SiO2 one-dimensional photonic crystal with ultra-low infrared emissivity in the 3–5 μm band

Journal Pre-proof Preparation and characterization of Si/SiO2 one-dimensional photonic crystal with ultra-low infrared emissivity in the 3-5 ␮m band Weigang Zhang, Dandan Lv

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S0030-4026(19)31636-5

DOI:

https://doi.org/10.1016/j.ijleo.2019.163738

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IJLEO 163738

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Optik

Received Date:

19 August 2019

Accepted Date:

7 November 2019

Please cite this article as: Zhang W, Lv D, Preparation and characterization of Si/SiO2 one-dimensional photonic crystal with ultra-low infrared emissivity in the 3-5 ␮m band, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163738

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Preparation and characterization of Si/SiO2 one-dimensional photonic crystal with ultra-low infrared emissivity in the 3-5 μm band

Weigang Zhang∗ [email protected], Dandan Lv

239000, China

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Corresponding author. Tel.: +86 550 3511055, (W.G. Zhang).

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∗

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College of Materials and Chemical Engineering, Chuzhou University, Hui feng Road 1, Chuzhou

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ABSTRACT: Si/SiO2 one-dimensional photonic crystal (1DPC) with ultra-low

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infrared emissivity in the 3-5 µm band was successfully prepared by alternating deposition Si layer and SiO2 layer on the quartz substrate via the high vacuum

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electron beam coating technology. The microstructure and spectral emissivity of the photonic crystal were tested by scanning electron microscopy (SEM) and fourier

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transform infrared spectrometer (FTIR). The microstructure measure result shows that the as-prepared 1DPC has obvious multilayer structural characteristics, and the thicknesses of Si layer and SiO2 layer are basically the same as the design values. The test result of spectral emissivity shows that the average infrared emissivity in the 3-5 µm band of the as-prepared 1DPC can be as low as 0.076, which can fully reach the

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low emissivity level of conventional precious metal films. The results of this paper show that ultra-low infrared emissivity materials can still be prepared via a reasonable one-dimensional photonic structural design. Keywords: Ultra-low infrared emissivity; One-dimensional photonic crystal; High

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vacuum electron beam coating technology; Microstructure

1. Introduction

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Low infrared emissivity materials have attracted extensive attention of many

scholars because of their characteristics of reducing the infrared radiation intensity of

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the target and achieving the target infrared stealth [1-4]. In particular, the resin/metal

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composite coating has the most engineering application prospect due to its advantages of low emissivity, simple preparation, convenient construction, low cost and

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application is not limited by the target geometry [5]. However, more than 50% of the compositions in the resin/metal composite coating are organic resin, making it

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difficult to apply to the surface of high temperature parts such as aircraft engine tail

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nozzles [6,7]. Therefore, the development of low infrared emissivity materials with high temperature resistance prepared from inorganic materials has important practical significance. The emissivity of low infrared emissivity materials with high temperature resistance has been reported to be still not low enough [8], and there is still a large gap from practical applications. To the best of our knowledge, high conductive precious metal films such as gold and platinum films are the only reported 2

ultra-low infrared emissivity materials which can be lower than 0.1 [9,10]. However, the high glossiness performance of precious metal films limits their use in the field of infrared stealth. Therefore, to develop a novel ultra-low infrared emissivity material by using non-precious metal is quite important. One-dimensional photonic crystals (1DPCs) can provide selective strong reflection of incident light, so they can be applied to the design of various optical

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materials [11-13]. In addition, low infrared emissivity materials require materials to have strong reflection properties of incident light in a particular infrared light band

such as 3~5 μm, the higher the reflectivity, the lower the emissivity [14,15]. Therefore,

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the 1DPC with low emissivity in the 3-5 μm band can be achieved by designing a

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1DPC with strong reflection characteristics of 3-5 μm band. To the best of our knowledge, the existing reports on low infrared emissivity photonic crystals are

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mainly for their theoretical design [16]. Therefore, it has great practical significance

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to design and prepare a 1DPC with ultra-low infrared emissivity. In this paper, Si/SiO2 1DPC with ultra-low infrared emissivity in the 3-5 μm

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band was designed and prepared via the high vacuum electron beam coating technology. The effect of the number of periods on the infrared emissivity of 1DPC

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was systematically analyzed. The composition structure and spectral emissivity of as-prepared 1DPC were systematically investigated. 2. Experimental 2.1. Materials

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Si particles (purity 99.99 wt%, refractive index 3.4) and SiO2 particles (purity 99.99 wt%, refractive index 1.45) were purchased from Nanjing Chemical Reagent Limited Company, China. All reagents were analytical grade and were used as received without further treatment. 2.2. Preparation of the 1DPC

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Round quartz substrate (surface roughness 10 nm, diameter 5 cm, thickness 1 mm), properly cleaned by ultrasonic bath, was used as the substrate to prepare the 1DPC.

The 1DPC with low infrared emissivity in the 3-5 μm atmospheric window band was

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designed via the characteristic matrix method, then the thickness and number of periods of each structural layer (Si and SiO2) were obtained. Si and SiO2 were

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alternating deposited on the quartz substrate by high vacuum electron beam coating

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machine (OTFC-900) to fabricate the 1DPC with low emissivity in the 3~5 μm band. Pure Si particles and SiO2 particles were pressed into billets as targets. The

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target-to-substrate distance was 60 cm. The high energy electron beam bombarded the target to evaporate it, then gradually deposited on the surface of the quartz substrate to

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form a film. During the whole deposition process, the deposition rates of Si layer and

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SiO2 layer were 0.4 nm/s and 0.6 nm/s, respectively, the substrate temperature was maintained at 250 ℃, the chamber pressure 0.9×10-3 Pa, the accelerating voltage and current were 6 kV and 24 mA, respectively. 2.3. Characterization The Photographs of the quartz substrate and 1DPC were recorded by Nikon digital

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camera (COOLPIXL22). The morphology, microstructure and energy spectrum of the 1DPC were characterized by field emission scanning electron microscopy (S-4800). The sample was sputtered with a thin layer of Au prior to imaging. The normal spectral emissivity at the wavelength of 3-5.25 µm of the 1DPC was measured by fourier transform infrared spectrometer (JASCO FTIR-6100) at 100 ℃. The Landcal R1500T blackbody furnace was used as the near-blackbody source. The normal

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spectral emissivity is the ratio of the radiance of a sample to that of a blackbody at the same temperature level and for the same spectral and normal directional conditions.

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3.1. Theoretical analysis and design of the 1DPC

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3. Results and discussion

The characteristic matrix method for 1DPC was used to calculate the reflection

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spectra in the 2.5-6 µm of Si/SiO2 1DPC with the calculation software of Translight 3.01b [17]. In order to make the 1DPC to have the lowest emissivity, it must be

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ensured that it has the strongest reflectivity [15]. In order to make the 1DPC has the

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strongest reflectivity to achieve the lowest emissivity under the same conditions, the optical thicknesses (the product of the physical thickness and refractive index of the

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dielectric layer) of the two dielectric layers (Si layer and SiO2 layer) are designed equal to a quarter of center wavelengths (4 µm) of the reflection peak in the 3~5 μm band [17], then the thicknesses of Si layer (0.294 µm) and SiO2 layer (0.690 µm) are calculated. The number of periods of photonic crystals has an important influence on the intensity of their reflection peaks, so the reflection spectra of Si/SiO2 1DPCs with

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2-6 periods were calculated (Fig. 1). It can be seen that as the number of periods increases, the intensity of the reflection spectra of the 1DPC gradually increases, and the band gap of the reflection spectra gradually becomes wider. When the number of periods is increased to 5, the 1DPC has the strongest reflection peak and the widest band gap, so that the 1DPC can exhibit a high reflectance characteristic in the 3-5 µm band. The corresponding reflectivity and emissivity in the 3-5 µm band of the

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calculated 1DPC are shown in Table 1. It can be seen that the reflectivity of the 1DPC can be increased from 0.669 at 2 periods to 0.983 at 5 periods, and the corresponding emissivity can be decreased from 0.331 at 2 periods to 0.017 at 5 periods, and then

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tends to be stable. When the 1DPC has 5 periods, it already has ultra-low emissivity

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in the 3~5 μm band, so we designed the number of periods was 5 for Si/SiO2 1DPC

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(Fig. 2).

3.2. Microstructure and infrared emissivity property of the 1DPC

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The Si/SiO2 1DPC according to the structural model of Fig. 2 was successfully prepared by using the high vacuum electron beam coating technology (Fig. 3(b)). It

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can be seen that the 1DPC has a purple-red structural color which is not possessed by

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materials such as Si and SiO2, and the color can change with the observation angle. This is caused by a special reflection peak of the 1DPC in the visible light band, indicating that the as-prepared 1DPC has the basic characteristics of a one-dimensional photonic crystal [12]. Fig. 4(a) shows the cross-sectional SEM image of the Si/SiO2 1DPC according to the structural model. It can be seen that the 1DPC is periodic stacked by two different dielectric materials and have distinct 6

one-dimensional photonic structural features. The EDS patterns (Fig. 4(c), (d)) of points A and B in Fig. 4(b) illustrate that the corresponding dielectric layers are Si layer and SiO2 layer, respectively. The as-prepared 1DPC has uniform thicknesses of Si layer and SiO2 layer, the average thicknesses of Si layer and SiO2 layer are 0.324 µm and 0.652 µm, respectively. The measurement results are basically the same as the thicknesses of Si layer and SiO2 layer in the structural model, which is conducive to

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achieving low emissivity performance consistent with our design.

Fig. 5 shows the normal spectral emissivity at the wavelength of 3-5.25 µm of

Si/SiO2 1DPC according to the structural model. It can be seen that the shape of the

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emissivity spectrum substantially matches the shape of the simulated reflection

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spectra. The low emissivity characteristics of 3-5 µm in the emissivity spectrum are consistent with the strong reflection characteristics in the simulated reflection spectra.

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In addition, the as-prepared 1DPC has ultra-low infrared emissivity in the 3-5 µm

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band, the average emissivity in the 3-5 µm band can be as low as 0.076. The above emissivity value has fully reached the low emissivity level of conventional precious

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metal films [9,10]. The above results show that the ultra-low emissivity performance of less than 0.1 can also be obtained by a reasonable one-dimensional photonic

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structure design. Which provides a new idea for the design of ultra-low infrared emissivity materials. 4. Conclusions In summary, Si/SiO2 1DPC with ultra-low infrared emissivity in the 3-5 µm band was successfully designed and prepared by using the high vacuum electron beam 7

coating technology. The as-prepared 1DPC has a regular multilayer structural characteristic, which is consistent with the designed structural model. The test result of spectral emissivity shows that the as-prepared 1DPC has ultra-low infrared emissivity in the 3-5 µm band, the average emissivity can be as low as 0.076, which can fully reach the low emissivity level of conventional precious metal films. The results of this paper indicate that with a reasonable one-dimensional photonic

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structural design, it can achieve ultra-low emissivity performance of less than 0.1 in the 3-5 µm band. Which is conducive to enriching the design method of ultra-low

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infrared emissivity materials. Acknowledgements

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This work was financially supported by the National Natural Science Foundation

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of China (61705029), Natural Science Foundation of Anhui Province (1808085MF187) and Demonstration Experiment and Training Center of Anhui

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translight.

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Province (2017sxzx33). We appreciate Andrew L. Reynolds to share the software of

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Fig. 1. Calculated reflection spectra of Si/SiO2 1DPCs with different numbers of

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periods.

Fig. 2. Structural model of Si/SiO2 1DPC with ultra-low infrared emissivity in the 3-5 µm band.

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Fig. 3. Photographs of quartz substrate (a) and Si/SiO2 1DPC according to the

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structural model (b).

Fig. 4. (a) Cross-sectional SEM image of Si/SiO2 1DPC according to the structural model. (b) A partial magnified image of (a). (c) EDS pattern of point A in (b). (d) EDS pattern of point B in (b).

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Fig. 5. Spectral emissivity of Si/SiO2 1DPC according to the structural model.

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Table 1 Calculated infrared emissivity at the wavelength of 3-5 µm of Si/SiO2 1DPCs with different numbers of periods. Average reflectivity

Average emissivity

2

0.669

0.331

3

0.912

0.088

4

0.979

0.021

5

0.983

6

0.981

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Number of periods

0.017

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0.019

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