Influence of the bombarding ion energy and surface composition on the ground‐state atom fraction in solids analysis using multiphoton resonance ionization

Abstract

Multiphoton resonance ionization (MPRI) is used to probe the desorption characteristics of ion‐bombarded surfaces of Fe, In and Ni. The effects of primary ion kinetic energy and surface chemistry on the sensitivity and accuracy of MPRI detection are examined. The relative Ni*/Ni° and In2°/In° ratios are found to increase as the energy of the incident Ar+ ion is varied from 300 eV to 1000 eV. A reflecting time‐of‐flight mass spectrometer is employed to collect efficiently the photoions as well as secondary ions, permitting accurate determination of the ground‐state atom fraction and thereby completing a detailed fundamental analysis of the analytical capabilities of the MPRI approach. The ground‐state atom fractions are found to parallel changes in surface composition and represent 30–90% of the material desorbed from ion beam‐cleaned and air‐exposed Fe and In matrices. In contrast, the corresponding secondary ion fractions vary over several orders of magnitude and are difficult to correlate with surface chemistry. Copyright © 1992 John Wiley & Sons Ltd.