Epitaxial structures of self-organized, standing-up pentacene thin films studied by LEEM and STM |
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Authors: | A Al-Mahboob T Nishihara K Nakajima T Sakurai |
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Institution: | Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan |
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Abstract: | Growth of pentacene (Pn) thin films has been studied in situ by means of low-energy electron microscopy (LEEM) and scanning tunneling microscopy (STM). A very low nucleation density of Pn grains has been observed on Bi(0 0 0 1)/Si(1 1 1) template, resulting in formation of large, monolayer-high Pn grains with diameter exceeding several hundreds of micrometers. We determined that formation of self-organized, standing-up Pn epitaxial layers was stabilized by a weak interaction between the substrate and Pn molecules and by the presence of the commensurate structure between the oblique Pn lattice and trigonal substrate surface lattice. The ‘point-on-line’ commensurability has been found along a-axis of Pn and one of the primitive vectors of substrate surface lattice. Strong ‘point-on-line’ commensurability in Pn/Bi(0 0 0 1)/Si(1 1 1) system resulted in a bulk-like epitaxial thin film growth, starting from the first layer. The presence of twins, often having a mirror line parallel to the direction of the ‘point-on-line’ matching, has been also detected using an asymmetric dark-field imaging mode in LEEM experiments, which, we believe, is the first LEEM demonstration of molecular tilt imaging. |
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Keywords: | Low-energy electron microscopy (LEEM) Low-energy electron diffraction (LEED) Scanning tunneling microscopy Epitaxy Self-assembly Pentacene |
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