  Measurements of the Casimir force require the elimination of electrostatic
interactions between the surfaces. However, due to electrostatic patch
potentials, the voltage required to minimize the total force may not be
sufficient to completely nullify the electrostatic interaction. Thus, these
surface potential variations cause an additional force, which can obscure the
Casimir force signal. In this paper, we inspect the spatially varying surface
potential (SP) of e-beamed, sputtered, sputtered and annealed, and template
stripped gold surfaces with Heterodyne Amplitude Modulated Kelvin Probe Force
Microscopy (HAM-KPFM). It is demonstrated that HAM-KPFM improves the spatial
resolution of surface potential measurements compared to Amplitude Modulated
Kelvin Probe Force Microscopy (AM-KPFM). We find that patch potentials vary
depending on sample preparation, and that the calculated pressure can be
similar to the pressure difference between Casimir force calculations employing
the plasma and Drude models.
