Heterodyne Frequency Modulation in Photoinduced Force Microscopy

Abstract

In the variant of atomic force microscopy (AFM) known as photoinduced force microscopy (PiFM), amplitude-modulation techniques have been used to detect the photoinduced force. In such approaches the signal is also affected by other forces, which damp the motion of the probe's cantilever. This study proposes a heterodyne (sideband-detection) $f\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}q\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}y$-modulation technique that enables one to obtain the photoinduced force without artifacts from the photothermal force and the changes in the resonance frequency of the cantilever, and thus to realize true optical imaging at the nanoscale.