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Pure BaMgSiO4:Eu2+ phosphor, prepared by a solid state reaction method under N2 atmosphere, exhibited a strong green emission at 500 nm and a weak emission at 405 nm. Heat treatment under NH3 atmosphere causes changes in the PL intensity: the green emission at 500 nm gradually decreases and completely disappears after heat treatment for 3 h, whereas a new blue emission peak, centered at 445 nm, appears and becomes very strong. The results of the analyses with electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) spectroscopy suggest that the heat treatment causes the generation of a large amount of oxygen vacancies. This resulted in the aforementioned color changes of the BaMgSiO4:Eu phosphor, which are confirmed by the results of DFT+U calculations. In particular, these calculations showed that Eu prefers to occupy Ba(3) sites, which are six coordinated to oxygen atoms. The emission at 500 nm was attributed to the 4f-5d transition energy of Eu in Ba(3) site, calculated as 2.54 eV. It was also shown that Eu 4f energy level decreases when oxygen is removed from the oxygen position adjacent to Eu, which results in a larger Eu 4f-5d transition energy and shorter wavelengths of emission peaks. [ABSTRACT FROM AUTHOR]

Birefringence plays a great role in phase matching of the nonlinear optical (NLO) crystals. Small birefringence restricts various crystals from achieving deep-ultraviolet laser output although they exhibit short UV cutoff edges and high second-harmonic generation (SHG) intensities. An access to achieve deeper coherent light output through external pressure on NLO crystal, K3B6O10Cl is proposed and demonstrated through computer experiment based on the first principles theory. The "hot spot" in structure that determine the SHG effects and birefringence were highlighted. The shortest achievable phase-matching wavelengths are predicted based on calculated refractive indices. It is found that the quasi-planar (B6O10)2- group is the dominant contributing unit to optical anisotropy. The pressure-induced increase of polarizability anisotropy of (B6O10)2- group can notably enlarge birefringence which extends the shortest achievable wavelength of K3B6O10Cl frequency conversion. The results show that pressure engineering may be a promising scheme to overcome the drawback of small birefringence of some NLO crystals. [ABSTRACT FROM AUTHOR]

The performance of thin-film transistors with a novel poly-Si nanowire channel prepared by solid-phase crystallization is investigated in this paper. As compared with conventional planar devices having self-aligned source/drain, the new devices show an improved ON-current per unit width and better control over the short channel effects. The major conduction mechanism of the OFF-state leakage is identified as the gate-induced drain leakage, and it is closely related to the source/drain implant condition and the unique device structure. [ABSTRACT FROM AUTHOR]

The electro-optical modulation effect of a (10,0) boron nitride nanotube is investigated by first-principles, density functional theory calculations. The optical properties of boron nitride nanotubes can be tuned through perturbation by a transverse electric field. Large optical anisotropy in variations of the absorption spectra and refractive indices in response to external electric field is found. In addition, a method called the band-resolved absorption density analysis technique is developed to investigate the detailed optical absorption transition processes. The result is consistent with the recent experimental observation [M. Ishigami et al., Phys. Rev. Lett. 94, 56804 (2005)] and suggests that the boron nitride nanotubes can be a promising material for electro-optical modulation device applications. [ABSTRACT FROM AUTHOR]

Hydrogenation reaction, as one of the simplest association reactions on surfaces, is of great importance both scientifically and technologically. They are essential steps in many industrial processes in heterogeneous catalysis, such as ammonia synthesis (N[sub 2]+3H[sub 2]→2NH[sub 3]). Many issues in hydrogenation reactions remain largely elusive. In this work, the NH[sub x] (x=0,1,2) hydrogenation reactions (N+H→NH, NH+H→NH[sub 2] and NH[sub 2]+H→NH[sub 3]) on Rh(111) are used as a model system to study the hydrogenation reactions on metal surfaces in general using density-functional theory. In addition, C and O hydrogenation (C+H→CH and O+H→OH) and several oxygenation reactions, i.e., C+O, N+O, O+O reactions, are also calculated in order to provide a further understanding of the barrier of association reactions. The reaction pathways and the barriers of all these reactions are determined and reported. For the C, N, NH, and O hydrogenation reactions, it is found that there is a linear relationship between the barrier and the valency of R (R=C, N, NH, and O). Detailed analyses are carried out to rationalize the barriers of the reactions, which shows that: (i) The interaction energy between two reactants in the transition state plays an important role in determining the trend in the barriers; (ii) there are two major components in the interaction energy: The bonding competition and the direct Pauli repulsion; and (iii) the Pauli repulsion effect is responsible for the linear valency-barrier trend in the C, N, NH, and O hydrogenation reactions. For the NH[sub 2]+H reaction, which is different from other hydrogenation reactions studied, the energy cost of the NH[sub 2] activation from the IS to the TS is the main part of the barrier. The potential energy surface of the NH[sub 2] on metal surfaces is thus crucial to the barrier of NH[sub 2]+H reaction. Three important factors that can affect the barrier of association reactions are generalized: (i) The bonding competition effect; (ii) the local charge densities of the reactants along the reaction direction; and (iii) the potential energy surface of the reactants on the surface. The lowest energy pathway for a surface association reaction should correspond to the one with the best compromise of these three factors. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Owing to high quantum efficiency, adjustable composition and antioxidation properties of oxynitride phosphors, extensive investigations have focused on their photoluminescence properties under low-energy light excitation (UV or blue light). However, the vacuum ultraviolet (VUV) luminescence properties of oxynitride phosphors are rarely researched. Present work studies the structure and VUV luminescence properties of an oxynitride phosphor: AlON: Eu, Mg, which is synthesized by solid-state reaction. Under 147 nm excitation, it was found that AlON: Eu, Mg phosphor shows a blue emission band centered at about 470 nm. The first principle calculation is used to analyze the origin of the VUV absorption. Compared with BaMgAl10O17: Eu2+ phosphor, AlON: Eu, Mg phosphor shows better thermal stability. [ABSTRACT FROM AUTHOR]

The article presents a case study of a 55-year-old woman who undergo a flap harvest of a right gastroepiploic lymph node with the use of robot-assisted technique known as Da Vinci Surgical System.

Molecular construction using good optically active microscopic units is vital to efficiently explore good nonlinear optical (NLO) materials, a type of important optoelectronic functional materials. In this work, we highlight the planar (C3N3O3)3- anion, the main fundamental building block in inorganic metal cyanurates, as an outstanding candidate of building blocks for NLO materials. Several noncentrosymmetric metal cyanurates containing the (C3N3O3)3- groups are studied by the first-principles calculations for the first time. It is shown that these materials possess wide band gaps (Eg > 5.5 eV), high SHG coefficients (d22 > 2 × BBO), and large birefringence values (Δn > 0.1) and thus have good potentials in the ultraviolet NLO applications. Moreover, the key role of the (C3N3O3)3- groups to the good NLO performance in the cyanurates is elucidated. On the basis of the first-principles analysis, some possible searching directions of good NLO materials containing (C3N3O3)3- groups are proposed. [ABSTRACT FROM AUTHOR]

The introduction of fluorine (F) into the borate crystals is proven to be an effective approach in designing novel non-centrosymmetric crystals, which is a requirement for nonlinear optical (NLO) materials. In this contribution, the electronic structure and optical properties of borate fluoride crystals are determined by the first-principles method. First-principles calculations indicate that the key second-harmonic generation (SHG) factor is attributed not only to borate groups but also to the bonding of the F anions with cations where F coordinates to cations (Sr, Ba). The electron withdrawing effect of the F atom leads to the higher values for anisotropy of the polarizability around cation-centered polyhedra, ultimately making it easy for the external electric field of incident light to effect the dielectric susceptibility. The direct contribution of anion on the NLO properties is observed as fluorine-induced variation of electronic structure. [ABSTRACT FROM AUTHOR]