. The copper film is etched away, and the spin-coated PMMA / graphene film is separated from the substrate and floats on the surface of the solution. After three changes of deionized water, the residual ammonium persulfate solution and metal impurities are cleaned, and the patterned graphene is salvaged using an intrinsic silicon substrate.

[0063] 8. Prepare the gold backplane using thermal evaporation method: Place the intrinsic silicon substrate / patterned graphene / PMMA into the gold spraying equipment to prepare the gold film; Place the intrinsic silicon substrate / patterned graphene / PMMA sample into the deposition area, place high-purity gold particles on the heated tungsten boat, turn on the vacuum system, and evacuate the coating chamber to 5.5×10 -4 Pa; adjust the evaporation source potentiometer to 230A-260A, turn on the film thickness meter after stabilization for 30s, and open the evaporation source baffle, and evaporate for 40min-70min; after the evaporation is completed, close the evaporation source baffle, turn off the film thickness meter, slowly adjust the potentiometer to 0A, and wait for the temperature of the deposited gold film to drop to room temperature.

[0064] 9. Patterned graphene terahertz material debonding: Soak the PMMA / patterned graphene / intrinsic silicon substrate / gold film sample in acetone solution for 10 minutes, then take it out and soak it in isopropanol for 10 minutes. After taking it out, blow dry the graphene with a nitrogen gun, and finally anneal it at 240°C in a high vacuum furnace for 30 minutes.

[0065] The vacuum annealing temperature is 240°C and the annealing time is 30 minutes.

[0066] Example 1

[0067] A method for preparing a multilayer graphene terahertz metamaterial comprises the following steps:

[0068] 1. Patterned Graphene Design: Using electromagnetic simulation software, the graphene terahertz metamaterial was designed. The multilayer graphene pattern was a G-shaped pattern consisting of a first horizontal structure, a 3 / 4 circular structure, and a second horizontal structure, all connected in sequence. The first and second horizontal structures were parallel to each other. The first and second horizontal structures had equal lengths (w = 15 μm). The 3 / 4 circular structure had an inner diameter (R1) of 10 μm and an outer diameter (R2) of 15 μm.

[0069] The designed periodic structure unit length p=50 μm, the pattern is G-type, the interval is 10 μm, and the designed thickness of graphene is 2-4 atomic layers.

[0070] 2. Use 3D printing technology to produce a patterned graphene metamaterial mask, where the printing mask accuracy is 100μm.

[0071] Among them, the 3D printing material is industrial-grade plastic ABS, which can withstand a temperature of 200°C.

[0072] 3. Preparation of patterned copper film: The patterned copper film was prepared by physical vapor deposition: the sapphire substrate was ultrasonically cleaned in acetone, deionized water, anhydrous ethanol, and deionized water for 20 minutes in sequence. After the substrate was taken out, the substrate surface was blown dry with a nitrogen gun. The substrate was placed on a patterned mask and placed in the deposition area of a vacuum evaporation coating apparatus. High-purity copper powder was placed on a heated tungsten boat. The vacuum system was turned on and the coating chamber was evacuated to 1.5×10 -4 Pa; turn on the rotating bracket, adjust the evaporation source potentiometer to 30A-40A, preheat the copper powder for 30s-60s, continue adjusting the potentiometer to the target power current, and after stabilization for 30s, turn on the film thickness meter and open the evaporation source baffle, and measure the thickness according to the designed film thickness; after the evaporation is completed, close the evaporation source baffle and the film thickness meter, slowly adjust the potentiometer to 0A, and continue operating the vacuum system for 15-20 minutes, waiting for the temperature of the deposited copper film to cool to room temperature. Turn off the vacuum system and the rotating bracket switch, fill the vacuum chamber with nitrogen to atmospheric pressure, open the vacuum chamber, and remove the substrate to obtain the patterned copper film prepared on the sapphire substrate surface.

[0073] The evaporation current intensity is 90A, and the heating is turned off for 10 minutes after every 15 minutes of evaporation to ensure the flatness of the copper surface.

[0074] Preparation of patterned multilayer graphene: Chemical vapor deposition (CVD) was used to prepare patterned multilayer graphene. The substrate, after patterned copper film growth, was wrapped with copper foil, ensuring a certain distance between the copper foil and the copper film to prevent adhesion of the copper film to each other during the annealing process. The substrate was placed in a vacuum tube furnace, introduced with a H2 flow rate of 50 sccm and an Ar flow rate of 200 sccm. The temperature was raised from room temperature to 1050°C over 50 minutes, and annealed for 60 minutes. Then, at 1050°C, a CH4 flow rate of 20 sccm was introduced, and the H2 and Ar flow rates were adjusted to 20 sccm and 500 sccm, respectively, for 15 minutes. After the reaction, the gas flow rates were maintained constant, and the sample was cooled to room temperature in the furnace to obtain a patterned multilayer graphene / copper film / sapphire substrate sample.

[0075] The annealing temperature zone temperature is 1050° C., the H2 flow rate is 50 sccm, the Ar flow rate is 200 sccm, and the annealing time is 60 min; the growth temperature is 1050° C., the growth time is 15 min, the CH4 flow rate is 20 sccm, the H2 flow rate is 20 sccm, and the Ar flow rate is 500 sccm.

[0076] 5. Prepare a polymethyl methacrylate (PMMA) solution: Add PMMA to deionized water to prepare a 4 wt% solution, and disperse under electromagnetic stirring for 5-24 hours to prepare a 4 wt% PMMA solution. Place the solution in a sealed tank and stir under electromagnetic heating for 8 hours at a heating temperature of 110°C.

[0077] 6. Prepare ammonium persulfate solution: Add ammonium persulfate to deionized water and ultrasonically disperse for 20 minutes to prepare a 2 mol / L ammonium persulfate solution.

[0078] 7. Transfer of patterned multilayer graphene: The multilayer graphene film sample grown on the patterned copper film is placed on a spin coater, and PMMA solution is dropped on the sample. The sample is spin-coated at 500 rpm for 10 seconds, 2000 rpm for 90 seconds, and 500 rpm for 10 seconds, respectively. After spin coating, it is placed on a heating table and dried at 150°C for 15 minutes. Then, the second spin coating is performed with the same parameters and then dried. The multilayer graphene after spin coating is placed in a 2 mol / L ammonium persulfate solution and etched for 16 hours. The copper film is etched away, and the spin-coated PMMA / graphene film is separated from the substrate and floats on the surface of the solution. After three changes of deionized water, the residual ammonium persulfate solution and metal impurities are cleaned, and the patterned graphene is salvaged using a SiO2 substrate.

[0079] Among them, the SiO2 substrate is a double-sided oxidized 1000nm intrinsic oxide silicon wafer.

[0080] 8. Prepare the gold backplane using thermal evaporation method: Place the SiO2 / patterned graphene / PMMA into the gold spraying equipment to prepare the gold film; Place the SiO2 / patterned graphene / PMMA sample into the deposition area, place high-purity gold particles on the heated tungsten boat, turn on the vacuum system, and evacuate the coating chamber to 5.5×10 -4 Pa; adjust the evaporation source potentiometer to 230A-260A, turn on the film thickness meter after stabilization for 30s, and open the evaporation source baffle, and evaporate for 40min-70min; after the evaporation is completed, close the evaporation source baffle, turn off the film thickness meter, slowly adjust the potentiometer to 0A, and wait for the temperature of the deposited gold film to drop to room temperature.

[0081] 9. Patterned graphene terahertz material debonding: Soak the PMMA / patterned graphene / SiO2 / gold film sample in acetone solution for 10 minutes, then take it out and soak it in isopropanol for 10 minutes. After taking it out, blow dry the graphene with a nitrogen gun, and finally anneal it at 240℃ in a high vacuum furnace for 30 minutes.

[0082] The vacuum annealing temperature is 240°C and the annealing time is 30 minutes.

[0083] Example 2

[0084] A method for preparing a multilayer graphene terahertz metamaterial comprises the following steps:

[0085] 1. Patterned graphene design: Graphene terahertz metamaterials were designed using electromagnetic simulation software. The designed multilayer graphene pattern is a 'G'-shaped pattern consisting of a first horizontal structure, a 3 / 4 circular structure, and a second horizontal structure connected in sequence. The first and second horizontal structures are parallel to each other. The lengths of the first and second horizontal structures are equal, w = 20 μm; the inner diameter of the 3 / 4 circular structure is R1 = 15 μm, and the outer diameter is R2 = 20 μm.

[0086] Among them, the designed periodic structure unit length is 50μm, the pattern is G-type, the interval is 30μm, and the designed thickness of graphene is 2-4 atomic layers.

[0087] 2. Use 3D printing technology to produce a patterned graphene metamaterial mask, where the printing mask accuracy is 100μm.

[0088] Among them, the 3D printing material is industrial-grade plastic ABS, which can withstand a temperature of 200°C.

[0089] 3. Preparation of patterned copper film: The patterned copper film was prepared by physical vapor deposition: the sapphire substrate was ultrasonically cleaned in acetone, deionized water, anhydrous ethanol, and deionized water for 20 minutes in sequence. After the substrate was taken out, the substrate surface was blown dry with a nitrogen gun. The substrate was placed on a patterned mask and placed in the deposition area of a vacuum evaporation coating apparatus. High-purity copper powder was placed on a heated tungsten boat. The vacuum system was turned on and the coating chamber was evacuated to 1.5×10 -4Pa; turn on the rotating bracket, adjust the evaporation source potentiometer to 30A-40A, preheat the copper powder for 30s-60s, continue adjusting the potentiometer to the target power current, and after stabilization for 30s, turn on the film thickness meter and open the evaporation source baffle, and measure the thickness according to the designed film thickness; after the evaporation is completed, close the evaporation source baffle and the film thickness meter, slowly adjust the potentiometer to 0A, and continue operating the vacuum system for 15-20 minutes, waiting for the temperature of the deposited copper film to cool to room temperature. Turn off the vacuum system and the rotating bracket switch, fill the vacuum chamber with nitrogen to atmospheric pressure, open the vacuum chamber, and remove the substrate to obtain the patterned copper film prepared on the sapphire substrate surface.

[0090] The evaporation current intensity is 90A, and the heating is turned off for 10 minutes after every 15 minutes of evaporation to ensure the flatness of the copper surface.

[0091] 4. Preparation of patterned multilayer graphene: Patterned multilayer graphene was prepared using chemical vapor deposition. The substrate on which the patterned copper film had grown was wrapped with copper foil, ensuring a certain distance between the copper foil and the copper film to prevent adhesion of the copper film to each other during the annealing process. The substrate was placed in a vacuum tube furnace, and an H2 flow rate of 50 sccm and an Ar flow rate of 200 sccm were introduced. The temperature was set to rise from room temperature to 1050°C over 50 minutes, and annealed for 60 minutes. Then, at 1050°C, a CH4 flow rate of 20 sccm was introduced, and the H2 and Ar flow rates were adjusted to 20 sccm and 500 sccm, respectively, and the reaction was carried out for 20 minutes. After the reaction, the gas flow rates were maintained unchanged, and the sample was cooled to room temperature in the furnace to obtain a patterned multilayer graphene / copper film / sapphire substrate sample.

[0092] The annealing temperature zone temperature is 1050° C., the H2 flow rate is 50 sccm, the Ar flow rate is 200 sccm, and the annealing time is 60 min; the growth temperature is 1050° C., the growth time is 20 min, the CH4 flow rate is 20 sccm, the H2 flow rate is 20 sccm, and the Ar flow rate is 500 sccm.

[0093] 5. Prepare a polymethyl methacrylate (PMMA) solution: Add PMMA to deionized water to prepare a 4 wt% solution, and disperse under electromagnetic stirring for 5-24 hours to prepare a 4 wt% PMMA solution. Place the solution in a sealed tank and stir under electromagnetic heating for 8 hours at a heating temperature of 110°C.

[0094] 6. Prepare ammonium persulfate solution: Add ammonium persulfate to deionized water and ultrasonically disperse for 20 minutes to prepare a 2 mol / L ammonium persulfate solution.

[0095] 7. Transfer of patterned multilayer graphene: The multilayer graphene film sample grown on the patterned copper film is placed on a spin coater, and PMMA solution is dropped on the sample. The sample is spin-coated at 500 rpm for 10 seconds, 2000 rpm for 90 seconds, and 500 rpm for 10 seconds, respectively. After spin coating, it is placed on a heating table and dried at 150°C for 15 minutes. Then, the second spin coating is performed using the same parameters and then dried. The multilayer graphene after spin coating is placed in a 2 mol / L ammonium persulfate solution and etched for 16 hours. The copper film is etched away, and the spin-coated PMMA / graphene film is separated from the substrate and floats on the surface of the solution. After three changes of deionized water, the residual ammonium persulfate solution and metal impurities are cleaned, and the patterned graphene is salvaged using a sapphire substrate.

[0096] 8. Prepare the gold backplane using thermal evaporation method: Place the sapphire substrate / patterned graphene / PMMA into the gold spraying equipment to prepare the gold film; Place the sapphire substrate / patterned graphene / PMMA sample into the deposition area, place high-purity gold particles on the heated tungsten boat, turn on the vacuum system, and evacuate the coating chamber to 5.5×10 -4 Pa; adjust the evaporation source potentiometer to 230A-260A, turn on the film thickness meter after stabilization for 30s, and open the evaporation source baffle, and evaporate for 40min-70min; after the evaporation is completed, close the evaporation source baffle, turn off the film thickness meter, slowly adjust the potentiometer to 0A, and wait for the temperature of the deposited gold film to drop to room temperature.

[0097] 9. Patterned graphene terahertz material debonding: Soak the PMMA / patterned graphene / sapphire substrate / gold film sample in acetone solution for 10 minutes, then take it out and soak it in isopropanol for 10 minutes. After taking it out, blow dry the graphene with a nitrogen gun, and finally anneal it at 240℃ in a high vacuum furnace for 30 minutes.

[0098] The vacuum annealing temperature is 240°C and the annealing time is 30 minutes.

[0099] Example 3

[0100] A method for preparing a multilayer graphene terahertz metamaterial comprises the following steps:

[0101] 1. Patterned graphene design: Graphene terahertz metamaterials were designed using electromagnetic simulation software. The designed multilayer graphene pattern is a 'G'-shaped pattern consisting of a first horizontal structure, a 3 / 4 circular structure, and a second horizontal structure connected in sequence. The first and second horizontal structures are parallel to each other. The lengths of the first and second horizontal structures are equal, w = 30μm; the inner diameter of the 3 / 4 circular structure is R1 = 5μm, and the outer diameter is R2 = 30μm.

[0102] Among them, the designed periodic structure unit length is 80μm, the pattern is G-type, the interval is 40μm, and the designed thickness of graphene is 2-4 atomic layers.

[0103] 2. Use 3D printing technology to produce a patterned graphene metamaterial mask, where the printing mask accuracy is 100μm.

[0104] Among them, the 3D printing material is industrial-grade plastic ABS, which can withstand a temperature of 200°C.

[0105] 3. Preparation of patterned copper film: The patterned copper film was prepared by physical vapor deposition: the sapphire substrate was ultrasonically cleaned in acetone, deionized water, anhydrous ethanol, and deionized water for 20 minutes in sequence. After the substrate was taken out, the substrate surface was blown dry with a nitrogen gun. The substrate was placed on a patterned mask and placed in the deposition area of a vacuum evaporation coating apparatus. High-purity copper powder was placed on a heated tungsten boat. The vacuum system was turned on and the coating chamber was evacuated to 1.5×10 -4 Pa; turn on the rotating bracket, adjust the evaporation source potentiometer to 30A-40A, preheat the copper powder for 30s-60s, continue adjusting the potentiometer to the target power current, and after stabilization for 30s, turn on the film thickness meter and open the evaporation source baffle, and measure the thickness according to the designed film thickness; after the evaporation is completed, close the evaporation source baffle and the film thickness meter, slowly adjust the potentiometer to 0A, and continue operating the vacuum system for 15-20 minutes, waiting for the temperature of the deposited copper film to cool to room temperature. Turn off the vacuum system and the rotating bracket switch, fill the vacuum chamber with nitrogen to atmospheric pressure, open the vacuum chamber, and remove the substrate to obtain the patterned copper film prepared on the sapphire substrate surface.

[0106] The evaporation current intensity is 90A, and the heating is turned off for 10 minutes after every 15 minutes of evaporation to ensure the flatness of the copper surface.

[0107] 4. Preparation of patterned multilayer graphene: Patterned multilayer graphene was prepared using chemical vapor deposition. The substrate on which the patterned copper film had grown was wrapped with copper foil, ensuring a certain distance between the copper foil and the copper film to prevent adhesion of the copper film to each other during the annealing process. The substrate was placed in a vacuum tube furnace, and an H2 flow rate of 50 sccm and an Ar flow rate of 200 sccm were introduced. The temperature was set to rise from room temperature to 1050°C over 50 minutes, and annealed for 60 minutes. Then, at 1050°C, a CH4 flow rate of 20 sccm was introduced, and the H2 and Ar flow rates were adjusted to 20 sccm and 500 sccm, respectively, and the reaction was carried out for 20 minutes. After the reaction, the gas flow rates were maintained unchanged, and the sample was cooled to room temperature in the furnace to obtain a patterned multilayer graphene / copper film / sapphire substrate sample.

[0108] The annealing temperature zone temperature is 1050° C., the H2 flow rate is 50 sccm, the Ar flow rate is 200 sccm, and the annealing time is 60 min; the growth temperature is 1050° C., the growth time is 20 min, the CH4 flow rate is 20 sccm, the H2 flow rate is 20 sccm, and the Ar flow rate is 500 sccm.

[0109] 5. Prepare a polymethyl methacrylate (PMMA) solution: Add PMMA to deionized water to prepare a 4 wt% solution, and disperse under electromagnetic stirring for 5-24 hours to prepare a 4 wt% PMMA solution. Place the solution in a sealed tank and stir under electromagnetic heating for 8 hours at a heating temperature of 110°C.

[0110] 6. Prepare ammonium persulfate solution: Add ammonium persulfate to deionized water and ultrasonically disperse for 20 minutes to prepare a 2 mol / L ammonium persulfate solution.

[0111] 7. Transfer of patterned multilayer graphene: The multilayer graphene film sample grown on the patterned copper film is placed on a spin coater, and PMMA solution is dropped on the sample. The sample is spin-coated at 500 rpm for 10 seconds, 2000 rpm for 90 seconds, and 500 rpm for 10 seconds, respectively. After spin coating, it is placed on a heating table and dried at 150°C for 15 minutes. Then, the same parameters are used for a second spin coating and then drying. The multilayer graphene after spin coating is placed in a 2 mol / L ammonium persulfate solution and etched for 16 hours. The copper film is etched away, and the spin-coated PMMA / graphene film is separated from the substrate and floats on the surface of the solution. After three changes of deionized water, the residual ammonium persulfate solution and metal impurities are cleaned, and the patterned graphene is salvaged using a polyimide substrate.

[0112] 8. Prepare the gold backplane using thermal evaporation method: Place the polyimide substrate / patterned graphene / PMMA into the gold spraying equipment to prepare the gold film; Place the polyimide substrate / patterned graphene / PMMA sample into the deposition area, place high-purity gold particles on the heated tungsten boat, turn on the vacuum system, and evacuate the coating chamber to 5.5×10 -4 Pa; adjust the evaporation source potentiometer to 230A-260A, turn on the film thickness meter after stabilization for 30s, and open the evaporation source baffle, and evaporate for 40min-70min; after the evaporation is completed, close the evaporation source baffle, turn off the film thickness meter, slowly adjust the potentiometer to 0A, and wait for the temperature of the deposited gold film to drop to room temperature.

[0113] 9. Patterned graphene terahertz material debonding: Soak the PMMA / patterned graphene / polyimide substrate / gold film sample in acetone solution for 10 minutes, then take it out and soak it in isopropanol for 10 minutes. After taking it out, blow dry the graphene with a nitrogen gun, and finally anneal it at 240°C in a high vacuum furnace for 30 minutes.

[0114] The vacuum annealing temperature is 240°C and the annealing time is 30 minutes.

[0115] Figure 1 This is a photo of the gate-type copper thin film in step 3 of comparative example 1; Figure 2 The relationship between the terahertz absorption intensity and frequency of the multilayer graphene terahertz metamaterial obtained in Comparative Example 1 is shown in FIG. Figure 2 It can be seen that the intensity of the absorption peak at a frequency of 1THz-5THz is only 6%. Figure 3 This is the Raman spectrum of the multilayer graphene prepared in Comparative Example 1. From the ratio of the 2D peak to the G peak, it can be seen that the graphene has a multilayer structure. Figure 4 Schematic diagram of the multi-layer graphene terahertz metamaterial structure designed in step 1 of Example 1. x is the direction of electric field polarization, H y is the magnetic field polarization direction, K z is the incident direction of the terahertz wave. Figure 5 This is a photo of the 'G' type copper film in step 3 of Example 3. Figure 6 This is a graph showing the relationship between the terahertz absorption intensity and frequency of the multilayer graphene terahertz metamaterial obtained in step nine of Example 1. It can be clearly observed from the graph that within the frequency range of 1.2 THz-3.2 THz, the intensity of the terahertz absorption peak can reach more than 80%, and the absorption width is significantly better than that of Comparative Example 1. Figure 7 The electromagnetic field distribution of the multilayer graphene terahertz metamaterial obtained in step 9 of Example 1 is shown in Figure 1. (a) is the y-axis polarization electric field distribution; (b) is the x-axis polarization electric field distribution. The width is only 0.3 THz.

[0116] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A multi-layer graphene terahertz metamaterial structure, characterized by: The invention comprises a graphene layer, a substrate layer and a gold thin film layer, wherein the graphene layer is arranged on the upper surface of the substrate layer, and the gold thin film layer is arranged on the lower surface of the substrate layer; the graphene layer comprises multilayer graphene, and the graphene layer comprises a plurality of graphene periodic structural units, and the growth pattern of the graphene in each graphene periodic structural unit is a 'G'-shaped pattern; the 'G'-shaped pattern is composed of a first horizontal structure, a 3 / 4 circular structure and a second horizontal structure connected in sequence, and the first horizontal structure and the second horizontal structure are parallel to each other; the length p of each graphene periodic structural unit is 50-100 μm, and the length w of the first horizontal structure is equal to that of the second horizontal structure; the inner diameter R1 of the 3 / 4 circular structure is 5-25 μm, and the outer diameter R2 is 10-30 μm; the difference between the outer diameter and the inner diameter of the 3 / 4 circular structure is 5-25 μm.

2. The multi-layer graphene terahertz metamaterial structure according to claim 1, characterized in that: The substrate layer is a SiO2 substrate, a sapphire substrate, an intrinsic silicon substrate or a polyimide substrate.

3. The multi-layer graphene terahertz metamaterial structure according to claim 1, characterized in that: The thickness of the graphene layer is 0.001-0.01 μm, the thickness of the substrate layer is 15-150 μm, and the thickness of the gold thin film layer is 0.5-1.5 μm.

4. A method for preparing the multilayer graphene terahertz metamaterial according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: Design and optimize the graphene growth pattern using electromagnetic simulation software; Step 2: placing the substrate on a mask having a graphene growth pattern, and vacuum evaporating a patterned copper film on the substrate; Step 3: Wrap the outer periphery of the copper film with copper foil, leaving a gap between the copper foil and the copper film, and grow patterned multilayer graphene on the copper film using a chemical vapor deposition method; Step 4: coating the surface of the multilayer graphene grown on the copper film with glue and then drying it, etching the copper film with an etching solution, and using a substrate to pick up the coated multilayer graphene; Step 5: evaporating a gold film on the side of the substrate away from the multilayer graphene to obtain a glue-coated multilayer graphene / substrate / gold film; Step 6: Remove the adhesive layer to obtain a multilayer graphene terahertz metamaterial with a multilayer graphene / substrate / gold film structure.

5. The preparation method according to claim 4, characterized in that: Step 2: Use 3D printing technology to print a mask with a graphene growth pattern on industrial plastic.

6. The preparation method according to claim 4, characterized in that: In step 3, the gap between the copper foil and the copper film is 0.5-3.5 mm.

7. The preparation method according to claim 4, characterized in that: In step 4, the glue is a polymethyl methacrylate solution; the etching solution includes a combination of one or more of a ferric chloride solution, a dilute sulfuric acid solution, or an ammonium persulfate solution.

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