Abstract

Polythiophene thin films with useful nonlinear optical properties have been deposited by a novel plasma-based technique. In the work, an excited argon metastable flow is created by a 13.56-MHz plasma discharge. A gas flow of 2,5-dichlorothiophene in an argon carrier gas is then injected downstream of the discharge so that the monomer is not subjected to the harsh plasma environment. We believe that electronically excited argon atoms excite the monomer by Penning ionization, with the ions depositing onto the growing film. 2,5-dichlorothiophene is required to drive 2,5-polymerization and to achieve piconjugation in the films: thiophene starting material results in films with random 2,5- and 2,4-polymerization, limiting the conjugation. The resulting films are microscopically dense and smooth, and a third-order susceptibility of 10^-11 esu has been measured at 602 nm by degenerate four-wave mixing.

© 1991 Optical Society of America