Structural Properties of Opals Grown with Vertical Controlled Drying

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• 作者：Alex Hartsuiker ; Willem L. Vos
• 刊名：Langmuir
• 出版年：2008
• 出版时间：May 6, 2008
• 年：2008
• 卷：24
• 期：9
• 页码：4670 - 4675
• 全文大小：346K
• 年卷期：v.24,no.9(May 6, 2008)
• ISSN：1520-5827

文摘

We have grown thin opals of self-assembled silica colloids by the well-known vertically controlled drying method.The volume fraction at the start of the growth and the temperature were systematically varied. We have quantitativelycharacterized the lateral domain sizes by scanning electron microscopy. The sample thickness as a function of positionwas obtained from Fabry-Pérot fringes measured in optical reflectivity. We observe that the sample thickness stronglyincreases from top to bottom, independent of temperature, in agreement with a model that we propose. The inhomogeneityin thickness contrasts with earlier reports. The lateral domain shapes of the single-crystal domains are found to varyfrom irregular near the top to rectangular near the bottom. A surprising observation is that, grosso modo, the lateraldomain extents increase linearly with thickness (i.e., thin crystals are small, and thick crystals are large). This behavioragrees qualitatively with results on completely different colloids such as disordered slurries. The consequence of ourresults for optical applications, including photonic crystals, is that unwanted scattering due to grain boundaries isreduced for large domains that are thick. Conversely, thin crystals will scatter relatively strongly from grain boundaries.