Comparison of gaseous contamination of thin tungsten and gold coatings deposited from ablated plasma generated by Intense Pulsed Ion Beams

Abstract

The paper presents experimental results on C, N and O contamination in thin tungsten and gold coatings deposited on GaAs substrates from ablated plasma generated by intense pulsed ion beams accelerated in a magnetically insulated diode. The coating thickness was controlled by energy-dispersive X-Ray Fluorescence analysis. Depth profiles of C, N and O concentrations in the coatings were determined using quantitative Auger Electron Spectroscopy (AES) with ion sputtering. Non-destructive charged particle activation analysis via the nuclear reactions 12C(d,n)13N, 14N(d,n)15O and 16O(d,n)17F, induced by 3 MeV deuterons of extracted from a cyclotron was used to calibrate the AES determination of C, N and O. The gold coating was found to be devoid of detectable amounts of all gases, while carbon dominated by an order of magnitude over nitrogen and oxygen in tungsten coatings. Carbon contamination increased linearly with an increase in the number of ion shots applied. It was concluded that the main source of gas contamination is the residual atmosphere of the working chamber and the purest coatings can be obtained at the highest deposition rates per shot. A significant increase of oxygen admixture was found in the tungsten coatings after the samples were stored in the ambient atmosphere for 25 years. The storage did not affect the purity of the gold coating, but carbon seemed to diffuse from the Au/GaAs interface to the coating surface.