Thickness and Substrate Dependent Thin Film Growth of Picene and Impact on the Electronic Structure

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• 作者：Takuya Hosokai ; Alexander Hinderhofer ; Fabio Bussolotti ; Keiichirou Yonezawa ; Christopher Lorch ; Alexei Vorobiev ; Yuri Hasegawa ; Yoichi Yamada ; Yoshihiro Kubozoro ; Alexander Gerlach ; Satoshi Kera ; Frank Schreiber ; Nobuo Ueno
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：December 31, 2015
• 年：2015
• 卷：119
• 期：52
• 页码：29027-29037
• 全文大小：743K
• ISSN：1932-7455

文摘

Thickness and substrate dependence of film growth, morphology, unit-cell structure, and electronic structures was thoroughly investigated for picene, the zigzag connected 5-ring molecule, by employing complementary techniques of in situ real-time X-ray reflectivity/diffraction, in situ electron spectroscopies, and atomic force microscopy. A different kind of thickness dependent structural transition was observed on SiO₂ and graphite, resulting in a distinct electronic structure. On SiO₂ picene films with 3D crystalline domains are formed with nearly upright molecular orientation from the initial growth stage. With increasing the film thickness the in-plane dimensions of the unit cell in the initially grown domains become smaller (in other words, more compressed), and, at the same time, crystalline domains with a more relaxed structure are nucleating on top of the compressed domains. In spite of such structural changes, the electronic structure, namely energy position of the highest occupied molecular orbital and threshold ionization potential (IP^T), is not significantly altered. On graphite, on the other hand, we found a transition from a 2D (layer) to a 3D (island) growth mode with a variation of the molecular orientation from flat-lying to tilted one. The IP^T changes significantly between the 2D and 3D growth regime in contrast to the SiO₂ system. The origin of the different IP^Ts of these picene thin films is discussed. The present results are compared with other planar π-conjugated compounds, in particular pentacene which is a structural isomer of picene and shows electronic properties strongly different from picene thin films.