Preparation method of large-area metal nano needle tip on flexible substrate

Abstract

The invention belongs to the technical field of nano metal preparation, and particularly relates to a preparation method of a large-area metal nano needle tip on a flexible substrate. The preparation method comprises the following steps: preparing a chromium film with a micron hole array on the surface of a silicon substrate, etching by using an alkali solution to obtain inverted pyramid-shaped silicon holes, depositing a metal film on the silicon surface by using an electron beam thermal evaporation or sputtering mode, and removing a metal layer on the surface of a silicon wafer by using an adhesive tape to obtain the micro-porous silicon film. A flexible polymer is poured on the surface of a silicon wafer, a silicon substrate is corroded through alkali liquor after solidification, and the large-scale metal nano needle tip array on the flexible substrate is obtained. The template for preparing the metal nano needle tip can be repeatedly used, and the used metal only covers the surface of the needle tip, but does not influence the performance requirement of the metal needle tip, so that the preparation cost is greatly reduced; the prepared metal nano needle tip has extremely flat and sharp tip appearance.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for preparing large-area metal nanoneedles on a flexible substrate. Background Technology

[0002] Metal nanotipes hold significant promise for applications in micro / nano printing and plasmonic devices due to their unique morphology. Firstly, nanotips are crucial components of various probe devices; their microstructures enable the resolution and fabrication of extremely small nanopatterns. Metal nanotips, with their excellent electrical conductivity, can be extended into micro / nano electrical characterization and detection applications. Secondly, the nanostructures of the tip morphology converge surface plasmon waves propagating on its surface, thus holding important applications in plasmonic catalysis and plasmonic heating. While existing micro / nano fabrication techniques have relatively mature process parameters for preparing silicon nanotips, the fabrication of micro / nano-scale metal nanotips remains challenging. Therefore, achieving large-scale, low-cost fabrication of metal nanotips is a crucial current research direction. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for fabricating large-area metal nanoparticles on flexible substrates. Compared with traditional fabrication techniques, the method of fabricating large-area metal nanoparticles on flexible transparent substrates has significant advantages: First, the template for fabricating metal nanoparticles can be reused repeatedly, and the metal used only covers the surface of the tip without affecting its performance requirements, thus greatly reducing fabrication costs; second, the tips fabricated using this method have extremely smooth surfaces and sharp tip morphologies, resulting in superior performance in nanoparticle printing and plasmonic devices.

[0004] To achieve the above technical objectives, the technical solution adopted in the embodiments of the present invention is as follows: A method for fabricating large-area metal nanoneedles on a flexible substrate includes the following steps: Step S1: Prepare a chromium thin film with a porous structure on a clean silicon substrate; Step S2: Use an alkaline solution to etch inverted pyramid-shaped silicon holes; Step S3: Deposit a metal film on the sample surface and remove the gold film from the silicon wafer surface using adhesive tape; Step S4: Cast a flexible polymer onto the surface of a silicon wafer, and after solidification, etch away the silicon substrate with an alkaline solution to obtain a large-scale array of metal nanoneedles on the flexible substrate.

[0005] Furthermore, in step S1, a chromium thin film with a porous structure is formed on the silicon substrate using one of the following methods: Method A includes the following steps: (1a) A chromium thin film is formed on a clean silicon substrate and photoresist is spin-coated and dried using a hot plate. (2a) Use exposure technology to prepare a photoresist hole pattern array, followed by development and fixing; (3a) Use a cerium ammonium nitrate solution with a concentration of 0.1 ~ 0.5 g / mL to etch and remove the metal chromium film that is not protected by the photoresist pattern, exposing the surface of the underlying silicon substrate; Method B includes the following steps: (1b) Spin-coat photoresist onto a clean silicon substrate and dry it using a hot plate; (2b) A square columnar pattern array of photoresist was prepared using exposure technology, followed by development and fixing; (3b) A chromium film is formed on a silicon substrate, and the chromium film on the photoresist surface is removed using acetone, leaving the chromium film with holes on the silicon substrate.

[0006] Further, in step (1a) or step (1b), the silicon substrate has a surface lattice orientation of <111> Silicon wafers; The photoresist is an electron beam photoresist or a deep ultraviolet photoresist.

[0007] Furthermore, when the photoresist is an electron beam photoresist, the solute of the electron beam photoresist is polymethyl methacrylate, and the weight-average molecular weight of the polymethyl methacrylate is 50,000 to 950,000. The polymethyl methacrylate is dissolved in an organic solvent, wherein the organic solvent is at least one of chloroform and dimethyl ether; The mass percentage concentration of polymethyl methacrylate in the electron beam photoresist is 1-9%.

[0008] Furthermore, in step (1a) or step (1b), the rotation speed is 2000 to 6000 rpm when spin-coating the photoresist; The drying temperature is 100-220℃, and the drying time is 1-10 minutes.

[0009] Furthermore, when the photoresist is a deep ultraviolet photoresist, the type selected is a positive photoresist.

[0010] Furthermore, when electron beam photoresist is selected in step (1a) or step (1b), the exposure method in step (2a) or step (2b) is electron beam exposure, wherein the accelerating voltage of the electron beam exposure is 10-20 kV and the exposure dose is 210-430 μC / cm. 2 ; When deep ultraviolet photoresist is selected in step (1a) or step (1b), a deep ultraviolet lithography machine is used for exposure in step (2a) or step (2b); In step (2a) or step (2b), the developing time is 0.5 to 2 minutes and the fixing time is 0.5 to 2 minutes.

[0011] Further, in step S2, the alkaline solution is a KOH solution or a NaOH solution, the mass concentration of the alkaline solution is 20%~50%, and the etching temperature is 20~100℃.

[0012] Furthermore, in step S3, the metal thin film is deposited by sputtering or thermal evaporation, and the deposition rate is 0.1~1.0 Å / s.

[0013] In a further step S4, the flexible polymer is one of polydimethylsiloxane (PDMS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polyvinyl chloride (PVC).

[0014] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: The method for large-area fabrication of metal nanoneedles on flexible transparent substrates has significant advantages over traditional fabrication techniques: First, the template for fabricating metal nanoneedles can be reused repeatedly, and the metal used only covers the surface of the tip without affecting its performance requirements, thus greatly reducing the fabrication cost; Second, the tips fabricated by this method have extremely flat surfaces and sharp tip morphologies, resulting in better performance in nanoneedle printing and plasmonic devices. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a chromium thin film with an array of holes fabricated on a silicon substrate.

[0016] Figure 2 This is a schematic diagram of a structure that uses alkaline etching to create an inverted pyramid-shaped hole.

[0017] Figure 3 This is a schematic diagram of a metal thin film deposited on the sample surface.

[0018] Figure 4 This is a schematic diagram of a structure that uses adhesive tape to remove the metal thin film layer on the surface of a silicon substrate.

[0019] Figure 5This is a schematic diagram of a structure in which PDMS is cast onto the sample surface and then self-leveled.

[0020] Figure 6 This is a schematic diagram of a flexible substrate with an array of metal tips formed by etching away the silicon substrate in an alkaline solution.

[0021] Figure 7 This is an SEM image of a nanoneedle array with a gold thin film on its surface obtained in Example 1 of the present invention.

[0022] Figure 8 This is a magnified SEM image of the nanoneedle array with a titanium thin film on its surface obtained in Example 2 of the present invention.

[0023] Figure 9 This is a magnified SEM image of the nanoneedle array with a gold thin film on its surface obtained in Example 3 of the present invention.

[0024] Figure labeling: 1-Silicon substrate; 2-Chromium thin film; 3-Inverted pyramid-shaped hole; 4-Metal thin film layer; 5-Adhesive tape; 6-PDMS thin film. Detailed Implementation

[0025] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "inner" and "outer", "upper" and "lower", "left" and "right" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention.

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Example 1 A method for fabricating large-area metal nanoneedle tips on a flexible substrate includes the following steps: (1) A silicon substrate covered with a 50 nm thick chromium film (wherein the silicon substrate has a 111 lattice orientation) is cut into 1 cm × 1 cm pieces. These pieces are then sonicated for five minutes each with acetone, anhydrous ethanol, and deionized water, and dried with nitrogen gas. The small silicon pieces are labeled as substrate i. Figure 1 As shown; On substrate i, polymethyl methacrylate photoresist of model 671.04 (Allresist GmbH) was spin-coated at a speed of 4000 rpm. The solute of the photoresist was polymethyl methacrylate, the solvent was chloroform, the weight average molecular weight of polymethyl methacrylate was 495,000, and the mass concentration of the photoresist was 4%. The photoresist was baked at 180°C for 2 minutes to obtain a photoresist layer with a thickness of 300 nm. (2) The sample i with polymethyl methacrylate photoresist spin-coated was placed in an electron beam lithography machine (Raith e_Line) and lithographically accelerated at 10 kV at 240 μC / cm. 2 The pre-designed pattern is obtained by exposure with a dose of 25.6nm minimum step size, development for 60 seconds, and fixing for one minute. At this time, the polymethyl methacrylate photoresist pattern obtained by exposure is a square hole array with a side length of 10 micrometers. (3) Use a 0.25 g / mL cerium ammonium nitrate solution to etch and remove the chromium film without photoresist protection, exposing the underlying silicon substrate surface, and use acetone to remove the photoresist pattern, such as... Figure 1 As shown; (4) Immerse sample i in a 30% KOH solution and etch it at 95°C for 20 minutes with stirring to obtain an inverted pyramid-shaped hole, as shown. Figure 2 As shown; (5) A 100 nm gold film was prepared on the sample surface using ion beam sputtering at a sputtering rate of 0.5 Å / s. The metal film layer on the silicon surface was then removed using adhesive tape. Figure 3 and 4 As shown; (6) Cast a 1 mm thick PDMS film on the silicon substrate surface, remove air bubbles in a vacuum chamber, with a PDMS main agent to coagulant volume ratio of 10:1, and bake on a hot plate at 100°C for 45 minutes to solidify the PDMS. Figure 5 As shown; (7) The bottom Si substrate is etched away in a 1M KOH solution to obtain a gold nanoneedle array, such as... Figure 6 and 7 As shown.

[0028] Example 2 A method for fabricating large-area metal nanoneedle tips on a flexible substrate includes the following steps: (1) Cut a silicon substrate covered with a 50-nanometer chromium film (wherein the silicon substrate has a lattice orientation of 111) into small pieces of 1cm×1cm, sonicate them for five minutes with acetone, anhydrous ethanol and deionized water respectively, and dry them with nitrogen for later use. Mark the above small pieces of silicon wafers as substrate i. AZ 1350 (MicroChem) UV photoresist was spin-coated on substrate i at a speed of 2000 rpm, and baked at 100°C for 10 minutes to obtain a photoresist layer with a thickness of 2 micrometers. (2) The sample i with AZ 1350 spin-coated was placed in a deep ultraviolet exposure machine and exposed with G line for 30 seconds to obtain the pre-designed pattern. It was developed in a NaOH solution with a mass concentration of 6‰ for 30 seconds and fixed for one minute to obtain a square hole array with a side length of 10 micrometers. (3) Use a cerium ammonium nitrate solution with a concentration of 0.25 g / mL to etch and remove the metal chromium film without photoresist protection, and use acetone to remove the photoresist pattern; (4) Immerse sample i in a 20% KOH solution and etch it at 95°C for 20 minutes to obtain an inverted pyramid-shaped hole; (5) A 100 nm titanium film was prepared by ion beam sputtering, and the titanium film layer on the silicon surface was removed by adhesive tape. The sputtering speed was 0.5 Å / s. (6) Cast a PDMS film with a thickness of 1 mm, remove air bubbles in a vacuum chamber, the volume ratio of PDMS main agent to coagulant is 10:1, and bake on a hot plate at 100°C for 45 minutes to solidify the PDMS. (7) The bottom silicon substrate is etched away in a 1M KOH solution to obtain a titanium nanoneedle array, such as Figure 8 As shown.

[0029] Example 3 A method for fabricating large-area metal nanoneedle tips on a flexible substrate includes the following steps: (1) Cut the silicon substrate (wherein the silicon substrate has a lattice orientation of 111) into small pieces of 1cm × 1cm, and sonicate them for five minutes each in acetone, anhydrous ethanol, and deionized water, respectively. Dry them with nitrogen gas and set aside. Label the above small silicon pieces as substrate i. Figure 1 As shown; On substrate i, polymethyl methacrylate photoresist of type 671.06 (Allresist GmbH) was spin-coated at a speed of 2000 rpm. The photoresist solute was polymethyl methacrylate, the solvent was chloroform, the weight average molecular weight of polymethyl methacrylate was 950,000, and the mass concentration of the photoresist was 6%. The photoresist was baked at 180°C for 4 minutes to obtain a photoresist layer with a thickness of 1.2 micrometers. (2) The sample i with polymethyl methacrylate photoresist spin-coated was placed in an electron beam lithography machine (Raith e_Line) and lithographically accelerated at 20 kV at 430 μC / cm. 2The pre-designed pattern was obtained by exposure with a dose of 25.6nm minimum step size, followed by 90 seconds of development and one minute of fixing. The resulting polymethyl methacrylate photoresist pattern was a square array with a side length of 10 micrometers. (3) A chromium film with a thickness of 50 nanometers was deposited on sample i by electron beam thermal evaporation at an evaporation rate of 0.2 Å / s. The chromium film on the photoresist surface was washed away in acetone by lift-off method, leaving a chromium film with voids on the silicon substrate. (4) Immerse sample i in a 30% KOH solution and etch it at 95°C for 20 minutes with stirring to obtain an inverted pyramid-shaped hole, as shown. Figure 2 As shown; (5) A 100 nm gold film was prepared on the sample surface using ion beam sputtering at a sputtering rate of 0.5 Å / s. The metal film layer on the silicon surface was then removed using adhesive tape. Figure 3 and 4 As shown; (6) Spin-coat a PVC film with a thickness of 0.5 mm onto the surface of a silicon substrate, and bake it on a hot plate at 150°C for 5 minutes to solidify the PC; (7) The bottom silicon substrate is etched away in a 1M KOH solution to obtain a gold nanoparticle array, such as... Figure 9 As shown.

[0030] To ensure sample cleanliness, all experimental operations were performed in a 100% cleanroom; all equipment in contact with the samples was ultrasonically cleaned with acetone, anhydrous ethanol, and deionized ultrapure water; and the sample preparation and electron beam lithography operations were conducted under the corresponding high vacuum (10⁻⁶) of the instruments. -2 Pa-10 -4 Pa)

[0031] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing large-area metal nanoneedle tips on a flexible substrate, characterized in that, Includes the following steps: Step S1: Prepare a chromium thin film with a porous structure on a clean silicon substrate; Step S2: Use an alkaline solution to etch inverted pyramid-shaped silicon holes; Step S3: Deposit a metal film on the sample surface and remove the metal film from the silicon wafer surface using adhesive tape; Step S4: Cast a flexible polymer onto the surface of a silicon wafer, and after solidification, etch away the silicon substrate with an alkaline solution to obtain a large-scale array of metal nanoneedles on the flexible substrate.

2. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 1, characterized in that, In step S1, a chromium thin film with a porous structure is formed on the silicon substrate using one of the following methods: Method A includes the following steps: (1a) A chromium thin film is formed on a clean silicon substrate and photoresist is spin-coated and dried using a hot plate. (2a) Use exposure technology to prepare a photoresist hole pattern array, followed by development and fixing; (3a) Use a cerium ammonium nitrate solution with a concentration of 0.1 ~ 0.5 g / mL to etch and remove the metal chromium film that is not protected by the photoresist pattern, exposing the surface of the underlying silicon substrate; Method B includes the following steps: (1b) Spin-coat photoresist onto a clean silicon substrate and dry it using a hot plate; (2b) A square columnar pattern array of photoresist was prepared using exposure technology, followed by development and fixing; (3b) A chromium film is formed on a silicon substrate, and the chromium film on the photoresist surface is removed using acetone, leaving the chromium film with holes on the silicon substrate.

3. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 2, characterized in that, In step (1a) or step (1b), the silicon substrate has a surface lattice orientation of <111> Silicon wafers; The photoresist is an electron beam photoresist or a deep ultraviolet photoresist.

4. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 3, characterized in that, When the photoresist is an electron beam photoresist, the solute of the electron beam photoresist is polymethyl methacrylate, and the weight-average molecular weight of the polymethyl methacrylate is 50,000 to 950,000. The polymethyl methacrylate is dissolved in an organic solvent, wherein the organic solvent is at least one of chloroform and dimethyl ether; The mass percentage concentration of polymethyl methacrylate in the electron beam photoresist is 1%-9%.

5. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 2, characterized in that, In step (1a) or step (1b), the spin coating speed is 2000 to 6000 rpm; The drying temperature is 100-220℃, and the drying time is 1-10 minutes.

6. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 3, characterized in that, When the photoresist is a deep ultraviolet photoresist, the type selected is positive photoresist.

7. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 3, characterized in that, When electron beam photoresist is selected in step (1a) or step (1b), the exposure method in step (2a) or step (2b) is electron beam exposure, wherein the accelerating voltage of the electron beam exposure is 10-20 kV and the exposure dose is 210-430 μC / cm. 2 ; When deep ultraviolet photoresist is selected in step (1a) or step (1b), a deep ultraviolet lithography machine is used for exposure in step (2a) or step (2b); In step (2a) or step (2b), the developing time is 0.5 to 2 minutes and the fixing time is 0.5 to 2 minutes.

8. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 1, characterized in that, In step S2, the alkaline solution is a KOH solution or a NaOH solution, the mass concentration of the alkaline solution is 20%~50%, and the etching temperature is 20~100℃.

9. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 1, characterized in that, In step S3, the metal thin film is deposited by sputtering or thermal evaporation, and the deposition rate is 0.1~1.0 Å / s.

10. The method for preparing large-area metal nanoneedles on a flexible substrate according to claim 1, characterized in that, In step S4, the flexible polymer is one of polydimethylsiloxane, polymethyl methacrylate, polycarbonate, and polyvinyl chloride.

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