FAST ATOM AND ION SURFACE STUDIES LEADING TO THE DEVELOPMENT OF A TIME OF FLIGHT FAST ATOM SCATTERING SPECTROMETER

This paper describes work that was originated in order to study the relative surface damage caused by neutral (fast atom) and ion bombardment of insulating surfaces. Two atom/ion sources were used in the investigation, a saddle field cold cathode source and an electron impact source. These sources were fully characterised and the results of the characterisation and design and development of the apparatus employed, in particular time of flight apparatus, are reported. It has been shown in bombardment experiments on rutile powder and single crystal material, that atoms produce significantly less surface damage than do ions of the same energy and species. With this knowledge and using the sensitive time of flight spectrometer developed for characterisation of the electron impact source, a fast atom scattering spectrometer has been developed based on ion scattering principles, but employing a pulsed atom source rather than a dc ion source. Preliminary results from this fast atom scattering spectrometer are encouraging. Results of the study of surface contamination on copper surfaces by helium ion bombardment and of dissociative scattering experiments using water molecules are also presented. The experiments show that hydrocarbon contamination persists even after prolonged periods of ion bombardment. The dissociative experiments show that the scattering cross-section for the water molecular products is significantly higher than that for the noble gases.