STOCHASTIC RESONANCE AND COOPERATIVE BEHAVIOR IN SCANNING PROBE MICROSCOPY

A substantial amount of scanning probe microscopy (SPM) imaging must b e performed at nanometer or angstrom resolution. This requires a very high dynamic range from the z-displacement DAC or feedback ADC, so tha t this fine detail tends to be very coarsely digitized. This paper exa mines some nonlinear effects that occur at the level of least-bit digi tization and that can affect the resolution of atomic-scale detail. In particular, the interactions of limit cycling and cooperative behavio r are examined. We show that in most cases the maximum signal-to-noise ratio is obtained for some finite non-zero noise level, and that in s ome cases the optimum noise level can be predicted beforehand. In many cases, the correct noise level can be implemented by adjustment of fe edback control parameters.