Accessing the robustness of adventitious carbon for charge referencing (correction) purposes in XPS analysis: Insights from a multi-user facility data review

An assessment of X-ray photoelectron spectroscopy (XPS) results from 1237 samples submitted to a multi-user facility from a five year period investigates the usage and effectiveness of common charge referencing methodologies for insulating samples. Carbon 1s (C 1s) starting peak-fitting routines for common graphitic-like materials and for adventitious carbon (AdC) are presented. An average adventitious carbon (AdC) C 1s binding energy of 284.91 eV (Std. Dev. 0.25 eV) was found for 117 samples that also contained a secondary charge reference possibility. With an understanding of the limits and possible issues with using AdC for charge referencing purposes and by incorporating other methodologies (Auger parameter, checks for data self-consistency, well-established peak-fitting routines) it was found that using AdC C 1s for charge referencing gave satisfactory and meaningful results in 95% of the 522 cases assessed. Differential charging is a common issue including in studies assessing AdC binding energies. This work demonstrates that electrical isolation (floating) of mixed insulating/semi-conducting/conducting samples significantly improves outcomes by mitigating differential charging issues.