M. Yahaya

The detection of pesticides in water using ZnCdSe quantum dot films

This paper reports an attempt to develop a sensor system for detecting pesticides based on the effect of an analyte on the photoluminescence (PL) intensity of ZnCdSe quantum dot (QD) films. The ZnCdSe QDs were synthesized using a wet-chemical process. The sensor system comprises an excitation light source made of a laser diode, a dual arm fibre optic probe, a spectrometer and a sensor chamber. The QD films were deposited by dropping QD solution onto the probe surface and drying them at ambient temperature. The pesticides used in this study were Dipel, Siven 85% WP and Water-Dispersible Granules WG insecticides. The detection of pesticides was done by comparing the photoluminescence (PL) spectra of the films dipped in the deionized water and in pesticide solutions by varying the concentration of the pesticide solutions from 2.5 to 2500 μg l−1. It was observed that the PL intensity of the films was quenched by the presence of the pesticide molecules. The quenching degree increased with the concentration of the pesticide solutions. There is a linear relationship between the pesticide solution concentrations and the QD film sensor sensitivities. The sensitivity of the sensor system depended on the type of pesticides successively from the highest to lowest sensitivity in the order Siven 85% WP, Dipel and Water-Dispersible Granules WG. The QD films could be used as fluorescence sensors to detect water that is contaminated by pesticides.

Electroluminescent from hybrid of Cdse quantum dot-organic light emitting diode

This paper reports the fabrication of a quantum dots (QD)-organics hybrids light-emitting diode (LED) for potential light sources. Organic light emitting diode (OLED) have become a focus of attention since past decades for potential light sources in a flat panel displays applications. Despite their intriguing performance in producing rich-color light emission, they still faced several critical defects, such as relatively low-brightness, low-chemical and photostability and short lifetime. Here, we demonstrate a novel system for the production of pure-color light emission with exceptionally high brightness by utilizing quantum dots that are hybridizing with light emitting organic materials, as an active material in light - emitting diode devices. Organic-quantum dots hybrid LED devices was fabricated by sandwiching the quantum dots monolayer between the electron transport layer (ETL) and hole transport layer (HTL) in a conventional OLED structure (ITO/ETL/QD/HTL/Al). Quantum dots of CdSe (ZnS) core-shell structure were function as the emitting layer. The ETL and HTL were poly(vinyl carbazol), PVK and tris(8-quinolinolato)aluminum(III), Alq3; respectively. The current-voltage (I-V) characterization on the device was found that the hybrid LED exhibited a strong blue emission under a relatively low bias voltage, of which their turn-on voltage was as low as 5.0 V.

The Use of Photoluminescence Spectra of TiO2 Nanoparticles Coated With Porphyrin Dye Thin Film for Grading Agarwood Oil

This paper explores the possibility using nanostructure thin film of TiO2 nanoparticles coated with porphyrin dye based on fluorescence technique to grade agarwood oil. The sensing material was prepared using synthesized of TiO2 nanoparticles colloid is in a sol-gel form. Then the nanoparticles were coated with dye, Iron (III) meso tetraphenyl porphine chloride. The coated nanoparticles were deposited on quartz substrate using self- assembly through dip coating technique. The sensing properties of the thin film toward five grades of agarwood oil were studied using luminescence spectrometer. It was found that the thin film produced different emission spectra peaks for different grades of agarwood oil. Hence the thin film potentially be use as sensing material for grading agarwood oil and others nature product for the future.

Solid state photoelectrochemical cells utilising graphite thin films counter electrode

This paper reports the use of graphite thin films as a counter electrode of a solid state photoelectrochemical cells of ITO/TiO2/PVC-LiClO4/graphite. The photoelectrochemical cells material was a screen-printed layer of titanium dioxide onto an ITO-covered glass substrate which was used as a working electrode of the device. The solid electrolyte used was PVC-LiClO4 that was prepared by solution casting technique. The graphite films which serve as a counter electrode were prepared onto glass substrate by electron beam evaporation technique at substrate temperatures variation of 25, 50, 100, 150 and 200 °C. The dependence of sheet resistance and surface morphology of the graphite films on substrate temperature were studied. The films deposited at 25 °C shows the smoothest surface morphology and the smallest grain size. Bigger grain size, rougher surface morphology of graphite film counter electrode. The current-voltage characteristics of four devices utilising the graphite counter electrode with different substrate temperature in dark as well as under illumination of 100 mWcm−2 light from a tungsten halogen lamp were recorded at room temperature and at 50 °C, respectively. It was found that the photovoltaic parameters of the device such as short-circuit current density, Jsc and open-circuit voltage, Voc increases with the decreasing average grain size of the graphite counter electrode. The device whose graphite film counter electrode was deposited onto the glass substrate at 25 °C gave the highest Jsc of 0.32 µA/cm2 and Voc of 117 mV, respectively.

The effect of dopants on the sensing selectivity of SnO/sub 2/ thin films-based gas sensors

The development of metal oxide gas sensor devices with optimized selectivity and sensitivity has been gaining prominence in recent years. This paper reports the influence of doping to optimize the selectivity of the SnO/sub 2/ thin films doped with Pt, Pd, CuO, ZnO and TiO/sub 2/ toward the variety of vapor gases such as cyclohexane, chloroform, benzene and acetone. The films were prepared by using electron beam evaporation. The sensing selectivity was based on the electrical change of the films when being exposed to vapor gases. Each film shows a different response toward different vapor gases. The selectivity of these films was observed to be depended markedly on the doping materials.

Study of X-ray diffraction patterns in Langmuir-Blodgett films using the few-slits model of diffraction

Abstract Multilayer films of cadmium 22-tricosenoiate were deposited by using the Langmuir-Blodgett technique in the Z-mode of deposition. The films were then irradiated with various γ-irradiation doses. Small-angle X-ray diffraction patterns of the films before and after γ-irradiation were studied by applying the model of diffraction by a few slits. The X-ray diffraction patterns of the films before γ-irradiation show nine equidistant peaks, indicating the presence of a regular periodic structure in the film. The intensities of the even-order diffraction peaks are relatively less than those from the neighbouring odd-order peaks. This phenomenon, known as even-odd intensity oscillation, was successfully explained by this model. The position of the X-ray diffraction peaks taken for films after different γ-irradiation doses does not change, indicating that the average spacing in the film is unaffected by γ-irradiation. However, the intensity of the diffraction peaks of the film does change with γ-irradiation dose. This change can be explained by the change of electron density along the molecular chain in the layer before and after various γ-irradiation doses.

Growth And Synthesis Of ZnO Nanorod Arrays By A Chemical Solution Method

ZnO is an n‐type, wide band gap II–VI compound semiconductor with a band gap energy of 3.37 eV at room temperature. ZnO possesses a large exciton binding energy hence its nanowires and nanorods have been regarded as one of the most promising materials for nanoscale electronic and optoelectronic devices such as laser diodes, optical detectors and switches. Several techniques have been utilized to fabricate ZnO nanoscale materials, such as molecular beam epitaxy, sputtering, chemical vapor deposition, spray pyrolysis, pulsed laser deposition (PLD), anodic alumina oxide (AAO) template, electrochemical deposition, and aqueous solution deposition methods. In an attempt to prepare the best quality nanowires, we chose a chemical solution method. This paper reports the preparation and characterization of nanorod arrays of ZnO on ITO glass substrates which were pre‐coated with ZnO. The structural and optical properties of ZnO nanorod arrays were investigated using scanning electron microscopy, X‐ray diffraction an...

Fabrication of CdSe quantum dots-PHF organic hybrid light emitting diodes

Quantum dots (QDs) have been attracted an active interest for light emitting device due to their unique high luminescence efficiency and narrow emission spectra as a result of the strong electrons confinement in its nanoscale core that is potential for production of pure colour light emission. In this work, a CdSe quantum dot-PHF organic hybrid light emitting devices have been fabricated. To study the effect of the CdSe QDs layer in the performance of the devices, variations of QDs layer were prepared. It is found that the present of the QDs layer improved the electroluminescence property of the device. In this article, we report the fabrication of light emitting diode using quantum dots that hybridize with PHF organic material. The light emitting device was found to give a bright green colour emission centering at 533.61 nm. The effect of QDs layer on the performance of light emitting devices was discussed.