We have developed a technique capable of mapping variations in the thickness of thin dielectric films, such as organic photoreceptors. This technique is based on accurately recording the capacitance between a spherical probe and the conductive substrate of a dielectric film. Once the capacitance has been recorded, and assuming the dielectric constant is known, the thickness of the film can be readily extracted. In the current experimental configuration, the probe can be raster scanned with respect to the surface of the dielectric film, enabling one to record 3D images and observe any spatial variations in sample thickness. The spatial and thickness resolution of the technique is primarily dictated by the size of the probe. This technique is applicable to any dielectric film on a conductive substrate, assuming the dielectric constant is known.
John Graham, Zoran Popovic, "Capacitance Based Scanner for Thickness Mapping of Thin Dielectric Films" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP18), 2002, pp 554 - 557, https://doi.org/10.2352/ISSN.2169-4451.2002.18.1.art00030_2