Akifumi Yao

Extremely low thermal conductivity of high density and ordered 10 nm-diameter silicon nanowires array

We present the fabrication and thermal conductivity of a high-density and ordered 10 nm-diameter Si nanowires (SiNWs) array for thermoelectric devices, realized through the use of a bio-template mask as well as neutral beam etching techniques. The SiNWs were embedded into spin-on-glass (SoG) to measure the thermal conductivity of the SiNWs-SoG composites. By decreasing the thickness of SiNWs-SoG composites from 100 nm to 30 nm, the thermal conductivity was drastically decreased from 1.8 ± 0.3 W m−1 K−1 to 0.5 ± 0.1 W m−1 K−1. Moreover, when the electrical conductivities of 100 nm-long SiNWs were 1.7 × 10 S m−1, 6.5 × 103 S m−1 and 1.3 × 105 S m−1, their thermal conductivities of SiNWs-SoG composites were 1.8 ± 0.3 W m−1 K−1, 1.6 ± 0.2 W m−1 K−1 and 0.7 ± 0.2 W m−1 K−1, respectively. The cross-plane thermal conductivity of the fabricated 10 nm diameter SiNWs-SoG composites was dependent on their thickness and the electrical conductivity of SiNWs, which were significantly decreased from bulk.

Composite films of highly ordered Si nanowires embedded in SiGe0.3 for thermoelectric applications

We fabricated a high-density array of silicon nanowires (SiNWs) with a diameter of 10 nm embedded in silicon germanium (SiGe0.3) to give a composite thin film for thermoelectric device applications. The SiNW array was first fabricated by bio-template mask and neutral beam etching techniques. The SiNW array was then embedded in SiGe0.3 by thermal chemical vapor deposition. The cross-plane thermal conductivity of the SiNW–SiGe0.3 composite film with a thickness of 100 nm was 3.5 ± 0.3 W/mK in the temperature range of 300–350 K. Moreover, the temperature dependences of the in-plane electrical conductivity and in-plane Seebeck coefficient of the SiNW–SiGe0.3 composite were evaluated. The fabricated SiNW–SiGe0.3 composite film displayed a maximum power factor of 1 × 103 W/m K2 (a Seebeck coefficient of 4.8 × 103 μV/K and an electrical conductivity of 4.4 × 103 S/m) at 873 K. The present high-density SiNW array structure represents a new route to realize practical thermoelectric devices using mature Si processe...

Synthesis and evaluation of fluorinated nano diamond for application of polymer composite

This paper reports on the preparation and evaluation of fluorinated nano diamond (FND) for application of polymer composite. The fluorination of the nano diamond (ND) not only removes the impurities carbon layers of ND surface but also improves the solvent dispersibility of ND. ND and FND were successfully fabricated by composite of epoxy resin. Especially, FND was well-dispersed in the epoxy matrix due to its good solvent dispersibility of FND. The measured thermal conductivity of the ND/epoxy composite and FND/epoxy composite were 0.38W/mK at ND-1wt.% and 0.41W/mK at FND-5wt.%, respectively. High electrical insulation and thermal conductivity of FND/epoxy composites are promising for an application of the electrical package field.

Evaluation of etching property in C 3 H X F (6−X) plasma

The etching properties of C₃F₆, C₃HF₅, C₃H₂F₄, and C₃H₃F₃ were evaluated to investigate the effects of replacement of fluorine atoms to hydrogen atoms in the unsaturated fluorocarbon. Etching rates of SiO₂ were decreased, and deposition rates of CFn films on p-Si wafer were increased with increasing the hydrogen atoms in the molecule. XPS spectra show that the contribution of strong C-C bond in the CFn film was also increased with increasing the hydrogen atoms in the molecule. Consequently, the highest selectivity for SiO₂/PR was obtained in C₃H₂F₄ plasma, while the highest etching rate of SiO₂ was obtained in C₃F₆ plasma. The SiO₂ etching was performed using patterned holes of 40 nm diameters in C₃H₂F₄ plasma to evaluate the feasibility of C₃H₂F₄ for the contact hole etching gas. The cross section SEM image shows that the vertical shaped holes without bowing or tapering were obtained with C₃H₂F₄ plasma. The fine etch property of C₃H₂F₄ was obtained as a result of the appropriate balance between fluorine atoms and hydrogen atoms in the molecule.

Thermal conductivity of 10 nm-diameter silicon nanowires array fabricated by bio-template and neutral beam etching

In this paper, we present the fabrication and thermal conductivity measurements of a 10 nm-diameter Si nanowires (SiNWs) array for thermoelectric (TE) devices applications. The SiNWs were fabricated by bio-template and neutral beam etching techniques. Then, the SiNWs were embedded into spin-on-glass (SOG) for the measurement of the thermal conductivity. The measured thermal conductivities of the SiNWs with lengths of 50 nm and 100 nm were 2.1 ± 0.6 W/mK and 9.5 ± 1.4 W/mK, respectively.