AVS 47th International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF-WeA

Paper OF-WeA4
Low Energy Electron Microscopy Studies of the Growth of Thin Pentacene Films

Wednesday, October 4, 2000, 3:00 pm, Room 313

Session: Self-Assembled Monolayers: Electron Transfer and Film Properties
Presenter: R.M. Tromp, IBM T.J. Watson Research Center
Authors: R.M. Tromp, IBM T.J. Watson Research Center
F. Meyer zu Heringdorf, IBM T.J. Watson Research Center
C. Dimitrakopoulos, IBM T.J. Watson Research Center
J. Shaw, IBM T.J. Watson Research Center
Correspondent: Click to Email
We have used Low Energy Electron Microscopy (LEEM) to study the growth and structural evolution of thin pentacene films on a variety of surfaces and substrates. LEEM allows the growth process to be followed in real time with high spatial resolution (5 nm), and at videorate. Thin film nucleation and subsequent growth can be studied in much detail. For instance, diffusion of pentacene on the starting substrate (for instance clean Si, or SiO2) is isotropic, giving rise to fractal two-dimensional islands. These islands are nonetheless crystalline. The second layer grows on this crystalline template, with highly anisotropic diffusion. Substrate and substrate preparation give a certain degree of control over the polycrystalline grain size. In addition to the growth morphology, LEEM allows the observation of what appear to be molecular size defects in the film, giving rise to charge trapping. Such traps charge and discharge on timescales of 0.1 to several seconds. The density of such traps depends critically on the growth conditions. It appears that traps can be eliminated by careful control of the evaporation parameters. These studies, the first to observe the growth of organic semiconductors in real space, and in real time, enable a detailed understanding of the basic processes underlying the growth process. Direct parallels can be drawn between organic thin film growth, and the epitaxial growth of very different materials such as Si and Pt. These basic insight allow a careful optimization of the growth conditions, optimizing defect densities, grain size, and growth morphology.