Auger electron spectroscopic depth profiling techniques applied to ultrathin electrochemically deposited metal layers

Abstract

The Auger electron spectroscopic depth profiling technique is applied to the study of the initial equivalent monolayer of electrodeposited Ag on thin‐film Pt electrodes. The ultimate depth resolution of this technique is determined by examining ultrathin layers of Ag which have been ion deposited from a zeolite source in ultrahigh vacuum. The exponential decay apparent in the examination of such layers is explained from elementary considerations of the sputtering process. These are seen to be the resolution‐limiting factor for these layers. The depth resolution is shown to be on the order of 5 Å. Examination of monolayer and submonolayer films of Ag electrodeposited from an AgClO4/sulfolane solution shows that there is an adsorbed overlayer of S (of solvent origin) followed by the electrodeposited Ag film, which is rich in Cl (of solute origin), followed by the Pt substrate, which also contains high levels of Cl. The absence of underpotential deposition is clearly demonstrated. There appears to be two chemical states of Cl present which are distinguished by their relative thermal stabilities.