Collisions of low-energy Ar+, N2+, and D2+ ions with room-temperature and heated surfaces of mixed beryllium–tungsten thin films of different composition

Abstract

Collisions of Ar+, N2+, and D2+ ions of incident energies 20–100eV with thin mixed beryllium–tungsten films of different composition (BeW(90:10); BeW(50:50); BeWO(60:22:11)) and different temperatures of the samples (room temperature, 150°C, 300°C) were investigated using a tandem mass spectrometer system. Mass spectra of product ions arising from Ar+ collisions with the three samples showed sputtering of the basic material of the sample substrate (Be+, BeH+, BeOH+; Li+, Na+, K+) and of hydrocarbon ions from the hydrocarbon coverage of the sample that decreased with increasing temperature. Sputtering of W+ or its compounds could not be detected. Normalized relative ion yields of Be+ and its compounds were not proportional to the Be content in the sample. Mass spectra from N2+ collisions were very similar to those of Ar+. Surface-induced dissociation of N2+ to N+ was not detected. The most conspicuous difference between mass spectra from D2+ impact and from Ar+ impact was a much lower sputtering efficiency of D2+ (by a factor of 50–100 or, for alkali ions, even more). The relative ion yield of Be+ strongly increased when the temperature of the sample was raised to 400°C and 450°C. A surface chemical reaction between the incident D2+ and surface Be leading to BeD+ was observed. The data may be of interest as basic information relevant to plasma–wall interactions in fusion devices.