Koichi Niihara

Chemical vapour-deposited silicon nitride: Part 2 Density and formation mechanism

Chemical vapour-deposited Si3N4 (pyrolytic Si3N4) has been prepared from a SiCl4 + NH3/H2 system at 1100 to 1500° C under total pressures of 5 to 300 Torr. The densities of crystalline deposits are 3.15 to 3.18 g cm−3, nearly independent of the deposition conditions. On the other hand, the densities of amorphous deposits depend strongly on the deposition conditions and have a minimum value of 2.60 g cm−3 at 1200° C and 40 Torr. The deposition rate of Py-Si3N4 obeys a linear law. The rate of increase in thickness is markedly affected by the deposition conditions, its maximum value being 0.73 mm h−1 for cystalline deposits at 1400° C and 40 Torr, and 0.36 mm h−1 for the amorphous deposits at 1300° C and 40 Torr. The activation energies of formation of Py-Si3N4 are 30 to 33 and 53 kcal mol−1 for the amorphous and crystalline deposits, respectively. The formation mechanism is also discussed.

Formation of carbon nanocapsules with SiC nanoparticles prepared by polymer pyrolysis

Carbon nanocapsules with SiC nanoparticles were produced by thermal decomposition of polyvinyl alcohol with SiC clusters at 500 °C in Ar gas atmosphere. High-resolution electron microscopy also showed the formation of carbon hollow structures such as nanoparticles, polyhedra, and clusters. The present work indicates that the pyrolysis of polymer materials with clusters is a useful fabrication method for the mass-production of carbon nanocapsules at low temperatures compared to the ordinary arc discharge method.

Synthesis of TiO2 Nanosized Powder by Pulsed Wire Discharge

Nanosized powders of TiO2 have been synthesized by pulsed wire discharge (PWD) using titanium wire in oxygen gas. The relative energy (R, R = Ei/Ev), which is the ratio of the charged energy of the capacitor (Ei) to the vaporization energy of the wire (Ev), was changed from R = 1.9 to 52.1. The X-ray diffraction patterns of nanosized powders synthesized at various relative energies showed that all the samples had peaks of rutile and anatase. The rutile content increased with the increase in the relative energy, and changed from 6 to 84 vol % at 100 kPa. The median particle diameter decreased from 30.9 to 20.4 nm. Control of the rutile content and particle size was possible by varying the relative energy used for PWD.

Elementary Analysis of Diamond-Like Carbon Film Formed by Focused-Ion-Beam Chemical Vapor Deposition

This is the first report on the precise elemental composition of a diamond-like carbon (DLC) thin film fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD). The atomic fraction of the FIB-CVD DLC film has been determined to be C:Ga:H=87.4:3.6:9.0 at. % using Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). The hydrogen content of the FIB-CVD DLC film was lower than that of DLC films formed using other CVD methods.

Specific heat and thermal conductivity of HoN and ErN at cryogenic temperatures

The rare earth nitrides, HoN and ErN, were synthesized by the hot isostatic pressing method. Their specific heat CH(T) and the thermal conductivity κ were measured at cryogenic temperatures. In zero field, the peak values of the C0(T) of HoN and ErN are larger than those of the magnetic regenerators such as Er3Ni. The peak values of the adiabatic temperature change ΔT(T) of HoN and ErN showed similar or larger values compared with those of the candidate materials for the magnetic refrigerants such as ErAl2. The thermal conductivity of HoN and ErN are comparable to those of the magnetic regenerators such as Er3Ni. The present results indicate that HoN and ErN are promising materials as the magnetic refrigerant and regenerator for the cryogenic refrigeration system.

Effects of Annealing on Material Characteristics of Diamond-Like Carbon Film Formed by Focused-Ion-Beam Chemical Vapor Deposition

The effects of annealing on the material characteristics of a diamond-like carbon (DLC) thin film fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) were investigated. The elementary analysis, using Rutherford backscattering spectrometry and elastic recoil detection analysis, and measurement of hardness and Youngs modulus, using a nanoindentation technique, were performed on the FIB-CVD DLC thin film by annealing for 1 h in the temperature range from room temperature to 1273 K. Elementary analysis indicated that the Ga content in the FIB-CVD DLC film used as an ion source began to decrease considerably at 523 K and the H content also began to decrease at 773 K. On the other hand, the hardness and Youngs modulus of the FIB-CVD DLC film were found to decrease beyond 773 K. This decrease in hardness is ascribed to the variation in H content rather than in Ga content in the film.

Densely Packed Linear Assembles of Carbon Nanotube Bundles in Polysiloxane-Based Nanocomposite Films

Linear assemblies of carbon nanotubes (LACNTs) were fabricated and controlled in polysiloxane-based nanocomposite films and the effects of the LACNTs on the thermal and electrical properties of the films were investigated. CNTs were dispersed by mechanical stirring and sonication in a prepolymer of polysiloxane. Homogeneous suspensions were cast on polyamide spacers and oriented by linear-assembly by applying DC and switching DC electric fields before the mixture became cross-linked. Densely packed LACNTs that fixed the composite film surfaces were fabricated with various structures and thicknesses that depended on the DC and switching DC conditions. Polymer nanocomposites with different LACNT densities exhibited enhanced thermal and electrical conductivities and high optical transmittances. They are considered promising structural materials for electronic sectors in automotive and aerospace applications.

Mechanical properties and residual stress in AlN/Al mixed films prepared by ion-beam-assisted deposition

Mixed films composed of aluminum and aluminum nitride (AlN) were prepared on a silicon substrate by evaporation of aluminum and simultaneous irradiation with a nitrogen ion beam, ion-beam-assisted deposition, where the nitrogen ion beam current was changed so as to obtain different compositional films. The composition of the films and chemical states of aluminum and nitrogen were analyzed by x-ray photoelectron spectroscopy (XPS). Mechanical properties of the films were characterized by a nano-indentation method. Residual stresses in the films were evaluated by film curvature measured with an optical cantilever system. The XPS studies show that the chemical state of aluminum changes from metallic to nitride with increasing the ion beam current density during synthesis. The nano-indentation tests reveal that the film hardness increases and the recovery behavior changes from plastic to elastic as the ion beam current density increases. From both results, it is proposed that the films change from mainly meta...

Synthesis of

A pulsed wire discharge method was used in the synthesis of zirconia-alumina nanocomposite powders by mixing zirconium plasma with aluminum plasma and cooling them together in an oxygen atmosphere. The products formed were characterized by powder X-ray diffractometry, transmission electron microscopy, and Brunauer-Emmet-Teller surface-area analysis. These powders showed a sphere morphology with less agglomeration. Specific surface area of these powders was 25-137 m2 /g depending on the oxygen pressure. Typically, this powder could be densified at 1100 degC, which is important for producing a high-toughness nanocomposite

hboxAl_2hboxO_3

Chromium magnesium oxynitride ((Cr,Mg)(N,O)) thin films have been prepared by pulsed laser deposition (PLD) method with changing the surface area ratio of Mg target (SR) from 0 to 100 %. As a result of the analysis by energy dispersive X-ray spectroscopy (EDX), it was found that magnesium content in the total metallic elements (Cr1-x, Mgx) are controlled by changing SR from 0 to 100 % to be the x ranging from 0 to 1.0. Since the crystal structure of main phase in all thin films was found to be NaCl type, the XRD results showed that the thin films were mainly consisted of (Cr,Mg)(N,O). The hardness of (Cr,Mg)(N,O) thin films were increased almost linearly up to SR = 50 %, above which it decreases rapidly. The maximum Vickers hardness (HV) of 3600 was obtained for the thin film which was prepared by SR = 50 %, and the minimum HV of 1650 was obtained for the thin film which was prepared by SR = 100 %.