| 研究実績の概要 |
It has been known that phonon is responsible for the transmission of heat in solids. Acoustic phonons carry thermal energy along the temperature gradient direction from the high temperature area to low temperature area, forming the basic heat transport process. It is therefore very crucial to study the phonon spectroscopy for investigating the thermal properties of materials. Here, we aim at using an ultra-sensitive MEMS thermometer as a novel tool for investigating the photon spectroscopy. In particular, we are interested in the phonon prorogation in artificial phononic structures, i.e. phononic crystals.
In FY2017, we have succeeded in integrating phononic crystal structures of different designs on MEMS thermometers (GaAs MEMS bean resonators). BY using the thermistor, we measured the reduction of thermal conductance of the GaAs thin beam.
In FY2018, we have focused on constructing the phonon spectroscopy system by using an ultra-short pulse laser (femtosecond laser). Two light pulses with a modulated time delay were send to heat the MEMS beam, and then we measured the average temperature rise on the beam as a function of the time delay between two light pulses. We have succeeded in observing a very small phonon interference signal, and the phonon frequencies lies in the sub-terahertz range, which reasonably agrees with the theoretical expectation given by the size of the light absorption area. We believe this is an important result in the study of phonon spectroscopy in semiconductor micro/nano structures.
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