Ryoichi Urao

Method for Cross-sectional Transmission Electron Microscopy Specimen Preparation of Composite Materials Using a Dedicated Focused Ion Beam System

: A new method for transmission electron microscope (TEM) specimen preparation using a focused ion beam (FIB) system that results in a lower rate of gallium (Ga) implantation has been developed. The method was applied to structural and analytical studies of composite materials such as silicon (Si)-devices and magneto-optical disk. To protect the specimens against Ga ion irradiation, amorphous tungsten (W) was deposited on the surface of the specimen prior to FIB milling. The deposition was quite effective in reducing the Ga implantation rate, and energy-dispersive X-ray (EDX) analysis of these specimens detected 0.3-1.5% Ga incorporated in the thinned area. FIB milling times for these specimens were 1.5-2 hr, with a starting thickness of about 50 µm. Although the milling rate was high, all the materials were properly prepared for TEM study, and clear crystal lattice images were observed on all specimens.

Effect of nitriding and TiN coating temperatures on the corrosion resistance of the combined surface modification layer

Abstract There are great demands that components become smaller, lighter and more efficient, and the environment of their use become severe. The combined surface modification techniques consisting of TiN coating on the nitrided steel have been studied to improve wear resistance for components used in severe environment. Our earlier studies indicate that the combination layer of nitriding and PVD TiN coating improves adhesion between coating layer and substrate of a tool steel, SKD11, but the corrosion resistance of the tool steel could not improve. The nitriding at approximately 400 °C improved the corrosion resistance of the steel compared to nitriding at 500–550 °C. The corrosion resistance of the steel coated with TiN at 450 °C after low temperature nitriding could not improve. The purpose of this study is to confirm an influence of coating temperature on corrosion resistance. The corrosion resistance of the steel heated at 480 °C in vacuum after nitriding at approximately 400 °C was less than that of the steel without heated at 480 °C in vacuum. Diffraction from ‘S-phase’ was detected in XRD measurement of the steel nitrided at approximately 400 °C. The S-phase did not appear from the nitrided layer at high temperature in the earlier study and could not be found from the steel heated at 480 °C in vacuum after nitriding at approximately 400 °C. When the S-phase appeared, the corrosion resistance of the layer improved. The relation between the S-phase and the high corrosion resistance was clarified. Adhesion of the combined layers was measured with a scratch tester. The adhesion of the steel nitrided at approximately 400 °C and with TiN at 350 °C was superior to the steel coated with TiN at the higher temperature without nitriding in a scratch examination. It clarified that the combined layer with superior adhesion and corrosion resistance was formed by the steel coated with TiN at low temperature after low temperature nitriding.

Method for Cross-sectional Thin Specimen Preparation from a Specific Site Using a Combination of a Focused Ion Beam System and Intermediate Voltage Electron Microscope and Its Application to the Characterization of a Precipitate in a Steel

In this study, we discuss a method for cross-sectional thin specimen preparation from a specific site using a combination of a focused ion beam (FIB) system and an intermediate voltage transmission electron microscope (TEM). A FIB-TEM compatible specimen holder was newly developed for the method. The thinning of the specimen using the FIB system and the observation of inside structure of the ion milled area in a TEM to localize a specific site were alternately carried out. The TEM fitted with both scanning transmitted electron detector and secondary electron detector enabled us to localize the specific site in a halfway milled specimen with the positional accuracy of better than 0.1 &mgr;m. The method was applied to the characterization of a precipitate in a steel. A submicron large precipitate was thinned exactly at its center for the characterization by a high-resolution electron microscopy and an elemental mapping.

Cross-sectional Specimen Preparation and Observation of a Plasma Sprayed Coating Using a Focused Ion Beam/Transmission Electron Microscopy System.

A focused ion beam (FIB) technique was applied to cross-sectional specimen preparation to observe an interface between a plasma sprayed coating and an aluminum (Al) substrate by transmission electron microscopy (TEM). The surface of the sprayed coating film has a roughness of several tens of microns. Sputter rates for the coating film and the substrate are greatly different. The rough surface and the difference in sputter rate cause problems in making TEM specimens with smooth side walls. The top surface of the coating film was planerized by the FIB before fabricating the TEM specimen. The interfaces were investigated by TEM and energy-dispersive X-ray (EDX) analysis. The TEM observation revealed that there is a 10 nm thick amorphous layer at the interface between the coating film and substrate. The coating film consists of two kinds of sublayers with bright and dark contrast. The bright contrast sublayers were amorphous layers with thickness of 2 approximately 10 nm. The Al/Fe X-ray intensity ratio was larger in bright contrast sublayers than that in dark contrast sublayers.

Plasma oxidation of Cu, Ti and Ni and the photoelectrochemical properties of the oxide layers formed

Abstract Plasma oxidation of Ti, Cu and Ni was carried out using a conventional diode-type glow discharge system. Structural and photoelectrochemical properties of the oxide layers formed were examined. Electron diffraction confirmed the formation of a TiO2, Cu2O/CuO, and NiO layer on the Ti, Cu, and Ni surfaces, respectively, after the plasma oxidation. Photoelectrochemical solar cells were fabricated using the oxide layers formed as a semiconductor electrode. The TiO2 electrodes showed moderate photoresponse under anodic potentials in a methanol aqueous solution, while the Cu2O/CuO and NiO electrodes showed a weak photoresponse under cathodic potentials. In conclusion, the TiO2 layers prepared by plasma oxidation work well as a semiconductor electrode for a photoelectrochemical cell and are stable in methanol solution.

Surface morphology of polycrystalline diamond films etched by Ar+ beam bombardment

Polycrystalline diamond films etched by Ar+ beam bombardment were investigated by scanning electron microscopy and Raman spectroscopy. In an ion sputtering apparatus, an etching rate of 14 μm C−1 was obtained when 10 kV-accelerated Ar+ ions penetrated with an angle of 15–30° from the normal. A number of cavities were created on the surface treated at low incidence angle. In contrast, micro-prominence was seen under the condition of high incidence angle. The degree of surface roughness on etched films was also changed with the incidence angle of the beam. A relatively smooth surface appeared after the treatment with an incidence angle of ⩾ 15°. Raman spectroscopy revealed that the physical etching of diamond is effective in obtaining high quality surface of polycrystalline diamond films.

Simultaneous plasma treatment for carburizing and carbonitriding using hollow cathode discharge

Ion carburizing and nitriding are effective processes for saving energy and providing polutionless surface treatment but have the disadvantage of using much electric energy. A cylindric subsidiary cathode was set up around a rod-shaped workpiece with a gap, and hollow cathode discharge for ion carburizing was studied. Thus, simultaneous plasma treatments for ion carburizing and ion car-bonitriding in one workpiece were researched using Cr-Mo steel to save electric treatment power. First, the effects of the gap between the test piece and subsidiary cathode and the pressure of electric discharge gas, including methane gas, on fundamental plasma treatment conditions were experimen-tally researched. It was found that the temperature for ion carburizing in a H2-N2-Ar-CH4 gas mixture was 1123 to 1193 K with a gap of 3 to 5 mm under a gas pressure of 133 to 532 Pa. Next, the test piece was ion carburized with hollow cathode discharge and carbonitrided with normal glow dis-charge simultaneously. The ion-carburized layer was formed in the area covered by the subsidiary cathode. The surface hardness was 800 Hv, the effective case depth was 0.6 mm, and the surface carbon content was 0.75 wt pct. An ion carbonitriding layer was formed in the area without the subsidiary cathode. The surface hardness was 700 Hv and the case depth was 0.1 mm. It is useful to form the different layers of ion carburizing and ion carbonitriding in one treatment process and to give different mechanical and tribological properties on one workpiece simultaneously.

Effects of lead on annealing properties of cold-drawn copper wire

Cold-drawn copper wires were made by cold-drawing after hot-rolling tough pitch copper rods which had been pre-heated at 673–973 K. The wires were annealed at 293–673 K to study their annealing properties. The effects of pre-heating the hot-rolled tough pitch copper rods, including lead, on the recrystallization behaviour of the cold-drawn copper wires were investigated by tensile tests, electrical resistivity measurements and structural observations. The half-softening temperature of annealed cold-drawn copper wires decreased when the hot-rolled copper rods were pre-heated at 873 K before cold-drawing. This behaviour was attributed to separation of lead dissolved in the copper matrix which is known to lower the half-softening temperature.

Characterization of TiB2 coated layer by X-ray lattice constant measurement

Abstract The internal stress in a TiB 2 coated layer, which is promising as a candidate surface coating material on the first wall of a fusion reactor, is determined from x-ray lattice constant measurements. The TiB 2 films on substrates such as Mo, Cu, Poco graphite, Ti-coated Mo and Al-coated Mo were prepared by using d.c. magnetron sputtering method. It was found that the tensile stress along the film plane was present in TiB 2 layers. The lowest stress value measured in specimens was 2.2 × 10 10 dyn / cm 2 for TiB 2 /Poco-graphite. The highest one was 19.6 × 10 10 dyn / cm 2 for TiB 2 /Cu. The difference of thermal expansions between TiB 2 and the substrate, and lattice defects introduced in the process of sputtering and/or the stoichiometry in the film are presumed to be the origin of the tensile stress. Experimental results obtained by using a 1 MeV HVEM are also reported.

Substrate temperature measured by a film-on-plate thermocouple during diamond growth using the combustion flame technique

Substrate temperature was monitored during combustion flame-assisted diamond growth. A platinum-coated copper plate was fabricated as not only the substrate for diamond growth but also the thermocouple to measure the substrate temperature. The Pt-Cu thermocouple demonstrated stable thermoelectric characteristics in a high-temperature argon atmosphere. The thermal electromotive force reached 15.9–16.0 mV at the initial heating to 970 °C. This was independent of the Pt film thickness. In addition, the thermoelectric characteristic of a 2 μm-thick sample was unchanged after second and third heatings. Diamond was deposited on the Pt-Cu thermocouple, having > 2 μm in Pt thickness, by a combustion flame technique using an oxyacetylene torch. A linear least-squares fit inserted in the relation between the substrate temperature and the growth rate suggests that the apparent activation energy for this experiment is 23 kcal mol−1.