Multifrequency, repulsive-mode amplitude-modulated atomic force microscopy

An imaging method where a cantilever is driven at or near two of its flexural resonant eigenmodes is described. For most cantilevers, these eigenmodes are nonharmonic. The cantilever and imaging parameters are chosen such that the tip-sample interactions are repulsive. The driven second eigenmode amplitude and phase show strikingly different contrasts from those same fundamental eigenmode signals on graphite samples imaged in air and λ-digest deoxyribonucleic acid samples imaged in water.