CN110695515B - Method and system for fabricating nanocone arrays on silk thin film by femtosecond laser - Google Patents

Abstract

The invention relates to a method and a system for processing a nano-cone array on a silk film by using a femtosecond laser, and belongs to the technical field of femtosecond laser applications. The invention firstly prepares the silk film by chemical method, then focuses a single femtosecond laser pulse to the surface of the silk film through a microscope objective lens, and adjusts the energy flux incident on the surface of the silk film to obtain a diameter of 200-500 nm and a height of 17 ~170nm nanocone structure. Under the irradiation of femtosecond laser pulse sequence, the silk thin film was continuously moved by an electronically controlled translation stage, and the nanocone arrays with a pitch of 600nm-1500nm were fabricated. The method of the invention is based on the multi-photon absorption and expansion effect of silk fibroin on femtosecond laser, and realizes the processing of nano-cone arrays far smaller than the diffraction limit on the surface of the silk film. The invention has the advantages of high precision, high flexibility, non-contact, no mask, and can be carried out in atmospheric environment, and provides a feasible method for preparing bio-photoelectric devices.

Description

Method and system for fabricating nanocone arrays on silk thin film by femtosecond laser

technical field

The invention relates to a method and a system for processing a nano-cone array on a silk film by using a femtosecond laser, and belongs to the technical field of femtosecond laser applications.

Background technique

With the development of biomedical technology, the demand for biocompatible sensors and optoelectronic devices is becoming more and more urgent. Silk is a natural protein fiber, which is expected to become a bridge connecting the biological world and the optoelectronic world due to its special structural form, excellent mechanical properties, optical properties, good biocompatibility and biodegradability. Currently, chemical methods are commonly used to convert silk into transparent films or bulk materials. Further, different micro-nano structures were prepared on the surface of silk films by nano-imprinting, nano-casting, soft etching, electron beam irradiation and other micro-nano processing methods, thereby obtaining holographic gratings, microlens arrays, two-dimensional nanophotonic crystals, biological Micro-nano optoelectronic devices such as active sensors.

The above methods have greatly expanded the application of silk in the biomedical field, but there are still some problems with these technologies. For example, methods such as nano-imprinting, nano-casting, and soft etching need to prepare a processing template first, and the processing flexibility is poor; electron beam processing needs to be carried out in a vacuum environment, and the processing conditions are relatively harsh.

Existing "a method of processing nano-blind holes on the surface of a single silk by using a femtosecond laser" (Chinese patent, application number: 201910233029.7), which is used to prepare an independent single oval nano-blind hole on the surface of a single silk . There is still a lack of a method to flexibly fabricate nanoscale pyramid-shaped protrusion arrays on silk thin films in an atmospheric environment.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a method for processing nanocone arrays on the surface of silk film by using femtosecond laser, improve the existing method, utilize the multiphoton absorption expansion effect in the process of interaction between femtosecond laser and silk, through reasonable regulation and control Femtosecond laser parameters were used to obtain nanocone arrays of different sizes and spacings, so as to flexibly perform nanoscale processing on the surface of silk thin films in an atmospheric environment.

The method for processing nanocone arrays on silk thin films by using femtosecond lasers proposed by the present invention comprises the following steps:

(1) utilize chemical method to prepare silk film, and the process is as follows:

(1-1) Boil the cocoons in a sodium carbonate solution for 30 to 40 minutes, remove sericin, obtain silk fibers, and air dry the silk fibers naturally;

(1-2) adding the silk fibers of step (1-1) into the lithium bromide solution to completely dissolve the silk fibers, sealing the completely dissolved silk fibers, and placing them at 60° C. for 4 to 6 hours to obtain silk fibroin solution;

(1-3) Dialyzing and centrifuging the silk fibroin solution in step (1-2) to obtain a silk fibroin aqueous solution with a concentration of 7%, and placing the silk fibroin aqueous solution in a 4°C environment for preservation;

(1-4) spin-coating the silk fibroin aqueous solution of step (1-3) on a silica substrate to obtain a silk film with a thickness of 500 nm to 1000 nm, and naturally drying the silk film;

(2) The femtosecond laser pulse with a single energy flux of 6-8 J/cm ² is vertically focused on the surface of the silk film in step (1), and a diameter of 200-500 nm and a height of 17-170 nm are processed on the silk film. conical protrusion;

(3) Set the repetition frequency of the femtosecond laser to 1 kHz, control the femtosecond laser to scan along a straight line at a moving speed of 600-1500 μm/s, and process a line of equidistant conical protrusions with a spacing of 600 nm to 1500 nm on the silk film ;

(4) Line-feed scanning, repeating step (3) many times to make the distance between two lines 600nm-1500nm, and processing nanocone arrays with a spacing of 600nm-1500nm on the silk film.

The system for processing nanocone arrays on silk films by using femtosecond lasers proposed by the present invention includes femtosecond lasers, neutral density attenuators, electronically controlled shutters, dichroic mirrors, microscope objective lenses, illumination light sources, transflectors mirror, imaging lens, camera, electronically controlled translation stage, signal delay generator and computer; the femtosecond laser pulse sequence emitted by the femtosecond laser sequentially passes through the neutral density attenuator, the electronically controlled shutter, the dichroic mirror and the After the microscope objective lens is focused on the surface of the silk film to be processed, a processing optical path is formed; the white light emitted by the illumination light source is irradiated to the surface of the silk film to be processed after passing through the semi-transparent mirror, the dichroic mirror and the microscope objective lens in turn, The illumination light path is formed; the illumination light reflected by the surface of the silk film passes through the microscope objective lens, the dichroic mirror, the semi-transparent mirror and the imaging lens in turn and then irradiates the camera, and finally is imaged to the computer display through the data line to form the imaging light path ; The processing optical path and the illumination optical path overlap after passing through the dichroic mirror, the imaging optical path and the lighting optical path overlap between the silk film and the semi-transparent mirror, the silk film to be processed is fixed on the electronically controlled translation stage, and the computer passes through the The data lines are respectively connected with the electronically controlled translation stage, the signal delay generator and the camera, and the signal delay generators are respectively connected with the electronically controlled shutter and the femtosecond laser through the data lines.

A method and system for processing nanocone arrays on silk thin films by using femtosecond lasers proposed by the present invention have the following advantages:

1. Compared with the existing methods such as nano-imprinting, nano-casting, soft etching, electron beam irradiation, etc., the method of the present invention is a high-precision, high-flexibility, non-contact, mask-free, and can be used in atmospheric environment. processing method in .

2. The method of the present invention determines that when a single femtosecond laser pulse with an energy flux of 6-8 J/cm ² is vertically incident on the surface of the silk film, a nanocone structure with a diameter of 200-500 nm and a height of 17-170 nm can be obtained.

3. The method of the present invention is a processing method with biocompatibility, which can be used to prepare bioactive sensors and other devices that require high biocompatibility.

Description of drawings

FIG. 1 is a schematic structural diagram of a system for processing a nanocone array on a silk film by using a femtosecond laser proposed by the present invention.

In Figure 1, 1 is a femtosecond laser, 2 is a neutral density attenuator, 3 is an electronically controlled shutter, 4 is a dichroic mirror, 5 is a microscope objective, 6 is a silk film, 7 is an electronically controlled translation stage, and 8 It is a half mirror, 9 is an illumination light source, 10 is an imaging lens, 11 is a camera, 12 is a signal delay generator, and 13 is a computer.

Detailed ways

The method for processing nanocone arrays on silk thin films by using femtosecond lasers proposed by the present invention comprises the following steps:

(1) utilize chemical method to prepare silk film, and the process is as follows:

(1-1) Boil the cocoons in a sodium carbonate solution for 30 to 40 minutes, remove sericin, obtain silk fibers, and air dry the silk fibers naturally;

(1-2) adding the silk fibers of step (1-1) into the lithium bromide solution to completely dissolve the silk fibers, sealing the completely dissolved silk fibers, and placing them at 60° C. for 4 to 6 hours to obtain silk fibroin solution;

(1-3) Dialyzing and centrifuging the silk fibroin solution in step (1-2) to obtain a silk fibroin aqueous solution with a concentration of 7%, and placing the silk fibroin aqueous solution in a 4°C environment for preservation;

(1-4) spin-coating the silk fibroin aqueous solution of step (1-3) on a silica substrate to obtain a silk film with a thickness of 500 nm to 1000 nm, and naturally drying the silk film;

(2) The femtosecond laser pulse with a single energy flux of 6-8 J/cm ² is vertically focused on the surface of the silk film in step (1), and a diameter of 200-500 nm and a height of 17-170 nm are processed on the silk film. conical protrusion;

(3) Set the repetition frequency of the femtosecond laser to 1 kHz, control the femtosecond laser to scan along a straight line at a moving speed of 600-1500 μm/s, and process a line of equidistant conical protrusions with a spacing of 600 nm to 1500 nm on the silk film ;

(4) Line-feed scanning, repeating step (3) many times to make the distance between two lines 600nm-1500nm, and processing nanocone arrays with a spacing of 600nm-1500nm on the silk film. The distance between the conical protrusions in the nanocone array and the distance between the scanning lines may or may not be equal.

The system for processing nanocone arrays on silk films by femtosecond laser proposed by the present invention has a structure as shown in Figure 1, including a femtosecond laser 1, a neutral density attenuator 2, an electronically controlled shutter 3, and a dichroic mirror 4 , microscope objective lens 5, illumination light source 9, semi-transparent mirror 8, imaging lens 10, camera 11, electronically controlled translation stage 7, signal delay generator 12 and computer 13; The laser pulse sequence passes through the neutral density attenuator 2, the electronically controlled shutter 3, the dichroic mirror 4 and the microscope objective lens 5 in turn and is focused on the surface of the silk film 6 to be processed to form a processing optical path; the illumination light source 9 emits The white light is irradiated to the surface of the silk film 6 to be processed after passing through the semi-transparent mirror 8, the dichroic mirror 4 and the microscope objective lens 5 in turn to form an illumination light path; The objective lens 5, the dichroic mirror 4, the half mirror 9 and the imaging lens 10 are irradiated on the camera 11, and finally imaged to the display of the computer 13 through the data line, forming an imaging optical path; After the color mirror 4 is overlapped, the imaging optical path and the illumination optical path overlap between the silk film 6 and the semi-transparent mirror 8, the silk film 6 to be processed is fixed on the electronically controlled translation stage 7, and the computer 13 is respectively connected with the data line through the data line. The electronically controlled translation stage 7 , the signal delay generator 12 and the camera 13 are connected, and the signal delay generator 12 is respectively connected with the electronically controlled shutter 3 and the femtosecond laser 1 through data lines.

Below in conjunction with accompanying drawing and embodiment, the present invention is further introduced:

The present invention is implemented in a femtosecond laser processing system as shown in FIG. 1 , and the system includes three parts: a processing subsystem, an observation subsystem and a control subsystem. The processing subsystem includes a femtosecond laser 1 , a neutral density attenuator 2 , an electronically controlled shutter 3 , a dichroic mirror 4 , a microscope objective lens 5 , a silk film 6 and an electronically controlled translation stage 7 . The observation subsystem includes an illumination light source 9 , a half mirror 8 , a microscope objective lens 5 , an imaging lens 10 , a CCD camera 11 and a computer 13 . The control subsystem includes a femtosecond laser 1 , an electronically controlled shutter 3 , an electronically controlled translation stage 7 , a signal delay generator 12 and a computer 13 .

In the processing subsystem, the femtosecond laser pulse sequence output by the femtosecond laser 1 passes through the neutral density attenuator 2 to adjust the energy, passes through the electronically controlled shutter 3 and is fully reflected by the dichroic mirror 4, and then passes through the microscope objective lens 5. Focus on the silk film 6 surface. The silk film 6 is fixed on the electronically controlled translation stage 7 for precise control of the position of each nanocone in the nanocone array. The parameters of the femtosecond laser 1 in the embodiment are: the center wavelength of the femtosecond laser is 800 nm, the repetition frequency is 1 kHz, and the pulse width is 35 fs. The parameters of the microscope objective lens 5 are: a magnification of 50 times, a numerical aperture of 0.5, and a working distance of 10.6 mm.

In the observation subsystem, the illumination light emitted by the illumination light source 9 passes through the half mirror 8 and the dichroic mirror 4 and is focused by the microscope objective lens 5 onto the surface of the silk film 6 for illuminating the processing area. The real-time image of the processing area is enlarged by the microscope objective lens 5 and then transmitted through the dichroic mirror 4 , and then reflected by the half mirror 8 into the imaging lens 10 . The imaging lens 10 is used to image the enlarged real-time image on the CCD camera 11 and transmit it to the display of the computer 13 through the signal line for observing the processing process.

In the control subsystem, the computer 13 is connected with the electronically controlled translation stage 7 and the signal delay generator 12 through a data line. The signal delay generator 12 is connected to the femtosecond laser 1 and the electronically controlled shutter 3 through a data line. The signal delay generator 12 is used for calibrating the moment when the laser sends out the pulse signal. It can collect the laser pulse signal from the femtosecond laser 1, and can send an opening signal to the electronically controlled shutter 3 after any delay. In the embodiment, the signal delay generator 12 starts to collect the laser pulse signal sent by the laser 1 after clicking the start processing command under the control of the computer 13, and opens the electronically controlled shutter when it collects the first signal for 0.1 ms. At the same time, the computer-controlled electronically controlled translation stage starts to move.

The debugging process of the femtosecond laser processing system is: turn on the femtosecond laser, generate femtosecond laser pulses, and adjust the repetition frequency to 1kHz. Adjust the height of the translation stage so that the diameter of the ablation spot produced by a single pulse at a fixed energy on the surface of the silk film is the smallest, and at this time the femtosecond laser is accurately focused on the surface of the silk film. Through computer control, after clicking the start processing command, the signal delay generator starts to collect the laser pulse signal sent by the laser, and opens the electronically controlled shutter when it collects the first laser pulse signal for 0.1ms. At the same time, the computer-controlled electronically controlled translation stage starts to move to complete the debugging of the femtosecond laser processing system.

Following are the concrete steps of the inventive method:

Step 1, utilize chemical method to prepare silk film, and step 1 specifically includes:

Step 1.1) Boil the cocoons in a sodium carbonate solution with a concentration of 0.02M for 30 minutes, wash with ultrapure water 3 times, remove sericin, obtain silk fibers and dry them at room temperature for later use;

Step 1.2) Completely dissolve the silk fiber obtained in step 1.1 with a lithium bromide solution with a concentration of 9M, seal it and place it at 60°C for 4 hours to obtain a silk fibroin solution;

Step 1.3) The silk fibroin solution obtained in step 1.2 was dialyzed in water for 48 hours to remove lithium bromide, followed by centrifugation, and the obtained supernatant was an aqueous solution of silk fibroin with a concentration of about 7%. The above aqueous solution was placed in an environment of 4 °C and stored for later use.

Step 1.4) Take 500 μL of the silk fibroin aqueous solution obtained in step 1.3 and spin-coat it on a silica substrate to obtain a silk film. The spin-coating speed is 2,000 r/min and the spin-coating time is 30s.

Step 2, install the processed silk film sample and focus the femtosecond laser pulse sequence on the surface of the silk film 6 through the microscope objective lens 5 . Step 2 specifically includes:

Step 2.1) Fix the silk film 6 obtained in step 1 to the upper surface of the electronically controlled translation stage 7 with tape. Turn on femtosecond laser 1 to generate femtosecond laser pulses. By adjusting the direction of the dichroic mirror 4, the femtosecond laser is vertically incident on the surface of the silk film 6;

Step 2.2) Adjust the height of the electronically controlled translation stage 7 so that the diameter of the ablation spot generated by a single pulse at a fixed energy on the surface of the silk film is the smallest. At this time, the femtosecond laser is accurately focused on the surface of the silk film.

Step 3, set the processing parameters, and process the nanocone array. Step 3 specifically includes:

Step 3.1), by adjusting the neutral density attenuation sheet 2, the single pulse energy flux incident on the surface of the silk film 6 is 6-8 J/cm ² .

Step 3.2), set the moving speed of the translation stage to be 600-1500 μm/s, and the scanning interval to be 600-1500 nm to obtain a nanocone array with a spacing of 600-1500 nm.

Using the method of the invention, nanocone arrays with diameters of 200-500 nm, heights of 17-170 nm and spacings of 600-1500 nm are formed on the surface of the silk film.

Embodiments of the inventive method are introduced below:

Example 1:

Adjust the neutral density attenuation sheet 2, set the energy flux of a single pulse to 6.2J/cm ² , the moving speed of the translation stage to be 800 μm/s, and the scanning interval to be 800 nm. The diameter of the silk film 6 is 210 nm and the height is 17.55 nm. Array of nanocones with a pitch of 800 nm.

Example 2:

Adjust the neutral density attenuation sheet 2, set the energy flux of a single pulse to 7J/cm ² , the moving speed of the translation stage to be 1000 μm/s, and the scanning interval to be 1000 nm. On the silk film 6, the diameter is 320 nm, the height is 44.4 nm, and the spacing is 320 nm. 1000nm nanocone array.

Example 3:

Adjust the neutral density attenuation sheet 2, set the energy flux of a single pulse to 7.7J/cm ² , the moving speed of the translation stage to be 1500 μm/s, and the scanning interval to be 1500 nm. On the silk film 6, the diameter is 420 nm, the height is 168 nm, and the spacing is 168 nm. 1500nm nanocone array.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (1)

1. A method for processing a nanocone array on a silk film by using femtosecond laser is characterized in that: the method comprises the following steps:

(1) the silk film is prepared by a chemical method, and the process is as follows:

(1-1) boiling the silkworm cocoons in a sodium carbonate solution for 30-40 minutes, removing sericin to obtain silk fibers, and naturally drying the silk fibers;

(1-2) adding the silk fibers obtained in the step (1-1) into a lithium bromide solution to completely dissolve the silk fibers, sealing the completely dissolved silk fibers, and standing at 60 ℃ for 4-6 hours to obtain a silk fibroin solution;

(1-3) dialyzing and centrifuging the silk fibroin solution obtained in the step (1-2) to obtain a 7% silk fibroin aqueous solution, and storing the silk fibroin aqueous solution in an environment at 4 ℃;

(1-4) spin-coating the silk fibroin aqueous solution obtained in the step (1-3) on a silicon dioxide substrate to obtain a silk film with the thickness of 500-1000 nm, and naturally drying the silk film;

(2) the method comprises the following steps of constructing a system for processing a nanocone array on a silk film by using femtosecond laser, wherein the system comprises a femtosecond laser, a neutral density attenuation sheet, an electric control shutter, a dichroic mirror, a microscope objective, a lighting source, a semi-transparent semi-reflecting mirror, an imaging lens, a camera, an electric control translation stage, a signal delay generator and a computer; the femtosecond laser pulse sequence emitted by the femtosecond laser sequentially passes through the neutral density attenuation sheet, the electric control shutter, the dichroic mirror and the microscope objective lens and then is focused on the surface of the silk film to be processed to form a processing light path; white light emitted by the illumination light source sequentially passes through the semi-transparent semi-reflecting mirror, the dichroic mirror and the microscope objective lens and then irradiates the surface of the silk film to be processed to form an illumination light path; the illumination light reflected by the surface of the silk film sequentially passes through the microscope objective, the dichroic mirror, the semi-transmitting and semi-reflecting mirror and the imaging lens and then is irradiated onto the camera, and finally is imaged to a computer display through a data line to form an imaging light path; the processing light path and the lighting light path are overlapped after passing through the dichroic mirror, the imaging light path and the lighting light path are overlapped between the silk film and the semi-transparent semi-reflective mirror, the silk film to be processed prepared in the step (1) is fixed on the electric control translation table, the computer is respectively connected with the electric control translation table, the signal delay generator and the camera through data lines, and the signal delay generator is respectively connected with the electric control shutter and the femtosecond laser through the data lines;

(3) the single energy flux is 6-8J/cm²The femtosecond laser pulse is vertically focused on the surface of the silk film in the step (2), and conical bulges with the diameter of 200-500 nm and the height of 17-170 nm are processed on the silk film;

(4) setting the repetition frequency of the femtosecond laser to be 1kHz, controlling the femtosecond laser to scan along a straight line at the moving speed of 600-1500 mu m/s, and processing a row of equidistant conical bulges with the spacing of 600-1500 nm on the silk film;

(5) and (5) line changing scanning is carried out, the step (4) is repeated for multiple times, the distance between two lines is 600 nm-1500 nm, and the nano cone arrays with the spacing of 600 nm-1500 nm are processed on the silk film.

Images