Transparent p‐NiO/n‐ZnO diodes used in circuit rectifiers

We report on the fabrication of a transparent photostable cell circuit composed of drive and resistor diodes which are face‐to‐face connected to each other with different device area. The diodes consisted of e‐beam evaporated p‐NiO on sputter‐deposited n‐ZnO for p/n diode formation on indium‐tin‐oxide glass. Our transparent diodes show photostable rectifying behavior, about 10³ on/off current ratio and even dynamic rectification at a maximum frequency of 100 Hz AC input signal in ambient light. The noticeable photo‐responsivity of the circuit was obtained only under ultraviolet (UV) light. We conclude that our transparent diode circuit is promising in enriching the field of transparent device electronics. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Advantages of Adaptive Speckle Filtering Prior to Application of Iterative Deconvolution Methods for Optical Coherent Tomography Imaging

The axial resolution of optical coherence tomography (OCT) is closely related to the light source spectrum width. Unfortunately, most basic sources providing the required power for decent OCT image have narrow spectra, which generate a resolution loss. Assuming the OCT system is linear shift-invariant, we can consider the system output as the convolution of the theoretical signal with a system impulse response due to this spectrum narrowness. It becomes then possible to enhance this resolution through iterative deconvolution methods (IDM). However those methods have a significant drawback, as they usually significantly enhance speckle, which is another consequence of the source spectrum narrowness. To compensate this, we rely on preliminary speckle filtering, and especially the adaptative ones, which allow tackling the speckle without blurring the image. We first studied enhancement proposed by most popular IDMs on OCT images, and then the effect of preliminary adaptive speckle filtering (ASF) by different common adaptive methods. Then, among those methods, we combined Frost filter and Richardson-Lucy deconvolution in the appropriated way; this way we both enhanced resolution by 2 and reduced speckle (raising CNR from 0.7 to 1.3)     

Native oxide buried InAlAs ridge waveguide laser diode

InAlAs wet thermal oxidation process was adopted to fabricate ridge waveguide laser diodes. First, applying the oxidation process on the whole etched surface of an InAlAs upper cladding layer, we formed a current blocking and optical confining layer of ridge waveguide laser diode. This is a self-aligned structure, which makes the laser diode fabrication steps much simpler and etching-depth control less important. Assessment of the fabricated laser diode revealed that current-voltage characteristics and slope efficiency did not worsen, and threshold current was reduced by the oxidation process. PACS 85.35.Be; 42.55.Px     

Simultaneous Determination of Acetylsalicylic Acid and Caffeine in Pharmaceutical Formulation by First Derivative Synchronous Fluorimetric Method

A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Δλ=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Δλ=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 μg ml⁻¹ (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 μg ml⁻¹ (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40–102% for acetylsalicylic acid and 90–100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97–99% for acetylsalicylic acid and 97–98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 μg ml⁻¹ and 0.0306 μg ml⁻¹ for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 μg ml⁻¹ of acetylsalicylic acid is 2.75% and for 2.2 μg ml⁻¹of caffeine is 1.7%.     

Efficient inverse radiation analysis in a cylindrical geometry using a combined method of hybrid genetic algorithm and finite-difference Newton method

An inverse radiation problem was considered to estimate boundary conditions such as temperature distribution and emissivity in axisymmetric absorbing, emitting, and scattering medium, given the measured incident radiative heat fluxes. The finite-volume method was employed to solve a direct radiative transfer equation for a two-dimensional axisymmetric geometry. Various parameter estimators, such as conjugate-gradient method, hybrid genetic algorithm, and finite-difference Newton method, were employed to solve the inverse problems, while discussing their performances in terms of estimation accuracy and computational efficiency. Based on this, we proposed, as a best inverse analysis tool, a new combined method that adopted the hybrid genetic algorithm as an initial value selector and used the finite-difference Newton method as a parameter estimator.     

Investigation of the Doughnut Effect in Cy3-Labeled Protein Microarrays using Scanning Near-Field Optical Microscope

We demonstrate the fluorescence mapping of protein microarrays by the technique of scanning near-field optical microscopy (SNOM) and confocal microscopy. Micron sized spots (300 μm) of human Immunoglobulin G (hIgG) protein with and without a Cy3 dye labeling have been fabricated on glass substrates by an immobilization method which makes use of calixcrown derivatives termed Prolinker. We have also tried to probe into the well-known “doughnut effect” observed in fluorescence images of proteins using the SNOM technique. The topographic and fluorescence SNOM images revealed that the number of proteins at the boundary of the spot were more than at the center in the case of the microarray spot which showed brighter luminescence at the edge than at the center in the confocal image.     

Influence of organic capping layers on the performance of transparent organic light-emitting diodes

We investigate a set of transparent organic LEDs (TOLEDs) with different organic capping layer (OC) thicknesses to understand the capping layer effect. We find that thickness variation of the OC strongly influences the emission properties of TOLEDs and exhibits different trends for top or bottom emission. The external quantum efficiency for the top side can be enhanced by a factor of 63%, but that of the bottom side only by 4% compared to a reference device without an OC. Additionally, we demonstrate that the introduction of the OC is an effective method to control the bottom-to-top emission ratio within a measured range from 2.87 to 6.05.