XPS Mapping Case Study: Mapping the elemental distribution of a titanium alloy surface

Figure 1. XPS imaging sample raster                                                        Figure 2. XPS imaging of Ti 2p and O 1s on an alloy surface

SnapMap is a rapid XPS imaging method that uses the micro-focused X-ray source in unison with the SnapMap stage raster to generate high-resolution and fully-focused, quantified chemical state images. This allows positional information, acquired from small-area and large-area SnapMap images, to be analysed to identify features down to 10 um, as well as the chemical distribution across the sample surface. More precisely, SnapMap images contain full spectra that enable specific areas of interest to be analysed.

The Monash X-ray Platform's Nexsa Surface Analysis System can perform SnapMap as well as numerous other correlative analytical techniques to provide detailed characterisation of a materials surface. To generate SnapMap images, the sample stage moves under a stationary X-ray beam to effectively raster the X-ray spot across the sample surface Photoelectrons are continuously collected by the spectrometer. Individual pixel points can be investigated for chemical information using mathematical processes, including PCA (principle component analysis), TFA (target factor analysis) and NLSF (non-linear least squares fitting).

In this work, elemental SnapMaps of Ti 2p and O 1s from an alloy surface were recorded to assess their elemental distribution across the alloy surface. Using an X-ray spot size of 65 um, a region of 3 mm² was imaged for both elements. The raw SnapMaps were then processed using PCA to extract common peak shapes in the spectra for each pixel point, and then overlaid to positional identify the chemical composition of Ti and O within an image.

Sample courtesy of Erin Brodie, Department of Materials Science and Engineering, Monash University