ELECTROCATALYSIS AT A MICRODISK ELECTRODE MODIFIED WITH A REDOX SPECIES

The current equation of the electrocatalytic reaction at a microdisk electrode modified with redox species has been described and verified experimentally. There exists a linear relationship between plateau limiting current and the radius of the microdisk electrode for a catalytic process. The influence of the dimensions of the microdisk electrode on catalytic efficiency is discussed. The polyvinylferrocene (PVFc)-modified microdisk electrode prepared by the coating method was taken as a typical example, on which the electrocatalytic oxidation of ascorbic acid could be studied. The catalytic reaction rate constants were determined as an average value of 1.5 X 10(-7) cm3/mol s by this method, and are consistent with those obtained at a conventional electrode.

Mode Simulation for Midinfrared Microsquare Resonators With Sloped Sidewalls and Confined Metals

EQUILATERAL-TRIANGLE; MU-M; LASERS; MICROLASERS; MICRODISK Abstract: Mode characteristics for midinfrared microsquare resonators with sloped sidewalls and confined metal layers are investigated by finite-difference time-domain (FDTD) techniques. For a microsquare with a side length of 10 mu m, the mode quality (Q)-factors of 8329, 4772, and 2053 are obtained for TM5,7 mode at wavelength 7.1 mu m by three-dimensional FDTD simulations, as the tilting angles of the side walls are 90 degrees, 88 degrees, and 86 degrees, respectively. Furthermore, microsquare resonators laterally surrounded by SiO2 and metal layers are investigated by the two-dimensional FDTD technique for the metal layers of Au, Ti-Au, Ag-Au, and Ti-Ag-Au, respectively.

Multimode resonances in metallically confined square-resonator microlasers

Directional emission InP/AlGaInAs square-resonator microlasers with a side length of 20 mu m are fabricated by standard photolithography and inductively coupled-plasma etching technique. Multimode resonances with about seven distinct mode peaks in a free-spectral range are observed from 1460 to 1560 nm with the free-spectral range of 12.1 nm near the wavelength of 1510 nm, and the mode refractive index versus the photon energy E (eV) as 3.07152+0.18304E are obtained by fitting the laser spectra with an analytical mode wavelength formula derived by light ray method. In addition, mode field pattern is simulated for cold cavity by two dimensional finite-difference time-domain technique.

Analysis of coupled microcircular resonators coupled to a bus waveguide with high output efficiency

Coupled microcircular resonators tangentially coupled to a bus waveguide, which is between the resonators, are numerically investigated by the finite-difference time-domain technique. For symmetrically coupled microcircular resonators with refractive index of 3.2, radius of 2 mu m, and width of the bus waveguide of 0.4 mu m, a mode Q factor of the order of 105 is obtained for a mode at the frequency of 243 THz. An output coupling efficiency of as high as 0.99 is calculated for a mode with a Q factor ranging from 10(3) to 10(4). The mode Q factor is 2 orders larger than that of the modes confined in a single circular resonator tangentially coupled to the same bus waveguide. Furthermore, the high Q traveling modes in the coupled microcircular resonators are suitable for optical single processing.

Design of quantum cascade microcavity lasers based on Q factor versus etching depth

The choice of the etching depth for semiconductor microcavities is a compromise between a high Q factor and a difficult technique in a practical fabricating process. In this paper, the influences of the etching depth on mode Q factors for mid-infrared quantum cascade microcylinder and microsquare lasers around 4.8 and 7.8 mu m are simulated by three-dimensional (3D) finite-difference time-domain (FDTD) techniques. For the microcylinder and the microsquare resonators, the mode Q factors of the whispering-gallery modes (WGMs) increase exponentially and linearly with the increase in the etching depth, respectively Furthermore, the mode Q factors of some higher order transverse WGMs may be larger than that of the fundamental transverse WGM in 3D microsquares. Based on the field distribution of the vertical multilayer slab waveguide and the mode Q factors versus the etching depth, the necessary etching depth is chosen at the position where the field amplitude is 1% of the peak value of the slab waveguide. In addition, the influences of sidewall roughness on the mode Q factors are simulated for microsquare resonators by 2D FDTD simulation. (C) 2009 Optical Society of America

Analysis of mode characteristics for equilateral-polygonal resonators with a center hole

Mode characteristics for equilateral triangles, squares, and hexagonal resonators with a center hole are numerically simulated by the finite-different time domain (FDTD) technique. The center hole does not break the symmetry behavior of the original resonators and can result in modification of the mode field patterns and mode Q factors. In an equilateral triangle resonator the center hole can suppress the symmetry state of degenerate states with the merit of single mode operation. In a square resonator, the Q factor can be enhanced for some modes with a suitable size of the hole. For a hexagonal resonator with a side length of 1 mu m and a refractive index of 3.2, the mode Q factors first gradually decrease with the increase of the hole diameter for modes at a wavelength of about 1500 nm, then the modes transform to that of a microdisk with a jump of the mode wavelength as the hole diameter approaches 0.7 mu m. Finally, the mode Q factors greatly enhance as the hole diameter reaches about 1 mu m. The results indicate that the center hole can greatly modify mode characteristics, especially that of the mode Q factor. (C) 2009 Optical Society of America

Investigation of mode characteristics for a square cavity with a pedestal by a three-dimensional finite-difference time-domain technique

Mode characteristics of a strongly confined square cavity suspended in air via a pedestal on the substrate are investigated by a three-dimensional finite-difference time-domain technique. The mode wavelengths and mode quality factors (Q factors) are calculated as the functions of the size of the pedestal and the slope angle 0 of the sidewalls of the square slab, respectively For the square slab with side length of 2 mu m, thickness of 0.2 mu m, and refractive index of 3.4, on a square pedestal with refractive index of 3.17, the Q factor of the whispering-gallery (WG)-like mode transverse-electric TE(3.5)o first increases with the side length b of the square pedestal and then quickly decreases as b > 0.4 mu m, but the Q factor of the WG-like mode TE(4.6)o drops down quickly as b > 0.2 mu m, owing to their different symmetries. The results indicate that the pedestal can also result in mode selection in the WG-like modes. In addition, the numerical results show that the Q factors decrease 50% as the slope angle of the sidewalls varies from 90 degrees to 80 degrees. The mode characteristics of WG-like modes in the square cavity with a rectangular pedestal are also discussed. The results show that the nonsquare pedestal largely degrades the WG-like modes. (c) 2006 Optical Society of America

Whispering-gallery-likel modes in square resonators

The mode frequencies and field distributions of whispering-gallery (WG)-like modes of square resonators are obtained analytically, which agree very well with the numerical results calculated by the FDTD technique and Pade approximation method. In the analysis, a perfect electric wall for the transverse magnetic mode or perfect magnetic wall for the transverse electric mode is assumed at the diagonals of the square resonators, which not only provides the transverse mode confinement, but also requires the longitudinal mode number to be an even integer. The WG-like modes of square resonators are nondegenerate modes with high-quality factors, which make them suitable for fabricating single-mode low-threshold semiconductor microcavity lasers.

Analysis of mode quality factors for equilateral triangle semiconductor microlasers with rough sidewalls

The eigenmode characteristics for equilateral triangle resonator (ETR) semiconductor microlasers are analysed by the finite-difference time-domain technique and the Pade approximation. The random Gaussian correlation function and sinusoidal function are used to model the side roughness of the ETR. The numerical results show that the roughness can cause the split of the degenerative modes, but the confined modes can still have a high quality factor. For the ETR with a 3 mum side length and the sinusoidal fluctuation, we can have a quality factor of 800 for the fundamental mode in the wavelength of 1500 nm, as the amplitude of roughness is 75 mn.

Influence of output waveguide on mode quality factor in semiconductor microlasers with an equilateral triangle resonator

Semiconductor microlasers with an equilateral triangle resonator (ETR) and an output waveguide are proposed and analyzed by the finite-difference time-domain technique and the Pade approximation. The numerical results show that microlasers with an output waveguide still have a high-quality factor (Q factor) and are suitable to realize directional emission. For the ETR with a 0.46-mum-width opening in one of the vertices connected to the output waveguide, we have the Q factor of 1.5x10(3) and 2.5x10(2) for the TM fundamental mode at the wavelength of 1.55 mum, as the side length of the ETR is 5 and 3 mum. The simulated intensity distributions are presented for the fundamental mode in the ETR with a side length of 3 mum and an opening of 0.23 mum. (C) 2000 American Institute of Physics. [S0003-6951(00)01749-6].

Anisotropic radiation pattern from InGaAlP quantum well mesa-like microdisks

To overcome the isotropic directional emission of an ideal circular microdisk, two kinds of cylindrical mesa-like InGaAlP single quantum well (SQW) microdisks emitting at a visible red wavelength of 0.66 mu m have been fabricated. An anisotropic luminescence pattern was revealed by the microscopic fluorescence (FL) image. FL intensity, preferentially enhanced with twofold symmetry, appeared at the circumference of the InGaAlP SQW microdisks. Our results demonstrated that anisotropic radiation can be achieved by geometry shaping of the disks on the top view two-dimensional boundary slightly deformed from circular shape and/or on the side-view cross-section of the circular mesa by wet etching anisotropic undercut. (C) 2000 Elsevier Science Ltd. All rights reserved.

AlGaInAs-InPMicrocylinder Lasers Connected With an Output Waveguide

AlGaInAs-InPmicrocylinder lasers connected with an output waveguide are fabricated by planar technology. Room-temperature continuous-wave operation with a threshold current of 8 mA is realized for a microcylinder laser with the radius of 10 mu m and the output waveguide width of 2 mu m. The mode Q-factor of 1.2 x 10(4) is measured from the laser spectrum at the threshold. Coupled mode characteristics are analyzed by 2-D finite-difference time-domain simulation and the analytical solution of whispering-gallery modes. The calculated mode Q-factors of coupled modes are in the same order as the measured value.

Eigenmode confinement in semiconductor microcavity lasers with an equilateral triangle resonator

We analyze the mode behaviors for semiconductor lasers with an equilateral triangle resonator by deriving the mode field distribution and the eigenvalue equation. The eigenvalue equation shows that the longitudinal mode wavelength interval is equivalent to that of a Fabry-Perot cavity with the cavity length of 1.5a, where a is the side length of the equilateral triangle resonator. The transverse waveguiding is equivalent to as a strip waveguide with the width of root 3a/ 2, and the number of transverse modes supported by the resonator is limited by the total reflection condition on the sides of the equilateral triangle. Semiconductor microcavity laser with an equilateral triangle resonator is suitable to realize single mode operation, and the mode wavelength can be adjusted by changing the side length.

Quality analysis of herbal medicine products prepared from Herba sarcandrae by capillary electrophoresis with electrochemical detection

A capillary electrophoresis with electrochemical detection(CE-ED) method was developed for the quality analysis of herbal medicine products prepared from the same herb of Herba Sarcandrae: Fufang Caoshanhu tablets, Qingrexiaoyanning capsules, and Xuekang oral liquids. Under the optimal analysis conditions, the low detection limit[1.0x10(-7) mol/L(S/N=3)] and the wide linear range(1.0x10(-7)-1.0x10(-4) mol/L) were obtained for quality standard compound of isofraxidin. The precisions of the peak current and the migration time(as RSDs) for the real sample analysis were 2.0%-2.6%, and 1.2%-1.8% for isofraxidin, respectively.

Electrochemical Detection of Hydrazine Based on Electrospun Palladium Nanoparticle/Carbon Nanofibers

In this work, we developed an electrochemical method for the detection of hydrazine based oil palladium nanoparticle/carbon nanofibers (Pd/CNFs). Pd/CNFs were prepared by electrospinning technique and subsequent thermal treatments. The electrocatalytic behaviors of Pd/CNFs modified glassy carbon electrode (Pd/CNF-GCE) for hydrazine oxidation were evaluated by cyclic voltammetry (CV), an obvious and well-defined oxidation peak appeared at -0.32 V (vs. Ag/AgCl). The mechanism of the oxidation of hydrazine at Pd/CNF-GCE was also studied, which demonstrated an irreversible diffusion-controlled electrode process and a four-electron transfer involved in the overall reaction. Furthermore, the wide linear range, low detection limit, good reproducibility and excellent storage stability were obtained utilizing differential pulse voltammetry (DPV).