Brownian Motion of Microscopic Solids under the Action of Fluctuating Electromagnetic Fields

The Brownian motion of a microscopic solid under the action of fluctuating electromagnetic fields was detected using atomic-force microscopy. The distance dependence of the noise spectrum of free cantilever oscillations, of the resonance frequency, and of the damping coefficient were investigated under ultrahigh vacuum conditions. An analytic expression for the damping coefficient of a metallic tip--sample system was obtained on the basis of fluctuating electrodynamics. Our calculation is in good agreement with experimental data.