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In this paper, different efficiency behaviors of blue LEDs fabricated on the conventional sapphire substrate (C-LEDs) and patterned sapphire substrate (PSSLEDs) by metal organic chemical vapor deposition are investigated. Maximum external quantum efficiency (EQE) of PSSLEDs shows about 23.5 % improvement compared with that of C-LEDs. However, PSSLEDs have lower peak-efficiency-current at which the EQE reaches maximum, and suffer more serious efficiency droop. Besides, slight changes of efficiency droop for these two type LEDs in aging experiments indicate that structure defects do not play major roles for efficiency droop, and faster broadenings of the full width at half maximum of the electro-luminescence (EL) spectrum when injection current increases suggest stronger band filling effects in PSSLEDs. From the rate equation analyses, the value of coefficient C' is found to be two orders larger than Auger coefficient, and PSSLEDs have a greater coefficient C', which implies more carriers overflow from QWs in PSSLEDs. Therefore, it is suggested that, compared to Auger recombination, carrier overflow from QWs would play a more important part in the efficiency droop of blue LEDs. [ABSTRACT FROM AUTHOR]

Nanostructures with high electrical conductivity were fabricated on silicon surfaces using a laser-assisted scanning tunneling microscope (LA-STM). The nanostructures, dots and lines, were fabricated on H-passivated p-doped silicon (110) surfaces. By precisely controlling the experimental conditions such as pulse energy and tip-surface gap distance, feature sizes (dot diameters and line widths) and heights of the fabricated nanostructures could be controlled. For instance, a dot with a diameter of 30 nm and a line with a width of 30 nm were obtained. In addition, scanning tunneling microscopy investigation of the structures revealed that their band gaps were changed during the LA-STM process. As a consequence, the local conductivity (more precisely the tunneling probability) was enhanced. Numerical simulations based upon the finite-difference-time-domain algorithm provide detailed insight into the spatial distribution of the enhanced optical field underneath the STM tip and associated physical phenomena. Potential applications of the developed nanostructuring process are anticipated in various nanotechnology fields, particularly in the field of nanoelectronics. [ABSTRACT FROM AUTHOR]

A technique was developed to achieve enhanced Raman scattering of the silicon photon modes using closely packed micro- and submicron silica spherical particles. Investigation on the particle-size dependence of Raman enhancement revealed that the strongest enhancement occurs when the particle diameter is equal to the spot size of the incident laser beam. Calculations using the OPTIWAVE™ software based on the finite difference time domain algorithm under the perfectly matched layer boundary conditions were carried out. The results showed that photonic nanojets are formed in the vicinity outside the particles along the propagation direction of incident light. It was found that the nanojets are confined to a length of 100 nm with a waist of 120 nm. The presence of the strongly localized electromagnetic fields within the nanojets accounts for the enhanced Raman scattering. This technique has potential applications both in modern and traditional areas of surface science such as surface oxidation, adhesion, corrosion, and catalytic processes, and many other areas in biology, chemistry, materials science, and microelectronics. [ABSTRACT FROM AUTHOR]

Laser-assisted chemical vapor deposition was applied in fabricating three-dimensional (3D) spherical-shell photonic band gap (PBG) structures by depositing silicon shells covering silica particles, which had been self-assembled into 3D colloidal crystals. The colloidal crystals of self-assembled silica particles were formed on silicon substrates using the isothermal heating evaporation approach. A continuous wave Nd:YAG laser (1064 nm wavelength) was used to deposit silicon shells by thermally decomposing disilane gas. Periodic silicon-shell/silica-particle PBG structures were obtained. By removing the silica particles enclosed in the silicon shells using hydrofluoric acid, hollow spherical silicon-shell arrays were produced. This technique is capable of fabricating structures with complete photonic band gaps, which is predicted by simulations with the plane wave method. The techniques developed in this study have the potential to flexibly engineer the positions of the PBGs by varying both the silica particle size and the silicon-shell thickness. Ellipsometry was used to investigate the specific photonic band gaps for both structures. [ABSTRACT FROM AUTHOR]

Focuses on a study which described pulsed laser deposition of hydrogenated amorphous diamond-like carbon films from a polymer target. Experimental details; Results and discussion; Summary and conclusion.

Spectrally broad frequency comb generation over 510-555 nm range was reported on chirped quasi-phase-matching (QPM) χ(2) nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 μm to 7.1 μm. When pumped with nanosecond infrared (IR) frequency comb derived from a QPM optical parametric oscillator (OPO) and spanned over 1040 nm to 1090 nm wavelength range, the 520 nm to 545 nm up-converted green spectra were shown to consist of contributions from (a) second-harmonic generation among the signal or the idler modes, and (b) sum-frequency generation (SFG) from the neighboring pairs of the signal or the idler modes. These mechanisms led the up-converted green frequency comb to have the same mode spacing of 450 GHz as that in the IR-OPO pump comb. As the pump was further detuned from the aforementioned near-degeneracy point and moved toward the signal (1020-1040 nm) and the idler (1090-1110 nm) spectral range, the above QPM parametric processes were preserved in the chirped QPM devices to support up-converted green generation in the 510-520 nm and the 545-555 nm spectral regime. Additional 530-535 nm green spectral generation was also observed due to concurrence of multi-wavelength SFG processes between the (signal, idler) mode pairs. These mechanisms facilitate the chirped QPM device to support a single-pass up-conversion efficiency ~10% when subject to an IR-OPO pump comb with 200 mW average power operated near- or off- the degeneracy point. [ABSTRACT FROM AUTHOR]

Transmission electron microscopic observation showed that TiO[sub 2] nanotubes synthesized via a simple hydrothermal chemical process formed a crystalline structure with open-ended and multiwall morphologies. Unlike multiwalled carbon nanotubes, the TiO[sub 2] nanotube walls were not seamless. During alkali treatment, crystalline TiO[sub 2] raw material underwent delamination in the alkali solution to produce single-layer TiO[sub 2] sheets. TiO[sub 2] nanotubes were formed by rolling up the single-layer TiO[sub 2] sheets with a rolling-up vector of [001] and attracting other sheets to surround the tubes. [ABSTRACT FROM AUTHOR]

This study aims at the design and development of electromagnetic-type intermittent shock wave generation in a liquid. The shock wave generated is focused at a focal point through an acoustic lens. This hardware device mainly consists of a full-wave bridge rectifier, 6 capacitors, a spark gap, and a flat coil. A metal disk is mounted in a liquid-filled tube and is placed in close proximity to the flat coil. Due to the repulsive force existing between the coil and disk shock waves are generated, while an eddy current is induced in the metal disk. Some components and materials associated with the device are also described. By increasing the capacitance content to enhance electric energy level, a highly focused pressure can be achieved at the focal point through an acoustic lens in order to lyse fat tissue. Focused pressures were measured at the focal point and its vicinity for different operation voltages. The designed shock wave generator with an energy intensity of 0.0016 mJ/mm(2) (at 4 kV) and 2000 firings or higher energy intensities with 1000 firings is found to be able to disrupt pig fat tissue.