A magnetically driven oscillating probe microscope for operation in liquids

Oscillating probe atomic force microscopy in fluids is simplified when an oscillating force is applied directly to a magnetized cantilever using a solenoid. The response of the detector is simpler than that obtained with acoustic excitation. Reliable operation over a broad frequency range is achieved with excitation amplitudes of a few nm. This lower amplitude appears to facilitate imaging by means of small asperities on the tip. Images of a DNA plasmid bound weakly to mica in water have a full width of 5 nm when scanned with tips of a nominal macroscopic radius of curvature of 50 nm.