Application of Digital SIMS Imaging to Light Element and Trace Element Mapping

Abstract

The determination of the relationship of compositional microstructure to morphological microstructure is often critical for elucidating structure-property relationships in materials. Traditionally, the study of the lateral distribution of elemental constituents has been carried out in the electron probe x-ray microanalyzer. Because of the inherent properties of x-rays, electron probe compositional maps suffer several significant deficiencies: (1) Light elements with atomic number < 11 (sodium) are detected with poor sensitivity; below carbon detection in an imaging mode effectively ceases. (2) While detection limits for heavier elements can be as low as 100 ppm for analysis at a single location, the practical detection limit in images with 256×256 pixels is about 0.1 weight percent. Imaging by secondary ion mass spectrometry (SIMS) offers two special capabilities which extend substantially beyond the limitations of electron probe microanalysis. These capabilities, light element and trace element imaging, have been employed in this work in attacking two materials science problems: (1) the distribution of lithium in Al-Li alloys and (2) the origin of differences in the secondary electron coefficient observed in crystals in reaction-bonded SiC.