Band engineering of silicon for light emission: First-principles approach to the effect of co-doping with nitrogen and fluorine

A Si-based light emitter has long been the final key component for electronic and photonic integrated circuits on Si, because Si has an indirect band gap. Atomistic and electronic structures and energy gains of formation of possible nitrogen (N) and fluorine (F) complexes in Si have been researched from first-principles, in order to engineer the band structure of Si for light emission. The calculated results show that the substitutional nitrogen N_S and bond center fluorine F_BC pair complex has large stabilization energy, and that the pair-complex-doped Si has direct band gap, which is reduced with respect to that of Si. These results lead to the possibilities of doping-based engineering of Si optical properties with introduction of deep-level impurity and charge compensation.     

Second-harmonic generation with a high-index-clad waveguide

Theoretical and experimental analyses of second-harmonic generation (SHG) with a high-index-clad waveguide are reported. It was found that confinement of the propagation modes and the overlap between the fields of fundamental and second-harmonic waves could be increased in this waveguide. This structure was achieved in an x-cut MgO:LiNbO (3) quasi-phase-matched (QPM) waveguide by use of Nb(2)O(5) as a cladding layer. With the QPM SHG device, harmonic blue light of 5.5 mW at the 434-nm wavelength was generated with a normalized conversion efficiency of 1200%/W cm(2).     

Novel materials for electronic device fabrication using ink-jet printing technology

Novel materials and a metallization technique for the printed electronics were studied. Insulator inks and conductive inks were investigated. For the conductive ink, the nano-sized copper particles were used as metallic sources. These particles were prepared from a copper complex by a laser irradiation process in the liquid phase. Nano-sized copper particles were consisted of a thin copper oxide layer and a metal copper core wrapped by the layer. The conductive ink showed good ink-jettability. In order to metallize the printed trace of the conductive ink on a substrate, the atomic hydrogen treatment was carried out. Atomic hydrogen was generated on a heated tungsten wire and carried on the substrate. The temperature of the substrate was up to 60 °C during the treatment. After the treatment, the conductivity of a copper trace was 3 μΩ cm. It was considered that printed wiring boards can be easily fabricated by employing the above materials.     

An energy-conserving Galerkin scheme for a class of nonlinear dispersive equations

A Galerkin scheme is presented for a class of conservative nonlinear dispersive equations, such as the Camassa–Holm equation and the regularized long wave equation. The scheme has two advantageous features: first, it is conservative in that it keeps the discrete analogue of the continuous energy conservation property in the original equations; second, it can be formulated only with cheap H¹$H^1$-elements even if the original equations include third derivative u_xxx$u_{\mathit{xxx}}$. Numerical experiments confirm the stability and effectiveness of the proposed scheme.     

High-precision sample stage for photoemission microscopy of organic films

A high-precision sample stage for photoemission microscopy has been constructed to translate the sample by ±3 mm with accuracy better than 100 nm. The stage is actuated by step motors settled outside the vacuum. The accuracies of the translations were measured by observing a standard patterned sample with a photoemission electron microscope (PEEM) of 50 nm resolution. The accuracy was nearly independent of the distance of each translation step and the error was not accumulated by repeated steps. After round-trip translations up to 0.2 mm, the sample came back to the original position with accuracy of ±50 nm. The performance of the stage was demonstrated by observing growth processes of lead phthalocyanine (PbPc) films formed on graphite.     

A Flat Spectral Response AWG Demultiplexer Composed of Slabs with Islands and Peninsulas

Phase adjustment elements called islands and peninsulas are introduced to obtain an AWG demultiplexer with a flat spectral response. Use of the peninsulas enables us to achieve a 1dB bandwidth of 0.5 nm.     

Visualization of phase conjugate ultrasound waves passed through inhomogeneous layer

Compensation of phase distortions of ultrasound beams by means of parametric phase conjugation is visualized. Quasi-plane and focused primary beams were distorted by a polymer aberration layer introduced between the primary wave source and the wave phase conjugator. It is demonstrated acousto-optically that, while the acoustic field is strongly irregular in the area between aberration layer and conjugator, the phase conjugate wave visibly reproduces the primary beams in the area between the layer and the primary wave source. The phenomenon is observed in supercritical mode of parametric amplification when intensity of phase conjugate wave is high enough for manifestations of acoustic nonlinearities in water.     

Softening of Cu-O bond stretching phonons in tetragonal HgBa2CuO4+delta

Phonons in nearly optimally doped HgBa(2)CuO(4+delta) were studied by inelastic x-ray scattering. The dispersion of the low-energy modes is well described by a shell model, while the Cu-O bond stretching mode at high energy shows strong softening towards the zone boundary, which deviates strongly from the model. This seems to be common in the hole-doped high-T(c) superconducting cuprates, and, based on this work, not related to a lattice distortion specific to each material.