Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray...

Area of Science:

• Materials Science
• Surface Science
• Metrology

Background:

• Traditional intensity scale calibration for X-ray photoelectron spectrometers (XPS) relies on gold, silver, and copper, which have limitations.
• An interlaboratory study was conducted under the Versailles Project on Advanced Materials and Standards to explore alternative calibration materials.
• Low-density polyethylene (LDPE) was investigated as a potential alternative reference material for XPS intensity calibration.

Purpose of the Study:

• To evaluate the effectiveness of low-density polyethylene (LDPE) for intensity scale calibration of X-ray photoelectron spectrometers (XPS).
• To develop and refine an LDPE-based calibration protocol.
• To assess the feasibility of establishing a standardized XPS intensity calibration method using LDPE.

Main Methods:

• Development of improved LDPE reference spectra using data from an interlaboratory study, corrected for instrument geometry with a quartz-monochromated Al Kα x-ray source.
• Calculation of transmission functions for participant datasets using the new LDPE reference spectra.
• Comparison of LDPE calibration results against traditional gold calibration methods (NPL reference spectra).

Main Results:

• The LDPE intensity calibration method achieved an average absolute offset of ~3.0% and a systematic deviation of ±6.5% across participants.
• Higher pass energies (≥90 eV) yielded better results (~5.8% offset, ±5.7% deviation) compared to lower pass energies (<90 eV) (~4.9% offset, ±8.8% deviation).
• Surface roughness of LDPE and issues like low count rates at lower pass energies impacted calibration accuracy.

Conclusions:

• LDPE is a viable alternative material for XPS intensity scale calibration, offering comparable accuracy to traditional methods.
• An updated LDPE intensity calibration protocol was developed to address identified issues and improve usability.
• There is a need for a consistent, traceable intensity calibration standard in the XPS community, with LDPE proposed as a pathway towards an international standard.