Observation of tip-to-sample heat transfer in near-field optical microscopy using metal-coated fiber probes

Metal-coated scanning near-field optical microscopy fiber probes can undergo significant heating due to partial absorption of the coupled light by the metallic film covering the apical zone. In this letter we report experimental evidence of tip-to-sample heat transfer on a 7,7?,8,8?-tetracyanoquinodimethane molecular crystal. Local melting is observed at nanometric tip-sample distances, when increasing the laser power injected into the fiber above a threshold of 8.8 mW. Hole formation and material displacement are observed, as well as failure of the shear-force-based imaging process, due to partial sticking of the melted material to the probe.