Showing papers by "Omer Nur published in 2011"

The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes

Abstract: In this article, the electroluminescence (EL) spectra of zinc oxide (ZnO) nanotubes/p-GaN light emitting diodes (LEDs) annealed in different ambients (argon, air, oxygen, and nitrogen) have been investigated. The ZnO nanotubes by aqueous chemical growth (ACG) technique on p-GaN substrates were obtained. The as-grown ZnO nanotubes were annealed in different ambients at 600°C for 30 min. The EL investigations showed that air, oxygen, and nitrogen annealing ambients have strongly affected the deep level emission bands in ZnO. It was concluded from the EL investigation that more than one deep level defect is involved in the red emission appearing between 620 and 750 nm and that the red emission in ZnO can be attributed to oxygen interstitials (Oi) appearing in the range from 620 nm (1.99 eV) to 690 nm (1.79 eV), and to oxygen vacancies (Vo) appearing in the range from 690 nm (1.79 eV) to 750 nm (1.65 eV). The annealing ambients, especially the nitrogen ambient, were also found to greatly influence the color-rendering properties and increase the CRI of the as - grown LEDs from 87 to 96.

Selective potentiometric determination of uric acid with uricase immobilized on ZnO nanowires

Abstract: In this study, a potentiometric uric acid biosensor was fabricated by immobilization of uricase onto zinc oxide (ZnO) nanowires. Zinc oxide nanowires with 80-150 nm in diameter and 900 nm to 1.5 mu ...

Selective determination of urea using urease immobilized on ZnO nanowires

Abstract: Well-aligned zinc oxide (ZnO) nanowire arrays were fabricated on gold-coated plastic substrates using a low-temperature aqueous chemical growth (ACG) method. The ZnO nanowire arrays with 50-130 nm ...

Zinc oxide nanorods/polymer hybrid heterojunctions for white light emitting diodes

Abstract: Zinc oxide (ZnO) with its deep level defect emission covering the whole visible spectrum holds promise for the development of intrinsic white lighting sources with no need of using phosphors for light conversion. ZnO nanorods (NRs) grown on flexible plastic as substrate using a low temperature approach (down to 50 °C) were combined with different organic semiconductors to form hybrid junction. White electroluminescence (EL) was observed from these hybrid junctions. The configuration used for the hybrid white light emitting diodes (LEDs) consists of two-layers of polymers on the flexible plastic with ZnO NRs on the top. The inorganic/organic hybrid heterojunction has been fabricated by spin coating the p-type polymer poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT : PSS) for hole injection with an ionization potential of 5.1 eV and poly(9, 9-dioctylfluorene) (PFO) is used as blue emitting material with a bandgap of 3.3 eV. ZnO NRs are grown on top of the organic layers. Two other configurations were also fabricated; these are using a single MEH PPV (red-emitting polymer) instead of the PFO and the third configuration was obtained from a blend of the PFO and the MEH PPV. The white LEDs were characterized by scanning electron microscope, x-ray diffraction (XRD), current–voltage (I–V) characteristics, room temperature photoluminescence (PL) and EL. The EL spectrum reveals a broad emission band covering the range from 420 to 800 nm, and the emissions causing this white luminescence were identified.

Single nanowire-based UV photodetectors for fast switching

Abstract: Relatively long (30 µm) high quality ZnO nanowires (NWs) were grown by the vapor-liquid-solid (VLS) technique. Schottky diodes of single NW were fabricated by putting single ZnO NW across Au and Pt electrodes. A device with ohmic contacts at both the sides was also fabricated for comparison. The current-voltage (I-V) measurements for the Schottky diode show clear rectifying behavior and no reverse breakdown was seen down to -5 V. High current was observed in the forward bias and the device was found to be stable up to 12 V applied bias. The Schottky barrier device shows more sensitivity, lower dark current, and much faster switching under pulsed UV illumination. Desorption and re-adsorption of much smaller number of oxygen ions at the Schottky junction effectively alters the barrier height resulting in a faster response even for very long NWs. The NW was treated with oxygen plasma to improve the switching. The photodetector shows high stability, reversibility, and sensitivity to UV light. The results imply that single ZnO NW Schottky diode is a promising candidate for fabricating UV photodetectors.

Intracellular K $^+$ Determination With a Potentiometric Microelectrode Based on ZnO Nanowires

Abstract: The fabrication and application of an intracellular K+ -selective microelectrode is demonstrated. ZnO nanowires with a diameter of 100-180 nm and a length of approximately 1.5 μm are grown on a borosilicate glass microcapillary. The ZnO nanowires were coated by a K+ -ionophore-containing membrane. The K+-selective microelectrode exhibited a K+-dependent potentiometric response versus an Ag/AgCl reference microelectrode that was linear over a large concentration range (25 μM-125 mM) with a minimum detection limit of 1 μM. The measured K+ concentrations in human adipocytes and in frog oocytes were consistent with values of K+ concentrations reported in the literature. The sensor has several advantages including ease of fabrication, ease of insertion into the cells, low cost, and high selectivity features that make this type of sensor suitable to characterize physiologically relevant ions within single living cells.

Forward- and reverse-biased electroluminescence behavior of chemically fabricated ZnO nanotubes/GaN interface

Abstract: Electroluminescence characteristics of an n-ZnO nanotubes/p-GaN heterostructure light-emitting diode (LED) have been investigated at forward and reverse bias. Distinctly different emission spectra have been observed and the location of the recombination of electron–hole is analyzed under both configurations. The forward-biased emission spectrum shows two peaks centered at around 450 and 560 nm, while the reverse-biased spectrum exhibits a single emission peak at 650 nm. By comparing the current transport mechanisms, it is suggested that the violet-blue emission peak (450 nm) observed only under forward bias is originating from the heterojunction of the ZnO nanotubes/p-GaN LED. The influence on the emission intensity of the device with the increase in temperature at constant current is studied in the range from 25 to 65 °C, to check its compatibility for practical applications and under harsh conditions.

Wireless remote monitoring of glucose using a functionalized ZnO nanowire arrays based sensor.

Abstract: This paper presents a prototype wireless remote glucose monitoring system interfaced with a ZnO nanowire arrays-based glucose sensor, glucose oxidase enzyme immobilized onto ZnO nanowires in conjunction with a Nafion® membrane coating, which can be effectively applied for the monitoring of glucose levels in diabetics. Global System for Mobile Communications (GSM) services like General Packet Radio Service (GPRS) and Short Message Service (SMS) have been proven to be logical and cost effective methods for gathering data from remote locations. A communication protocol that facilitates remote data collection using SMS has been utilized for monitoring a patient’s sugar levels. In this study, we demonstrate the remote monitoring of the glucose levels with existing GPRS/GSM network infra-structures using our proposed functionalized ZnO nanowire arrays sensors integrated with standard readily available mobile phones. The data can be used for centralized monitoring and other purposes. Such applications can reduce health care costs and allow caregivers to monitor and support to their patients remotely, especially those located in rural areas.

ZnO nanorods-polymer hybrid white light emitting diode grown on a disposable paper substrate

Abstract: We demonstrate intrinsic white light emission from hybrid light emitting diodes fabricated using an inorganic-organic hybrid junction grown at 50 C on a paper substrate. Cyclotene was first spin co ...

Effect of the polymer emission on the electroluminescence characteristics of n-ZnO nanorods/p-polymer hybrid light emitting diode

Abstract: Hybrid light emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods and polymers (single and blended) were fabricated and characterized. The ZnO nanorods were grown by the chemical bath deposition method at 50°C. Three different LEDs, with blue emitting, orange-red emitting or their blended polymer together with ZnO nanorods, were fabricated and studied. The current–voltage characteristics show good diode behavior with an ideality factor in the range of 2.1 to 2.27 for all three devices. The electroluminescence spectrum (EL) of the blended device has an emission range from 450 nm to 750 nm, due to the intermixing of the blue emission generated by poly(9,9-dioctylfluorene) denoted as PFO with orange-red emission produced by poly(2-methoxy-5(20-ethyl-hexyloxy)-1,4-phenylenevinylene) 1,4-phenylenevinylene) symbolized as MEH PPV combined with the deep-band emission (DBE) of the ZnO nanorods, i.e. it covers the whole visible region and is manifested as white light. The CIE color coordinates showed bluish, orange-red and white emission from the PFO, MEH PPV and blended LEDs with ZnO nanorods, respectively. These results indicate that the choice of the polymer with proper concentration is critical to the emitted color in ZnO nanorods/p-organic polymer LEDs and careful design should be considered to obtain intrinsic white light sources.

Selective zinc ion detection by functionalised ZnO nanorods with ionophore

Abstract: In this paper, highly dense and well aligned single-crystal zinc oxide nanorods were grown along the c-axis on a gold coated glass substrate using a low temperature aqueous chemical growth approach ...

Polycation stabilization of graphene suspensions

Abstract: Graphene is a leading contender for the next-generation electronic devices. We report a method to produce graphene membranes in the solution phase using polymeric imidazolium salts as a transferring medium. Graphene membranes were reduced from graphene oxides by hydrazine in the presence of the polyelectrolyte which is found to be a stable and homogeneous dispersion for the resulting graphene in the aqueous solution. A simple device with gold contacts on both sides was fabricated in order to observe the electronic properties.

Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light emitting diodes

Abstract: Light-emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods grown by vapor-liquid-solid catalytic growth method were irradiated with 2-MeV helium (He+) ions. The fabricated LEDs were irradiated with fluencies of approximately 2 × 1013 ions/cm2 and approximately 4 × 1013 ions/cm2. Scanning electron microscopy images showed that the morphology of the irradiated samples is not changed. The as-grown and He+-irradiated LEDs showed rectifying behavior with the same I-V characteristics. Photoluminescence (PL) measurements showed that there is a blue shift of approximately 0.0347 and 0.082 eV in the near-band emission (free exciton) and green emission of the irradiated ZnO nanorods, respectively. It was also observed that the PL intensity of the near-band emission was decreased after irradiation of the samples. The electroluminescence (EL) measurements of the fabricated LEDs showed that there is a blue shift of 0.125 eV in the broad green emission after irradiation and the EL intensity of violet emission approximately centered at 398 nm nearly disappeared after irradiations. The color-rendering properties show a small decrease in the color-rendering indices of 3% after 2 MeV He+ ions irradiation.

Study of intrinsic white light emission and its components from ZnO-nanorods/p-polymer hybrid junctions grown on glass substrates

Abstract: We report white-light luminescence from ZnO-organic hybrid light emitting diodes grown on glass substrate by low temperature aqueous chemical growth. The configuration used for the hybrid white light emitting diodes (HWLEDs) consists of two-layers of polymers (PEDOT:PSS/PFO) on glass with top ZnO nanorods. Electroluminescence spectra of the HWLEDs demonstrate the combination of emission bands arising from the radiative recombination in polymer and ZnO nanorods. In order to distinguish emission bands we used a Gaussian function to simulate the experimental data. The emitted white light was found to be the superposition of a blue line at 454 nm, a green emission at 540 nm, orange line at 617 nm, and finally a red emission at 680 nm. The transitions causing these emissions are identified and discussed in terms of the energy band diagram of the hybrid junction. Color coordinates measurement of the WLED reveals that the emitted light has a white impression with 70 color rendering index and correlated color temperature 5500 K. Comparison between ITO and aluminum top contacts and its influence on the emitted intensity is also discussed.

Study of the Distribution of Radiative Defects and Reabsorption of the UV in ZnO Nanorods-Organic Hybrid White Light Emitting Diodes (LEDs).

Abstract: In this study, the low temperature aqueous chemical growth (ACG) method was employed to synthesized ZnO nanorods to process-organic hybrid white light emitting diodes (LEDs) on glass substrate. Electroluminescence spectra of the hybrid white LEDs demonstrate the combination of emission bands arising from radiative recombination of the organic and ZnO nanorods (NRs). Depth resolved luminescence was used for probing the nature and spatial distribution of radiative defects, especially to study the re-absorption of ultraviolet (UV) in this hybrid white LEDs structure. At room temperature the cathodoluminescence (CL) spectra intensity of the deep band emission (DBE) is increased with the increase of the electron beam penetration depth due to the increase of defect concentration at the ZnO NRs/Polyfluorene (PFO) interface and probably due to internal absorption of the UV. A strong dependency between the intensity ratio of the UV to the DBE bands and the spatial distribution of the radiative defects in ZnO NRs has been found. The comparison of the CL spectra from the PFO and the ZnO NRs demonstrate that PFO has a very weak violet-blue emission band, which confirms that most of the white emission components originate from the ZnO NRs.

The correlation between radiative surface defect states and high color rendering index from ZnO nanotubes

Abstract: Combined surface, structural and opto-electrical investigations are drawn from the chemically fashioned ZnO nanotubes and its heterostructure with p-GaN film. A strong correlation has been found between the formation of radiative surface defect states in the nanotubes and the pure cool white light possessing averaged eight color rendering index value of 96 with appropriate color temperature. Highly important deep-red color index value has been realized > 95 which has the capability to render and reproduce natural and vivid colors accurately. Diverse types of deep defect states and their relative contribution to the corresponding wavelengths in the broad emission band is suggested.

Applications of zinc oxide nanowires for bio-photonics and bio-electronics

Abstract: Using zinc oxide (ZnO) nanostructures, nanorods (NRs) and nanoparticles (NPs) grown on different substrates (sub-micrometer glass pipettes, thin silver wire and on plastic substrate) different bio-sensors were demonstrated. The demonstrated sensors are based on potentiometric approach and are sensitive to the ionic metals and biological analyte in question. For each case a selective membrane or enzyme was used. The measurements were performed for intracellular environment as well as in some cases (cholesterol and uric acid). The selectivity in each case is tuned according to the element to be sensed. Moreover we also developed photodynamic therapy approach based on the use of ZnO NRs and NPs. Necrosis/apoptosis was possible to achieve for different types of cancerous cell. The results indicate that the ZnO with its UV and white band emissions is beneficial to photodynamic therapy technology.

The effect of post-growth annealing on the colour properties of n-ZnO nanorods/p-GaN white LEDs:

Abstract: The effect of post-growth annealing on the colour properties of the light emitted by n-ZnO nanorods/p-GaN white LEDs has been investigated. The as-grown ZnO nanorods were annealed in nitrogen, oxyg ...

Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodes

Abstract: Annealing effects on optical and electrical properties of n-ZnO/p-Si heterojunction diodes are studied. ZnO nanorods are grown on p-Si substrate by aquous chemical growth technique. As grown sample ...