Planar-waveguide quasi-phase-matched second-harmonic-generation device in Y-cut MgO-doped LiNbO3

We designed a planar-waveguide quasi-phase-matched second-harmonic-generation device, which consists of a Y-cut periodically poled 5 mol.% MgO-doped LiNbO3 core and SiO2 claddings, that provided a 1.08 W green light with 30% conversion efficiency by using a 7 mm long sample at room temperature. The highest conversion efficiency of 49% at 0.88 W second-harmonic generation was attained by using an 18 mm long device.     

Single atomic contact adhesion and dissipation in dynamic force microscopy

By combining dynamic force microscopy experiments and first-principles calculations, we have studied the adhesion associated with a single atomic contact between a nanoasperity--the tip apex--and a semiconductor surface--the Ge(111)-c(2 x 8). The nanoasperity's termination has been atomically characterized by extensive comparisons of the measured short-range force at specific sites with the chemical forces calculated using many atomic models that vary in structure, composition, and relative orientation with respect to the surface. This thorough characterization has allowed us to explain the dissipation signal observed in atomic-resolution images and force spectroscopic measurements, as well as to identify a dissipation channel and the associated atomic processes.     

Experimental demonstration of the time reversal Aharonov-Casher effect

We demonstrate the time reversal Aharonov-Casher (AC) effect in small arrays of mesoscopic semiconductor rings. By using an electrostatic gate we can control the spin precession rate and follow the AC phase over several interference periods. We show that we control the precession rate in two different gate voltage ranges; in the lower range the gate voltage dependence is strong and linear and in the higher range the dependence in almost an order of magnitude weaker. We also see the second harmonic of the AC interference, oscillating with half the period. We finally map the AC phase to the spin-orbit interaction parameter alpha and find it is consistent with Shubnikov-de Haas analysis.     

Selective area metal-organic vapor-phase epitaxy of InN,GaN and InGaN covering whole composition range

To investigate mask effects on InGaN selective area metal-organic vapor-phase epitaxy (SA-MOVPE), in-plane thickness profiles of InGaN were investigated with various indium contents covering between InN and GaN. A numerical simulation employing vapor-phase diffusion (VPD) model was also carried out for the quantitative analysis of VPD effect. At the growth temperatures of 650 and 700 °C, the indium content in the vapor phase and that in the solid phase exhibited almost linear relationship, suggesting that the growth of InGaN can be approximated as the superposition of the growth of InN and GaN. The effective vapor-phase diffusion length D/k_s of GaN was much smaller than InN. The profile of the InGaN growth rate in the selective area became more gradual as the solid indium content increased, and the trend seems to be the linear interpolation between the profiles of GaN and InN. However, as the indium content increases, deposition selectivity between mask and crystal surface become degenerated, and the VPD effect was almost canceled when the solid indium content exceeds 0.5. Although further improvement on the growth conditions is necessary to improve selectivity, basic information for the design of the SA-MOVPE of InGaN has been obtained, which will contribute to InGaN-based monolithically integrated multi-wavelength devices.     

Existence of solutions for a nonlinear elliptic problem on a Riemannian manifold

Let (M,g) be a noncompact, connected, orientable smooth N-dimensional Riemannian manifold without boundary. We consider the existence of solutions of problem

(P)     

Permanence for nonautonomous Lotka–Volterra cooperative systems with delays

In this paper, we consider a class of nonautonomous two species Lotka–Volterra cooperative population systems with time delays, and establish sufficient conditions which ensure the system to be permanent. We improve and extend the known condition of the permanence in [G. Lu and Z. Lu, Permanence for two species Lotka–Volterra cooperative systems with delays, Math. Biosci. Eng. 5 (2008) 477–484] to nonautonomous two-species Lotka–Volterra cooperative systems. Moreover, our conditions need no restriction on the size of time delays.     

Base-promoted aromatic [3,3] sigmatropic rearrangement of N-acyl-O-arylhydroxylamine derivatives

The base-promoted aromatic [3,3] sigmatropic rearrangement of N-acyl-O-arylhydroxylamines giving α-(2-hydroxyphenyl)amides was successfully demonstrated. The substrates were prepared from N-substituted hydroxylamines by N-acylation followed by copper(I)-mediated O-arylation with boronic acids. Treatment of the substrates with lithium hexamethyldisilazide (LiHMDS) in THF at 0?°C to room temperature generated the corresponding amide enolates. The aromatic [3,3] rearrangement of the enolates provided the desired products in moderate to good yields. A crossover experiment produced only intramolecular products and clarified that the reaction proceeds via the aromatic [3,3] sigmatropic rearrangement, not a bond-cleavage–recombination process. Our method is a formal α-arylation of amides.     

Acceleration of nickel diffusion by high tensile stress in cold-worked type 316 stainless steel at 450°C

The effect of tensile stress on diffusion was studied by the diffusion couple method. A diffusion couple was prepared by electroless plating a nickel thin layer on the round notch surface of a compact tension-type specimen of 20% cold-worked Type 316 stainless steel. The couple was diffused at 450°C for 4003?h under the maximum tensile stress of 553?MPa in the load direction. A rapid diffusion coefficient of nickel in the Type 316 stainless steel was observed at the high tensile stress zone that was 6.5 times faster than that at the low-stress zone.     

Ionic diffusion and structural changes in lithium compounds

⁷Li NMR measurements have been performed to study milling effects on ionic diffusion in lithium cobalt oxide, LiCoO₂ and piezoelectric compound, LiNbO₃ prepared by mechanical milling method. The milling process gives quite different effects on NMR spectra of these compounds. Both ⁷Li MAS and static NMR spectra of the milled LiCoO₂ show the line broadening with increasing milling time. ⁵⁹Co static spectra also show specific changes in the line shape with increasing milling time. These results would be attributed to the change in an electronic state of Co 3d orbitals because of charge compensation associated with oxygen vacancies and/or defects. ⁷Li static NMR spectrum of milled LiNbO₃ shows complicated line shape with increasing milling time. It is explained by superposition of two spectra arising from mobile Li⁺ ions and non-mobile ones settled on the fixed site. It is shown that the ratio of mobile Li⁺ ions increases up to a maximum of 9.4% with increasing milling time. Milling effects on the Li⁺ ionic diffusion in LiCoO₂ and LiNbO₃ are discussed in connection with changes in local structure.     

Development of dry polymer electrolyte based on polyethylene oxide with co-bridging agent crosslinked by electron beam

Polyethylene oxide (PEO)-based electrolytes were crosslinked using electron beam (EB) irradiation. The gel contents of a polymer film were increased after irradiation doses of 0, 140, 280, and 420 kGy, with ionic conductivities of 0.831, 1.55, 6.08, and 7.95 (× 10^? 5) S cm^? 1 at 40 °C, respectively. The slight decrease in conductivity at higher temperatures after irradiation is due to the retardation of polymer motion by crosslinking. The electrolyte with higher EB dose amount exhibits higher conductivity due to stabilization of the amorphous state. The EB crosslinking with a co-bridging agent shows enhanced conductivities of 4.71, 6.59, and 7.18 (× 10^? 5) S cm^? 1 at 40 °C, after irradiation with 140, 280, and 420 kGy. Addition of the co-bridging agent is effective for developing a crosslinked structure with a smaller EB dose. Tensile strength becomes two to three times higher with irradiation compared to the non-treated polymer. Combination of the EB technique with a co-bridging agent is a simple and effective method to prepare strong dry polymer electrolyte films with improved room temperature conductivity.