The Role of XPS

XPS was used to determine the presence and interaction of the NHC. Through analysis of the NHC salts and the NHC modified Pd catalysts, it was found that care had to be taken in their analysis (see SI for this paper). Coupled with the low levels of Pd (1 wt% or less) for the modified catalysts, this degradation becomes significant for prolonged analysis which may be required. The NHCs were found to degrade under X-ray analysis, with degrees of reduction seemingly dependent on the organic ligands. As such, as protocol had to be created to minimise reduction whilst still obtaining XPS data which was characteristic of the modified catalysts. This protocol consisted of running on a might sensitivity, broad spot XPS spectrometer allowing for high transmission of photoelectrons to the detector, whilst minimising sample degradation through a larger x-ray spot, rather than micro-focussing a high intensity flux to a smaller analysis area. Through studies of the salts, and our understanding of degradation in XPS through the work of our technical manager (Dr David Morgan), then we could optimise acquisition conditions to give spectra, that whilst contain some noise, are quantifiable and more importantly, with minimal degradation artefacts.