When the thin film growth mode is determined by an Auger Electron Spectroscopy (AES) experiment, several important factors which compose the experiment are methods for cleaning substrates, an evaporation source which keeps a constant evaporation speed, a reliable thickness measurement and a reliable AES experiment. They must be carefully taken into consideration and these technical details are described in this article. After defining these factors, AES signals from Ag on Au showed a good agreement with the theoretical estimate which can be expected, when Ag is considered as a monolayer over-growth on a Au substrate.