The nanometric roughness of mass standards and the effect of BIPM cleaning-washing techniques

Abstract

A method based on light scattering has been used to characterize the surface roughness of four standard kilograms made from XSH alacrite, in order to determine the root-mean-square height and the correlation length . The values of these two parameters, which have been found to lie between 2 nm and 5 nm and between 170 nm and 250 nm, respectively, show the high surface quality that it is possible to obtain by mechanical polishing of XSH alacrite. Cartographies made by light scattering, as well as and values, have shown that in spite of identical manufacturing conditions the kilograms present a significant difference in surface roughness. We have observed that the lower bases were in general rougher than the upper ones. This was explained by the different histories of the upper and lower bases. On the other hand, the same value of was found for both bases of a given kilogram. We have also found that the smoother the kilogram, the smaller the mass loss. This clearly shows the effect of surface roughness on the stability of mass standards. Finally, significant variations in the values of and have been observed after the cleaning-washing process at the Bureau International des Poids et Mesures. We have also shown that the variations noted after several successive cleaning-washings are mainly the result of the first of these. This agrees with observations made during earlier gravimetric studies.

Atomic force microscopy studies of surface contamination on stainless steel weights

“…Results from ultrasonic cleaning in ethanol (figure 2) show that contamination was removed mainly from the grooves, which arise from machining of stainless steel. This result agrees with Zerrouki et al [21], who suggested that initial cleaning removes fine particles and dust from scratches in the surface. The contamination that was removed is assumed to be carbonaceous contamination, which has accreted on the surface during the years.…”

Thermal desorption mass spectrometer for mass metrology

“…Storage conditions (air, vacuum, inert gas) and cleaning methods (alcohol, UV/Ozone, plasma, or thermal desorption) are also factors that affect mass stability. [12][13][14][15][16][17] To understand how surface behaviour affects mass stability after the artefact has been cleaned using different methods and stored under different conditions, it is essential to characterize surface quality by rugosimetric methods (for example, optical scatterometer or X-ray reflectometer, SNOM, or atomic force microscopy 18,19 ) to evaluate mass stability by gravimetric methods by means of mass comparators as well as to identify surface contaminants using spectrometric techniques (for example, XPS (X-Ray photoelectron spectrometry) or ToF-SIMS (Time-of-Flight Secondary ion mass spectrometry)).…”

An investigation of methods for cleaning stainless-steel weights

“…The initial loss in mass is generally much larger than subsequent changes. Zerrouki et al [13] have suggested that the initial cleaning removes fine particles and dust from holes and scratches in the surface.…”