Preparation method of quantum dot spatial light emitting modulation device using metasurface

Abstract

The application discloses a preparation method of a quantum dot space light-emitting modulation device using a super surface, and has the characteristics that by adjusting the period structure of a unit structure and the properties of quantum dots, the plasmon mode in the period structure is matched with the photo-induced light-emitting mode of the quantum dots, and by photo-induced light-emitting modulation of the quantum dots, focusing and vortex phase of different wave bands are realized, so that the device can respond to different circularly polarized light. Compared with the prior art, the application has the advantages that by processing elliptical nano-hole unit structures with different arrangement angles on a metal surface, the selection of modulation wave bands is realized, the film thickness and other parameters do not need to be changed, the repeatability and stability are good, and by photo-induced light-emitting modulation of the quantum dots, light-emitting focusing and vortex light of different wave bands are realized, so that the application has potential application prospects in the fields of spatial light modulation and optical communication.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of super surface, in particular to a preparation method of quantum dot spatial light emitting modulation device using super surface. BACKGROUND

[0002] Spatial light modulation device is an optical device used to select the required radiation waveband, and controls the spatial light of a specific waveband, which plays an important role in daily life and scientific research, high-tech applications. The spatial light modulation device controls the selected light field by reflecting (transmitting) the light wave of a single wavelength or a small range of wavebands selected with precision. The spatial light modulation device can control, adjust and change the transmission, reflection, polarization or phase state of light by changing the film thickness.

[0003] In recent years, quantum dots with good fluorescence efficiency have attracted more and more attention, and some optical phenomena have been proposed and further studied. As a low-dimensional metamaterial, quantum dots have been applied in many fields due to their superior light emitting performance. Quantum dots provide more possibilities for light waveband control, and super surfaces have been designed to produce super natural optical properties by changing the geometry and material of their unit structure. The super surface has shown unprecedented ability in light field control. The combination of metal super surface and quantum dots can bring more optical properties. However, how to precisely control the light emission of quantum dots and super surfaces, accurately determine the mode position, and realize the function of spatial light modulation is still a challenge.

[0004] The phase type spatial light modulator of the prior art can only control a single wavelength, cannot meet the control of multi-wavelength laser, and has high cost. SUMMARY

[0005] The present application is aimed at the deficiencies of the prior art and provides a preparation method of quantum dot spatial light emitting modulation device using super surface. The method arranges the elliptical nano-hole structure to form a super surface, so that it can respond to different circularly polarized light, and realizes the focusing and vortex phase of different wavebands through the photoluminescence control of quantum dots. The method arranges the unit structure at a specific angle to form a corresponding super surface, so that it can be processed according to the requirements of the required waveband. The simple metal periodic array structure is rotated by an angle to form a super surface, which can control the selected light field by reflecting (transmitting) the light wave of a single wavelength or a small range of wavebands selected with precision. The phase type spatial light modulator is realized by processing the metal surface and spin coating it with quantum dots, so as to realize the selection of different light waveband filtering and the control of multi-wavelength laser, produce a more flexible and convenient spatial light modulator, and have potential application prospects in the fields of spatial light control and optical communication.

[0006] The technical scheme of the present application is: a preparation method of a quantum dot spatial light modulation device using a metasurface, characterized in that: unit structures are arranged at specific angles to form a corresponding metasurface, which is processed according to the required waveband, and a simple metal periodic array structure is rotated to form a metasurface, which can use a single waveband or accurately select a small range of wavebands to modulate the selected light field through reflection (transmission), and the metal surface is processed and coated with quantum dots to select different waveband filters and realize the possibility of a multi-wavelength spatial light modulation device, thereby producing a more flexible and convenient spatial light modulation device, and the method comprises the following steps:

[0007] Step 1: An Al film is prepared on a substrate and the thickness of the film is measured to ensure that the film thickness is 400-600 nm, so that the sample will not transmit other impurity light, and the sample is stored in a super-clean environment before focused ion beam processing to avoid contamination of the sample.

[0008] The preparation of the film includes one or a combination of physical vapor deposition (PVD), chemical vapor deposition (CVD), hydrothermal method, spin coating and self-assembly. The film thickness is measured using a method that does not damage the surface, using a film thickness gauge or a non-contact film thickness measuring instrument. Based on the super-clean environment, the sample is vacuum treated, including sample vacuumization and storage in a nitrogen cabinet. The film thickness is at most 600 nm, and the prepared film has a quartz substrate.

[0009] Step 2: The Al film deposited on the substrate is subjected to a first focused ion beam processing to form a nanohole array on the Al-coated SiO2 substrate, obtaining an unit structure with an elliptical nanohole array; the processing focused ion beam voltage is 30 kV, and the required current is 7.7-24 pA; the unit structure is a hole array structure on the Al-coated SiO2 substrate, and the structure is adjusted by adjusting the different rotation angles of the rotation platform.

[0010] Step 3: The elliptical nanohole array structure prepared above is subjected to a second focused ion beam processing to obtain a metasurface structure with different arrangement angle hole structures.

[0011] Step 4: The prepared metasurface structure is spin-coated with quantum dots, and the thickness of the quantum dot film is generally not more than 30 nm. Through the photoluminescence regulation of quantum dots, different waveband focusing and vortex phases are realized, and a multi-wavelength quantum dot spatial light modulation device is obtained.

[0012] Compared with the prior art, the present application has the following beneficial technical effects and significant technical progress:

[0013] 1) The application realizes the selection of the modulation wave band by processing the elliptical nano-hole unit structure with different arrangement angles on the metal surface. The method has the advantages of no need to change the film thickness and other parameters, good repeatability and stability. Only the required rotation processing angle is needed to produce a specific sample, without additional exploration.

[0014] 2) The application forms a metasurface in a predictable way by using a focused particle beam. By adjusting the periodic structure of the structure and the properties of the quantum dots, the plasmonic mode in the periodic structure is matched with the photoluminescence mode of the quantum dots, so that the metasurface can be formed to modulate the quantum dot luminescence. As long as the resonance frequency of the periodic structure is close to the wavelength of the quantum dot photoluminescence, the quantum dot luminescence will be effectively modulated by the metasurface, realizing the modulation of the quantum dot luminescence field of the metasurface by laser irradiation. In this sense, the laser irradiation process can be regarded as a feedback control irradiation process. Even if there is an additional amount of laser pulse interference in the process, the influence of the laser pulse interference on the light field modulation of the quantum dot metasurface can be ignored. This is because the metasurface with propagating phase only modulates the incident laser in a certain space, and has a certain focal point. At this time, the resonant absorption can be ignored, so the influence on the quantum dots and the metasurface is very small, and can even be ignored.

[0015] 3) The application forms a metasurface by arranging simple elliptical nano-hole structures, so that it can respond to different circularly polarized light, and realize the focusing and vortex light of different wave bands by modulating the photoluminescence of the quantum dots.

[0016] 4) The application has potential application prospects in the fields of spatial light modulation and optical communication. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The flowchart of the application;

[0018] Figure 2 The structure diagram of the quantum dot spatial light modulation device prepared in Example 1;

[0019] Figure 3 The schematic diagram of the metasurface unit structure;

[0020] Figure 4 The spectral diagram of the metasurface unit structure;

[0021] Figure 5 The polarization conversion efficiency diagram of the quantum dot spatial light modulation device prepared in Example 1;

[0022] Figure 6 The reflection spectral diagram of the quantum dot spatial light modulation device before and after spin-coating the quantum dots;

[0023] Figure 7 The light field diagram of the quantum dot spatial light modulation device before and after spin-coating quantum dots. DETAILED DESCRIPTION

[0024] The application will be further described below in conjunction with the embodiments and drawings, but not as the basis for limiting the application.

[0025] Embodiment 1

[0026] The application adjusts the periodic structure of the unit structure and the properties of the quantum dots, matches the plasmon mode in the periodic structure with the photoluminescence mode of the quantum dots, and realizes focusing and vortex phase of different wave bands through photoluminescence regulation of the quantum dots. The method specifically comprises the following steps:

[0027] Referring to Figure 1 A layer of metal thin film is deposited on the substrate, and the thickness of the thin film is about 400 nanometers. The thin film itself does not have transmittance.

[0028] Referring to Figure 1 a Figure 1 c, describes the processing flow of a spatial light modulation device. The Al film deposited on the substrate is processed by a focused ion beam ion source.

[0029] Referring to Figure 1 a, the Al thin film prepared on the quartz substrate is grown on the substrate, and the thickness of the thin film is 400 nanometers.

[0030] Referring to Figure 1 b, the above-mentioned thin film is processed by the first FIB (focused ion beam) to form a unit structure with an array of elliptical nanoholes.

[0031] Referring to Figure 1 c, the above-mentioned nanohole array structure is arranged, and the super surface structure formed after FIB (focused ion beam) processing.

[0032] The above Figure 1 a describes a layer of thin film grown on a substrate. The figure is a side view of the structure, which shows the thickness of the overall film and the array structure after processing. The substrate serves as a suitable base material for preparing the thin film, and the thin film deposition process plays a crucial role in processing. The uniformity of the thin film directly affects the structure of the micro-nano processed spatial light modulation device.

[0033] In Figure 1 a, the method for preparing the thin film includes one or more combinations of physical vapor deposition (PVD), chemical vapor deposition (CVD), hydrothermal method, spin coating and self-assembly. The above-mentioned thin film deposition techniques can be used to obtain the thin film. Figure 1The thickness of the metal in a ensures that the transmission of the quartz wafer in the infrared is avoided, which ensures that all the transmission spectra are caused by the micro- and nano-structures of the aluminum.

[0034] The measurement of the thickness of the thin film can be carried out by optical means, such as a film thickness meter, an interferometer, and other optical detection means. The advantage of using optical methods for detection is that the thin film structure is not easily damaged, and the thin film grown on the substrate can be regarded as an optical resonator. The interface between the thin film and the surrounding medium acts as a reflecting surface, in this sense, the thin film acts as a plasmonic resonator, which can resonate with the external optical field generated by a narrow-band light source.

[0035] In Figure 1 In a, the method for preparing the thin film includes PVD, CVD, ALD, PLD, spin coating, thermal deposition, and a hybrid method from the above steps. Among them, PVD, CVD, and ALD are physical vapor deposition, chemical vapor deposition, and atomic layer deposition, which refer to different thin film deposition techniques. Any of the above thin film deposition techniques can be used to provide the thin film. For example, a physical vapor deposition technique (PVD for short) is used to prepare the thin film. This technique represents a large category of vapor and plasma coating processes. The common point of PVD technology is that the final shaped coating, i.e., the thin film, has at least one component in solid form in the deposited coating, such as a metal or semiconductor material (such as silicon). Therefore, before it becomes a coating, this solid component first enters the gas phase. The phase change of this material from solid to gas can be carried out in various ways, such as thermal evaporation or sputtering. The thin film material in the gas phase condenses on the substrate, thereby forming a deposited thin film on the top of the substrate.

[0036] In Figure 1 In b, a side view of the unit processing structure is shown, which is very critical in determining the size of the period. Focused ion beam is a technology for processing micro- and nano-structures using an ion source. The advantage of this technology is that it generates almost no heat during processing, which can better avoid experimental errors caused by thermal expansion of the material during processing. A smaller period length was used in the first FIB processing.

[0037] Figure 1In b, the FIB processing technique is that the FIB processing voltage is 30 kV, the processing current is less than 7.7 PA, the processing period is 400 nm, the hole long axis is an ellipse of about 280 nm, and the short axis is about 240 nm. In this embodiment, the advantage of using this voltage and current is that the Al film surface is easy to conduct electricity, and a larger current will affect the processing accuracy, resulting in inaccurate processing period and hole, thereby affecting the desired super surface effect. The advantage of selecting a period of 450 nm, a hole long axis of about 280 nm, and a short axis of about 240 nm is that more number of holes can be processed in the same area, so that the prepared spatial light modulator can generate a higher Q value. Q is the quality factor of the optical resonant cavity, which measures the energy storage and frequency selection capability of the optical resonant cavity. It can be simply understood that Q = wavelength / full width at half maximum of the spectrum, which makes the modulation more complete.

[0038] In this embodiment, the laser light source is used to irradiate the film, and the laser light source moves relative to the film supported by the substrate, while the substrate is stationary. The film grown on the substrate is fixed on a platform that can move and position in the plane, which facilitates the selection of appropriate processing positions. At the same time, the laser light source is kept stable in space, and the laser light source moves relative to the film. The fixing device includes a clamp for fixing the film and substrate on the platform, or a vacuum connection for adsorbing the substrate to the platform device, or double-sided tape.

[0039] In this embodiment, the sample is kept stationary, and the narrow-band light source moves relative to the film. The advantage is that a larger area than the laser light source processing area can be processed, so that a nanostructure area beyond the laser light source processing area can be generated. Figure 1 In c, the characteristic region after FIB processing is shown, which demonstrates the spatial light modulator after processing. The structure is controlled using the same voltage, current, period, and hole diameter as in 1b. The advantage is that FIB processing can accurately control the size requirements of the spatial light modulator, and can ensure the consistency of the sample after the first and second FIB processing as much as possible. During the processing, the sample is not damaged again. In this embodiment, the processing method is to move the laser irradiation position of the FIB, and the substrate is stationary. The film grown on the substrate is fixed by a displacement table and a machine. In order to ensure the conductivity and stability of the sample, carbon tape and copper tape are respectively pasted on the bottom and around the sample.

[0040] Embodiment 2

[0041] The quantum dot spatial light emitting modulator prepared by the present application is at least a two-dimensional nano-plane structure in this embodiment.

[0042] ReferenceFigure 2 a, shows a schematic diagram of the device structure prepared in the example, which is expected to achieve wavelength change regulation of the super surface by photoluminescence of the quantum dots. The product is a super surface with a lens shape, which generally includes a set of circular structures with quantum dots attached, and the set of super surfaces can make the laser focus or vortex.

[0043] Referring to Figure 2 b, it can be seen that the surface of the Al film forms a complete super surface structure after FIB processing, effectively proving the accuracy of the application. Among them, a plurality of nano structures are arranged in such a way that they form a super surface with phase regulation function. In this case, the thin film aluminum grows on the glass substrate, and the light incident on the film can propagate through the bottom of the film and the glass substrate. In this way, the recombined thin film aluminum and glass substrate play the role of light field regulation, and the noise effect on the light field regulation after the suspension of quantum dots can be ignored.

[0044] Example 3

[0045] Referring to Figure 3 , shows the scanning electron microscope pictures of two different structure spatial light modulation devices prepared after FIB processing in this example. Among them, Figure 3 a is a spatial light modulation device without quantum dots, Figure 3 b is a spatial light modulation device with quantum dots, which is etched after FIB processing to achieve the desired effect.

[0046] Referring to Figure 3 b, the spatial light modulation device coated with quantum dots can obviously see the difference in the surface of the spatial light modulation device, and the quantum dots form a relatively dense film on the surface of the structure, but will not affect the metal structure morphology itself, proving that the spin-coated quantum dot film is thin. Selecting geometric phase as the principle formula for processing super surface, each unit structure can be coupled with quantum dots. The PB phase design principle is shown in the following (a) formula:

[0047]

[0048] Among them, r and r are complex reflection coefficients, the first term in the equation is the scattered light in the same direction as the incident light, and the second term is the orthogonal circularly polarized light with a phase of 2θ, and the second term 2σθ is the geometric phase. Set the phase delay to φ, only need to set the rotation angle of the nanorod to φ / 2.

[0049] According to the above (a) formula design, the lens spatial phase distribution is given by the following (b) formula by arranging any phase profile on the lattice to select the manufacture of focusing and vortex beam generator:

[0050]

[0051] where f is the focal length of the lens, (x, y) is the in-plane coordinate, and λ is the design wavelength.

[0052] The spatial phase φ distribution of the focused vortex beam generator is represented by the following (c) formula:

[0053]

[0054] where l is an integer representing the orbital angular momentum state, f is the focal length of the lens, (x, y) is the in-plane coordinate, λ is the design wavelength, and θ is the azimuth angle of the lens plane. In order to reduce interference, the focal lengths of LCP (f LCP = 30 nm) and RCP (f RCP = 20 nm) are adjusted.

[0055] The geometric phase has the following characteristics: 1) circularly polarized light is required for incidence; 2) the length and width of each unit structure are the same, and the rotation angle is different; and 3) the rotation angle is half of the phase delay.

[0056] The advantage of processing the rotation angle with a fixed formula is that the structure of the nano array is more predictable. The original structure is a periodic array with a period of 450 nm, and after arrangement, the phase modulation requirement is met.

[0057] In the present application, the thin film to be processed is a pre-processed thin film, and the pre-processing includes: chemical treatment of the original thin film; the chemical treatment can be understood as a treatment method of related chemical properties, such as chemical mechanical polishing, chemical mechanical planarization, photolithography, wet etching, dry etching or reactive ion etching, and the use of chemical treatment as the pre-processing of the thin film has certain advantages, such as the realization of a thin film with a very smooth surface.

[0058] In the present application, the step of growing a thin film on a substrate includes: pre-treating the substrate before the thin film is deposited on the substrate. The step of pre-treating the substrate can include: chemical treatment of the substrate, such as chemical mechanical polishing. The advantage of using a pre-processed thin film as a processing object is that the morphology of the nano structure is more predictable. The surface of the original thin film generally has a certain roughness, so that the thickness of the thin film has local fluctuations throughout the thin film, and therefore the laser processing may not be completely stable throughout the thin film. By using a pre-processing process to make the thin film smooth, the surface roughness of the thin film can be reduced, so that the thickness of the thin film has less fluctuations throughout the thin film, which will make the morphology of the nano structure appearing after irradiating the thin film more predictable.

[0059] Example 4

[0060] Reference Figure 4The spectrum of the unit structure processed in the embodiment is tested, that is, the processed array structure is tested by a visible light spectrometer, and the array structure is composed of a 450 nm array period structure. The tested spectrum is a transmission spectrum, and it is found in the test that there is a significant response under different polarization angles. The array after the rotation angle changes with the polarization angle, but all have a significant spectral characteristic frequency, and the reflection spectrum can be determined according to λ=na. Since the metal array structure is plated on a quartz sheet, the refractive index of the transmission interface depends on the quartz sheet, so n=1. Therefore, the visible light spectrum can be predicted, and the prediction result is 450 nm.

[0061] Referring to Figure 4 a, it can be seen from the experimental test that the prepared sample has obvious reflection characteristic peaks under different polarizations, and the reflection characteristic peaks almost do not change with the change of the polarization, which shows that the device prepared by using the application can modulate any polarization.

[0062] Referring to Figure 4 b, it can be seen from the simulation that the simulation result of the obtained reflection spectrum is basically consistent with the experiment, which shows that the preparation of the metasurface spatial light modulator prepared by using the application meets the design requirements and is consistent with the design result.

[0063] Embodiment 5

[0064] Referring to Figure 5 The polarization conversion efficiency of the device processed in the embodiment is simulated and optimized, in order to make the wavelength of the metasurface controllable and have good polarization conversion efficiency. Since the metal array structure is plated on a quartz sheet, the refractive index of the transmission interface depends on the air environment. In the embodiment, the thin film is metal, because the refractive index of the thin film and the refractive index of the air have a large refractive index difference, especially the refractive index of the thin film is much higher than the refractive index of the air, and a thin film with high refractive index is used to manufacture a thin film product showing optical effects related to high refractive index. The thin film is a stacked layer of a single thin film material; the thin film includes a single layer of material; the substrate includes an insulating material such as a polymer or glass.

[0065] Embodiment 6

[0066] Referring to Figure 6 In order to further determine the completeness of the device prepared in the above embodiment, the device is tested by left-handed circularly polarized light and right-handed circularly polarized light.

[0067] Referring to Figure 6, the reflectance spectra of the spatial light modulation device before and after spin-coating quantum dots, as shown in the spectral diagram, it is found that there is a significant response before and after spin-coating quantum dots for both left circularly polarized light and right circularly polarized light. With the change of circularly polarized light, the characteristic peak position of the spectrum does not change significantly with the polarization angle. Because according to the design principle of the structure shown in Figure 2 b, the structure is relatively consistent and will not affect the spectrum, and the geometric phase will not affect the resonance frequency of the unit structure.

[0068] Example 7

[0069] In order to further determine the modulation performance of the device prepared in the above examples for different waveband lasers, the super surface without quantum dots and the super surface coated with quantum dots are selected for light field test under 532 nm and 405 nm laser.

[0070] Referring to Figure 7 , wherein, Figure 7 a and b respectively represent the light field diagram of the super surface without quantum dots with different polarized light. An example of realizing a product by the nanostructure focused ion beam processing method described in the embodiments of the present application is illustrated. The product is a spatial light modulation device that can distinguish left circularly polarized light and right circularly polarized light at 532 nm and can realize focusing and vortex phase modulation, such as nanostructures with geometric phase. This set of nanostructures can function as phase modulation.

[0071] Referring to Figure 7 c and Figure 7 d, respectively, represent the light field diagram of the super surface coated with quantum dots with different polarized light, illustrating an example of realizing a product by the nanostructure focused ion beam processing method described in the embodiments, which is a spatial light modulation device that can distinguish left circularly polarized light and right circularly polarized light at 405 nm and can realize focusing and vortex phase modulation, such as nanostructures with geometric phase, and this set of nanostructures can function as phase modulation.

[0072] Referring to Figure 7 , it can be seen that by carefully selecting the laser parameters and the substrate and film material and thickness, the production of a film product can be realized, which includes reorganized film and substrate and has good optical effect. As described, by modifying the morphology of the film aluminum grown on the substrate quartz, a micro-super surface with a diameter usually less than 60 microns can be created, and the super surface coated with quantum dots also has light field modulation function.

[0073] The above examples are only further illustrations of the present application and do not limit the present application. Any equivalent implementation of the present application shall be included in the scope of the claims of the present application.

Claims

1. A method for fabricating a quantum dot spatial light emission modulation device using metasurface modulation, characterized in that, By adjusting the periodic structure of the unit cell and the properties of the quantum dots, the plasmonic modes in the periodic structure are matched with the photoluminescence modes of the quantum dots. Furthermore, by modulating the photoluminescence of the quantum dots, focusing and vortex phases at different wavelengths are achieved. This method specifically includes the following steps: Step 1: Thin Film Preparation An Al thin film with a thickness of 400–600 nanometers was prepared on a quartz substrate; Step 2: First processing with focused ion beam The Al thin film deposited on the substrate was subjected to a first focused ion beam processing to form a nanopore array on the SiO2 substrate coated with Al film, resulting in a unit structure with an elliptical nanopore array. Step 3: Second processing with focused ion beam The elliptical nanopore array structure prepared above was subjected to a second focused ion beam processing to obtain a metasurface structure with pore structures of different arrangement angles; Step 4: Quantum Dot Spin Coating The metasurface structure prepared above was spin-coated with quantum dots, and the focusing and vortex phase of different wavelengths were achieved by controlling the photoluminescence of quantum dots, thus obtaining a multi-wavelength quantum dot spatial light emission modulation device.

2. The method for fabricating a quantum dot spatial light emission modulation device using metasurface modulation according to claim 1, characterized in that, The preparation of the thin film includes one or more of the following: physical vapor deposition (PVD), chemical vapor deposition (CVD), hydrothermal method, spin coating, and self-assembly.

3. The method for fabricating a quantum dot spatial light emission modulation device using metasurface modulation according to claim 1, characterized in that, The different arrangement angles of the hole structures are adjusted using a focused ion beam rotary displacement stage, and the structure is controlled by the same voltage, current, period and hole diameter.

4. The method for fabricating a quantum dot spatial light emission modulation device using metasurface modulation according to claim 1, characterized in that, The quantum dots were prepared by spin-coating the quantum dot solution using a spin coater to obtain a quantum dot film with a thickness of <30 nanometers.

5. The method for fabricating a quantum dot spatial light emission modulation device using metasurface modulation according to claim 2, characterized in that, The focused ion beam processing uses a voltage of 30 kV, a current of 7.7–24 pA, and a processing cycle of 400–600 nanometers. Different processing cycles are selected to adjust the ratio of the long axis to the short axis of the elliptical nanopores.

Images