Cellulose as the in situ reference for organic XPS. Why? Because it works

X‐ray photoelectron spectroscopy (XPS) has become popular for polymeric and biological surface analysis. However, several experimental factors may bias XPS data interpretation. Ex situ contamination, outgassing, reactions due to ultra‐high vacuum or X‐ray exposure, and charging problems are not uncommon. They are reflected in the high variability of data quality of recent reports. In order to enhance the reliability and reproducibility of XPS data, especially for organics and polymers, a suitable in situ reference material would be of a great help. At Aalto's CHEM XPS laboratory, we use 100% cellulosic filter paper as a reference for all XPS experiments. Nature derived macrofibrillar cellulose is not an obvious candidate for an in situ reference material in XPS; however, it is not only the most abundant biopolymer on the biosphere but it also qualifies surprisingly well as a generic in situ XPS reference.