(417a) Interference-Based Characterization of Microspheres: Radius, Local Curvature and Roughness Determination

Accurate measurement of microspheres size and roughness is fundamentally important in manufacturing settings; therefore, the use of characterization techniques capable of simultaneously measure micrometer-sized particles and nanometer-scale features offers a significant advantage. Interference-based techniques are known for their setup simplicity and practical implementation while offering nanometer/microsecond-scale resolution. However, the accurate use of interference for the study of microscopic objects has been difficult to achieve because current methods for the analysis of interferograms are strictly valid only when dealing with planar-like geometries.

Here, we describe work aimed at overcoming these barriers. Interferograms obtained from microspheres observed using reflection interference contrast microscopy (RICM) are analyzed with novel methods that allow accurate measurements of the microspheres size. In addition, RICM offers a unique non-invasive “view from below” perspective that provides valuable information about the nanometer-scale topography of the microspheres in close proximity to a transparent substrate, making it possible to measure roughness and local deviations from the overall particle radius. Two parameters possibly related to the surface roughness of microspheres are considered: first, a finite separation distance between the particles and the substrate measured by RICM when the surfaces are in contact and, second, fringe visibility in RICM interferograms.