| AVS 55th International Symposium & Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF-WeM |
| Session: | Chemical Vapor Deposition |
| Presenter: | A. Amassian, Cornell University |
| Authors: | A. Amassian, Cornell University S. Hong, Cornell University T.V. Desai, Cornell University S. Kowarik, University of California at Berkeley J.E. Goose, Cornell University A. Papadimitratos, Cornell University V.A. Pozfin, Cornell University A.R. Woll, Cornell High Energy Synchrotron Source D.M. Smilgies, Cornell High Energy Synchrotron Source F. Schreiber, Universität Tübingen, Germany P. Clancy, Cornell University G.G. Malliaras, Cornell University J.R. Engstrom, Cornell University |
| Correspondent: | Click to Email |
The performance of organic electronic devices is closely tied to the packing structure and morphology of molecular semiconductors at the semiconductor-insulator interface, which in turn are intricately linked to molecular-scale processes operant during thin film growth. Tunable supersonic molecular beams have emerged as a versatile method to manipulate the state of incident molecules (e.g., kinetic energy, vibro-rotational states) and to promote novel growth behavior on the surface of the insulator (i.e., SiO2). The growth of small-molecule thin films of pentacene and diindenoperylene from molecular beam sources tunable in kinetic energy (1 to 10eV) and flux was investigated in situ using synchrotron-based time-resolved X-ray reflectivity and grazing incidence X-ray diffraction techniques and ex situ by non-contact atomic force microscopy. Time-resolved X-ray scattering experiments reveal significant acceleration of the growth rate between the submonolayer and the multilayer thickness regimes. The acceleration of growth rate is not observed in thermal processes; it is operant when molecules are incident at hyperthermal kinetic energy and further enhanced by increasing the energy of molecules. Rate equation modeling of X-ray reflectivity data suggests that small-molecules incident at hyperthermal kinetic energy are trapped much more efficiently by a molecular monolayer formed on the surface of the "hard" insulator than by the bare insulator itself. Molecular dynamic simulations reveal that energetic molecules undergo a so-called "soft-landing" on molecular monolayers, during which can insert the molecular layer near step edges and transfer most of their kinetic energy to the "soft" molecular layer. Organic thin film transistors of pentacene and diindenoperylene fabricated from molecular beams tunable in energy exhibit significant increases – by a factor of five for pentacene and by an order of magnitude for diindenoperylene – of the field effect mobility in conditions of high kinetic energy. The relationship between the kinetics of growth and improved charge transport characteristics of conjugated small-molecule semiconducting thin films is discussed.