Friday, January 11, 2008

NIST's new approach to surface profiling

Stylus profilometry is the conventional way to determine surface roughness. NIST researchers have found that 2-D profilometry, typically extrapolated to provide a 3-D roughness determination, may not be accurate.

NIST’s approach uses data from a scanning laser confocal microscope (SLCM), an instrument that builds a point-by-point image of a surface in three dimensions. The data from a single SLCM image are analyzed using mathematical techniques that treat every point in the image simultaneously to produce a roughness measure that effectively considers the entire 3-D surface rather than a collection of 2-D stripes.

One early finding is that the generally accepted linear relationship between surface roughness and material deformation is wrong. The more accurate data from the 3-D analysis shows that a more complicated relationship was masked by the large uncertainties of the linear profilometers.