CN116068793A

CN116068793A - Photonic crystal structure color film based on phase change material and preparation method thereof

Info

Publication number: CN116068793A
Application number: CN202310076613.2A
Authority: CN
Inventors: 卜轶坤; 杨坚; 陈楠; 段珍珍; 陈炜杰; 蔡光师; 何泽湘
Original assignee: Xiamen University
Current assignee: Xiamen University
Priority date: 2023-01-17
Filing date: 2023-01-17
Publication date: 2023-05-05

Abstract

The invention discloses a photonic crystal structure color film based on a phase change material, which has the structure that: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, L represents a low-refractive-index dielectric layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index dielectric layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer. The invention also provides a phase change material-based materialAccording to the preparation method of the photonic crystal structure color film, the prepared film can have a structure color with larger chromatic aberration before and after phase change through phase change of the phase change layer.

Description

Photonic crystal structure color film based on phase change material and preparation method thereof

Technical Field

The invention relates to the technical field of optics, in particular to a photonic crystal structure color film based on a phase change material and a preparation method thereof.

Background

By phase-changeable material is meant that the physical structure of the material can be changed by changing its temperature over a range of temperatures and has an almost fixed phase-change temperature. The working principle of the phase change material is that when the ambient temperature is higher than the phase change temperature, the phase change material stores heat; when the ambient temperature is below the phase transition temperature, it releases its stored energy. Currently, phase change materials are widely applied to energy storage, medical fields, data storage fields and the like. In the field of optical films, phase change materials are mostly applied to heat absorption and insulation in the field of aerospace, mid-far infrared camouflage in the field of military, and the like.

The main phase change methods of the phase-changeable material can be known by the working principle of the phase-changeable material to directly or indirectly heat an object, and the phase change can be completed by using a high-temperature annealing process, electric heating and optical stimulation (laser pulse phase change). To measure the phase change performance of a material, a phase change figure of merit (FOM) is generally used to define how good it is in its phase change capability. The greater the FOM value, the greater the refractive index difference between the amorphous and crystalline materials is required; meanwhile, the smaller the extinction coefficient of the film in the crystalline state is, the better. In order to make the photonic crystal film exhibit better phase change performance, higher saturation and larger phase change chromatic aberration, a phase change material is needed, but the research on the optical field based on the phase change material is less at present.

Typical phase change materials such as chalcogenide semiconductor materials represented by Ge2Sb2Te5 (abbreviated as GST) can realize sub-nanosecond phase change by electric pulse and optical pulse, and the optical and electrical characteristics of the GST material can also be in two different states due to the rapid and repeated switching of the phase change, which makes the GST material a reliable material for manufacturing nonvolatile memories. Although GST materials are widely used in photonic devices such as nonvolatile displays, optical switches, photonic memories, all-optical computers, etc., they are rarely used in the field of phase-changeable thin film structure colors.

Doping and modification are performed on the basis of GST, a classical Phase Change Material (PCM). Experiments show that the replacement of part of Te in Ge2Sb2Te5 by Se can reduce the extinction coefficient of the material in the visible light region, so that the brightness of the structural color of the formed film is enhanced, but too much Se can also cause the material to lose the phase transformation capability. Ge2Sb2Se4Te1 (GSST for short) is a critical material which ensures the phase-change capability under the premise of reducing the material absorption as much as possible.

GSST has been used as a novel material with significant optical performance advantages over classical phase change material GST for fabricating silicon-based three-dimensional waveguide mode optical switches (CN 114995010 a), phase change bragg grating based multiparameter tunable filters (CN 216248399U), DBS algorithm based programmable arbitrary power splitters (CN 113191115 a), etc. But in the field of phase-changeable film structure color, GSST material has great application prospect.

The Chinese patent No. CN202011061690 discloses a resonant cavity film system with nonvolatile, multi-structural color, multi-gear and high transmittance contrast ratio and a preparation method, the composite double-cavity film system uses two different PCM materials to achieve the targets of high transmittance and multi-gear, the two PCM materials must adopt the element composition of (GeTe) x (Sb 2Te 3) 1-x, and the film system has difficulty in designing structural colors with high brightness, high saturation and large phase change difference considering that the FOM values of GeTe and Sb2Te3 are not as good as GST and GSST.

Some novel electrochromic materials are proposed, for example, an electrochromic structural color designed by CN202211003546, and metal particles can be controlled to deposit and dissolve on a transparent electrode by adjusting the magnitude and the direction of an applied voltage, so that the thickness of the film structure is changed to enable the film structure to show transparent color from visible light to have a certain color. The color conversion that can be achieved by this tuning method is very limited and its phase change color is also relatively single, and how to design a film that can achieve a larger color phase change without changing the structure of the resulting film is a hotspot in current research.

Disclosure of Invention

Therefore, the invention aims to provide a photonic crystal structural color film based on a phase change material, which can enable the prepared film to have structural colors with larger chromatic aberration before and after phase change through phase change of a phase change layer.

In order to achieve the technical purpose, the invention adopts the following technical scheme: a photonic crystal structure color film based on a phase change material, the structure of the film is as follows: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, L represents a low-refractive-index dielectric layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index dielectric layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer.

Further, the high refractive index dielectric layer H is a material film layer with a refractive index of more than or equal to 1.55 in the range of 400 nm-780 nm, and lanthanum titanate, amorphous silicon, indium tin oxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, zirconium dioxide, zinc sulfide or silicon monoxide is adopted; the thickness range of the high refractive index dielectric layer H is 20-500nm.

Furthermore, the phase-change layer P adopts GSST material or GST material, and the GSST material has two different crystalline states at different temperatures, namely an amorphous state and a crystalline state; the GST material has three different crystalline states at different temperatures, namely an amorphous state, a metastable state and a crystalline state; the thickness of the phase-change layer P ranges from 5 nm to 30nm.

Further, the low refractive index medium layer L is a material film layer with a refractive index smaller than 1.55 in the range of 400 nm-780 nm, and silicon dioxide, magnesium fluoride, cerium fluoride, lanthanum fluoride, sodium aluminum fluoride, neodymium fluoride, currency fluoride, barium fluoride, calcium fluoride or lithium fluoride are adopted; the thickness of the low refractive index medium layer L ranges from 20nm to 600nm.

Further, the number of repeated stacking times s of the equivalent high refractive index unit is in the range of 1-5; when the number of s is 2 to 5, (HP) ^s The s layers of high refractive index medium layers H are made of the same material or at least two layers of the same material or different materials, (HP) ^s The s phase-change layers P in the (a) are made of the same material or at least two layers of the same material or different materials.

The invention also provides a preparation method of the photonic crystal structure color film based on the phase change material, which comprises the following steps:

step 1, designing a photonic crystal structure color film based on a phase change material according to the requirement of a user, wherein the structure of the film is as follows: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index medium layer, P represents a phase-change layer, L represents a low-refractive-index medium layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index medium layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer;

step 2, adjusting the thickness and the materials of each layer in the structure of the film, so that the film shows different color changes in different temperature ranges;

step 3, determining structural parameters required for preparing the film according to a design result;

step 4, taking the surface-flattened object as a substrate, and placing the substrate in a cavity of film forming equipment; when the film does not need to be subjected to demolding treatment, executing the step 5; when the film needs to be subjected to demolding treatment, executing the step 6;

Step 5, growing a first layer and a second layer … … of the film on the substrate according to the structural parameters until reaching the last layer, wherein the high-refractive-index dielectric layers H and the phase-change layers P are sequentially and alternately stacked according to the number of s between the first layer and the second layer, the middle-most layer is a low-refractive-index dielectric layer L, and the middle-most layer and the last layer are symmetrically grown by taking L as a center; completing the preparation of the film;

step 6, growing a layer of release agent on the substrate; growing a first layer, a second layer … … of the film on a release agent according to the structural parameter until a final layer; the high refractive index medium layers H and the phase change layers P are sequentially and alternately stacked according to the number of s between the first layer and the second layer, the middle-most layer is a low refractive index medium layer L, and the middle-most layer and the last layer symmetrically grow by taking L as a center; and dissolving the release agent by using a solvent corresponding to the release agent, so that the film is separated from the release agent, and the film is obtained independently, thereby completing the preparation of the film.

Further, the step 2 specifically includes:

step 21, designing the thickness and the material of each layer in the structure of the film;

step 22, according to (HP) ^s The materials adopted by the s-layer phase-change layers P in the step (2) determine different temperature thresholds, if the s-layer phase-change layers P are GSST materials, the temperature threshold is determined to be T1, and the step (23) is carried out; if the s layers of phase change layers P are all GST materials, determining that the temperature threshold values are T2 and T3, and entering a step 24; if the phase change layer P of the s layers has GSST material and GST material at the same time, determining that the temperature threshold values are T2, T1 and T3, and entering a step 25;

Step 23, recording a first color represented by the film in a temperature range smaller than T1, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T1, recording a second color represented by the film at the moment again, comparing color changes before and after phase change, and if the color difference changes are large, indicating that the thickness and the material of each layer in the designed film structure are reasonable; if the color difference change is small, step 21 is carried out to readjust the thickness and the material of each layer in the structure of the film;

step 24, recording a first color represented by the film in a temperature range smaller than T2, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T2 and smaller than T3, recording a second color represented by the film again, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T3, recording a third color represented by the film again, comparing the color change in the phase change process, and if the color difference change is large, indicating that the thickness and the material of each layer in the designed film structure are reasonable; if the color difference change is small, step 21 is carried out to readjust the thickness and the material of each layer in the structure of the film;

Step 25, recording a first color represented by the film in a temperature range smaller than T2, then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T2 and smaller than T1, recording a second color represented by the film at the moment again, then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T1 and smaller than T3, recording a third color represented by the film at the moment again, and then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T3, and recording a fourth color represented by the film at the moment again; comparing the color change in the phase change process, if the color difference change is large, indicating that the thickness and the material of each layer in the designed film structure are reasonable; if the color difference variation is small, step 21 is entered to readjust the thickness and material of each layer in the structure of the film.

Furthermore, the phase change process of the phase change layer P is completed by a high-temperature annealing process, electric heating or laser pulse phase change mode.

Further, the structural parameters comprise the total number of layers, the materials adopted by each layer, the thickness of each layer and the distribution condition among the layers; the temperature threshold T1 is 310 degrees, the temperature threshold T2 is 220 degrees, and the temperature threshold T3 is 400 degrees.

Further, the substrate is made of polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, polycarbonate/polymethyl methacrylate composite material, polyimide, polypropylene, polyvinyl chloride, polyvinyl butyral, ethylene vinyl acetate copolymer, polyurethane elastomer, polytetrafluoroethylene, fluoroethyl propylene or polyvinylidene fluoride; the release agent is made of fluoride, chloride or organic material which is easy to dissolve in water.

By adopting the technical scheme, compared with the prior art, the invention has the beneficial effects that: the invention prepares a photonic crystal film structure color device which can change the color of a film by heating or laser illumination only through high temperature or laser pulse on the basis of not changing the film structure by using a phase-changeable material (GSST or GST) according to the optical characteristics of the phase-changeable material, so that the prepared film can have the structure color with larger color difference before and after the phase change.

The structure applies the chalcogenide phase-changeable material GSST to the field of film structure color, not only creatively provides the application of the material in the field of tunable structure color, but also can solve the problems of insufficient color display capability and unobvious phase change effect of the traditional phase-changeable material such as GST and the like in the application of the tunable structure color. Moreover, because of the very rich colors that the design structure can make, the design structure provides a novel tunable scheme for the application of the design structure in the field of color printing and micro-nano color display. GSST is used as a semiconductor material, the application of the GSST on optical devices is very wide, and various color displays can be realized on some special optical devices by combining the electrical and optical characteristics of the GSST, so that other characteristics of the GSST, such as electricity, can provide visual feedback for the phase change of the GSST in an application scene. Compared with the previous research, the method provided by the invention has the advantages of multiple tunable structures, good tunable effect, easiness in mass production and the like. The advantages enable the non-volatile high-saturation color filter to have wide application potential in the fields of color display panels, photodetectors, automotive paints, color printing and the like.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of a photonic crystal structural color film (including a substrate) based on a phase change material according to the present invention.

Fig. 2 is a schematic structural diagram of a photonic crystal structural color film (containing a substrate and a release agent) based on a phase change material.

Fig. 3 is a flowchart of a preparation method of a photonic crystal structure color film based on a phase change material.

Fig. 4 is a schematic structural diagram of a photonic crystal structural color film based on a phase change material (without a substrate and a release agent, the number of s is 1) provided by the invention.

Fig. 5 is a schematic structural diagram of a photonic crystal structural color film based on a phase change material (without a substrate and a release agent, the number of s is 2) provided by the invention.

FIG. 6 is an optical constant of an amorphous state of a GSST phase change material provided by the present invention in the visible range.

FIG. 7 is an optical constant of a GSST phase change material provided by the invention in a crystalline state in the visible range.

FIG. 8 is a reflection spectrum of an amorphous state at normal incidence for example 1.

FIG. 9 is a reflection spectrum of the crystalline state of example 1 at normal incidence.

Fig. 10 is a graph of amorphous and chromas of example 1 at normal incidence.

Fig. 11 is a graph of crystalline and chromated coordinates at normal incidence for example 1.

FIG. 12 is a reflection spectrum of an amorphous state at normal incidence for example 2.

FIG. 13 is a reflectance spectrum of the crystalline state of example 2 at normal incidence.

Fig. 14 is a graph of amorphous and chromatograms of example 2 at normal incidence.

Fig. 15 is a graph of crystalline and chromatograms of example 2 at normal incidence.

FIG. 16 is a reflection spectrum of an amorphous state at normal incidence for example 3.

FIG. 17 is a reflectance spectrum of the crystalline state of example 3 at normal incidence.

Fig. 18 is a graph of amorphous and chromated coordinates at normal incidence for example 3.

Fig. 19 is a graph of crystalline and chromated coordinates at normal incidence for example 3.

FIG. 20 is a reflection spectrum of an amorphous state at normal incidence for example 4.

FIG. 21 is a reflectance spectrum of the crystalline state of example 4 at normal incidence.

Fig. 22 is a graph of amorphous and chromated coordinates at normal incidence for example 4.

Fig. 23 is a graph of crystalline and chromatograms of example 4 at normal incidence.

FIG. 24 is a reflection spectrum of an amorphous state at normal incidence for example 5.

FIG. 25 is a reflectance spectrum of the crystalline state of example 5 at normal incidence.

Fig. 26 is a graph of amorphous and chromatograms of example 5 at normal incidence.

Fig. 27 is a graph of crystalline and chromatograms of example 5 at normal incidence.

FIG. 28 is a reflection spectrum of an amorphous state at normal incidence for example 6.

FIG. 29 is a graph showing the metastable reflectance spectrum at normal incidence in example 6.

FIG. 30 is a reflectance spectrum of the crystalline state of example 6 at normal incidence.

Fig. 31 is a chromaticity diagram of the amorphous state of example 6 at normal incidence.

FIG. 32 is a graph of the chromaticity of example 6 in a metastable state at normal incidence.

Fig. 33 is a chromaticity diagram of the crystalline state of example 6 at normal incidence.

FIG. 34 is a reflectance spectrum at normal temperature under normal incidence in example 7.

FIG. 35 is a reflectance spectrum of example 7 after annealing to 220℃at normal incidence.

FIG. 36 is a reflectance spectrum at 310℃under normal incidence for example 7.

FIG. 37 is a reflectance spectrum of example 7 after annealing to 400℃at normal incidence.

Fig. 38 is a chromaticity diagram of example 7 at normal temperature at normal incidence.

FIG. 39 is a chromaticity diagram of example 7 after annealing to 220℃at normal incidence.

FIG. 40 is a graph of chromaticity after example 7 was annealed to 310℃at normal incidence.

FIG. 41 is a chromaticity diagram of example 7 annealed to 400℃at normal incidence.

Detailed Description

The invention is described in further detail below with reference to the drawings and examples. It is specifically noted that the following examples are only for illustrating the present invention, but do not limit the scope of the present invention. Likewise, the following examples are only some, but not all, of the examples of the present invention, and all other examples, which a person of ordinary skill in the art would obtain without making any inventive effort, are within the scope of the present invention.

Referring to fig. 1, fig. 2, fig. 4 and fig. 5, a photonic crystal structure color film based on a phase change material according to the present invention has the following structure: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, L represents a low-refractive-index dielectric layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index dielectric layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer.

In this embodiment, the high refractive index dielectric layer H is in the range of 400nm to 780nmThe material film layer with internal refractive index greater than or equal to 1.55 is made of lanthanum titanate (H4), amorphous silicon (a-Si), indium Tin Oxide (ITO), titanium dioxide (TiO) ₂ ) Tantalum pentoxide (Ta) ₂ O ₅ ) Hafnium oxide (HfO) ₂ ) Zirconium dioxide (ZrO) ₂ ) Zinc sulfide (ZnS) or silicon monoxide (SiO); the thickness range of the high refractive index dielectric layer H is 20-500nm.

In this embodiment, the phase-change layer P is made of GSST material (the phase-change layer P is made of chalcogenide phase-change material, wherein GSST (Ge 2Sb2Se4Te 1) is the preferred material) or GST material, and the GSST material has two different crystalline states at different temperatures, namely an amorphous state and a crystalline state; the GST material has three different crystalline states at different temperatures, namely an amorphous state, a metastable state and a crystalline state; the thickness of the phase-change layer P ranges from 5 nm to 30nm.

The amorphous forming ability of GSST in amorphous form is enhanced compared to GST, which increases amorphous thermal stability, prolongs film phase change shelf life, and increases the maximum useful thickness of the phase-changeable material. But on the other hand GSST, due to its enhanced amorphous thermal stability, also loses the metastable face-centered cubic (FCC) phase of GST, which after high temperature annealing at 310 ℃ directly converts to the final steady-state hexagonal phase, i.e. its phase transition temperature is greatly increased, which also gives the possibility of the use of this film system at a specific height of Wen Changjing. Experiments have shown that GSST maintains an amorphous structure before 310 ℃ and that its single layer optical constants are shown in figure 6. After high temperature annealing at 310 ℃, GSST structure is transformed into hexagonal crystalline state with optical constants as shown in fig. 7.

The structure can also adopt a phase change material GST which can be in an amorphous state at normal temperature, can be in a metastable state at a high temperature of 220 ℃ and can be in a crystalline state after being annealed at a high temperature of 400 ℃, so that three color changes can be shown in the structure applied to the design. Moreover, the structure in the design can mix and match different phase-change layers P with GSST and GST, and can display more phase-change colors through the control of different annealing temperatures. For example, when s is 2, (HP) ^s Has a 2-layer phase change layer P structure, wherein P ¹ And P ² The material of (2) may be selected from GSST or GST materials, such as P ¹ Selecting GSST material and P ² GST material or P ¹ GST material is selected and P is ² GSST material is selected.

In this embodiment, the low refractive index dielectric layer L is a material film layer with a refractive index less than 1.55 in a range of 400nm to 780nm, and the low refractive index dielectric layer L is admittedly matched with the high refractive index dielectric layer H; by using silicon dioxide (SiO) ₂ ) Magnesium fluoride (MgF) ₂ ) Cerium fluoride (CeF) ₃ ) Lanthanum fluoride (LaF) ₃ ) Sodium aluminum fluoride (Na) ₃ AIF or NasAlFA), neodymium fluoride (NdF) ₃ ) Fluorinated banknote (SmF) ₃ ) Barium fluoride (BaF) ₂ ) Calcium fluoride (CaF) ₂ ) Or lithium fluoride (LiF); the thickness of the low refractive index medium layer L ranges from 20nm to 600nm. In this embodiment, the more the number of the repeating stacking times s of the equivalent high refractive index units is in the range of 1 to 5,s, the less obvious the structural color change before and after the phase change is; when the number of s is 2 to 5, (HP) ^s The s layers of high refractive index medium layers H are made of the same material or at least two layers of the same material or different materials, (HP) ^s The s phase-change layers P in the (a) are made of the same material or at least two layers of the same material or different materials. The invention can design the structural color films with different colors by adjusting the material and thickness of each layer.

In this embodiment, s is 1, and the specific structure is shown in fig. 4. The film layer structure comprises a high refractive index medium layer H, a phase change layer P, an intermediate medium layer L, a phase change layer P and a high refractive index medium layer H from the substrate to the top. Because the material required by the phase-change layer P has an easily-oxidizable property, the phase-change layer P cannot be directly placed on the surface layer to contact with air, and thus the phase-change layer P is interposed between the high-refractive-index dielectric layer H and the intermediate dielectric layer L. According to the symmetrical design of the film system, the thicknesses and materials of the two high-refractive-index medium layers H which are vertically symmetrical to each other are the same, and the thicknesses and materials of the phase-change layers P which are vertically symmetrical to each other to each medium layer L are the same.

The F-P film filter is a simple narrow-band filter and is improved on the basis of a Fabry-Perot interferometer. The filter is mainly composed of a middle parallel cavity layer and two high-reflectivity layer layers at two ends, and can be divided into a metal-medium type structure and an all-medium type structure according to the materials of the two high-reflectivity layers at the two ends. The metal-dielectric type F-P filter mainly comprises two parallel metal layers and a dielectric spacing layer in the middle, and main parameters of the F-P filter are calculated according to a thin film reflection transmission theory.

Of the various performance parameters of the filter, the one characterized mainly by the central wavelength lambda ₀ Peak Full Width Half Maximum (FWHM), transmittance at center wavelength T, and free spectral range (Free Spectral Range) FSR.

F-P filter transmittance expression:

wherein T is ₁ 、T ₂ 、R ₁ And R is ₂ The transmittance and reflectance of the two metal reflective layers, respectively (e.g., the transmittance and reflectance of the first metal reflective layer, respectively, is T ₁ And R is ₁ The transmissivity and reflectivity of the second metal reflecting layer are respectively T ₂ And R is ₂ )；

Wherein->

Is the bit thickness of the spacer layer +.>

And->

Respectively two layers of reflection phases.

The wavelength at maximum transmittance, the center wavelength expression:

the Free Spectral Range (FSR) of the F-P film filter represents the spectral range between two maximum transmission peaks, and is mainly used for representing the maximum wavelength difference of the partial wave for preventing the overlapping of different interference fringes in optics, and the specific calculation formula is as follows:

Δλ _FSR ＝λ ² /(2nd)

the Full Width Half Maximum (FWHM) is simply referred to as half width, which represents the width of the passband at half the transmission or reflection peak of the filtered waveform, and represents the width of the passband, and the calculation formula is:

wherein the method comprises the steps of

Wherein R is ₁ And R is ₂ The reflectivity of the dielectric layer and the reflective layer, respectively.

Because r+t+a=1, the absorption of a is approximately constant, in order to improve the overall reflectivity performance of the film system, the conventional F-P film filter structure color film needs to reduce the transmittance according to the transmittance expression, firstly, the reflectivity of two metal layers is increased, and secondly, the phase thickness of the middle interval dielectric layer is adjusted. However, the inherent large absorption of the metal itself and the phase matching requirement of the intermediate spacer dielectric layer control the full width at half maximum of the spectrum peak and the free spectrum range, which makes it difficult to realize multiple colors with high reflectivity for the structural color of the conventional F-P film filter.

The invention utilizes the interference effect of the dielectric film, utilizes the equivalent characteristics of the refractive index and the phase thickness of the symmetrical film system structure, can realize the required refractive index by optimizing the design through a computer and changing the material types and the physical thickness of the high refractive index dielectric layer and the intermediate dielectric layer. We know when the refractive index is n _g Is coated with a substrate having an optical thickness lambda ₀ High refractive index of/4

After the film layer, the reflectivity can be greatly increased due to the co-phase of the reflected light at the interface of the air/film layer and the film layer/substrate. For a center wavelength lambda ₀ Admittance of an equivalent combination of monolayer film and substrate is n ₁ ² /n _g The reflectivity at normal incidence is:

wherein each group (HP) or (PH) of the film system of the design is formed into an equivalent high refractive index unit, and each layer lambda is alternated by a high refractive index layer and a low refractive index layer ₀ The multilayer film of/4 enables higher reflectivity to be obtained. This is because the light beams reflected from all interfaces have the same phase when they return to the interfaces, thereby generating constructive interference, and different reflectivities can be obtained according to this theory. In the present structure n is used _H Represents the refractive index of the high refractive index layer, using n _L Indicating the refractive index of the low refractive index layer. Then at the central wavelength lambda ₀ The equivalent interfacial admittance Y of the whole film system structure is as follows:

Wherein 2s+1 is the number of layers of the multilayer film, and the center wavelength lambda ₀ The reflectance, i.e. the maximum reflectance, is:

according to the film layer of the structural design, an absorption formula with the outermost layer being a high-refractive-index film layer is selected, and the absorption loss is as follows:

the outermost layer is selected asThe high refractive index film layer is because the film layer having a lower refractive index than the outermost layer has a larger absorption according to its absorption formula, resulting in a decrease in reflectance. K in the formula _H Is the extinction coefficient k of the high refractive index dielectric layer _L Is the extinction coefficient of the low refractive index layer. As can be seen from the formula of absorption and maximum reflectance, the refractive index and extinction coefficient of the high refractive index dielectric layer H and the phase change layer P in the structure affect the reflectance of the central wavelength. The maximum reflectivity of the film layer can be positioned at different center wavelength positions by changing the physical thickness of the high refractive index medium layer H and the phase change layer P, so that the color of the film layer is changed. n is n _H And n _L The difference of the ratio can also change the maximum value of the reflectivity of the center wavelength, so that the selection of different materials can also change the peak value of the reflectivity in the design structure. GSST in the phase change layer P can be converted into a crystalline state from an amorphous state by high-temperature annealing at 310 ℃ after the preparation of the film is completed, the refractive index and the extinction coefficient of the film are changed, the reflectivity of the center wavelength can be obviously changed according to the formula characteristics of the reflectivity, the structural color displayed by the film system is changed, and the function of color change after the preparation of the film is completed is achieved.

In view of the wide variety of color related functions that the designed films can then be used on other devices, the present invention contemplates a symmetrical film-based structure that can be peeled from the fabrication substrate and then used for device coating. The structure has the advantages that the color of the film structure can be designed in the aspect of observing the color of the film structure from the front side or the back side, and unlike other structures based on F-P film filters of the traditional structure color film system, the structure needs thick metal of the bottom layer as a reflecting layer, and the bottom layer has a thick metal layer which can provide higher peak reflectivity, but also provides different difficulties for the application scene and the preparation process of the structure.

As shown in fig. 3, the invention also provides a preparation method of the photonic crystal structure color film based on the phase change material, which comprises the following steps:

Step 2, adjusting the thickness and the materials of each layer in the structure of the film, so that the film shows different color changes in different temperature ranges; the phase-change layer P is made of a phase-change material, and on the basis that the film structure can not be changed in the visible light region according to the optical characteristics of the phase-change material, the phase-change material (GSST or GST) is used for preparing the photonic crystal film structure color device which can change the color of the film by heating or laser illumination only through high temperature or laser pulse on the basis that the film structure is not changed, and finally, the prepared film can have a structure with larger color difference before and after the phase change.

The color of the colored object can be divided into pigment color and structure color according to whether the colored object absorbs light or not. Pigment color formation involves primarily absorption involving coordination field effect transitions, which appear to be chemical colors as well. The structural color mainly comprises physical optical effects such as grating, single-layer film, multi-layer film, photon crystal, rayleigh scattering, mie scattering and the like, and the reflected color becomes structural color.

The photonic crystal structure color film realized by using GSST material is not developed and researched, and the method has important application prospect in the fields of optical devices, color printing, optical display, and the like, considering that the prepared film has the advantages of high phase change speed, good non-volatility, small absorption, large phase change interval, various colors, simple design structure and the like.

In this embodiment, the step 2 specifically includes:

step 22, according to (HP) ^s S layer in (3)Determining different temperature thresholds by using materials adopted by the phase-change layer P, determining the temperature threshold as T1 if the phase-change layers P are GSST materials, and entering a step 23; if the s layers of phase change layers P are all GST materials, determining that the temperature threshold values are T2 and T3, and entering a step 24; if the phase change layer P of the s layers has GSST material and GST material at the same time, determining that the temperature threshold values are T2, T1 and T3, and entering a step 25;

step 23, recording a first color represented by the film in a temperature range smaller than T1, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T1, recording a second color represented by the film at the moment again, comparing color changes before and after phase change, if the color difference changes greatly, indicating that the thickness and the materials of each layer in the designed film structure are reasonable, and if the temperature is reduced to a temperature range smaller than T1, reducing the color back to the first color; if the color difference change is small, step 21 is carried out to readjust the thickness and the material of each layer in the structure of the film;

Step 24, recording a first color represented by the film in a temperature range smaller than T2, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T2 and smaller than T3, recording a second color represented by the film again, then carrying out phase change treatment on the film so that the temperature of the film is increased to a temperature range not smaller than T3, recording a third color represented by the film again, comparing color changes in a phase change process, and if the color difference changes are large, indicating that the thickness and materials of each layer in the designed film structure are reasonable, and if the temperature is reduced to a temperature range not smaller than T2 and smaller than T3, reducing the color back to the second color, and if the temperature is reduced to a temperature range smaller than T2, reducing the color back to the first color; if the color difference change is small, step 21 is carried out to readjust the thickness and the material of each layer in the structure of the film;

step 25, recording a first color represented by the film in a temperature range smaller than T2, then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T2 and smaller than T1, recording a second color represented by the film at the moment again, then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T1 and smaller than T3, recording a third color represented by the film at the moment again, and then performing phase change treatment on the film to enable the temperature of the film to rise to a temperature range not smaller than T3, and recording a fourth color represented by the film at the moment again; comparing the color change in the phase change process, if the color difference change is large, the thickness and the materials of each layer in the designed film structure are reasonable, at the moment, if the temperature is reduced to be within a temperature range which is not less than T1 and less than T3, the color is reduced back to the third color, if the temperature is reduced to be within a temperature range which is not less than T2 and less than T1, the color is reduced back to the second color, and if the temperature is reduced to be within a temperature range which is less than T2, the color is reduced back to the first color; if the color difference variation is small, step 21 is entered to readjust the thickness and material of each layer in the structure of the film.

In this embodiment, the phase change process of the phase change layer P is performed by a high temperature annealing process, electric heating or laser pulse phase change; the temperature threshold T1 is 310 degrees, the temperature threshold T2 is 220 degrees, and the temperature threshold T3 is 400 degrees.

Step 3, determining structural parameters required for preparing the film according to a design result, wherein the structural parameters comprise the total number of layers, materials adopted by each layer, the thickness of each layer and the distribution condition among the layers;

in this embodiment, the substrate is made of polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate (PET), cellulose Triacetate (TAC), polymethyl methacrylate (PMMA), polycarbonate/polymethyl methacrylate composite (PC/PMMA), polyimide (PI), polypropylene (PP), polyvinyl chloride (PVC), polyvinyl butyral (PVB), ethylene vinyl acetate copolymer (EVA), polyurethane elastomer (TPU), polytetrafluoroethylene (PTFE), fluoroethyl propylene (FEP), or polyvinylidene fluoride (PVDF);

step 6, growing a layer of release agent on the substrate, wherein the release agent is made of fluoride, chloride or organic material which is soluble in water; growing a first layer, a second layer … … of the film on a release agent according to the structural parameter until a final layer; the high refractive index medium layers H and the phase change layers P are sequentially and alternately stacked according to the number of s between the first layer and the second layer, the middle-most layer is a low refractive index medium layer L, and the middle-most layer and the last layer symmetrically grow by taking L as a center; and dissolving the release agent by using a solvent corresponding to the release agent, so that the film is separated from the release agent, and the film is obtained independently, thereby completing the preparation of the film.

Step 7, after the film is prepared, the film is coated on the outer surface of the equipment, and at the moment, the outer surface of the equipment has different colors at different temperatures; if the phase-change layer P is made of GSST material only, the outer surface of the device exhibits a first color in a temperature range of less than 310 degrees, and in particular, what color is to be exhibited is determined according to the thickness and material of each layer, and the transition from the crystalline state to the amorphous state can be performed by high-temperature annealing to a temperature range of not less than 310 degrees, and the outer surface of the device exhibits a second color, and different colors are to be exhibited according to the specific design requirements and conditions of step 1-2. When the temperature is slowly reduced to normal temperature by continuing to supply heat after the second color is displayed at the temperature of not less than 310 ℃, the structure of the film is not changed, and the color is continuously in the second color; if the second color is to be restored to the first color, the film can be heated to a temperature higher than 310 ℃ and then quickly cooled to normal temperature, and the process can be realized by adopting a laser pulse method. Therefore, the film system structure can be changed from the color after the phase change to the structure color before the phase change, and the phase change adjustment of the repeated structure color is realized. Similarly, if the phase-change layer P is made of GST material only, the outer surface of the device exhibits a first color in a temperature range of less than 220 degrees, and specifically what color is determined according to the thickness and material of each layer, and then the outer surface of the device exhibits a second color by high-temperature annealing to a temperature range of not less than 220 degrees to less than 400 degrees, and then the outer surface of the device exhibits a third color by high-temperature annealing to a temperature range of not less than 400 degrees, and the different colors are realized by specific design requirements and conditions of steps 1-2. When the temperature is slowly reduced to normal temperature by continuing to supply heat after the third color is displayed at the temperature of not less than 400 ℃, the structure of the film is not changed, and the color is continuously in the third color; if the third color is to be reduced back to the first color, the film may be first heated to a temperature above 400 c and then rapidly cooled to ambient temperature. The rapid cooling can be realized by adopting a laser pulse method. Therefore, the film system structure can be changed from the color after the phase change to the structure color before the phase change, and the phase change adjustment of the repeated structure color is realized.

The invention is further described below with reference to the accompanying drawings.

Example 1

As shown in FIG. 4, the structural color device is composed of a substrate Sub (not shown), a high refractive index dielectric layer H (TiO ₂ ) Phase change layer P (GSST), low refractive index dielectric layer L (MgF) ₂ ) Phase change layer P (GSST), high refractive index dielectric layer H (TiO) ₂ ) The composition of the substrate was K9 glass deposited film with a diameter of 80 mm, a thickness of 2 mm and a surface quality of 20/10. The specific thickness of each layer is given in table 1. According to the thickness values given in table 1, it is possible to prepare a material which is observed to be red at a temperature of less than 310 degrees and to be purplish red after annealing at a high temperature to a crystalline state at a temperature of not less than 310 degrees. FIGS. 8 and 9 show embodiment 1 in a range smaller than that of the present embodimentFig. 10 and 11 are graphs showing reflectance spectra of an amorphous state at 310 degrees and a crystalline state at not less than 310 degrees, respectively, and are chromaticity coordinates of the amorphous state and the crystalline state of example 1 at a normal incidence angle. From the graph, it can be seen that the reflectance spectrum after phase change decreases from 74% to 56% at maximum reflectance and increases from 10% to 30% at 300nm, with a significant change. The shift presented at the chromaticity coordinate point is large, and the shift from (0.37,0.5) to (0.38,0.45) shows good color change characteristics.

TABLE 1

Example 2

Example 2 the same material as in example 1 was maintained and the thicknesses of the high refractive index dielectric layer H and the low refractive index dielectric layer L were changed to allow different colors to appear before and after the phase change. The structural color device consists of a substrate Sub, a high refractive index dielectric layer H (TiO ₂ ) Phase change layer P (GSST), low refractive index dielectric layer L (MgF) ₂ ) Phase change layer P (GSST), high refractive index dielectric layer H (TiO) ₂ ) The composition of the substrate was K9 glass deposited film with a diameter of 80 mm, a thickness of 2 mm and a surface quality of 20/10. The specific thickness of each layer is given in table 2. According to the thickness values given in Table 2, it is possible to prepare a material which is orange in color at less than 310 degrees and grey purple in color after the temperature becomes not less than 310 degrees to the crystalline state after the high-temperature annealing. Fig. 12 and 13 are reflectance spectra of example 2 at an amorphous state of less than 310 degrees and a crystalline state of not less than 310 degrees, and fig. 14 and 15 are chromaticity diagrams of example 2 at normal incidence. From the figure, it can be seen that the shift of the position of the reflectance maximum in the visible light range of the phase-change reflection spectrum from 735nm to 400nm and the shift of chromaticity coordinates from (0.33,0.51) to (0.24,0.4) are large, and good color change characteristics are exhibited.

TABLE 2

Example 3

Example 3 employed a completely different material than the high and low index dielectric layers of example 1. The structural color device comprises a substrate Sub, a high refractive index dielectric layer H (ZnS), a phase change layer P (GSST), a low refractive index dielectric layer L (SiO) ₂ ) The phase-change layer P (GSST) and the high-refractive-index dielectric layer H (ZnS) are formed, and the substrate is the same as the material used before. The specific thickness of each layer is given in table 3. According to the thickness values given in Table 3, it is possible to prepare a material which is observed to be yellow at less than 310 degrees and brown after the high temperature annealing is raised to not less than 310 degrees and then changed to a crystalline state. Fig. 16 and 17 are reflectance spectra of example 3 at an amorphous state of less than 310 degrees and a crystalline state of not less than 310 degrees, and fig. 18 and 19 are chromaticity diagrams of example 3 at normal incidence. From the graph, it can be seen that the position of the reflectance maximum value of the phase-change reflection spectrum in the visible light range is shifted from 600nm to 631nm, and the reflectance peak value is also changed to a great extent.

TABLE 3 Table 3

Example 4

Example 4 is a substrate Sub, a high refractive index dielectric layer H (Ta ₂ O ₅ ) Phase change layer P (GSST), low refractive index dielectric layer L (SiO ₂ ) Phase change layer P (GSST), high refractive index dielectric layer H (Ta) ₂ O ₅ ) The composition, substrate and materials used before. The specific thickness of each layer is given in table 4. According to the thickness values given in Table 4, it is possible to prepare a material which is observed to be pink at less than 310 degrees and to be blue-violet after being changed to a crystalline state after being heated to not less than 310 degrees by high temperature annealing. FIGS. 20 and 21 illustrate the amorphous state and absence of example 4 at less than 310 degreesFig. 22 and 23 are chromaticity diagrams of the amorphous and crystalline states of example 4 at normal incidence, in which the change in color is evident from the chromaticity diagram, and the coordinates move from (0.31,0.45) to (0.18,0.26).

TABLE 4 Table 4

Example 5

The material of example 5 is the same as that of example 1, with only a certain adjustment of the thickness of each layer. From a substrate Sub, a high refractive index dielectric layer H (TiO ₂ ) Phase change layer P (GSST), low refractive index dielectric layer L (MgF) ₂ ) Phase change layer P1 (GSST), high refractive index dielectric layer H1 (TiO) ₂ ) The composition, substrate and materials used before. The specific thickness of each layer is given in table 5. According to the thickness values given in Table 5, it is possible to prepare a material which is seen as purple at a temperature of less than 310 degrees and blue after the high temperature annealing is raised to a temperature of not less than 310 degrees and then changed to a crystalline state. Fig. 24 and 25 are reflectance spectra of example 5 at an amorphous state of less than 310 degrees and a crystalline state of not less than 310 degrees, and fig. 26 and 27 are chromaticity diagrams of example 5 at normal incidence with respect to the amorphous and crystalline states.

TABLE 5

Example 6

The phase change layer P of example 6 is a GST material. Is composed of substrate Sub, high-refractive-index dielectric layer H (Ta ₂ O ₅ ) Phase change layer P (GST), low refractive index dielectric layer L (SiO) ₂ ) Phase change layer P (GST), high refractive index dielectric layer H (Ta) ₂ O ₅ ) The composition, substrate and materials used before. The specific thickness of each layer is given in table 6. According to the thickness values given in Table 6, a film having an orange color at less than 220℃and a thickness of not less than 2 at high temperature can be producedOrange-yellow after 20 degrees and less than 400 degrees, and brown after high-temperature annealing to not less than 400 degrees and becoming crystalline. Fig. 28, 29, and 30 are reflectance spectra of example 6 in amorphous state of less than 220 degrees, metastable state of not less than 220 degrees and less than 400 degrees, and crystalline state of not less than 400 degrees, and fig. 31, 32, and 33 are chromaticity coordinates of example 6 in amorphous state, metastable state, and crystalline state at normal incidence.

TABLE 6

Example 7

The phase change layer P of example 7 uses GST in combination with GSST. A high refractive index dielectric layer H (Ta) ₂ O ₅ ) Phase change layer P (GSST), high refractive index dielectric layer H (Ta) ₂ O ₅ ) Phase change layer P (GST), low refractive index dielectric layer L (SiO) ₂ ) Phase change layer P (GST), high refractive index dielectric layer H (Ta) ₂ O ₅ ) Phase change layer P (GSST) and high refractive index dielectric layer H (Ta ₂ O ₅ ) The composition, substrate and materials used before. The specific thickness of each layer is given in table 7. According to the thickness values given in Table 7, it is possible to prepare a material which is observed to be yellowish green at less than 220 ℃, to be emerald after being annealed to 220 to 310 ℃ at a high temperature, to be brown after being annealed to 310 to 400 ℃ at a high temperature, and to be brown after being annealed to 400 ℃ to be crystallized. Fig. 34, 35, 36, and 37 are reflection spectrum diagrams of example 7 after high temperature annealing at less than 220, 220-310 degrees, 310-400 degrees, and not less than 400 degrees, and fig. 38, 39, 40, and 41 are chromaticity diagram of example 7 at normal incidence angle after high temperature annealing at less than 220, 220-310 degrees, 310-400 degrees, and not less than 400 degrees.

TABLE 7

The foregoing description is only a partial embodiment of the present invention, and is not intended to limit the scope of the present invention, and all equivalent devices or equivalent processes using the descriptions and the drawings of the present invention or directly or indirectly applied to other related technical fields are included in the scope of the present invention.

Claims

1. The photonic crystal structure color film based on the phase change material is characterized in that the structure of the film is as follows: (HP) ^s L(PH) ^s The structure of the film is a symmetrical structure taking L as a center, wherein H represents a high-refractive-index dielectric layer, P represents a phase-change layer, L represents a low-refractive-index dielectric layer, each group (HP) or (PH) forms an equivalent high-refractive-index unit, each group of equivalent high-refractive-index units is formed by stacking the high-refractive-index dielectric layer H and the phase-change layer P, s represents the repeated stacking times of the equivalent high-refractive-index units, and s is a positive integer.

2. The photonic crystal structural color film based on phase change material according to claim 1, wherein the high refractive index dielectric layer H is a material film layer with a refractive index of 1.55 or more in the range of 400nm to 780nm, and lanthanum titanate, amorphous silicon, indium tin oxide, titanium dioxide, tantalum pentoxide, hafnium dioxide, zirconium dioxide, zinc sulfide or silicon monoxide is used; the thickness range of the high refractive index dielectric layer H is 20-500nm.

3. The photonic crystal structural color film based on phase change material according to claim 1, wherein the phase change layer P is made of GSST material or GST material, and the GSST material has two different crystalline states at different temperatures, namely an amorphous state and a crystalline state; the GST material has three different crystalline states at different temperatures, namely an amorphous state, a metastable state and a crystalline state; the thickness of the phase-change layer P ranges from 5 nm to 30nm.

4. The photonic crystal structural color film based on phase change material as claimed in claim 1, wherein the low refractive index dielectric layer L is a material film layer with refractive index less than 1.55 in the range of 400nm to 780nm, and silicon dioxide, magnesium fluoride, cerium fluoride, lanthanum fluoride, sodium aluminum fluoride, neodymium fluoride, banknote fluoride, barium fluoride, calcium fluoride or lithium fluoride is adopted; the thickness of the low refractive index medium layer L ranges from 20nm to 600nm.

5. A photonic crystal structured color film based on phase change material according to claim 1, wherein the number s of repeated stacks of equivalent high refractive index units is in the range of 1 to 5; when the number of s is 2 to 5, (HP) ^s The s layers of high refractive index medium layers H are made of the same material or at least two layers of the same material or different materials, (HP) ^s The s phase-change layers P in the (a) are made of the same material or at least two layers of the same material or different materials.

6. The preparation method of the photonic crystal structure color film based on the phase change material is characterized by comprising the following steps of:

7. The method for preparing a photonic crystal structure color film based on phase change materials as claimed in claim 6, wherein the step 2 specifically comprises:

8. The method for preparing a photonic crystal structure color film based on a phase change material according to claim 6, wherein the phase change process of the phase change layer P is performed by a high temperature annealing process, electric heating or laser pulse phase change.

9. The method for preparing a photonic crystal structural color film based on phase change materials according to claim 6, wherein the structural parameters include total number of layers, materials adopted by each layer, thickness of each layer and distribution among layers; the temperature threshold T1 is 310 degrees, the temperature threshold T2 is 220 degrees, and the temperature threshold T3 is 400 degrees.

10. The method for preparing a photonic crystal structural color film based on phase change material according to claim 6, wherein the substrate is made of polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, polycarbonate/polymethyl methacrylate composite, polyimide, polypropylene, polyvinyl chloride, polyvinyl butyral, ethylene vinyl acetate copolymer, polyurethane elastomer, polytetrafluoroethylene, fluoroethyl propylene or polydifluoroethylene; the release agent is made of fluoride, chloride or organic material which is easy to dissolve in water.