Nanothermometry of electrons and phonons

Infrared radiation thermometry, which derives temperature of an object from the intensity of emitted radiation, suffers from diffraction-limited insufficient spatial resolution. This limit is overcome by introducing a terahertz near-field technique to locally probe fluctuating electromagnetic (EM) evanescent fields. We report here nanoscale hot electron temperature distribution directly mapped with a newly developed near-field technique, called scanning noise microscope (SNoiM). Nanoscale lattice temperature distribution in the same sample was also mapped with a commercially available contact-type scanning thermal microscope (SThM). By comparison, subtle but essential difference has been found between the distributions of the lattice temperature and the electron temperature, leading to detailed understanding of the hot electron kinetics along with the phonon-relaxation process.