A scanning probe microscope in which the probe is oscillated at a frequency lower than its resonant frequency, a force sensor that is sensitive to the bending of the cantilever and minimally sensitive to the oscillation is used to measure tip-sample interaction force. The sensor signal is then converted to a force gradient signal by electronics. The gradient signal is kept constant by a feedback mechanism as the tip is scanned across the surface of a sample, and force and topographical information are mapped.