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Yang, Zheng. "Doping in zinc oxide thin films." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3359913.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 12, 2010). Includes bibliographical references. Also issued in print.
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Deyu, Getnet Kacha. "Defect Modulation Doping for Transparent Conducting Oxide Materials." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI071.
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Le dopage des matériaux semi-conducteurs est une partie fondamentale de la technologie moderne. Les oxydes conducteurs transparents (TCO) constituent une famille de semi-conducteurs, qui sont optiquement transparents et électriquement conducteurs. La conductivité électrique élevée est généralement obtenue grâce à un dopage associant des impuretés de substitution hétérovalentes comme dans In2O3 dopé au Sn (ITO), SnO2 dopé au fluor (FTO) et ZnO dopé à l'Al (AZO). Cependant, ces approches classiques ont dans de nombreux cas atteint leurs limites tant en ce qui concerne la densité de porteurs de charge atteignable, que pour la valeur de la mobilité des porteurs de charge. Le dopage par modulation est un mécanisme qui exploite l'alignement de la bande d'énergie à une interface entre deux matériaux pour induire une densité de porteurs de charges libres dans l’un d’entre eux ; un tel mécanisme a permis de montrer dans certains cas que la limitation liée à la mobilité pouvait ainsi était évitée. Cependant, la limite de densité de porteuse ne peut pas être levée par cette approche, du fait de l'alignement des limites de dopage par défauts intrinsèques. Le but de ce travail était de mettre en œuvre cette nouvelle stratégie de dopage pour les TCO. La stratégie repose sur l’utilisation de large bande interdite pour doper la surface des couches de TCO, ce qui résulte à un piégeage du niveau de Fermi pour la phase dopante et à un positionnement du niveau de Fermi en dehors de la limite de dopage dans les TCO. La méthode est testée en utilisant un TCO comme In2O3 non dopé, In2O3 dopé au Sn et SnO2 phase hôte et Al2O3 et SiO2-x en tant que phase de dopant gap à large bandeThe doping of semiconductor materials is a fundamental part of modern technology.Transparent conducting oxides (TCOs) are a group of semiconductors, which holds the features of being transparent and electrically conductive. The high electrical conductivity is usually obtained by typical doping with heterovalent substitutional impurities like in Sn-doped In2O3 (ITO), fluorine-doped SnO2 (FTO) and Al-doped ZnO (AZO). However, these classical approaches have in many cases reached their limits both in regard to achievable charge carrier density, as well as mobility. Modulation doping, a mechanism that exploits the energy band alignment at an interface between two materials to induce free charge carriers in one of them, has been shown to avoid the mobility limitation. However, the carrier density limit cannot be lifted by this approach, as the alignment of doping limits by intrinsic defects. The goal of this work was to implement the novel doping strategy for TCO materials. The strategy relies on using of defective wide band gap materials to dope the surface of the TCO layers, which results Fermi level pinning at the dopant phase and Fermi level positions outside the doping limit in the TCOs. The approach is tested by using undoped In2O3, Sn-doped In2O3 and SnO2 as TCO host phase and Al2O3 and SiO2−x as wide band gap dopant phase
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Taub, Samuel. "Transition metal oxide doping of ceria-based solid solutions." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18845.
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The effects of low concentration Co, Cr and Mn oxide, singly and in combination, on the sintering and electrical properties of Ce0.9Gd0.1O1.95 (CGO) have been investigated with possible mechanisms suggested to explain this modified behaviour. The influence of these dopants on the densification kinetics of CGO were primarily investigated using constant heating rate dilatometry. Whilst low concentration Co and Mn-oxide were found to improve the sinterability of CGO, the addition of Cr-oxide was found to inhibit the densification kinetics of the material. The location and concentration of these dopants were investigated as a function of relative density using scanning transmission electron microscopy combined with energy dispersive x-ray mapping. All materials showed a gradual reduction in the grain boundary dopant concentration with sintering time, leading eventually to the formation of a second phase that was subsequently analysed by either electron energy loss spectroscopy or synchrotron x-ray powder diffraction. The improved densification of both the Co-doped and Mn-doped materials was believed to be related to an increased rate of lattice and grain boundary cation diffusion, associated with the segregation of the transition metal dopant to the grain boundary. In both cases the onset of rapid densification was correlated with the reduction of the transition metal cation leading to an increase in cerium interstitials, which are suggested to be the defects responsible for cerium diffusion. The inhibiting effects of Cr-addition were similarly related to changes in the defect chemistry, with the Cr ions creating a blocking effect that hindered the dominant grain boundary pathway for cation diffusion. The effects of these dopants on the electrical conductivity of CGO were examined using a combination of AC impedance spectroscopy and Hebb-Wagner polarisation measurements. Whilst Co-doping was found to enhance the specific grain boundary conductivity of CGO, the addition of either Cr or Mn resulted in an approximate 2 orders of magnitude decrease, even at dopant concentrations as low as 100 ppm. Despite these differences in ionic conductivity, both Co and Cr-doping were found to significantly enhance the electronic contribution to the conductivity along the boundaries, particularly within the p-type regime. The modified electrical behaviour was related to the formation of a continuous, transition metal-enriched grain boundary pathway and a change in the driving force for grain boundary Gd segregation, leading to a depletion of oxygen vacancies within the space charge regions and the consequent reduction of oxygen transport across the boundaries. The effects of this segregation were finally examined with mono-layer sensitivity using low energy ion scattering incorporating a novel method of self-standardisation. These analyses provided strong support for the conductivity mechanisms previously outlined.
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PRADA, STEFANO. "Enhancing oxide surface reactivity by doping or nano-structuring." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/50011.
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Wide band-gap simple oxides are rather inert materials, which found applications in heterogeneous catalysis mainly as supports for active metal nanoparticles. This thesis investigates tailored modifications of the oxide characteristics aimed at making these substrates more reactive in catalytic processes. In particular we are interested in engineering the charge transfer with supported metal catalysts in order to enhance their activity and selectivity. By using first principles calculations in the framework of the density functional theory, we have explored two main routes in this field: 1) nanostructuring, in particular nanothick oxide films supported on metals, and 2) doping of oxides with substitutional metal ions. After addressing methodological aspects related to the theoretical simulations of these materials, we have considered the role of oxide doping in optimizing the structural and electronic properties of supported gold adparticles; we have shown that depending on the dopant and the nature of the oxide it is possible to finely tune the shape and the charge state of adsorbed metal particle. Moreover we have combined oxide doping and nanostructuring in modifying the work function of metal substrates. By varying parameters like nature, position, and concentration of dopants within the metal-supported oxide films, it is possible in principle to modify the work function of the metallic support in a desired way.
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Wellenius, Patrick. "Nitrogen Doping and Ion Beam Processing of Zinc Oxide Thin Films." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-01042006-015801/.
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The modification of single crystal epitaxial ZnO thin films grown by Pulsed Laser Deposition on c-axis oriented sapphire substrates by Ion Beam Processing was investigated. Nitrogen doping of the films was attempted using nuclear transmutation using the 16O (3He, 4He) 15O reaction at 6.6 MeV. The 15O product is unstable and decays to 15N after several minutes by positron emission. There are several potential advantages to using nuclear transmutation including producing nitrogen atoms on the correct lattice site for doping and reduced crystal damage as compared to conventional ion beam implantation. In the experiments in this thesis the doping levels achieved ~1014 cm-3 were too low to be expected to dope the films to p-type. However several beneficial effects due to the ion beam processing were observed, including large increases in resistivity, reduction of defect luminescence, and substantial increases in the response of photoconductive detectors. In addition to desired effects in some films it was also found that in some films bubble like structures approximately 10 ìm in diameter were formed where the thin film delaminated from the surface. It was assumed that mechanism for the bubble formation was the build up of helium gas at the sapphire/ZnO interface.
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Trapatseli, Maria. "Doping controlled resistive switching dynamics in transition metal oxide thin films." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/423702/.
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Transition metal oxide thin films have attracted increasing attention due to their potential in non-volatile resistive random access memory (RRAM) devices, where such thin films are used as active layers in metal-insulator-metal (MIM) configurations. Titanium dioxide is one of the most celebrated oxides among the ones that exhibit resistive switching behaviour due to its wide band gap, high thermal stability, and high dielectric constant. RRAM devices with various materials as active layers, have demonstrated very fast switching performance but also huge potential for miniaturisation, which is the bottleneck of FLASH memory. Nevertheless, these devices very often suffer poor endurance, physical degradation, large variability of switching parameters and low yields. In most cases, the physical degradation stems from high electroforming and switching voltages. Doping of the active layer has been often employed to enhance the performance of RRAM devices, like endurance, OFF/ON ratio, forming voltages, etc. In this work, doping in TiO2-x RRAM devices was used to engineer the electroforming and switching thresholds so that device degradation and failure can be delayed or prevented. Al and Nb were selected with basic criteria the ionic radius and the oxidation state. The doped RRAM devices, showed improved switching performance compared to their undoped counterparts. Alternative approaches to doping were also investigated, like multilayer stacks comprising Al2O3-y and TiO2-x thin films. Furthermore, Al:TiO2-x/Nb:TiO2-x bilayer RRAM devices were fabricated, to prove whether a diode behaviour of the p-n interface inside the RRAM was feasible. The latest would be a particularly interesting finding towards active electronics.
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Li, Zheng. "Phase behavior of iron oxide doping with ethylbenzene dehydrogenation catalyst promoters." [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3355517.
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Rashidi, Nazanin. "Cation and anion doping of ZnO thin films by spray pyrolysis." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:e8261559-8901-409d-8d08-a3fc04b6d734.
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ZnO is an n-type semiconducting material with high optical transparency in the visible range (400 - 750 nm) of the electromagnetic spectrum. When doped with group 13 or 14 metal oxides, ZnO exhibits almost metallic electrical conductivity. ZnO thin films have been recognised as promising alternative material for the currently widely-used but expensive indium oxide in the form of indium tin oxide (ITO), in terms of their low cost and the high abundance of zinc. At the moment, even the best solution-processed ZnO films still can not compete for ITO replacement especially in solar energy utilization and OLED lighting applications, and the performance of ZnO films needs to be further improved. The objective of this work was to enhance the electrical and optical properties of spray pyrolysed ZnO thin films by simultaneous cation and anion doping. This was achieved by growing several series of undoped, single-doped, and co-doped ZnO thin films over a wide range of conditions, in order to understand the growth behaviour of undoped and doped ZnO, and to establish the optimum growth procedure. Spray pyrolysis process has advantages over vacuum-based techniques in terms of its low-cost, high deposition rate, simple procedure and can be applied for the production of large area thin films. Various techniques were employed to characterize the properties of the prepared thin films, and thus determine the optimum growth conditions (i.e. X-ray difiraction (XRD), Xray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-Vis-NIR spectroscopy and Hall effect measurement). The growth of doped ZnO on glass substrates using Si and F as dopants, yielded highly conducting and transparent thin films. The co-doped thin films exhibited distinct widening of band gap upon increasing deposition temperature and doping concentration as a result of increasing electron concentration up to 4.8 x 1020 cm-3 upon doping with Si and F at the same time. The resistivity of the films deposited from Zn(acac)2 · xH2O solutions and at the optimum temperature of 450 °C, was found to decrease from 4.6 x 10-2 Ωcm for the best undoped ZnO film to 3.7 x 10-3 Ωcm, upon doping with 3% Si. The films co-doped with Si and F in the ratios of [Si] / [Zn]= 3 - 4 mol% and [F] / [Zn]=30 - 40 mol% were the most conducting (p ∼ 2.0 x 10-3 Ωcm). The associated optical transmittance of co-doped ZnO was above 85% in the whole visible range. Results compare favourably with In-doped ZnO deposited under similar conditions. Si+F co-doped ZnO films offer a suitable replacement for ITO in many applications such as LCD and touch screen displays.
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Gharavi-Naeini, Jafar. "Doping and temperature dependence of the Raman spectra lanthanum strontium copper oxide." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0028/NQ51865.pdf.
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Litzelman, Scott J. "Modification of space charge transport in nanocrystalline cerium oxide by heterogeneous doping." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/46681.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Includes bibliographical references (p. 161-170).
In the search for new materials for energy conversion and storage technologies such as solid oxide fuel cells, nano-ionic materials have become increasingly relevant because unique physical and transport properties that occur on the nanoscale may potentially lead to improved device performance. Nanocrystalline cerium oxide, in particular, has been the subject of intense scrutiny, as researchers have attempted to link trends in electrical conductivity with the properties of space charge layers within the material. In this thesis, efforts designed to intentionally modify the space charge potential, and thus the space charge profiles and the macroscopic conductivity, are described.Nanocrystalline CeO2 thin films with a columnar microstructure were grown by pulsed laser deposition. A novel heterogeneous doping technique was developed in which thin NiO and Gd203 diffusion sources were deposited on the ceria surface and annealed in the temperature range of 7008000C in order to diffuse the cations into the ceria layer exclusively along grain boundaries. Time-offlight secondary ion mass spectrometry (ToF-SIMS) was utilized to measure the diffusion profiles. A single diffusion mechanism, identified as grain boundary diffusion, was observed. Using the constant source solution to the diffusion equation, grain boundary diffusion coefficients on the order of 10-15 to 10-13 cm2/s were obtained for Ni, as well as Mg diffusion emanating from the underlying substrate. Microfabricated Pt electrodes were deposited on the sample surface, and electrical measurements were made using impedance spectroscopy and two-point DC techniques. The asdeposited thin films displayed a total conductivity and activation energy consistent with reference values in the literature. After in-diffusion, the electrical conductivity decreased by one order of magnitude. Novel electron-blocking electrodes, consisting of dense yttria-stabilized zirconia and porous Pt layers were fabricated in order to deconvolute the ionic and electronic contributions to the total conductivity. In the as-deposited state, the ionic conductivity was determined to be pO2-independent, and the electronic conductivity displayed a slope of -0.30. The ionic transference number in the as-deposited state was 0.34.
(cont.) After annealing either with or without a diffusion source at temperatures of 700-8000C, both the ionic and electronic partial conductivities decreased. The ionic transferene numbers with and without a diffusion source were 0.26 and 0.76, respectively. Based on the existing framework of charge transport in polycrystalline materials, carrier profiles associated with the Mott-Schottky and Gouy-Chapman models were integrated in order to predict conductivity values based on parameters such as grain size and the space charge potential. Mott-Schottky profiles with a space charge potential of 0.44V were used to describe the behavior of the ceria thin films in the as-deposited state. It is proposed that annealing at temperatures of 700TC and above resulted in segregation of acceptor impurity ions to the grain boundary, resulting in GouyChapman conditions. The best fit to the annealed data occurred for a space charge potential of 0.35 V: a decrease of approximately 90 mV from the as-deposited state. In addition, a high-conductivity interfacial layer between the CeO2 and substrate was detected and was determined to influence samples with no surface diffusion source to a greater degree than those with NiO or Gd203.
by Scott J. Litzelman.
Ph.D.
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Song, Myung-Eun. "Processing, Structure and Properties of High Temperature Thermoelectric Oxide Materials." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/98542.
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High temperature thermal energy harvesting has attracted much attention recently. In order to achieve stable operation at high temperatures there is emerging need to develop efficient and oxidation-resistant materials. Most of the well-known materials with high dimensionless figure of merit (ZT) values such as Bi2Te3, PbTe, skutterudites, and half-Heusler alloys, are not thermally stable at temperatures approaching 500°C or higher, due to the presence of volatile elements. Oxide thermoelectric materials are considered to be potential candidates for high temperature applications due to their robust thermal and chemical stability in oxidizing atmosphere along with the reduced toxicity, relatively simpler fabrication, and cost. In this dissertation, nanoscale texturing and interface engineering were utilized for enhancing the thermoelectric performance of oxide polycrystalline Ca3Co4O9 materials, which were synthesized using conventional sintering and spark plasma sintering (SPS) techniques. In order to tailor the electrical and thermal properties, Lu and Ga co-doping was investigated in Ca3Co4O9 system. The effect of co-doping at Ca and Co sites on the thermoelectric properties was quantified and the anisotropic behavior was investigated. Because of the effective scattering of phonons by doping-induced defects, lower thermal conductivity and higher ZT were achieved. The layered structure of Ca3Co4O9 has strong anisotropy in the transport properties. For this reason, the thermoelectric measurements were conducted for the samples along both vertical and horizontal directions. The ZT value along the vertical direction was found to be 3 to 4 times higher than that along the horizontal direction. Metallic inclusions along with ionic doping were also utilized in order to enhance the ZT of Ca3Co4O9. The texturing occurring in the nanostructured Ca3Co4O9 through ion doping and Ag inclusions was studied using microscopy and diffraction analysis. Multi-length scale inclusions and heavier ion doping in Ca3Co4O9 resulted in higher electrical conductivity and reduced thermal conductivity. The maximum ZT of 0.25 at 670°C was found in the spark plasma sintered Ca2.95Ag0.05Co4O9 sample. In literature, limited number of studies have been conducted on understanding the anisotropic thermoelectric performance of Ca3Co4O9, which often results in erroneous estimation of ZT. This study addresses this limitation and provides systematic evaluation of the anisotropic response with respect to platelet microstructure. Textured Ca3Co4O9/Ag nanocomposites were fabricated using spark plasma sintering (SPS) technique and utilized for understanding the role of microstructure towards anisotropic thermoelectric properties. The thermoelectric response was measured along both vertical and horizontal direction with respect to the SPS pressure axis. In order to achieve enhanced degree of texturing and increase electrical conductivity along ab planes, a two-step SPS method was developed. Ag nanoinclusions was found to increase the overall electrical conductivity and the thermoelectric power factor because of improved electrical connections among the grains. Through two-step SPS method, 28% improvement in the average ZT values below 400°C and 10% improvement above 400°C in Ca3Co4O9/Ag nanocomposites was achieved.
Lastly, this dissertation provides significant progress towards understanding the effect of synthesis method on thermoelectric properties and evolution of textured microstructure. The anisotropy resulting from the crystal structure and microstructural features is systematically quantified. Results reported in this study will assist the continued progress in developing Ca3Co4O9 materials for practical thermoelectric applications.PHD
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Randell, Heather Eve. "Applications of stress from boron doping and other challenges in silicon technology." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010292.
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Afal, Aysegul. "Hydrothermal Method For Doping Of Zinc Oxide Nanowires And Fabrication Of Ultraviolet Photodetectors." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614463/index.pdf.
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Nanotechnology comprises of the understanding and control of materials and processes at the nanoscale. Among various nanostructured materials, semiconducting nanowires attract much interest for their novel physical properties and potential device applications. The unique properties of these nanowires are based on their high surface to volume ratio and quantum confinement effect.
Zinc oxide, having a direct, wide bandgap and large exciton binding energy, is highly appealing for optoelectronic devices. Due to excellent optical and electrical properties, zinc oxide nanowires have been utilized to fabricate various devices such as solar cells, light emitting diodes, transistors and photodetectors. Furthermore, zinc oxide, in its natural state exhibits n-type conductivity. Addition of impurities often
leads to remarkable changes in their electrical and optical properties, which open up new application areas.
Among the many synthesis methods for zinc oxide nanowires, hydrothermal method is an attractive one due to its easy procedure, simple equipment and low temperature requirements.
In this thesis, zinc oxide nanowires were grown and doped by hydrothermal method. Different metal dopants such as copper, silver and aluminum were used for this purpose. These metals were selected as dopants due to their effect on magnetic properties, p-type conduction and electrical conductivity of ZnO nanowires, respectively. Doped nanowires were fully characterized and the changes in their physical properties were investigated.
In addition, hydrothermally synthesized pure and aluminum doped zinc oxide nanowires were used as the electrically active components in ultraviolet photodetectors. Silver nanowires were utilized as transparent electrodes. Optoelectronic properties of the detectors were examined. Effect of in-situ annealing and nanowire length was investigated. Short recovery time, around 4 seconds, with a decent on/off ratio of 2600 was obtained. This design provides a simple and cost effective approach for the fabrication of high performance ultraviolet photodetectors.
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Wang, Junwei. "Chemical doping of metal oxide nanomaterials and characterization of their physical-chemical properties." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1333829935.
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Allard, Garvin Richard Johan. "Synthesis and characterization of zinc-doped magnetic nanoparticles for diagnostic studies." University of the Western Cape, 2015. http://hdl.handle.net/11394/4815.
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Magister Scientiae - MScIn the present study we report the synthesis and characterization of iron oxide magnetic nanoparticles doped with zinc in an attempt to enhance the magnetic properties. The nanoparticles were prepared via the co-precipitation route and capped with 3-phosphonopropionic acid (3-PPA). The amount of zinc dopant was varied to yield nanoparticles with the general formula ZnxFe3-xO4 (x=0, 0.1, 0.2, 0.3, 0.4). Characterization was carried out using high resolution transmission electron microscopy (HRTEM), X-ray diffraction spectroscopy (XRD), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and superconducting quantum interference device (SQUID) analysis. Results from HRTEM, XRD and SQUID confirm that doping took place and x=0.2 was found to be the doping limit for these nanoparticles with a maximum size of 10.73 nm and saturation magnetization of 73.37 emu/g. The EDS further confirmed successful doping with zinc, while FTIR and TGA confirmed successful capping with 3-PPA. Despite agglomeration at all doping levels, these nanoparticles show great potential for application in breast cancer diagnostic studies.
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Han, Donglin. "Doping Behavior of Cations in Perovskite-type Oxide Materials for Protonic Ceramic Fuel Cells." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/151976.
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Chai, Jessica Hui Ju. "Combining Zinc Oxide and Silver for Potential Optoelectronic Applications." Thesis, University of Canterbury. Electrical and Computer Engineering, 2010. http://hdl.handle.net/10092/3529.
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Semiconductors represent the enabling technology that underpins the many advances that define modern society. One semiconductor that shows considerable promise in the fabrication of new devices is zinc oxide (ZnO). A fundamental understanding of the properties of a material is required in order to exploit its properties. The behaviour of dopants and defects relevant to optoelectronic device fabrication is of particular interest. However, acceptor doping of ZnO is currently controversial, as successful and reproducible acceptor doping has not yet been achieved. Acceptor doping of ZnO using silver (Ag) is explored in this thesis to contribute towards the understanding of defect introduction in ZnO. In addition, there is also increasing interest in exploring materials with unconventional properties, commonly referred to as metamaterials, particularly for optical applications. The previously unexplored unique combination of Ag and ZnO may enable the fabrication of those devices. Several key factors that affect heteroepitaxy film quality, and ultimately its properties, are buffer layers and substrate temperature. A lattice match between sapphire and ZnO was provided by using buffer layers of 1 nm magnesium oxide (MgO) and 7.9 nm low temperature ZnO. The highest quality film was grown at the highest temperature (800°C), with rms roughness of 2.9 nm, carrier concentration of 3.6x10¹⁶ cm⁻³, and mobility of 105 cm²/Vs. In contrast, dopant (Ag) incorporation occurs more readily below 600°C, with dopant incorporation of up to 1020 cm⁻³ measured. Ag manifests as a deep acceptor (up to 94% substitutionally on Zn lattice sites), as evident from decreasing carrier concentration with increasing Ag flux, and DLTS measurements indicating an acceptor trap at 319 meV. This suggests that Ag is suitable for introducing compensation in ZnO, but Ag acceptors are not sufficiently shallow to result in p-type material. However, the unique combination of ZnO and Ag also enables the fabrication of a novel device, namely a superlens. Initial experimental results show the possibility of imaging a 100 nm line as 132 nm, compared with the diffraction-limited resolution of 332 nm for the same line feature.
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Paradisi, Andrea. "Ultra-high carrier modulation in two dimensions through space charge doping : graphene and zinc oxide." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066297/document.
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La modulation de la densité de charge est un aspect important de l'étude de les transitions de phase électroniques ainsi que des propriétés électroniques des matériaux et il est à la base de plusieurs applications dans la micro-électronique. L'ajustement de la densité des porteurs de charge (dopage) peut être fait par voie chimique, en ajoutant des atomes étrangers au réseau cristallin du matériau ou électrostatiquement, en créant un accumulation de charge comme dans un Transistor é Effet de Champ. Cette dernier m ethode est réversible et particuliérement appropriée pour les matériaux bidimensionnels (2D) ou pour des couches ultra-minces. Le Dopage par Charge d'Espace est une nouvelle technique inventée et développée au cours de ce travail de thèse pour le dopage electrostatique de matériaux déposés sur la surface du verre. Une charge d'espace est créée à la surface en provoquant le mouvement des ions sodium présents dans le verre sous l'effet de la chaleur et d'un champ électrique extérieur. Cette espace de charge induit une accumulation de charge dans le matériau déposé sur la surface du verre, ce qui peut être supérieure à 10^14/cm^2. Une caractérisation détaillée faite avec mesures de transport, effet Hall, mesures Raman et mesures de Microscopie a Force Atomique (AFM) montrent que le dopage est réversible, bipolaire et il ne provoque pas des modifications chimiques. Cette technique peut être appliquée a des grandes surfaces, comme il est montré pour le cas du graph ene CVD. Dans une deuxiéme partie le dopage par espace de charge est appliqué à des couches ultra-minces (< 40 nm) de ZnO_(1-x). Le résultat est un abaissement de la résistance par carré de 5 ordres de grandeur. Les mesures de magnéto-transport faites à basse température montrent que les électrons dop es sont confinés en deux dimensions. Une transition remarquable de la localisation faible à l'anti-localisation est observée en fonction du dopage et de la température et des conclusions sont tirées à propos des phénoménes de diffusion qui gouverne le transport électronique dans des diff erentes conditions dans ce matériauCarrier modulation is an important parameter in the study of the electronic phase transitions and the electronic properties of materials and at the basis for many applications in microelectronics. The tuning of charge carrier density (doping) can be achieved chemically, by adding foreign atoms to the crystal structure of the material or electrostatically, by inducing a charge accumulation like in a Field Eect Transistor device. The latter method is reversible and particularly indicated for use in two dimensional (2D) materials or ultra-thin films. Space Charge Doping is a new technique invented and developed during this thesis for the electrostatic doping of such materials deposited on a glass surface. A space charge is created at the surface by causing sodium ions contained in glass to drift under the Eect of heat and an external electric field. This space charge in turn induces a charge accumulation in the material deposited on the glass surface which can be higher than 10^14/cm^2. Detailed characterization using transport, Hall effect, Raman and AFM measurements shows that the doping is reversible, ambipolar and does not induce chemical changes. It can be applied to large areas as shown with CVD graphene. In a second phase the space charge doping method is applied to polycrystalline ultra-thin films (< 40 nm) of ZnO_(1-x). A lowering of sheet resistance over 5 orders of magnitude is obtained. Low temperature magneto-transport measurements reveal that doped electrons are confined in two dimensions. A remarkable transition between weak localization and anti-localization isobserved as a function of doping and temperature and conclusions are drawn concerning the scattering phenomena governing electronic transport under different conditions in this material
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Wang, Li. "Study of sintering behaviours and mechanical properties of barium strontium cobalt iron oxide ceramics." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/study-of-sintering-behaviours-and-mechanical-properties-of-barium-strontium-cobalt-iron-oxide-ceramics(cefae647-0ab8-4f69-9aa6-f91c6aa8239e).html.
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The thesis studies the sintering behaviours and mechanical properties of perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) ceramics. The sintering behaviours of BSCF are studied by sintering BSCF powder using a series of sintering temperatures and dwell times. Under all circumstances, only a cubic perovskite structure is identified in as-sintered samples. The relative density of BSCF increases with increasing sintering temperature and dwell time, but shows a more significant increase with increasing temperature. While the grain size increases with increasing sintering temperature and dwell time, it is found that the increasing temperature contributes much more significantly than increasing dwell time in grain growth. The shape of grain size distribution profile is independent of sintering temperature and dwell time, but the profile shifts with different sintering conditions. The grain maintains an aspect ratio of 1.8 irrespective of sintering conditions. Similar findings are also made on the Ni-doped BSCF, but it is found that Ni doping inhibits the grain growth and retards the densification of BSCF while it has little influence on the grain size distributions and grain aspect ratio distributions. The grain growth exponent (n) and apparent activation energy (Q) are also systematically studied. It is found that grain boundary diffusion is the dominant controlling mechanism for BSCF while both grain boundary and lattice diffusions are the equally dominant controlling mechanisms for BSCF-Ni8. The fracture stress of BSCF is measured by both three-point and ring-on-ring bending tests at room and high temperatures. The fracture stress determined by three-point bending tests is consistently higher than that value measured by ring-on-ring tests for a given temperature. By utilising Weibull statistics a close prediction is made of the three-point values from the ring-on-ring values. Compared with the Young’s modulus of BSCF obtained from three-point bending tests between RT and 800 °C, the values determined from ring-on-ring tests shows a fairly good agreement. However, the Young’s modulus measured by both bending tests is lower than that value determined by micro-indentation tests. Hardness and fracture toughness are independent of grain size and grain orientation. Porosity is the dominant factor in Young’s modulus, hardness and fracture toughness of BSCF. The intrinsic hardness, intrinsic Young’s modulus and intrinsic fracture toughness of BSCF are also determined. The subcritical crack growth (SCG) of BSCF is also studied using constant load method at RT and constant stress rate method at 800 °C. It is found that that BSCF is not susceptible to SCG at RT but becomes relatively sensitive to SCG at 800 °C. The results are subsequently used as a basis for a strength–probability–time (SPT) lifetime prediction. Ni doping increases the Young’s modulus, hardness and fracture toughness of BSCF determined micro-indentation tests at RT. Both hardness and Young’s modulus show a non-monotonic trend with Ni doping content, which is attributed to the porosity and secondary phase. The intrinsic hardness, intrinsic Young’s modulus and intrinsic fracture toughness of 8 mol% Ni-doped BSCF are determined. Dopants have little influence on grain orientation and the distribution of grain boundary misorientation angles of BSCF.
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THANNEERU, RANJITH. "VACANCY ENGINEERED DOPED AND UNDOPED NANOCRYSTALLINE RARE EARTH OXIDE PARTICLES FOR HIGH TEMPERATURE OXIDATION RESISTANT COATING." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3986.
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Rare earth oxides with trivalent lattice dopants have been of great interest to researchers in the recent years due to its potential applications in catalysis and high temperature protective coatings. The ability to store oxygen in rare earths is the basis for catalysis because of the ability to change valence states which causes the presence of intrinsic oxygen vacancies in the crystal lattice. Although, several doped-rare earth oxide systems in micron scale have been investigated, the doping effect in cerium oxide nanoparticles with well characterized particle size has not been studied. The doping of ceria at that small size can be very beneficial to further improve its catalytic properties and alter the high temperature phases in alloy systems. Cost effective room temperature chemical methods are used in the current work to synthesize uniformly distributed undoped and doped (dopants: La, Nd, Sm, Gd, Y and Yb) rare earth oxide nanoparticles. In the present study, the variation of the properties in nanocrystalline ceria (NC) synthesized by microemulsion method is studied as a function of dopant size and its concentration. To further understand, the role of dopant (cation) size on the oxygen vacancy concentration, doped nanocrystalline oxide powders were analyzed by Raman Spectroscopy, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). XRD studies showed that lattice parameter change in nanocrystalline oxide by doping trivalent rare earth elements is largely depending on size of trivalent ions. It showed that by doping larger cations (Gd3+ and Y3+) compare to Ce3+ causes lattice expansion where as smaller cations (Yb3+) leads to lattice contraction. It also showed that the lattice expansion or contraction is directly proportional to dopant concentration. The results of Raman Spectroscopy showed that the correlation length decreases resulting in increase in oxygen vacancies for larger trivalent dopants (Sm3+, Gd3+ and Y3+). However, the correlation length increases resulting in decrease in oxygen vacancies for smaller trivalent dopants (Yb3+) compare to nanocrystalline ceria. These nanostructured oxides are further applied to develop high temperature oxidation resistance coatings for austenitic steels. The present study investigates the role of oxygen vacancies in the performance of high temperature oxidation resistance as a function of various trivalent dopants and dopant concentration. NC and La3+ doped nanocrystalline ceria (LDN) particles were coated on AISI 304 stainless steels (SS) and exposed to 1243K in dry air for longer duration and subjected to cycling. The results are further compared with that of micro-ceria (MC) coatings. The coated samples showed 90% improvement in oxidation resistance compared to uncoated and MC coated steels as seen from the SEM cross-sectional studies. XRD analysis showed the presence of chromia in both NC and 20 LDN samples which is absent in uncoated steels. From SIMS depth profiles, Fe, Ni depletion zones are observed in presence of LDN coated sample indicating diffusion through the oxide layer. The role of oxygen vacancies in the nanoceria coatings on the early formation of protective chromia layer is discussed and compared to its micron counterpart. This study helps in understanding the role of oxygen vacancies to protect austenitic stainless steel at high temperature and confirms the oxygen inward diffusion rather cation outward diffusion in rare earth oxide coatings. It also gives an idea to identify the type of dopant and its concentration in nanocrystalline cerium oxide which supplies the critical oxygen partial pressure required at high temperature to form primarily impervious chromia layer.M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE
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Smith, Steven P. "Lanthanide-containing Nanostructured Materials." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145459.
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The research described in this Dissertation is concerned generally with the exploration of the potential use of lanthanide elements in nanostructured materials for the purpose of modification of the magnetic and optical properties. This is explored through a focus on the development of lanthanide-containing iron oxide nanosystems. Our objectives of producing lanthanide containing nanostructured materials with potentially useful optical and magnetic applications has been achieved through the development of lanthanide-doped Fe3O4 and -Fe2O3 nanoparticles, as well as a unique core-shell magnetic-upconverting nanoparticle system.Necessary background information on nanomaterials, rationale for the study of lanthanide-containing iron oxide nanosystems and context for discussion of the results obtained in each project is provided in the Introduction Chapter. The syntheses of Fe3O4 nanoparticles doped with Eu(III) and Sm(III) are discussed, along with structural characterization and magnetic property investigation of products In Chapter 2. The following Chapter expands the study of lanthanide doping to -Fe2O3, a closely related yet distinct magnetic nanoparticle system. A completely different synthesis is attempted, and comparisons between the two systems are made.The development of novel synthetic methodologies used to create such products has yielded high-quality lanthanide-containing materials and are evidenced by TEM images displaying nearly monodisperse particles in each of our efforts. The modifications to the magnetic properties resulting from lanthanide doping include theobservation of ferromagnetism in the Fe3O4 system and increased magnetic saturation of -Fe2O3 nanoparticles, and are characterized by VSM and the visual observation of magnetic alignment of products. Our efforts towards developing a novel methodology capable of producing high quality Fe3O4 nanoparticles, and subsequent characterization of products, were published in the Journal of the American Chemical Society.Optically active, magnetic, core-shell nanoparticles are investigated in Chapter 4 for the potential uses in diagnosis and treatment of cancer. This multifunctional system uses Fe3O4 as a magnetic core, shelled by upconverting lanthanide-containing nanomaterials, and is rendered biocompatible through encapsulation of the core-shell structure by a silica shell. Added functionality is achieved through amine functionalization of the silica surface, with the goal of coupling the inorganic nanoparticle with drug targeting groups. TEM results indicate successful formation of the core-shell nanoparticles, and expected magnetic and optical properties are shown by visual observation and luminescence spectroscopy, respectively.
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Pilli, Aparna. "Atomic Layer Deposition of Boron Oxide and Boron Nitride for Ultrashallow Doping and Capping Applications." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1752373/.
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The deposition of boron oxide (B₂O₃) films on silicon substrates is of significant interest in microelectronics for ultrashallow doping applications. However, thickness control and conformality of such films has been an issue in high aspect ratio 3D structures which have long replaced traditional planar transistor architectures. B₂O₃ films are also unstable in atmosphere, requiring a suitable capping barrier for passivation. The growth of continuous, stoichiometric B₂O₃ and boron nitride (BN) films has been demonstrated in this dissertation using Atomic Layer Deposition (ALD) and enhanced ALD methods for doping and capping applications.
Low temperature ALD of B₂O₃ was achieved using BCl₃/H₂O precursors at 300 K. In situ x-ray photoelectron spectroscopy (XPS) was used to assess the purity and stoichiometry of deposited films with a high reported growth rate of ~2.5 Å/cycle. Free-radical assisted ALD of B₂O₃ was also demonstrated using non-corrosive trimethyl borate (TMB) precursor, in conjunction with mixed O₂/O-radical effluent, at 300 K. The influence of O₂/O flux on TMB-saturated Si surface was investigated using in situ XPS, residual gas analysis mass spectrometer (RGA-MS) and ab initio molecular dynamics simulations (AIMD). Both low and high flux regimes were studied in order to understand the trade-off between ligand removal and B₂O₃ growth rate. Optimization of precursor flux was discovered to be imperative in plasma and radical-assisted ALD processes.
BN was investigated as a novel capping barrier for B₂O₃ and B-Si-oxide films. A BN capping layer, deposited using BCl₃/NH₃ ALD at 600 K, demonstrated excellent stoichiometry and consistent growth rate (1.4 Å/cycle) on both films. Approximately 13 Å of BN was sufficient to protect ~13 Å of B₂O₃ and ~5 Å of B-Si-oxide from atmospheric moisture and prevent volatile boric acid formation. BN/B₂O₃/Si heterostructures are also stable at high temperatures (>1000 K) commonly used for dopant drive-in and activation. BN shows great promise in preventing upward boron diffusion which causes a loss in the dopant dose concentration in Si.
The capping effects of BN were extended to electrochemical battery applications. ALD of BN was achieved on solid Li-garnet electrolytes using halide-free tris(dimethylamino)borane precursor, in conjunction with NH₃ at 723 K. Approximately 3 nm of BN cap successfully inhibited Li₂CO₃ formation, which is detrimental to Li-based electrolytes. BN capped Li-garnets demonstrated ambient stability for at least 2 months of storage in air as determined by XPS. BN also played a crucial role in stabilizing Li anode/electrolyte interface, which drastically reduced interfacial resistance to 18 Ω.cm², improved critical current density and demonstrated excellent capacitance retention of 98% over 100 cycles. This work established that ALD is key to achieving conformal growth of BN as a requirement for Li dendrite suppression, which in turn influences battery life and performance.
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Deyu, Getnet Kacha [Verfasser], Andreas [Akademischer Betreuer] Klein, and Lambert [Akademischer Betreuer] Alff. "Defect Modulation Doping for Transparent Conducting Oxide Materials / Getnet Kacha Deyu ; Andreas Klein, Lambert Alff." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1205070095/34.
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Gunti, Srikanth. "Enhanced Visible Light Photocatalytic Remediation of Organics in Water Using Zinc Oxide and Titanium Oxide Nanostructures." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6852.
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The techniques mostly used to decontaminate air as well as water pollutants have drawbacks in terms of higher costs, require secondary treatment, and some methods are very slow. So, emphasis has been given to water though the use of photocatalysts, which break organic pollutants to water and carbon dioxide and leave no trace of by-products at the end. Photocatalytic remediation aligns with the waste and wastewater industries’ zero waste schemes with lower cost, eco-friendly and sustainable treatment technology. The commonly used photocatalysts such as titanium oxide (TiO2), zinc oxide (ZnO), tungsten oxide (WO3) have band gap of nearly 3.2 eV. The lower energy band-gap of a semiconductor makes it a better photocatalyst. The major drawbacks of photocatalysts are its inefficiency to work under visible light and high photocorrosion which limits its uses. These limitations can be mitigated through dopants and the formation of varying morphologies like nanowires, nanoparticles, nanotubes etc. Several organic pollutants are insoluble in water, which inhibits the pollutant (insoluble) to come in contact with photocatalytic material thus hindering remediation characteristic of a photocatalyst. Binder material used to immobilize the photocatalytic material tends to decompose due to oxidative and reduction reactions around the photocatalyst which causes the loss of photocatalytic material.
This investigation displays the advantage of organic remediation in visible radiation using graphene (G) doped TiO2 nanoparticles and nanowires. The nanostructured G-TiO2 nanoparticles and G-TiO2 nanowires were synthesized using sol-gel and hydrothermal methods. The nanostructured materials were characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR) and particle analyser procedures. The remediation of organic compounds (methyl orange) in water was achieved under visible radiation using graphene doped nanostructured photocatalytic materials. The sol-gel synthesized G-TiO2 nanoparticles has shown complete remediation of methyl orange (MO) in less than four hours, thus displaying enhanced photocatalytic activity achieved through graphene doping on TiO2 nanostructures
The dopant and structure introduced in zinc oxide (ZnO) nanomaterials bring foundation for enhanced photocatalytic activity due to lowering of the band gap, and decreasing of photocorrosion through delaying of electron-hole recombination. The challenge to synthesize both nanowire and nanoparticle structures of ZnO doped with graphene (G) are carried out by simple and cost effective hydrothermal as well as super saturation precipitation techniques, respectively. Various nanostructures of ZnO have been synthesized using precipitation and hydrothermal methods are ZnO nanoparticles, G doped ZnO nanoparticles, ZnO nanowires, G doped ZnO nanowires, TiO2 seeded ZnO nanowires and G doped TiO2 seeded ZnO nanowires The synthesized ZnO based nanostructures were characterized using SEM, TEM, XRD, UV-vis, FTIR and particle analyser methods respectively. The standard organic pollutant methyl orange (MO) dye was employed in the water to understand the effective remediation using ZnO nanostructured materials under visible light radiation. The G-ZnO NW structure has shown effective remediation of MO in water in three hours compared to other synthesized nanostructured ZnO materials.
The petroleum compounds were photocatalytically remediated from water using G- TiO2 nanoparticles material in visible light radiation. The G-TiO2 nanoparticle was synthesized using sol-gel technique and used on various petroleum-based chemicals (toluene, naphthalene and diesel) were remediated, and samples were analysed using optical and gas chromatography (GC) techniques. The importance of pollutant to come in contact with photocatalyst have been demonstrated by employing surfactant along with G-TiO2 nanoparticles to remediate naphthalene.
Earlier studies in this investigation have shown that graphene (G) doping in both titanium oxide (TiO2) and zinc oxide (ZnO), has brought about a reduction in photocorrosion, and an increase in the photocatalytic efficiency for remediation of organics under visible light (λ > 400nm). However, the graphene doped photocatalysts have proven to be hard to coat on a surface, due to the strong hydrophobic nature of graphene. So, attempts have been made to use polyaniline (PANI), a conducting polymer, as a binder material by insitu polymerization of aniline over G-TiO2 nanoparticles (G-TiO2 NP) and G-ZnO nanowires (G-ZnO NW) & characterized using SEM, XRD, UV-vis and FTIR techniques. The photocatalytic, as well as photoelectrochemical catalytic performance of PANI:G-TiO2 NP and PANI:G-ZnO NW, were investigated. The standard MO in water was used for both PANI:G-TiO2 NP and PANI:G-ZnO NW electrodes on conducting substrates. 1:1 PANI:G-TiO2 NP shows an increase of 31% in the remediation of MO in water at potential of +1000 mV, and with the ease in coating PANI:G-TiO2 NP and PANI:G-ZnO NW on various substrates, on top of the visible light remediation allows for the use of these materials and process to be used for practical applications of remediation of organics from water.
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Mavlonov, Abdurashid. "Doping Efficiency and Limits in Wurtzite (Mg,Zn)O Alloys." Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-214372.
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In this thesis, the structural, optical, and electrical properties of wurtzite MgxZn1-xO:Al and MgxZn1-xO:Ga thin films have been investigated in dependence on Mg and dopant concentration. Among the transparent conductive oxides (TCOs), ZnO based compounds have gained renewed interest as a transparent electrode for large scale applications such as defroster windows, at panel displays, touch screens, and thin film solar
cells due to low material and processing cost, non-toxicity, and suitable physical properties. In general, these applications require transparent electrodes with lowest possible resistivity of rho < 10^-3 Ohmcm and lower [1]. Recently, it has been reported that Ga and Al doped ZnO thin films can be deposited with respective resistivity of 5x10^-5 Ohmcm [2] and 3 x10^-5 Ohmcm [3] which are similar to the data obtained for other practical TCOs, i.e. the resistivity of about 4x 10^-5 Ohmcm for Sn doped In2O3 (ITO) thin films [4]. Moreover, the bandgap of ZnO can be increased by alloying with Mg offering band alignment between transparent electrode and active (or buffer) layer of the device, e.g. Cu(In,Ga)Se2 solar cells [5]. The tunable bandgap of these transparent electrodes can further increase the efficiency of the devices by avoiding energy losses in the interface region of the layers. From this point of view, this work has been aimed to investigate the doping efficiency and limits in transparent conductive (Mg,Zn)O alloys. For this purpose, the samples investigated in this work have been grown by pulsed-laser deposition (PLD) using a novel, continuous composition spread method (CCS). In general, this method allows to grow thin films with lateral composition gradient(s) [6, 7]. All MgxZn1-xO:Al and MgxZn1-xO:Ga thin films have been deposited on 2-inch in diameter glass, c- or r-plane sapphire substrates using threefold segmented PLD targets in order to grow thin films with two perpendicular, lateral composition gradients, i.e. the Mg composition is varied in one direction whereas the Al/Ga concentration is varied in a perpendicular direction [7, 8]. In order to investigate the influence of the temperature, samples grown at different substrate temperatures in the range of 25 to 600 C were investigated. The
optical and electrical measurements have been carried out on (5x 5)mm^2 samples that were cut from the CCS wafers along the respective composition gradients, i.e. Mg and Al/Ga contents. Subsequently, physical properties of thin films have been analyzed for a large range of Al/Ga content between 0.5 and 7 at.%, which corresponds to doping
concentrations between 2x 10^20 and 3x 10^21 cm^-3, for different Mg contents x(Mg) ranging from 0.01 to 0.1.
It has been found that practically the limiting the dopant concentrations is about 2 x10^21 cm^-3. Further, the electrical data suggests, that the compensating intrinsic defect is doubly chargeable hinting to the zinc vacancy (V_Zn) as microscopic origin. Increasing the dopant concentration above 2 x10^21 cm^-3 leads to a degradation of electrical and
structural properties [8].
Further, the influence of growth and annealing temperatures on structural, electrical and optical properties of the films has been studied. For that purpose, Al and Ga doped (2.5 at.% = 1x10^21 cm^-3) Mg0.05Zn0.95O thin films have been chosen from CCS samples grown at T_g = (25 - 600) C . For both doping series, the samples grown at higher temperatures exhibit better crystalline quality compared to the samples grown at lower growth temperatures. As a result, samples grown at higher temperatures reveal
higher Hall mobility. For the Al-doping series, the highest free charge carrier density of n = 8.2x 10^20 cm^-3 was obtained for an Mg0.05Zn0.95O:Al thin film grown at 200 C, with corresponding Hall mobility of mu = 13.3 cm^2/Vs, a resistivity of rho = 5.7x10^-4 Ohmcm,
and optical bandgap of E_g = 3.8 eV. Interestingly, the free charge carrier density of n = (5 - 8) x 10^20 cm^-3 for samples grown with T_g > 300 C is clearly higher than the value of n = 1.25 x 10^20 cm^-3 that was obtained for the high temperature grown sample, i.e. at T_g = 600 C. Furthermore, for all T_g, Al-doped films have a higher doping efficiency than the Ga-doped counterparts. In order to look deeper into the microscopic origin of this behavior, the samples were post-annealed in vacuum at 400 C.
Experimental results showed that the free charge carrier density of Al-doped samples first decreased and saturated afterward with increasing annealing time. On the other hand, the free charge carrier density of the Ga-doped samples first slightly increased and saturated with increasing annealing time. For both doping series, the saturation value of n ~ 1 x 10^20 cm^-3 was very close to the data that has been observed for (i) high temperature grown samples and (ii) the solubility limit of Al in ZnO of 0.3 at.% =
1.2x 10^20 cm^-3, that has been determined by Shirouzu et al. for high temperature grown (T_g > 600 C) Al-doped ZnO [9]. Correspondingly, the optical bandgap also changed, i.e. increased (decreased) for Al- (Ga-) doping series, and approached a constant value of 3.5 0 +- 0.1 eV which is explained by generation of acceptor-like compensating defects, and
the solubility limit of the dopants. From XRD data, no secondary phases were found for as-grown and post-annealed films. However, the slight improvement of crystalline quality has been observed on post-annealed samples. Further, it has been shown that the growth and annealing temperatures are important as they strongly affect the metastable state of
the solid solution that samples grown at low temperature represent. The low solubility limit of the dopants, i.e. 0.3 at.% for Al in ZnO under equilibrium condition, can be increased by preparing samples by non-equilibrium growth techniques [10]. This is also consistent with experimental results of this work that Al- as well as Ga-doped metastable ZnO and (Mg,Zn)O thin films can be prepared with highest possible doping efficiency for the dopant concentration up to 2.5 at.% when growth or annealing temperatures
below 400 C are used.
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Giordano, Anthony J. "Altering the work function of surfaces: The influential role of surface modifiers for tuning properties of metals and transparent conducting oxides." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53989.
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This thesis focuses on the use of surface modifiers to tune the properties of both metals and metal oxides. Particular attention is given to examine the modification of transparent conducting oxides (TCOs) including indium tin oxide and zinc oxide both through the use of phosphonic acids as well as organic and metal-organic dopants. In this thesis a variety of known and new phosphonic acids are synthesized. A subset of these molecules are then used to probe the relationship between the ability of a phosphonic acid to tune the work function of ITO and how that interrelates with the coverage and molecular orientation of the modifier on the surface. Experimental techniques including XPS, UPS, and NEXAFS are coupled with theoretical DFT calculations in order to more closely examine this relationship.
Literature surrounding the modification of zinc oxide with phosphonic acids is not as prevalent as that found for the modification of ITO. Thus, effort is placed on attempting to determine optimal modification conditions for phosphonic acids on zinc oxide. As zinc oxide is already a low work function metal oxide, modifiers were synthesized in an attempt to further decrease the work function of this substrate in an effort to minimize the barrier to carrier collection/injection. Etching of the substrate by phosphonic acids is also examined.
In a related technique, n- and p-dopants are used to modify the surfaces of ITO, zinc oxide, and gold and it was found that the work function can be drastically altered, to approximately 3.3 – 3.6 eV for all three of the substrates examined. Surface reactions are straightforward to conduct typically taking only 60 s to achieve this change in work function.
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Crowley, Kyle McKinley. "Electrical Characterization, Transport, and Doping Effects in Two-Dimensional Transition Metal Oxides." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1597327584506971.
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Patel, Bhavnesh. "Photoluminescence and kinetics of zinc oxide doped with rare earths." Ohio : Ohio University, 1998. http://www.ohiolink.edu/etd/view.cgi?ohiou1176402695.
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Amani, Hamedani Hoda. "Development of novel heteronanostructures engineered for electrochemical energy conversion devices." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52158.
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Heterogeneous nanostructures such as coaxial nanotubes, nanowires and nanorods have been of growing interest due to their potential for high energy-conversion efficiencies and charge/discharge rates in solar cell, energy storage and fuel cell applications. Their superior properties at nanoscale as well as their high surface area, fast charge transport along large interfacial contact areas, and short charge diffusion lengths have made them attractive components for next generation high efficiency energy-conversion devices. The primary focus of this work was to understand the doping mechanism of TiO2 nanotube exclusively with strontium as an alkaline earth metal to shine light on the relation between the observed enhancement in photocatalytic properties of doped TiO2 nanotubes and its structural and electronic characteristics. The mechanism of Sr incorporation into the TiO2 nanotube structure with the hypothesis of possibility of phase segregation has been explored in low concentrations as a dopant and in very high concentrations by processing of SrTiO3 nanotube arrays. Detailed experimental examination of the bulk and surface of the Sr-doped nanotubes has been performed to understand the effect of dopant on electronic structure and optical properties of the TiO2 nanotubes. Moreover, in order to minimize the polarizations associated with the ionic/electronic charge transport in the electrolyte and anode of solid oxide fuel cells (SOFCs), a new platform is developed using vertically oriented metal oxide nanotube arrays. This novel platform, which is made of coaxial oxide nanotubes on silicon substrates, has the potential to simultaneously lower the operating temperature and production cost leading to significant enhancement in the performance of micro-SOFCs.
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Guo, Lei. "Synthesis of Zinc Oxide Fiber and Its Application in Dye Sensitized Solar Cells." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1283204966.
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Patil, Swanand. "FUNDAMENTAL ASPECTS OF REGENERATIVE CERIUM OXIDE NANOPARTICLES AND THEIR APPLICATIONS IN NANOBIOTECHNOLOGY." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3156.
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Cerium oxide has been used extensively for various applications over the past two decades. The use of cerium oxide nanoparticles is beneficial in present applications and can open avenues for future applications. The present study utilizes the microemulsion technique to synthesize uniformly distributed cerium oxide nanoparticles. The same technique was also used to synthesize cerium oxide nanoparticles doped with trivalent elements (La and Nd). The fundamental study of cerium oxide nanoparticles identified variations in properties as a function of particle size and also due to doping with trivalent elements (La and Nd). It was found that the lattice parameter of cerium oxide nanoparticles increases with decrease in particle size. Also Raman allowed mode shift to lower energies and the peak at 464 cm-1 becomes broader and asymmetric. The size dependent changes in cerium oxide were correlated to increase in oxygen vacancy concentration in the cerium oxide lattice. The doping of cerium oxide nanoparticles with trivalent elements introduces more oxygen vacancies and expands the cerium oxide lattice further (in addition to the lattice expansion due to the size effect). The lattice expansion is greater for La-doped cerium oxide nanoparticles compared to Nd-doping due to the larger ionic radius of La compared to Nd, the lattice expansion is directly proportional to the dopant concentration. The synthesized cerium oxide nanoparticles were used to develop an electrochemical biosensor of hydrogen peroxide (H2O2). The sensor was useful to detect H2O2 concentrations as low as 1µM in water. Also the preliminary testing of the sensor on tomato stem and leaf extracts indicated that the sensor can be used in practical applications such as plant physiological studies etc. The nanomolar concentrations of cerium oxide nanoparticles were also found to be useful in decreasing ROS (reactive oxygen species) mediated cellular damages in various in vitro cell cultures. Cerium oxide nanoparticles reduced the cellular damages to the normal breast epithelial cell line (CRL 8798) induced by X-rays and to the Keratinocyte cell line induced by UV irradiation. Cerium oxide nanoparticles were also found to be neuroprotective to adult rat spinal cord and retinal neurons. We propose that cerium oxide nanoparticles act as free radical scavenger (via redox reactions on its surface) to decrease the ROS induced cellular damages. Additionally, UV-visible spectroscopic studies indicated that cerium oxide nanoparticles possess auto-regenerative property by switching its oxidation state between Ce3+ and Ce4+. The auto-regenerative antioxidant property of these nanoparticles appears to be a key component in all the biological applications discussed in the present study.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
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Cornelius, Steffen. "Charge transport limits and electrical dopant activation in transparent conductive (Al,Ga):ZnO and Nb:TiO2 thin films prepared by reactive magnetron sputtering." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-156145.
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Transparent conductive oxides (TCOs) are key functional materials in existing and future electro-optical devices in the fields of energy efficiency, energy generation and information technology. The main application of TCOs is as thin films transparent electrodes where a combination of maximum electrical conductivity and transmittance in the visible to nearinfrared spectral range is required. However, due to the interdependence of the optical properties and the free electron density and mobility, respectively, these requirements cannot be achieved simultaneously in degenerately doped wide band-gap oxide semiconductors. Therefore, a detailed understanding of the mechanisms governing the generation of free charge carriers by extrinsic doping and the charge transport in these materials is essential for further development of high performance TCOs and corresponding deposition methods.
The present work is aimed at a comprehensive investigation of the electrical, optical and structural properties as well as the elemental composition of (Al,Ga) doped ZnO and Nb doped TiO2 thin films prepared by pulsed DC reactive magnetron sputtering. The evolution of the film properties is studied in dependence of various deposition parameters through a combination of characterization techniques including Hall-effect, spectroscopic ellipsometry, spectral photometry, X-ray diffraction, X-ray near edge absorption, Rutherford backscattering spectrometry and particle induced X-ray emission.
This approach resulted in the development of an alternative process control method based on the material specific current-voltage pressure characteristics of the reactive magnetron discharge which allows to precisely control the oxygen deficiency of the sputter deposited films.
Based on the experimental data, models have been established that describe the room temperature charge transport properties and the dielectric function of the obtained ZnO and TiO2 based transparent conductors. On the one hand, these findings allow the prediction of material specific electron mobility limits by identifying the dominating charge carrier scattering mechanisms. On the other hand, new insight is gained into the origin of the observed transition from highly conductive to electrically insulating ZnO layers upon the incorporation of increasing concentrations of Al at elevated growth temperatures.
Moreover, the Al and Ga dopant activation in ZnO have been quantified systematically for a wide range of Al concentrations and deposition conditions. A direct comparison of the Ga and Al doping efficiency demonstrates that Ga is a more efficient electron donor in ZnO. Further, it has been shown that high free electron mobilities in polycrystalline and epitaxial Nb:TiO2 layers can be achieved by reactive magnetron sputtering of TiNb alloy targets. The suppression of rutile phase formation and the control of the Nb dopant activation by fine tuning the oxygen deficiency have been identified as crucial for the growth of high quality TiO2 based TCO layers.
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Coles-Aldridge, Alice. "Substituted ceria materials for applications in solid oxide fuel cells." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/14622.
Full textAbstract:
Cerias, appropriately doped with trivalent rare earth ions in particular, can have high oxide ion conductivity and are attractive as both SOFC (solid oxide fuel cell) electrolytes and anodes. Here, four groups of candidate electrolyte materials were synthesised using a low temperature method in order to determine the effect of multiple doping on their microstructure and ionic conductivity. In an initial study, seven compositions of Ce0.8SmxGd[sub]yNd[sub]zO1.9 (where x, y and z = 0.2, 0.1, 0.0667 or 0 and x + y + z = 0.2) were synthesised and the properties of multiply-doped materials were compared with the corresponding singly-doped parent materials. The effect of co-doping with Gd and Sm was investigated in more detail by preparing and studying five compositions of Ce1−2xSmxGdxO2−x (where x = 0.125, 0.1, 0.0875, 0.075 or 0.05) and seven compositions of Ce0.825SmxGd0.175−xO1.9125 (where x = 0.175, 0.14, 0.105, 0.0875, 0.07, 0.035 or 0). The effect of additional doping with a divalent ion- Ca2+- was studied in six compositions of Ce[sub](0.825+y)Sm[sub](0.0875-y)Gd[sub](0.0875-y)Ca[sub]yO1.9125 (where y = 0, 0.00875, 0.0175, 0.02625, 0.035 or 0.04375). The materials were characterised using scanning and transmission electron microscopy, inductively coupled plasma mass spectrometry and X-ray diffraction. Crystallite sizes were determined in the powders and relative densities and grain size distributions were obtained in sintered pellets. Total, bulk and grain boundary conductivities were obtained using impedance spectroscopy and corresponding activation energies and enthalpies of ion migration and defect association were calculated. The most promising material for SOFCs operating at intermediate temperatures was found to be Ce0.825Sm0.0875Gd0.0875O1.9125 which had a total conductivity at 600 °C of 2.23 S m−1. Lastly, doped ceria materials, primarily Ce0.8Sm0.2O1.9, were employed as catalytic supports for Pd and PdO nanoparticles and these were investigated as SOFC anode materials.
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Peleckis, Germanas. "Studies on diluted oxide magnetic semiconductors for spin electronic applications." Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20070821.145447/index.html.
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Dahlberg, Tobias. "The first order Raman spectrum of isotope labelled nitrogen-doped reduced graphene oxide." Thesis, Umeå universitet, Institutionen för fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-116699.
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The topic of this thesis is the study of nitrogen functionalities in nitrogen-doped reduced graphene oxide using Raman spectroscopy. Specifically, the project set out to investigate if the Raman active nitrogen-related vibrational modes of graphene can be identified via isotope labelling. Previous studies have used Raman spectroscopy to characterise nitrogen doped graphene, but none has employed the method of isotope labelling to do so. The study was conducted by producing undoped, nitrogen-doped and nitrogen-15-doped reduced graphene oxide and comparing the differences in the first-order Raman spectrum of the samples. Results of this study are inconclusive. However, some indications linking the I band to nitrogen functionalities are found. Also, a hypothetical Raman band denoted I* possibly related to \spt{3} hybridised carbon is introduced in the same spectral area as I. This indication of a separation of the I band into two bands, each dependent on one of these factors could bring clarity to this poorly understood spectral area. As the results of this study are highly speculative, further research is needed to confirm them and the work presented here serves as a preliminary investigation.
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Nakayama, Ryo. "Exploration into an Innovative Science of Hydrogen Functional Materials Using Low-temperature Ion Beam Irradiation." Kyoto University, 2019. http://hdl.handle.net/2433/236604.
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Pant, Bharat Raj. "A Comparative Study on P-type Nickel Oxide and N-type Zinc Oxide for Gas Sensor Applications." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1525473245395728.
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Coathup, David James. "The effect of interface layers and doping on the multiferroic properties of bismuth titanate oxide thin films on silicon." Thesis, Aston University, 2017. http://publications.aston.ac.uk/38210/.
Full textAbstract:
For the development of magnetoelectric memory devices, the development of artificial magnetoelectric materials is necessary. Previous work in the field had focused on the multiferroic properties of this material in bulk form, however, for a practical device, a thin film investigation is needed. This thesis details the author's investigation into the multiferroic properties of bismuth titanate oxide, Bi4Th012, (BTO) thin films doped with lanthanum, niobium, iron and cobalt, to form the novel material Bi3.2slao.7sLTb.sNbo.2sFeo.mCoo.m012 (BTFC), and how different interface layers influence their structural and electronic properties when they are deposited on silicon substrates. The aim of this research is to achieve a multiferroic BTO thin film with strong ferroelectric and ferromagnetic properties by utilising a novel combination of dopants. Chapter 1is the introduction, providing insight into the layout and structure of the thesis making it easier for the reader to follow. Chapter 2 is the background literature review, which discusses the real life industrial demands of this work, and is followed by a discussion of the physics and material science principles behind this investigation. Chapter 3 is the experimental literature review, in which the material synthesis, device fabrication and characterisation techniques utilised in this work are discussed. The experimental chapters begins with Chapter 4, in which the effect of a zinc oxide (ZnO) interface layer on crystalline properties of BTFC on silicon is investigated. Chapter 5 follows this investigation up by investigating ferroelectric propertied of BTFC thin films on silicon with ZnO interface layers. Finally chapter 6 looks at BTFC thin films on silicon substrates with platinum interface layers, and both simultaneous ferroelectric and ferromagnetic properties were present, confirming multiferroic behaviour. Initial investigations into the deposition onto silicon were unsuccessful, but were overcome by utilising ZnO interface layers. The ZnO interface layer eliminated some critical difficulties; however high resolution transmission electron microscopy (HRTEM) analysis showed zinc atoms from inside the interface layer diffusing into the BTFC thin film. The investigation into the ferroelectric properties of thin films using the triangular voltage waveform method confirmed ferroelectric domain switching, but were inhibited by the need for a vacuum annealing environment to prevent the oxidation of the silicon substrate. This resulted in the generation of oxygen vacancies within the BTFC thin film, which limited driving voltage during the measurement, presenting ferroelectric saturation. The final investigation was focused on BTFC deposited on platinised-silicon substrates. Platinum is proved to be the superior interface layer, due to its chemical and thermal stability. The investigation found high quality crystalline BTFC, with a high dielectric constant and leakage current, which can be attributed to the doping effect. The ferroelectric measurements demonstrated a fully saturated ferroelectric loop, and a remnant polarisation and coercivity of 2Pr = 11.03!lC/cm 2, and 2Ec = 196.5kV/em on the optimised thin films. Ferromagnetic measurements of the sample were challenging, due to the small total magnetisation of the thin film resulting from its low volume and mass. Using a Superconducting Quantum User Interface Device {SQUID) vibrating sample microscopy {VSM), Ferromagnetisum was presented in the bulk and thin film form, however, the remnant magnetisation of the thin film could not be determined, due to its noise level value. This discovery proves the existence of simultaneous ferroelectric and ferromagnetic phases in BTFC thin film, confirming muitiferroic behaviour of the deposited thin films had been achieved with the chosen dopants.
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Kwiatkowski, Maciej. "ZnO(core)/TiO2(shell) composites: influence of TiO2 microstructure, N-doping and decoration with Au nanoparticles on photocatalytic and photoelectrochemical activity." Doctoral thesis, Bourgogne Franche-Comté, 2017. https://depotuw.ceon.pl/handle/item/2244.
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Efficient use of renewable energies is one of the most difficult technological challenges facing humanity. Among all renewable energy sources, the sunlight is considered as the most abundant and accessible one. To convert it into usable and controllable form, the modern technology relies on generation of electron-hole pairs in semiconductors upon light absorption. The obtained separated charge carriers possess extra energy brought by the converted sunlight which can be further utilized in various ways. Currently, the most common approach consists in its direct transformation into electricity in p-n junctions. Alternatively, the electrons and holes can be used to perform chemical reactions. The electrons can be transferred to reduce various organic compounds or inorganic species, while simultaneously the holes can play the role of oxidizer by subtracting the electrons from the other substances. Through these reactions it would be possible to accumulate the solar energy in chemical species allowing thus to alleviate the intermittence of the sunlight. Unfortunately, the existing materials do not easily cross the laboratory level to realize this approach on industrial scale. That is why the development of new semiconductor photocatalysts, which harvest and convert efficiently the visible part of solar spectrum, is of paramount importance.
For many years the most often studied photocatalytic materials have been ZnO and TiO2. However, it has been recently shown that composites based on ZnO and TiO2 possess even more promising properties than many other semiconductors in various photocatalytic applications. Despite many works reporting high photoactivity of these composites in different applications, the detailed information about the structure–properties correlation is lacking. In order to fill this gap we decided to focus our attention to study the influence of microstructure of ZnO/TiO2 composites on their properties in photocatalytic degradation of organic pollutants, and in application in half-reaction of ‘solar fuel’ generation, namely photoassisted water electro-oxidation. To realize such study the composites should satisfy the requirements of a high surface area and good electric conductivity. We chose therefore the design based on ZnO nanorods supported on ITO (Indium Tin Oxide)-coated glass electrode. The ZnO nanorods (NRs) were then covered with a layer of TiO2 under different deposition conditions. The composition and microstructure of the obtained ZnO(core)/TiO2(shell) composites were modified in the aim to elucidate how these parameters influence their photocatalytic activity. Consequently, the efforts were made to impart visible light activity to the elaborated ZnO/TiO2 composites by modifying titanium dioxide layers with nitrogen and decoration with Au nanoparticles.
The thesis consists of three parts: Bibliography, Experimental and Results and Discussion.
First part of the present PhD thesis, Bibliography, is dedicated to the analysis of literature concerning fundamental properties of semiconductor materials, solid/electrolyte interface as well as principles of photocatalysis and photoelectrochemical water oxidation. Also, the photocatalytic properties of ZnO and TiO2, and those of their composites are reviewed in this section. Furthermore, methods for improvement visible-light absorption are also described, i.e. N-doping and surface plasmonic effects due to the noble metal nanoparticles (Au NPs) deposited on semiconductors.
The second part, Experimental, covers the preparation procedures and characterization techniques used in the work. First, the details are given for electrochemical seeding of ITO support, hydrothermal growth of ZnO nanorods, sol-gel deposition of TiO2 (and N-doped TiO2), and photodeposition of Au NPs. Second, the characterization techniques used in realization of this project are described: SEM (Scanning Electron Microscopy), HAADF-STEM and HR-TEM (High Angle Annular Dark Field Scanning Electron Transmission Microscopy and High Resolution Transmission Electron Microscopy), XRD (X-ray Diffraction Analysis), XPS (X-ray Photoelectron Spectroscopy), EDS ‘or EDX’ (Energy Dispersive Spectroscopy) analyses connected with electron microscopy techniques, UV-vis Spectroscopy and DRS (Diffuse Reflectance UV-vis Spectroscopy, TGA-DSC (Thermogravimetry Differential Scanning Calorimetry Analysis), TOC (Total Organic Carbon) analysis, RT-PL (Room Temperature Photoluminescence Spectroscopy), electrochemical techniques including: LSV (Linear Sweep Voltammetry), CV (Cyclic Voltammetry), chronoamperometry, chronopotentiometry, as well as the set-ups elaborated by the author for the purpose of photocatalytic and photoelectrochemical measurements.
The main results of the PhD thesis are presented in the third part, Results and Discussion, consisting of four chapters.
In the first chapter (Chapter 4.1), the results of the studies on electrochemical seeding of ITO-electrode in Zn(CH3COO)2 solution are presented. The length and width of ZnO nanorods grown by hydrothermal method from Zn(NO3)2 aqueous solution on Zn/ZnO-seeded ITO substrate were shown to depend strongly on initial Zn2+ concentration and the synthesis duration. The arrays of well-separated ZnO ‘obelisk-like’ nanorods of width varied from 100 nm at tips to ~ 300 nm at bottom and average length of 1.9 µm were prepared under optimized conditions, and used as starting point for further fabrication of (core)ZnO/TiO2(shell) composites.
In the second chapter (Chapter 4.2), a simple and low-cost sol-gel method was developed in order to form TiO2 thin layers on ZnO nanorods by hydrolysis of titanium(IV) butoxide. The results of studies lead to elaboration of two most distinctive variants of sol-gel procedure that allow to deposit TiO2 layers of controlled thicknesses and different morphology (rugged or compact). The rugged TiO2 layers were obtained after 6 hours of one step sol-gel synthesis followed by calcination of the sample at
450 oC, ensuring formation of anatase-TiO2, whereas the uniform coating of 25 nm –
40 nm thickness was obtained via three successive 30 min-synthesis with the intermediate calcination of the sample after each deposition cycle. The composite containing the rugged TiO2 layer was shown to possess significantly higher activity in model pollutant (methylene blue, MB) degradation and in photoassisted H2O electro-oxidation under 400 nm monochromatic light irradiation. This improved photoactivity was correlated with the composite microstructure and attributed to a higher porosity and better accessibility of ZnO/TiO2 interface region through the rugged TiO2 layer by the reagents. The TiO2 (shell) layers of similar morphology were also prepared by atomic layer (ALD) and chemical vapor deposition (CVD) techniques and it was shown that the composites fabricated by us with the use of simple sol-gel procedure yield comparable (or even higher) photoactivity. Finally, it was confirmed by total organic carbon (TOC) analysis that the ZnO/TiO2 composites elaborated in this work are also active in decomposition of the pollutants in a dumb hill leachate solution (waste water) under 400 nm monochromatic irradiation.
In Chapter 4.3 it is shown that the ZnO/TiO2 interface plays a key role in enhancement of photodecomposition of MB under 400 nm illumination. The increase of photocatalytic activity was attributed to the shift of absorption edge of ZnO/TiO2 towards visible light in comparison to that of the ZnO(core)-etched TiO2. Further enhancement of photocatalytic activity of ZnO/TiO2 was achieved through its additional calcination at 450 °C for 3 h. This simple treatment brings 40% increase in the rate of MB decomposition and a two-fold rise of the photocurrent in H2O oxidation. Measurements of open circuit potential (VOC) showed that the improved properties of additionally calcined ZnO/TiO2 composites stem from the decrease of electron-hole recombination rate. STEM (Scanning Transmission Electron Microscopy) studies showed that the additional calcination resulted in formation of voids at the ZnO/TiO2 interface. EDX (Energy Dispersive X-ray) analysis and XPS (X-ray Photoelectron Spectroscopy) results proved that formation of voids is accompanied by the outward diffusion of Zn ions into TiO2 layer and allowed to conclude about the existence of the Kirkendall effect at ZnO/TiO2 interface. Occurrence of this effect observed for the first time at unusually moderate temperature (450 °C) was shown and attributed to a highly defective nature of the surface layer of the ZnO nanorods.
In the last chapter (Chapter 4.4), the composites consisting of ITO-supported ZnO nanorods covered with nitrogen-doped titanium dioxide, TiO2(N), shell were decorated with gold nanoparticles (Au NPs) in order to improve their photocatalytic activity under visible light. The photocatalytic properties of ZnO/TiO2/Au and ZnO/TiO2(N)/Au ternary composites were studied under illumination with Xe lamp equipped with a
400 nm cut-off filter. It was found that low Au NPs loading (0.37% at.) resulted in 60% enhancement of photocatalytic decolorization of MB under visible light with respect to the Au-free sample owing to plasmonic effects. Also, a simultaneous N-doping and Au NPs-decoration allows to multiply by three the photocurrent in photoelectrochemical water oxidation at the potential of 0.8 V vs. Ag/AgCl. It was also demonstrated that the Au-decorated composites possess a strong electrocatalytic activity in reduction O2 to active oxygen species (via formation of O2⦁– radicals) under a small negative bias
(–0.25 V vs. Ag/AgCl) in dark. Illumination of the polarized sample with visible light was shown to enhance this process resulting in rapid decomposition a model pollutant (MB) even in the presence of Na2SO4. This approach allows to completely overcome a problem of inhibition of the photocatalytic process by dissolved inorganic salts on non-polarized catalysts, thus meeting the aim of promising material for photoelectrocatalytic remediation of waste water, often containing a significant amount of inorganic ions.
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POLO, ANNALISA. "TERNARY OXIDE SEMICONDUCTOR PHOTOANODES FOR SOLAR ENERGY CONVERSION." Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/827287.
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Solar energy conversion and storage into hydrogen is a valuable approach to capture the energy that is freely available from sunlight and to turn it into a clean fuel. Photoelectrochemical (PEC) water splitting through the dual-absorber tandem cell technology has emerged as a promising strategy to this aim. The work conducted in the frame of this PhD thesis aimed at playing a part in the development and optimization of efficient oxide-based semiconductor photoanodes for water oxidation, which is the kinetic bottleneck of the overall PEC water splitting process.
Photoanodes based on films of absorbing materials were successfully synthesized with a high optical transparency as important requirement for maximizing the solar energy conversion efficiency of the final tandem cell device. Subsequently, their intrinsic properties as single photoabsorber photoanodes were largely improved, on the basis of the results obtained through comprehensive PEC studies in parallel with thorough structural, morphological, and spectroscopic investigations.
The attention was focused on three different classes of promising ternary metal oxides, able to absorb a large portion of the solar spectrum, namely i) BiVO4 (bandgap Eg = 2.4 eV), known for its excellent solar light to hydrogen conversion efficiency, ii) the copper tungstate-based materials CuWO4 (Eg = 2.3 eV) and CuW(1-x)Mo(x)O4 (Eg = 2.0 eV), ideal to be employed as visible-light active alternative to WO3, and iii) ZnFe2O4 (Eg = 2.0 eV) belonging to the spinel ferrites class, possessing excellent photothermal and chemical stability.
Specifically, BiVO4 was studied either as a visible light sensitizer towards TiO2 or as a single photoanode material to focus on the identification and improvement of its intrinsically poor electron transport and interfacial transfer properties. In the first case, the TiO2/BiVO4 heterojunction system was proved to be effective in producing highly reductive electrons, suitable for overall water splitting, through TiO2 sensitization towards visible light. This, together with the counterintuitive mechanism at the basis of the observed impressive functionality, was effectively disclosed through combined PEC and photocatalytic reduction test studies. The multifaceted role of Mo6+ doping onto both the bulk and surface properties of BiVO4 films was also revealed through an in-depth PEC and impedance spectroscopy study. By improving either the bulk conductivity or the interfacial charge transfer of optimized Mo6+ doped BiVO4 photoanodes a conspicuous enhancement was attained of their photoactivity towards water oxidation with respect to the pure material.
The presence of intra-gap states in CuWO4, acting as electron traps and thus being responsible for a severe internal charge recombination, was verified by means of the first ultrafast transient absorption study performed with this material, in combination with both an electrochemical and a photochromic characterization. This issue, which strongly limits the PEC performance of CuWO4 photoanodes, was addressed by adopting a 50% Mo for W substitution resulting in CuW0.5Mo0.5O4 photoanodes, exhibiting not only a greatly extended visible light-induced photoactivity compared to the pure material, as a result of enhanced absorption, but also a considerably improved charge separation. All these factors contributed to the much better PEC performance attained with respect to CuWO4 electrodes. This study was finalized by the identification of a suitable hole scavenger species for copper tungstate-based materials, able to ensure enhanced photocurrent generation compared to pure water oxidation while minimizing dark currents.
Finally, in the frame of my seven months stage in Prof. Sivula’s group at the EPFL in Lausanne, a thorough study was performed on the impact that several parameters, such as the annealing temperature, the film thickness and the creation of oxygen vacancies through a reductive treatment in hydrogen atmosphere, have on the PEC performance of ZnFe2O4 photoanodes. The verified synergism between the higher crystallinity of the films subjected to a high-temperature annealing treatment and the hydrogenation efficiency, which proved effective in optimizing charge separation in the thicker photoactive layers, allowed one to maximize the performance of ZnFe2O4 electrodes for water oxidation. This study also shed light onto the strict correlation occurring between structural parameters, i.e. the film crystallinity and the spinel inversion degree, and the resulting PEC performance, which proved to be in turn controlled by the film morphology.
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Steiner, James David. "Understanding and Controlling the Degradation of Nickel-rich Lithium-ion Layered Cathodes." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/85281.
Full textAbstract:
Consumers across the world use lithium-ion batteries in some fashion in their
everyday life. The growing demand for energy has led to batteries dying quicker than
consumers want. Thus, there are calls for researchers to develop batteries that are longer
lasting. However, the initial increase in battery life over the years has been from better
engineering and not necessarily from making a better material for a battery.
This thesis focuses on the understanding of the chemistry of the materials of a
battery. Throughout the chapters, the research delves into the how and why materials
with extra nickel degrade quickly. Then, it investigates a method of making these nickelrich
materials last longer and how the chemistry within these materials are affected by the
addition of a different metal. Overall, the findings indicate that the addition of titanium
creates a more stable material because it mitigates the release of oxygen and prevents
irreversible changes within the structure of the material.
It determines that the chemistry behind the failings of nickel-rich lithium-ion
batteries and a potential method for allowing the batteries to last longer. It also provides
insight and guidance for potential future research of stabilization of lithium-ion materials.Master of Science
Consumers across the world use lithium-ion batteries in some fashion in their everyday life. The growing demand for energy has led to batteries dying quicker than consumers want. Thus, there are calls for researchers to develop batteries that are longer lasting. However, the initial increase in battery life over the years has been from better engineering and not necessarily from making a better material for a battery. This thesis focuses on the understanding of the chemistry of the materials of a battery. Throughout the chapters, the research delves into the how and why materials with extra nickel degrade quickly. Then, it investigates a method of making these nickel-rich materials last longer and how the chemistry within these materials are affected by the addition of a different metal. Overall, the findings indicate that the addition of titanium creates a more stable material because it mitigates the release of oxygen and prevents irreversible changes within the structure of the material. It determines that the chemistry behind the failings of nickel-rich lithium-ion batteries and a potential method for allowing the batteries to last longer. It also provides insight and guidance for potential future research of stabilization of lithium-ion materials.
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Tang, Yin. "Synthesis and Characterization of Tin Oxide for Thin Film Gas Sensor Applications." Case Western Reserve University School of Graduate Studies / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=case1089995414.
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Hou, Yue. "Enhancement of Nanocrystalline Zinc Oxide based Electronic Gas Sensor by Surface Modification." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1396609072.
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Milliken, Damion Alexander. "Uranium doping of silver sheathed bismuth-strontium-calcium-copper-oxide superconducting tapes for increased critical current density through enhanced flux pinning." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20040810.154223/index.html.
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Kekuda, Dhananjaya. "Property Modulation Of Zinc Oxide Through Doping." Thesis, 2007. http://hdl.handle.net/2005/465.
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Semi conductors are of technological importance and attracted many of the re-searchers. ZnO belongs to the family of II-VI semiconductors and has material properties well suitable to UV light emitters, varistors, Schottky diodes, gas sensors, spintronics, ferroelectric devices and thin film transistors. It has been considered as a competitor to GaN, which belongs to the family of III-V semiconductors. This is due to the fact that ZnO of high quality can be deposited at lower growth temperatures than GaN, leading to the possibility of transparent junctions on less expensive substrates such as glass. This will lead to low-cost UV lasers with important applications in high-density data storage systems etc. One of the most popular growth techniques of ZnO is physical sputtering. As compared to sol-gel and chemical-vapor deposition, the magnetron sputtering is a preferred method because of its simplicity and low operating temperatures. Hence, detailed investigations were carried out on undoped and doped ZnO thin films primarily deposited by magnetron sputtering. The obtained results in the present work are presented in the form of a thesis.
Chapter 1: A brief discussion on the crystal structure of ZnO material and its possible applications in the different areas such as Schottky diodes, spintronics, ferroelectric devices and thin film transistors are presented.
Chapter 2: This chapter deals with various deposition techniques used in the present study. It includes the magnetron sputtering, thermal oxidation, pulsed-laser ablation and sol-gel technique. The experimental set up details and the deposition procedures are described in detail i.e., the deposition principle and the parameters that will affect the film properties. A brief note on the structural characterization equipments namely, X-ray diffraction, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and the optical characterization equipments namely, transmission spectroscopy is presented. The transport properties of the films were studied which include Dielectric studies, impedance studies, device characterization and are discussed.
Chapter 3: The optimization of ZnO thin films for Schottky diode formation and
The characterization of various Schottky diodes is presented in this chapter. P-type conductivity in ZnO was implemented by the variation of partial pressure of oxygen during the sputtering and are discussed. A method to achieve low series resistance hetero-junction was achieved using thermal oxidation method and the detailed transport properties were studied. The optical investigation carried out on the ZnO thin films under various growth conditions are also presented.
Chapter 4: This chapter deals with the processing, structural, electrical, optical and magnetic properties of Mn doped ZnO thin films grown by pulsed laser ablation. Structural investigations have shown that the Mn incorporation increases the c-axis length due to the relatively larger ionic size of the Mn ions. Studies conducted both at low and high concentration region of Zn1¡xMnxO thin films showed that the films are anti-ferromagnetic in nature. The transport measurements revealed that the electrical conductivity is dominated by the presence of shallow traps. Optical investigations suggested the absence of midgap absorption and confirm the uniform distribution of Mn in wurtzite structure.
Chapter 5: Carrier induced ferromagnetism in Co doped ZnO thin films were studied and the results are presented in this chapter. High density targets were prepared by solid state reaction process and the thin films were deposited by pulsed laser ablation technique. Two compositions were studied and it was found that with increase in substrate temperature, c-axis length decreases. Optical studies suggested a strong mid gap absorption around 2eV and could be attributed to the d-d transitions of tetrahedral coordinated Co2+. The presence of ferromagnetism in these films makes them potential candidates for spintronics applications.
Chapter 6: It has been reported in literature that o®-centered polarization will drive ferroelectric phase transition. Motivated by such results, substitution of Lithium in ZnO was studied in detail. The structural and electrical properties were investigated over a wide range of composition (0-25%). The ferroelectric studies were carried out both in metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) configuration and are presented in this chapter. The appearance of Ferro electricity in these films makes them potential candidates for ferroelectric memory devices.
Chapter 7: This chapter describes the studies conducted on Mg doped ZnO
Thin films grown by multi-magnetron sputtering. The hexagonal phases of the films were evaluated. All the films exhibited c-axis preferred orientation towards (002) orientation. Micro structural evolutions of the films were carried out through scanning electron microscopy and atomic force microscopy. Ferroelectric properties were investigated in both metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) configurations. It was observed that the Mg concentration increases the band gap and the details on optical investigations are also presented in this chapter.
Chapter 8: ZnO based thin film transistors have been fabricated and characterized using ZnO as active channel layer and Mg doped ZnO as dielectric layer. Excellent leakage properties of the gate dielectric were studied and presented in this chapter. These studies demonstrated that Mg doped ZnO thin films are suitable candidates for gate dielectric applications.
Conclusions: This section presents the conclusions derived out of the present work. It also includes a few suggestions on future work on this material.
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Cho, Jinhyun. "Zinc Oxide Nanostructures: Synthesis, Doping and Growth Mechanism." Diss., 2013. http://hdl.handle.net/10161/8186.
Full textAbstract:
Over the past decade, the study of zinc oxide (ZnO) II-VI semiconducting nanostructures has been a burgeoning research area because of this material's unique electrical and optical properties. Despite the promise of its characteristics for numerous applications, usage of ZnO in the fabrication of nanoscale devices on a commercial scale remains a challenge because of our lack of knowledge of the underlying physics and chemistry of nanostructures. Sustainable progress in nanowire manufacturing techniques requires that we first undertake basic studies to address these poorly understood underlying concepts before we embark on applied engineering. If these fundamental studies prove successful, then characterization, fabrication, and large-scale integration of nanostructures that use ZnO could be applied to a range of engineering fields. This doctoral dissertation is primarily concerned with the synthesis and doping required for the creation of novel ZnO nanostructures and the growth mechanisms of such structures. Numerous studies have been made of various kinds of ZnO nanostructures. However, no studies have been reported of systematic theoretical modeling that uses both density functional theory and as-synthesized nanostructures to explain the growth mechanisms involved in these devices. First, sulfur-doped ZnO nanostars, synthesized through a hydrothermal method, will be discussed. This section uses ab initio simulations in discussing the synthesis of novel ZnO nanostructures and their proposed growth mechanisms. Moreover, this discussion also addresses the optical properties of ZnO structures that cause sulfur doping to enhance their emission of green light. The next section introduces a novel synthetic methodology to reliably produce well-aligned vertical ZnO nanowire arrays on amorphous substrates. Vertical alignment of nanowires significantly improves the performance of devices like LEDs and solar cells. Because these vertically aligned arrays have historically been made using sapphire substrates that hinder their commercialization, substantial effort has been invested in using ZnO nanocrystal seeds to grow vertically aligned ZnO nanowires on silicon substrates. Well-known synthetic methods, such as zinc acetate dissolved in methanol or zinc acetate combined with sodium hydroxide (or potassium hydroxide), have typically been used in pursuit of this goal without a detailed understanding of the mechanisms of seed creation. The consequence of this lack of knowledge has been inconsistent reproducibility in growing vertically aligned nanowires on silicon substrates. This discussion includes the details of mechanisms that explain the why and how of creation of vertical/misoriented ZnO nanocrystal seeds on silicon substrates. In addition, a preferential c-axis-oriented ZnO nanocrystal seed has been successfully synthesized using a solution composed of ammonium hydroxide (NH4OH) and zinc acetate (Zn(O2CCH3)2). Lastly, the synthesis of sea urchin-like microstructures known as ZnO sea urchins will be introduced. Among the various kinds ZnO structures, the ZnO sea urchin is a integrated structure composed of a 3-D microsphere and 1-D nanowires. Dye-sensitized solar cells (DSSCs) made of ZnO sea urchins have shown a higher power conversion efficiency than planar nanowires. This is because ZnO sea urchins have a higher surface area per unit of volume than planar nanowire arrays. This larger surface area allows larger amounts of dye to access the semiconducting nanowires. We have synthesized the sea urchin structures composed of ZnOxPy microspheres, a mixed of zinc phosphide (Zn3P2) and ZnO phase, encapsulated in an array of ZnO nanowires. Synthesis of these interesting structures was achieved without resorting to the prefabricated 3-D microsphere templates that other groups used in previous studies. This new approach to the synthesis of ZnO sea urchin structures was accomplished by simply adding Zn3P2 powder to the C (graphite) and ZnO source powders in a chemical vapor transport method. The ZnO sea urchin's material properties and growth mechanism will be characterized and discussed in detail.
Dissertation
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Deyu, Getnet Kacha. "Defect Modulation Doping for Transparent Conducting Oxide Materials." Phd thesis, 2020. https://tuprints.ulb.tu-darmstadt.de/9700/1/Getnet%20Kacha%20Deyu-Ph.D.%20Thesis.pdf.
Full textAbstract:
The doping of semiconductor materials is a fundamental part of modern technology.
Transparent conducting oxides (TCOs) are a group of semiconductors, which holds the
features of being transparent and electrically conductive. The high electrical conductivity
is usually obtained by typical doping with heterovalent substitutional impurities like in
Sn-doped In2O3 (ITO), fluorine-doped SnO2 (FTO) and Al-doped ZnO (AZO). However,
these classical approaches have in many cases reached their limits both in regard to
achievable charge carrier density, as well as mobility. Modulation doping, a mechanism
that exploits the energy band alignment at an interface between two materials to induce
free charge carriers in one of them, has been shown to avoid the mobility limitation.
However, the carrier density limit cannot be lifted by this approach, as the alignment of
doping limits by intrinsic defects. The goal of this work was to implement the novel
doping strategy for TCO materials. The strategy relies on using of defective wide band
gap materials to dope the surface of the TCO layers, which results Fermi level pinning
at the dopant phase and Fermi level positions outside the doping limit in the TCOs.
The approach is tested by using undoped In2O3, Sn-doped In2O3 and SnO2 as TCO
host phase and Al2O3 and SiO2−x as wide band gap dopant phase.
The study was divided into two parts by the approaches followed experimentally. The
first part deals with a physical approach, in which sputtered TCOs are used as a host
materials and covered with dopant layers. To test the versatility of the approach the
second part deals with a chemical approach, in which SnO2 based nanocomposite films
produced in spray pyrolysis deposition.
In the physical approach, ITO/ALD-Al2O3, In2O3/ALD-Al2O3, and In2O3/sputtered
SiO2−x thin film systems were exploited. The study was conducted mostly by photoelectron
spectroscopy and Hall effect measurements. ITO films prepared in different
conditions showed an increase of conductivity after ALD-Al2O3 deposition at 200 °C.
This was mostly due to an increase in carrier concentrations. However, Al2O3 deposition
also resulted in a chemical reduction of ITO. The diffusivity of compensating oxygen interstitial (Oi) defects at 200 °C is sufficiently screen the high Fermi level induced by Al2O3, which disable the use of defect modulation doping at this temperature. The
results indicate that achieving higher carrier concentration in ITO thin films requires
a control of the oxygen pressure in combination with low-temperature ALD process.
Undoped In2O3 films also showed an increase of conductivity upon deposition of upto
10-cycles of ALD-Al2O3. These increases indicate the occurrence of defect modulation
doping. However, in order to improve the interface properties and firmly prove the
modulation doping effect, more detailed studies required on the doped interfaces. The
approach was further examined by depositing reactively sputtered SiO2−x dopant phase
from Si target on the top of In2O3 films. The resulting conductivity of In2O3/sputtered
SiO2−x do not show enhancement of electrical properties. This is due to the implantation
of oxygen species during SiO2 deposition on the surface of In2O3, which counteract the
defect modulation doping by reducing concentration of oxygen vacancies (VO) in In2O3.
Therefore, further studies on the deposition conditions of the dopant phase is still vital
to see enhanced electrical properties.
In the chemical approach two different routes were followed: embedding nanoparticles
in TCO host matrix and formation of demixed composite films. In the first route,
Al2O3 and TiO2 nanoparticles (NPs) were chosen as dopant phases and were deposited
together with SnO2 TCO precursors. Different characterization of the produced films
do not confirm the presence nanoparticles into tin oxide films. Therefore to realise
modulation effect further optimization deposition conditions and sample preparation
techniques are needed. For the second route, mixture of SnCl4 ·5(H2O) and Al(acac)3
precursor solutions in different composition are used to produce SnO2/Al2O3 demixed
composite films. Different physicochemical studies shows that under the deposition
conditions followed during this study Al3+ preferably substitute Sn4+ than forming
another Al2O3 separated phase. Al was acting as an acceptor doping on SnO2 films.
Therefore, enhanced conductivity was not observed on the probed samples. For this
route further optimization of deposition condition is clearly required.
The results of this dissertation are relevant for the usage of TCOs in the emerging field
of oxide thin film electronics in particular in field where the surface to bulk ratio is much
higher than in conventional films, as the approach is near surface phenomena. However,
further utilization of both the processing conditions and material selection are vital.
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Ho, ChiaTung, and 何家棟. "Preparation of Doping Antimony Tin Oxide Nano Crystals by Hydrtothermal Process." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/75106383965609105218.
Full textAbstract:
碩士國立臺灣大學
化學工程學研究所
87
The object of this thesis is to systematically discuss the relation between Sb/SnO2 crystal growth and hydrothermal process variables, which include hydrothermal treatment temperature, treatment duration time, salt effect, concentration of original sol. The aqueous Sb/SnO2 sol was prepared by ethanol-water-stannic chloride, and then mixed SnO2 sol with methyl alcohol which contained antimony chloride. Under 260℃and 1 hour duration of hydrothermal treatment, well-distributed crystals of 7.55nm size were formed and the resistivity value of the sol coated on a substrate in the form of film is 3.87ohm-cm. In the aspect of researching the relation between crystal growth and hydrothermal treatment temperature, crystals grew rapidly between 230℃to 260℃under the same duration time. Furthermore, in 260℃but different duration time treatment conditions, crystals grew expeditiously in 1 hour but tardily in longer than 1 hour duration. As the concentration of original sol raised, the distribution of crystal size showed a wider orientation after hydrothermal treatment. In the salt effect discussion, stable sol containing different salt all agglomerated after 260℃1 hour hydrothermal treatment. Between sol-type and gel-type hydrothermal process, the results of which revealed that the crystallite of sol-type was higher.
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YIN, LIU PING, and 劉丙寅. "Application of Doping Antimony Tin Oxide Nano Material on Electrochemical Capacitor." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/84926168115019542410.
Full textAbstract:
碩士國立臺灣大學
化學工程學研究所
89
Abstract In this thesis, we report preparation of highly crystallized antimony doped Tin oxide (ATO) sol, by using sol-gel process followed by hydrothermal process. The highly crystallized sol was used to prepare electrochemical capacitor electrode without adding any binder, which insist to characterize the properties of these electrodes in different conditions, and we have also used the ATO thin film electrodes as current-collector to increase the capacitance in various methods. The performance of ATO thin film electrodes exhibited not only typical double-layer capacitance, but also semiconducting nature. It was found that the performance of capacitance was strongly affected by space charge, crystallization, specific surface area and the pore microstructure. It was also found the optimum heat-treated temperature was 500oC,and at this temperature, the oxide thin film was fully crystallized. The capacitance in vacuum at the optimum heat-treat temperature was observed double to the capacitance in air at the same temperature. We used the fully crystallized ATO thin film electrode as current-collector, and formed RuO2 on the electrodes via two methods: 1.Thermal pyrolysis 2.Cyclic voltammetry. It’s behavior changed from typical EDLC to pseudocapacitance.
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Huang, Kuo-Lun, and 黃國綸. "Effect of Doping Aluminum Oxide and Cobalt Oxide on the Mechanical and Optical Properties of Sintered Zirconia." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/38jaq3.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
95
Tetragonal zirconia polycrystal (TZP, ZrO2-3mol%Y2O3) was doped with cobalt oxide (0.5, 1.0, or 1.5 wt％) and aluminum oxide (0.5, 1.0, or 1.5 wt％) by a solution coating method in the powder state. After sintering the pressed specimens in air at 1430 degC, the relative density of the sintered specimens could be enhanced for the specimens having the approximately equivalent molar ratios of cobalt oxide and aluminum oxide, due to the formation of a spinel phase. The mechanical properties of the doped TZP were only slightly affected by the dopants. A minor fraction of monoclinic phase of larger grain was induced if the doping concentration of cobalt oxide was higher than that of aluminum oxide, while the grain size of zirconia became slightly smaller if the doping concentration of aluminum oxide was higher than that of cobalt oxide. The color of the doped TZP became dark blue if the concentration of cobalt oxide was high, but became royal blue if the relative abundance of the spinel phase of cobalt oxide and aluminum oxide was high. A high doping concentration of aluminum oxide could reduce the reflection ratio of visible light spectrum.