Fusao Hojo

Preparation and characterization of thermoconductive polymer nanocomposite with branched alumina nanofiber

A highly thermoconductive resin with branched filler is reported. The filler was fabricated by calcination of aluminium isopropoxide adsorbed onto paper filter (cellulose fibers). Scanning electron microscopy and x-ray diffraction measurement demonstrated that the filler consists of α-alumina nanofiber with a branched structure. The thermal conductivity of the filler-resin nanocomposite was two to five times larger than that predicted by the well-known Bruggeman equation, which postulates the composite with spherical filler in the matrix. The branched shape of the α-alumina nanofiber increased the probability of formation of phonon paths with lower thermal resistance, leading to the high thermal conductivity of the nanocomposite.

Highly Thermoconductive Polymer Nanocomposite with a Nanoporous α-Alumina Sheet

A highly thermoconductive insulative polymer nanocomposite with a nanoporous alpha-alumina sheet was reported. The thermal conductivity of the nanocomposite along the surface normal was 12 W m(-1) K(-1) (41 vol % alumina), a value as high as that predicted theoretically for a nanocomposite with thermoconductive fillers that form a perfectly connected thermoconductive network. The high thermal conductivity is probably due to the continuous alpha-alumina phase that functions as an efficient phonon path in the nanocomposite. The results suggest that the structure of the filler is important for the design of highly thermoconductive materials.

Silicon–germanium alloys prepared by the heat treatment of silicon substrate spin-coated with organo-soluble germanium cluster

Abstract A novel technique for obtaining Si–Ge alloys using coating technique was developed, where an organo-soluble germanium cluster was spin-coated on a silicon substrate and the heat treatment of the substrate leads to the formation of a Si–Ge alloy on the substrate. The structural changes of the thin film and the silicon surface by alloying germanium into silicon were investigated by micro-Raman spectroscopy.

Nanocrystalline Silicon Film Prepared by Laser Annealing of Organosilicon Nanocluster.

A novel process for the formation of nanocrystalline silicon film using an organosilicon nanocluster as a precursor was developed. A thin-film coating of the organosilicon nanocluster, soluble in common organic solvents, is preheated and then annealed by an excimer laser to yield a film of nanocrystalline silicon with approximately 10 nm in size. The structural changes of the precursor film caused by preheating and excimer laser annealing were investigated by Raman spectroscopy.

Effect of Hydrogen Plasma Treatment on Formation of Amorphous Silicon Film Using Organosoluble Silicon Cluster as a Precursor

A novel process for the formation of amorphous silicon thin film by a coating technique using an organosoluble silicon cluster as a precursor was developed. The process of conversion of organic silicon film to inorganic silicon film was investigated by Raman and Fourier transform infrared (FT-IR) spectroscopies. Upon heat treatment of the precursor film, the disappearance of the organic substituent and the appearance of the transverse optical phonon band of amorphous silicon were observed in Raman spectra. The combination of heat and hydrogen plasma treatments of the thin film reduced the conversion temperature dramatically.

Silicon-germanium alloy prepared by laser-induced pyrolysis of organogermanium nanocluster spin-coated on Si substrate

Abstract The application of the laser-induced pyrolysis to the organogermanium nanocluster (OGE) spin-coated on a Si substrate provides a novel method to form a Si–Ge alloy. The structural and morphological changes via increasing the number of laser shots were studied by micro-Raman spectroscopy and scanning electron microscopy (SEM).

Formation of Liquid Crystalline Order and Its Effect on Thermal Conductivity of AlN/Liquid Crystalline Epoxy Composite

ABSTRACT The liquid crystalline (LC) order was introduced on aluminum nitride particles by the surface effect to increase the thermal conductivities of aluminum nitride/LC epoxy composites. X-ray diffraction and grazing incidence small-angle X-ray scattering analyses revealed that the LC epoxy resin cured on the surface of an α-Al2O3 substrate formed homeotropically aligned smectic layers to increase the thermal conductivity. Therefore, thermally treated aluminum nitride particles, which formed α-Al2O3 layers on their surfaces, were applied to prepare the composites with high thermal conductivity. The thermal conductivities of the resulting composites were 11–36% higher than those with the composites prepared using untreated aluminum nitride particles. GRAPHICAL ABSTRACT