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Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Bio-Inspired Bottom-Up Assembly of Diatom-Templated Ordered Porous Metal Chalcogenide Meso/Nanostructures

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2009
Han Zhou
Abstract We put forward a novel and straightforward sonochemical process as a generic bottom-up assembly routeto produce ordered porous metal chalcogenide meso/nanostructures by templating of diatom frustules. We work with one of the most beautiful species of diatoms, Coscinodiscus lineatus, as a representative of diatoms with central symmetry, and with ZnS as the prototype, as it is a high refractive index material and is a typical material widely used in optics and photonics. ZnS replicas have been successfully synthesized from the interaction between the reactive surfaces of the frustules and the precursors under ultrasound. The inorganic replicas copy the morphology of the ordered porous structure and inherit its optical property, such as the existence of the photonic bandgap of the diatom frustules. It is possible to achieve tunable photonic properties in the replicas by assembly of various metal chalcogenide semiconductors of different refractive indexes. This bio-inspired discovery provides insight into the facile synthesis of elaborate meso/nanostructures from these marine microbes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Green monolithic II,VI vertical-cavity surface-emitting laser operating at room temperature

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004
C. Kruse
Abstract The realization of a monolithic all II,VI-based vertical cavity surface emitting laser (VCSEL) for the green spectral region is reported. Optically pumped lasing operation was achieved up to room temperature using a planar VCSEL structure. Taking advantage of distributed Bragg-reflectors based on MgS/Zn(Cd)Se superlattices as the low-refractive index material and ZnS0.06Se0.94 layers as the high-index material with a refractive index contrast of ,n = 0.6, a quality factor exceeding Q = 2000 is reached by using only 18 Bragg periods for the bottom DBR and 15 Bragg periods for the top DBR. The threshold power density is 0.32 MW/cm2 at a temperature of 10 K (emission wavelength 498.5 nm) and 1.9 MW/cm2 at room temperature (emission wavelength 502.3 nm). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Large enhancement of GaN-UV light emission using silver mirror resonator

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
N. M. Ahmed
Abstract In this paper we used new microcavity resonator design of extracting light with high efficiency from a high index material (GaN), n > 2 for use in light emitting diode (LED) and laser diode (LD). A GaN/sapphire structure as an active layer was sandwiched between two silver mirrors. For the study two types of microcavity were fabricated: (air/GaN/sapphire/silver) and (silver/GaN/sapphire/silver). Via photo-luminescence measurements we observed 2-fold intensity enhancement in the UV region (364 nm) at room temperature by using 400 nm silver back mirror compared with uncoated sample. The amplitude of the photoluminescence is enhanced 10-times when we used 400 nm back coated together with 50 nm silver as front mirror. Further, a tremendous enhancement was obtained when a small hole was made in the front mirror with 50 nm thickness. The large increment of GaN/sapphire light emission in this microcavity could be caused by few important factors: increasing absorption in the cavity, optical field enhancement due to the resonator and coupling of plasmon in the metallic layer with the UV light. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

On the development of efficient FDTD-PML formulations for general dispersive media

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2008
Konstantinos P. Prokopidis
Abstract A novel implementation of the perfectly matched layer (PML) absorbing boundary condition (ABC) to terminate the finite-difference time-domain (FDTD) algorithm for general dispersive and negative index materials is presented. The proposed formulation also adopts the complex frequency-shifted (CFS) approach, involves simple FDTD expressions and avoids complex arithmetic. Several FDTD-PML simulations with different parameters are conducted for the termination of various dispersive media validating the stability, accuracy and effectiveness of the schemes and indicating the advantage of the CFS-PML. Copyright © 2008 John Wiley & Sons, Ltd. [source]