Chemically specific identification of carbon in XPS imaging using Multivariate Auger Feature Imaging (MAFI)

Until now, a difficult prospect in XPS imaging has been the identification of similar chemical states of carbon. With the advent of novel nano-carbons such as nanotubes and graphene, the ability to easily and unambiguously identify materials of varying sp²/sp³ nature in XPS spectra and images is becoming increasingly important. We present herein methods for the identification of such species in XPS images by shifting focus from the traditionally analysed C1s region to the X-ray induced carbon Auger feature. By extracting the D-Parameter from XPS data, we have generated what we refer to as "D-Parameter Images", that clearly identify regions of different carbon hybridisation in an image of a graphite flake mounted on carbon tape, and areas of reduced graphene oxide (GO) in a laser-scribed GO film. This method is then enhanced by multivariate analysis, a technique we call "Multivariate Auger Feature Imaging", where the distinction between varying sp² carbon content on a surface is improved.