Neutralization of slow helium ions scattered from single crystalline aluminum and tantalum surfaces and their oxides

Abstract

We investigated the impact of surface oxygen on the ion yield for He + ions scattered from different single crystalline surfaces in low-energy ion scattering. Initially clean Al(111) and Ta(111) were exposed to molecular oxygen and ion spectra for different oxidation stages and different primary energies were recorded. A comparison of ion yields normalized to the differential scattering cross section as well as experimental factors allows obtaining information about the influence of oxygen on charge exchange processes. The decrease in the ion yield of both metals with exposure cannot be explained by different surface coverages exclusively, but requires the neutralization efficiency to be dependent on the chemical structure of the surface. For Ta, additionally, a different energy dependency of the ion yield obtained in the metal and oxide occurs. The ion yield for O shows in both surfaces a significantly weaker energy dependency than the investigated metals.

Derivation of an Improved Semi-empirical Expression for the Re-ionisation Background in Low Energy Ion Scattering Spectra

“…A considerable number of scattered projectile ions is detected at smaller energy than the single scattering peak, suggesting that these particles underwent a higher energy loss due to multiple binary collisions on their path through the solid surface region. The origin of this continuum is discussed in [4] and more recently [5,6] deal especially with the role of oxygen for the re-ionisation. The most likely and consistent explanation of these findings is that a projectile ion is scattered multiple times at deeper layers below the surface and re-ionised when leaving the surface.…”

Surface and interface diffusion processes in nanoscale thin films

“…In rare cases, the so-called matrix effect is observed, where the neutralization probability, and thus the intensity of the LEIS signal, depends on the matrix or the neighboring atoms. 59,[64][65][66] For such cases, quantification of surface composition becomes extremely complex. Also, if the reference sample deviates considerably from the investigated sample in terms of surface roughness, contamination, crystallinity and surface orientation, the quantification of the surface composition will not be reliable.…”