CN112305827B

CN112305827B - A low-angle-dependent real-time color-changing film based on electric field manipulation

Info

Publication number: CN112305827B
Application number: CN202011190031.XA
Authority: CN
Inventors: 张金英; 王瑞; 李卓; 王欣; 杨苏辉
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2021-07-23
Anticipated expiration: 2040-10-30
Also published as: CN112305827A

Abstract

The invention relates to a low-angle-dependent color-changing film based on electric field manipulation, and belongs to the field of color-changing materials. The invention mainly realizes discoloration by changing the dielectric constant (refractive index), and realizes multiple diffraction and scattering through uneven and irregular surfaces, so that the light reflected by the film has a low angle dependence, so that both real-time discoloration and Can greatly reduce the angle dependence of color. When the observation angle is 0 degrees to 30 degrees, the reflection peak moves within 10 nm, and the color reflected by the film has almost no change; and it can change color in real time; the present invention can be used in stealth, because the detection is long-distance, that is, the target object and the detection The device has a considerable distance, and the detection device has a small field of view in this case, that is, the detection is also a detection of a small angle range. Camouflage stealth can be achieved if angle-independent color is achieved within a small angular range (0 degrees to 30 degrees).

Description

Low-angle-dependence real-time color-changing film based on electric field control

Technical Field

The invention relates to a low-angle-dependence color-changing film based on electric field control, and belongs to the field of color-changing materials.

Background

Due to the application requirements of the color-changing material in military and civil fields, the color-changing technology becomes a hot topic of scientific research at present. Scientists classify the types of colors in nature into two categories, one is chemical and one is structural. The chemical coloring is achieved by chemical coloring agents and by pigment pigments. This method may cause problems such as resource destruction and environmental pollution. Compared with plain colors, the structural color has the advantages of corrosion resistance, no environmental pollution, no fading and the like. Structural colors have structural sensitivity. By structural sensitivity is meant that it will appear differently to different structural and material parameters. Therefore, the color change can be realized by changing the structural parameters or the material parameters of the micro-nano structure. Such as changing the geometric dimension of the micro-nano structure, changing the refractive index ratio or changing the material filling ratio, etc. With respect to structural color, most of the current research is being conducted around photonic crystals. The photonic crystal is formed by periodically arranging materials with different dielectric constants. However, the structural color generated by the photonic crystal has an inevitable defect, namely the iridescence effect. I.e. the color produced by the photonic crystal is dependent on the viewing angle. The Bragg law of the photonic crystal can be derived through the Bragg diffraction law and the Snell's law, as shown in formula (1)

Wherein λ_maxIs the reflection peak wavelength, d is the periodic structure size, theta is the angle between the incident ray and the normal, n_effIs the effective refractive index of the photonic crystal.

Through the Bragg formula of the photonic crystal, the position lambda of the reflection peak of the photonic crystal can be seen_maxAnd angle of incidence theta. Since in many color shifting applications it is desirable that the observed color be independent of the angle of incidence θ. To overcome this problem, two methods have been proposed: the first is short-range order, which is a microstructure that is uniformly scattered in all directions and thus exhibits a non-iridescent effect, i.e., low angular dependence. Zhang Xin in [ Brilliant structural tubular files with changeable stop-band and enhanced mechanical properties by the cobbed rod]Using short range ordered SiO₂The particles achieve an angle-independent structural color. And the group was by changing SiO₂The particle radius to achieve the color change, which is already determined after the microstructure is prepared, and thus the color change cannot be achieved in real time. The second method is to make ellipsoids, or concave spheres. Zhoujinming patent [ a photon crystal particle with controllable shape and no angle dependence of color and preparation method thereof]It is proposed to realize a color independent of an incident angle by making photonic crystal particles into an ellipsoidal or concave spherical shape. This method also does not allow real-time color change. In the current research on photonic crystal structure color-changing materials, few research teams consider solving the problem of angle dependenceIn the research for solving the angle dependence of the photonic crystal, most research teams only generate structural color with low angle dependence and do not realize the function of real-time color change.

Disclosure of Invention

In order to solve the problems, the invention provides a low-angle-dependence real-time color-changing film based on electric field control. When the observation visual angle is 0-30 degrees, the reflection peak moves within 10nm, and the color reflected by the film is almost unchanged; and can change color in real time; the invention can be used in connection with stealth, since the detection is remote, i.e. the object is at a considerable distance from the detection device, which in this case has a small field of view, i.e. the detection is also a detection of a small angular range. Camouflage stealth can be achieved if the angle-independent colors are achieved within a small angular range (0 to 30 degrees).

The invention realizes color change mainly by changing the dielectric constant (refractive index), realizes multiple diffraction and scattering by the rugged and irregular surface, and ensures that the light reflected by the film has low angle dependence, thereby not only changing color in real time, but also greatly reducing the angle dependence of color.

The material adopted by the invention is a ferroelectric film-Barium Strontium Titanate (BST) which can be tuned electrically. The refractive index of BST materials is related to various microscopic polarization modes existing inside the materials, mainly relaxation polarization and orientation polarization at low and high frequencies, mainly ion displacement polarization at infrared band, and mainly electron displacement polarization at visible band. The invention mainly uses the property that the refractive index of the BST material in the light wave band changes with the electric field. The refractive index of BST in the visible band changes if a voltage is applied across the BST material. Because the time for establishing or eliminating the microscopic polarization influencing the BST material refractive index in the visible light wave band is milliseconds or even microseconds or less, the BST material refractive index can be changed in real time, and further the color can be changed in real time.

For the problem of low angular dependence of color, the uneven and irregular BST thin film is formed by growing the BST thin film on an uneven and irregular substrate. The uneven and irregular surface micro-nano structure can generate multiple diffraction and scattering, so that the dependence of reflected light on the angle is weakened.

The purpose of the invention is realized by the following technical scheme.

An electric field-based manipulation of a low angle-dependent real-time color-changing film, comprising: uneven and irregular BST film, substrate, bottom electrode and top electrode; the bottom electrode is connected with the substrate, the BST film is connected with the bottom electrode and the top electrode, when voltage is applied to two ends of the electrodes, the refractive index of the BST film changes, and the position of a film reflection peak changes, so that color change is realized, and real-time color change can be realized; if the voltage is removed, the color is restored to the color when the voltage is not applied, namely, the low-angle-dependence real-time color-changing film has reversible characteristics.

The BST film is a single-layer film, and the BST film uniformly grows on the uneven and irregular substrate surface, so that the BST surface becomes uneven and irregular.

The refractive index of the BST thin film is between 2.2 and 2.5.

The thickness of the BST thin film is between 100nm and 135 nm.

The dependence of the reflection peak on the angle is weakened by multiple scattering and diffraction mainly through preparing uneven and irregular BST films, and simulation shows that the position of the reflection peak has stronger angle dependence for a flat single-layer film, and when the incident angle is changed from 0 degree to 30 degrees, the position of the reflection peak is moved to be more than 10 nm. For rugged, irregular BST films, the position of the reflection peak has relatively low angular dependence, with the position of the reflection peak shifting less than 10nm both before and after discoloration. The film has low integral reflectivity and large spectral width which is close to the color of the natural world, so the BST film can generate the color which is close to the natural world, and the electrically tunable BST film has high refractive index change speed, thereby realizing real-time color change.

Advantageous effects

1. The invention solves the problem of the angle dependence of the structural color by a simple and feasible method.

2. Compared with the prior method that no angle dependence is generated through the short-range order of the microsphere arrangement, the method has simple manufacturing process and low cost and can be produced in a large scale.

3. The film simultaneously realizes the functions of low angle dependence and real-time color change.

4. Different from the bright color generated by the traditional structural color, the film can generate the color similar to the natural color, and has more potential in the aspect of camouflage.

Drawings

FIG. 1 is a flat single-layer film structure

FIG. 2 is a schematic view of a rugged, irregular BST film structure;

FIG. 3 is a reflection spectrum of a flat film with no applied electric field, a refractive index of 2.4, at normal incidence;

FIG. 4 is a reflection spectrum of the planarized film with a refractive index of 2.4, 0 and 30 incident angles;

FIG. 5 is a reflection spectrum of a flat film, without an applied electric field, with a refractive index of 2.2, at normal incidence;

FIG. 6 is a reflection spectrum of the planarized film with a refractive index of 2.2, 0 and 30 degree incidence;

FIG. 7 is a reflection spectrum of a rugged, irregular BST film with no applied electric field, a refractive index of 2.4, at normal incidence;

FIG. 8 is a reflection spectrum of uneven, irregular BST film with a refractive index of 2.4 at 0 and 30 incident degrees;

FIG. 9 is a reflection spectrum of a thin film with a refractive index of 2.2 for a rugged, irregular BST film at normal incidence;

FIG. 10 is a reflection spectrum of a rugged, irregular BST film with a refractive index of 2.2 at 0 and 30 incident angles;

FIG. 11 is a diagram of the electric field mode field for an uneven, irregular BST film with a refractive index of 2.2, an incident wavelength of 550nm, and an incident angle of 47 degrees.

Wherein, 1-substrate, 2-bottom electrode, 3-flat BST film, 4-top electrode;

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described with reference to the accompanying drawings and examples.

Comparative example 1

As shown in fig. 1, a BST target material of a desired composition of strontium and barium is prepared, and the initial refractive index of the BST material is 2.4 in the absence of an applied electric field by adjusting the composition of strontium and barium. A layer of transparent electrode, called bottom electrode, is grown on a smooth silicon substrate, and the transparent electrode is made of Indium Tin Oxide (ITO) material and is grown in a magnetron sputtering mode. And growing a layer of flat BST film again, growing the film in a magnetron sputtering or pulse laser deposition mode, wherein the thickness of the film is 121nm, and then growing the same transparent electrode on the upper layer, namely the top electrode. When light is vertically incident on the surface of the film without an electric field, as shown in fig. 3, the center wavelength of the reflection spectrum is about 583.2nm, the peak value of the reflection spectrum is about 35%, and the spectral width of the reflection spectrum is about 120nm, which shows yellow color close to that of the natural world. The reflection spectra at 0 degree incidence and 30 degree incidence are shown in FIG. 4, in which the position of the reflection peak is shifted by 14.9nm and the position of the reflection peak is shifted by more than 10nm, indicating that the reflectivity of the film has strong angle dependence. Then, a voltage was applied across the transparent electrodes to change the refractive index of the BST thin film to 2.2, and as shown in fig. 5, the wavelength of the reflection peak was around 531.2nm, and the peak was still around 35%, showing a blue color close to that of nature. Similarly, the reflection spectra at 0 degree and 30 degree incidence are shown in FIG. 6, the shift of the reflection peak position is 16.4nm, the shift of the reflection peak position is more than 10nm, which shows that the film still has strong angle dependence when the refractive index is 2.2,

discoloration can be achieved by practical example 1, but the problem of the angle dependence of the reflected wavelength cannot be solved.

Example 2

Because the irregular surface is complex in shape, theoretical calculation and multi-parameter optimization are quite difficult when studying the action of light and the irregular surface, the optimal parameters of film design are obtained by simulation by adopting a numerical simulation method, in the simulation process, a curve which fluctuates randomly is designed firstly, then an uneven film is generated, the fluctuation degree of the curve is controllable, different fluctuation degrees are obtained by changing the parameters, namely the roughness degree of the film can be simulated, in the simulation, when the parameters N for regulating the roughness are 30 and b is 5, the thickness of the film is 122nm, the reflection peak can move by less than 10nm within 30 degrees, and the color hardly changes when observed within a small angle range. The stealth effect is achieved.

As shown in fig. 2, a BST target material of a desired composition of strontium and barium is prepared, and the initial refractive index of the BST material is 2.4 in the absence of an applied electric field by adjusting the composition of strontium and barium. And roughening the silicon substrate to form a micro-nano structure with uneven concave-convex surface and irregular surface. And growing a layer of transparent electrode on the roughened silicon substrate, wherein the transparent electrode is continuously made of Indium Tin Oxide (ITO) material and is grown in a magnetron sputtering mode. And a layer of BST film is grown again, the BST film is grown by adopting a magnetron sputtering (high-temperature sputtering and low-temperature annealing) or pulse laser deposition mode, and the integral thickness of the BST film is controlled to be 122 nm. The same transparent electrode is then grown on top of the BST.

When light vertically enters the surface of the thin film without an electric field, as shown in fig. 7, the center wavelength of the reflection spectrum is about 582nm, the peak value of the reflection spectrum is about 35%, and the reflection spectrum is yellow green similar to that in the natural world. The reflection spectra at 0 and 30 degrees are shown in fig. 8, and after oblique incidence, the reflection peak is shifted to a short wave direction, shifted by 7.2nm and less than 10nm, and the color is almost unchanged when observed at a small angle. At this time, the film exhibits low angle dependence.

Then, a voltage is applied across the upper and lower transparent electrodes to change the refractive index of the BST thin film to 2.2, and as shown in fig. 9, the wavelength of the reflection peak is at about 532nm, and the peak is still at about 35%, which shows a blue color close to that of nature. Also, as shown in fig. 10, in the reflectance spectra at 0 degree and 30 degree incidence, also after oblique incidence, the peak of the reflectance peak shifts to a short wavelength, shifted by 7.3nm and less than 10nm, and the color hardly changes when observed at a small angle, that is, the film can be made to have a reflectance spectrum with low angle dependence both before and after discoloration. As shown in FIG. 11, the electric field pattern at a wavelength of 550nm and an incident angle of 47 degrees,

it can be seen that the entire BST film has a diffractive and scattering effect on light, and it is this diffraction and scattering that makes its reflectivity have a low angular dependence. The film exhibits low angular dependence at refractive indices of 2.4 and 2.2.

Example 3

The BST film roughness is further optimized to a film thickness of 121nm at N20 and b 1.4, but this time the desired refractive index is changed, so the strontium and barium compositions are adjusted to achieve the desired refractive index. It is achieved that the position of the reflection peak is shifted by less than 10nm within 30 degrees and that the color is hardly changed when viewed within a small angle range. The stealth effect is achieved.

As shown in fig. 2, a BST target material of a desired composition of strontium and barium is prepared, and the initial refractive index of the BST material is 2.5 in the absence of an applied electric field by adjusting the composition of strontium and barium. And roughening the silicon substrate to form a micro-nano structure with uneven concave-convex surface and irregular surface. And growing a layer of transparent electrode on the roughened silicon substrate, wherein the transparent electrode is continuously made of Indium Tin Oxide (ITO) material and is grown in a magnetron sputtering mode. And a layer of BST film is grown again, the BST film is grown by adopting a magnetron sputtering (high-temperature sputtering and low-temperature annealing) or pulse laser deposition mode, and the integral thickness of the BST film is controlled to be 121 nm. The same transparent electrode is then grown on top of the BST.

Under the condition of no electric field, when light vertically enters the surface of the film, the central wavelength of a reflection spectrum is about 582nm, the peak value of the reflection spectrum is about 30%, and the reflection spectrum is yellow green similar to that of the natural world. After 30 degrees oblique incidence, the reflection peak shifts to the short wave direction, moving less than 10nm, and the color hardly changes when observed at a small angle. At this time, the film exhibits low angle dependence.

Then, voltage is applied to two ends of the upper and lower layers of transparent electrodes, so that the refractive index of the BST film is changed to 2.3, the wavelength of a reflection peak is about 532nm, the peak value is still about 30%, and the BST film presents blue color close to nature. Similarly, after 30-degree incidence, the reflection peak moves to a short wave direction, which is less than 10nm, and the color is hardly changed when observed at a small angle, namely, the film can be made to have a reflection spectrum with low angle dependence before and after discoloration.

Summary of the examples and comparative examples

Comparative example 1 can realize real-time color change, but the relationship between the generated structural color and the angle is large, even at a low angle, the position shift of the reflection peak is large and is more than 10nm, and examples 2 and 3 realize that the position shift of the reflection peak within 30 degrees is less than 10nm by optimizing the roughness of the rough BST film and changing the initial refractive index by applying voltage. When observed at a small angle, the color is almost independent of the angle, and the stealth is realized.

The above detailed description is further intended to explain the objects, technical solutions and advantages of the present invention in detail, and it should be understood that the above description is only an example of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. The utility model provides a control real-time color-changing film of low angle dependence based on electric field which characterized in that: the method comprises the following steps: the surface of the BST thin film is uneven and irregular, and the BST thin film comprises a substrate, a bottom electrode and a top electrode; the bottom electrode is connected with the substrate, the BST film is connected with the bottom electrode and the top electrode, when voltage is applied to two ends of the electrodes, the refractive index of the BST film changes, and the position of a film reflection peak changes, so that color change is realized, and real-time color change can be realized; if the voltage is removed, the color is recovered to the color when no voltage is applied, namely the low-angle dependence real-time color-changing film has reversible characteristics; the BST film is an electrically tunable ferroelectric film-barium strontium titanate.

2. The real-time color-changing film of claim 1, wherein: the BST film is a single-layer film, and the BST film uniformly grows on the surface of an uneven and irregular substrate, so that the surface of the BST becomes uneven and irregular.

3. The real-time color-changing film according to claim 1 or 2, wherein: the refractive index of the BST thin film is between 2.2 and 2.5.

4. The real-time color-changing film according to claim 1 or 2, wherein: the thickness of the BST thin film is between 100nm and 135 nm.