Post-deposition reorganization of pentacene films deposited on low-energy surfaces Article

Amassian, A, Pozdin, VA, Desai, TV et al. (2009). Post-deposition reorganization of pentacene films deposited on low-energy surfaces . JOURNAL OF MATERIALS CHEMISTRY, 19(31), 5580-5592. 10.1039/b907947e

cited authors

  • Amassian, A; Pozdin, VA; Desai, TV; Hong, S; Woll, AR; Ferguson, JD; Brock, JD; Malliaras, GG; Engstrom, JR

authors

abstract

  • We demonstrate that small-molecule organic thin films of pentacene deposited from thermal and supersonic molecular beam sources can undergo significant reorganization under vacuum or in N 2 atmosphere, beginning immediately after deposition of thin films onto SiO 2 gate dielectric treated with hexamethyldisilazane (HMDS) and fluorinated octyltrichlorosilane (FOTS). Films deposited on bare SiO 2 remain unchanged even after extended aging in vacuum. The changes observed on low-energy surfaces include the depletion of molecules in the interfacial monolayer resulting in the population of upper layers via upward interlayer transport of molecules, indicating a dewetting-like behavior. The morphology of pristine, as-deposited thin films was determined during growth by in situ real-time synchrotron X-ray reflectivity and was measured again, ex situ, by atomic force microscopy (AFM) following aging at room temperature in vacuum, in N 2 atmosphere, and in ambient air. Important morphological changes are observed in ultra-thin films (coverage < 5 ML) kept in vacuum or in N 2 atmosphere, but not in ambient air. AFM measurements conducted for a series of time intervals reveal that the rate of dewetting increases with decreasing surface energy of the gate dielectric. Films thicker than ∼5 ML remain stable under all conditions; this is attributed to the fact that the interfacial layer is buried completely for films thicker than ∼5 ML. This work highlights the propensity of small-molecule thin films to undergo significant molecular-scale reorganization at room temperature when kept in vacuum or in N 2 atmosphere after the end of deposition; it should serve as a cautionary note to anyone investigating the behavior of organic electronic devices and its relationship with the initial growth of ultra-thin molecular films on low-energy surfaces. © 2009 The Royal Society of Chemistry.

publication date

  • August 10, 2009

published in

Digital Object Identifier (DOI)

start page

  • 5580

end page

  • 5592

volume

  • 19

issue

  • 31