Abstract: The inventive “Substrate Effect Model” represents an improvement over the “Ebel Model,” a conventional XPS-based methodology for determining carbonaceous overlayer thickness. The Ebel Model generally predicts a higher value than the measured value for the ratio of the carbon's C1s electron emission peak to the carbon's CKVV electron emission peak. The invention recognizes the existence and influence of the “Substrate Effect,” whereby photoelectrons from the underlying substrate cause additional core-level ionizations in the carbon layer. The failure of the Ebel Model to account for the Substrate Effect is responsible for the variance between Ebel Model prediction and actual x-ray photoelectron spectroscopic measurement. In essence, the invention “corrects” the Ebel Model by accounting for the Substrate Effect.