Traceability of mass II: a study of procedures and materials

Abstract

Abstract The surface contamination of various metallic samples upon cyclic transfer from vacuum to ambient pressure air or dry nitrogen was studied using x-ray photoelectron spectroscopy (XPS) for surface chemical analysis. The venting methods were vacuum–air–vacuum, vacuum–N 2 –air–vacuum and vacuum–N 2 –vacuum. In addition, the dependence on the initial surface chemical state was investigated by using different cleaning methods such as the traditional washing and cleaning (nettoyage-lavage), low-pressure hydrogen plasma and UV/ozone as starting conditions. We found that cyclic exposure to air after UV/ozone and nettoyage-lavage has very little effect on the surface contamination. In contrast, hydrogen plasma removes the initial contamination almost completely. Until a first layer of contaminants is built up, the growth is very rapid but slows down exponentially with the number of cycles. Exposure directly to ambient pressure air causes the fastest and largest recontamination, followed by the cyclic transfer vacuum–N 2 –air–vacuum. Venting with dry nitrogen exclusively exhibits the slowest growth of contaminants but continues with further cycling until the first layer is completed. A list of precedence for existing and potential new materials and for the processes applied is presented in order to test and evaluate the best materials for future primary mass standards and to find the best working practice.

Cite this work

No public copy is stored for this record, so only the metadata is cited.

Stored only when both papers are in the corpus — 9 citations exist upstream.

Papers that cite the same references — the relational fallback while embeddings are still backfilling.