(a) Schematics of experimental setup. An electrical current circulates along the arms of a thermal AFM cantilever (phosphorous-doped Si) and heats up the end section above the tip (intrinsic Si). A high-NA objective excites and collects the fluorescence emitted by a diamond-nanocrystal (that hosts a nitrogen-vacancy centre, NV) attached to the AFM tip. A wire on the sample surface serves as the source of mw. The resistance (and thus temperature) of the intrinsic segment of the cantilever can be determined from the measured current Ih=Vs/Rs and applied voltage V0. Our experiments are carried out in the presence of a magnetic field B along the direction normal to the sample.
(b) Optically detected magnetic resonance spectra of an NV centre attached to the thermal tip at three different heater temperatures Th. The right (left) dip corresponds to the mS=0↔mS=+1 transition (the mS=0↔mS =−1 transition) between the levels of the NV ground-state spin triplet. The line splitting originates from a ∼1-mT magnetic field aligned along the NV axis. Spectra have been displaced vertically for clarity. (c) NV-assisted thermal conductivity image of a 18-nm-thick gold structure on sapphire. The heater temperature Th is 465 K. White circles indicate example patches of low (high) conductivity inside (outside) the gold structure that do not correlate with the substrate topography.
(d) Fluorescence image of the cantilever end and tip. Light from the tip-attached nanocrystal can be clearly separated from the background (yellow circle).