Burke S A, Topple J M, Grütter P
Department of Physics, University of California Berkeley, Berkeley, CA, USA.
J Phys Condens Matter. 2009 Oct 21;21(42):423101. doi: 10.1088/0953-8984/21/42/423101. Epub 2009 Sep 8.
Recent attention given to the growth and morphology of organic thin films with regard to organic electronics has led to the observation of dewetting (a transition from layer(s) to islands) of molecular deposits in many of these systems. Dewetting is a much studied phenomenon in the formation of polymer and liquid films, but its observation in thin films of the 'small' molecules typical of organic electronics requires additional consideration of the structure of the interface between the molecular film and the substrate. This review covers some key concepts related to dewetting and molecular film growth. In particular, the origins of different growth modes and the thickness dependent interactions which give rise to dewetting are discussed in terms of surface energies and the disjoining pressure. Characteristics of molecular systems which may lead to these conditions, including the formation of metastable interface structures and commensurate-incommensurate phase transitions, are also discussed. Brief descriptions of some experimental techniques which have been used to study molecular dewetting are given as well. Examples of molecule-on-insulator systems which undergo dewetting are described in some detail, specifically perylene derivatives on alkali halides, C(60) on alkali halides, and the technologically important system of pentacene on SiO(2). These examples point to some possible predicting factors for the occurrence of dewetting, most importantly the formation of an interface layer which differs from the bulk crystal structure.
近期，针对有机电子学中有机薄膜的生长和形态学所给予的关注，已导致在许多此类体系中观察到分子沉积物的去湿现象（即从层状到岛状的转变）。去湿现象在聚合物和液膜形成过程中已得到广泛研究，但在有机电子学典型的“小分子”薄膜中观察到该现象，需要额外考虑分子膜与基底之间界面的结构。本综述涵盖了一些与去湿和分子膜生长相关的关键概念。特别地，从表面能和分离压力的角度讨论了不同生长模式的起源以及导致去湿的厚度依赖性相互作用。还讨论了可能导致这些情况的分子体系特征，包括亚稳界面结构的形成以及共格 - 非共格相变。此外，还简要介绍了一些用于研究分子去湿的实验技术。详细描述了一些发生去湿的绝缘体上分子体系的实例，特别是碱金属卤化物上的苝衍生物、碱金属卤化物上的C(60)以及二氧化硅上并五苯这个具有重要技术意义的体系。这些实例指出了一些去湿现象发生的可能预测因素，最重要的是形成与体相晶体结构不同的界面层。
