The application of laser ionization mass spectrometry to the study of thin films and near‐surface layers

Abstract

AbstractThe laser ionization mass analyser, LIMA, was originally developed as a bulk microprobe instrument giving elemental information similar to that obtained from the conventional electron probe microanalyser, but with the advantage of full periodic table coverage. The LIMA is therefore capable of detecting all elements including hydrogen, helium, lithium, and beryllium, which are inaccessible to EPMA. Other advantages of LIMA over EPMA are isotope discrimination and the ability to obtain chemical information from materials as a result of the emission of complex ionic fragments from surfaces under laser irradiation. As experience grew with the use of the prototype LIMA at Aldermaston, it became clear that the technique was a particularly versatile tool which could not only perform well as a bulk microprobe, but with suitable experimental procedures could also be used as a sensitive depth profiling instrument with moderate depth resolution (≥0.01 μm). It became apparent that in its performance parameters, and in many of its applications in bulk and surface analysis, LIMA was directly comparable with dynamic SIMS. This paper is, therefore, concerned with the applications of LIMA when operated in a surface sensitive mode. In general, this involves using low power densities, and a defocused laser—the defocusing means that some sacrifice in lateral resolution must be made. Nonetheless, it is shown in this paper that the LIMA has a genuine contribution to make in depth profiling and thin film analysis.