Materials Science Forum Vols. 783-786

Abstract: We investigated local strain distribution in a cross-sectional area throughout the thickness of a thick aluminum nitride (AlN) film epitaxially grown on a trench-patterned AlN/α-Al₂O₃ template using X-ray microdiffraction measurements for AlN and Bragg reflections. The results show that the presence of voids caused by the trench pattern strongly influences on the distribution of the strain components in the and directions, which are perpendicular to the trench lines. Discrepancy between strain values obtained from the two Bragg reflections was shown to be the result of twisting of the crystal domains about the axis in the thick AlN film.

Abstract: We report characteristics of quantum dot (QD) sensitized solar cells using Si nanoparticles and Ge nanoparticles. Si nanoparticles were synthesized by multi-hollow discharge plasma chemical vapor deposition, whereas Ge nanoparticles were done by a radio frequency magnetron sputtering using Ar+H₂ under high pressure conditions. The electrical power generation from Si QDs and Ge QDs was confirmed. Si QD sensitized solar cells show an efficiency of 0.024%, fill factor of 0.32, short-circuit current of 0.75 mA/cm² and open-circuit voltage of 0.10 V, while Ge QD sensitized solar cells show an efficiency of 0.036%, fill factor of 0.38, short-circuit current of 0.64 mA/cm² and open-circuit voltage of 0.15 V.

Abstract: Heterogeneous integration of III-V compound semiconductors and Ge on the Si platform is one of the promising technologies for enhancing the performance of metal-oxide-semiconductor field effect transistors (MOSFETs) beyond the 10-nm technology node because of their high carrier mobilities. In addition, the III-Vs and Ge are also promising materials for photonic devices. Thus, we have investigated III-V/Ge device engineering for CMOS photonics, enabling monolithic integration of high-performance III-V/Ge CMOS transistors and III-V/Ge photonics on Si. The direct wafer bonding of III-V on Si has been investigated to form III-V on Insulator for III-V CMOS photonics. Extremely-thin-body InGaAs MOSFETs with the gate length of approximately 55 nm have successfully been demonstrated by using the wafer bonding. InP-based photonic-wire waveguide devices including micro bends, arrayed waveguide gratings, grating couplers, optical switches, and InGaAs photodetectors have also been demonstrated on the III-V-OI wafer. The gate stack formation on Ge is one of the critical issues for Ge MOSFETs. Recently, we have successfully demonstrated high-quality GeO_x/Ge MOS interfaces formed by thermal oxidation and plasma oxidation. High-performance Ge pMOSFET and nMOSFET with thin EOT have been obtained using the GeO_x/Ge MOS interfaces. We have also demonstrated that GeO_x surface passivation is effective to reduce the dark current of Ge photodetectors in conjunction with gas-phase doped junction. We have also investigated strained SiGe optical modulators. We expect that compressive strain in SiGe enhances modulation efficiency, and an extremely small V_πL of 0.033 V-cm is predicted. III-V/Ge heterogeneous integration is one of the promising ways for achieving ultrahigh performance electronic-photonic integrated circuits.

Abstract: The present work examines pore formation on type 316 stainless steel, Inconel 600 alloy and Co-Cr alloy. Ordered pore arrays are formed on the metallic substrates by electrochemical treatments in organic solvents containing perchlorate ions under optimized conditions. It is revealed that the key to form pore arrays is to control electrolyte composition. The formation of ordered pore arrays on stainless steel can be useful as the surface modification of the metallic biomaterial as the presence of pore arrays on stainless steel can enhance biocompatibility.

Abstract: The catalytic activity of Ni-Al (Ni25Al) nanoparticles fabricated by thermal plasma evaporation was examined for methanol decomposition and CO oxidation. The nanoparticles exhibited high activity for both reactions. Characterization of the nanoparticles revealed that the fabricated nanoparticles were mainly comprised of Ni and Ni₃Al phases. During CO oxidation, the Ni phase was oxidized to NiO, while the Ni₃Al phase remained unchanged. The NiO phase is supposed to serve as the active sites for CO oxidation. In contrast, during methanol decomposition, no obvious oxidation was observed for both Ni and Ni₃Al phases. The Ni and Ni₃Al phases are supposed to contribute to the high activity for methanol decomposition.

Abstract: Increase of CO₂ concentration in the atmosphere is one of reasons for the global warming. Development of energy circulation systems, which do not emit CO₂ in the atmosphere, is an emergent issue for present-generation scientists [1]. As an answer, we have proposed a new type of energy circulation system, namely, carbon-neutral energy (CN) cycle. With a practical application in mind, three limitations are imposed on the CN cycle; (1) no CO₂ emissions, (2) utilization of liquid fuels and (3) minimizing the use of precious metal catalysts. In anticipation of a practical use in the near future, an alkaline fuel cell will be adapted for the CN cycle where non-platinum catalysts can work. For our purpose, electric power will be generated by partial oxidation of alcohols to carboxylic acids.[2] In view of ease in handling, fuels having a high boiling point (b.p.) are favorable for the CN cycles. To this end, glycol (EG) of which b.p. is 470 K an ideal candidate as a fuel. In this case, an oxidized product of EG can be oxalic acid. Compared to the energy obtained by the complete oxidation of EG into CO₂, we can derive ca. 80 % of energy even in the partial oxidation of EG to oxalic acid, implying that the EG/oxalic cycle possibly works as an energy cycle. We herein show an example of selective EG oxidation catalysts working in alkaline conditions.

Abstract: The wettability of hydrogen plasma-treated cubic boron nitride (cBN) films is studied. The films are prepared on Si substrates by inductively coupled plasma (ICP)-enhanced chemical vapor deposition, and further treated by pure hydrogen ICP and microwave plasma (MWP) separately. The surface roughness of the films and the cBN content in the films show only minor changes after the plasma treatment in any treatment condition. The contact angle of polar water and apolar 1-bromonaphthalene is reduced greatly with the ICP post-treatment, while it is reduced only moderately with the MWP post-treatment. The highly hydrophilic behavior with very low contact angles is attributed to a marked increase in the polar component of the apparent surface free energy up to 34 mJ/m².

Abstract: Diffraction methods for lattice strain measurement provide useful information concerning the nature of grains behaviour during elastoplastic deformation. The main advantage of the diffraction methods is the possibility of studying mechanical properties of polycrystalline materials separately in each phase and in groups of grains with a specific orientation. In this work we present application of the neutron and X-ray diffraction to study “in situ” deformation of two phase stainless steels during tensile loading. The experimental results are compared with self-consistent model.

Abstract: There exists the orbital-modulated (OM) state in the layered manganite Ca_2-xNd_xMnO₄ (CNMO) with 0.20 ≤ x ≤ 0.50. To understand the effect of the tilting of MnO₆ octahedra to the stability of the OM state, the crystallographic features of CNMO samples prepared by a solid-state reaction have been investigated mainly by transmission electron microscopy. For 0.30 ≤ x ≤ 0.50, it was found that the (LTO → Pccn/LTT) structural transition occurred on cooling from room temperature, where the LTO and Pccn/LTT structures are, respectively, characterized by tilting displacements of oxygen octahedra about one and two of the <110> directions. The notable feature of the (LTO → Pccn/LTT) transition is that its progress strongly suppresses the growth of the OM state for 0.30 ≤ x ≤ 0.45. As a result of the suppression, the OM state exhibits a re-entrant behavior for its appearance. This is an indication that the Pccn/LTT tilting is not favorable for the stabilization of the OM state.

Abstract: We present effectivity of an event-recording system in neutron diffraction experiments at the Engineering Materials Diffractometer TAKUMI at the Materials and Life Science Experimental Facility in J-PARC. We developed an event-recording system for recording information of neutron generation and detection and sample environmental conditions like load, strain, etc. as events with synchronized timing tag across whole system, and developed a software to handle the event data. It gave us several advantages by allowing us flexible data reduction depending on users’ purposes, especially for time resolved experiments. We demonstrated in situ neutron diffraction measurements using these new recording system and software to show the advantages. These new system and software are very attractive to be applied for measurements that need stroboscopic data collection such as fatigue tests.