Epitaxial structures of self-organized, standing-up pentacene thin films studied by LEEM and STM

• Published in: Surface science 2007-03, Vol.601 (5), p.1304-1310
• Main Authors: Al-Mahboob, A., Sadowski, J.T., Nishihara, T., Fujikawa, Y., Xue, Q.K., Nakajima, K., Sakurai, T.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Epitaxy; Exact sciences and technology; Low-energy electron diffraction (LEED); Low-energy electron microscopy (LEEM); Pentacene; Physics; Scanning tunneling microscopy; Self-assembly
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2006.12.064

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.