Optical properties of nanoscopic materials have been intensively pursued over last couple of decades due to their tunable optical properties. Recent interests in this field have been mainly focused on the preparation of ordered arrays of nano materials and study of their optical properties. These interests have been motivated by the applications of such systems for nano photonic devices. Theoretical predictions from such systems reveal complex absorption and emission properties, different from individual ones mainly because of energy transfer between them. These properties can be controlled further by preparing hybrid arrays of nanostructures, including nano crystals of different types. Hybrid arrays with semiconductor quantum dots and metallic nanoparticles are an example of such system. Optical properties of such a system can be tuned by controlling the interaction between excitons and plasmons. This thesis presents the experimental studies on optical properties of polymer capped nanoparticles, quantum dot arrays and hybrid arrays with semi conducting quantum dot and metal nanoparticles. A brief summary of the experimental methods and results have been highlighted below. In this thesis, we study the controlling decay dynamics of CdSe quantum dots by 2D photonic-plasmonic and metamaterial templates. In Chapter 1 we provide a detailed background on the theoretical methods of Light-Matter interaction at nano scale. We also have given the detailed information on both weak and strong coupling region in the light-matter interaction. This chapter includes the discussion controlling light-matter interaction with both photonic crystals and plasmonic materials with some appropriate examples from the literature. In this chapter we have also explained the relevance of our work in this area and organization of the chapters and there importance has given. In chapter 2 we provide details about various experimental methods used in this thesis. A brief introduction is given on the materials used, their synthesis and the preparation of different type of self assembled plasmonic-photonic templates. This chapter starts with an explanation of the materials used along with the justification; moves on to the preparation of different 2D wire metamaterial. The characterization techniques for these different types of templates like spectroscopic ellipsometer, atomic force spectroscopy, scanning electron microscopy and transmission electron microscopy are discussed. We also discussed optical spectroscopic techniques like confocal optical microscopy and near field optical microscopy techniques. The first two chapters form the basis of all the experiments discussed in the forth coming chapters. In chapter 3 Finite difference time domain (FDTD) simulations were performed on two different plasmonic sub wavelength photonic templates embedded with CdSe quantum dots. Tunable loading of these templates with plasmonic nano antenna allowed control of the emission from the embedded quantum dots. We discuss how large loading of nano antenna can effectively control the optical density of states for the quantum dots leading to enhancement of their radiative decay rates as observed in experiments. On the other hand, at low level of loading, while FDTD fails to capture the observed enhancement of decay rates in experiment, an alternative mechanism is suggested to exist in such cases. Thus, subtle interplay of multiple mechanisms engineered by appropriate placement and loading of plasmonic nano antenna in such templates is demonstrated as an effective method to control optical density of states and hence spontaneous emission of embedded quantum dots. In Chapter 4 we report results of controlled tuning of the local density of states (LDOS) in versatile, flexible and hierarchical self assembled plasmonic templates. Using 5 nm diameter gold (Au) spherical nano antenna within a polymer template randomly dispersed with quantum dots, we show how the photo-luminescence intensity and lifetime anisotropy of these dots can be significantly enhanced through LDOS tuning. Finite difference time domain simulations corroborate the experimental observations and extend the regime of enhancement to a wider range of geometric and spectral parameters bringing out the versatility of these functional plasmonic templates. It is also demonstrated how the templates act as plasmonic resonators for effectively engineer giant enhancement of the scattering efficiency of these nano antenna embedded in the templates. Our work provides an alternative method to achieve spontaneous emission intensity and anisotropy enhancement with true nanoscale plasmon resonators. In chapter 5 we reported enhancement optical properties of quantum dot monolayers on top of the functional, flexible and hierarchical self-assembled plasmonic template using extremely small gold (Au) nanoparticles of diameter 5 nm. We reported how the LODS changes with different polarizations for CdSe quantum dot present on top of the template. We observed the enhanced radiative LDOS from the nano antenna filled pores indicating plasmonic enhanced emission from these templates. The difference in spectral and spatial profile of LDOS and Pur-cells with polarization of quantum dot emission results in the anisotropic emission in these templates. In chapter 6 we reported the emergence of strong coupling between quantum emitters and 2D hyperbolic metamaterials (HMM). We studied both spectral dependence and effect of filling fraction of the HMM on strong interaction. We also show the controlling of the transition from weak coupling region to strong coupling region by changing the distance between QD monolayer and HMM. By using FDTD simulation we are able to calculate both spectral function S(!) and coupling efficiency. In chapter 7 as a conclusion we concluded the work done in this thesis. We also indicated the future directions in this field and possible application.

[pt] Recentemente, os nanocristais semicondutores, também conhecidos como pontos quânticos, tornaram-se muito atrativos em abordagens de detecção por fotoluminescência devido as suas propriedades ópticas peculiares, tais como fluorescência intensa e com perfil estreito, comprimento de onda máximo ajustável através do controle do tamanho das partículas e maior fotoestabilidade em comparação com os corantes orgânicos convencionais. As nanopartículas sintetizadas foram avaliadas como sondas fotoluminescentes (na forma de dispersão aquosa) para a determinação de captopril, histamina, canamicina e tiroxina (analitos não fotoluminescentes na temperatura ambiente) evitando o uso de procedimentos complexos de derivatização química e permitindo quantificações de forma simples e com sensibilidade. Nanopartículas de CdTe modificadas com o ácido tioglicólico (TGA) e com o ácido 2-mercaptopropiônico (2MPA) e também nanopartículas de ZnS modificadas com L-cisteína foram sintetizadas pela abordagem em fase aquosa coloidal. Estas foram caracterizadas usando métodos microscópicos e espectroscópicos adequados. A fotoluminescência da nanopartícula 2MPA-CdTe foi consideravelmente mais intensa quando na presença de captropil. Sob condições ótimas, o modelo de calibração (isoterma de ligação de Langmuir) foi linear até 4,8 x 10-4 mol L-1 com constante de equilíbrio de ligação de 3,2 x 104 L mol-1 e limite de detecção (LOD) de 6,2 x 10-6 mol L-1 (1,3 (micro)g mL-1). Aplicações em soro sanguíneo humano fortificado com captropil e em formulações farmacêuticas foram demonstradas. A fotoluminescência das nanopartículas de TGA-CdTe foi reduzida (supressão) após adição de diferentes concentrações de histamina seguindo o modelo de Stern- Volmer. A resposta linear cobriu uma faixa de concentração até 5,7 x 10-4 mol L-1, com LOD de 9,6 x 10-6 mol L-1 (1,1 (micro)g mL-1). A abordagem proposta foi utilizada para determinação de histamina em carne de atum. Já a presença de aminoglicosídeos aumentou a fluorescência das nanopartículas de TGA-CdTe (seguindo o modelo da isoterma da adsorção de Langmuir). A kanamicina foi o aminoglicosídeo escolhido para estudar o efeito do aumento da intensidade da fotoluminescência das nanopartículas de TGA-CdTe disperso em solução aquosa. A faixa linear estendeu-se até 8,2 x 10-7 mol L-1 com LOD de 2,5 x 10-8 mol L-1 (14,2 ng mL-1). As constantes de ligação entre diversos aminoglicosídeos e TGACdTe foram calculadas e indicou que existe uma relação entre o número de grupos amino primários disponíveis e o aumento da luminescência. Essa abordagem foi aplicada com sucesso para a análise de amostras de leite e água de riacho, ambos fortificados com kanamicina, usando procedimento de extração em fase sólida com um polímero impresso molecularmente (MIP). A intensidade da fotoluminescência da nanopartícula cisteína-ZnS em solução contendo brometo de cetiltrimetilamônio (CTAB) foi reduzida (quenched) após adição de tiroxina. A redução total do sinal (quenching) seguiu o modelo de Stern-Volmer com resposta linear até 4,0 x 10-6 mol L-1 de concentração do analito, o LOD foi 6,2 x 10-8 mol L-1 (48,3 ng mL-1). A dispersão aquosa da cisteína-ZnS foi usada como sonda óptica para a determinação de tiroxina em formulações farmacêuticas e em saliva humana fortificada com analito. / [en] Recently, semiconductor nanocrystals, also known as quantum dots, have become very attractive for photoluminescence based sensing approaches due to their unique optical properties like intense photoluminescence with narrow profile, maximum wavelength adjustable by the control of particle size and higher photostability in comparison of conventional organic dyes. Different synthesized nanoparticles were evaluated as photoluminescent probes (as aqueous dispersions) for the determination of captopril, histamine, kanamycin and thyroxine (nonphotoluminescent analytes at room-temperature) avoiding the use of complex chemical derivatization procedures and enabling simple and sensitive quantifications. Thioglycolic acid (TGA) and 2-mercapoprionic acid (2MPA) modified CdTe nanoparticles and L-cysteine modified ZnS nanoparticles were synthesized via the colloid aqueous phase route. Their characterization was made using proper microscopic and spectroscopic methods. The emission intensity of 2MPA-Cdte is greatly enhanced in the presence of captopril. Under optimum conditions, the calibration model (Langmuir binding isotherm) was linear up to 4.8 x 10-4 mol L-1 with equilibrium binding constant of 3.2 x 104 L mol-1 and limit of detection (LOD) of 6.2 x 10-6 mol L-1 (1.3 (micro)g mL-1). Applications in captopril fortified human serum and in pharmaceutical formulations were demonstrated. The photoluminescence of TGA-CdTe nanoparticles was quenched by histamine in a concentration dependent manner (Stern-Volmer model). The linear response covered the concentration range up to 5.7 x 10-4 mol L-1 with LOD of 9.6 x 10-6 mol L-1 (1.1 (micro)g mL-1). The proposed method was used for the analysis of tuna fish. The presence of aminoglycosides enhanced the photoluminescence of the TGA-CdTe nanoparticles (following a Langmuir binding isotherm model). Kanamycin was used as a model aminoglycoside in order to study its effect on the photoluminescence enhancement of TGA-CdTe quantum dots dispersed in aqueous solution. The linear range extended up to 8.2 x 10-7 mol L-1 with LOD of 2.5 x 10-8 mol L-1 (14.2 ng mL-1). Binding constants were calculated for several aminoglycosides indicating that there is a relationship between the number of available primary amino groups and the increasing in photoluminescence. This approach was successfully applied for determination of kanamycin fortified milk and in stream water samples after solid phase extraction using a molecular imprinted polymer produced using a kanamycin template. The photoluminescence intensity of cysteine-ZnS in solution containing cetyltrimethyl ammonium bromide (CTAB) was quenched by thyroxine. The overall quenching followed a Stern-Volmer model with linear response coveing an analyte concentration range up to 4.0 x 10-6 mol L-1. LOD was 6.2 x 10-8 mol L-1 (48.3 ng mL-1). The aqueous dispersion of cysteine-ZnS was used as optical probe for the determination of thyroxine in pharmaceutical formulations and in analyte fortified human saliva.

A size-selected series of water-soluble luminescent Ag–In–S (AIS) and core/shell AIS/ZnS QDs were produced by a precipitation technique. Up to 10–11 fractions of size-selected AIS (AIS/ZnS) QDs emitting in a broad color range from deep-red to bluish-green were isolated with the photoluminescence (PL) quantum yield reaching 47% for intermediate fractions. The size of the isolated AIS (AIS/ZnS) QDs varied from ~2 nm to ~3.5 nm at a roughly constant chemical compo- sition of the particles throughout the fractions as shown by the X-ray photoelectron spectroscopy. The decrease of the mean AIS QD size in consecutive fractions was accompanied by an increase of the structural QD imperfection/disorder as deduced from a notable Urbach absorption “tail” below the fundamental absorption edge. The Urbach increased from 90–100 meV for the largest QDs up to 350 meV for the smallest QDs, indicating a broadening of the distribution of sub-bandgap states. Both the Urbach energy and the PL bandwidth of the size-selected AIS QDs increased with QD size reduction from 3–4 nm to ~2 nm and a distinct correlation was observed between these parameters. A study of size-selected AIS and AIS/ZnS QDs by UV photoelectron spectroscopy on Au and FTO substrates revealed their valence band level EVB at ~6.6 eV (on Au) and ~7 eV (on FTO) and pinned to the Fermi level of conductive substrates resulting in a masking of any possible size- dependence of the valence band edge position.

[pt] Como (1) aponta, a previsibilidade acerca da política monetária pode melhorar a eficácia da política de estabilização de um Banco Central. Nesse artigo, procuramos reduzir a incerteza a respeito de um instrumento de Forward Guidance do Banco Central norte-americano (o Federal Reserve) estimando distribuições de probabilidade completas sobre todas as associações possíveis entre seus membros e o dot plot de taxa de juros para cada reunião. Nossa contribuição para a literatura ocorre em duas frentes: primeiro, propomos um algoritmo Bayesiano geral que estima essas hipóteses de associação entre agentes e ações sempre que elas não são observadas. Além disso, elaboramos uma maneira nova e menos subjetiva para quantificar textos em dados numéricos, usando Alocação Latente Dirichlet (LDA) e modelos econométricos de seleção. Esse método apresenta algumas características desejáveis como uma correlação positiva entre o presidente do FOMC e o resto do comitê, e um ordenamento na postura de política monetária que reflete, ainda que parcialmente, visões de analistas de mercado a respeito desse espectro entre membros mais duros e mais lenientes com a taxa de juros. Nosso algoritmo de rastreamento de alvos também tem bom desempenho num ambiente simulado, no sentido em que, em média, considera como mais provável a verdadeira associação entre membros e dots. Usando dados reais de discursos individuais e dots, ele também consegue atribuir a maior probabilidade para a associação correta na única reunião em que ela é conhecida de fato. / [en] As (1) points out, monetary policy predictability can enhance a Central Bank stabilization policy efficacy. In this paper we aim to reduce uncertainty about one Federal Reserve forward guidance instrument by estimating full association probabilities distributions between members and the interest rate dot plot for each FOMC meeting. Our contribution to the literature is twofold: first, we propose a general Bayesian algorithm which estimates these association hypotheses between agents and actions whenever they are not observed. Second, we elaborate a novel and less subjective technique for quantifying text into data, using Latent Dirichlet Allocation (LDA) and shrinkage econometric tools. This method shows some desirable features such as positive correlation between the FOMC chair and the rest of the committee, and a policy stance ordering which partially reflects analysts and market participants views on this hawk-dove spectrum. Our tracking algorithm performs successfully in a simulated environment, in a sense that it on average considers the correct member-to-dot association as the most likely one. Using real data on speeches and Fed dots, it is also able to attribute the highest probability to the correct assignment hypothesis in the only meeting it is known for sure.

[EN] In this Doctoral Thesis, it has been studied the photophysical and photochemical properties of new nanomaterials based on carbon as graphene derivatives (GO, rGO, graphene (N,O)-codoped and graphene reconstituted halogenated) and two different types of carbon nanoparticles (C-dots and C-NOR). These materials have been applied in the photocatalytic hydrogen generation, such as gas sensors and bioimaging techniques. In a first stage the material was characterized with different spectroscopic and microscopic techniques, and subsequently was studied the behavior of these materials as semiconductors. Using the techniques of fluorescence spectroscopy and absorbance transition has been proven generation state of charge separation after excitation. The different strategies used in the modification of graphene are aimed at getting systems with higher lifetimes of charge separation to harness the energy absorbed from light. It has been observed that the lifetime and quantum yield of charge separation is greater in rGO than GO. For graphenes (N,O)-codoped, which were prepared by pyrolysis natural chitosan, has shown that there is a direct relationship between the percentage of dopants and the energy of the conduction band and the quantum yield of charge separation state. In the case of reconstituted graphenes halogenated it has been shown the influence of the nature of the halogen in the generation charge separation. The charge separation lifetime obtained in these materials is in the scale of microseconds which is encouraging for possible application in photocatalysis and optoelectronic devices. For this reason we use these materials as photocatalysts for hydrogen generating from a methanol-water mixture and yields were higher for the sample (Cl)G that were seven times higher than the starting GO. Nanoparticles have been prepared using two different carbon methodologies. In one case they have been used zeolites with different pore size as templates, being those of small pore size with a directing agents with large structure, such as ITQ-29 and ITQ-12, were the most suitable for production of photoluminescent carbon dots. Pyrolysis of structure directing agent of these zeolites results in carbon quantum dots with particle sizes between 5 and 12 nm and photoluminescence quantum yield of 0.4 to that were used as photoluminescent oxygen sensors. Another methodology involves the synthesis of carbon nanomaterials from annealing of a mixture of PTCA and PEG under air atmosphere. Nanoobjects are obtained with height of 2.5 nm and with an average size of 40 nm. The morphology of the C-NOR is similar to an onion formed by concentric circles. These nanoparticles can be internalized in the human carcinoma HeLa cells and Hep 3B and they have interesting photoluminescent properties, in the same way as in solution. They showed a remarkable biocompatibility affecting in a very low way to cell viability to short periods of exposure according to the test MTT. In order to address the possible use of this nanoparticles in bioimaging a complete toxicology study was performed in vitro. It was performed feasibility assessments, proliferation, apoptosis studies generation and oxidative stress experiments after continuous and limited exposure, and also varying concentrations. It was observed that both nanoparticles showed no toxicity in the two situations at low and higher concentration, although some toxicity was determined at higher concentrations under continuous exposure. These results support the potential use of nanoparticles C-NOR and C-NOR(Eu) as bioimaging agents. / [ES] En esta Tesis Doctoral se han estudiado las propiedades fotofísicas y fotoquímicas de nuevos nanomateriales basados en carbono como son los derivados de grafeno (GO, rGO, grafenos (N,O) codopados y grafenos reconstituidos halogenados) y dos tipos diferentes de nanopartículas de carbono (C-dots y C-NOR). Estos materiales se han aplicado en la generación fotocatalítica de hidrógeno, como sensores de gases y en técnicas de bioimagen. En una primera etapa se ha caracterizado el material con distintas técnicas espectroscópicas y de microscopia, y a posteriori se ha estudiado el comportamiento de estos materiales como semiconductores. Mediante las técnicas de espectroscopia de fluorescencia y de absorbancia de transición se ha comprobado la generación del estado de separación de cargas tras su excitación. Las distintas estrategias utilizadas en la modificación del grafeno van dirigidas a conseguir sistemas con tiempos de vida del estado de separación de cargas elevados que permitan aprovechar la energía absorbida de la luz. Se ha observado que el tiempo de vida y el rendimiento cuántico de la separación de cargas es mayor en el rGO que en el GO. Para los grafenos (N,O)-codopados, que han sido preparados por pirólisis del quitosano natural, se ha demostrado que existe una relación directa entre el porcentaje de dopantes y la energía de la banda de conducción y el rendimiento cuántico de la separación de cargas. Para el caso de los grafenos reconstituidos halógenados se ha demostrado la influencia de la naturaleza del halógeno en la generación del estado de separación de cargas. El tiempo de vida del estado de separación de cargas obtenido en estos materiales se encuentra en la escala de los microsegundos lo cual resulta esperanzador para su posible aplicación en fotocatálisis y en dispositivos optoelectrónicos. Por este motivo utilizamos estos materiales como fotocatalizadores para la generación de hidrógeno a partir de una mezcla metanol agua y los rendimientos más altos fueron para la muestra (Cl) G que fueron siete veces más elevadas que el GO de partida. Se han preparado nanoparticulas de carbono empleando dos metodologías distintas. En un caso se han utilizado zeolitas de distinto tamaño de poro como plantillas, siendo las de tamaño de poro pequeño con agentes directores de estructura voluminosos, como la ITQ-29 y ITQ-12, las más adecuadas para obtener puntos de carbono fotoluminiscentes. La pirólisis del agente director de estructura de estas zeolitas da lugar a puntos cuánticos de carbono con tamaños de partícula entre 5 y 12 nm y un rendimiento de fotoluminiscencia cuántica de 0.4 que fueron utilizados como sensores de oxígeno fluorescentes. La otra metodología consiste la síntesis de nanomateriales de carbono a partir de un recocido de una mezcla de PTCA y PEG bajo atmosfera de aire. Se obtiene nanoobjetos de 2.5 nm de altura y con un tamaño medio de 40 nm. La morfologia de los C-NOR es de círculos concéntricos similar a una cebolla. Estas nanopartículas pueden internalizarse en las células de carcinoma humano HeLa y Hep 3B y presentan propiedades fotoluminiscentes interesantes, de la misma manera que en disolución. Demostraron una notable biocompatibilidad afectando de manera poco perceptible a la viabilidad celular a cortos periodos de exposición según la prueba MTT. Con el fin de abordar el posible uso de esta nanopartículas en bioimagen y su toxicidad se realizó un estudio toxicológico completo in vitro. Se realizaron evaluaciones de viabilidad, proliferación, estudios de generación de apoptosis y estrés oxidativo tras la exposición limitada o continua variando las concentraciones. Se observó que ambas nanopartículas no mostraron toxicidad en las dos situaciones a baja concentración, aunque cierta toxicidad se ha determinado a concentraciones superiores bajo exposición continua. / [CA] En aquesta tesi doctoral s'han estudiat les propietats fotofísiques i fotoquímiques de nous nanomaterials basats en carboni com són els derivats de grafè (GO, rGO, grafens (N,O) codopats i grafenos reconstituïts halogenats) i dos tipus diferents de nanopartícules de carboni ( C-dots i C-NOR). Aquests materials s'han aplicat en la generació fotocatalítica d'hidrogen, com a sensors de gasos i en tècniques de bioimatge. En una primera etapa s'ha caracteritzat el material amb diferents tècniques espectroscòpiques i de microscòpia, i a posteriori s'ha estudiat el comportament d'aquests materials com semiconductors. Mitjançant les tècniques d'espectroscòpia de UV-Vis i d'absorbància de transició (T.A.S.) s'ha comprovat la generació de l'estat de separació de càrregues després de la seva excitació. Les diferents estratègies utilitzades en la modificació del grafè van dirigides a aconseguir sistemes amb temps de vida de l'estat de separació de càrregues elevats que permetin aprofitar l'energia absorbida de la llum. S'ha observat que el temps de vida i el rendiment quàntic de la separació de càrregues és més gran en el rGO que al GO. Per als grafenos (N,O)-codopats, que han estat preparats per piròlisi del quitosan natural, s'ha demostrat que existeix una relació directa entre el percentatge de dopants i l'energia de la banda de conducció i el rendiment quàntic de la separació de càrregues. Per al cas dels grafens reconstituïts halogenats s'ha demostrat la influència de la naturalesa de l'halogen en la generació de l'estat de separació de càrregues. El temps de vida de l'estat de separació de càrregues obtingut en aquests materials es troba en l'escala dels microsegons la qual cosa resulta esperançador per a la seva possible aplicació en fotocatàlisi i en dispositius optoelectrònics. Per aquest motiu utilitzares aquests materials com fotocatalitzadors per a la generació de hidrogen a partir de una mescla metanol- aigua y els rendiments mes alts van ser per la mostra (Cl)G que van ser set vegades mes elevades que el GO de partida. S'han preparat nanoparticules de carboni emprant dues metodologies diferents. En un cas s'han utilitzat zeolites de diferent grandària de porus com plantilles, sent les de mida de porus petit amb agents directors d'estructura voluminosos, com la ITQ-29 i ITQ-12, les més adequades per obtenir punts de carboni fotoluminiscents. La piròlisi de l'agent director d'estructura d'aquestes zeolites dóna lloc a punts quàntics de carboni amb mides de partícula entre 5 i 12 nm i un rendiment de fotoluminiscència quàntica de 0.4 que van ser emprats com a sensors d'oxigen fluorescents. L'altra metodologia consisteix en la síntesi de nanomaterials de carbono a partir d'un recuit d'una barreja de PTCA i PEG sota atmosfera d'aire. S'obté nanoobjectes de 2.5 nm d'alçada i amb una longitud mitjana de 40 nm. La morfologia dels C-NOR és de cercles concèntrics similar a una ceba. Aquestes nanopartícules poden internalitzar-se en les cèl·lules de carcinoma humà HeLa i Hep 3B i presenten propietats fotoluminiscents interessants, de la mateixa manera que en dissolució. Van demostrar una notable biocompatibilitat afectant de manera poc perceptible a la viabilitat cel·lular a curts períodes d'exposició segons la prova MTT. Per tal d'abordar el possible ús d'aquesta nanopartícules en bioimatge i la seva toxicitat es va realitzar un estudi toxicològic complet in vitro. Es van realitzar avaluacions de viabilitat, proliferació, estudis de generació d'apoptosi i estrès oxidatiu després de l'exposició limitada o contínua amb diferents concentracions. Es va observar que les dos nanopartícules no van mostrar toxicitat en les dues situacions a baixa concentració, encara que certa toxicitat s'ha determinat a concentracions superiors sota exposició contínua. Aquests resultats donen suport a la possible utilització de nanopartícules C-NOR i C-NOR(Eu) com a agents / García Baldoví, H. (2016). Preparación y propiedades fotofísicas de materiales grafénicos y puntos cuánticos basados en carbono. Aplicaciones en nanotecnología [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68505 / Premios Extraordinarios de tesis doctorales

Diese Dissertation besteht aus zwei Teilen von Studien. Der erste Teil demonstriert die Steuerung der Elektron-Kern-Spin-Systems in II-VI Halbleiter Quantum Dots (QDs) durch elektrische Ströme über Mikrospulen. Mikrometer-große Leiterschleifen sind auf der Oberseite von Heterostrukturen mit geladenen CdSe/ZnS QDs hergestellt worden. Eine Strominjektion erzeugt magnetische Felder im Bereich von einige 10 mT, welche stark genug sind, um die Hyperfeinwechselwirkung in CdSe QDs modulieren zu können. Der Durchmesser des Spulen im Mikrometer-Bereich ermöglicht die Generation von schnellen Feld transienten im Bereich von wenigen ns. Mit diesen Vorteilen der Mikrospulen werden die Steuerungs des Spins der residenten Elektronen sowie das Auslesen des Kernspinzustandes durch elektrische Impulse nachgewiesen. Der zweite Teil befasst sich mit der Ladungsträger-Spindynamik in ZnO Quantum Well (QW) Strukturen und Epitaxieschichten, die mittels des optischen Übergang von negativ geladenen Exzitonen X− beziehungsweise des am neutralen Donator gebunden Exziton D0X untersucht werden. Der Loch-Spin kann direkt über die zirkular polarisierten Photolumineszenz der beiden Komplexe zurückverfolgt werde. Die Spin-Relaxationszeit von QW und Epiplyer verfolgt werden. Der Spin des Donatorelektronens wird über die Ausbleichung des Spin-selektive Anregungprozesses nachgewiesen. Es werden longitudinale Loch-Spinrelaxationszeiten von 80 bis 140 ps für D0X und X− gefunden. Deutlich längere longitudinalen Elektronen-Spin-Relaxationszeiten in Bereich von mehreren 100 ns werden gefunden, wenn die Hyperfeinwechselwirkung durch ein geeignetes externes Magnetfeld unterdrückt wird. Eine Feldstärke von 2 mT ist groß genug. Dies zeigt den extrem kleinen Wert des Overhauser-Feldes in ZnO auf, der durch die sehr begrenzte Anzahl von magnetischen Kernen in Wechselwirkung mit dem Elektronen innerhalb des Volumens des Donators verursacht wird. / This work is composed of two parts of studies. The first part represents an electron-nuclear spin control in II-VI semiconductor quantum dots (QDs) by electrical currents via micro coils. Micrometer single turn coils are fabricated on top of heterostructures with charged CdSe/ZnSe QDs. Current injection creates magnetic fields in the range of some 10 mT which is strong enough to modulate the hyperfine interaction in CdSe. The micrometer-range diameter of coil allows for generation of fast field transient in the range of few ns. Using these advantages of micro coils, local control of the resident electron spin as well as read out of the nuclear spin state are demonstrated by electrical pulses. The second part presents charged carrier spin dynamics in ZnO quantum wells and epilayers using the optical transition of the negatively charged exciton X− and the neutral donor bound exciton D0X, respectively. The hole spin can be directly traced by the circular polarized photoluminescence of both complexes. The spin relaxation of the resident electrons and donor electrons is accessed via the bleaching of the spin selective excitation process. Longitudinal hole spin relaxation times of 80 and 140 ps are found for D0X and X−, respectively. Much longer longitudinal electron spin relaxation times in the several 100 ns range are uncovered if the hyperfine interaction is suppressed by a proper external magnetic field. A field strength of 2 mT is large enough proving that the extremely small value of the Overhauser field in ZnO caused by the very restricted number of magnetic nuclei interacting with the electron inside the donor volume.

Doctor of Philosophy / Department of Chemical Engineering / Vikas Berry / Graphene - a single atom thick two dimensional sheet of sp[superscript]2 bonded carbon atoms arranged in a honeycomb lattice - has shown great promise for both fundamental research & applications because of its unique electrical, optical, thermal, mechanical and chemical properties. Derivatization of graphene unlocks a plethora of novel properties unavailable to their pristine parent “graphene”. In this dissertation we have synthesized various structural and chemical derivatives of graphene; characterized them in detail; and leveraged their exotic properties for diverse applications. We have synthesized protein/DNA/ethylenediamine functionalized derivatives of graphene via a HATU catalyzed amide reaction of primary-amine-containing moieties with graphene oxide (GO) – an oxyfunctional graphene derivative. In contrast to non-specificity of graphene, this functionalization of GO has enabled highly specific interactions with analytes. Devices fabricated from the protein (concanavalin – A) and DNA functionalized graphene derivatives were demonstrated to enable label-free, specific detection of bacteria and DNA molecules, respectively, with single quanta sensitivity. Room temperature electrical characterization of the sensors showed a generation of ~ 1400 charge carriers for single bacterium attachment and an increase of 5.6 X 10[superscript]12 charge carriers / cm[superscript]2 for attachment of a single complementary strand of DNA. This work has shown for the first time the viability of graphene for bio-electronics and sensing at single quanta level. Taking the bio-interfacing of graphene to the next level, we demonstrate the instantaneous swaddling of a single live bacterium (Bacillus subtilis) with several hundred sq. micron (~ 600 µm[superscript]2) areal protein-functionalized graphene sheets. The atomic impermeability and high yield strength of graphene resulted in hermetic compartmentalization of bacteria. This enabled preservation of the dimensional and topological characteristics of the bacterium against the degrading effects of harsh environments such as the ultrahigh vacuum (~ 10[superscript]-5 Torr) and high intensity electron beam (~ 150 A/cm[superscript]2) in a transmission electron microscope (TEM) column. While an unwrapped bacterium shrank by ~ 76 % and displayed significant charge buildup in the TEM column; a wrapped bacterium remained uncontracted and undamaged owing to the graphenic wraps. This work has shown for the first time an impermeable graphenic encasement of bacteria and its application in high vacuum TEM imaging without using any lengthy traditional biological TEM sample preparation techniques. In an inch-scale, we fabricated robust free-standing paper composed of TWEEN/Graphene composite which exhibited excellent chemical stability and mechanical strength. This paper displayed excellent biocompatibility towards three mammalian cell lines while inhibiting the non-specific binding of bacteria (Bacillus cereus). We predict this composite and its derivatives to have excellent applications in biomedical engineering for transplant devices, invasive instrument coatings and implants. We also demonstrate a novel, ultra-fast and high yield process for reducing GO to reduced graphene oxide (RGO) using a facile hydride-based chemistry. The RGO sheets thus-produced exhibited high carrier mobilities (~ 100-600 cm[superscript]2/V•s) and reinstatement of the ambipolar characteristic of graphene. Raman spectra and UV-Vis spectroscopy on the RGO sheets displayed a high degree of restoration of the crystalline sp2 lattice with relatively low defects. We fabricated graphene nanoribbons (GNRs) – 1D structural derivatives of graphene – using a nano-scale cutting process from highly oriented pyrolytic graphite (HOPG) blocks, with widths pre-determinable between 5 nm to 600 nm. The as-produced GNRs had very high aspect ratio in the longitudinal direction (~ 0.01); exhibited predominantly mono-layered structure (< 10 % bilayer); and smooth edges (Raman I[subscript]D/G ~ 0.25 -0.28). Low temperature electrical transport measurements on back-gated thin film GNR devices were performed and a carrier mobility of ~ 20 ± 4 cm[superscript]2/V•s with sheet resistances of 2.2-5.1 MΩ / □ was extracted. Despite the ~ 50 nm thicknesses of the films, a clear bandgap scaling was observed with transport via variable range hopping (VRH) in 2 and 3 dimensions. This work demonstrates the first fully functional narrow pristine GNR thin-film field effect transistors (FETs). In addition we fabricated graphene quantum dots (GQDs) – 0D derivatives of graphene with dimensions < 100 nm – using a slight variation of our nano-scale cutting strategy, where the cleavage process is carried out in two dimensions. A high degree of control on the dimensions (Std. Dev. of ~ 5 nm for 50 X 50 nm square GQDs) and shape (pre-determinable between square, rectangle, triangle and trapezoid) of the as-synthesized GQDs is demonstrated. The optical properties of the GQDs such as the UV-Vis absorbance and photoluminescence were studied and their facile tunability was demonstrated depending on their dimensions. This work demonstrates for the first time the high throughput fabrication of GQDs with tunable dimensions and shape.

This quantitative, descriptive study investigated factors that contributed to TB patients registered in four Tembisa clinics in 2001, defaulting treatment. An interview schedule with closed and open-ended questions was used for 30 patients who could be traced who had interrupted treatment. The reasons for treatment interruption were related to socio-economic, TB policy-related and health care worker-related factors. The findings illustrate that TB management requires a multi-sectoral approach and joint efforts to tackle the disease that continues to kill people even though it is curable. / Health Studies / M.A. (Health Studies)

The use of microfluidic tools to develop two novel approaches to surface-based oligonucleotide hybridization assays has been explored. In one of these approaches, immobilized oligonucleotide probes on a glass surface of a microfluidic channel were able to quantitatively hybridize with oligonucleotide targets that were electrokinetically injected into the channel. Quantitative oligonucleotide analysis was achieved in seconds, with nM detection limits and a dynamic range of 3 orders of magnitude. Hybridization was detected by the use of fluorescently labeled target. The fluorescence intensity profile evolved as a gradient that could be related to concentration, and was a function of many factors including hybridization reaction rate, convective delivery speed, target concentration and target diffusion coefficient. It was possible to acquire kinetic information from the static fluorescence intensity profile to distinguish target concentration, and the length and base-pair mismatches of target sequences. Numerical simulations were conducted for the system, and fit well with the experimental data. In a second approach, a solid-phase nucleic acid assay was developed using immobilized Quantum Dot (QD) bioprobes. Hybridization was used to immobilize QDs that had been coated with oligonucleotides having two different sequences. The hybridization of one oligonucleotide sequence conjugated to a QD (a linker sequence) with a complementary sequence that was covalently attached to a glass substrate of a microfluidic channel was shown to be an immobilization strategy that offered flexibility in assay design, with intrinsic potential for quantitative replacement of the sensing chemistry by control of stringency. A second oligonucleotide sequence conjugated to the immobilized QDs provided for the selective detection of target nucleic acids. The microfluidic environment offered the ability to manipulate flow conditions for control of stringency and increasing the speed of analytical signal by introduction of convective delivery of target sequences to the immobilized QDs. This work introduces a stable and adaptable immobilization strategy that facilitates solid-phase QD-bioprobe assays in microfluidic platforms.

Les phénomènes de diffusion cohérente non-linéaire ont été récemment proposés en alternatives à la fluorescence comme processus de marquage en microscopie multiphotonique. Les matériaux couramment appliqués dans ce contexte buttent toutefois sur une limite inférieure en taille déterminée par le seuil de détection de signaux faibles en optique non-linéaire. Aucun des efforts récents en détection en génération de second-harmonique (GSH), qui est le processus non-linéaire d’ordre le plus bas, n’a permis de descendre à ce jour au-dessous d’une barrière en taille de 40nm même en ayant recours aux techniques de détection les plus sensibles telles que le comptage de photons uniques. Les nanoparticules (NPs) restent ainsi dans la famille des nano-diffuseurs de “grande“ taille. Il apparaît toutefois possible de déplacer de façon significative cette limite inférieure vers les plus petites tailles en substituant aux isolants diélectriques ou aux semi-conducteurs à grands gaps des particules quantiques (PQs) à base de semi-conducteurs à gaps directs.Dans ce travail, un nouveau type de nanosondes hautement non-linéaires a été conçu et développé de façon à franchir cette barrière de taille minimale pour atteindre l’échelle de nanoparticules uniques. Nous considérons ainsi l’excitation résonnante à deux photons de nanoparticules quantiques individuelles à base de CdTe (de la famille des “zinc-blendes”) d’un diamètre d’environ 12.5nm, qui fournissent une émission cohérente efficace par GSH jusqu’à hauteur de 105 comptages de photons par seconde. Elles présentent de plus l’avantage d’une remarquable sensibilité à l’orientation de leur réseau cristallin octupolaire.De plus, il a été démontré que les effets de confinement quantique déterminent fortement les caractéristiques de la susceptibilité non-linéaire du second-ordre χ(2). La caractérisation quantitative du χ(2) des PQs, en particulier leur dispersion spectrale et leur dépendance en taille est menée par spectroscopie de particules uniques ainsi qu’en moyenne d’ensemble par diffusion Hyper-Rayleigh (HRS). Nous fournissons en particulier la preuve que sous certaines conditions, le χ(2) de structures à base de semi-conducteurs en mode de confinement quantique peut très largement dépasser sa valeur en milieu massif. De plus, un nouveau type de PQs hybridant des semi-conducteurs en géométries de type “bâtonnet sur sphère” (BS) a été développé sur la base de composantes cristallines de symétries différentes, afin d’augmenter leur non-linéarité quadratique effective, tout en maintenant leur taille dans un régime proche d’un fort confinement quantique. Le nouveau tenseur hybride complexe χ(2) est analysé en terme d’interférence des susceptibilités constitutives, en prenant en compte les différentes formes et symétries associées aux composantes octupolaires et dipolaires.Il en résulte pour de telles structures une exaltation significative du χ(2), qui excède celle des PQs à constituant unique compte tenu du couplage entre matériaux non-linéaires et d’un temps de décohérence plus long, que nous attribuons à un effet de separation de charge photo-induit. / Nonlinear coherent scattering phenomena from single nanoparticles have been recently proposed as alternative processes for fluorescence in multiphoton microscopy staining. Commonly applied nanoscale materials, however, have reached a certain limit in size dependent detection efficiency of weak nonlinear optical signals. None of the recent efforts in detection of second-harmonic generation (SHG), the lowest order nonlinear process, have been able to cross a ~40 nm size barrier for nanoparticles (NPs), thus remaining at the level of “large” nanoscatterers, even when resorting to the most sensitive detection techniques such as single-photon counting technology. As we realize now, this size limitation can be significantly lowered when replacing dielectric insulators or wide gap semiconductors by direct-gap semiconducting quantum dots (QDs). Herein, a new type of highly nonlinear nanoprobes is engineered in order to surpass above mentioned size barrier at the single nanoparticle scale. We consider two-photon resonant excitation in individual zinc-blende CdTe QDs of about 12.5 nm diameter, which provide efficient coherent SHG radiation, as high as 105 Hz, furthermore exhibiting remarkable sensitivity to spatial orientation of their octupolar crystalline lattice. Moreover, quantum confinement effects have been found to strongly contribute to the second-order nonlinear optical susceptibility χ(2) features. Quantitative characterization of the χ(2) of QDs by way of their spectral dispersion and size dependence is therefore undertaken by single particle spectroscopy and ensemble Hyper-Rayleigh Scattering (HRS) studies. We prove that under appropriate conditions, χ(2) of quantum confined semiconducting structures can significantly exceed that of bulk. Furthermore, a novel type of semiconducting hybrid rod-on-dot (RD) QDs is developed by building up on crystalline moieties of different symmetries, in order to increase their effective quadratic nonlinearity while maintaining their size close to a strong quantum confinement regime. The new complex hybrid χ(2) tensor is analyzed by interfering the susceptibilities from each component, considering different shape and point group symmetries associated to octupolar and dipolar crystalline structures. Significant SHG enhancement is consequently observed, exceeding that of mono-compound QDs, due to a coupling between two nonlinear materials and slower decoherence, which we attribute to the induced spatial charge separation upon photoexcitation.