Roughness of microspheres for force measurements

We have investigated the morphology and surface roughness of several commercially available microspheres to determine their suitability for force measurements using the atomic force microscope. The roughness varies considerably, depending on sphere size and material, ranging from nearly ideally flat up to micrometer-sized features. Because surface roughness significantly influences the magnitude and accuracy of measurement of surface forces, the results presented here should be helpful for colloid physicists and in particular for those performing force measurements.