Understanding lithium-ion insertion/extraction mechanisms in battery electrode materials is of crucial importance in developing new materials with better cycling performance. In this thesis, these mechanisms are probed for two different potential cathode materials by a combination of electrochemical and single-crystal X-ray diffraction studies. The materials investigated are V6O13 and cubic LiMn2O4 spinel. Single-crystal X-ray diffraction studies of lithiated phases in the LixV6O13 system (x=2/3 and 1) exhibit superlattice phenomena and an underlying Li+ ion insertion mechanism which involves the stepwise addition of Li+ ions into a two-dimensional array of chemically equivalent sites. Each successive stage in the insertion process is accompanied by a rearrangement of the Li+ ions together with an electron redistribution associated with the reduction of specific V-atoms in the structure. This results in the formation of electrochemically active sheets in the structure. A similar mechanism occurs in the LiMn2O4 delithiation process, whereby lithium is extracted in a layered arrangement, with the Mn atoms forming charge-ordered Mn3+/Mn4+ layers. Lithium-ion insertion/extraction processes in transition-metal oxides would thus seem to occur through an ordered two-dimensional arrangement of lithium ions extending throughout the structure. The lithium ions and the host structure rearrange cooperatively to form superlattices through lithium and transition-metal ion charge-ordering. A picture begins to emerge of a universal two-dimensional lithium-ion insertion/extraction mechanism analogous to the familiar staging sequence in graphite.

Detection of mid-wavelength infrared radiation is crucial for many industrial, military and biomedical applications. Photon detectors in the market can operate at only low temperature which increases weight, power consumption and total cost. Type-II InAs/GaSb superlattice infrared detectors are expected to have a major role in the infrared detector market with providing high quality detection characteristics at higher temperatures. Therefore, in the past decade, there has been an increasing interest in infrared detectors based on type-II InAs/GaSb superlattice technology due to their long range adjustable bandgap, low tunneling current and Auger recombination rates which bring potential of high temperature operation. Characterization of this photodiodes requires detailed investigations on different aspects. This study focuses on various optical and electrical characterization techniques for single pixel infrared detectors: responsivity characterization using FTIR and blackbody source, dark I-V and R-V characterizations, response time measurement. Characterizations of detector noise with respect to frequency and bias voltage are studied in detail. These characterization techniques are carried out in order to observe the effects of design with three different &ldquo / standard&rdquo / and a new &ldquo / N&rdquo / structure designs and also to understand the effects of surface passivation with atomic layer deposited Al2O3 layer and ordinary PECVD deposited Si3N4 and SiO2 layers. When standard photodiodes are compared, we observed that the one with the thickest active absorber region has the highest response and dark current density values. &ldquo / N&rdquo / structure design photodiode has very low dark current density while its optical performance is not as high as the standard designs. Si3N4 passivation degrades both optical and electrical performances. SiO2 and Al2O3 passivation layers improve optical and electrical characteristics of photodiodes. Theoretical and experimental dark current noise values of SiO2 passivated sample in agreement up to 0.18V reverse bias while those values of unpassivated and Si3N4 passivated samples agree only at zero bias. Temperature dependent R-V characteristics of photodiodes are analyzed and the surface limited activation energy is calculated in order to investigate the additional noise. At the end, surface recombination noise is proposed to cover the deficit on the noise calculation.

Energy harvesting is an interesting topic for today since we face running out of energy source, a serious problem in the world. Thermoelectric devices are a good candidate. They can convert heat (i.e. temperature gradient) to electricity. This result leads us to use them to harvest waste heat from engines or in power plants to generate electricity. Moreover, thermoelectric devices also perform cooling by applied voltage to device. This process is clean, which means that no greenhouse gases are emitted during the process. However, the converting efficiency of thermoelectrics are very low compare to a home refrigerator. The thermoelectric figure of merit (ZTm) is a number which defines the converting efficiency of thermoelectric materials and devices. ZTm is defined by Seebeck coefficient, electrical conductivity and thermal conductivity. To improve the converting efficiency, nanolaminated materials are good candidate.   This thesis studies TiN/ScN artificial nanolaminates, or superlattices were grown by reactive dc magnetron sputtering from Ti and Sc targets. For TiN/ScN superlattice, X-ray diffraction (XRD) and reciprocal space map (RSM) show that we can obtain single crystal TiN/ScN superlattice. X-ray reflectivity (XRR) shows the superlattice films have a rough surface, supported by transmission electron microscopy (TEM). Also, TiN/ScN superlattices grew by TiN as starting layer has better crystalline quality than ScN as starting layer. The electrical measurement shows that our superlattice films are conductive films.   Ca-Co-O system for inherently nanolaminated materials were grown by reactive rf magnetron sputtering from Ca/Co alloy target. The XRD shows we maybe get the [Ca2CoO3]xCoO2 phase, so far. The energy dispersive X-ray spectroscopy (EDX) reported that our films have Al conmination. We also discovered unexpected behavior when the film grown at high temperature showed larger thickness instead of thinner, which would have been expected due to possible Ca evaporation. The Ca-Co-O system requires further studies.

Understanding thermal transport in nanoscale is important for developing nanostructured thermolelectric materials and for heat management in nanoelectronic devices. This dissertation is devoted to understand thermal transport through SiGe based superlattices. First, we systematically studied the cross-plane thermal conductivity of SiGe superlattices by varying the thickness of Si(Ge) spacers thickness. The observed additive character of thermal resistance of the SiGe nanodot/planar layers allows us to engineer the thermal conductivity by varying the interface distance down to ~1.5 nm. Si-Ge intermixing driven by Ge surface segregation is crucial for achieving highly diffusive phonon scattering at the interfaces. By comparing the thermal conductivity of nanodot Ge/Si superlattices with variable nanodot density and superlattices with only wetting layers, we find that the effect of nanodots is comparable with that produced by planar wetting layers. This is attributed to the shallow morphology and further flattening of SiGe nanodots during overgrowth with Si. Finally, the experiments show that the interface effect on phonon transport can be weakened and even eliminated by reducing the interface distance or by enhancing Si-Ge intermixing around the interfaces by post-growth annealing. The results presented in this dissertation are expected to be relevant to applications requiring optimization of thermal transport for heat management and for the development of thermoelectric materials and devices based on superlattice structures. / Verständnis des thermischen Transport auf Nanoskala ist sowohl grundlegend für die Entwicklung nanostrukturierter Materialien, als auch für Temperaturkontrolle in nanoelektronischen Bauteilen. Diese Dissertation widmet sich der Erforschung des thermischen Transports durch SiGe basierenden Übergittern. Variationen, der Si(Ge) Schichtdicken, wurden zur systematischen Untersuchung der Normalkomponente zur Wachstumsrichtung der Wärmeleitfähigkeit, von SiGe Übergittern, genutzt. Die Beobachtung des additiven Charakters, des thermischen Widerstands, der SiGe Schichten, mit oder ohne Inselwachstum, ermöglicht die Erstellung von Strukturen mit bestimmter Wärmeleitfähigkeiten durch die Variation der Schichtdicken bis zu einer Minimaldistanz zweier Schichtübergänge von ~1.5nm. Die Ge Segregation führt zu einer Vermischung, von Si und Ge, welche eine essentielle Rolle zur diffusen Phononenstreuung spielt. Unsere Untersuchungen, von planaren Übergittern und Übergittern mit variabler Inseldichte, zeigen, dass Inseln und planare Schichten zu einer vergleichbaren Reduktion, der Wärmeleitfähigkeit, führen. Diese Beobachtung lässt sich, sowohl auf die flache Morphologie als auch die Abplattung der SiGe Inseln, aufgrund der Überwachsung mit Si, zurückführen. Die Experimente zeigen außerdem, dass sich der Barriereneffekt, der Schichtgrenzen, durch Reduktion der Schichtabstände und durch verstärkte Vermischung im Bereich der Schichtgrenzen, durch Erhitzung, eliminieren lässt. Die präsentierten Messungen sind sowohl, für die Entwicklung jener Bauteile, die eine Optimierung des thermischen Transports oder Temperaturmanagment erfordern, als auch von thermoelektrischen Matieralien und Bauteilen, basierend auf Übergittern, relevant.

Made available in DSpace on 2014-12-17T15:15:05Z (GMT). No. of bitstreams: 1 CarlosAAA.pdf: 386122 bytes, checksum: 5912e9682005147cb0db6bc16a139bab (MD5) Previous issue date: 2007-06-15 / In this work we present a theoretical study about the properties of magnetic polaritons in superlattices arranged in a periodic and quasiperiodic fash?ons. In the periodic superlattice, in order to describe the behavior of the bulk and surface modes an effective medium approach, was used that simplify enormously the algebra involved. The quasi-periodic superlattice was described by a suitable theoretical model based on a transfer-matrix treatment, to derive the polariton's dispersion relation, using Maxwell's equations (including effect of retardation). Here, we find a fractal spectra characterized by a power law for the distribution of the energy bandwidths. The localization and scaling behavior of the quasiperiodic structure were studied for a geometry where the wave vector and the external applied magnetic field are in the same plane (Voigt geometry). Numerical results are presented for the ferromagnet Fe and for the metamagnets FeBr2 and FeCl2 / Neste trabalho apresentamos um estudo te?rico sobre as propriedades dos polaritons magn?ticos em super-redes organizadas em padr?es peri?dico e quasiperi?dico. Na super-rede peri?dica, objetivando descrever o comportamento destes modos, tanto no volume quanto na superf?cie, foi utilizada a teoria do meio efetivo, que facilita enormemente a ?lgebra envolvida. Para a superrede quasi-peri?dica usamos um conveniente modelo te?rico baseado no trata mento da matriz-tranfer?ncia, para derivar a rela??o de dispers?o, utilizando as equa??es de Maxwell (incluindo efeitos de retardamento). Aqui, encontramos um espectro fractal caracterizado por uma lei de pot?ncia para a distribui??o de bandas de energia. A localiza??o e o comportamento de escala da estrutura quasi-peri?dica s?o estudadas numa geometria onde o vetor de onda e o campo aplicado est?o no mesmo plano (geometria de Voigt). Resultados num?ricos s?o apresentados para o ferromagneto Fe e para os metamagnetos FeBr2 e FeCl2

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / This is an account of the synthesis of several drastically different forms of silver nanoparticles: Bare metal nanoparticles, dry nanoparticulate powders, aqueous soluble particles, and organic ligand coated monodisperse silver nanoparticles were all produced. The synthetic method was adapted from previous studies on gold nanoparticles and investigated to understand the optimal conditions for silver nanoparticle synthesis. Also the procedure for refinement of the nanoparticles was studied and applied to the formation of alloy nanoparticles. This extraordinary procedure produces beautifully colored colloids of spherical metal nanoparticles of the highest quality which under suitable conditions self-assemble into extensive three dimensional superlattice structures. The silver nanoparticle products were later tested against several biological pathogens to find dramatic increases in antimicrobial potency in comparison to commercially available silver preparations.

Ce travail de thèse porte sur le développement et l'étude de diodes laser moyen infrarouge dont la zone active est constituée d'un super réseau (SR) à très courte période InAs/GaSb/InSb élaboré par épitaxie par jets moléculaires. La gamme de longueur d'onde d'émission visée est 3 - 3,5 µm qui est très intéressante pour des applications d'analyse de gaz par spectroscopie optique mais pour laquelle il n'y a encore aucun composant performant. Nous avons tout d'abord étudié les propriétés optoélectroniques du SR InAs/GaSb/InSb. La structure de bandes a été modélisée dans une approche k-p. L'interface sans atome commun InAs/GaSb est simulée arbitrairement par une monocouche de InAsxSb1-x dont la composition varie avec les conditions de croissance et donc avec l'interface réelle. Un bon accord est obtenu entre le gap effectif calculé et l'énergie des spectres de photoluminescence. Une attention particulière a été portée à l'impact de l'insertion contrôlée d'InSb dans le SR. Le raccordement de bandes du SR avec le guide d'onde, capital pour fabriquer un laser, a aussi été étudié. Un premier dessin de zone active a été proposé pour atteindre l'objectif. Par la suite, les performances intrinsèques des diodes lasers à SR ont été calculées par l'intermédiaire de la modélisation du gain du SR. L'effet laser avec une densité de courant de seuil proche de 0,5 kA/cm² est théoriquement possible. Les lasers à SR InAs/GaSb/InSb ont alors été étudiés expérimentalement. Nous avons fait varier de nombreux paramètres : composition et épaisseur du SR, du guide d'onde et des couches de confinement, procédé technologique? Les résultats expérimentaux ont montré des comportements proches des modélisations effectuées. L'effet laser à la température ambiante a été obtenu avec une densité de courant de seuil de l'effet laser de 2 kA/cm² à 3,2 µm et de 1,8 kA/cm² à 3,1 µm. Des perspectives d'optimisation des composants sont proposées en conclusion. / This work reports the development and study of infra-red laser diodes with InAs/GaSb/InSb short-period super lattice (SL) active region grown by molecular beam epitaxy. The target wavelength range of emission is 3 - 3.5 µm which is very interesting for gas application analysis by optical spectroscopy. There is no efficient component in this range. Firstly, we have studied the optoelectronic properties of the InAs/GaSb/InSb SL. The band structure was modelled with the k-p approach. The non-common atom InAs/GaSb interface is simulated by an arbitrary InAsxSb1-x monolayer whose composition depends with the growth conditions. A good agreement is obtained between the calculated effective gap and the energy of the photoluminescence spectra. A special attention was focus on the impact of InSb insertion in the SL. The SL band offset with the waveguide, capital to obtain high laser performance, was also studied. A first design of active zone was proposed to achieve the objective. Then, the intrinsic performances of SL lasers diode were calculated via modelling of the SL gain. Laser operation with a threshold current density close to 0.5kA/cm² is theorically possible. Lasers based on InAs/GaSb/InSb SL were then experimentally investigated. We studied several parameters: composition and thickness of SL, waveguide and cladding, technology process? The experimental results showed behaviours close to modelling. Laser operation was obtained at room temperature with a threshold current density of 2kA/cm² at 3.2µm and 1.8kA/cm² at 3.1µm. Prospects for device optimization are proposed in conclusion.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21598号 / 理博第4505号 / 新制||理||1647(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 小野 輝男, 教授 吉村 一良, 教授 島川 祐一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

[pt] Dispositivos opto-eletrônicos são elementos semicondutores que convertem radiações eletromagnéticas em corrente elétrica, e vice e versa. Os fotodetectores são dispositivos desse tipo, os quais possuem grande relevância na atualidade, devido a suas diversas aplicações. As pesquisas atuais se concentram no estudo de fotodetectores à base de poços quânticos para operar no infravermelho médio (2-20 m), mais especificamente em super-redes. No presente trabalho foi desenvolvido um fotodetector de duas cores baseado em super-redes assimétricas. O fotodetector construído possui uma rede com duas sessões. A primeira sessão tem cinco poços quânticos e cinco barreiras com 2 nm e 3.5 nm de espessura, respectivamente. A segunda sessão possui cinco poços quânticos e cinco barreiras de 2 nm e 7 nm de espessura, respectivamente. Entre as seções existe um poço quântico de 2.5 nm. O material que forma os poços quânticos é de InGaAs e o material das barreiras é de AlInAs. Esse dispositivo foi capaz de operar como um fotodetector de duas cores operando no modo fotovoltaico detectando radiações de 309 meV e 415 meV. O dispositivo foi capaz de operar em altas temperaturas. A temperatura máxima de operação foi de 245 K. Além disso, ao se aplicar tensões no dispositivo, é possível selecionar a radiação a ser detectada pelo fotodetector. Sendo elas 309 meV ou 415 meV. / [en] Opto-electronic devices are semiconductor elements that convert electromagnetic radiation in electric current. Photodetectors are devices of this type, which are the main relevant ones today due to their diverse applications. Current research focuses on the study of photodetectors based on quantum wells for operation in the medium infrared (2-20 m), more specifically with superlattices. In the present work a photodetector of two cores based on asymmetric superlattice was developed. The built-in photodetector had a superlattice with two sessions The first session had five quantum wells and five barriers with 2 nm and 3.5 nm of thickness, respectively. The second session had five quantum wells and five barriers of 2 nm and 7 nm thick, respectively. Between the sessions there is a 2.5 nm quantum well. The material that formed the quantum wells was InGaAs and the material of the barriers was AlInAs. This device was able to operate as a dual color photodetector operating in the photovoltaic mode detecting radiation of 309 meV and 415 meV. The device was able to operate at high temperatures. The maximum operating temperature was 245 K. In addition, when applying voltages to the device, it is possible to select the detection energy of the photodetector :309 meV or 415 meV.

In this study the effect of hydrogenation on the optical properties in the wavelength range 400-1023 nm of an ultrathin iron-vanadium superlattice is investigated. Specifically, mea- surements of transmission are performed under different states of hydrogenation, along with measurements of absolute hydrogen concentration and hydrogen site occupancy. The trans- mission measurements are used to construct pressure-concentration isotherms. Isotherms and transmission data are in turn correlated to concentration and hydrogen occupancy.  The results show a wavelength dependent decrease in transmission with hydrogenation. The decrease is greatest around 550 nm, and the wavelength of maximum decrease shifts to higher wavelengths with increasing hydrogen pressure. The non-uniform decrease will make the use of transmission as a measurement of hydrogen concentration dependent on the wavelength of the probing light.  15N resonant NRA is used to perform direct, real-space measurement of absolute hydro- gen concentration. The achieved concentrations are 0.092, 0.38 0.40 H/V. Comparing the concentrations and corresponding transmissions to the location of the plateau region in the transmission based isotherms, it appears that the system is in a single phase at 0.38 and 0.40 H/V, and in a mixed phase at 0.092 H/V. Using a combination of resonant NRA and RBS, while exploiting crystal lattice ion channeling, indirect measurements of hydrogen site occupancy are performed. At all investigated concentrations the system does not display tetrahedral site occupancy, but it remains uncertain whether the occupancy is octahedral or some dislocated octahedral-tetrahedral intermediate.  The relation of hydrogen concentration and optical transmission is investigated via a linear regression analysis. The data points generally deviate by more than one standard deviation from the fitted lines, and lie outside of the error estimation. These deviations might indicate that a linear model is inappropriate, where one possible explanation could be that the mapping from transmission to concentration is dependent on the phase of the system. / Den här studien undersöker upptag av väte i en supertunn kristallstruktur bestående av omväxlande lager av vanadin och järn, samt vätets inverkan på de optiska egenskaperna i våglängdsområdet 400-1023 nm. Specifikt genomförs mätningar av genomsläpp av ljus, under olika nivåer av väteupptag. I samband med dessa mätningar genomförs också mätningar av absolut vätekoncentration och av väteatomernas position i kristallstrukturen. Mätningarna av ljusgenomsläpp används för att skapa isotermkuror över tryck och koncentration. Isotermkurvorna och genomsläppligheten av ljus korreleras till vätekoncentration och väteatomernas position i kristallstrukturen.  Resultaten visar en våglängdsberoende minskning av ljusgenomsläppligheten med en ökande mängd väte i kristallstrukturen. Minskningen är som störst omkring 550 nm, samtidigt som våglängden för störst minskning flyttas mot högre våglängder med högre koncentration av väte. Att minskningen i genomsläpplighet är beroende av våglängd innebär att ljusgenomsläpp som metod för att mäta vätekoncentration är beroende av den ljusvåglängd som används. Metoden 15N resonant NRA används för att genomföra direkta mätningar av absolut vätekoncentration. De uppmätta koncentrationerna är 0.092, 0.38 och 0.40 H/V. När dessa koncentrationsmätningar jämförs med genomsläpplighet och tillhörande isotermkurvor, så verkar det som att systemet befinner sig i en enskild fas vid koncentrationerna 0.38 och 0.40 H/V, och i en blandad fas vid koncentrationen 0.092 H/V. Indirekta mätningar av vätets position i kristallstrukturen genomförs baserat på en kombination av resonant 15N NRA och RBS, där det utnyttjas att projektiljonerna under vissa förutsättningar kan komma att styras in i kristallstrukturen (på engelska crystal lattice ion channeling). Vid de tre uppmätta koncentrationerna så visar systemet inga tecken på att väteatomerna finns på tetrahedrala positioner. Det är inte helt uppenbart om väteatomerna istället finns på oktahedrala positioner, eller om det handlar om förskjutna positioner som är mellanliggande till oktahedrala och tetrahedrala. Relationen mellan vätekoncentration och optisk genomsläpplighet analyseras med linjär regression. Datapunkterna avviker generellt med mer än en standardavvikelse från de anpassade linjerna, och ligger utanför feluppskattningen. De här avvikelserna kan indikera att en linjär modell inte är lämplig, och en möjlig förklaring kan vara att ljusgenomsläppligheten beror av den fas i vilken systemet befinner sig.