LAUSR

Photoinduced force microscopy (PiFM) measures changes in the force between an atomically sharp tip and the sample under the influence of applied radiation. Several mechanisms contribute to the overall force, including forces introduced due to thermal heating of the sample and the tip. In this paper, we study the effect of laser heating of the retracted tip under illumination conditions relevant to PiFM and how it affects the mechanical resonance properties of the cantilever. Using a gold-coated silicon cantilever with its tip irradiated by a tightly focused 532-nm laser beam, we find that the tip temperature increases linearly at 7.5 K/mW of average laser power, irrespective of whether the laser is pulsed or continuous wave. The temperature rise gives rise to a decrease of the cantilever's spring constant and an increase of the damping coefficient. We demonstrate that for retracted tips, these thermally induced changes to the mechanical resonance only moderately impact the measured photoinduced force, as the measured scattering force is at least an order of magnitude stronger than the effective force introduced by laser heating under experimentally relevant conditions.