Thesis (Ph. D. in Chemical Engineering)--Vanderbilt University, Aug. 2008. / Title from title screen. Includes bibliographical references.

Thesis (M.Sc.-Res.)--University of Wollongong, 2007. / Typescript. Includes bibliographical references.

Thesis (M.S.)--Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Al based alloy powders (Al₈₅Ni₅Y₆Co₂Fe₂) are produced by spray atomization method. High energy ball milling is done to modify the surface topology and particle size for better electrochemical performance. X ray diffraction (XRD), differential scanning calorimeter (DSC), scanning electron microscope (SEM) and transmission electron microscope (TEM) were conducted to characterize the microstructure of the alloys after ball milling. It is found that 5 hours ball milling gives the minimum crystallization and structure change. Thin film sample is also deposited on stainless steel substrate by pulsed laser deposition (PLD) method for electrochemical test. The capacity and reversibility for different samples are compared and discussed. A capacity of 200mAh/g is obtained for the battery with thin film sample as anode and a capacity of 140mAh/g is obtained for that with electrode from powder sample. Both of the batteries give up to 94% capacity retention after 20 cycles. / Singapore-MIT Alliance (SMA)

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: High Temperature Superconductors (HTS) exhibit exceptional electrical properties that make them attractive candidates for numerous electronic devices and applications. However, constructing working devices can be challenging due to fabrication difficulties of these brittle ceramics. This thesis investigates new methods to make the fabrication of high quality YBa2Cu3O7 (YBCO) thin films easier and compatible with more materials. We present the development of a universal add-on method that can be used in situ to improve the quality of superconducting thin films deposited by Pulsed Laser deposition (PLD). We investigate the in situ application of electric fields and voltage biasing to improve the thin film growth. Considering various electrode configurations, we have developed a final electrode design that is stable and produces reproducible results. By introducing an insulated high voltage (HV) electrode into the chamber during deposition, the quality of the deposited thin films can be modulated depending on the polarity of the voltage applied. Applying a positive voltage improves the film quality obtained. Applying a negative voltage degrades the superconducting properties of the films. A simple proof-of-concept HTS dual-mode microwave filter was designed, fabricated and tested. Only the filter produced using our novel PLD technique displayed the correct filtering action upon cooling to 77K. This is attributed to the thin films better superconducting properties due to our developed technique. / AFRIKAANSE OPSOMMING: Hoë Temperatuur Supergeleiers (HTS) vertoon aantreklike elektriese eienskappe wat hulle goeie kandidate maak vir verskeie elektroniese toepassings. Om werkende toestelle te ontwikkel kan 'n uitdaging wees, as gevolg van die vervaardigings probleme wat bestaan vir hierdie bros keramiek materiaal. Hierdie tesis ondersoek nuwe metodes om die vervaardiging van 'n hoë gehalte YBa2Cu3O7 (YBCO) dun films makliker en versoenbaar te maak met verskeie materiale. Ons toon die ontwikkeling van 'n algemene metode wat maklik bygevoeg kan word om in situ die gehalte van supergeleidende dun films, wat deur gepulseerde laser deponering (PLD) gedeponeer is, te verbeter. Ons ondersoek die in situ toepassing van elektriese velde en spannings om die dun film groei te verbeter. Verder oorweeg ons verskeie elektrode konfigurasies en ontwikkel 'n finale elektrode ontwerp wat stabiel is en herhaalbare resultate produseer. Die kwaliteit van die gedeponeerde dun films kan gemoduleer word deur die byvoeging van 'n geïsoleerde hoogspannings (HV) elektrode tydens deponering, afhangende van die polariteit van die aangelegde spanning. 'n Positiewe spanning verhoog die film kwaliteit, terwyl 'n negatiewe spanning die supergeleidende eienskappe van die films verlaag. 'n Eenvoudige HTS dubbele-modus mikrogolffilter is ontwerp, vervaardig en getoets, om as toepassings voorbeeld te dien. Slegs die filter wat geproduseer was met behulp van ons nuwe PLD tegniek, vertoon die beste filter oordrag by 77K. Dit word toegeskryf aan die beter supergeleidende eienskappe van die dun film, as gevolg van die toepassing van ons ontwikkelde tegniek.

abstract: Transparent conductive oxides (TCOs) are used as electrodes for a number of optoelectronic devices including solar cells. Because of its superior transparent and conductive properties, indium (In) tin (Sn) oxide (ITO) has long been at the forefront for TCO research activities and high-volume product applications. However, given the limited supply of In and potential toxicity of Sn-based compounds, attention has shifted to alternative TCOs like ZnO doped with group-III elements such as Ga and Al. Employing a variety of deposition techniques, many research groups are striving to achieve resistivities below 1E-4 ohm-cm with transmittance approaching the theoretical limit over a wide spectral range. In this work, Ga-doped ZnO is deposited using pulsed laser deposition (PLD). Material properties of the films are characterized using a number of techniques. For deposition in oxygen at pressures >1 mTorr, post-deposition annealing in forming gas (FG) is required to improve conductivity. At these higher oxygen pressures, thermodynamic analysis coupled with a study using the Hall effect measurements and photoluminescence spectroscopy suggest that conductivity is limited by oxygen-related acceptor-like defects in the grains that compensate donors, effectively reducing the net carrier concentration and creating scattering centers that reduce electron mobility. Oxygen is also responsible for further suppression of conductivity by forming insulative metal oxide regions at the grain edges and oxygen-related electron traps at the grain boundaries. The hydrogen component in the FG is thought to passivate the intra-grain acceptor-like defects and improve carrier transport across these grain boundaries. Given this deleterious effect of oxygen on conductivity, depositions are performed in pure argon (Ar), i.e., the only oxygen species in the growth ambient are those ejected directly from the PLD solid source target. Ga-doped ZnO deposited in Ar at 200 °C and 10 mTorr have resistivities of 1.8E-4 ohm-cm without the need for post deposition annealing. Average transmittance of the Ga-doped films is 93% over the visible and near infrared (IR) spectral regions, but free carrier absorption is a limiting factor further into the IR. After annealing in FG at 500 °C, a 300 nm Ar film has a Haacke figure of merit of 6.61E-2 sq. ohm. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2011

Abstract In this thesis work, crystal and phase structure, chemical composition and gas sensing properties of pulsed laser deposited vanadium oxide thin films were studied. Pulsed laser deposition was used to manufacture vanadium oxide thin films with various crystal structures, film morphologies and phase compositions. Both the well-known vanadium pentoxide V2O5, and a totally new stable phase in a solid-state thin-film form, V7O16, was produced. The existence of these phases was proven by several different characterization methods such as, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The resistive gas sensing measurements of the films with pure V2O5 composition, and mixed phase compositions of V2O5 and V7O16, showed that behaviour of the electrical response to different gases at various measurement temperatures was dependent on the phase composition of the thin films. It was proved that in certain conditions the mixed phase films show p-type semiconducting gas sensing behaviour, instead of the pure n-type behaviour of V2O5. Both types of film compositions were shown to be highly sensitive to ammonia gas, down to 40 ppb-level. The mixed phase composition showed a higher response to ammonia compared to the pure V2O5 phase; however the pure V2O5 showed better long-term stability. Both sensing layer types also showed high selectivity to ammonia in comparison to NO and CO gases. Nanostructured pure V2O5 layers were successfully deposited on commercial microheater platforms and then used as a gas sensor. The V2O5 nanostructures were proven to be very promising candidates as gas sensor material to control the Selective Catalytic Reduction process used in the reduction of NOx gas emissions. The surface valence states of the thin film structures with various phase compositions were studied spectroscopically, and a clear connection between the valence states of the film surfaces and gas sensing properties was found. It was concluded that the pure V2O5 films also had some V4+ ions in the surface, and in the mixed phase thin films, the amount V4+ ions was already quite high, indicating a higher amount of oxygen vacancies in the thin film surface – another proof of the existence of V7O16 phase in the film composition. It is also suggested that the particular quantity of oxygen vacancies is one of the reasons for the high gas-sensing response of the thin films. / Tiivistelmä Tässä työssä tutkittiin pulssilaserkasvatettujen vanadiinioksidiohutkalvojen kide- ja faasirakenteita sekä ominaisuuksia kaasuantureina. Vanadiinioksidiohutkalvoja, jotka omaavat erilaiset kide- ja faasirakenteet, sekä erilaiset morfologiat valmistettiin pulssilaserkasvatuksella. Tunnetun V2O5 -faasin lisäksi myös V7O16 -faasi onnistuttiin valmistamaan ensimmäistä kertaa kiinteän aineen epäorgaanisena faasina ohutkalvorakenteeseen. Näiden erilaisten faasirakenteiden olemassaolo todistettiin käyttämällä useita menetelmiä kuten röntgendiffraktiota, Raman spektroskopiaa ja röntgenfotoelektronispektroskopiaa. Sekä ainoastaan V2O5 -faasia sisältäviä ohutkalvoja, että V2O5 ja V7O16 sekafaasirakenteen omaavia ohutkalvoja tutkittiin kaasuanturina, ja mittaustulokset osoittivat erilaisten kalvojen sähköisten kaasuanturivasteiden ominaisuuksien voimakkaan riippuvuuden kalvojen faasirakenteesta. Havaittiin myös, että sekafaasirakenne omaa tietyissä olosuhteissa p-tyyppisen puolijohteen sähkönjohtavuusmekanismin, toisin kuin puhdas V2O5-rakenne, joka on täysin n-tyyppinen. Molemmat ohutkalvotyypit todennettiin olevan erityisen herkkiä ammoniakki (NH3) kaasulle, jopa 40 miljardisosatasolle. Kalvo, jossa oli sekafaasirakenne, omasi korkeamman sähköisen kaasuvasteen kuin puhtaasta V2O5 faasista koostuva ohutkalvo, joka taas toisaalta omasi paremman stabiiliuden pidemmällä aikavälillä. Molemmat kaasuanturimateriaalit havaittiin selektiiviseksi NH3 -kaasulle verrattuna NO- ja CO-kaasuihin. Puhdas V2O5 nanorakenne onnistuttiin myös kasvattamaan kaupalliselle anturialustalle, ja käyttämään menestyksekkäästi herkkänä NH3- kaasuanturina. Lisäksi puhtaan V2O5 nanorakenteen todennettiin olevan erittäin lupaava kaasuanturimateriaali hyödynnettäväksi NOx-kaasupäästöjen vähentämiseen käytettävän SCR-katalyysiprosessin (Selective Catalytic Reduction) ohjauksessa. Ohutkalvotyyppien pinnan sähköistä rakennetta tutkittiin röntgenspektroskopiamenetelmillä, ja selvä yhteys materiaalien pintojen valenssitilojen ja kaasuanturiominaisuuksien välillä havaittiin. Huomattiin, että myös puhdas V2O5 ohutkalvo omaa pinnallaan pienen määrän V4+ -ioneja, ja että ohutkalvossa, jossa on sekafaasirakenne, V4+ -ionien määrä on suuri, ollen yksi todiste lisää V7O16 faasin olemassaoloon kalvon rakenteessa. Tästä johtuva happivakanssien olemassaolo on yksi syy näiden ohutkalvojen korkeaan kaasuherkkyyteen.

With increasing focus on the ill health and environmental effects of lead there is a greater push to develop Pb-free devices and materials. To this extent, ecofriendly and earth abundant LiNbO3-type ZnSnO3, a derivative of the ABO3 perovskite structure, has a high theoretically predicted polarization making it an excellent choice as a suitable alternative to lead based material such as PZT. In this work we present a novel synthesis procedure for the growth of various ZnSnO3 nanostructures by combined physical/chemical processes. Various ZnSnO3 nanostructures of different dimensions were grown from a ZnO:Al template layer on a Si (100) substrate deposited by pulsed laser deposition followed by a strategic solvothermal process. The ferroelectric properties of each sample were explored and a remanent polarization as high as nearly 30 μC/cm2 was found in aligned nanowire arrayed films. An in-depth understanding of the structure-property relationship is key to the future development of this material and is the subject of future investigations.

Ce travail de thèse porte sur la croissance par dépôt laser pulsé (PLD) et l’étude des propriétés dedifférents systèmes d’oxydes pérovskites. Ainsi, les hétérostructures LaAlO3/SrTiO3, SrVO3/SrTiO3,LaAlO3/SrVO3 ont fait l’objet de travaux de recherche. Ces études ont été menées afin d’analyser lespropriétés des interfaces de ces différents systèmes composés, notamment, de titane et devanadium, deux métaux de transition et ainsi d’étudier et de comparer les effets de l’orbitale 3d enpassant d’une configuration 3d0, pour Ti, à 3d1, pour V.Dans une première partie, les travaux réalisés sur le système LaAlO3/SrTiO3 sont présentés. Lacroissance des échantillons, les caractérisations structurales, de transport et de magnétisme sontdétaillées. A partir cette étude, des résultats majeurs ont été obtenus, concernant l’effet desconditions de croissance par PLD sur la stoechiométrie des films minces et les conséquences sur lespropriétés électroniques de l’interface, avec la mise en évidence de différentes phases électroniques.Dans une seconde partie, la croissance de films minces et ultraminces de SrVO3 par PLD et la mise enévidence expérimentale de la Transition Métal-Isolant (TMI) sont développées. Les mesures despropriétés structurales et de transport ont permis de déterminer l’origine de cette TMI. Enfin, lesmécanismes physiques de conduction dans ce système sont révélés à partir de modélisations.Enfin, la dernière partie est consacrée aux travaux réalisés sur les hétérostructures LaAlO3/SrVO3réalisées sur substrats de SrTiO3 et de LaAlO3. Pour ces systèmes, les caractérisations de transportainsi que les analyses chimiques menées dans le but d’étudier les propriétés des interfaces de cessystèmes et de les comparer avec le système LaAlO3/SrTiO3. Différents mécanismes de conductionont ainsi été mis en évidence, corrélés par une analyse chimique, pour les échantillons réalisés surSrTiO3, démontrant l’effet de la couche de LaAlO3. / This thesis work has been led to study the growth by Pulsed Laser Deposition (PLD) and theproperties of different perovskite oxide systems including heterostructures of LaAlO3/SrTiO3,SrVO3/SrTiO3 and LaAlO3/SrVO3. This work is motivated by the need to measure and analyze theinterface properties in these systems which are composed with transition metal elements titaniumand vanadium but with different electronic configuration, 3d0 for Ti and 3d1 for V that can modify theproperties.In a first part, growth and characterizations – structural, transport and magnetism – is presented.Major results are obtained and demonstrate the effect of growth conditions – oxygen pressure andlaser fluence – on LaAlO3 thin films stoichiometry and interface electronic properties finally provingthe existence of an electronic phase transition.In the second part, growth of thin and ultrathin SrVO3 films is detailed and an experimentalobservation of the Metal-Insulator Transition (MIT) is brought out. The origin of this MIT isdemonstrated by structural and Transport properties investigation. Furthermore, physicalmechanisms of conduction in this system are revealed through modelisation work.Finally, the last part is devoted to the work done on LaAlO3/SrVO3 heterostructures grown on SrTiO3and LaAlO3 substrates. Transport characterizations and chemical analysis realized in order to studythe interface properties and to compare with LaAlO3/SrTiO3. Different conduction mechanisms havebeen brought out which are correlated by chemical analysis – for samples grown on SrTiO3 – anddemonstrate the effect of LaAlO3 thin films in this hétérostructure.