"Mycobacterium tuberculosis causes tuberculosis, one of the most life-threatening diseases of all time. It infects the host macrophages and survives in its phagosome. The host phagosome is a very hostile environment where M. tuberculosis copes with high concentration of transition metals (Zn2+, Cu2+), low levels of others (Mn2+, Fe2+) and acidic pH. P-ATPases are membrane proteins that transport various ions against their electrochemical gradients utilizing the energy of ATP hydrolysis. Based on their primary sequences; seven of the twelve mycobacterial ATPases are classified as putative heavy metal transporters and a K+-ATPase, while the substrate of four (CtpE, CtpF, CtpH and CtpI) remains unknown. Consistent with their membrane topology and conserved amino acids, CtpE and CtpF are possibly P2 or P3-ATPases that transport alkali metals or protons. We examined the cellular roles of orthologous CtpE and CtpF in M. smegmatis, a non-pathogenic model organism. We hypothesized that these novel P- ATPases play an important role in transporting alkali metals and/or protons. We analyzed growth fitness of strains carrying mutations of the coding gens of these enzymes, in presence of various metals and different pHs, as well as the gene expression levels under different stress conditions. We observed that the M. smegmatis mutant strains, lacking of CtpF or CtpE, are sensitive to high concentrations (mM) of Mn2+. Furthermore, CtpE mutant is sensitive to alkali pH. Our results indicate that CtpE and CtpF might be an Mn2+ or H+-ATPase that are required for cell’s homeostasis sustainability."

Abstract In this work, H2, CH4, and O2 are used as gas sources and C3H903B is used as the doping source, microwave plasma chemical vapor deposition and a two-steps deposition process will be applied to the growth of boron-doped diamond on p-type(111) silicon substrate. In this work, nucleation and growth of diamond film have been studied. A series of experiments are focused on the depenence of experimental pressure, temperature, power, dc bias, flow rates of O2, and doping concentration of C3H903B. The samples are examined by SEM, Raman, XRD, FTIR, and I-V. The results show that if nucleation is assisted by a negative dc bias, it can reach high density. The growth of diamond and the boron-doped diamond film is in multi steps. After 90 minutes of growth, the mechanism of deposition will be changed.

Zinc oxide is a semiconducting material that has received lot of attention due to its numerous proeprties such as wide direct band gap, piezoelectricity, and numerous low cost and robust methods of synthesizing nanomaterials. Its piezoelectric properties have been harnessed for use in energy production through nanogenerators, and to tune carrier transport, birthing a field known as piezotronics. However, one weakness of ZnO is that it is notoriously difficult to dope p-type. Antimony was investigated as a p-type dopant for ZnO, and found to have a stability of up to 3 years, which is completely unprecedented in the literature. Furthermore, a variety of zinc oxide structures ranging from ultra-long nanowires to thin films were produced and their piezotronic properties were demonstrated. By making p-n homojunctions using doped and undoped ZnO, enhanced nanogenerators were produced which could see application in gesture recognition. As a proof of concept, a simple photodetector was also derived from a core-shell nanowire structure. Finally, the ability to integrate this material with other semiconductors was demonstrated by growing a heterojunction with silicon nanowires, and investigating its electrical properties. All this work together lays the foundation for a fundamentally new material that could see application in future electronics, optoelectronics, and human-machine interfacing.

none

Polarization behaviours of copper diffused p-type GaAs was studied in 1. 0M NaCl and 1. 0M NaNO₃ by means of pitting scan and linear sweep potentiodynamic polarization techniques. The thermodynamic potential-pH diagram of the GaAs-H₂O system was constructed. The observed electrode behaviours of GaAs were compared and correlated to the potential-pH diagram. Freely corroding potential, passivation behaviour and pitting potential were examined as a function of a number of factors. These included the effects of different annealing and polishing pretreatments, the bulk solution pH and polarization methods. The corrosion potential (Ecorr) , pitting potential (Epit) and passivation behaviour were affected by the different pretreatments which changed the surface condition of GaAs. For mechanically polished samples, pitting corrosion was found in pH 7.0 solution only. The Ecorr and Eplt were independent of NO₃⁻ and Cl⁻ at pH 7.0. Initial polarization behaviour of p-GaAs at pH 2.0 and 12.0 followed the Tafel Law for semiconductors quite well. There was a reasonable correlation between the experimental observations and the potential-pH diagram of GaAs-H₂O system. SEM images of polarized samples showed that pits formed in NaCl and NaNO₃ had a different shape, being more elongated in NaCl. However, the walls of all pits appeared to be composed of {111} planes. In general, the pit distribution appeared to be similar to the dislocation distribution. A model of pitting corrosion of GaAs was proposed based on strain induced breakdown of the oxide film, localized changes in solution chemistry and the structure of the compound semiconductor. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

For III-nitride wide-bandgap materials, the lack of efficient p-type wide bandgap semiconductors limits the full potential of group-III nitride-based optoelectronic devices. Conventional wide bandgap p-type materials consisting of magnesium-doped gallium nitride (GaN:Mg) and magnesium-doped aluminum gallium nitride (AlGaN:Mg) typically exhibit low hole carrier concentrations of <1018 cm-3 . Hence, I used different wide bandgap inorganic p-type materials as a promising solution, e.g., copper thiocyanate (CuSCN). CuSCN has multiple attractive properties that hold potential for applications in III-nitride materials. For example, its energy band gap is up to 3.9 e.V and its electron effective mass is higher than its hole effective mass. These two key features make CuSCN a potential wide bandgap p-type material for III-nitride systems. By exposing CuSCN to chlorine, Cl2-infused CuSCN thin film achieves a hole concentration up to 3 × 1018 cm-3 and maintains its visible-light-blind optical properties. Based on these desirable features, p CuSCN/n-GaN heterojunction ultraviolet photodetectors, as well as the p-CuSCN and n GaN interface, were fabricated to investigate the potential applications of p-CuSCN in III nitride devices. Moreover, p-CuSCN also benefits the corresponding organic solar cells; p CuSCN-based organic solar cells perform better in power conversion efficiency and stability tests under various conditions than intrinsic CuSCN-based organic solar cells. This work on p-CuSCN not only paves the way for new III-nitride semiconductor devices, but may also potentially enable the development of organic devices with better performance and longer lifetime. To explore the potential of transition metal oxides in UV photodetectors, NiO was selected to proceed with device fabrication because of its wider energy bandgap and lower hole effective mass than other transition metal oxides. Since single crystal quality is required to maintain its visible-light-blind optical property, brand-new templates were invented to grow single-crystal NiO thin films, TiN/MgO, and TiN/Si. Use of TiN thin film between NiO and the substrates provides a good back-side metal contact for NiO-based semiconductor devices. Several tools were employed to ascertain the single-crystal quality of as-grown NiO thin films on TiN/MgO and TiN/Si. I demonstrate NiO/TiN/MgO and NiO/TiN/Si bilayer structures may pave the way towards better NiO-based ultraviolet optoelectronic devices.

Transparent oxide electronics have emerged as promising materials to shape the future of electronics. While several n-type oxides have been already studied and demonstrated feasibility to be used as active materials in thin film transistors, high performance p-type oxides have remained elusive. This dissertation is devoted to the study of transparent p-type oxide semiconductor tin monoxide and its use in the fabrication of field effect devices. A complete study on the deposition of tin monoxide thin films by direct current reactive magnetron sputtering is performed. Carrier density, carrier mobility and conductivity are studied over a set of deposition conditions where p-type conduction is observed. Density functional theory simulations are performed in order to elucidate the effect of native defects on carrier mobility. The findings on the electrical properties of SnO thin films are then translated to the fabrication of thin films transistors. The low processing temperature of tin monoxide thin films below 200 oC is shown advantageous for the fabrication of fully transparent and flexible thin film transistors. After careful device engineering, including post deposition annealing temperature, gate dielectric material, semiconductor thickness and source and drain electrodes material, thin film transistors with record device performance are demonstrated, achieving a field effect mobility >6.7 cm2V-1s-1. Device performance is further improved to reach a field effect mobility of 10.8 cm2V-1s-1 in SnO nanowire field effect transistors fabricated from the sputtered SnO thin films and patterned by electron beam lithography. Downscaling device dimension to nano scale is shown beneficial for SnO field effect devices not only by achieving a higher hole mobility but enhancing the overall device performance including better threshold voltage, subthreshold swing and lower number of interfacial defects. Use of p-type semiconductors in nonvolatile memory applications is then demonstrated by the fabrication of hybrid ferroelectric field effect transistors composed of organic ferroelectric layer polyvinylidene fluoride trifluoroethylene and inorganic p-type semiconductor tin monoxide. Both rigid and flexible devices are demonstrated, showing the advantages of low temperature oxides over polymer semiconductors by achieving much better performance, such as order of magnitude higher hole mobility.

Metal oxides are a very important class of materials with a wide range of photovoltaic applications. Transparent conducting oxides (TCOs) are the primary front contact materials used in thin film solar cells. Identification of methods for reducing the resistivity of these materials would have significant benefits. Development of p-type TCOs would provide alternative back contact materials and could enable further development of technologies such as bifacial, window and multijunction cells. A series of studies into these areas is presented in this work. Aluminium doped zinc oxide (AZO) is a well-known n-type TCO consisting entirely of Earth-abundant materials. Targets were manufactured from AZO powder, which was synthesised using a patented emulsion detonation process developed by Innovnano S.A. All films showed good optical transmission. Resistivity was found to decrease with both increasing time and temperature up to 300 degree C. Temperatures above 300 degree C were found to be detrimental to film formation, with increasing amounts of damage to the crystal structure and consequent increases in the resistivity. The effect of alloying molybdenum oxide with molybdenum nitride through reactive sputtering in a mixed oxygen-nitrogen atmosphere was investigated. All alloys were found to show p-type behaviour. Resistivity was found to improve with increased nitrogen content, in contrast to optical transmission, which reduced. A selection of compositions were deposited onto CdTe cells as back contacts. These cells showed an increase in efficiency with increasing nitrogen content. Work function was found to increase with increasing oxygen content, but all work functions were low. Resistivity was shown to correlate strongly with efficiency, caused by a corresponding increase in cell voltage. This implies that to form an ohmic contact on CdTe with p-type materials, work function may be less important than resistivity. The copper oxides are p-type, but uses are limited by the narrow band gaps. Cupric oxide was chosen for investigation and for alloying with other oxides with the aim of increasing the band gap. It was found that temperature and deposition environment have significant impacts on sputtered cupric oxide (CuO) films, with low temperatures and high oxygen environments producing the lowest resistivities. Extrinsic sodium doping was found to reduce the resistivity by up to four orders of magnitude. High oxygen content sodium-doped films were found to have carrier concentrations two orders of magnitude higher than that of indium tin oxide.

"Tuberculosis is a deadly disease caused by bacteria of the genus Mycobacterium. One-third of the world’s population is infected with Mycobacterium tuberculosis. Two million these deaths occur each year in immunocompromised AIDS patients. M. tuberculosis has co-evolved with humans for many thousands of years. The bacillus has developed tactics to overcome the immune defense system and multiply in the macrophage. At the interface of the host and pathogen interactions, there is an interchange of metals and electrolytes. The host on one hand reduces the availability of metals essential for pathogen survival, like manganese and iron, in the macrophage and increases potassium ions which reduces pH in the phagolysosome. The host also generates Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS), to create toxic affects through interactions with metals and metalloproteins. M. tuberculosis copes with the hostile environment in the macrophage by preventing the acidification of the phagolysosome, secreting antioxidant enzymes such as alkylhydroperoxidase (AhpF) and peroxiredoxin (AhpC), superoxide dismutase, SodA and SodC, and catalase KatG through the SecA system. M. tuberculosis contains 28 metal transporters, among them there are 12 unique P-type ATPases. This is an unusually high number of P-type ATPases in an organism. These ATPases transport several monovalent and divalent metals (Cu+, Cu2+, Ag+, Zn2+, Na+, K+, Ca2+, Cd2+, Pb2+, Mn2+, Mg2+, and Co2+) across biological membranes, using energy from ATP hydrolysis. Our analysis has revealed that these P-type ATPases have homologs in other intracellular symbiotic/pathogenic bacteria and certain chemolithotrophic archaea and bacteria. A corelation can hence be drawn among these pumps and the capability of surviving in noxious environments and coping with adverse redox conditions. Possible substrates were identified by determining the consensus sequences in different helices of these ATPases. However, out of the 12 P-type ATPases confirmed, transported substrate could be postulated for four of these proteins; CtpA, CtpB, CtpV and KdpB. Using bioinformatic approaches we have characterized the possible genetic environment of these genes. The transmembrane regions were analyzed for consensus sequences and the N-terminals and C-terminals were scrutinized for metal binding domains, and we were able to categorize these ATPases into P1 type and P2 type ATPases. In an attempt to determine the substrate specificity, two of these ATPases (CtpC and ctpG) were cloned and transformed into Escherichia coli cells. Cells expressing CtpC were grown in different concentrations of metals and pHs. In these experiments CtpC was found to show an interaction with copper and cadmium. Pure protein was obtained by His-tag purification and para-Nitro Phenol Phosphatase (pNPPase) assay was performed with different metals, it was found that copper and zinc activated the phosphatase activity of the enzyme; and cobalt and manganese were inhibitory. Inhibition of the pNPP assay could mean that there would be activation in the ATPase assay, meaning that cobalt and manganese could be possible substrates to this enzyme. "

The rapid progress of n-type metal oxide thin film transistors (TFTs) has motivated research on p-type metal oxide TFTs in order to realise metal oxide-based CMOS circuits which enable low power consumption large-area electronics. Cuprous oxide (Cu2O) has previously been proposed as a suitable active layer for p-type metal oxide TFTs. The two most significant challenges for achieving good quality Cu2O TFTs are to overcome the low field-effect mobility and an unacceptably high off-state current that are a feature of devices that have been reported to date. This dissertation focuses on improving the carrier mobility, and identifying the main origins of the low field-effect mobility and high off-state current in Cu2O TFTs. This work has three major findings. The first major outcome is a demonstration that vacuum annealing can be used to improve the carrier mobility in Cu2O without phase conversion, such as oxidation (CuO) or oxide reduction (Cu). In order to allow an in-depth discussion on the main origins of the very low carrier mobility in as-deposited films and the mobility enhancement by annealing, a quantitative analysis of the relative dominance of the main conduction mechanisms (i.e. trap-limited and grain-boundary-limited conduction) is performed. This shows that the low carrier mobility of as-deposited Cu2O is due to significant grain-boundary-limited conduction. In contrast, after annealing, grain-boundary-limited conduction becomes insignificant due to a considerable reduction in the energy barrier height at grain boundaries, and therefore trap-limited conduction dominates. A further mobility improvement by an increase in annealing temperature is explained by a reduction in the effect of trap-limited conduction resulting from a decrease in tail state density. The second major outcome of this work is the observation that grain orientation ([111] or [100] direction) of sputter-deposited Cu2O can be varied by control of the incident ion-to-Cu flux ratio. Using this technique, a systematic investigation on the effect of grain orientation on carrier mobility in Cu2O thin films is presented, which shows that the [100] Cu2O grain orientation is more favourable for realising a high carrier mobility. In the third and final outcome of this thesis, the temperature dependence of the drain current as a function of gate voltage along with the C-V characteristics reveals that minority carriers (electrons) cause the high off-state current in Cu2O TFTs. In addition, it is observed that an abrupt lowering of the activation energy and pinning of the Fermi energy occur in the off-state, which is attributed to subgap states at 0.38 eV below the conduction band minimum. These findings provide readers with the understanding of the main origins of the low carrier mobility and high off-state current in Cu2O TFTs, and the future research direction for resolving these problems.