13:00 〜 13:15
▲ [13p-N324-1] Observation of thermal evanescent fields on metal film by cryogenic THz near-field microscope
キーワード：Cryogenic near-field microscopy, THz microscopy, Thermal evanescent fields
The nanoscale thermal emission is difficult to detect for submicron devices, especially in extreme extremely low temperature (LT) environment. Passive THz scattering-type scanning near-field optical microscopy (s-SNOM), where no external light source is used, has been applied to probe thermally excited electromagnetic (EM) evanescent fields induced by fluctuating charge/current/dipole below sample surface at room temperature. For expanding the application of the passive THz s-SNOM to low-temperature studies, we developed a cryogenic one that can provide a 4.2 K high vacuum environment for specimens. The extremely weak thermally excited THz evanescent fields locally scattered by a metal probe with tip-height modulation method. The scattered near-field (NF) component is collected by confocal microscope with a highly sensitive THz detector (λ = 10.2 ± 0.9 μm). To show the LT s-SNOM capability, we fabricated a U-shaped NiCr filament (thickness and width of 30 nm and 3 μm, respectively) on a SiO2 substrate to generate Joule heating with electrical currents. The NF signals clearly detected on the NiCr/SiO2 sample with a step of 300 and 3 s of integration time. The shear-force control probe tip is operated in non-contact mode. We kept the bottom height of the probe tip was 5 nm from the sample surface during the scan. According to the NF decay profile, the NF signals observed on the NiCr surface are ascribed to the EM evanescent fields induced by the thermal excited random motion of conduction electron. After analyzing the relation between NF signal and temperature, we expect it can further study some thermal management in electronic circuits, applied in space and quantum computing, or LT electron transport in novel materials.