Nucleation and strain-stabilization during organic semiconductor thin film deposition.
The nucleation mechanisms during solution deposition of organic semiconductor thin films determine the grain morphology and may influence the crystalline packing in some cases. Here, in-situ optical spectromicroscopy in reflection mode is used to study the growth mechanisms and thermal stability of 6,13-bis(trisopropylsilylethynyl)-pentacene thin films. The results show that the films form in a supersaturated state before transforming to a solid film. Molecular aggregates corresponding to subcritical nuclei in the crystallization process are inferred from optical spectroscopy measurements of the supersaturated region. Strain-free solid films exhibit a temperature-dependent blue shift of optical absorption peaks due to a continuous thermally driven change of the crystalline packing. As crystalline films are cooled to ambient temperature they become strained although cracking of thicker films is observed, which allows the strain to partially relax. Below a critical thickness, cracking is not observed and grazing incidence X-ray diffraction measurements confirm that the thinnest films are constrained to the lattice constants corresponding to the temperature at which they were deposited. Optical spectroscopy results show that the transition temperature between Form I (room temperature phase) and Form II (high temperature phase) depends on the film thickness, and that Form I can also be strain-stabilized up to 135 °C.
Department of Physics and Materials Science Program, University of Vermont, Burlington VT 005, USA.
Yang
Y
Li
Department of Physics and Materials Science Program, University of Vermont, Burlington VT 005, USA.
Jing
J
Wan
Cornell High Energy Synchrotron Source, Cornell University, Ithaca NY 14853, USA.
Detlef-M
DM
Smilgies
Microscopy Imaging Center, College of Medicine, University of Vermont, Burlington VT 05405, USA.
Nicole
N
Bouffard
Angstrom Sun Technologies Inc. 31 Nagog Park, Acton MA 01720, USA.
Richard
R
Sun
Department of Physics and Materials Science Program, University of Vermont, Burlington VT 005, USA.
Randall L
RL
Headrick
D003460:Crystallization; D005898:Glass / Q000737:chemistry; D008853:Microscopy; D009279:Naphthacenes / Q000737:chemistry*; D061848:Optical Imaging; D012666:Semiconductors; D013057:Spectrum Analysis; D013816:Thermodynamics; D014961:X-Ray Diffraction
D009279:Naphthacenes; C523499:pentacene