Determination of the surface area of annealed continuous gold film and pyrex glass in situ by the BET adsorption isotherm and ex situ by Atomic Force Microscopy in air

The relative surface area, Rsa, of annealed continuous thin gold film, thermally evaporated onto a Pyrex glass substrate at 78 K in an ultrahigh-vacuum (UHV) environment, and Pyrex glass has been determined in situ by the BET (Brunauer–Emmett–Teller) isotherm method, as well as ex situ by Atomic Force Microscopy (AFM) in air. It has been measured by the BET isotherm method that Rsa for clean, continuous and annealed gold film, investigated under UHV conditions, is equal to 6.3, whereas after its exposure to air, at about 100 Pa, Rsa decreased from 6.3 to 5.7. Further exposure to air, at atmospheric pressure, reduced Rsa from 5.7 to 2.2, whereas the exposure of contaminated Au film to the atomic hydrogen flux caused the increase of Rsa from 2.2 to 4.2. On the other hand, Rsa calculated directly from the AFM image of gold film in air is equal to 1.0. In contrast to thin gold film, the Pyrex glass surface area, measured under UHV conditions by the BET adsorption isotherm and in air by the AFM technique, is equal to its geometric area, i.e., Rsa=1.0.