CN102560650B - Porous aluminum oxide photonic crystal and preparation method and applications thereof - Google Patents

Abstract

The invention discloses a porous alumina photonic crystal, a preparation method and application thereof. The crystal is composed of a backbone layer and a bifurcation layer, and a defect layer is placed in a local area within it. The thickness of the crystal is 75-85 μm, the backbone layer is composed of main holes, and the bifurcation layer is composed of bifurcated holes. The two ends of one of the bifurcated holes communicate with the main holes of the upper and lower trunk layers of the bifurcated layer respectively, and the defect layer is composed of straight holes whose two ends are respectively connected with the main hole. The method is to oxidize the aluminum sheet first, and then anodize it under a periodic voltage to obtain an aluminum oxide sheet containing a backbone layer and a bifurcation layer, and then apply grease to the front part of it, and then place it Anodize under periodic voltage to obtain an aluminum oxide sheet with a defective layer in a local area inside it. After removing the grease on it, first place it under periodic voltage for anodization, and then remove the excess aluminum on the back. Get the product. It can be used for optical anti-counterfeiting in the 780-1400nm band.

Description

Porous alumina photonic crystal and its preparation method and application

technical field

The invention relates to a photonic crystal and its preparation method and application, in particular to a porous alumina photonic crystal and its preparation method and application.

Background technique

It is well known that photonic crystals composed of porous alumina films have different transmittances to light of different wavelengths due to their different pore structures. Therefore, people have made some attempts and efforts in order to explore and expand the application range of porous alumina photonic crystals, such as a kind of "with Porous aluminum oxide thin film filter with bifurcated holes and its preparation method". The filter is a porous aluminum oxide film with a linear through hole with a diameter of 40-60nm, and more than two layers of bifurcated holes are placed on the hole wall. The angle between the through holes is 50-70 degrees, the backbone layer formed by the straight through holes between the bifurcated holes and the bifurcated layer formed by the bifurcated holes change periodically, and the thickness of the film is 60-180 μm; the preparation method is as follows: Place the aluminum sheet in an acid solution with a concentration of 0.2-0.4M, and anodize it under arc-tooth wave voltage for at least 5 minutes. ~3.5min, a porous aluminum oxide film filter with bifurcated holes was prepared. Although this kind of optical filter composed of porous alumina film can selectively filter the light in the 500-1500nm band, there is also a problem that only the same alumina film can have the same optical properties, that is, the same alumina film has the same optical properties. The thin film can only filter a certain wavelength of light, but it cannot be used for optical anti-counterfeiting, that is, the same aluminum oxide film can achieve different optical properties in local areas; in addition, the preparation method cannot be used for optical anti-counterfeiting. Anti-counterfeit aluminum oxide film.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a porous alumina photonic crystal which has the same optical properties under visible light but different optical properties in local areas under infrared light.

Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned porous alumina photonic crystal.

Another technical problem to be solved by the present invention is to provide a use of the above-mentioned porous alumina photonic crystal.

In order to solve the technical problem of the present invention, the adopted technical solution is: the porous alumina photonic crystal is composed of a trunk layer and a bifurcation layer, especially,

The photonic crystal has a thickness of 75-85 μm, and a defective layer is placed in a local area within it;

The number of layers of the backbone layer and the bifurcation layer is 375-425 layers, and the thickness ratio between them is 2-3:1;

The trunk layer is composed of main holes, and the bifurcated layer is composed of two bifurcated holes. The angle between the two bifurcated holes is 30-50 degrees. The main holes of the upper and lower backbone layers of the bifurcation layer are connected;

The diameter of the main hole located on the upper surface of the photonic crystal is 80-110 nm, and the diameter of the holes in other layers shrinks linearly until the diameter of the hole on the lower surface of the photonic crystal is 17-20 nm;

The layer thicknesses of the backbone layer and the bifurcation layer at the upper surface of the photonic crystal are 300-350 nm and 100-140 nm respectively, and the layer thicknesses of other layers shrink linearly until the layer thickness at the lower surface of the photonic crystal is 130 nm. ～150nm and 50～70nm;

The defect layer is 30-32 μm away from the upper surface of the photonic crystal, and is composed of straight holes with a diameter of 60-70 nm and a length of 260-1060 nm, and the two ends of the straight holes communicate with the main hole respectively.

As a further improvement of the porous alumina photonic crystal, the axis of the main hole in the backbone layer is perpendicular to the plane of the photonic crystal; the axis of the straight hole in the defect layer is perpendicular to the plane of the photonic crystal.

In order to solve another technical problem of the present invention, another technical solution adopted is: the preparation method of the above-mentioned porous alumina photonic crystal adopts the anodic oxidation method, especially the completion steps are as follows:

Step 1, first place the aluminum sheet in an oxalic acid solution with a concentration of 0.2-0.4M, anodize it at a DC voltage of 51-55V for 2.5-3.5 hours, and then place it in a phosphochromic acid solution for 4-5 hours of corrosion. An alumina sheet containing densely packed pores is obtained;

Step 2, put the aluminum oxide sheet containing densely packed holes in an oxalic acid solution with a temperature of 16-20°C and a concentration of 0.2-0.4M, and anodize it under a periodic asymmetric voltage for 74-78 cycles, wherein, the cycle The waveform of the asymmetrical voltage is as follows: the voltage increases from 23V to 53V according to the law of sine wave during 30s, and then linearly decreases from 53V to 23V during 180s. Alumina flakes;

Step 3, apply grease on the front part of the alumina sheet containing the backbone layer and the fork layer, and then place the grease-coated alumina sheet containing the backbone layer and the fork layer at a temperature of 16-20°C. In an oxalic acid solution with a concentration of 0.2-0.4M, anodize at a periodic specific voltage for 1 to 4 cycles, wherein the waveform of the periodic specific voltage is, after the voltage linearly drops from 53V to 38V during 80s, it remains constant at 100s at 23V, 180s per cycle, to obtain an aluminum oxide sheet containing a defective layer in a partial area inside it, and then remove the grease on the aluminum oxide sheet containing a defective layer in a partial area inside it;

Step 4, first place the aluminum oxide sheet with the defective layer that has been removed from the oil in an oxalic acid solution with a temperature of 16-20°C and a concentration of 0.2-0.4M, and anodize 275-325 sheets under a periodic asymmetric voltage period, wherein the waveform of the periodic asymmetric voltage is the same as that described in step 2, and then it is placed in a cupric chloride solution or a tin chloride solution to remove excess aluminum on the back to make a porous alumina photonic crystal.

As a further improvement of the preparation method of porous alumina photonic crystals, the purity of the aluminum sheet is ≥99.9%; the phosphoric chromic acid solution is phosphoric acid with a concentration of 4-8 wt% and chromium with a concentration of 1.6-2 wt%. A mixed solution of acid; the described part is an artificially set pattern; the described grease is vacuum grease, or lubricating grease, or edible fat; Clean with acetone, ultrasonic and deionized water in sequence.

In order to solve another technical problem of the present invention, another technical solution adopted is: the use of the above-mentioned porous alumina photonic crystal is to use the porous alumina photonic crystal for optical anti-counterfeiting in the 780-1400nm band.

Compared with the beneficial effects of the prior art, first, the obtained target product is characterized by scanning electron microscopy and ultraviolet-visible-near-infrared spectrometer respectively. From the results, it can be seen that the target product is composed of a backbone layer and a bifurcated layer. A porous aluminum oxide photonic crystal with a thickness of 75-85 μm is formed by stacking, and a defect layer is placed in a local area of the photonic crystal. Among them, the number of layers of the backbone layer and the bifurcation layer is 375-425 layers, and the thickness ratio between them is 2-3:1; The angle between the holes is 30-50 degrees, and the two ends of one of the bifurcated holes are respectively connected with the main holes of the upper and lower trunk layers of the bifurcated layer; the main hole is located on the upper surface of the photonic crystal. The hole diameter is 80-110nm, and the hole diameters of other layers shrink linearly until the hole diameter at the lower surface of the photonic crystal is 17-20nm; ~350nm and 100~140nm, the thickness of other layers shrinks linearly until the layer thickness at the lower surface of the photonic crystal is 130~150nm and 50~70nm respectively; the distance between the defect layer and the upper surface of the photonic crystal is 30~32μm, which is formed by the hole It consists of straight holes with a diameter of 60-70nm and a pore length of 260-1060nm, and the two ends of the straight holes are respectively connected with the main hole. Photonic crystals have the same optical transmission performance for visible light, but in different regions, that is, the region where the defective layer is placed, it also has the performance of infrared transmission; The porous alumina photonic crystal with a defect layer in the local area, because the porosity of the backbone layer and the bifurcation layer is different, the refractive index of the effective medium is also different, thus forming a periodic layered structure with high and low refractive index distribution , that is, the Bragg reflector structure, coupled with the introduction of microstructure defects, that is, straight channels with consistent apertures up and down, so that the infrared rays that could not be transmitted can also be transmitted in the local area of the alumina sheet, and finally make the photonic crystal in the local area. optical properties, thereby achieving the same optical properties on the same piece of alumina photonic crystal under natural light or white light irradiation, and under infrared irradiation, each local area of the alumina sheet (which can be used for design patterns, shape) have different optical properties, such as infrared penetration and cut-off technical effects. It can be used not only for storing information, but also for optical anti-counterfeiting in the infrared band. It also has the advantages of low cost, one-time use, convenient reading of information, and less damage to the human body compared with ultraviolet anti-counterfeiting technology. It has excellent applications. Prospect; third, the preparation method is scientific and effective, the required equipment is simple, the process is convenient, controllable, repeatable, and the production cost is low, which is suitable for large-scale industrial production.

As a further embodiment of the beneficial effect, one is that the hole axis of the main hole in the backbone layer is preferably perpendicular to the plane of the photonic crystal, and the hole axis of the straight hole in the defect layer is preferably perpendicular to the plane of the photonic crystal, which is conducive to full play of the anti-counterfeiting effect; The 2nd, the purity of aluminum flake is preferably ≥ 99.9%, has guaranteed the quality of photonic crystal; 3rd, the phosphoric chromic acid solution preferably is that concentration is the mixed solution of the phosphoric acid of 4～8wt% and the chromic acid that concentration is 1.6～2wt%, is beneficial to The formation of densely packed holes on the alumina sheet; the fourth is that the partial pattern is preferably artificially set to facilitate the identification of anti-counterfeiting marks; the fifth is that the oil is preferably vacuum grease, or lubricating grease, or edible fat, which not only makes the source of raw materials more abundant, It also makes the preparation process easier to implement and flexible; the sixth is to remove the grease on the aluminum oxide sheet containing the defective layer in the local area, preferably using acetone cleaning, ultrasonic cleaning and deionized water cleaning in order to ensure the effect of removing grease.

Description of drawings

The preferred modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Figure 1 is one of the results of characterizing the prepared target product using a scanning electron microscope (SEM). Fig. 1a is the SEM photo of target product surface topography, can find out therefrom, the aperture of target product is about 100nm; Fig. 1b, Fig. 1c and Fig. 1d are the SEM photos of the top, middle and bottom of target product longitudinal section respectively, by It can be seen from these SEM photos that the pore diameter of the target product gradually decreases from 100nm to 20nm, and the layer thickness gradually decreases from 450nm to 200nm. The shaded area in Figure 1c is the fork layer, and the middle part is the backbone layer.

Fig. 2 is one of the results of characterizing the defective parts of the target product prepared using a scanning electron microscope. Figure 2a is the SEM photo of the longitudinal section of the artificially set pattern boundary area. It can be seen from the SEM photo that there is no straight channel defect on the left side of the boundary, and there is a straight channel defect on the right side of the boundary. The length of the straight channel from the left side to the right side increases gradually, as shown by the dashed line in the SEM photograph. Figure 2b is an enlarged photo of the straight channel defect in Figure 2a, from which it can be seen that the area between the two dotted lines is a straight channel defect.

Fig. 3 is a schematic diagram of the morphology of the target product shown in Fig. 1 and Fig. 2 .

Fig. 4 is one of the results of characterizing the target product prepared using a UV-visible-near-infrared spectrometer. The solid curve in the figure is the position and bandwidth of the photon band gap, and the dotted curve is the transmission spectrum of the pattern area; the dotted curve shows that the infrared rays originally falling within the photon band gap range can propagate in the alumina photonic crystal, and in the visible light spectrum All regions of the alumina photonic crystal within the range have the same optical transmission performance.

Fig. 5 is one of the results of characterizing the target product under the irradiation of visible light and infrared light source respectively. Figure 5a is the picture captured by the camera under the irradiation of visible light source (white LED light source); Figure 5b is the picture captured under the irradiation of infrared light source, the target product presents areas with different light and dark, and the areas with high brightness correspond to infrared retransmission, The dark region corresponds to the photonic forbidden band, within which infrared light cannot be transmitted.

Detailed ways

First purchased from the market or prepared by conventional methods:

Aluminum flakes with a purity ≥ 99.9%; a mixed solution made of phosphoric acid with a concentration of 4-8% by weight and chromic acid with a concentration of 1.6-2% by weight - phosphochromic acid solution; vacuum grease, lubricating grease and edible fat as oil ;acetone.

then,

Example 1

The concrete steps of preparation are:

In step 1, the aluminum sheet is first placed in an oxalic acid solution with a concentration of 0.2M, and anodized at a DC voltage of 51V for 3.5 hours; wherein, the purity of the aluminum sheet is 99.9%. Then it was corroded in phosphoric chromic acid solution for 4 hours to obtain an alumina sheet containing densely packed pores.

Step 2, put the aluminum oxide sheet containing densely packed pores in an oxalic acid solution with a temperature of 16°C and a concentration of 0.2M, and anodize it under a periodic asymmetric voltage for 74 cycles; among them, the waveform of the periodic asymmetric voltage The voltage is increased from 23V to 53V according to the law of sine wave during 30s, and then linearly decreased from 53V to 23V during 180s. Each cycle is 210s, and the alumina sheet containing the backbone layer and the bifurcation layer is obtained.

In step 3, grease is applied to a part of the front surface of the aluminum oxide sheet containing the trunk layer and the bifurcation layer; wherein, the part is an artificially set pattern, and the grease is vacuum grease. Then put the aluminum oxide sheet coated with grease and containing the main layer and the bifurcation layer in the oxalic acid solution with a temperature of 16°C and a concentration of 0.2M, and anodize at a periodic specific voltage for one cycle; wherein, the periodic specific voltage The waveform of the voltage is, after the voltage linearly drops from 53V to 38V during 80s, it is kept at 23V for 100s, and each cycle counts 180s to obtain an alumina sheet with a defect layer in a local area inside it. Next, remove the grease on the aluminum oxide sheet containing the defective layer in the partial area inside; wherein, remove the grease on the aluminum oxide sheet containing the defective layer in the local area by using acetone cleaning, ultrasonic cleaning and deionized water cleaning in sequence.

Step 4, first place the alumina sheet with the defective layer removed from the oil in an oxalic acid solution with a temperature of 16°C and a concentration of 0.2M, and anodize for 275 cycles under a periodic asymmetric voltage; wherein, the periodic The waveform of the asymmetrical voltage is the same as that described in step 2. Then put it in copper chloride solution or tin chloride solution to remove excess aluminum on the back, and make porous alumina similar to that shown in Figure 1, Figure 2 and Figure 3, and the curve shown in Figure 4 Photonic crystals.

Example 2

The concrete steps of preparation are:

In step 1, the aluminum sheet is first placed in an oxalic acid solution with a concentration of 0.25M, and anodized at a DC voltage of 52V for 3.3 hours; wherein, the purity of the aluminum sheet is 99.99%. Then it was corroded in phosphoric chromic acid solution for 4 hours to obtain an alumina sheet containing densely packed pores.

Step 2, put the aluminum oxide sheet containing densely packed pores in an oxalic acid solution with a temperature of 17°C and a concentration of 0.25M, and anodize it for 75 cycles under a periodic asymmetric voltage; among them, the waveform of the periodic asymmetric voltage The voltage is increased from 23V to 53V according to the law of sine wave during 30s, and then linearly decreased from 53V to 23V during 180s. Each cycle counts 210s, and an alumina sheet containing a backbone layer and a bifurcation layer is obtained.

In step 3, grease is applied to a part of the front surface of the aluminum oxide sheet containing the trunk layer and the bifurcation layer; wherein, the part is an artificially set pattern, and the grease is vacuum grease. Then put the grease-coated alumina sheet containing the trunk layer and the bifurcation layer in an oxalic acid solution with a temperature of 17°C and a concentration of 0.25M, and anodize for 2 cycles at a periodic specific voltage; among them, the periodic specific voltage The waveform of the voltage is, after the voltage linearly drops from 53V to 38V during 80s, it is kept at 23V for 100s, and each cycle counts 180s to obtain an alumina sheet with a defect layer in a local area inside it. Next, remove the grease on the aluminum oxide sheet containing the defective layer in the partial area inside; wherein, remove the grease on the aluminum oxide sheet containing the defective layer in the local area by using acetone cleaning, ultrasonic cleaning and deionized water cleaning in sequence.

Step 4, first place the aluminum oxide sheet containing the defective layer that has been removed from the oil in an oxalic acid solution with a temperature of 17°C and a concentration of 0.25M, and anodize for 288 cycles under a periodic asymmetric voltage; wherein, the periodic The waveform of the asymmetrical voltage is the same as that described in step 2. Then put it in copper chloride solution or tin chloride solution to remove excess aluminum on the back, and make porous alumina similar to that shown in Figure 1, Figure 2 and Figure 3, and the curve shown in Figure 4 Photonic crystals.

Example 3

The concrete steps of preparation are:

Step 1, the aluminum sheet is first placed in an oxalic acid solution with a concentration of 0.3M, and anodized at a DC voltage of 53V for 3 hours; wherein, the purity of the aluminum sheet is ≥99.9%. Then it was corroded in phosphoric chromic acid solution for 4.5 hours to obtain an alumina sheet containing densely packed pores.

Step 2, put the aluminum oxide sheet containing densely packed pores in an oxalic acid solution with a temperature of 18°C and a concentration of 0.3M, and anodize it under a periodic asymmetric voltage for 76 cycles; among them, the waveform of the periodic asymmetric voltage The voltage is increased from 23V to 53V according to the law of sine wave during 30s, and then linearly decreased from 53V to 23V during 180s. Each cycle counts 210s, and an alumina sheet containing a backbone layer and a bifurcation layer is obtained.

In step 3, grease is applied to a part of the front surface of the aluminum oxide sheet containing the trunk layer and the bifurcation layer; wherein, the part is an artificially set pattern, and the grease is vacuum grease. Then put the aluminum oxide sheet coated with grease and containing the main layer and the bifurcation layer in the oxalic acid solution with a temperature of 18°C and a concentration of 0.3M, and anodize for 3 cycles under a periodic specific voltage; wherein, the periodic specific voltage The waveform of the voltage is, after the voltage linearly drops from 53V to 38V during 80s, it is kept at 23V for 100s, and each cycle counts 180s to obtain an alumina sheet with a defect layer in a local area inside it. Next, remove the grease on the aluminum oxide sheet containing the defective layer in the partial area inside; wherein, remove the grease on the aluminum oxide sheet containing the defective layer in the local area by using acetone cleaning, ultrasonic cleaning and deionized water cleaning in sequence.

Step 4, first place the aluminum oxide sheet containing the defective layer that has been removed from the oil in an oxalic acid solution with a temperature of 18°C and a concentration of 0.3M, and anodize for 300 cycles under a periodic asymmetric voltage; wherein, the periodic The waveform of the asymmetrical voltage is the same as that described in step 2. Then put it in copper chloride solution or tin chloride solution to remove the excess aluminum on the back, and make the porous alumina photon as shown in Figure 1, Figure 2 and Figure 3, and the curve shown in Figure 4 crystals.

Example 4

The concrete steps of preparation are:

In step 1, the aluminum sheet is first placed in an oxalic acid solution with a concentration of 0.35M, and anodized at a DC voltage of 54V for 2.8 hours; wherein, the purity of the aluminum sheet is ≥99.99%. Then it was corroded in phosphoric chromic acid solution for 5 hours to obtain an alumina sheet containing densely packed pores.

Step 2, put the aluminum oxide sheet containing densely packed pores in an oxalic acid solution with a temperature of 19°C and a concentration of 0.35M, and anodize it for 77 cycles under a periodic asymmetric voltage; among them, the waveform of the periodic asymmetric voltage The voltage is increased from 23V to 53V according to the law of sine wave during 30s, and then linearly decreased from 53V to 23V during 180s. Each cycle is 210s, and the alumina sheet containing the backbone layer and the bifurcation layer is obtained.

In step 3, grease is applied to a part of the front surface of the aluminum oxide sheet containing the trunk layer and the bifurcation layer; wherein, the part is an artificially set pattern, and the grease is vacuum grease. Then put the aluminum oxide sheet coated with grease and containing the trunk layer and the bifurcation layer in the oxalic acid solution with a temperature of 19°C and a concentration of 0.35M, and anodize for 4 cycles under a periodic specific voltage; wherein, the periodic specific voltage The waveform of the voltage is, after the voltage linearly drops from 53V to 38V during 80s, it is kept at 23V for 100s, and each cycle counts 180s to obtain an alumina sheet with a defect layer in a local area inside it. Next, remove the grease on the aluminum oxide sheet containing the defective layer in the partial area inside; wherein, remove the grease on the aluminum oxide sheet containing the defective layer in the local area by using acetone cleaning, ultrasonic cleaning and deionized water cleaning in sequence.

Step 4, first place the alumina sheet with the defective layer removed from the oil in an oxalic acid solution with a temperature of 19°C and a concentration of 0.35M, and anodize for 313 cycles under a periodic asymmetric voltage; wherein, the periodic The waveform of the asymmetrical voltage is the same as that described in step 2. Then put it in copper chloride solution or tin chloride solution to remove excess aluminum on the back, and make porous alumina similar to that shown in Figure 1, Figure 2 and Figure 3, and the curve shown in Figure 4 Photonic crystals.

Example 5

The concrete steps of preparation are:

In step 1, the aluminum sheet is first placed in an oxalic acid solution with a concentration of 0.4M, and anodized at a DC voltage of 55V for 2.5 hours; wherein, the purity of the aluminum sheet is ≥99.9%. Then it was corroded in phosphoric chromic acid solution for 5 hours to obtain an alumina sheet containing densely packed pores.

Step 2, put the aluminum oxide sheet containing densely packed pores in an oxalic acid solution with a temperature of 20°C and a concentration of 0.4M, and anodize it under a periodic asymmetric voltage for 78 cycles; among them, the waveform of the periodic asymmetric voltage The voltage is increased from 23V to 53V according to the law of sine wave during 30s, and then linearly decreased from 53V to 23V during 180s. Each cycle is 210s, and the alumina sheet containing the backbone layer and the bifurcation layer is obtained.

In step 3, grease is applied to a part of the front surface of the aluminum oxide sheet containing the trunk layer and the bifurcation layer; wherein, the part is an artificially set pattern, and the grease is vacuum grease. Then put the aluminum oxide sheet coated with grease and containing the trunk layer and the bifurcation layer in the oxalic acid solution with a temperature of 20°C and a concentration of 0.4M, and anodize for 4 cycles under a periodic specific voltage; among them, the periodic specific voltage The waveform of the voltage is, after the voltage linearly drops from 53V to 38V during 80s, it is kept at 23V for 100s, and each cycle counts 180s to obtain an alumina sheet with a defect layer in a local area inside it. Next, remove the grease on the aluminum oxide sheet containing the defective layer in the partial area inside; wherein, remove the grease on the aluminum oxide sheet containing the defective layer in the local area by using acetone cleaning, ultrasonic cleaning and deionized water cleaning in sequence.

Step 4, first place the alumina sheet with the defective layer removed from the oil in an oxalic acid solution with a temperature of 20°C and a concentration of 0.4M, and anodize for 325 cycles under a periodic asymmetric voltage; wherein, the periodic The waveform of the asymmetrical voltage is the same as that described in step 2. Then put it in copper chloride solution or tin chloride solution to remove excess aluminum on the back, and make porous alumina similar to that shown in Figure 1, Figure 2 and Figure 3, and the curve shown in Figure 4 Photonic crystals.

Select vacuum grease or lubricating grease or edible fat as grease respectively again, repeat above-mentioned embodiment 1～5, have made as or be similar to as shown in Fig. 1, Fig. 2 and Fig. 3 equally, and as shown in the curve among Fig. 4 porous alumina photonic crystals.

The application of the porous alumina photonic crystal is that the porous alumina photonic crystal is used for optical anti-counterfeiting in the 780-1400nm band.

Apparently, those skilled in the art can make various changes and modifications to the porous alumina photonic crystal and its preparation method and application of the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (10)

1. A porous aluminum oxide photonic crystal is composed of a backbone layer and a bifurcation layer, and is characterized in that: The photonic crystal has a thickness of 75-85 μm, and a defective layer is placed in a local area within it; The number of layers of the backbone layer and the bifurcation layer is 375-425 layers respectively, and the thickness ratio between them is 2-3:1; The trunk layer is composed of main holes, and the bifurcated layer is composed of two bifurcated holes. The angle between the two bifurcated holes is 30-50 degrees. The main holes of the upper and lower backbone layers of the bifurcation layer are connected; The diameter of the main hole located on the upper surface of the photonic crystal is 80-110 nm, and the diameter of the holes in other layers shrinks linearly until the diameter of the hole on the lower surface of the photonic crystal is 17-20 nm; The layer thicknesses of the backbone layer and the bifurcation layer at the upper surface of the photonic crystal are 300-350 nm and 100-140 nm respectively, and the layer thicknesses of other layers shrink linearly until the layer thickness at the lower surface of the photonic crystal is 130 nm. ～150nm and 50～70nm; The defect layer is 30-32 μm away from the upper surface of the photonic crystal, and is composed of straight holes with a diameter of 60-70 nm and a length of 260-1060 nm, and the two ends of the straight holes communicate with the main hole respectively. 2. The porous alumina photonic crystal according to claim 1, characterized in that the axis of the main hole in the backbone layer is perpendicular to the plane of the photonic crystal. 3. The porous alumina photonic crystal according to claim 1, characterized in that the hole axes of the straight holes in the defect layer are perpendicular to the plane of the photonic crystal. 4. a preparation method of the porous alumina photonic crystal described in claim 1, adopts anodic oxidation method, is characterized in that finishing step is as follows: Step 1, first place the aluminum sheet in an oxalic acid solution with a concentration of 0.2-0.4M, anodize it at a DC voltage of 51-55V for 2.5-3.5 hours, and then place it in a phosphochromic acid solution for 4-5 hours of corrosion. An alumina sheet containing densely packed pores is obtained; Step 2, put the aluminum oxide sheet containing densely packed holes in an oxalic acid solution with a temperature of 16-20°C and a concentration of 0.2-0.4M, and anodize it under a periodic asymmetric voltage for 74-78 cycles, wherein, the cycle The waveform of the asymmetrical voltage is as follows: the voltage increases from 23V to 53V according to the law of sine wave during 30s, and then linearly decreases from 53V to 23V during 180s. Alumina flakes; Step 3, apply grease on the front part of the alumina sheet containing the backbone layer and the fork layer, and then place the grease-coated alumina sheet containing the backbone layer and the fork layer at a temperature of 16-20°C. In an oxalic acid solution with a concentration of 0.2-0.4M, anodize at a periodic specific voltage for 1 to 4 cycles, wherein the waveform of the periodic specific voltage is, after the voltage linearly drops from 53V to 38V during 80s, it remains constant at 100s at 23V, 180s per cycle, to obtain an aluminum oxide sheet containing a defective layer in a partial area inside it, and then remove the grease on the aluminum oxide sheet containing a defective layer in a partial area inside it; Step 4, first place the aluminum oxide sheet containing the defective layer that has been removed from the grease in an oxalic acid solution with a temperature of 16-20°C and a concentration of 0.2-0.4M, and anodize under a periodic asymmetric voltage for 275-325 cycles , wherein, the waveform of the periodic asymmetric voltage is the same as that described in step 2, and then it is placed in a copper chloride solution or a tin chloride solution to remove excess aluminum on the back to make a porous alumina photonic crystal. 5. The preparation method of porous alumina photonic crystal according to claim 4, characterized in that the purity of the aluminum sheet is ≥99.9%. 6. The preparation method of porous alumina photonic crystal according to claim 4, characterized in that the phosphochromic acid solution is a mixed solution of phosphoric acid with a concentration of 4-8 wt% and chromic acid with a concentration of 1.6-2 wt%. 7. The preparation method of the porous alumina photonic crystal according to claim 4, characterized in that the partial pattern is artificially set. 8. The preparation method of porous alumina photonic crystal according to claim 4, characterized in that the grease is vacuum grease, or lubricating grease, or edible fat. 9. The preparation method of porous alumina photonic crystal according to claim 4, characterized in that removing the grease on the alumina sheet containing the defect layer in the local area is to use acetone cleaning, ultrasonic cleaning and deionized water cleaning in sequence. 10. the purposes of a kind of porous alumina photonic crystal described in claim 1, it is characterized in that: The porous alumina photonic crystal is used for optical anti-counterfeiting in the 780-1400nm band.