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1 Sep 2008

Volume 93, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 93, 091901 (2008); http://dx.doi.org/10.1063/1.2976330 (3 pages)

Fang-Fang Ren, M. B. Yu, J. D. Ye, Q. Chen, S. T. Tan, G. Q. Lo, and D. L. Kwong
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Strong vertical light output from thin silicon rich oxide/SiO2 multilayers via in-plane modulation of photonic crystal patterns

Fang-Fang Ren, M. B. Yu, J. D. Ye, Q. Chen, S. T. Tan, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 93, 091901 (2008); http://dx.doi.org/10.1063/1.2976330 (3 pages) | Cited 4 times

Online Publication Date: 2 September 2008

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Three-dimensional-confined structures with triangular-lattice air-hole photonic crystal patterns were fabricated to enhance the light output from silicon rich oxide/SiO2 multilayer stack. The intensity and profile of spontaneous emission were found to be efficiently modulated by controlling the optical modes of the periodic arrays via varying their structural parameters. With lattice constant/radius of 700 nm/280 nm, the photoluminescence intensity was found to be enhanced by nearly nine times in the vertical direction. The mechanisms for different enhancement features have been theoretically analyzed based on coherent scattering and quantum electrodynamic effects, well supporting the experimental observation.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.65.Ac Multilayers
42.79.Wc Optical coatings

Enhancement in middle-ultraviolet emission in a surface-plasmon-assisted coaxial nanocavity

Qingrui Zhuang, Xia Feng, Zhilin Yang, Junyong Kang, and Xiaoli Yuan

Appl. Phys. Lett. 93, 091902 (2008); http://dx.doi.org/10.1063/1.2973159 (3 pages) | Cited 3 times

Online Publication Date: 2 September 2008

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Cathodoluminescence spectrum of a single Zn–Zn2SiO4 core-shell nanocable exhibits a strong emission at 293 nm accompanied with a weaker splitting peak at its long wavelength side. Experiment and ab initio calculation results indicate that the UV emissions are associated with the Zn2SiO4 surface states. Finite-difference time-domain simulations show that a surface-plasmon-assisted nanocavity can selectively confine and enhance the electric field energy of the 293 nm light due to the smallest mode volume and the highest finesse among surface plasmon resonance, whispering gallery, and waveguide modes. Further temperature dependence experiment and correlative theoretical derivation suggest that the splitting is associated with a strong coupling between the nanocavity and the emitter.
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78.60.Hk Cathodoluminescence, ionoluminescence
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.15.-m Methods of electronic structure calculations
73.20.At Surface states, band structure, electron density of states
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.40.Ns Metal-nonmetal contacts

Ultrafast electron dynamics and cubic optical nonlinearity of freestanding thin film of double walled carbon nanotubes

N. Kamaraju, Sunil Kumar, B. Karthikeyan, Alexander Moravsky, R. O. Loutfy, and A. K. Sood

Appl. Phys. Lett. 93, 091903 (2008); http://dx.doi.org/10.1063/1.2977463 (3 pages) | Cited 3 times

Online Publication Date: 3 September 2008

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Ultrafast degenerate pump-probe experiments performed on a freestanding film of double walled carbon nanotubes near the first metallic transition energy of outer tube show ultrafast (97 fs) photobleaching followed by a photoinduced absorption with a slow relaxation of 1.8 ps. Femtosecond closed and open aperture z-scan experiments carried out at the same excitation energy show saturation absorption and negative cubic nonlinearity. From these measurements, real and imaginary part of the third order nonlinear susceptibility are estimated to be Re(χ(3)) ∼ −2.2×10−9 esu and Im(χ(3)) ∼ 4.5×10−11 esu.
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78.47.J- Ultrafast spectroscopy (<1 psec)
68.55.-a Thin film structure and morphology
42.65.An Optical susceptibility, hyperpolarizability
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
78.67.Ch Nanotubes

The α−γ−ε triple point of iron investigated by high pressure–high temperature neutron scattering

S. Klotz, Y. Le Godec, Th. Strässle, and U. Stuhr

Appl. Phys. Lett. 93, 091904 (2008); http://dx.doi.org/10.1063/1.2976128 (3 pages) | Cited 6 times

Online Publication Date: 3 September 2008

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We present high pressure–high temperature diffraction data in the 0–10 GPa and 300–1000 K range of all three main iron phases. The refinements of the diffraction patterns give molar volumes to high precision and show that the α−γ−ε triple point is located at 8.2±0.1 GPa and 678 K. These values are significantly lower than currently admitted (10.4 GPa/740 K), but are consistent with reported in situ x-ray diffraction data obtained in multianvil presses. These measurements have been made possible by the use of a high P/T cell which uses metallic toroidal gaskets and which suffers from less absorption, gives clean diffraction patterns, and shows better pressure performance than other setups.
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64.70.-p Specific phase transitions
81.40.Vw Pressure treatment
64.60.Kw Multicritical points
62.50.-p High-pressure effects in solids and liquids

A yellow-emitting Ce3+ phosphor, La1−xCexSr2AlO5, for white light-emitting diodes

Won Bin Im, Young-Il Kim, Natalie N. Fellows, Hisashi Masui, G. A. Hirata, Steven P. DenBaars, and Ram Seshadri

Appl. Phys. Lett. 93, 091905 (2008); http://dx.doi.org/10.1063/1.2976138 (3 pages) | Cited 44 times

Online Publication Date: 3 September 2008

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A yellow-emitting phosphor, La1−xCex3+Sr2AlO5, is reported that displays a peak in the excitation at 450 nm and a peak in the emission at 556 nm. When this phosphor is pumped by a blue InGaN light-emitting diode (λmax = 450 nm) we obtain white light with color rendering index (Ra) between 81 and 85 and color temperatures between 4200 and 5500 K, suggesting that this material is competitive as a blue-pumped yellow phosphors.
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78.55.Hx Other solid inorganic materials
85.60.Jb Light-emitting devices
61.66.Fn Inorganic compounds

Magnetic field-induced reverse transformation in B2-type NiCoMnAl shape memory alloys

R. Kainuma, W. Ito, R. Y. Umetsu, K. Oikawa, and K. Ishida

Appl. Phys. Lett. 93, 091906 (2008); http://dx.doi.org/10.1063/1.2965811 (3 pages) | Cited 29 times

Online Publication Date: 4 September 2008

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Effects of the addition of Co to the NiMnAl alloy on the martensitic and magnetic properties were investigated. The magnetic properties of the parent (P) phase drastically changed from paramagnetic to ferromagnetic, while the magnetization in the martensite (M) phase slightly decreased with increasing Co composition. Consequently, in the Ni40Co10Mn33Al17 alloy with the B2 ordered structure, the martensitic transformation from a ferromagnetic P to a weak magnetic M phase was obtained. The martensitic transformation temperatures in this alloy decreased by about 30 K with the application of a magnetic field of 7 T and a metamagnetic phase transformation was confirmed.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Transformation from molecular to polymeric nitrogen at high pressures and temperatures: In situ x-ray diffraction study

I. A. Trojan, M. I. Eremets, S. A. Medvedev, A. G. Gavriliuk, and V. B. Prakapenka

Appl. Phys. Lett. 93, 091907 (2008); http://dx.doi.org/10.1063/1.2975375 (3 pages) | Cited 1 time

Online Publication Date: 4 September 2008

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We studied the mechanism of the structural transformation of molecular nitrogen to atomic single-bonded nitrogen with a cubic gauche (cg-N) crystal structure using x-ray diffraction in situ at a pressure of ∼ 140 GPa and temperatures up to 2000 K in a diamond anvil cell. The anvils, with a toroidal shape, allowed us to drastically increase the volume of the sample, reduce the acquisition time of the diffraction pattern, and improve the quality of the Raman spectra. Molecular nitrogen transforms to the cg-N phase through an intermediate disordered state. The Raman spectra are in good agreement with recent theoretical calculations.
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64.70.kt Molecular crystals
62.50.-p High-pressure effects in solids and liquids
61.66.Bi Elemental solids
78.30.Am Elemental semiconductors and insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Theory of grain boundary diffusion induced by the Kirkendall effect

Hui-Chia Yu, A. Van der Ven, and K. Thornton

Appl. Phys. Lett. 93, 091908 (2008); http://dx.doi.org/10.1063/1.2978161 (3 pages) | Cited 10 times

Online Publication Date: 5 September 2008

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A set of coupled diffusion equations is numerically solved to demonstrate that grain boundary diffusion is significantly enhanced when diffusing atomic species have dissimilar atomic hop frequencies in the bulk. The model is based on a rigorous treatment of two-component substitutional diffusion where vacancies are treated as an additional species. By examining the concentration fields and the eigenvalues of the diffusivity matrix, the origin of the enhanced grain boundary diffusion is explained in terms of the Kirkendall effect.
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61.72.Mm Grain and twin boundaries
66.30.Lw Diffusion of other defects
61.72.jd Vacancies
66.30.Ny Chemical interdiffusion; diffusion barriers

Improved performance of Schottky diodes on pendeoepitaxial gallium nitride

T. Zheleva, M. Derenge, D. Ewing, P. Shah, K. Jones, U. Lee, and L. Robins

Appl. Phys. Lett. 93, 091909 (2008); http://dx.doi.org/10.1063/1.2978404 (3 pages) | Cited 4 times

Online Publication Date: 5 September 2008

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We designed experiments to investigate the role of dislocation density on the performance of Schottky diodes fabricated on a GaN material grown conventionally and by pendeo-epitaxy. Devices of varying geometries were fabricated on low defect density GaN regions grown selectively via pendeo-epitaxy. In addition, corresponding devices were fabricated on the conventional GaN material with a high density of dislocations. Schottky diodes fabricated on pendeo-material showed nearly two orders of magnitude lower leakage current and displayed improved ideality factor, while diodes built on a conventional material displayed nonideal characteristics.
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85.30.Kk Junction diodes
71.55.Eq III-V semiconductors
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