Hidetoshi Saitoh

Preparation and characterization of nanocrystalline cubic boron nitride by microwave plasma‐enhanced chemical vapor deposition

Polycrystalline boron nitride films have been deposited using microwave plasma‐enhanced chemical vapor deposition. IR absorption spectra of films deposited using NaBH4 as the boron source in NH3 and H2 gases showed absorptions which are nearly the same as the characteristic vibrational modes seen in cubic and pyrolytic boron nitrides. Films deposited at 5 Torr also showed electron diffraction patterns for pyrolytic boron nitride, turbostratic boron nitride and cubic boron nitride. At higher gas pressures, only rings consistent with the formation of amorphous and cubic boron nitride were observed. Although the Raman spectra from a film deposited at 60 Torr showed broad peaks at ∼1080 and ∼1310 cm−1, the positions of the Raman lines for cubic boron nitride, no x‐ray diffraction lines could be observed except that of the silicon substrate.

Epitaxial Growth of Zinc Oxide Whiskers by Chemical-Vapor Deposition under Atmospheric Pressure.

ZnO whiskers were epitaxially grown by a chemical-vapor deposition technique employed at atmospheric pressure. Highly oriented ZnO whiskers grew at a substrate temperature of 550°C on (0001)α-Al2O3 substrates with a growth rate of 3.7 nm/s. X-ray diffractometry revealed that the epitaxial relationship between the whiskers and the substrate was determined as ZnO[1010](0001)//Al2O3[1210](0001) or ZnO[1210](0001)//Al2O3[1010](0001). In addition, the full-width at half maximum value of the (0002) reflection was as low as 0.43°. Images obtained using a scanning electron microscope were analyzed and it was found that the whisker tip likely has a radius of curvature of approximately 20 nm. The typical number density of the whiskers has reached 1.3×105mm-2.

Conductive indium-doped zinc oxide films prepared by atmospheric-pressure chemical vapour deposition

Abstracts are not published in this journal

Growth of cubic boron nitride from vapor phase

Abstract Both physical and chemical vapor deposition (PVD and CVD) methods for the growth of cubic boron nitride ( c -BN) have been reported. These experiments, reviewed in this article, produced a mixture of phases with some evidence of cubic materials. These materials were of limited crystallite size and perfection, much too poor to be useful for electronic devices or for hard coating applications. Using a solid boron source, NaBH 4 , the preparation of c -BN by microwave plasma enhanced CVD has been investigated. When the deposition rate is low, the BN film deposited on an untreated single crystal silicon wafer, displayed a weak infrared absorption spectra for the turbostratic structure of BN. With submicron diamond powder scattered on the substrate, the BN films displayed strong infrared absorption attributable to c -BN. Transmission electron microscopy revealed that c -BN crystals, 50–100 nm in size, grew from the diamond submicron crystals. This suggests that c -BN preferentially nucleates on diamond.

Hardness and elastic properties of Bi2O3-based glasses

The hardness and elastic properties of 20PbO · xBi2O3 · (80 − x)B2O3 glasses with x = 20–60 were evaluated through usual Vickers indentation and nanoindentation tests. The glass transition temperature (Tg = 295–421°C), Vickers hardness (Hv = 2.9–4.5 GPa), true hardness (H = 1.5–3.8 GPa) and Youngs modulus (E = 24.4–72.6 GPa) decreased monotonously with increasing Bi2O3 content. This compositional trend demonstrates that the strength of Bi–O chemical bonds in these glasses is considerably weak compared with B–O bonds and plastic deformations under indentation loading occur easily. The elastic recovery after unloading was about 45% for the glasses with x = 20–50, and the Poissons ratio was 0.27 for the glass with x = 20. The fracture toughness was evaluated to be 0.37–0.88 MPam1/2 from the values of Hv and E, and it was proposed that not only weak Bi–O bonds but also boron coordination polyhedra (BO3 or BO4) and their arrangements affect on crack formation. From the temperature dependence of Vickers hardness up to the glass transition region, it was suggested that the glasses with high Bi2O3 contents belong to the category to fragile glass-forming liquids.

Growth of cubic boron nitride on diamond particles by microwave plasma enhanced chemical vapor deposition

The nucleation and growth of cubic boron nitride (c‐BN) onto diamond powder using solid NaBH4 in low pressure gas mixtures of NH3 and H2 by microwave plasma enhanced chemical vapor deposition has been studied. Boron nitride was deposited on submicron diamond seed crystals scattered on (100) silicon single crystal wafers and evidence was found for the formation of the cubic phase. Diamond powder surfaces appear to preferentially nucleate c‐BN. In addition it was found that the ratio of c‐BN to turbostratic structure boron nitride (t‐BN) deposited increases with decreasing NH3 concentration in H2. It is suggested that this may be due to an increased etching rate for t‐BN by atomic hydrogen whose partial pressure may vary with NH3 concentration.

Rice Husk‐Derived Graphene with Nano‐Sized Domains and Clean Edges

A new synthetic method is demonstrated for transforming rice husks into bulk amounts of graphene through its calcination and chemical activation. The bulk sample consists of crystalline nano-sized graphene and corrugated individual graphene sheets; the material generally contains one, two, or a few layers, and corrugated graphene domains are typically observed in monolayers containing topological defects within the hexagonal lattice and edges. Both types of graphenes exhibit atomically smooth surfaces and edges.

Homogeneous Growth of Zinc Oxide Whiskers

Several common modes of crystal growth provide particularly simple and elegant examples of spontaneous pattern formation not only in nature but also under artificial circumstances. We have already reported that well-organized ZnO whiskers are epitaxially grown using a chemical vapor deposition technique [Satoh et al..: Jpn. J. of Appl. Phys. 38 (1999) L586]. One aim of this study is to determine the optimum growth conditions for obtaining the structure containing homogeneous whiskers grown with a relatively high growth rate. A substrate temperature of 550°C and a vaporizing temperature of 125°C are the most appropriate for obtaining homogeneous whiskers. Whiskers are highly oriented in the a-and c-axes directions of the hexagonal structure. The growth rate reached a maximum value as high as 7.5 nm/s.

Quantitative Analysis of Hydrogen in Amorphous Films of Hydrogenated Carbon Nitride

The amorphous phase of hydrogenated carbon nitride, a-CNx:H (0 x 1), films may have clusters consisting of a mixture of sp2- and sp3-hybridized materials with cluster sizes of 0.2–2 nm. The hydrogen termination limits the size of the carbon and carbon nitride clusters. It also influences the mechanical properties of the sample. In this experiment, the relationship between the hydrogen content and the mechanical properties of carbon and related materials was investigated using elastic recoil detection analysis (ERDA), nanoindentation techniques and Raman spectroscopy. The samples were classified into three categories of hardness: mechanically soft a-CNx:H (hardness: 1–8 GPa), mechanically hard a-CNx:H (8–30 GPa) and hard hydrogenated amorphous carbon (a-C:H) (more than 30 GPa). The hydrogen contents of the sample were 10–50 at.%, 5–40 at.%, and less than 3 at.% for soft a-CNx:H, hard a-CNx:H and hard a-C:H, respectively.

Synthesis of Amorphous Carbon Nitride Films Using Dissociative Excitation Reaction

In this investigation, we aim to produce highly nitrogen-doped carbon, so-called carbon nitride, films without the incorporation of hydrogen. In the physical vapor deposition process, irradiation by energetic nitrogen ions increases nitrogen content without the incorporation of hydrogen. In the chemical vapor deposition process, hydrogen should be included into the film due to the use of a hydrocarbon reactant. In this study, the synthesis of carbon nitride films having high nitrogen and low hydrogen contents was attempted using a chemical-vapor-deposition apparatus. First of all, a CH3CN+Ar mixture was selected as a reactant including hydrogen. Dehydrogenation of the reactant was carried out by plasma decomposition. Second, as a reaction system without hydrogen, BrCN+Ar was also selected for starting materials. The dissociative excitation reaction of cyanides with argon metastable atoms produces CN radicals, Ar(3P0,2)+BrCN →Ar+Br+CN(A2Πi, B 2Σ+, 4Σ+, 4Π). This finally proceeds to the deposition of CN radicals to form the carbon nitride film on a solid-state surface. When using the former reactant, large amounts of hydrogen remained in the amorphous carbon nitride films, although the amount of hydrogen varied with deposition conditions. The sample formed using the latter reactant was amorphous carbon nitride with very little hydrogen. The nitrogen fraction [N]/([N]+[C]) of the sample using the latter rectant is as high as ~0.3, higher than those obtained from the samples synthesized with the former reactant.