A new approach to surface metrology - Structured surfaces

All surfaces, be they at the nano, micro or even macro scale are made up of a collection of features at many different scales which constitute the surface texture. Functional surfaces are "engineered" to meet functional requirements such as good bearing properties and good electrical contact amongst others. The organisation of the surface features, the feature types, and sizes together with the material properties all have a fundamental effect on the resulting function of the surface. The ability to adequately characterise the surface geometry is crucial in the optimisation and control of such functional surfaces. The subject of the present paper is to outline recent developments in the analysis of structured surfaces and the concepts behind developing a generic approach to characterising them. Traditional concepts in surface texture, such as roughness, waviness, lay etc. are not useful when characterising these surfaces. Structured surfaces are usually made up of repeated features and the required metrology usually centres around classifying the geometric primitive and then quantifying the departures form that nominal primitive. This has lead to the re-evaluation of what exactly is the definition of surface texture and it is clear that the approach needed is a combination of surface metrology and more traditional co-ordinate metrology (CCM) with new concepts in segmentation mathematics.