Spectrum imaging of complex nanostructures using DualEELS: I. digital extraction replicas

This paper shows how it is possible to use Dual Electron Energy Loss Spectroscopy (DualEELS) to digitally extract spectrum images for one phase of interest in a complex nanostructured specimen. The specific cases studied here concern Nb or V precipitates, a few nanometres in size, in high manganese steels. The procedures outlined allow the extraction of the precipitate signal from the Fe–Mn matrix, as well as correction for surface oxide and any surface carbon contamination. The resulting precipitate-only spectrum images are then suitable for quantitative analysis of the precipitate chemistry. This procedure results in much improved background shapes under all edges of interest, mainly as a result of the removal of the extended electron loss fine structure (EXELFS) from the elements in the matrix. This allows the reliable extraction of even tiny quantities of elements, such as low levels of nitrogen in some carbide precipitates. As well as being relevant to precipitation in steels, these techniques will be widely applicable to the separation of chemically-distinct phases in complex nanostructured samples, and can be viewed as a digital version of the extraction replica technique.