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首页> 外文期刊>Crystal growth & design >Dissolution on cholesterol monohydrate single-crystal surfaces monitored by in situ atomic force microscopy
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Dissolution on cholesterol monohydrate single-crystal surfaces monitored by in situ atomic force microscopy

机译：原位原子力显微镜监测胆固醇一水合物单晶表面的溶解

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摘要

The mechanism(s) and dissolution rates on the (001) surface of cholesterol monohydrate (ChM) in aqueous solutions containing 10-50% ethanol were monitored using in situ atomic force microscopy (AFM). Dissolution was found to proceed mechanistically via the layer-by-layer retreat of 34 A bilayer or multilayer steps and/or the creation and expansion of bilayer and multilayer etch pits. In general, the dissolution rate is very strongly dependent on the local surface topography, which is highly variable on (001) ChM. Since the overall dissolution on the surface is by necessity a function of the relative density of different types of surface features, dissolution on both typical "smooth" and "rough" micron-sized areas was examined. For areas exhibiting low topographical relief, the rate of solute loss from isolated surface features was monitored by tracing the position of particular step fronts in sequential images over time. Although the absolute local dissolution rates are variable, the loss of solute molecules from isolated bilayer islands and/or pits occurred on the order of similar to 10(5) molecules/min. The critical interstep distance for nondissolving features (observed in multiple experiments) appeared to decrease with increasing ethanol concentration, suggesting that surface diffusion effects likely influence this process. Dissolution in regions exhibiting much greater topographical relief tended to occur most readily by the rapid expansion of multilayer pits rather than by bilayer step retreat. In such areas, the alternative method of roughness analysis provided a more reliable means to track surface changes over time. The relatively high frequency with which such pit features were observed presumably speaks to the significantly large defect density in conventionally grown ChM crystals.
机译：使用原位原子力显微镜（AFM）监测一水合胆固醇（ChM）在含10-50％乙醇的水溶液中的机理和溶解速率。发现溶解是通过34 A双层或多层步骤的逐层后退和/或双层和多层蚀刻坑的产生和扩展而机械地进行的。通常，溶出速率非常强烈地取决于局部表面形貌，该形貌在（001）ChM上变化很大。由于在表面上的总溶解度必然是不同类型表面特征的相对密度的函数，因此研究了在典型的“光滑”和“粗糙”微米尺寸区域上的溶解度。对于那些表现出低地形起伏的区域，通过追踪连续图像中特定阶跃前沿随时间变化的位置，可以监测从孤立的表面特征中溶质的损失速率。尽管绝对的局部溶解速率是可变的，但是从分离的双层岛和/或凹坑中溶质分子的损失发生的顺序类似于10/5分子/分钟。非溶解性特征的关键步距（在多个实验中观察到）似乎随着乙醇浓度的增加而减小，这表明表面扩散效应可能会影响该过程。通过多层凹坑的快速膨胀而不是通过双层台阶后退，最容易出现在具有较大地形起伏的区域中的溶解。在这样的区域，粗糙度分析的替代方法提供了一种更可靠的方法来跟踪表面随时间的变化。据推测，观察这种凹坑特征的频率相对较高，这表明常规生长的ChM晶体中的缺陷密度非常大。

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