Comparative SIMS investigations on surface contamination of Pt–Ir alloy treated by different cleaning procedures

A comparative study of the surface contamination of Pt–Ir alloy, treated by different cleaning procedures has been carried out using Secondary Ion Mass Spectrometry (SIMS) technique. The Pt–Ir (10%) alloy is basically the standard mass material of the international prototype of the Kilogram. The effect of the conventional cleaning method on the surface of one of the Pt–Ir sample is examined, not only on the top most surface but also a little deep inside the surface, to identify the causes of long term instability of primary standard mass material. In addition to the usual atmospheric contaminants (carbon and oxygen), the results obtained show the presence of contaminants such as sodium, calcium, potassium, magnesium, etc. on the surface of Pt–Ir alloy samples not hitherto observed using other surface analytical techniques like AES, and XPS. In another experiment, four samples, one uncleaned and three cleaned by solvent and/or steam washing, were studied to compare the effect of cleaning procedures on the Pt–Ir samples. It is concluded from the above results that steam cleaning may be advantageous for standard mass stability compared to other cleaning procedures where solvents are used.