An Investigation of Adsorbed Films by Means of a Photoelectric Counter

A photoelectric tube counter of special design has been used for investigating adsorbed layers on a gold surface. The high sensitivity of the counter allows accurate measurements of photoelectric thresholds to be made with continuous ultraviolet light from a source of moderate intensity. The variation of the work function φ with the amount of adsorbed material can thus be followed quantitatively and continuously. The formation of gold oxide layers proceeds over definite steps with increases of 0.35 volt in the work function. The adsorption of iodine is reversible and the resulting increase in the work function varies with the iodine pressure according to a Langmuir isotherm, the saturation value being Δφ = +0.21 volt. The adsorption of ethyl alcohol is also reversible, but gives rise to a double threshold, suggesting the existence of liquid islands on the gold surface.