Experimental study of the effect of loading condition on fracture surface contact features and crack closure behavior in a carbon steel

To better understand the crack closure effect in the fatigue process, influence of fatigue stress amplitude and R ratio on the contact features of fracture surfaces in an annealed carbon steel was studied via two special experimental approaches: (i) the collection of the fracture debris fallen from the crack surfaces, and (ii) the direct observation of the contact zones on the fracture surface through an ink dyeing method. The results of this study show that the change of fatigue CMOD value as a function of a/W ratio depends strongly on the loading condition; the fatigue stress amplitude and R ratio are the major factors that determine the contacting status between the mating fracture surfaces; the severity of the fracture surface contact can also be characterized by the dropping rate of the fracture debris particles collected during the fatigue test.     

Electrical conductivity increase of Al-doped ZnO films induced by high-energy-heavy ions

We have investigated the effects on electrical properties of Al-doped ZnO (AZO) semiconductor films induced by 90 MeV Ni, 100 MeV Xe and 200 MeV Xe ions. The AZO films with c-axis orientation on SiO₂-glass substrate were prepared by using a RF-sputter-deposition method at 400 °C. We find that the conductivity increases by two order of magnitude under high-energy-heavy ion irradiation, as has already been observed for 100 keV Ne ion irradiation. We also find that the efficiency of the conductivity enhancement, which is defined as the conductivity increment per a unit of ion fluence, scales super-linearly with the electronic stopping power (S_e). The carrier density and mobility for unirradiated and irradiated AZO films are presented.     

Use of Double Wash-Coatings of Platinum and Zeolite Catalysts to Improve Selective Reduction of NOx by Hydrocarbons

The selective catalytic reduction by hydrocarbons (HC-SCR) of NO _x under lean conditions has been improved by the use of double-layered catalysts with a lower layer of Pt/SiO₂ and an upper layer of a zeolite such as H-, Ce-, and Cu-ferrierite (-FER). H-FER wash-coated over Pt/SiO₂ (H-FER//Pt/SiO₂) performed best among the samples examined. The promotional effect was attributed to the synergy of the oxidation catalyst (Pt/SiO₂) in converting NO into NO₂, which is more reactive to C₃H₆, and the HC-SCR catalyst (H-FER). Cu-FER//Pt/SiO₂ was also effective at widening the temperature window, but with this combination the performance was attributed to a simple summation of the activity of two HC-SCR catalysts that were active at different temperatures.     

5 V, 10 Gbit/s optical receiver module using Si-bipolar IC

A 10 Gbit/s optical receiver module using a Si-bipolar IC has been developed. For low power and low cost, a pure Si-bipolar IC is used in place of a GaAs IC, which is commonly used for over 10 Gbit/s. To widen the frequency bandwidth, multifeedback techniques and a two-stage buffer configuration are used in the preamplifier IC. In addition, a differential circuit configuration is used for stable operation at high frequency. The IC was fabricated using 0.25 μm Si-bipolar technology. The module exhibits sensitivity of <-16 dBm for 10 Gbit/s data with an input dynamic range >15 dB. Small power consumption of 410 mW is achieved with the single power-supply voltage of +5 V     

Relevance of instrumented nano-indentation for the assessment of the mechanical properties of eutectic crystals and α-Al grain in cast aluminum alloys

To better understand the material properties of cast aluminum alloys, the mechanical properties of microscopic structures (the eutectic structure and the α-Al phase) have been systematically examined using a special nano-indentation hardness test machine. In this approach, a triangular indentation is applied directly to the eutectic structure or α-Al phase, and the mechanical properties evaluated through hardness and load-strain relationships. The hardness of the eutectic phase varied, depending on the structural characteristics of the different intermetallic compounds. High values of hardness were obtained structures of the DO₃ type, e.g., Al₅FeSi, but low hardness for CuAl₂ and Mg₂Si. The hardness of CuAl₂ and Mg₂Si had almost the same values as that of the α-Al matrix. In addition, from the nano-indentation hardness test, the effects of α-Al grain characteristics on the mechanical properties were clarified. The hardness of the α-Al grain was linearly related to the grain size and the distance from the grain boundary, where the higher the hardness, the smaller the grain size and the closer to the grain boundary. The hardness level was attributed to the different severity of slip resistance of the atoms during the indentation loading.     

Fabrication of poly-crystalline silicon films using plasma spray method

We have developed a new fabrication technique of poly-crystalline silicon (poly-Si) sheet for solar cells, namely the DC-RF hybrid plasma spray method. It has some advantages such as high deposition rate of more than 10 μm/s and large grain size of the obtained poly-Si films. Poly-Si films with a grain size of more than 20 μm and a defect density of 10⁶–10⁷ cm⁻² have been obtained at the initial stage trial. The solar cell conversion efficiency of 4.3% has been obtained using the plasma sprayed poly-Si. It is considered that the reasons for the low conversion efficiency are metallic impurity contamination, regions of micro grain due to rapid nucleation, and many defects in the films due to thermal stress.     

Deposition of polycrystalline SiGe by surface wave excited plasma

With application to underlayer of strained Si film in mind, polycrystalline SiGe films were deposited by plasma chemical vapor deposition (PCVD) using a high-density surface wave-excited plasma in SiH₄/GeH₄/H₂ gas. The atomic ratio of Si/Ge in the film was controlled by adjusting the gas flow rate ratio of SiH₄/GeH₄. The lattice spacing of the film was also controlled by the gas flow rate ratio. Polycrystalline SiGe film with large grain size of ∼ 200 nm and high crystallinity was successfully deposited by surface wave-excited plasma.     

Mechanical properties of austenitic stainless steel with high niobium contents

To better understand the influence of the microstructural characteristics on the mechanical properties of Fe-Cr₂₂-Ni₂₅-Nb_x austenitic stainless steel (ASS-Nb_x), the mechanical properties were investigated. Nb addition was conducted with four different amounts: 0, 0.29, 0.58 and 0.86%. With the increasing Nb content, the mean grain size for the Fe-Cr-Ni-based alloys decreased, while the size of Nb precipitate increased. Owing to the different microstructural characteristics, their mechanical properties were altered. The highest tensile strength was obtained for ASS-Nb_0.29 alloy. However, with the increasing Nb content in ASS-Nb_0.29–0.86 alloys, the tensile strength decreases despite the grain refinement. The mechanical properties of the ASS-Nb alloys were influenced by the Nb precipitation hardening and the grain boundary cohesive strength, arising from the size of Nb precipitations.     

RBS study of diffusion under strong centrifugal force in bimetallic Au/Cu thin films

The effect of the strong centrifugal force, mega-gravity (MG) on inter-diffusion between Au and Cu thin films was studied by using Au(60 nm)/Cu(500 nm)/α-Al₂O₃ (0 0 0 1) films. The Rutherford backscattering analysis of the Au and Cu depth profiles shows that Cu atoms diffuse through the Au layer, resulting in the formation of the Cu layer on the surface under both the thermal annealing at 220 °C and the application of 0.61 × 10⁶ G at 220 °C. The results indicate that the MG application enhances the layer thickness of the Cu layer on the surface.