FIBER OPTIC MICROMIRROR STUDIES OF THE INTERACTION OF THIN COPPER-FILMS WITH AN ORGANOPHOSPHONATE

In a pair of recent papers,1 the resistivity change in thin (100-angstrom) films of copper was used as a means to detect the presence of diisopropyl methylphosphonate (DIMP). In this paper we explore the copper/DIMP interaction by measuring changes In the reflectivity of thin copper films deposited on the end of optical fibers. This optical detection technique is a sensitive probe of the density of electronic states in thin metal films and, therefore, gives responses analogous to resistivity measurements. We find that DIMP in dry air slowly oxidizes the copper films to a definitive product, the optical properties of which suggest it to be a one-to-one adduct of Cu2O and CuO. Reversible DIMP-induced reflectivity changes are observed only when the films are partially oxidized, i.e., they have not been completely converted to the product oxide. Unfortunately, copper films in all stages of the oxidation process also respond to water vapor, precluding their use for selective detection of DIMP.