Interferometry of surfaces with well-defined topography in the surface force apparatus

•We study interferometry of surfaces with micron scale topographical features.•Features appear in the FECO as a result of the difference in optical path.•The shift in wavelength is used to determine the height of the features.•2D slices along two directions can map their orientation on the structured surface.•Features can broaden the fringes and lead to a larger error in surface separation.

We studied the multiple beam interferometry of surfaces with well-defined microscale features in the surface force apparatus (SFA). The structures investigated consist of hexagonal arrays of microscale cylindrical posts made out of the photoresist SU-8. The ability of the SFA to visualize the profile and topography of the interacting surfaces leads to the observation of discontinuities in primary fringes of equal chromatic order that are caused by the microscale structural features. The shift in wavelengths has been analyzed to extract the post height and compared to independent profilometry measurements. The analysis based on the shift in wavelength is shown to be viable only when the order of the fringe and the position of the discontinuity is precisely known and within the field of view. Analysis of the full profile of the interacting surface for two orthogonal 2-dimensional slices can be used to determine how the surface lattice is oriented within the point of closest approach. Finally, we discuss cases in which the structural features detrimentally affect the spatial resolution of the SFA.

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