Measurement of the short-range attractive force between Ge plates using a torsion balance.

We have measured the short-range attractive force between crystalline Ge plates, and found contributions from both the Casimir force and an electrical force possibly generated by surface patch potentials. Using a model of surface patch effects that generates an additional force due to a distance dependence of the apparent contact potential, the electrical force was parametrized using data at distances where the Casimir force is relatively small. Extrapolating this model, to provide a correction to the measured force at distances less than 5 microm, shows a residual force that is in agreement, within experimental uncertainty, with five models that have been used to calculate the Casimir force.