The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using X-ray Photoelectron Spectroscopy and X-ray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and Fowler-Nordheim I-V plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated. Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous research. The analytic chamber used in the field emission analysis demonstrated the ability to independently determine the value and changes in work function and emitter geometry by simultaneous measurement of the Field Emission Energy Distribution and Fowler-Nordheim I-V plots from single emitters. Iridium oxide coating was found to enhance the stability of molybdenum emission tips with a relatively low work function of 4.2 eV and inhibited the formation of high work function molybdenum oxides. However, the method of deposition of iridium and annealing in oxygen to form iridium oxide on molybdenum emitters left rather severe cracking in the protective oxide coating exposing the molybdenum substrate.

Iron Silicide (FeSi) films deposited on silicon substrates with the native SiO2 layer have shown a Metal-to-Insulator Transition (MIT) of more than four order of magnitude change in resistance. Modification of the SiO2/Si interface due to Fe diffusion has been attributed to the formation of this effect. In this research a systematic experimental investigation has been carried out to study the effect of the growth parameters and substrate doping type in the transition. In addition, transport properties of continuous and discontinuous films have been investigated to understand the mechanism of this metal-to-insulator transition.Four probe measurements of films deposited in p- and n-type doped Si substrates with resistivity in the range of 1-10 Omega cm showed similar temperature dependent resistance behavior with transition onsets at 250 K and 300 K respectively. These results indicate that the current transport takes place via tunneling through the SiO2 layer into the Si substrate up to the transition temperature. Current appears to switch to the film after the transition point due to the development of high interface resistance. Discontinuous FeSi films on silicon substrates showed similar resistance behavior ruling out possibility of current transport through inversion layer at the SiO2/Si interface. To investigate the role of the magnetic ion Fe, transport measurements of FeSi films were compared with those of non-magnetic metals such as Platinum (Pt) and Aluminum (Al). Absence of Metal-to-insulator transition on Pt and Al films show that the presence of magnetic moment is required for this transition.Temperature dependent Hall voltage measurements were carried out to identify the carrier type through the substrate for FeSi films deposited on p- and n-type Si substrates. Results of Hall voltage measurements proved that the type of conductivity flips from majority carriers to minority after the transition.Metal-to-insulating transition behavior of FeSi films depending on different laser fluences has been also investigated. Our results revealed as laser fluence is increased observed transition of the FeSi films reduces rapidly showing a highest magnitude of transition of about 1 M Omega for the films deposited with lowest laser fluence (0.64 J/cm2) and a lowest of about 10 Omega for the films deposited with highest laser fluence (3.83 J/cm2). Ion probe measurements indicated that the average kinetic energy of the ablated ion in the plume is considerably increased with the increase of the laser fluence. Consequently, magnitude drop in the transition can be considered due to the deeper penetration on Fe ion through the SiO2 layer. Thickness dependence study carried out for FeSi films deposited with high and low laser fluencies indicated transition slightly drops as thickness is increased, concluding the current transportation through the film becomes dominant after the transition temperature.

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)

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.

This work presents a study on stoichiometry and structure in perovskite-type oxide thin films and investigates the role of growth–induced defects on the properties of materials. It also explores the possibility to grow thin films with properties close or similar to the ideal bulk parent compound. A novel approach to the growth of thin films, atomic layer-by-layer (ALL) laser molecular beam epitaxy (MBE) using separate oxide targets is introduced to better control the assembly of each atomic layer and to improve interface perfection and stoichiometry. It also is a way to layer materials to achieve a new structure that does not exist in nature. This thesis is divided into three sections. In the first part, we use pulsed laser deposition (PLD) to grow LaAlO3 (LAO) thin films on SrTiO3 (STO) and LAO substrates in a broad range of laser energy density and oxygen pressure. Using x-ray diffraction (θ-2θ scan and reciprocal space mapping), transmission electron microscopy (TEM) and x-ray fluorescence (XRF) we studied stoichiometry and structure of LAO films as a function of growth parameters. We show deviation from bulk–like structure and composition when films are grown at oxygen pressures lower than 10-2 Torr. We conclude that the discussion of LAO/STO interfacial properties should include the effects of growth–induced defects in the LAO films when the deposition is conducted at low oxygen pressures, as is typically reported in the literature. In the second part, we describe a new approach to atomically layer the growth of perovskite oxides: (ALL) laser MBE, using separate oxide targets to grow materials as perfectly as possible starting from the first atomic layer. We use All laser MBE to grow Ruddlesden–Popper (RP) phase Lan+1NinO3n+1 with n = 1, 2, 3 and 4 and we show that this technique enables us to construct new layered materials (n=4). In the last and main section of this thesis, we use All laser MBE from separate oxide targets to build the LaNiO3 (LNO) films as near perfectly as possible by depositing one atomic layer at a time. We study the thickness dependent metal-insulator transition (MIT) in ultrathin LNO films on an LAO substrate. In LNO, the MIT occurs in thin films and superlattices that are only a few unit cells in thickness, the understanding of which remains elusive despite tremendous effort devoted to the subject. Quantum confinement and structure distortion have been evoked as the mechanism of the MIT; however, first-principle calculations show that LaNiO3 remains metallic even at one unit cell thickness. Here, we show that thicknesses of a few unit cells, growth–induced disorders such as cation stoichiometry, oxygen vacancies, and substrate-film interface quality will impact the film properties significantly. We find that a film as thin as 2 unit cells, with LaO termination, is metallic above 150 K. An oxygen K-edge feature in the x-ray absorption spectra is clearly inked to the transition to the insulating phase as well as oxygen vacancies. We conclude that dimensionality and strain are not sufficient to induce the MIT without the contribution of oxygen vacancies in LNO ultrathin films. Dimensionality, strain, crystallinity, cation stoichiometry, and oxygen vacancies are all indispensable ingredients in a true control of the electronic properties of nanoscale strongly–correlated materials. / Physics