Practical guides for x-ray photoelectron spectroscopy (XPS): Interpreting the carbon 1s spectrum

Abstract

The carbon 1s photoelectron spectrum is the most widely fit and analyzed narrow scan in the x-ray photoelectron spectroscopy (XPS) literature. It is, therefore, critically important to adopt well-established protocols based on best practices for its analysis, since results of these efforts affect research outcomes in a wide range of different application areas across materials science. Unfortunately, much XPS peak fitting in the scientific literature is inaccurate. In this guide, we describe and explain the most common problems associated with C 1s narrow scan analysis in the XPS literature. We then provide an overview of rules, principles, and considerations that, taken together, should guide the approach to the analysis of C 1s spectra. We propose that following this approach should result in (1) the avoidance of common problems and (2) the extraction of reliable, reproducible, and meaningful information from experimental data.

Comments on the XPS Analysis of Carbon Materials

“…This paper will not consider the fitting of adventitious or polymeric carbon species but will focus on predominantly graphitic and diamond-like materials. For discussion on the former, the reader is directed to [11].…”

“…The fitting of the graphitic C (1s) envelope is one of the most common errors encountered in the literature [15], and the asymmetric shape is something commonly ignored in The fitting of the graphitic C (1s) envelope is one of the most common errors encountered in the literature [15], and the asymmetric shape is something commonly ignored in may published papers. Recently, Linford et al [11] reported a method for fitting the C (1s) envelope of graphitic carbon materials, using a reference spectrum of clean graphite/HOPG as a model for the graphitic backbone. This method is useful and is indeed a method the current author has used for many years.…”

“…C 2021, 7, x FOR PEER REVIEW 3 of 9 may published papers. Recently, Linford et al [11] reported a method for fitting the C (1s) envelope of graphitic carbon materials, using a reference spectrum of clean graphite/HOPG as a model for the graphitic backbone. This method is useful and is indeed a method the current author has used for many years.…”

Box plots: A simple graphical tool for visualizing overfitting in peak fitting as demonstrated with X-ray photoelectron spectroscopy data

“…This situation is analogous to the "disproof by counterexample" method used by mathematicians in which a single counterexample is used to disprove a proposition. [29] In other words, one might question the validity of a fitting protocol if different starting conditions in it lead to significantly different results. The method developed in this work tests for local minima in a fit space.…”

“…Our interest in C 1s narrow scans is a result of a recent report that showed that they are the most frequently presented and researched narrow scans in the scientific literature, [18] and that they are often fit incorrectly. [29,30] Calculations for the four-component peak fits. We first created a 32 x 4 matrix of random numbers uniformly distributed between 0 and 1 using the following MATLAB script: >> rng shuffle >> x = rand (64,4) This algorithm for generating random numbers, D.E.…”