Investigation of etch pits on KDP crystals with porous sol–gel coatings
Investigation of etch pits on KDP crystals with porous sol–gel coatings
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DOI：
10.1007/s003390100982
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发表时间：
2002-06
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影响因子：
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通讯作者：
E. Wheeler;P. Whitman;T. Land;J. D. De Yoreo;C. Thorsness;J. H. McWhirter;M. Hanna;E. Miller
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文献类型：
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作者：
E. Wheeler;P. Whitman;T. Land;J. D. De Yoreo;C. Thorsness;J. H. McWhirter;M. Hanna;E. Miller
研究了多孔增透膜对磷酸二氢钾（KDP）晶体腐蚀坑形成的影响。在暴露于环境湿度之后，在溶胶-凝胶涂层下方形成蚀刻坑。蚀坑均匀分布，其密度和平均尺寸由相对湿度和涂层厚度决定。此外，蚀坑的形状是自相似的，并拥有对应于KDP的低能平面的刻面。从光学显微镜，光散射，和原子力显微镜的结果支持以下模型在这个系统中的蚀坑形成。从环境中吸收到多孔溶胶-凝胶涂层中的水接触晶体表面，导致在高度欠饱和下的蚀坑成核。从蚀刻坑中升起的KDP羽流缓慢地横向扩散，减少了欠饱和并切断了周围区域的成核。因为表面动力学与通过溶胶-凝胶的质量传输相比是快速的，所以蚀坑持续经历平衡以保持低能量几何形状并产生平均间距。生长继续进行，直到溶胶-凝胶中的水的储层被KDP饱和。粗化仅在高相对湿度环境中观察到。
We have investigated etch-pit formation on potassium dihydrogen phosphate (KDP) crystals with porous anti-reflective coatings. Etch pits develop beneath the sol–gel coatings after exposure to ambient humidity. The etch pits are homogeneously distributed with a density and an average size governed by the relative humidity and the coating thickness. Furthermore, the etch pits are self-similar in shape and possess facets corresponding to low-energy planes of KDP. Results from optical microscopy, light scattering, and atomic force microscopy support the following model for etch-pit formation in this system. Water adsorbed from the environment into the porous sol–gel coating contacts the crystal surface, causing etch-pit nucleation at high undersaturation. The plume of KDP rising from an etch pit slowly diffuses laterally, reducing the undersaturation and shutting off nucleation in the surrounding area. Because surface kinetics are rapid compared to mass transport through the sol–gel, etch pits continually undergo equilibration to maintain a low-energy geometry and generate an average spacing. Growth continues until the reservoir of water in the sol–gel is saturated with KDP. Coarsening is only observed in high relative humidity environments.