Study and comparison of two polishing methods for platinum–iridium surfaces, by means of three characterization techniques

Abstract

Machining the surface of mass standards is still of great importance [1][2][3][4][5]. This presentation details a comparative study of the roughness of two plane surfaces of platinum iridium alloy (90% of platinum and 10% of iridium).We carried out a comparative study of roughness, related to the two sides of a platinum-iridium disc, provided by the BIPM. These surfaces were polished according to two different techniques. Both were machined by means of a lathe using diamond tool. One of these surfaces was afterward treated by a manual polishing using diamond paste. Three characterization instruments were chosen to measure surface roughness: Scanning Near field Optical Microscope (SNOM) with shear force regulation, optical roughnessmeter and X-ray Reflectometer [6][7][8][9][10][11][12][13]. The two latter are based on angle resolved scattering (ARS) theory. The choice of these devices is mainly based on their non destructive character and their complementarities.Most of statistical and physical parameters characterizing the surface quality (topographical images, auto-correlation functions, distribution of heights, rms roughness δ and power-spectral-densities) are determined by means of SNOM. Visible and X ray measurements, using angle resolved scattering theory, can only provide the psd and rms height δ . When comparison is made on topographical images or distribution heights, we can clearly observe the difference between the two surfaces as expected. Thus, we noted that the measured height distributions were in agreement with Gaussian model, only in the case of manually polished surface. However, when comparing roughness (δ) of the two surfaces, we found that these seem to have the same surface state in spite of their different polishing: all results yielded to comparable values of δ (within uncertainties). This signifies that rms δ is a relative value which depends on several parameters and mainly on the spatial frequency bandwidth corresponding to measurements. This is clearly visible through the SNOM measurements, where the rms δ is determined in three spatial frequency bandwidths. The obtained values are different according to the considered bandwidth. Moreover, δ is slightly larger in the case of machined surface for low spatial frequencies.Concerning the autocorrelation function, the undulations observed for the machined surface reveal at least three types of pseudo-periodic defects, with a spatial period of about 7 µm. For the manually polished surface, the successive steps blurred some of the observed undulations, as it appears on the autocorrelation function. The latter presents only one weak peak of positive correlation around 15 µm. This might be correlated to the average spacing between holes observed on the topographic image.A complete characterization of surface is carried out by comparing the power-spectraldensities. Those provide a complementary explanation according to whether one compares

Present and future mass standards for the LNE watt balance and the future dissemination of the mass unit in France

“…In addition, the harder the material, the easier it is to adjust its mass close to its nominal value. Note that hardness combined with the size of the polishing diamond grains and that of metallographic grains of the material can cause surface quality defects such as an 'orange peel' effect, and the embedding of abrasive particles (phenomena observed with platinum-iridium alloy for instance [24]). -As great a density as possible to minimize volume and an active surface as small as possible thereby reducing the buoyancy effect when the artefact is used in air and sorption phenomena when it is transferred under vacuum [25][26][27][28][29][30][31].…”

Investigations of in situ reflectance of GaN layers grown by MOVPE on GaAs (0 0 1)

“…In the plot given by simulation, the surface roughness (r f = 82 nm) at600°C was estimated, using the optical model. roughness parameter as it depends deeply on the considered technique [49,50]. In fact, for reflectance measurements, the contribution of all surface defects and features is considered as the principal cause of light scattering, therefore of reflectance decrease, i.e.…”

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)).…”