Tomographic Spectral Imaging with Multivariate Statistical Analysis: Comprehensive 3D Microanalysis

A comprehensive three-dimensional ~3D! microanalysis procedure using a combined scanning electron microscope ~SEM!/focused ion beam ~FIB! system equipped with an energy-dispersive X-ray spectrom- eter ~EDS! has been developed. The FIB system was used first to prepare a site-specific region for X-ray microanalysis followed by the acquisition of an electron-beam generated X-ray spectral image. A small section of material was then removed by the FIB, followed by the acquisition of another X-ray spectral image. This serial sectioning procedure was repeated 10-12 times to sample a volume of material. The series of two-spatial- dimension spectral images were then concatenated into a single data set consisting of a series of volume elements or voxels each with an entire X-ray spectrum. This four-dimensional ~three real space and one spectral dimension! spectral image was then comprehensively analyzed with Sandia's automated X-ray spectral image analysis software. This technique was applied to a simple Cu-Ag eutectic and a more complicated localized corrosion study where the powerful site-specific comprehensive analysis capability of tomographic spectral imaging ~TSI! combined with multivariate statistical analysis is demonstrated.