Optimization of preparation conditions for highly ordered structures of vapor-deposited organic thin films

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Organic thin films with high performance require three-dimensional (3D) regulation of the position and the orientation of molecules in organic thin films. The 3D regulation appears to be feasible by combination of one-dimensional out-of-plane regulation and two-dimensional in-plane alignment. The out-of-plane regulation involves the molecular layer epitaxy method firstly demonstrated by the author, and the out-of-plane alignment can be controlled by the interfacial anisotropy induced by the external electric field, the substrate crystal structure and the rubbing of the substrate surface. The mechanism of the specific structure formation is discussed from the quartz crystal microbalance study on the basis of a novel theoretical model. The vapor deposition technique can produce organic thin films with a molecular orientation normal or lateral to the substrate, depending on the preparation condition, such as the substrate temperature and the deposition rate. Unfortunately, the mechanism is still unclear. In this study, thin film formation during vapor deposition of organic molecules has been investigated by using quartz crystal microbalance.