AVS 47th International Symposium
    Organic Films and Devices Thursday Sessions
       Session OF+EL+SS-ThM

Paper OF+EL+SS-ThM8
STM, AFM, & Electrochemical Investigations of Squaraine Thin Films

Thursday, October 5, 2000, 10:40 am, Room 313

Session: Organic Thin Films
Presenter: M.E. Stawasz, Colorado State University
Authors: M.E. Stawasz, Colorado State University
N. Takeda, Colorado State University
B.A. Parkinson, Colorado State University
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Squaraines are a class of organic photoconductors which have found industrial use in photoreceptors of laser printers and xerographic devices, as well as in ablative optical recording material. They have also been investigated for their nonlinear optical characteristics as well as their ability to sensitize large-bandgap semiconductors in photoelectrochemical solar cells. Central to its various uses and characteristics is the squaraine molecules' ability to form organized aggregates, both in solution and in the solid state. Few studies have been done, however, to relate the molecular structure of squaraines to the structure of the aggregates that spontaneously form in thin films. We report STM and AFM data which unambiguously determines thin film/monolayer aggregate structure for a series of hydroxylated and non-hydroxylated dialkylamino-phenyl squaraines with varying alkyl tail lengths deposited on HOPG. Results show that alkyl tail length significantly affects squaraine aggregate structure while the presence or absence of hydroxyl groups does not. Electrochemical investigations of the redox behavior of squaraine thin films using HOPG as the working electrode were also performed. Remarkable redox behavior was observed suggesting a structural change in the squaraine aggregate state upon oxidation. In addition, the effect of electrolyte anion and film thickness on the redox behavior of squaraines was observed, thus providing additional insight into the charge transfer abilities of the squaraine film in the direction normal to the substrate surface.