Tuning and engineering of ZnO and CuxO for sensor, solar cells and memory devices

In this thesis, the PhD candidate pursued the development of model sensors, solar cells and memory devices based on transition metal oxides, which are tuned and engineered in order to obtain enhanced properties. The author made informed choices regarding the incorporation of zinc oxide (ZnO) and copper oxides (CuxO) (cuprous oxide (Cu2O) and cupric oxide (CuO)) as the model transition metal oxides to achieve the goals of this PhD research. ZnO and CuxO are well investigated metal oxides, and a broad range of information regarding their fundamental properties, synthesis methods and applications is available. Their complimentary electronic nature is also required for the proposed studies in this dissertation: ZnO and CuxO are intrinsically n- and p-type semiconductors, respectively. This PhD research focuses on the engineering and tuning the morphology, crystallinity and stoichiometry of transition metal oxides in order to investigate and devise scenarios that result in the highest efficiencies for the abovementioned model devices. The author of this thesis thoroughly reviewed the physical and chemical properties, as well as methods of synthesis of CuxO and ZnO. He studied factors that have been previously employed for enhancing the targeted materials functionalities. This included tuning the synthesis’ parameters such as changes in temperature and pressure, the incorporation of seed layers or templates and nanostructuring. In summary, this PhD thesis provides the readers with an in-depth knowledge of the capabilities that tuning and engineering transition metal oxides provide in enhancing the performance of such materials for specific applications

Nanoporous Nb2O5 hydrogen gas sensor

This work presents the development of gas sensors based on nanoporous niobium oxide (Nb2O5) films for hydrogen gas sensing. Nanoporous Nb2O5 films were successfully synthesized by the anodization of niobium foil in fluoride-organic solvent containing a small percentage of water at 50 °C. These conditions helped to obtain nanovein-like networks with pore diameters of 30-50 nm. After annealing at 440 °C an orthorhombic phase of Nb2O5 was obtained. Contacts of the sensors were then established using platinum (Pt) that also acted as catalytic layers. The gas sensing properties of these nanoporous contacts were investigated for hydrogen gas sensing at different film thicknesses and temperatures

Fuel saving analysis and stability assessments of malaysian offshore fishing vessels fitted with dual fuel diesel and compressed natural gas

Malaysia fishing industries are heavily dependent on the fossil fuels to satisfy its energy demand. Fuel cost of fishing vessels normally accounts for more than 50% of the annual operating expenses. With the increasing of global fuel prices, the future of this industry has exposed fishermen to uncertain future. Nowadays, clean burning alternative fuel such natural gas has become a great interest for fuel saving. A duel fuel diesel engine is a diesel engine that has been fitted to use compressed natural gas (CNG). Dual fuel engines provide numerous potential advantages such as cost saving, fuel flexibility, lower emissions, better efficiency and easy conversion of existing diesel engines without major modifications. This paper describes a study to reduce fuel consumption by introducing a dual fuel diesel and CNG for Malaysian offshore fishing vessel. An analysis of fuel consumption reduction is presented, together with stability assessments. The results reveals that dual fuel diesel can provide noticeable lower fuel consumption compared to existing diesel engines and stability assessment signify that the conversion to dual fuel engine has no adverse effects to vessel stability

Effect of substrate placement in schott vial to hematite properties

In the present study, hematite (α-Fe2O3) nanostructures were deposited on fluorine doped tin oxide (FTO) coated glass substrate using sonicated immersion synthesis method. The effect of FTO glass substrate placement in Schott vial during immersion process was studied on the growth of the hematite nanostructure and its properties. XRD pattern has revealed seven diffraction peaks of α-Fe2O3 for both hematite nanostructures samples attributed to polycrystalline with rhombohedral lattice structure. The surface morphologies from FESEM have shown that the hematite nanostructures were grown uniformly in both samples with FTO conductive layer facing up and down. Hematite sample with FTO facing down exhibits a smaller size of nanorod, 26.7 nm average diameter, compared to the hematite sample that FTO face up with 53.8nm average diameter. Optical properties revealed higher transmittance in the sample with FTO facing down, probably due to smaller size of nanostructure. The optical band gap energy plotted and extrapolated at 2.50eV and 2.55eV for FTO face up and FTO face down hematite samples respectively, presenting the sample with FTO face up has a lower optical bandgap energy

Transparent functional oxide stretchable electronics: micro-tectonics enabled high strain electrodes

Fully transparent and flexible electronic substrates that incorporate functional materials are the precursors to realising nextgeneration devices with sensing, self-powering and portable functionalities. Here, we demonstrate a universal process for transferring planar, transparent functional oxide thin films on to elastomeric polydimethylsiloxane (PDMS) substrates. This process overcomes the challenge of incorporating high-temperature-processed crystalline oxide materials with low-temperature organic substrates. The functionality of the process is demonstrated using indium tin oxide (ITO) thin films to realise fully transparent and flexible resistors. The ITO thin films on PDMS are shown to withstand uniaxial strains of 15%, enabled by microstructure tectonics. Furthermore, zinc oxide was transferred to display the versatility of this transfer process. Such a ubiquitous process for the transfer of functional thin films to elastomeric substrates will pave the way for touch sensing and energy harvesting for displays and electronics with flexible and transparent characteristics

Characterization of metal contacts for two-dimensional MoS2 nanoflakes

While layered materials are increasingly investigated for their potential in nanoelectronics, their functionality and efficiency depend on charge injection into the materials via metallic contacts.This work explores the characteristics of different metals (aluminium, tungsten, gold, and platinum) deposited on to nanostructured thin films made of two-dimensional (2D) MoS2 flakes. Metals are chosen based on their work functions relative to the electron affinity of MoS2. It is observed, and analytically verified that lower work functions of the contact metals lead to smaller Schottky barrier heights and consequently higher charge carrier injection through the contact

Status and Prospects of ZnO-Based Resistive Switching Memory Devices

In the advancement of the semiconductor device technology, ZnO could be a prospective alternative than the other metal oxides for its versatility and huge applications in different aspects. In this review, a thorough overview on ZnO for the application of resistive switching memory (RRAM) devices has been conducted. Various efforts that have been made to investigate and modulate the switching characteristics of ZnO-based switching memory devices are discussed. The use of ZnO layer in different structure, the different types of filament formation, and the different types of switching including complementary switching are reported. By considering the huge interest of transparent devices, this review gives the concrete overview of the present status and prospects of transparent RRAM devices based on ZnO. ZnO-based RRAM can be used for flexible memory devices, which is also covered here. Another challenge in ZnO-based RRAM is that the realization of ultra-thin and low power devices. Nevertheless, ZnO not only offers decent memory properties but also has a unique potential to be used as multifunctional nonvolatile memory devices. The impact of electrode materials, metal doping, stack structures, transparency, and flexibility on resistive switching properties and switching parameters of ZnO-based resistive switching memory devices are briefly compared. This review also covers the different nanostructured-based emerging resistive switching memory devices for low power scalable devices. It may give a valuable insight on developing ZnO-based RRAM and also should encourage researchers to overcome the challenges

Thin films and nanostructures of niobium pentoxide: Fundamental properties, synthesis methods and applications

As one of the transition metal oxides, niobium pentoxide (Nb2O5) offers a broad variety of properties that make it a potentially useful and highly applicable material in many different areas. In comparison to many other transition metal oxides, Nb2O5 has received relatively little attention, which presents a significant opportunity for future investigations aimed at fundamentally understanding this material and finding new and interesting applications for it. In this article, a general overview of Nb2O5 is presented which focuses on its fundamental properties, synthesis methods and recent applications, along with a discussion on future research directions relevant to this material

Highly ordered anodized Nb2O5 nanochannels for dye-sensitized solar cells

Highly ordered anodized Nb2O5 nanochannels are synthesized and utilized as the photoanodes for dye-sensitized solar cells (DSSCs). We characterize these DSSCs to determine the optimum photoanode thickness for the best cell performance. The samples with thicknesses from 5 to 25 μm are obtained in glycerol based electrolyte at 180 °C and their photoconversion properties are investigated utilizing various techniques including photocurrent-voltage characteristic, photovoltage decay and electrochemical impedance spectroscopy. Overall, the DSSC incorporating a 10 um thick Nb2O5 photoanode shows the highest efficiency of 4.48%. We analyze the factors that limit the efficiency of DSSCs

Nanostructured copper oxide semiconductors: A perspective on materials, synthesis methods and applications

The oxides of copper (CuxO) are fascinating materials due to their remarkable optical, electrical, thermal and magnetic properties. Nanostructuring of CuxO can further enhance the performance of this important functional material and provide it with unique properties that do not exist in its bulk form. Three distinctly different phases of CuxO, mainly CuO, Cu2O and Cu4O3, can be prepared by numerous synthesis techniques including, vapour deposition and liquid phase chemical methods. In this article, we present a review of nanostructured CuxO focusing on their material properties, methods of synthesis and an overview of various applications that have been associated with nanostructured CuxO