Figure 2. NV-spin-assisted sensing of the AFM tip temperature.

(a) Optically detected magnetic resonance spectra of an NV centre attached to the thermal tip at three different heater temperatures T_h. The right (left) dip corresponds to the m_S=0↔m_S=+1 transition (the m_S=0↔m_S =−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. (b) Temperature dependence of the m_S=0↔m_S=+1 transition frequency ν_NV; the red trace is a quadratic fit. T_h is determined from the resistance of the intrinsic section of the cantilever (see Methods for details). The inset shows the diamond nanoparticle temperature T_t using the known relation with the NV resonance frequency as a function of the heater temperature T_h for a tip exposed to ambient. Comparison with the graph diagonal (solid blue trace) indicates that both coincide within experimental error. (c) Confocal image of the AFM cantilever in the vicinity of the tip after grafting multiple NV-hosting nanocrystals. (d) Frequency shift Δν_NV relative to room temperature for each of the nanocrystals imaged in c.