Achieving thermally or optically switchable material via Pump-Probe Detection

Growing technological demand for thermal management or optical manipulation at the nanoscale stems from pursuing high-density and high-performance microelectronics. Time-resolved pump-probe technique provides the platform for understanding physical properties of material below nanosecond-time and micrometer-space scales. Based on the pump-probe technique, we have studied thermal conduction in various oxide/nitride films with wide band gap, including degenerated semiconductor films. Both free electrons and phonons act as carriers of thermal conduction in degenerated semiconductor films. Importantly, free electron contribution is independent on phonon contribution, and it can be described by Wiedemann-Franz law, even in the metal-insulator-transition material VO₂. Such findings provide a new guideline to design thermal switching materials. By utilizing hydrogeneration/dehydrogenation reaction, we achieved a giant thermal switching ratio (~15) between metal Mg₂Ni and insulator Mg₂NiH₄, which is sufficient for designing thermal switch or thermal transistor.

Furthermore, the pump-probe technique also allows us to investigate the laser-driven optical switching at the nanoscale region. Transient increase in transmission can be tailored by the irradiation intensity of pumping laser in organic and inorganic semiconductor materials. These transient transmissions originate from the Pauli blocking in the conduction band or polaron states, which open a new way of designing ultrafast optical switching device.