Template-stripped gold surfaces with 0.4-nm rms roughness suitable for force measurements: Application to the Casimir force in the 20-100-nm range

Using a template-stripping method, macroscopic gold surfaces with root-mean-square roughness less than or equal to 0.4 nm have been prepared, making them useful for studies of surface interactions in the nanometer range. The utility of such substrates is demonstrated by measurements of the Casimir force at surface separations between 20 and 100 nm, resulting in good agreement with theory. The significance and quantification of this agreement are addressed, as well as some methodological aspects regarding the measurement of the Casimir force with high accuracy.