Thesis (M.Sc. (Physics)) -- University of Limpopo, 2017 / The undoped ZnO nanoparticles, In or Co single doped ZnO nanoparticles and the In and Co combinational doped ZnO nanoparticles were synthesised through sol-gel technique. The samples were characterised using XRD, TEM, FTIR, Raman spectroscopy, UV-Vis, PL and also tested for the gas sensing applications. XRD patterns revealed that the synthesised samples were of ZnO hexagonal wurtzite structure. The lattice parameters and the bond length of all the undoped and doped ZnO samples were determined and found to be similar to that of the Bulk ZnO. The average particle size of the undoped and doped ZnO nanoparticles were calculated and found to reduce with an introduction of dopants while increasing with an increase in temperature. The strain of all the prepared samples were also determined and observed to be in an inverse relation to the particle size. TEM images showed that the synthesised samples were spherically shaped and that was in agreement with XRD results, while the EDS results showed that In and Co were successfully doped into the ZnO nanoparticles. Raman and FTIR spectroscopy indicated that the prepared samples were indeed ZnO nanoparticles which confirmed the XRD results. The UV-Vis results showed a red-shift in the energy band gap with an introduction of dopants and that was related to the reduction of the particle size, this results were consistent with the PL results. Gas sensing results showed that doping Co and In into the ZnO nanoparticles has an effect into ZnO properties. Combinational-doping of In and Co was found to increase the response to the gases CH4, CO, NH3 and H2 as compared to the undoped and singly doped ZnO nanoparticle sensors. The response\recovery time was found to be affected with introduction of In and Co. Improvements were also observed in the operating temperature and the selectivity of the single doped and co-doped ZnO nanoparticles towards different gases used in this study. / University of Limpopo IBSA National Research Foundation (NRF)

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第20066号 / 農博第2195号 / 新制||農||1045(附属図書館) / 学位論文||H28||N5022(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 髙橋 千太郎, 教授 近藤 直, 教授 飯田 訓久 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Single-photon sources are essential building blocks in quantum photonic networks, where quantum-mechanical properties of photons are utilised to achieve quantum technologies such as quantum cryptography and quantum computing. In this thesis, a single-photon source driven by a surface acoustic wave (SAW) is developed and characterised. This single-photon source is based on a SAW-driven lateral n-i-p junction in a GaAs quantum-well structure. On this device, the lateral n-i-p junction is formed by gate-induced electrons and holes in two adjacent regions. The SAW potential minima create dynamic quantum dots in a 1D channel between these two regions, and are able to transport single electrons to the region of holes along the channel. Single-photon emission can therefore be generated as these electrons consecutively recombine with holes. After characterisation and optimisation in four batches of devices, clear SAW-driven charge transport and the corresponding electroluminescence (EL) can be observed on an optimised SAW-driven n-i-p junction. Time-resolved measurements have been carried out to study the dynamics of SAW-driven electrons. Time-resolved EL signals indicate that a packet of electrons is transported to the region of holes in each SAW minimum. In addition, the carrier lifetime of SAW-driven electrons in the region of holes is shown to be $\sim 100$ ps, which is much shorter than the SAW period of $860$ ps. Hence, it is promising to observe single-photon emission in the optimised device. In order to test single-photon emission, a Hanbury Brown-Twiss experimental setup has been employed to record an autocorrelation histogram of the SAW-driven EL signal at the single-electron regime. Suppression of autocorrelation coincidences at time delay $\Delta t = 0$ is evidence of photon antibunching. By fitting theoretical functions describing the SAW-driven EL signal, it is found that the second-order correlation function shows $g^{(2)}(0) = 0.39 \pm 0.05$, which is lower than the common criterion for a single-photon source $g^{(2)}(0) < 0.5$. Moreover, theoretical calculation and simulation suggest that, if a constant background signal can be filtered out, $\sim 80 \%$ of the SAW-driven EL is single-photon emission.

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Phenol, 2-chlorophenol (2-CP) is used in the manufacture of several chemical compounds including other chlorophenols, dyes, dentifrice and pesticides. The usage of these chemicals results in the discharge of 2-CP that is harmful to most biota in the environment. Therefore there is need to remove or degrade 2-CP from the environment, especially in water. This research focused on the synthesis, characterization and application of Ag doped semiconductor (TiO2, ZnO, and ZnS) nanoparticles for the removal of 2-CP from water. Sol-gel and co-precipitation methods were used to synthesize the nanoparticles with different Ag contents (1%, 3% and 5%). Silver metal was used as a doping agent due to its antibacterial activity and ability to improve the photocatalytic activity of the semiconductors for 2-CPdegradation under UV irradiation. Characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), Ultra-violet visible spectroscopy (UV-Vis) and photoluminescence spectra (PL) were used to characterize the structural, optical and physical properties of the nanoparticles, while Transmission electron microscopy (TEM) was used to characterize the surface of the nanoparticles. The XRD results confirmed the formation of anatase, wurtzite and blend phases of TiO2, ZnO and ZnS nanoparticles, respectively. The band gaps of the synthesized nanoparticles were 3.42 eV, 3.23 eV and 3.12 eV for TiO2, ZnO and ZnS nanoparticles respectively. The TEM images showed that all synthesized nanoparticles were uniform in shape. Photocatalytic degradation of 2-CP under UV irradiation confirmed that the semiconductor’s photocatalytic activities improved with the addition of Ag ions. The best removal percentage was obtained at doped Ag percentages of 5, 1 and 5 % using TiO2, ZnO and ZnS, respectively. In addition, the effects of various parameters affecting the photocatalytic degradation such as pH, initial concentrations of 2-CP and amount of catalyst (Ag doped TiO2, ZnO and ZnS, respectively) loading were examined and optimized. At the different initial concentrations of 2-CP, namely, 8, 20 and 50 ppm, the highest degradation efficiency was obtained at pH of 10.5 and 5 mg of catalyst dosage. However a decrease in initial concentration of 2-CP showed an increase in the photocatalytic efficiency. The degradation percentage of 2-CP obtained with Ag doped TiO2; ZnO and ZnS nanoparticles were 74.74, 57.8 and 45.49 %, respectively. Doping of these materials with Ag enhanced their photocatalytic activity; thus, they have the potential of degrading phenolic compounds, especially 2-chlorophenol, in water.

Undoped body multi gate (MG) Metal Oxide Semiconductor Field Effect Transistors (MOSFET) are appearing as replacements for single gate bulk MOSFET in forthcoming sub-45nm technology nodes. It is therefore extremely necessary to develop compact models for MG transistors in order to use them in nano-scale integrated circuit design and simulation. There is however a sharp distinction between the electrostatics of traditional bulk transistors and undoped body devices. In bulk transistor, where the substrate is sufficiently doped, the inversion charges are located close to the surface and hence the surface potential solely controls the electrostatic integrity of the device. However, in undoped body devices, gate electric field penetrates the body center, and inversion charge exists throughout the body. In contrast to the bulk transistors, depending on device geometry, the potential of the body center of undoped body devices could be higher than the surface in weak inversion regime and the current flows through the center-part of the device instead of surface. Several crucial parameters (e.g. Sub-threshold slope) sometimes become more dependable on the potential of body center rather than the surface. Hence the body-center potential should also be modeled correctly along with the surface-potential for accurate calculation of inversion charge, threshold voltage and other related parameters of undoped body multi-gate transistors. Although several potential models for MG transistors have been proposed to capture the short channel behavior in the subthreshold regime but most of them are based on the crucial approximation of coverting the 2D Poisson’s equation into Laplace equation. This approximation holds good only at surface but breaks down at body center and in the moderate inversion regime. As a result all the previous models fail to capture the potential of body center Correctly and remain valid only in weak-inversion regime. In this work we have developed semiclassical compact models for potential distribution for double gate (DG) and cylindrical Gate-All-Around (GAA) transistors. The models are based on the analytical solution of 2D Poisson’s equation in the channel region and valid for both: a) weak and strong inversion regimes, b) long channel and short channel transistors, and, c) body surface and center. Using the proposed model, for the first time, it is demonstrated that the body potential versus gate voltage characteristics for the devices having equal channel lengths but different body thicknesses pass through a single common point (termed as crossover point). Using the concept of “crossover point” the effect of body thickness on the threshold voltage of undoped body multi-gate transistors is explained. Based on the proposed body potential model, a new compact model for the subthreshold swing is formulated. Some other parameters e.g. inversion charge, threshold voltage roll-off etc are also studied to demonstrate the impact of body center potential on the electrostatics of multi gate transistor. All the models are validated against professional numerical device simulator.

In dieser Arbeit werden niederfrequente optische Messungen an vier neuartigen Supraleitern vorgestellt. Im Bereich von 100 GHz bis 3 THz zeigen die vier untersuchten Systeme – LuNi2B2C, Ba(Fe0,9Co0,1)2As2, T’-Pr2CuO4 und Si:Ga – ein sehr unterschiedliches Verhalten. Die beiden erst genannten Supraleiter sind Mehrbandsupraleiter, bei denen die Cooper-Paarkopplung unterschiedlich für verschiedene Fermiflächen ist. T’-Pr2CuO4 ist ein undotierter Kupratsupraleiter, der nach bisheriger Lehrmeinung nicht existieren dürfte. Mit THz-Spektroskopie konnte erstmals die Bildung einer Meißner-Phase in T’-Pr2CuO4 mit optischen Methoden beobachtet werden. Eine gewisse Sonderstellung nimmt Si:Ga als amorpher Supraleiter ein. Si:Ga wird durch Ionenimplantation von Gallium in einen Siliziumwafer hergestellt. Es besteht die Hoffnung, mit Si:Ga halb- und supraleitende Logikblöcke in großem Maßstab auf einem Chip vereinen zu können, da die Ionenimplantation mit den Produktionsprozessen der Halbleiterindustrie kompatibel ist.

In dieser Arbeit werden niederfrequente optische Messungen an vier neuartigen Supraleitern vorgestellt. Im Bereich von 100 GHz bis 3 THz zeigen die vier untersuchten Systeme – LuNi2B2C, Ba(Fe0,9Co0,1)2As2, T’-Pr2CuO4 und Si:Ga – ein sehr unterschiedliches Verhalten. Die beiden erst genannten Supraleiter sind Mehrbandsupraleiter, bei denen die Cooper-Paarkopplung unterschiedlich für verschiedene Fermiflächen ist. T’-Pr2CuO4 ist ein undotierter Kupratsupraleiter, der nach bisheriger Lehrmeinung nicht existieren dürfte. Mit THz-Spektroskopie konnte erstmals die Bildung einer Meißner-Phase in T’-Pr2CuO4 mit optischen Methoden beobachtet werden. Eine gewisse Sonderstellung nimmt Si:Ga als amorpher Supraleiter ein. Si:Ga wird durch Ionenimplantation von Gallium in einen Siliziumwafer hergestellt. Es besteht die Hoffnung, mit Si:Ga halb- und supraleitende Logikblöcke in großem Maßstab auf einem Chip vereinen zu können, da die Ionenimplantation mit den Produktionsprozessen der Halbleiterindustrie kompatibel ist.