AVS 52nd International Symposium
    Surface Science Wednesday Sessions
       Session SS+EM-WeA

Paper SS+EM-WeA9
Effects of Incident Kinetic Energy on the Nucleation and Morphological Evolution of Organic Thin Films

Wednesday, November 2, 2005, 4:40 pm, Room 202

Session: Organic Film Growth and Characterization
Presenter: J.R. Engstrom, Cornell University
Authors: A.S. Killampalli, Cornell University
T.W. Schroeder, Cornell University
J.R. Engstrom, Cornell University
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The deposition and growth of thin films of organic materials differs fundamentally from that of the more conventional inorganic materials. A key difference involves the presence of strong covalent and ionic bonding in the latter class of materials, whereas organic materials are often bound by rather weak dispersion forces. As a consequence, considerable promise exists in the use of energy tunable molecular beams for the deposition of organic thin films, as incident species with energies on the order of a few eV may produce substantial changes in the growth habit. We have been examining the deposition of pentacene thin films using a supersonic molecular beam source producing hyperthermal (E@subi@ = 1.4 - 10.6 eV ) kinetic energies. In both the monolayer and multilayer regimes of growth of pentacene on SiO@sub2@ we find that as E@subi@ is increased from 1.5 to 6.7 eV, the growth rate at a fixed incident flux decreases, consistent with trapping-mediated adsorption. In the monolayer regime the data is well explained by nucleation theory, where the critical island size is 4.5 ± 1.3. The situation is more complex in the multilayer regime - here the decrease in the rate is less than that observed in the monolayer regime, and at sufficiently large E@subi@ (> 4 eV), the rate of deposition in the multilayer regime exceeds that in the monolayer regime by about a factor of 3. The evolution of surface roughness provides additional clues as to the dynamics of growth in the multilayer regime. For all incident kinetic energies, the growth exponent, @beta@, is greater than 0.5, indicative of rapid roughening. Our results demonstrate clearly that the morphological evolution of organic thin films can be modified substantially at high incident kinetic energies.