DC and RF magnetron co-sputtering techniques are one of the most suitable techniques in fabrication of thin films with different compositions. In this work, Al2O3 and Si/Al2O3 thin films were fabricated by using magnetron co-sputtering technique. For Al2O3 films, the stoichiometric, optical and crystallographic analyses were performed. For Si contained Al2O3 films, the formation conditions of Si nanocrystals were investigated. To do so, these thin films were sputtered on Si (100) substrates. Post annealing was done in order to clarify the evolution of Al2O3 matrix and Si nanocrystals at different temperatures. Crystallographic properties and size of the nanocrystals were investigated by X-ray diffraction (XRD) method. The variation of the atomic concentrations and bond formations were investigated with X-ray photoelectron spectroscopy (XPS). The luminescent behaviors of Si nanocrystals and Al2O3 matrix were investigated with photoluminescence (PL) spectroscopy. Finally, the characteristic emissions from the matrix and the nanocrystals were separately identified.

Trapping centres and their distributions in as-grown TlGaSeS layered single crystals were studied using thermally stimulated current (TSC) measurements. The investigations were performed in the temperature range of 10&ndash / 160 K with various heating rates between 0.6&ndash / 1.2 K/s. Experimental evidence has been found for the presence of three electrons trapping centres with activation energies 12, 20, and 49 meV and one hole trapping centre located at 12 meV. Their capture cross-sections and concentrations were also determined. It is concluded that in these centres retrapping is negligible as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. The optical properties of TlGaSeS layered single crystals have been investigated by measuring the transmission and the reflection in the wavelength region between 400 and 1100 nm. The optical indirect transitions with a band gap energy of 2.27 eV and direct transitions with a band gap energy of 2.58 eV were found by analyzing the absorption data at room temperature. The rate of change v of the indirect band gap with temperature was determined from the transmission measurements in the temperature range of 10&ndash / 300 K. The oscillator and the dispersion energies, the oscillator strength, and the zero-frequency refractive index were also reported. The parameters of monoclinic unit cell and the chemical composition of TlGaSes crystals were found by X-ray powder diffraction and energy dispersive spectroscopic analysis, respectively.

<p>This thesis is concerned with kinetic characterisation of theinsertion compound LiMn2O4, which is used as positive electrodematerial in rechargeable lithium batteries. Three different typesof electrode configurations have been investigated, namely singleparticles, thin films and composite electrodes. Differentelectrochemical techniques, i.e. linear sweep voltammetry (LSV),electrochemical impedance spectroscopy (EIS), potential step, andgalvanostatic experiments were applied under various experimentalconditions. The majority of the experimental data were analysedby relevant mathematical models used for describing the reactionsteps of insertion compounds.</p><p>It was concluded that a model based on interfacialcharge-transfer, solid-phase diffusion and an external iR-dropcould be fairly well fitted to LSV data measured on a singleelectrode system over a narrow range of sweep rates. However, itwas also found that the fitted parameter values vary greatly withthe characteristic length and the sweep rate. This indicates thatthe physical description used is too simple for explaining theelectrochemical responses measured over a large range of chargeand discharge rates.</p><p>EIS was found to be a well-suited technique for separatingtime constants for different physical processes in the insertionand extraction reaction. It was demonstrated that the impedanceresponse is strongly dependent on the current collector used.According to the literature, reasonable values of theexchange-current density and solid-phase diffusion coefficientwere determined for various states-of-discharge, temperatures andelectrolyte compositions. Experiments were carried out in bothliquid and gel electrolytes. A method which improves thedistinction between the time constants related to thematerial’s intrinsic properties and possible porous effectsis presented. The method was applied to composite electrodes.This method utilises, in addition to the impedance responsemeasured in front of the electrode, also the impedance measuredat the backside of the electrode.</p><p>Finally, the kinetics of a composite electrode was alsoinvestigated by in situ X-ray diffraction (in situ XRD) incombination with galvanostatic and potentiostatic experiments. Noevidence of lithium concentration gradients could be observedfrom XRD data, even at the highest rate applied (i.e. ~6C), thusexcluding solid-phase diffusion and also phase-boundary movement,as described by Fick’s law, as the ratelimiting step.</p><p><b>Key words:</b>linear sweep voltammetry, electrochemicalimpedance spectroscopy, potential step, in situ X-raydiffraction, microelectrodes, electrode kinetics, LiMn2O4cathode, rechargeable lithium batteries</p>

<p>It is generally believed that one of the key parameterscontrolling the normal state and superconducting properties ofhigh temperature superconductors is the charge carrierconcentration<i>p</i>in the CuO₂planes.By changing the non-isovalent dopingconcentration on the RE site as well as the oxygen content in(RE)Ba₂Cu₃O_7−δ, an excellent tool is obtained tovary the hole concentration over a wide range from theunderdoped up to the overdoped regime.In the present thesis thefocus is on the doping effects on the structural and normalstate electrical properties in Nd-123 doped with Ca, La, Pr,Ca-Pr, and Ca-Th.T he effects of doping have been investigatedby X-ray and neutron powder diffraction, and by measurements ofthe resistivity, thermoelectric power<i>S</i>, and Hall coefficient R_H.T he thermoelectric power is a powerful tool forstudies of high temperature superconductivity and is highlysensitive to details of the electronic band structure.<i>S</i>as a function of temperature has been analyzed in twodifferent two band models.The parameters of these models arerelated to charactristic features of the electron bands and asemiempirical physical description of the doping dependence of<i>S</i>is obtained.So me important results are following:</p><p>(i)<i>The valence of Pr in the RE-123 family.</i>Results from thestructural investigations, the critical temperature Tc, and thethermoelectric power indicated a valence +4 at low dopingconcentration, which is in agreement with results of chargeneutral doping in the RE-123 family.(ii)<i>Hole localization</i>. The results of bond valence sum (BVS)calculations from neutron diffraction data showed that holelocalization on the Pr⁺⁴site was the main reason for the decrease of thehole concentration p.Differ ent types of localization wereinferred by S measurements for Ca-Th and Ca-Pr dopings.(iii)<i>Competition between added charge and disorder</i>. Theresults of RH measurements indicated that Ca doping introduceddisorder in the CuO₂planes in addition to added charge.This could bethe main reason for the observed small decrease of thebandwidth of the density of states in the description of aphenomenological narrow band model.(iv) Empirical parabolic relation between γ and p.S data were analyzed and well described by a two-band modelwith an additional linear T term, γT.An empiricalparabolic relation for γ as a function of holeconcentration has been found.</p><p><b>Key words:</b>high temperature superconductors, criticaltemperature, resistivity, thermoelectric power, Hallcoefficient, X-ray diffraction, Neutron diffraction, NdBa₂Cu₃O_7−δ, hole concentration,substitution.</p>

Thin films of GeTe₂ were deposited on glass substrates using RF magnetron sputtering with various hydrogen flow rates in the growth chamber. Transmission data of deposited films were taken and used to determine optical constants: refractive index (n), extinction coefficient (κ), and absorption coefficient (α)) and the energies: E₀₄, E₀₃, Tauc band gap E[subscript]Tauc and Urbach energy E[subscript]U. An increase of these energies was observed with increasing hydrogen flow rate. This increase is interpreted on the basis of the density of state model proposed by Mott and Davis. An increase of network disorder due to the inclusion of hydrogen into the GeTe₂ thin films was determined from the B[superscript]1/2 parameter, Urbach energy and full width at half maximum of Raman vibrational modes. The crystallization process induced by thermal annealing on GeTe₂ was studied. X-ray diffraction measurements were performed and the results suggest that crystallization of GeTe₂ occurs via a phase separation into Te and GeTe crystalline phases. This observation is in agreement with a previous report. The crystallization temperature increases with the addition of hydrogen. This increase is explained in terms of dangling bonds. A large change (approximately 60 percent decrease) of the optical transmission occurs after the phase change from amorphous to crystalline. This decrease is interpreted as a result of the observed phase separation.

No description available.

Structure determination of powdered crystals is still not a trivial task. For gas hydrates, the difficulty lies in how to determine the rotational disorder and cage occupancies of the guest molecules without other supporting information or constraints because the complexity of the problem for the powder diffraction technique generally depends on the number of atoms to be located in the asymmetric unit. Here, the crystal structures of gas hydrates of CO2, C2H6, C3H8, and Methylcyclohexane/CH4, as determined by the direct-space and Rietveld techniques are reported. The resultant structures and cage occupancies were consistent with results found from conventional experimental methods using single crystal x-ray diffraction or solid-state 13C-NMR. It was shown that the procedures reported in this study make it possible to determine guest disorder and absolute cage occupancy of gas hydrates even from powder crystal.

With continued push toward 3D integrated packaging, Through-Silicon Vias (TSVs) play an increasingly important role in interconnecting stacked silicon dies. Although progress is being made in the fabrication of TSVs, experimental and theoretical assessment of their thermomechanical reliability is still in infancy. This work explores the thermomechanical reliability of TSVs through numerical models and innovative experimental characterization techniques. Starting with free-standing wafers, this work examines failure mechanisms such as Si and SiO₂ cohesive cracking as well as SiO₂/Cu interfacial cracking. Such cohesive crack propagation and interfacial crack propagation are studied using fracture mechanics finite-element modeling, and the energy available for crack propagation is determined through crack extension using the proposed centered finite-difference approach (CFDA). In parallel to the simulations, silicon wafers with TSVs are designed and fabricated and subjected to thermal shock test. Cross-sectional SEM failure analysis is carried out to study cohesive and interfacial crack initiation and propagation under thermal excursions. In addition, local micro-strain fields under thermal excursions are mapped through synchrotron X-ray diffraction. To understand the 3D to 2D strain measurement data projection process, a new data interpretation method based on beam intensity averaging is proposed and validated with measurements. Building upon the work on free-standing wafers, this research studies the package assembly issues and failure mechanisms in multi-die stacks. Comprehensive design-of-simulations study is carried out to assess the effect of various material and geometry parameters on the reliability of 3D microelectronic packages. Through experimentally-measured strain fields, thermal cycling tests, and simulations, design guidelines are developed to enhance the thermomechanical reliability of TSVs used in future 3D microelectronic packages.

The goal of the work described in this dissertation was to investigate the structure of metal phosphonate frameworks which were composed of conforma-tionally flexible ligands. This goal was achieved through investigating new syn-thetic techniques, systematically changing structural aspects (i.e. chain length), and conducting in situ X-ray diffraction experiments under non-ambient condi-tions. First, the use of ionic liquids in the synthesis of metal phosphonates was in-vestigated. Reaction systems which had previously been studied in purely aqueous synthetic media were reinvestigated with the addition of a hydrophobic ionic liq-uid to the reaction. Second, the structural diversity of zinc alkylbisphosphonates was investigated through systematically varying the chain length and reaction conditions. Last, the structural changes associated with externally applied stimuli (namely temperature and pressure) on conformationally flexible metal phospho-nates were investigated. Elevated temperature was used to investigate the structur-al changes of a 1-D cobalt chain compound through three stages of dehydration and also applied pressures of up to 10 GPa were used to probe the structural resili-ence of two zinc alkylbisphosphonate materials under. The iminobis(methylphosphonic acid) type ligands are a good example of a small, simple, conformationally flexible ligand. There are three distinct different structural types, utilizing this ligand with cobalt metal, described in the literature, all of which contain bound or solvated water molecules. The addition of a hydrophobic ionic liquid to an aqueous synthesis medium resulted in new anhydrous compounds with unique structural features. Systematic investigations of zinc alkylbisphosphonate materials, construct-ed with three to six carbon linker ligands, resulted in four new families of com-pounds. Each of these families has unique structural features which may prove in-teresting in future applications developments. Importantly, it is shown that wheth-er the chain length is odd or even plays a role in structural type although it is not necessarily a requirement for a given structural type; furthermore, chain length itself is not strictly determinative of structural type. Dehydration in a cobalt phosphonate was followed via in situ single crystal X-ray diffraction. The compound goes through a two-stage dehydration mecha-nism in which the compound changes from a 1-D chain to a 2-D sheet. This pro-cess is reversible and shows unique switchable magnetic properties. The high pressure studies of an alkyl chain built zinc metal phosphonate showed that the chains provide a spring-like cushion to stabilize the compression of the system allowing for large distortions in the metal coordination environment, without destruction of the material. This intriguing observation raises questions as to whether or not these types of materials may play a role as a new class of piezo-functional solid-state materials.

No description available.