Utilization of Nonlinear Parametric Resonance in Micro Sensor Probes to Enhance Atomic Force Microscope Resolution.

Atomic Force Microscopy (AFM) uses oscillating cantilever-shaped microprobes to measure nanometer-scaled sample topography. Spatial resolution of AM-AFM is determined by the dynamics of the cantilever-sample system including thermomechanical noise of the cantilever. Conventional AFM systems drive the cantilever harmonically in resonance, where resolution can only be improved by changing system and process parameters. We take a different approach keeping cantilever, sample, and control method (AM-AFM) unchanged. Instead, we operate the AFM cantilever in nonlinear parametric resonance. The corresponding excitation scheme is produced via electronic feedback. Because of the artificial source of the nonlinear parametric excitation, we implement arbitrary system behavior and prove the theoretical findings experimentally. We analyze the influence of excitation parameters on dynamic system behavior including an explanation of the nonlinear limitation mechanism of the cantilever amplitude in parametric instability and amplitude reduction mechanism during approach of the cantilever to the sample. We find a mechanism which could reduce tip damage. The dependence of the cantilever's thermomechanical noise on parametric excitation is investigated. Our analysis yields the resolution of parametric resonance AFM and enables systematic selection of parametric excitation parameters to improve resolution of existing AFM systems. We provide evidence that responsivity is enhanced by 30%, thermomechanical noise by a factor of 4.5, and resolution by a factor of 5.7 for identical systems when parametric resonance AFM is used.