Reliability of spectral analysis in Interferometric Optical and Atomic Force Microscopies

M. Jobin
hepia, HES-SO, CH

Keywords: topography, power spectral density, roughness, atomic force microscopy


Both Interferometric Optical Microscopes (IOM) and Atomic Force Microscopes enable the acquisition of surface topographies with sub-nanometer vertical resolution. Each instrument has its own specific advantages (large fields of view and rapidity for IOM and lateral resolution for AFM). Those complementarities are often used in combined IOM/AFM instrument [1]. Spectral analysis (namely PSD, Power Spectral Density) has become a very popular mathematical tool to analyze nanotopogrphic data, both AFM and IOM. In this paper, we show that PSD is very powerful provided: i) several specific artifacts are avoided during the acquisition; ii) the data are properly processed before calculating the PSD) and; iii) the correct model is used for the interpretation. Unfortunately, some features in the IOM or AFM data inherent either to the acquisition or to the routinely used image processing tends to make such analysis irrelevant. We also explain how to compare efficiently the rms roughness (which is the integrated PSD) as given by AFM and IOM.