Off-resonance intermittent contact mode multi-harmonic scanning force microscopy

A robust off-resonance intermittent contact mode scanning force microscopy technique suitable for operation under different environmental conditions is presented. The technique relies on a multi-channel lock-in amplifier to measure multiple high harmonic magnitudes and phases. For distance control, the fundamental harmonic magnitude is used. With this, high intermittent contact frequencies become feasible even with older atomic force microscope data acquisition systems with limited measurement bandwidths, provided high frequency tip-sample distance actuation techniques are used. Suitable higher harmonic magnitude images provide a qualitative materials' contrast. If a sufficiently high number of high harmonic magnitudes and phases are recorded, force-distance curves at all imaged points can be reconstructed. From fitting models of the contact mechanics to force versus tip-sample penetration data, the elastic modulus of the sample can be obtained.