Sensitivity and spatial resolution for thermal conductivity measurements using noncontact scanning thermal microscopy with thermoresistive probes under ambient conditions

Thermoresistive probes are increasingly popular in thermal conductivity characterization using scanning thermal microscopy (SThM). A systematic analysis of the thermal conductivity measurement performance (sensitivity and spatial resolution) of thermoresistive SThM probe configurations that are available commercially is of interest to practitioners. In this work, the authors developed and validated 3D finite element models of noncontact SThM with self-heated thermoresistive probes under ambient conditions with the probe–sample heat transfer in transition heat conduction regime for the four types of SThM probe configurations resembling commercially available products: Wollaston wire (WW) type probe, Kelvin nanotechnology (KNT) type probe, doped silicon (DS) type probe and nanowire (NW) type probe. These models were then used to investigate the sensitivity and spatial resolution of the WW, KNT, DS and NW type probes for thermal conductivity measurements in noncontact mode in ambient conditions. The comparison of the SThM probes performance for measuring sample thermal conductivity and for the specific operating conditions investigated here show that the NW type probe has the best spatial resolution while the DS type probe has the best thermal conductivity measurement sensitivity in the range between 2 and 10 W·m−1·K−1. The spatial resolution is negatively affected by large probe diameters or by the presence of the cantilever in close proximity to the sample surface which strongly affects the probe–sample heat transfer in ambient conditions. An example of probe geometry configuration optimization was illustrated for the WW probe by investigating the effect of probe wire diameter on the thermal conductivity measurement sensitivity, showing ∼20% improvement in spatial resolution at the diameter with maximum thermal conductivity measurement sensitivity.