Laser-induced cantilever behaviour in apertureless scanning near-field optical microscopes

The laser-induced deformation of a typical commercial cantilever commonly used for scanning near-field optical microscopes was investigated by means of a software package based on the finite element method. The thermo-mechanical behaviour of such a cantilever whose tip was irradiated by a laser beam was calculated in the temperature regime between room temperature and 850 K. The spatial tip displacement was simulated at timescales <0.1 ms, since feedback-based constant force measurements exhibit reaction times in this range. It could be shown that in addition to former tip-based thermal expansion calculations the cantilever deformation is already significant at moderate temperatures, particularly when a reflective coating is present. The experimental and calculated results suggest that tip scanning in cantilever-based scanning probe microscopes for laser-based surface modification applications should be performed in thermal equilibrium. (paper)