Masahiro Nomura 교수

The world communicates to our senses of vision, hearing, and touch in the language of waves, because light, sound, and even heat essentially consist of microscopic vibrations of different media. The wave nature of light and sound has been extensively investigated over the past century and is now widely used in modern technology. However, the wave nature of heat has been the subject of mostly theoretical studies because its experimental demonstration, let alone practical use, remains challenging

We demonstrate room temperature continuous-wave laser operation at 1.3 mum in a photonic crystal nanocavity with InAs/GaAs self-assembled quantum dots by optical pumping. By analyzing a coupled rate equation and the experimental light-light characteristic plot, we evaluate the spontaneous emission coupling factor of the laser to be ~ 0.22. Three-dimensional carrier confinement and a low transparent carrier density due to volume effect in a quantum dot system play important roles in the cw laser

Phonon engineering is expected to contribute to further development of various fields and technologies such as electronics, photonics, thermal engineering, and materials science. Although phonons inherently exist in condensed matter, their behavior strongly depends on the scale of the system and the materials, and they play a major role in electrical, optical, thermal, and mechanical properties. Therefore, researchers have been attempting to find effective ways to control phonons to modify the m

We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain. The investigated nanocavities contain only 0.4 quantum dots on an average; an ultra-low density quantum dot sample (1.5 x 10(8) cm(-2)) is used so that a single quantum dot can be isolated from the surrounding quantum dots. Laser oscillation begins at a pump power of 42 nW under resonant condition, while the far-detuning conditions require ~145 nW for lasing. This spectral

Thermal transport at the nanoscale level is attracting attention not only because of its physically interesting features such as the peculiar behavior of phonons due to their pronounced ballistic and wave-like properties but also because of its potential applications in alleviating heat dissipation problems in electronic and optical devices and thermoelectric energy harvesting. In the last quarter-century, researchers have elucidated the thermal transport properties of various nanostructured mat

This paper describes newly developed delay and power monitoring schemes for minimizing power consumption by means of the dynamic control of supply voltage V/sub DD/ and threshold voltage V/sub TH/ in active and standby modes. In the active mode, on the basis of delay monitoring results, either VDD control or VTH control is selected to avoid any oscillation problem between them. In V/sub DD/ control, on the basis of delay monitoring results, VDD is adjusted so as to be maintained at the minimum v

Substituted phenylpropanoic acid derivatives were prepared as part of a search for subtype-selective human peroxisome proliferator activated receptor alpha (PPARalpha) activators. Structure-activity relationship studies indicated that the nature and the stereochemistry of the substituent at the alpha-position of the head part containing the carboxyl group, the distance between the carboxyl group and the central benzene ring, the linking group between the central benzene ring and the distal benze

In-plane thermal conduction and phonon transport in both single-crystalline and polycrystalline Si two-dimensional phononic crystal (PnC) nanostructures were investigated at room temperature. The impact of phononic patterning on thermal conductivity was larger in polycrystalline Si PnCs than in single-crystalline Si PnCs. The difference in the impact is attributed to the difference in the thermal phonon mean free path (MFP) distribution induced by grain boundary scattering in the two materials.

Thermal phonon transport in silicon nanowires (Si NWs) and two-dimensional phononic crystal (2D PnC) nanostructures was investigated by measuring thermal conductivity using a micrometer-scale time-domain thermoreflectance. The impact of nanopatterning on thermal conductivity strongly depends on the geometry, specularity parameter, and thermal phonon mean free path (MFP) distribution. Thermal conductivities for 2D PnC nanostructures were found to be much lower than that for NWs with similar chara

Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80 nm. The th

Temporal coherence of a continuous-wave photonic crystal nanocavity laser is investigated in detail using interference experiments at room temperature. The nanocavity laser operates at $1.3\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ with InAs quantum dot gain material and has a very high spontaneous emission coupling factor $\ensuremath{\beta}=0.9$ with a threshold absorbed pump power of $\ensuremath{\sim}375\phantom{\rule{0.3em}{0ex}}\mathrm{nW}$. The coherence around the laser thres

We demonstrate the power enhancement of planar-type uni-leg poly-Si thermoelectric generators by nano-patterning. The thermoelectric generators were fabricated on an SOI wafer by a conventional lithography-based process. The size of the phononic nano-patterning (300 nm in period) was designed based on the thermal phonon mean free path spectrum. The thermal conductivity of the Si membrane was reduced by 60% compared with an unpatterned one, which resulted in the doubled thermoelectric figure-of-m