ZnO Nanostructure Templates as a Cost-Efficient Mass-Producible Route for the Development of Cellular Networks

The development of artificial surfaces which can regulate or trigger specific functions of living cells, and which are capable of inducing in vivo-like cell behaviors under in vitro conditions has been a long-sought goal over the past twenty years. In this work, an alternative, facile and cost-efficient method for mass-producible cellular templates is presented. The proposed methodology consists of a cost-efficient, two-step, all-wet technique capable of producing ZnO-based nanostructures on predefined patterns on a variety of substrates. ZnO—apart from the fact that it is a biocompatible material—was chosen because of its multifunctional nature which has rendered it a versatile material employed in a wide range of applications. Si, Si3N4, emulated microelectrode arrays and conventional glass cover slips were patterned at the micrometer scale and the patterns were filled with ZnO nanostructures. Using HeLa cells, we demonstrated that the fabricated nanotopographical features could promote guided cellular adhesion on the pre-defined micron-scale patterns only through nanomechanical cues without the need for further surface activation or modification. The basic steps of the micro/nanofabrication are presented and the results from the cell adhesion experiments are discussed, showing the potential of the suggested methodology for creating low-cost templates for engineered cellular networks

Copper Indium Gallium Selenide Thin Film Solar Cells

The solar energy as one of the new energy sources and a regenerated energy is abundant and pollution-free. Most photovoltaic devices (solar cells) sold in the market today are based on silicon wafers, the so-called "first generation" technology. The market at present is on the verge of switching to a "second generation" of thin film solar cell technology which offers prospects for a large reduction in material costs by eliminating the costs of the silicon wafers. Cadmium telluride (CdTe), amorphous silicon (a-Si) and copper indium gallium selenide (CIGS) are three thin film technologies which have achieved commercial production. This chapter gives the review of the CIGS solar cells regarding the heterostructures, materials, technology and research advances. It also states the key findings in our research and provides suggestions for future research

Photocatalytic hollow TiO2 and ZnO nanospheres prepared by atomic layer deposition

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Enhancement of the Performance of GaAs based Solar Cells by using Plasmonic, Anti-Reflection Coating and Hydrophobic Effects

Investigation of renewable energy resources is gaining huge momentum in recent years due to the limited fossil fuels, and their detriment impact on the environment. Solar energy is promising to meet the increased energy demand. In order to achieve this goal, solar energy has to be harvested efficiently at low cost. Therefore, higher efficiency solar cells are the primary focus of research worldwide. Photovoltaics based on InAs/GaAs intermediate band solar cells and their device performance enhancements are investigated in this dissertation. The device enhancement is carried out by surface modification methods. The dissertation work is inspired by the need of improved efficiency solar cells to meet the new energy demands. In this project, InAs/GaAs intermediate band solar cell and their device performance enhancement are investigated. The device enhancement is carried out though implementing surface modification by using plasmonic effect, anti-reflection coatings and self-cleaning surfaces. Single junction and quantum dots solar cells performance has been unsatisfying due to several optical losses especially high surface reflection. Hence, in this project, potential application of plasmonic effect and significant device performance enhancement implementing anti-reflection coating are studied experimentally. Significantly, GaAs based photovoltaics solar cells efficiencies were improved by 40 - 50 %. In addition, self-cleaning surfaces with contact angle above 156o has been achieved. This self-cleaning surface can ensure proper functionality of the anti-reflection coatings

One-pot synthesis of multifunctional ZnO nanomaterials: study of superhydrophobicity and UV photosensing property

ZnO nanomaterials are synthesized using one-pot synthesis method. Equimolar solution of Zinc Nitrate hexahydrate (Zn(NO3)(2).6H(2)O) and Hexamethylenetetramine (C6H12N4) is used as a precursor for ZnO formation. Different nanostructures of ZnO are achieved by controlling the pH of the growth solution in the range 2-12 (acidic to alkali). ZnO nanostructures are evaluated for hydrophobic property using static contact angle measurement setup and UV photosensing activity. Surface morphology, structural properties and compositional analysis of ZnO nanostructures are examined by field emission scanning electron microscope (FE-SEM), energy dispersive X-ray analysis (EDX), high-resolution transmission electron microscope (FEG-TEM) and X-ray diffraction (XRD) measurements. Existence of ZnO wurtzite structure is confirmed from XRD study and is analyzed by Rietveld refinement method. Nanomaterials are characterized using Raman spectroscopy which confirms highest oxygen deficiency in ZnO nanorods. The material shows remarkable superhydrophobic and UV photosensing property and hence the name multifunctional. Among all morphologies grown at different pH values, ZnO nanorods show superhydrophobic nature with contact angle more than 170 degrees. Total surface energy value of ZnO nanostructures is calculated using Wendt two-component theory. Different ZnO nanostructures (with variation of pH value) are used to study UV photosensing property. Responsivity and photocurrent show a strong dependence on the morphology of ZnO

Atomic Layer Deposition Seeded ZnO Nanowires in Hybrid Carbon Fiber Composites: Synthesis, Characterization and Multifunctionality

Interfacial treatments of carbon fiber composites play a critical role in determining the overall performance as the surface of carbon fiber is smooth and inert causing low bonding to the polymer matrix. In this dissertation, atomic layer deposition (ALD) seeded ZnO nanowires were grown on carbon fiber as an enhanced interphase using two-step hydrothermal method for the first time. The effects of growth parameters of seed layers by ALD and nanowire growth in hydrothermal method were systematically investigated. Several morphologies of ZnO nanostructures were obtained and characterized using field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Single carbon fiber composites and carbon fiber composite laminates with ZnO nanowires were manufactured, then tested by single fiber fragmentation test, 3-point bending test, short beam 3-point bending test. It was found that the incorporation of ZnO nanowires significantly improved the mechanical properties of composites including interfacial shear strength, flexural strength and interlaminar shear strength by up to 286%,45.6% and 31.1%.The successful development and characterization of ZnO nanowires enhanced structural composites have great potential to lead to new generation of lightweight materials with increased mechanical properties for broad mechanical and aerospace engineering applications

Electrochemical and hydrothermal deposition of ZnO on silicon: from continuous films to nanocrystals

This article presents the study of the electrochemical deposition of zinc oxide from the non-aqueous solution based on dimethyl sulfoxide and zinc chloride into the porous silicon matrix. The features of the deposition process depending on the thickness of the porous silicon layer are presented. It is shown that after deposition process the porous silicon matrix is filled with zinc oxide nanocrystals with a diameter of 10–50 nm. The electrochemically deposited zinc oxide layers on top of porous silicon are shown to have a crystalline structure. It is also shown that zinc oxide crystals formed by hydrothermal method on the surface of electrochemically deposited zinc oxide film demonstrate ultra-violet luminescence. The effect of the porous silicon layer thickness on the morphology of the zinc oxide is shown. The structures obtained demonstrated two luminescence bands peaking at the 375 and 600 nm wavelengths. Possible applications of ZnO nanostructures, porous and continuous polycrystalline ZnO films such as gas sensors, light-emitting diodes, photovoltaic devices, and nanopiezo energy generators are considered. Aspects of integration with conventional silicon technology are also discussed

Solar Diodes: Novel Heterostructured Materials for Self-Powered Gas Sensors

The integration and correlation of multiple nanomaterial components and junctions in a singular device can open exciting new avenues for more advanced functionalities in nanodevices. One of the key challenges is to achieve controlled and reproducible synthetic protocols of such complex heterostructures with optimal material combinations and geometries. Due to the current global challenges including growing energy demand, limitation of natural resources, as well as envi-ronmental issues, research efforts have been devoted to the development of self-powered nanodevices that are capable of harvesting renewable energies such as solar and mechanical energies. Nevertheless, the current concept of self-powered nanodevices is based on coupling an external energy harvesting unit, such as a solar cell or piezo-electric nanogenerator, with the functional nanodevices. In this work, an innovative approach, named solar diode sensor (SDS), has been developed to realize an autonomously operated gas sensor with no additional need of coupling it to a powering devices. The SDS based on a CdS@n-ZnO/p-Si nanosystem unifies gas sensing (CdS@n-ZnO) and solar energy harvesting (n-ZnO/p-Si) functionalities in one single device. A novel sensing mechanism (change of open circuit voltage, ∆Voc), in comparison to the well-known conductometric sensors (∆R), was demonstrated. It was explained in terms of modulated polarization of the nanoparticles/nanowire interface, gas-material surface interactions and the subsequent changes in the donor density of ZnO (ND), which is manifested in the varia-tion of Voc in CdS@n-ZnO/p-Si. The fabricated sensors were capable of detecting oxidizing (e.g. oxygen) and reducing gases (such as ethanol and methane) with reproducible response at room temperature and with no need of any other energy source except solar light illumination to deliver a self-sustained gas sensor signal. The generality of the new concept was demonstrated by extending the approach to other nanomaterial geometries including radial heterojunctions of CdS@ZnO/p-Si nanowires and thin-film planar heterojunction. Additionally, the fabrication of stand-alone single nanowire devices was employed to study the inherent intrinsic electrical and functional properties of single coaxial heterostructures. In this work, the electrical characterization, the photovoltaic and gas sensing performances of a heterojunction device based on a single coaxial n-ZnO/p-Si nanowire were preliminary assessed