Fatigue strength of the Cu/Si interface in nano-components

The fracture behavior of the Cu/Si interface in a nano-cantilever specimen with a 200 nm-thick Cu film (Specimen-200), which possesses a nanometer-scale strain-concentrated region, is examined under a cyclic bending load. The fatigue strength is around GPa level owing to the high yield stress of the Cu nano-film and the deformation constraint associated with the neighboring hard materials. The S-N curve shows clear dependence of fatigue life on the applied stress in the high-stress range, Δσ. Specimens with a 20 nm-thick Cu film (Specimen-20) are also investigated for comparison. The stress range in the fatigue fracture of Specimen-20 is higher than that of Specimen-200 for the same fatigue life. However, there is good coincidence in the Δσ/σ_s (σ_s: strength in monotonic load) vs. N_f (number of cycles to fracture) at high Δσ. The S-N curves suggest the existence of a fatigue threshold (Δσ_w) at low Δσ. The ratio of fatigue limit to the fracture stress in a monotonic loading, Δσ_w/σ_s, is large compared with the magnitude of bulk metal, which suggests the brittle behavior of the interface. Moreover, the fatigue limits have good coincidence with their yield stresses.     

Scintillation properties of Tm-doped Lu3Al5O12 single crystals

Using the micro-pulling-down (μ-PD) method, Tm-doped Lu₃Al₅O₁₂ (Tm:LuAG) single crystals were grown to examine their scintillation properties. In transmittance spectra, they exhibited about 80% transparency in the wavelengths longer than 320 nm and five absorption lines due to Tm³⁺ 4f–4f transitions were observed. ²⁴¹Am α-ray excited radioluminescence spectra were measured and intense 4f–4f emission peaks were observed with the host emission. When excited by ¹³⁷Cs γ-Ray to obtain pulse height spectra, Tm 1% doped LuAG showed the highest light yield coupled with a photomultiplier (PMT) or a silicon avalanche photodiode (Si-APD). The light yield was estimated to be 5800 and 7300 photons/MeV for PMT and Si-APD, respectively. Decay time profiles consist of two exponential components and the fast and slow components are considered to be attributed to the host and the combination of the host and Tm³⁺ 4f–4f emission, respectively.     

Progress in ECRF antenna development for JT-60SA

Structural, mechanical and optical design work on antennas/launchers for the electron cyclotron range of frequency heating and current drive system in JT-60 Super Advanced (JT-60SA) have been advanced based on a linear motion antenna concept. A CAD model of the launcher was built with realistic component sizes. A mock-up of the steering structure consisting of two different bellows sections for poloidal and toroidal beam scanning was fabricated to test movement of the bellows. The poloidal (?40° to +20°) and toroidal (?15° to +15°) injection angle ranges required in JT-60SA were shown to be realized by this steering structure and mirrors.     

Oxygen doped Ge crystals Czochralski-grown from the B2O3-fully-covered melt

Local vibrations of oxygen in Ge crystals grown from a melt fully covered by B₂O₃ were evaluated by Fourier-transform infrared spectroscopy. Ge single crystals containing oxygen were grown by the Czochralski method under various growth conditions. Oxygen concentrations in the crystals were determined to be in the range between 8.5 × 10¹⁵ and 5.5 × 10¹⁷ cm⁻³ from the infrared absorption at 855 cm⁻¹ originating in local vibration of Ge-O_i-Ge quasi-molecules. Absorption peaks relating to GeO_x, SiO_x and Si-O_i-Si were not detected in the as-grown crystals. The calibration coefficient for determining oxygen concentration in Ge crystals from the absorption peak intensity at 1264 cm⁻¹ was estimated to be 1.15 × 10¹⁹ cm⁻².     

Cohesive zone criterion for cracking along the Cu/Si interface in nanoscale components

Crack initiation and propagation along the Cu/Si interface in multilayered films (Si/Cu/SiN) with different thicknesses of the Cu layer (20 and 200 nm) are experimentally investigated using a nano-cantilever and millimeter-sized four-point bending specimens. To examine the cohesive zone model (CZM) criterion for interfacial delamination along the Cu/Si interface in nanoscale stress concentration, an exponential type of CZM is utilized to simulate the observed delamination processes using the finite element method. After the CZM parameters for the Cu/Si interface are calibrated by experiment, interface cracking in other experiments is predicted. This indicates that the CZM criterion is universally applicable for describing cracking along the interface regardless of specimen dimensions and film thickness which include the differences in plastic behavior and residual stress. The CZM criterion can also predict interfacial cracking along Cu/Si interfaces with different stress singularities.     

Fabrication of porous SiC ceramics having pores shaped with Si grain templates

SiC porous ceramics were prepared by heating mixtures of Si powder and carbon black at 900 °C for 24 h in Na vapor. The grains of the Si powder were not only the source of Si for SiC but also served as templates for the pores in the SiC porous ceramics. Angular-shaped pores with sizes of 2-10, 10-150 and 50-150 μm were formed by angular Si grains with sizes of ≤10, ≤50 and ≤150 μm, respectively. The porosity of the SiC porous ceramics was around 55-59%. Spherical pores were also formed when spherical Si grains were used. A bending strength of 14 MPa was measured for the SiC porous ceramics prepared with the Si grains (≤50 μm).     

The Direct Spectroscopy of Positronium Hyperfine Structure Using a Sub-THz Gyrotron

Positronium is an ideal system for research on Quantum Electrodynamics (QED), especially in a bound state. A discrepancy of 3.9 standard deviations has been found between the measured hyperfine structure (Ps-HFS) and the QED predictions. This may be due to the contribution of unknown new physics or common systematic effects in previous measurements, in all of which the Zeeman effect was used. We propose a new method to directly measure the Ps-HFS using a high power gyrotron. We compare two resonators which have been developed to supply sufficient power to drive the direct transition, a Fabry-Pérot resonator and a ring resonator with a diffraction grating. We plan to perform first direct measurement of Ps-HFS within the next six months.     

Lithium Phenolate Complexes with a Pyridine‐Containing Polymer for Solution‐Processable Electron Injection Layers in PLEDs

A series of (vinylphenyl)pyridine‐based polymer binders, PVPh2Py, PVPh3Py, and PVPh4Py, are designed and synthesized and it is found that mixtures of Liq and the polymers exhibit superior electron injection characteristics as ultrathin (1.6 nm) electron injection layer (EIL) films. They are comparable to those of EILs composed only of Liq. The addition of the polymers does not deteriorate the performance of Liq EILs. Additionally, when the EIL thickness is increased from 1.6 nm to 16 nm, the driving voltages increase and the external quantum efficiencies decrease. The increase in the voltage and decrease in the EQE are suppressed in the device with mixed EILs compared to those observed for the device composed of 100 wt% Liq. Furthermore, the position of the nitrogen in the pyridine ring is considered to influence the electron transport properties of the EILs. The mixing PVPh4Py with Liq improves the driving voltage of the fabricated devices, even with a thick mixed EIL. This reduced dependence of the performance of EILs on their thickness will be advantageous for the coating of large areas using solution processes.     

Degradation mechanism of an H2-permselective amorphous silica membrane

Degradation mechanism of H₂ permselectivity under atmosphere of steam/N₂ = 3 at 773 K was investigated among amorphous silica membranes on γ-Al₂O₃-coated α-Al₂O₃ or Ni-doped γ-Al₂O₃-coated α-Al₂O₃ synthesized by counter diffusion chemical vapor deposition. Helium and H₂ permeance drastically decreased during the first few hours of hydrothermal exposure. On the other hand, N₂ permeance fluctuated during hydrothermal treatment in silica membrane on γ-Al₂O₃-coated α-Al₂O₃. The degree of N₂ permeance change depended on the hydrothermal stability of the intermediate layer. Hydrogen permselectivity was affected by both the densification of amorphous silica and the sintering of the intermediate layer during hydrothermal exposure.     

Study on the thermal decomposition of NaBH4 catalyzed by ZrCl4

The catalytic effect of zirconium tetrachloride (ZrCl₄) on the thermal dehydrogenation of NaBH₄ has been studied. The ZrCl₄ reduced to ZrCl₂ and metallic zirconium which exhibit the high catalytic activity during thermal dehydrogenation. The activation energy corresponding to dehydrogenation of NaBH₄ is remarkably reduced to 180 kJ/mol in the presence of a catalyst as compared to pure-NaBH₄ which was found to be 275 kJ/mol under the similar experimental conditions. The reduced activation energy leads to decreased onset dehydrogenation temperature (<300 °C). A substantial amount of sodium remained at the end of the dehydrogenation of catalyzed sample. The low-temperature dehydrogenation of catalyzed NaBH₄ could be useful to manage the evaporation of sodium metal.