IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Organic Films and Devices Wednesday Sessions
       Session OF+TF+EL-WeA

Paper OF+TF+EL-WeA5
Substrate Controlled Crystallisation of Ultra-thin Films of Perylene

Wednesday, October 31, 2001, 3:20 pm, Room 131

Session: Growth of Organic Thin Films
Presenter: Q. Chen, University of St Andrews, UK
Authors: Q. Chen, University of St Andrews, UK
N.V. Richardson, University of St Andrews, UK
P.J. Unwin, Imperial College of Science, Technology and Medicine, UK
T.S. Jones, Imperial College of Science, Technology and Medicine, UK
T. Rada, University of St Andrews, UK
A.J. McDowall, University of St Andrews, UK
Correspondent: Click to Email
There has been recent interest in the electronic and optoelectronic properties of polyaromatic hydrocarbons, such as tetracene, pentacene and perylene, because of their potential use as organic lasers, OLEDs and OFETs. Device performance is likely to be s trongly influenced by the structural quality of crystals or thin films. We have carried out a detailed investigation of the deposition and growth of ultra-thin films (0-30 monolayers) of perylene on a variety of substrates including Cu{110}, H/Si(111), InAs(111) and InSb(111), using STM, TPD, LEED and vibrational spectroscopies. The substrate has a profound influence on growth and subsequent crystallinity of the film. For example, films grown on a hydrogen terminated Si(111) surface show no evidence o f layer-by-layer growth and, from the earliest stages, small clusters of randomly oriented molecules are present which eventually cover the surface with a rough polycrystalline film. In contrast, vacuum deposition on a Cu{110} surface leads to large crysta l line domains upto one monolayer coverage. Electron energy loss spectroscopy confirms that the molecules are flat-lying and @pi@-bonded to the substrate. Multilayer growth takes place epitaxially layer-by-layer on this first monolayer into a structure whic h, although commensurate with the underlying copper surface along the <110> direction is incommensurate along <100> and is unrelated to the bulk crystal structure of perylene. The 2D unit cell at all layer thicknesses (to 30 monolayers) is rectangula r with dimensions 2nm x 1.9nm containing two, flat-lying molecules per layer at 90° to each other around an axis normal to the substrate surface. The molecular rows along <110> are out-of-phase with each other in the <100> direction from layer to layer, in an ABA packing sequence of rows along the growth direction. The implications for the modification of film properties implied by this control over film structure and crystallinity will be discussed.