Stability of sol-gel silica coatings under ISO Class 5 atmosphere condition
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摘要: 在常压百级洁净度环境下，采用三种不同折射率的SiO2溶胶在熔石英基底上涂制四种不同薄膜，利用光学理论计算模拟了三种胶体涂制的膜层稳定性，通过实验考查了膜层光学指标随时间的变化规律。SiO2薄膜能够显著提升光学元件透射率，但由于膜层表面的大量羟基及其多孔结构，SiO2薄膜易吸附周围环境中的有机污染物及水分填充膜层孔隙，从而导致膜层折射率发生变化，影响膜层透射率、反射率等光学性能。实验结果发现，三种溶胶凝胶化学膜在常压百级环境中的有效期为80 d(绝对变化率小于0.1%)，且三种胶体涂制的膜层稳定性由高到低依次为折射率1.19, 1.15, 1.25的膜层。Abstract: Sol-gel SiO2 anti-reflective coatings were prepared with three different sol-gels, and their optic performance under atmosphere condition was studied in detail.Three AR coatings maintained reflective indexes of 1.15, 1.19, 1.25 respectively. The porous silica coatings can increase transmittance observably, but are very sensitive to contaminants and humidity in surroundings due to their strong adsorptive capacity resulting from the hydroxyl on the coatings surface and their porous structure with large specific surface area. The pores of silica coating can be filled with contaminants and humidity adsorbed on the coatings, which will increase the refractive index of the coatings and also absorb or scatter the light and therefore reduce the transmittance and increase the reflectance simultaneously. The fused silica coated with AR coatings were placed in ISO Class 5 cleanroom (ISO 14644-1) for 180 days. The results show that the optic performance change of all coatings is significant after 80 days. The AR coating with a refractive index of 1.19 is more stable comparatively.
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Key words:
- SiO2 coating /
- atmosphere /
- ISO Class 5 cleanroom /
- transmittance /
- reflectance /
- refractive index
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图 1 环境污染物在膜层上的吸附机理图
Figure 1. Mechanism of the vapor adsorption of contamination and humidity in environment on the coating
图 2 不同折射率膜层的理论透射曲线
Figure 2. Theoretical transmission curves of coatings with different refractive index
图 3 最大透射率351 nm处透射率随折射率变化的理论计算曲线
Figure 3. Change of the maximum transmittance and the transmittance at 351 nm with the increase of refractive index
图 8 常压百级洁净度环境中自然污染前后4种膜系透射曲线对比图
Figure 8. Comparison of transmittance before and after contamination in ISO Class 5 cleanroom in atmosphere
图 9 膜层透射率和反射率之和随放置时间的变化规律
Figure 9. Change of the sum of transmittance and reflectance as a function of time
图 10 180 d内膜层折射率变化情况
Figure 10. Variation of the refractive index of four coatings in 180 days
图 11 180 d内膜层厚度变化情况
Figure 11. Variation of the thickness of four coatings in 180 days
表 1 四种膜层的提拉速度以及后处理后膜层光学特性参数
Table 1. Dipping speed (v) and optical properties after post processing of four kinds of coatings
film v/(mm·min-1) n d/nm peak/nm T351/% R351/% Rq/μm A 75 1.15 90.31 351 99.34 0.62 4.11 B 100 1.19 106.11 400 99.39 0.18 2.78 C 50 1.19 66.52 320 99.41 0.54 2.65 D 85 1.24 88.27 351 99.32 0.57 2.82 Note: d-thickness of coating; T351-transmittance at 351 nm; R351-reflectance at 351 nm; Rq-RMS roughness 
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表 2 四种膜层污染前后的光学性能变化与孔隙率变化
Table 2. Comparison of the optical properties and the porosity of four coatings before and after contamination
film before contamination after 180 d contamination (Ti-Tf)/% (Ri-Rf)/% $ \frac{n_{\mathrm{i}}-n_{\mathrm{f}}}{n_{\mathrm{i}}}$/% Vc/% Ti/% Ri/% ni/% Tf/% Rf/% nf/% A 99.34 0.62 1.15 99.66 0.34 1.17 0.32 0.28 1.74 2.70 B 99.49 0.18 1.19 99.27 0.41 1.21 0.22 0.23 1.68 2.44 C 99.41 0.54 1.21 99.18 0.79 1.23 0.23 0.25 1.65 2.44 D 99.32 0.57 1.24 99.67 1.13 1.27 0.35 0.56 2.42 8.29
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