Dependence of nanoscale heat transfer across a closing gap on the substrate material and ambient humidity

We investigate the heat transfer across a closing nanoscale gap between an operational microelectronic device and a static substrate in ambient conditions. The device contains an embedded microheater and a nanoscale metal wire that works as a thermometer. The heater causes a microscale protrusion by thermal expansion such that its surface approaches the substrate until contact occurs. Meanwhile, the metal wire located near the center of the protrusion surface measures the temperature of the protrusion, which is dependent on the size of the gap, the substrate material, and the ambient conditions. We study the nanoscale heat transfer using three different substrates and find that their thermal conductivity plays an essential role. Finally, the experiments are conducted under different relative humidity (RH) conditions. The results show that the ambient humidity can also affect the nanoscale heat transfer when RH>75%.