W 4f electron binding energies in amorphous W-B-C systems

In this paper, we critically evaluate the applicability of the procedure proposed in [Mirzaei et al., Surf. Coat. Technol. 358 (2019) 843-849] which is based on the fitting of the XPS spectrum of amorphous W-B-C material into three components with fixed peak positions to get the relative amount of W-W, W-B, and W-C bonds. We show that W-W bonds substantially influence positions of the peak components. We have verified this assumption by generating a set of models of amorphous W-B-C with different compositions (W:B:C ratio) and calculating the W 4f core electron binding energies employing ab initio methods. This enabled us to formulate the relationship between the W 4f electron binding energies (BE) and the local atomic environments of W atoms. Our analysis confirms the expected W 4f chemical shifts in W-B-C caused by W-B and W-C bonds and reveals that W-W bonds shift the W 4f electronic states in the same direction as W-B bonds, which has substantial implications for the correct interpretation of the measured XPS spectra.