In this study, epitaxial ZnO films were grown by chemical vapor deposition (CVD) on LSAT(100) substrate. A high-quality [100] (La0.3,Sr0.7)(Al0.65,Ta0.35)O3 (LSAT) single crystal with the diameter of 60mm was grown by Czochralski pulling technique in our lab. Epi-ready LSAT substrates with rms roughness of 0.30nm ~ 0.35nm were used for all of the experiments. Nonpolar ZnO with [11-20] orientation (a-plane) was directly grown on a (100) LSAT substrate without any buffer layer by chemical vapor deposition (CVD) method. (100) LSAT single crystal substrate is loaded in a 2¡¨ quartz tube inserted to a two-temperature zone furnace. Zinc acetylacetonate hydrate (Zn(C5H7O2)2¡DxH2O, Lancaster) source was vaporized at the lower temperature of 130~140oC. The vapor was carried by a mixture of N2/O2 gas flow into the high temperature zone where the (100) LSAT substrate was located. At first, the pressure of the quartz chamber was pumped to 8¡Ñ10-3 Torr, and then kept at 150 ~ 250 Torr. The flows rates of both O2 and N2 are 500sccm. During the growth, the temperature was varied from 700 to 780oC. The growth conditions were controlled by adjusting the growth temperatures and chamber¡¦s pressures. The overall reaction was: Zn(C5H7O2)2 +12O2¡÷ZnO+ 10CO2 +7H2O Scanning electron microscope [(SEM), JEOL JSM-6330TF)] is used to examine the different surface morphologies of ZnO epitaxial film. The orientation and structure were investigated by X-ray diffraction pattern (XRD) using a Siemens D5000 X-ray diffractometer with a Cu anode at 40 kV and 30 mA. The wavelength of X-ray radiated from the Cu K£\1 is 0.1540 nm. The X-ray scan step is 0.01¢X. A JEOL 3010 scanning transmission electron microscope (STEM) operated at 200kV was employed to characterize the microstructures and orientation of the nonpolar ZnO film. Cross-sectioned TEM samples were prepared using the focus ion beam lift-out method. A Pt layer of about 8nm in thickness was pre-deposited on the sample to prevent charging. Room temperature photoluminescence (RT-PL) measurements were performed using a 325nm He-Cd laser. The emitted light was detected by a Jobin-Yvon TRIAX 550 monochromator with 0.025nm resolution.

Couches minces multiferroiques d’YMnO3 (YMO) films ont été synthétisée par MOCVD sur desubstrats de Si, STO, LAO et LSAT orientées (100). L'effet de l'épaisseur des couches et de lacomposition chimique sur les propriétés structurales et magnétiques a été étudié. YMO peutcristalliser dans deux structure : hexagonale (h-YMO) et orthorhombique (o-YMO), généralementconsidérée comme les phases stables et métastables, respectivement. Les deux phases, ainsi queleur phase précurseur amorphe sont étudiées dans cette thèse. D'un côté, une croissance sélectivede la phase amorphe, h-YMO ou o-YMO est réalisé sur des substrats de Si en ajustant lesconditions de dépôt. Une étude approfondie des conditions optimales a été réalisée. Unetransformation de phase irréversible de l'état amorphe à la phase cristalline o-YMO a lieu à unetempérature à peu près constante (~ 700 ° C) et dans un court période de temps (min ~). La phaseo-YMO ainsi obtenue est stable au moins jusqu'à 900 ° C.De l'autre côté, la phase o-YMO est stabilisé par épitaxie sur des substrats de type perovskite (STO,LAO, LSAT). Les films sur STO et LSAT présentent principalement l’orientation (010) tandis queceux sur les substrats de LAO sont orientées (101). Une orientation secondaire de domaines estobservée en particulier sur des substrats de STO: rotation de 90 ° dans le plan du domaine (010).A des faibles épaisseurs les couches sont contraintes. Les mesures magnétiques montrent uncomportement de verre de spin pour chacune de phase o- ou h-YMO, indépendamment du substrat. / Multiferroic YMnO3 (YMO) films have been grown by MOCVD on (100)-oriented Si, STO, LAOand LSAT substrates. The effect of the film thickness and the chemical composition on structuraland magnetic properties has been investigated. YMO can crystallize in two structure: hexagonal(h-YMO) and orthorhombic (o-YMO), generally considered as stable and metastable phases,respectively. Both phases, together with their amorphous precursor phase, are studied in this thesis.On one side, a selective growth of the amorphous, o-YMO or h-YMO phase is achieved on Sisubstrates through the deposition conditions. An extensive study of the optimal conditions hasbeen carried out. An irreversible phase transformation from amorphous to crystalline o-YMOphase takes place at an almost constant temperature (~ 700 °C) and in a short period of time (~min). The o-YMO phase thus obtained is stable at least up to 900 °C.On the other side, the o-YMO phase is epitaxially stabilized on perovskite type substrates (STO,LAO, LSAT). The films on STO and LSAT substrates present mainly the (010) orientation whilethose on LAO substrate are (101)-oriented. Secondary domain orientation are observe in particularon STO substrates: (010) in plane with 90° rotation. Strained films are observed for smallthicknesses. The magnetic measurements show a spin glass behavior for either o- or h-YMO phase,independently of the substrate.

This study aims to investigate different orbit determination algorithms for the first Turkish remote sensing satellite, BiLSAT-1. The micro-satellite carries an onboard GPS receiver. Pseudorange measurements simulated from the position and velocity data supplied by T&Uuml / BiTAK-BiLTEN are used for the implementation of different orbit determination algorithms concluding to an estimate of the satellite&rsquo / s state. Satellite&rsquo / s position, velocity components and the GPS receiver&rsquo / s clock bias are selected as the state parameters to be estimated. Kalman filter algorithms are used for the estimation of these state parameters. The modeled affecting force components include / geopotential and atmospheric drag. The global gravity models EGM96 and EIGEN-CG03C have been utilized together with Harris Priester atmospheric density model for the force modeling. The effect of the changes during the implementation of the force models, numerical integration, and estimation algorithms are investigated. Software has been developed using MATLAB programming language for the implementation of all algorithms performed in this study for orbit determination.