Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene
Authors: Reed Benjamen P. , Cant David J. H. , Spencer Steve J. , Carmona-Carmona Abraham Jorge , Bushell Adam , Herrera-Gómez Alberto , Kurokawa Akira , Thissen Andreas , Thomas Andrew G. , Britton Andrew J. , Bernasik Andrzej , Fuchs Anne , Baddorf Arthur P. , Bock Bernd , Theilacker Bill , Cheng Bin , Castner David G. , Morgan David J. , Valley David , Willneff Elizabeth A. , Smith Emily F. , Nolot Emmanuel , Xie Fangyan , Zorn Gilad , Smith Graham C. , Yasufuku Hideyuki , Fenton Jeffery L. , Chen Jian , Counsell Jonathan D. P. , Radnik Jörg , Gaskell Karen J. , Artyushkova Kateryna , Yang Li , Zhang Lulu , Eguchi Makiho , Walker Marc , Hajdyła Mariusz , Marzec Mateusz M. , Linford Matthew R. , Kubota Naoyoshi , Cortazar-Martínez Orlando , Dietrich Paul , Satoh Riki , Schroeder Sven L. M. , Avval Tahereh G. , Nagatomi Takaharu , Fernandez Vincent , Lake Wayne , Azuma Yasushi , Yoshikawa Yusuke , Shard Alexander G. 
Published: November 2020

We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (&lt;90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.