Reflection optical microscopy, AFM topography, conduction images, and approximate color scale of ultrathin mica sheets on gold. (a) Reflection optical microscopy images of three mica sheets on semitransparent gold substrates with thicknesses in the 12- to 32-nm range. Inset: same as the main image but with artificially enhanced contrast. (b) AFM topographic image of the approximately 12-nm mica flake. Inset: corresponding conductive image. (c) Topographic profiles of the mica flakes shown in (a) taken along the indicated lines. (d) Approximate color scale for mica sheets as a function of the thickness with thickness in the 10- to 50-nm range.