A STUDY OF THE ADSORPTION OF ALKANES ON A THIN-METAL FILM

The adsorption of vapor on a thin gold film has been studied for three alkanes: pentane, hexane, and heptane. Adsorbed overlayers were monitored by coupling visible radiation to excite a surface plasmon on the gold film and detecting the minimum of reflectivity which is sensitive to the thickness of any overlayer. The relationship between the relative pressure of the vapor surrounding the gold film and the overlayer thickness has been investigated and found to have a linear form for sub-monolayer thicknesses. For overlayer thicknesses greater than about 4 nm the change in the chemical potential, deduced from the pressure measurements, is found to vary inversely as the square of the thickness. This behavior is compared with other experimental observations and theoretical predictions.