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Doping Effects and Reversibility Studies on Gas-Exposed (Alpha)-Sexithiophene Thin Films



C Kendrick, Stephen Semancik


The electronic effects produced by controlled gas exposures on [alpha]-sexithiophene thin films have been investigated using x-ray photoelectron spectroscopy (Incremental exposures of [alpha]6T to NO2, O2, NH3 in N2, and water vapor in N2 were performed in ultra-high vacuum, while repeated doses of O2, H2 in N2, and methanol vapor in N2 were performed ex situ at ambient pressure. In both conditions XPS spectra of gas-exposed films showed no evidence of chemical changes. However, the features in both XPS and UPS spectra were observed to shift as a function of gas dosage, with the magnitude dependent on each particular gas. These effects could be reversed by heating the films to temperatures around 100 K. This behavior is interpreted in terms of doping by weakly bonded gas species within the near-surface region of the [alpha]6T films. Greater doping effects were observed for films dosed at ambient pressures. We discuss possible gas adsorption models that may explain the differing gas sensitivities and their dependencies on pressure, temperature, and exposure time. Finally, temperature programmed desorption was used to study the reversibility and resistance to reaction of [alpha]6T films during this gas adsorption/desorption process. The films were found to be chemically stable to gas exposure and subsequent thermal desorption in the dosage ranges explored.
Journal of Vacuum Science and Technology A
No. 5


alpha-sexthiophene, doping, gas doping, gas sensing, UPS, XPS


Kendrick, C. and Semancik, S. (1998), Doping Effects and Reversibility Studies on Gas-Exposed (Alpha)-Sexithiophene Thin Films, Journal of Vacuum Science and Technology A (Accessed February 25, 2024)
Created September 1, 1998, Updated February 17, 2017