| AVS 54th International Symposium | |
| Surface Science | Friday Sessions |
| Session SS2+EM+TF-FrM |
| Session: | Organic Films II: Semiconductors and C@sub 60@ |
| Presenter: | J.R. Engstrom, Cornell University |
| Authors: | A. Amassian, Cornell University S. Hong, Cornell University S. Bhargava, Cornell University A.R. Woll, Cornell University T.W. Schroeder, Cornell University A.S. Killampalli, Cornell University J.D. Ferguson, Cornell University J.D. Brock, Cornell University G.G. Malliaras, Cornell University J.R. Engstrom, Cornell University |
| Correspondent: | Click to Email |
We have examined the growth of pentacene thin films on SiO2 using supersonic molecular beam techniques and in situ real-time synchrotron x-ray scattering. At low-to-modest rates of deposition [ca. 0.001 to 0.1 monolayer(ML)/s] we observe an abrupt transition from 2D, layer-by-layer growth to 3D, islanded growth after deposition of the first few monolayers of pentacene on SiO2. At high rates of deposition (ca. 1 ML/s), however, we find persistent 2D crystal growth, and the development of a highly textured film possessing significantly flatter and smoother surface morphology than at low rates of deposition. Concomitantly, in this regime we also observe new polymorphs of pentacene, as significant changes occur in the crystalline structure of the thin films. The transition to this anomalous, yet promising growth behavior corresponds very strongly with the onset of the formation of van der Waals clusters of pentacene within the supersonic expansion. We suggest that the presence of clusters in the incident flux acts to change the dynamics of growth due to a variety of reasons which we discuss. These findings raise the distinct possibility that organic crystals may be synthesized with ultra-flat surface morphology, making them suitable for use in a number of electronics applications where the requirement for abrupt and smooth interfaces has traditionally defaulted to the use of amorphous organic thin films.