Effect of hydrophobicity on the stability of sol–gel silica coatings in vacuum and their laser damage threshold
Effect of hydrophobicity on the stability of sol–gel silica coatings in vacuum and their laser damage threshold
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DOI：
10.1007/s10971-013-3137-z
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发表时间：
2013-08
影响因子：
2.5
通讯作者：
Yuan Liu;Jun Shen;Bin Zhou;Guang-ming Wu;Zhihua Zhang
中科院分区：
文献类型：
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作者：
Yuan Liu;Jun Shen;Bin Zhou;Guang-ming Wu;Zhihua Zhang
采用溶胶-凝胶法在硅片和K9玻璃基板上制备了六甲基二硅氮烷（HMDS）改性的二氧化硅增透膜。研究了HMDS对涂层抗沾污能力和激光损伤阈值的影响。透射电镜观察表明，在标准SiO2溶胶中加入适量的HMDS，可得到平均粒径约为15 nm的SiO2颗粒均匀分布的稳定溶胶。用改性溶胶，所得涂层是疏水性的，并且对水的接触角随着反应混合物中HMDS的量的增加而增加。这种疏水性的增加不是表面粗糙度的结果。经HMDS处理后，薄膜的抗反射性能得以保持，最大透射率在99%以上。当HMDS与四乙氧基硅烷的摩尔比为0.05：1时，将HMDS引入硅溶胶中也将涂层的LIDT从24.3增加到37.0 J cm-2。结果表明，HMDS改性降低了涂层的球化缺陷，使涂层组织均匀，从而提高了涂层的LIDT。通过甲基取代SiO2颗粒表面的羟基，使SiO2颗粒表面具有憎水性，提高了涂层在真空中的稳定性。改性后的涂层在真空条件下存放168 h，最大透过率仅下降0.25%.相比之下，标准溶胶-凝胶二氧化硅涂层在类似条件下降低约2%。改性涂层的LIDT仍然高达30.8 J cm−2，高于在空气中储存相同时间的标准涂层。
Silica antireflective coatings modified by hexamethyldisilazane (HMDS) were deposited on clean substrates (silicon wafer or K9 glass blanks) by sol–gel processing. The effects of HMDS on the contamination resistant capability and laser-induced damage threshold (LIDT) of coatings were investigated. Transmission electron microscopy revealed that a stable sol with uniformly distributed silica particles with an average particle size of about 15 nm was acquired by adding appropriate amount of HMDS into the standard SiO2sol. With the modified sol the resultant coatings were hydrophobic and the contact angle for water increased with increasing amount of HMDS in the reaction mixture. Such increase in hydrophobicity was not the result of surface roughness. The antireflective properties were retained after HMDS-treatment and the maximum transmission values were above 99 %. The introduction of HMDS into silica sols had also increased the LIDT of coatings from 24.3 to 37.0 J cm−2when the molar ratio of HMDS to tetraethoxysilane was 0.05:1. The increase in LIDT was attributed to the decrease of nodular defect and uniform microstructures of coatings as an effect of the HMDS modification. After some of the hydroxyl groups on the surface of the SiO2particle were replaced by methyl groups, from which the SiO2particle gained a water-repellent surface, the stability of coatings in vacuum was increased. The maximum transmission values of modified coatings decreased by only 0.25 % after storage under vacuum for 168 h. In contrast, the standard sol–gel silica coatings decreased about 2 % under similar conditions. The LIDT of modified coatings remained as high as 30.8 J cm−2, more than that of standard coatings stored for the same duration in air.