CN103698846B - A kind of preparation method of flexible metal photonic crystal - Google Patents

Abstract

The invention discloses a method for preparing a flexible metal photonic crystal, which belongs to the technical field of nano-photonic materials and devices. Prepare the photoresist nano-grating structure on the buffer layer of the buffer layer matrix, spin-coat the gold nanoparticle colloid on the grating surface and confine it to the grating groove, heat treatment to sublimate the organic ligand on the gold surface, and melt the gold nanoparticle , forming a metal photonic crystal; the flexible substrate solution mixed with a curing agent is applied to the metal photonic crystal, covered with another buffer layer matrix, heated for cross-linking polymerization, placed in hydrochloric acid or sulfuric acid solution, and the buffer layer is fully dissolved. The obtained samples were washed with distilled water. The device of the invention has important direct application value for the development of stress and deformation sensors and novel flexible optoelectronic devices.

Description

A kind of preparation method of flexible metal photonic crystal

technical field

The invention belongs to the technical field of nano-photonic materials and devices, and relates to a method for preparing a flexible metal photonic crystal.

Background technique

Metal photonic crystals are not only an important form of photonic crystals, but also a relatively independent form of nanophotonic structures due to their special photophysical properties such as plasmons. Metal photonic crystals have many irreplaceable application values in optoelectronic technology, sensor technology and optical engineering, and have developed into an important research field of nanophotonics. This makes the preparation technology of metal photonic crystals highlight its significance. The requirements for preparation technology are mainly reflected in the aspects of simple process, large preparation area, low cost, high efficiency, suitable for mass production, etc., which can provide fundamental technical guarantee for the engineering application of nanophotonic devices.

"Flexibility" has always been an important aspect of the functionalization of nanophotonic structures. The realization of "flexibility" not only enriches the form of nano-fabrication technology and nano-photonic structure, but more importantly, it greatly expands the application scope of nano-devices such as photonic crystals, especially in the application fields where ordinary flat-panel devices cannot be used. The development and application provide a broad space for development. Most directly, flexible devices can be applied to various stress, deformation, and displacement sensing devices, and can be integrated with various optical and optoelectronic systems to realize their "plasmonic polaritons" and "photonic crystals" under special space and shape conditions. "The function of the device.

Among the currently used flexible photonic crystal preparation technologies, nanoimprinting is the only relatively mature and widely used preparation technology. Although this method can realize the preparation of large-area nanophotonic structures, there are problems such as complex preparation process, defects introduced in the transfer process, resulting in reduced repeatability and success rate, and it is greatly affected by the type of material. In particular, nanoimprint technology has not yet achieved the preparation of metal photonic crystals. In this way, the preparation of flexible photonic crystals urgently needs a batch preparation technology with simple process and high success rate.

So far, there is no metal photonic crystal with a period of nanometer scale prepared on a flexible substrate. This is largely due to the multiple challenges involved in the associated nanofabrication process.

In view of the above problems, the present invention proposes a large-area and batch-scale preparation technology of a metal photonic crystal structure with a simple and practical process and a success rate of 100% at a nanoscale period.

Contents of the invention

The core content of the present invention is to realize the complete and non-destructive transfer printing of metal photonic crystals prepared on glass and other hard flat substrates to flexible substrates, such as PDMS, silicone glue, and glass glue material substrates, with a success rate of 100%. , to obtain a periodic array of plasmonic nanostructures with good ductility, bendability and flexibility.

A method for preparing a metal photonic crystal based on a flexible substrate of the present invention is characterized in that it comprises the following steps:

(1) Prepare a buffer layer on the flat substrate to obtain a buffer layer substrate, and then prepare a photoresist (PR) nano-grating structure (as shown in Figure 1a) on the buffer layer;

(2) Chemically synthesized gold nanoparticles (Au NPs) are formed into a colloidal solution in xylene, and the xylene colloidal solution of gold nanoparticles is spin-coated on the surface of the photoresist nano-grating in step (1). , the gold nanoparticles are confined to the grating grooves (as shown in Figure 1b);

(3) After heat-treating the sample on the buffer layer substrate prepared in step (2) in a muffle furnace at 200-450°C (preferably 350°C), the organic ligands on the surface of the gold nanoparticles are sublimated, and the gold nanoparticles are fully melted, All enter the grating groove, and form continuous gold nanowires along the grating groove (as shown in Figure 1c), and successfully prepare a metal photonic crystal composed of a gold nanowire array on the surface of the buffer layer substrate;

(4) Coat the flexible substrate liquid mixed with curing agent on the surface of the metal photonic crystal prepared in step (3), and then cover another piece of buffer layer matrix on top, and make the buffer layer contact with the flexible substrate liquid, The two sides between the two buffer layer substrates are supported by silicone rubber pads to ensure a uniform and controllable flexible substrate (as shown in Figure 1d and Figure 1e);

(5) Heating the sample prepared in step (4) at 100-120° C. to complete the cross-linking polymerization reaction of the flexible substrate, and the heating time is preferably 45 minutes to 1 hour;

(6) Place the sample obtained in step (5) in hydrochloric acid or sulfuric acid solution, so that the buffer layers on the upper and lower substrates are fully dissolved, and the flexible substrate and the tightly bonded metal photonic crystals on it are completely detached from the substrate ( as shown in Figure 1f);

(7) Finally, the flexible device obtained in step (6) was washed with distilled water to remove residual acid and possible impurities, and an independent flexible device (as shown in Figure 1g) was obtained to complete the preparation of the flexible metal photonic crystal.

The flexible substrate mentioned above is preferably a substrate made of PDMS, silicone glue, or glass glue. The material of the buffer layer is metal, metal oxide and other materials soluble in hydrochloric acid or sulfuric acid, and can be prepared on a flat substrate by thermal evaporation, magnetron sputtering, pulsed laser deposition and other processes, preferably an ITO layer.

The above-mentioned substrate is made of transparent materials, such as glass and quartz, which are insoluble in hydrochloric acid, sulfuric acid and other solutions and can withstand heat treatment processes below 450°C.

The above-mentioned gold nanoparticles are replaced with other metal nanoparticle materials with ligands on the surface which are insoluble in hydrochloric acid or sulfuric acid.

Preferably: the ITO layer on the upper and lower substrates is used as a buffer layer, and a silicon rubber pad with a thickness of 1 mm is used to isolate it, so as to control the thickness and parallelism of the final flexible substrate. Heat the whole device in an oven at 100° C. for 50-60 minutes to complete the cross-linking polymerization reaction. After cooling, soak in 20%-30% hydrochloric acid for 2 hours to realize the peeling off of the glass substrate and PDMS, thereby realizing the transfer printing of metal photonic crystals to PDMS. Wash the flexible metal photonic crystal device in deionized water to remove residual hydrochloric acid and other impurities attached to the surface, and dry it at room temperature to complete the preparation of the device.

The metal photonic crystal structure on the ITO glass substrate can be prepared by various nano-photonic structure methods such as solution method, thermal evaporation method, and reactive ion beam dry etching method. That is, the preparation method in the present invention is not limited by the photonic crystal preparation method.

Utilize the insolubility of nano-photonic structures composed of noble metals and dielectric materials (waveguide layer and template grating materials) in waveguide-coupled metal photonic crystals in hydrochloric acid and sulfuric acid, while the waveguide layer material indium tin oxide (ITO) has good solubility characteristics in it , and the good flexibility and stability of polydimethylsiloxane (PDMS) after cross-linking and polymerization, the complete transfer of metal photonic crystals from ITO glass hard substrates to PDMS has been realized, and the success rate can reach 100% %. Thus, a flexible metal photonic crystal device is obtained. This device has important direct application value for the development of stress and deformation sensors and new flexible optoelectronic devices.

Advantageous features of the present invention:

(1) The present invention realizes the preparation of metal photonic crystals on flexible substrates, and its core technology is to realize the complete transfer of metal photonic crystals from glass substrates to PDMS. In fact, this technology is not limited by the preparation method of metal photonic crystals.

(2) The preparation method is simple and easy, does not require expensive equipment, complicated process, special and expensive materials, precise manipulation and skills, and the preparation process is efficient.

(3) Utilizing the easy solubility of metal oxides in the buffer layer in hydrochloric acid and sulfuric acid, the complete non-destructive transfer of metal photonic crystals from the hard ITO glass flat substrate to the PDMS flexible substrate is realized, and the success rate of the transfer process reaches 100% %.

(4) The size and thickness of the flexible substrate can be freely controlled according to the needs, without affecting the transfer process of the metal photonic crystal.

(5) It is suitable for the transfer printing of metal photonic structures with any period and size and the preparation of flexible devices, and is not affected by the shape and dimension of metal photonic structures.

Description of drawings

Figure 1. Schematic diagram of the fabrication process of metal photonic crystals based on flexible substrates;

Figure 2. Physical photos and diffraction patterns of flexible metal photonic crystal devices;

A: PDMS flexible substrate; B: metal photonic crystal and its diffraction pattern under white light irradiation.

Figure 3. Electron microscopic images of metal photonic crystals prepared on ITO glass;

Figure 4. Electron micrographs of metal photonic crystals transferred onto PDMS;

Figure 5. Atomic force microscopy images of metal photonic crystals transferred onto PDMS;

Figure 6. Stretch sensing experiment of flexible metal photonic crystals;

A: metal photonic crystal prepared on PDMS flexible substrate, B: fixed bracket, C: translation stage, D: collimated white light source, E: focusing lens, F: collimating lens, G: fiber optic probe of fiber optic spectrometer, H: fiber optic spectrometer;

Fig. 7, the definition of flexible metal photonic crystal deformation sensing signal amplitude (A);

Fig. 8. Test results of stretching and recovery curves of flexible metal photonic crystals.

Detailed ways:

The present invention will be further described in conjunction with examples, but the present invention is not limited to the following examples. Example 1: Preparation of flexible metal photonic crystals.

(1) Spin-coat S1805 photoresist at 2000rpm on a glass substrate coated with a 200nm indium tin oxide (ITO) film.

(2) He-Cd laser with a wavelength of 325nm is used to carry out interference lithography in the S1805 photoresist film. The angle between the two laser beams participating in the interference lithography is controlled to be 48 degrees to ensure that the period of the photoresist grating is 400nm. The exposure time was controlled by an optical shutter for 20 s. Then develop in the developer for 6s. Then rinse with distilled water for 30 s. The cleaned sample was dried in an oven at 120° C. to obtain a photoresist grating structure.

(3) A colloidal solution of chemically synthesized gold nanoparticles in xylene with a concentration of 100 mg/ml was spin-coated on the surface of the photoresist grating at a rotational speed of 2000 rpm.

(4) The sample prepared in (2) was heated in a muffle furnace at 350° C. for 20 minutes to obtain a metal photonic crystal structure prepared on an ITO glass substrate.

(5) Mix PDMS and curing agent at a ratio of 10:1 and remove air bubbles with a vacuum pump.

(6) After placing a silicon rubber spacer with a thickness of about 1 mm on the metal photonic crystal obtained in (4), pour PDMS on the surface of the metal photonic crystal.

(7) Cover another piece of ITO glass on the metal photonic crystal coated with PDMS, and make the ITO film face the PDMS. And the upper ITO glass is supported on the silicon rubber pad.

(8) Place the sample in (7) in an oven and heat it at 100°C for 50 minutes to complete the cross-linking polymerization reaction of PDMS and become a transparent and flexible substrate.

(9) Prepare about 30 milliliters of hydrochloric acid aqueous solution with a concentration of 25%, and place it in a 50 milliliter beaker.

(10) Immerse the sample in step (8) in the hydrochloric acid solution, and let it stand at the bottom of the beaker for about 2 hours, so that the upper and lower ITO films are fully dissolved in the hydrochloric acid. PDMS and the metal photonic crystal thin film tightly bonded to it are naturally peeled off from the upper and lower glass substrates.

(11) Clean the metal photonic crystal obtained in (10) and transferred onto PDMS with clean water, and dry naturally to obtain a flexible metal photonic crystal device.

(12) Flexible metal photonic crystals exhibit strong tensile and bending toughness. Figure 2 shows a photo of a flexible metal photonic crystal bent under stress.

Example 2: Microstructure testing of flexible metal photonic crystals.

(1) Adopt Nova NanoSEM type scanning electron microscope to measure the microstructure of the metal photonic crystal prepared in example 1 step 4, as shown in Figure 3. Metal photonic crystals have a period of about 400nm and consist of periodically arranged gold nanowires. The average width of gold nanowires is about 165 nm. Some gold nanoparticles remain between the gold nanowires, and the diameters thereof are all less than 70nm.

(2) The metal photonic crystal structure transferred to PDMS was measured by FEI Phenom desktop scanning electron microscope. Since the PDMS substrate is non-conductive, it is impossible to complete high-resolution electron microscopic measurement, that is, the testing instrument used in step (1) cannot be used. The test results are shown in Figure 4. Since what is measured at this time is the bottom surface of the metal photonic crystal prepared on the ITO glass in step (1), and there is a photoresist between the gold nanowires, the SEM image in Figure 4 does not observe the gold nanowires between the gold nanowires. granular structure.

(3) The atomic force microscopy images of metal photonic crystals on flexible substrates were tested using the atomic force microscope integrated in the Witec SNOM system, and the test results are shown in Figure 5. The test results show that the modulation depth of metal photonic crystals on flexible substrates is about 18nm.

Example 3: Stretching realization of flexible metal photonic crystal and its stretching deformation sensor experiment.

(1) A self-built flexible photonic crystal tensile test platform is used. The schematic diagram of the device is shown in Figure 6. The two ends of the PDMS substrate of the flexible metal photonic crystal are respectively fixed on two independent precision translation stages. Move the two translation stages separately to make them in the middle of the scale range, and add a certain initial stress to the PDMS substrate to ensure that the substrate is flattened. Except for the stretching direction, the substrate has no deformation and stress in other directions.

(2) A broadband white light source is focused to irradiate the metal photonic crystal on the PDMS substrate, and the transmitted light is accepted by the probe of the fiber optic spectrometer in order to measure the transmission spectrum.

(3) Firstly, the transmission spectrum of the flexible metal photonic crystal under the initial stress is collected, which is recorded as I ₀ (λ,Δ=0), and it is used as the background spectrum.

(4) Use one of the translation stages to increase the deformation D, and record the transmission spectrum for every 100 μm increase, I _S (λ, Δ) until the deformation reaches 1 mm. Complete the stretch implementation process. Calculate the tensile strain spectrum - log ₁₀ [ _IS (λ,Δ)/I ₀ (λ,Δ=0)].

(5) Move the translation stage adjusted in (4) to gradually reduce the deformation amount, and record the transmission spectrum I _R (λ, Δ) every time the reduction is 100 μm, until the deformation amount returns to 0. Complete the reply experiment process. Deformation recovery spectra were calculated - log ₁₀ [I _R (λ,Δ)/I ₀ (λ,Δ=0)].

(6) Measure the sensing signal amplitudes corresponding to different deformations in the stretching and recovery experiments, respectively. The definition of sensor signal amplitude is shown in Fig. 7. Draw the stretch and recovery curves of the sensor, as shown in Figure 8. "A" indicates the amplitude of the sensing signal, and "D" indicates the amount of deformation. "■" indicates the tensile test curve. Represents the return to the experimental curve.

Claims (7)

1., based on a metal photonic crystal preparation method for flexible substrate, it is characterized in that, comprise the following steps:

(1) on flat base, prepare cushion, obtain cushion matrix, prepare photoresist (PR) nanometer grating structure on the buffer layer again;

(2) gold nano grain (Au NP) of chemosynthesis is formed colloidal solution in dimethylbenzene, the dimethylbenzene colloidal solution of gold nano grain is spin-coated on the surface of step (1) photoresist nanometer grating, under surface tension effects, gold nano grain is limited in grating groove;

(3) sample on cushion matrix step (2) prepared is in 200-450 DEG C of muffle furnace after thermal treatment, make organic ligand distillation on gold nano grain surface, the abundant melting of gold nano grain, all enter in grating groove, and form continuous print nanowires of gold along grating groove, the metal photonic crystal that Crystal structure is formed successfully has been prepared on the surface of cushion matrix;

(4) the flexible substrate liquid being mixed with hardening agent is coated on metal photonic crystal surface prepared by step (3), then top covers another sheet cushion matrix again, and buffering aspect is contacted with flexible substrate liquid, both sides silicone rubber pad between two panels cushion matrix supports, to ensure to obtain even, the controlled flexible substrate of thickness;

(5) by sample obtained in step (4) 100-120 DEG C of heating, complete flexible substrate cross-linking polymerization;

(6) sample that step (5) obtains is placed in hydrochloric acid or sulfuric acid solution, the cushion on upper and lower two matrixes is fully dissolved, flexible substrate and on the metal photonic crystal of combining closely separate from matrix up hill and dale;

(7) finally the flexible device distilled water that step (6) obtains is cleaned, remove remaining acid solution and issuable impurity, obtain independently flexible device, complete the preparation of flexible metal photonic crystal;

Matrix adopts and is insoluble to hydrochloric acid, sulfuric acid solution and can stand the transparent material of the heat treatment process of less than 450 DEG C; The material of cushion is the metal, the metal oxide materials that are dissolved in hydrochloric acid or sulfuric acid, and can be prepared on flat base by hot evaporation, magnetron sputtering or pulse laser deposition process process.

2. according to the method for claim 1, it is characterized in that, the preferred PDMS of flexible substrate, silicone adhesive, glass cement material substrate.

3. according to the method for claim 1, it is characterized in that, cushion is ITO layer.

4. according to the method for claim 1, it is characterized in that, flat base is glass or quartz.

5. according to the method for claim 1, it is characterized in that, the heat treatment temperature of step (2) is 350 DEG C.

6. according to the method for claim 1, it is characterized in that, the time that step (5) adds thermal response is 45 minutes-1 hour.

7. according to the method for claim 1, it is characterized in that, there is polydentate metal nano-particle material on the surface being applicable to be insoluble to hydrochloric acid or sulfuric acid that gold nano grain replaces with other.