Gul Amin

Influence of pH, precursor concentration, growth time, and temperature on the morphology of ZnO nanostructures grown by the hydrothermal method

We investigated the influence of the pH value, precursor concentration (C), growth time and temperature on the morphology of zinc oxide (ZnO) nanostructures. The pH of the starting solution was varied from1.8 to 12.5. It was found that the final pH reaches an inherent value of 6.6 independently of the initial pH solution. Various ZnO structures of nanotetrapod-like, flower-like, and urchin-like morphology were obtained at alkaline pH (8 to 12.5) whereas for pH solution lower than 8 rod-like nanostructures occurred. Moreover, we observed the erosion of the nanorods for a pH value less than 4.6. By changing the concentrations the density and size were also varied. On going from a high (C > 400mM) to lower (C < 25mM) C, the resulted ZnO nanostructures change from a film to nanorods (NRs) and finally nanowires (NWs). It was also found that the length and diameter of ZnO NRs follow a linear relation with time up to 10 hours, above which no further increase was observed. Finally the effect of growth temperature was seen as an influence on the aspect ratio.

Miniaturized pH Sensors Based on Zinc Oxide Nanotubes/Nanorods

ZnO nanotubes and nanorods grown on gold thin film were used to create pH sensor devices. The developed ZnO nanotube and nanorod pH sensors display good reproducibility, repeatability and long-term stability and exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl reference electrode over a large dynamic pH range. We found the ZnO nanotubes provide sensitivity as high as twice that of the ZnO nanorods, which can be ascribed to the fact that small dimensional ZnO nanotubes have a higher level of surface and subsurface oxygen vacancies and provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods, thus affording the ZnO nanotube pH sensor a higher sensitivity. Experimental results indicate ZnO nanotubes can be used in pH sensor applications with improved performance. Moreover, the ZnO nanotube arrays may find potential application as a novel material for measurements of intracellular biochemical species within single living cells.

Stable White Light Electroluminescence from Highly Flexible Polymer/ZnO Nanorods Hybrid Heterojunction Grown at 50°C

Stable intrinsic white light–emitting diodes were fabricated from c-axially oriented ZnO nanorods (NRs) grown at 50°C via the chemical bath deposition on top of a multi-layered poly(9,9-dioctylfluorene-co–N-(4-butylpheneylamine)diphenylamine)/poly(9,9dioctyl-fluorene) deposited on PEDOT:PSS on highly flexible plastic substrate. The low growth temperature enables the use of a variety of flexible plastic substrates. The fabricated flexible white light–emitting diode (FWLED) demonstrated good electrical properties and a single broad white emission peak extending from 420 nm and up to 800 nm combining the blue light emission of the polyflourene (PFO) polymer layer with the deep level emission (DLEs) of ZnO NRs. The influence of the temperature variations on the FWLED white emissions characteristics was studied and the devices exhibited high operation stability. Our results are promising for the development of white lighting sources using existing lighting glass bulbs, tubes, and armature technologies.

Buckling and elastic stability of vertical ZnO nanotubes and nanorods

Buckling and elastic stability study of vertical well aligned ZnO nanorods grown on Si substrate and ZnO nanotubes etched from the same nanorods was done quantitatively by nanoindentation technique. The critical load, modulus of elasticity, and flexibility of the ZnO nanorods and nanotubes were observed and we compared these properties for the two nanostructures. It was observed that critical load of nanorods (2890 μN) was approximately five times larger than the critical load of the nanotubes (687 μN). It was also observed that ZnO nanotubes were approximately five times more flexible (0.32 nm/μN) than the nanorods (0.064 nm/μN). We also calculated the buckling energies of the ZnO nanotubes and nanorods from the force displacement curves. The ratio of the buckling energies was also close to unity due to the increase/decrease of five times for one parameter (critical load) and increase/decrease of five times for the other parameter (displacement) of the two samples. We calculated critical load, critical s...

Recent progress on growth and device development of ZnO and CuO nanostructures and graphene nanosheets

Recent progress on the growth of zinc oxide (ZnO), copper oxide (CuO) and graphene nanosheets is presented and discussed. We here restrict the discussion to the hydrothermal low temperature growth regime. In view of this the most critical and important parameters for obtaining nanostructures with desired morphology are discussed and presented. Among all parameters, the temperature and the pH during growth were chosen due to their strong role in affecting the produced nanostructures. The application of this method to non-conventional substrates e.g. paper, is demonstrated. Different devices are fabricated using the grown material and their performance is discussed.

Scale-up synthesis of ZnO nanorods for printing inexpensive ZnO/polymer white light-emitting diode

In this study, possibilities of scaling up the synthesis of zinc oxide (ZnO) nanorods (NRs) by the hydrothermal method have been explored. It was found that batches yielding several grams can easily be made using common and easily available materials. Further, a printable composition was fabricated by mixing the obtained ZnO NRs into a common solvent-based screen printable varnish. Scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction, UV–vis spectroscopy analysis of the scaled up batch indicated that the ZnO nanostructures were of NRs shape, well crystalline and having less defects. Using the ZnO NRs-based printable composition a device fabrication on a flexible substrate was demonstrated, producing a flexible light-emitting device being highly tolerant to bending.

Highly efficient potentiometric glucose biosensor based on functionalized InN quantum dots

We present a fast, highly sensitive, and efficient potentiometric glucose biosensor based on functionalized InN quantum-dots (QDs). The InN QDs are grown by molecular beam epitaxy. The InN QDs are bio-chemically functionalized through physical adsorption of glucose oxidase (GOD). GOD enzyme-coated InN QDs based biosensor exhibits excellent linear glucose concentration dependent electrochemical response against an Ag/AgCl reference electrode over a wide logarithmic glucose concentration range (1 × 10−5 M to 1 × 10−2 M) with a high sensitivity of 80 mV/decade. It exhibits a fast response time of less than 2 s with good stability and reusability and shows negligible response to common interferents such as ascorbic acid and uric acid. The fabricated biosensor has full potential to be an attractive candidate for blood sugar concentration detection in clinical diagnoses.

Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes

The effects of the polymer concentration on the performance of hybrid light emitting diodes (LEDs) based on zinc oxide nanorods (ZnO NRs) and poly(9,9-dioctylfluorene) (PFO) were investigated. Various characterization techniques were applied to study the performance of the PFO/ZnO NR hybrid LEDs fabricated with various PFO concentrations. The fabricated hybrid LEDs demonstrated stable rectifying diode behavior, and it was observed that the turn-on voltage of the LEDs is concentration dependent. The measured room temperature electroluminescence (EL) showed that the PFO concentration plays a critical role in the emission spectra of the hybrid LEDs. At lower PFO concentrations of 2-6 mg/ml, the EL spectra are dominated by blue emission. However, by increasing the concentration to more than 8 mg/ml, the blue emission was completely suppressed while the green emission was dominant. This EL behavior was explained by a double trap system of excitons that were trapped in the β-phase and/or in the fluorenone defec...

Intrinsic white-light emission from zinc oxide nanorods heterojunctions on large-area substrates

Zinc oxide (ZnO) and especially in the nanostructure form is currently being intensively investigated world wide for the possibility of developing different new photonic devices. We will here present our recent findings on the controlled low temperature chemical growth of ZnO nanorods (NRs) on different large area substrates. Many different heterojunctions of ZnO NRs and p-substrates including those of crystalline e.g. p-GaN, p-SiC or amorphous nature e.g. p-polymer coated plastic and p-polymer coated paper will be shown. Moreover, the effect of the p-electrode of these heterojunctions on tuning the emitted wavelength and changing the light quality will be discussed. An example using ZnO NR/p-GaN will be shown and the electrical and electro-optical characteristics will be analyzed. For these heterojunctions the effect of post growth annealing and its effect on the electroluminescence (EL) spectrum will be shown. Finally, intrinsic white light emitting diodes based on ZnO NRs on foldable and disposable amorphous substrates (plastic and paper) will also be presented.

Fabrication and characterization of piezoelectric nanogenerator based on Al/ZnO/Au structure

Purpose The purpose of this research work is to harvest energy using the piezoelectric properties of ZnO nanowires (NW). Fabrication and characterization of the piezoelectric nanogenerator (NG), based on Al/ZnO/Au structure without using hosting layer, were done to harvest energy. The proposed method has full potential to harvest the cost-effective energy. Design/methodology/approach ZnO NW were fabricated between the thin layers of Al- and Au-coated substrates for the development of piezoelectric NG. To grow ZnO NW, ZnO seed layer was prepared on the Al-coated substrate, and then ZnO NW were grown by aqueous chemical growth method. Finally, Au top electrode was used to conclude the Al/ZnO/Au NG structure. The Al and Au electrodes were used to establish the ohmic and Schottky contacts with ZnO NW, respectively. Findings Surface morphology of the fabricated device was done by using scanning electron microscopy, and electrical characterization of the sample was performed with digital oscilloscope, picoammeter and voltmeter. The energy harvesting experiment was performed to excite the presented device. The fabricated piezoelectric-sensitive device revealed the maximum open circuit voltage up to 5 V and maximum short circuit current up to 30 nA, with a maximum power of 150 nW. Consequently, it was also shown that the output of the fabricated device was increased by applying the stress. The presented work will help for the openings to capture the mechanical energy from the surroundings to power up the nano/micro-devices. This research work shows that NGs have the competency to build the self-powered nanosystems. It has potential applications in biosensing and personal electronics. Originality/value The fabrication of simple and cost-effective piezoelectric NG is done with a structure of Al/ZnO/Au without using hosting layer. The presented method elucidates an efficient and cost-effective approach to harvest the mechanical energy from the native environment.