Thickness and Substrate Dependent Thin Film Growth of Picene and Impact on the Electronic Structure
Thickness and Substrate Dependent Thin Film Growth of Picene and Impact on the Electronic Structure
复制标题
DOI：
10.1021/acs.jpcc.5b10453
复制
发表时间：
2015-12-31
影响因子：
3.7
通讯作者：
Ueno, Nobuo
中科院分区：
文献类型：
--
作者：
Hosokai, Takuya;Hinderhofer, Alexander;Ueno, Nobuo
通过采用实时x射线反射/衍射、原位电子能谱和原子力显微镜等互补技术，深入研究了picene（一种之字形连接的5环分子）薄膜生长、形貌、单胞结构和电子结构对薄膜厚度和衬底的依赖性。在SiO2和石墨上观察到不同厚度的结构转变，导致不同的电子结构。在SiO2上，从生长初期开始就形成了分子取向接近直立的三维晶域晶膜。随着薄膜厚度的增加，初始生长区域的晶胞面内尺寸变小（换句话说，更压缩），同时，具有更松弛结构的晶体区域在压缩区域的顶部成核。尽管有这样的结构变化，但电子结构，即最高已占据分子轨道的能量位置和阈值电离势（IPT）并没有明显改变。另一方面，在石墨上，我们发现了从二维（层）到三维（岛）生长模式的转变，分子取向从平面到倾斜的变化。与SiO2体系相比，IPT在2D和3D生长体系之间发生了显著变化。并讨论了这些石墨烯薄膜中不同铟的来源。本文的研究结果与其它平面j共轭化合物进行了比较，特别是与蒎烯的结构异构体并五苯进行了比较，并表现出与蒎烯薄膜有很大不同的电子性质。
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 (IPT), 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 IPT changes significantly between the 2D and 3D growth regime in contrast to the SiO2 system. The origin of the different In of these picene thin films is discussed. The present results are compared with other planar Jr-conjugated compounds, in particular pentacene which is a structural isomer of picene and shows electronic properties strongly different from picene thin films.