Satoshi Iguchi

Diamond-like carbon films prepared by pulsed-laser evaporation

Diamond-like carbon thin films were prepared by pulsed-laser evaporation. In this method a carbon target was irradiated by a XeCl laser with a power density of 3×108 W/cm2 and carbon atoms, together with a small number of ions, were produced. Deposition rates and film properties changed sensitively with substrate temperature. The films deposited at 50°C were diamond-like, having reasonable hardness, high refractive index (2.1–2.2 at 633 nm), optical transparency in the infrared, electrical resistivity of 108 Ω cm and chemical inertness (no dissolution in a HF∶HNO3 solution). The band gap measured from optical absorption was 1.4 eV. Raman spectrum and infrared absorption, whose features varied with the substrate temperature, were also measured. The films were amorphous and no crystallinity was observed, as confirmed by x-ray diffraction, transmission electron diffraction and Raman spectroscopy. Hydrogen atoms were incorporated in the films with a typical H/C ratio of 0.3. The application of a negative bias to the substrate modified the deposition due to the presence of ions.

Deposition of Diamond-like Carbon Films by Pulsed-Laser Evaporation

Diamond-like carbon thin films were deposited by pulsed-laser evaporation. A carbon target was irradiated by a Xe-Cl laser with a power density of 3×108 W/cm2. Ions were mixed with vaporized atoms. Deposition rates were typically 200 A/ min. Film properties changed with substrate temperature. The films deposited at 50°C were diamond-like, as confirmed by refractive index (2.1 to 2.2), optical transparenty and chemical resistance. Hydrogen-free films were produced. Optical band gap was 1.4 eV and electrical resistivity was 108 Ω-cm. No crystallinity was observed.

Nitrogen CARS thermometry for a study of temperature profiles through flame fronts

Abstract Using coherent anti-Stokes Raman spectroscopy (CARS), we have performed detailed axial and radial temperature surveys in a premixed methane-air flame at atmospheric pressure with a special emphasis on measurements of temperature profiles through thin flame fronts. The temperature is inferred from N 2 CARS spectra. The thickness of flame fronts for flames with a stoichiometric mixture is about 700 μm, while it broadens considerably in a fuel rich flame. The spatial resolution for measuring the temperature profile is about 100 μm.

Effect of Hydrocarbon Molecular Structure on Diesel Exhaust Emissions Part 2: Effect of Branched and Ring Structures of Paraffins on Benzene and Soot Formation

In order to determine diesel fuel characteristics that might influence particulate matter (PM) emission, we have conducted a detailed investigation that combines combustion/exhaust emission measurements, in-cylinder observations, fuel analyses and chemical reactor experiments. A comparison between three representative diesel fuels, viz., “Base” (Japanese market fuel), “Improved”(lighter fuel with lower aromatics) and Swedish “Class-1” yielded the following results: (1) The amount of PM emission decreases in the order of “Base” > “Class-1” > “Improved”. Unexpectedly enough, “Class-1” produces more PM than “Improved” despite its significantly lower distillation temperature, and lower aromatics and sulfur content. (2) There is little difference in the combustion characteristics of the three fuels. (3) Only “Class-1” contains significant quantities of iso and naphthenic structures. (4) Flow reactor pyrolysis shows that “Class-1” produces the largest amount of PM precursors, such as benzene and toluene. These results suggest that the presence of branched and ring structures can increase exhaust PM emissions. This finding was confirmed by flowreactor and shock tube experiments using hexanes, which revealed that isoand cycloparaffins produce more benzene and soot than n-paraffins do. The results obtained in this study indicate that the specific molecular structure of the paraffinic components needs to be considered as one of the diesel fuel properties closely related to PM formation.

The Effects of ‘Inclination Angle of Swirl Axis’ on Turbulence Characteristics in a 4-Valve Lean-Burn Engine with SCV

It has been demonstrated that the in-cylinder turbulence of a 4 valve engine with a swirl control valve (SCV) is enhanced by inclined swirl. This paper examines the effects on turbulence of varying swirl inclination angle defied as the inverse tangent of the vertical component of total angular momentum divided by the horizontal component. Experiments were conducted on a 4-valve single cylinder engine with SCV using a backward-scatter LDV and BSA (Bust Spectrum Analyzer). The results show that although total angular momentum is greatest with horizontal swirl, turbulence intensity measured in the center of the combustion chamber attains a peak value when the swirl inclination angle is between 30 and 45 degrees from the cylinder axis under the same flow rate.

Lean combustion characteristics of locally stratified charge mixture: Basic studies of in-vessel combustion ignited by laser

Abstract In order to study the trade-off between improved lean combustion and reduced NO x emissions under a locally stratified charge mixture, this paper examines the effects of the rich mixture volume on combustion duration and the NO x emissions under the same total equivalence ratio in a combustion vessel. The rich methane-air mixture in a soap bubble was ignited at the center of the bubble by a pulsed YAG laser. As a result, it was found that the magnitude of the NO x emissions does not increase as the rich mixture volume increases up to a critical volume, but the combustion duration at that time shortens remarkably. The same tendency was also obtained by means of computer simulation using a 4-cylinder lean burn engine.

Photochemical Vapor Deposition of Aluminum Thin Films

Using dimethylaluminum hydride as the source gas and an ArF laser as the light source, aluminum thin films with low electrical conductivity were deposited via photochemical reactions. To emphasize surface reactions, vapor pressure was kept low with a t pical value of 6.7×10−3 Pa. The laser energy density was typically 23 mJ/cm 2 per pulse. The deposition rate of aluminum films became reasonably high above a substrate temperature of 90 °C and increased thereafter with substrate temperature. The electrical resistivity was about four times greater than the bulk aluminum value. A strongly nonlinear dependence of the deposition rates on laser energy density was observed. The incremental change in thickness per pulse increased with the inverse of the pulse repetition rate, which indicated, together with area selectivity, the importance of surface photolysis of absorbed molecules.

Deposition of a-Si Films Using Silane Molecular Beams Excited by Heated Wire and ArF Laser

Amorphous silicon films were deposited by using silane molecular beams excited either by ArF laser beams or heated tungsten wires. Reaction mechanisms are discussed on the basis of the dependence of deposition rates on substrate temperature and, in the case of the heated-wire method, on wire temperature.