Characterization of a thin copper film to investigate microbial biofilm formation

Abstract

Copper films, 6.7 nm nominal thickness, deposited by physical vapor deposition on germanium substrates appeared as coalescing aggregates of copper atoms when evaluated by atomic force microscopy. Evaluation of the Cu thin film by x-ray photoelectron spectroscopy indicated that the Cu at the surface of the film had the character of a 1 + oxidation state. These features were not significantly changed when the Cu thin film was exposed to ethylene oxide. No Ge signal was detectable prior to XPS depth profiling through the Cu thin film, indicating that the film was continuous. When films of this thickness were deposited on a cylindrical Ge internal reflection element and subsequently submerged in an aqueous medium, there was sufficient transmission of infra-red radiation through the Cu to obtain a significant water absorption band at 1640 cm−1. The intensity of the water absorption band was found to be very sensitive to changes in thickness of the copper thin film. This feature can be used to study the effect of microbial biofilms and their products on the integrity of oxidized copper surfaces in aqueous environments.