Dancing the tight rope on the nanoscale--Calibrating a heat flux sensor of a scanning thermal microscope

We report on a precise in situ procedure to calibrate the heat flux sensor of a near-field scanning thermal microscope. This sensitive thermal measurement is based on 1ω modulation technique and utilizes a hot wire method to build an accessible and controllable heat reservoir. This reservoir is coupled thermally by near-field interactions to our probe. Thus, the sensor's conversion relation V(th)(Q(GS)*) can be precisely determined. V(th) is the thermopower generated in the sensor's coaxial thermocouple and Q(GS)* is the thermal flux from reservoir through the sensor. We analyze our method with Gaussian error calculus with an error estimate on all involved quantities. The overall relative uncertainty of the calibration procedure is evaluated to be about 8% for the measured conversion constant, i.e., (2.40 ± 0.19) μV/μW. Furthermore, we determine the sensor's thermal resistance to be about 0.21 K/μW and find the thermal resistance of the near-field mediated coupling at a distance between calibration standard and sensor of about 250 pm to be 53 K/μW.