TITLE: Combining Surface Topography Measurements Across Instruments

CONTRIBUTOR: Simeona Hein, Graduate Student at the University of Pittsburgh

DESCRIPTION: After using the Surface Topography Challenge (STC) samples to evaluate individual measurement techniques, I wanted to explore how measurements from different instruments could be combined to characterize a surface over a broader range of spatial scales. Because atomic force microscopy (AFM) and stylus profilometry measure surface topography differently, I wanted to see how well their measurements agreed over similar length scales and whether combining them would produce a power spectral density (PSD) consistent with the published STC consensus.

OVERALL PROCESS: I measured the rougher STC surface using AFM and stylus profilometry, collecting 9 AFM measurements and 15 stylus profiles using a 2-μm radius tip. I uploaded the measurements to https://contact.engineering,, which combined the data and calculated the overall average PSD. I also calculated the average PSD and variability for each instrument separately, allowing me to assess their agreement across the overlapping range of size scales. Finally, I compared their combined PSD with the published STC consensus and its variability.

DETAILS: Here is the same standard operating procedure (SOP) that I used in the prior Use Case.

RESULT: As shown in the figure, AFM and stylus profilometry showed good agreement with each other at longer wavelengths, but the stylus PSD began to fall below the AFM (and consensus) PSD at shorter wavelengths. One possible explanation is the limited lateral resolution of the 2-μm stylus tip, which may not fully resolve smaller surface features. Despite these differences, the combined PSD showed good overall agreement with the published STC consensus. These results demonstrate how combining measurements from multiple instruments can provide more robust surface characterization than any technique in isolation.