The capillary force was measured by atomic force microscopy between a gold coated sphere mounted on a cantilever and gold surfaces with different roughnesses. For smooth surfaces the capillary adhesive force surpasses in magnitude any dispersion, e.g., van der Waals/Casimir and/or electrostatic forces. A substantial decrease in the capillary force was observed by increasing the roughness ampltitude a few nanometers in the range of 1-10 nm. From these measurements two limits can be defined: a smooth limit where a closely macroscopic size contact surface interacts through the capillary force and a rough limit where only a few asperities give a capillary contribution. (c) 2007 American Institute of Physics.
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