Pitch measurements validation of a structural coloured steel insert using Scanning Confocal Microscopy (SCM) and Atomic Force Microscopy (AFM)

The optical principle of structural colouration provides to a surface unnatural and iridescent colouring properties. Surface topographycombined with lighting characteristics are the physical driver of the phenomenon. Structural colouring arises from the presence on the specimen of nanoscale features distanced by a length comparable to the near visible light spectrum (300‐1000 nm).

The microstructures behave as a bandpass filter for certain light wavelengths, enabling an unnatural colouring effect. Elliptical Vibration Texturing (EVT) is an on development technology for fast texturing of gratings on metal inserts for structural colouration purposes.To identify the accuracy of EVT, in this study, two different microscopes assess an EVT grating with a 1000 nm nominal pitch on asteel flat surface.

On first, optical‐based metrology is selected adopting a Laser Scanning Confocal Microscope (SCM) with a 405 nm blue source to tackle the measuring purpose. Secondly, an Atomic Force Microscope (AFM) in Intermittent contact mode (IC‐AFM) isadopted. Considering the differences in set‐up time and scanning range, the objective of this research is to identify the mostfavourable measuring technique.On the sample images, five average profiles on different locations provide consistent information about the process repeatability.Pitch estimation comes by means of FFT algorithm on the extracted profiles.

The average result for SCM measures is 1002 ± 31 nmwhile for AFM is 972 ± 15 nm. At last, from these results, the estimation of EVT accuracy is presented.