Three non-peripherally substituted liquid crystalline bisphthalocyanine (Pc) compounds have been studied to examine the role of central metal ions lutetium (Lu), and gadolinium (Gd) and substituent chain lengths, i.e. octyl (C8H17) and hexyl (C6H13), in determining the physical properties. For the octyl substituted Pc molecules, the head-to-tail or Jaggregates within the as-deposited spun films produced a redshift of the optical absorption Q bands in relation to their 0.01 mgml-1 solutions. Annealing at 80˚C produced a well-ordered discotic liquid crystalline (LC) mesophase causing additional redshifts irrespective of the metal ion in case of C8LuPc2 and C8GdPc2. Formation of face-to-face or H-aggregated monomers led to blueshifts of the Q bands with respect to solution spectra for C6GdPc2, both as-deposited and annealed films. Stretching and bending vibrations of pyrrole, isoindole, and metal-nitrogen bonds in Pc rings showed Raman bands at higher energy for smaller metal ion. However, no change was observed for the difference in chain lengths. As-deposited C8LuPc2 and C6GdPc2 produced comparable Ohmic conductivity, of the value 67.55 Scm-1 and 42.31 Scm-1, respectively. C8GdPc2 exhibited two orders of magnitude less conductivity than the other two due to the size effect of the central ion and side chain length. On annealing, an increase of Ohmic conductivity was noticed in the isostructural octyl substituted phthalocyanines on contrary to a reduced conductivity in hexyl substituted one. An optical band shift of the C8LuPc2 and C8GdPc2 thin films occurred on oxidation by bromine vapour. Oxidations of Pc-coated ITO were also achieved by applying potential at 0.88 V and 0.96 V electrochemically for the C8LuPc2 and C8GdPc2 compounds, respectively. To explore the applications of these compounds in biosensing, in situ interaction studies between bromine oxidised compounds and biological cofactors nicotinamide adenine dinucleotide (NADH) and L-ascorbic acid (vitamin C) were carried out using optical absorption spectroscopy. Thin films of a non-peripherally octyl substituted LC lead phthalocyanine was exposed to 99.9 % pure hydrogen sulfide gas to produce hybrid nanocomposites consisting of lead sulphide quantum dots embedded in the analogous metal free phthalocyanine matrix. Trapping of charge carriers caused hysteresis in the current-voltage characteristics of the film on interdigitated gold electrodes. The charge hopping distance was found to be 9.05 nm, more than the percolation limit and responsible for forming two well-defined conducting states with potential application as a memristor.

Molecular beam epitaxy (MBE) grown metal has been a renewed area of interest recently in order to achieve high quality metal films or nanostructures for plasmonics. Recently MBE grown silver films have been shown to possess optical constants closer to that of intrinsic silver leading to lower losses and thus allowing for higher quality plasmonics. MBE has also been used to grow silver nanocrystals and indium droplets, or islands, for plasmonics. These self-assembled nanostructures can be grown in close proximity to quantum confined structures such as InAs/GaAs quantum dots or InGaAs/GaAs quantum wells in a single process, without post-processing and fabrication, allowing for increased plasmonic enhancement due to the improved interface between the semiconductor and plasmonic structures.In this dissertation, widely tunable plasmonic resonances of indium islands will be discussed and plasmonic enhancement results will be presented and compared to those of nanoantennas constructed from standard fabrication processes. The coupling between near-surface quantum confined structures, both fabricated and self-assembled, will be compared to the coupling in typical dielectric cavities, such as photonic crystal nanobeams. Beyond the plasmonic possibilities of indium islands, indium becomes superconducting at 3.4 K. With the proximity effect allowing for electrons in materials in contact with a superconductor to occupy a superconducting like state, allowing for the possibility for a hybrid superconductor/semiconductor optical source. The observation of superconductivity in indium islands will be presented and considerations for a superconductor/semiconductor source will be discussed.

Semiconductor quantum dots (QDs), particles several nanometers in diameter, exhibit a range of interesting properties that arise as a result of quantum confinement. Among these characteristics is photoluminescence, and unlike traditional fluorophores, the fluorescence emission of QDs is characterized by broad absorption and narrow emission that is a function of the particle diameter. This allows high spatial resolution to be achieved using spectral discrimination of closely spaced QDs.We propose applying QD fluorescence as a tool to sense the local environment of the QD to achieve wide-field sensing at high-resolution. Many factors influence QD fluorescence from the growth parameters and choice of ligand to the local environment of the QD post-fabrication. Nano-materials in the local QD environment influence the spectral or temporal characteristics of the QD fluorescence and detecting these changes enables identification of the location and motion of these nanoparticles with resolution on the order of a few nanometers.We have fabricated aqueous colloidal cadmium telluride QDs, experimenting with the choice of thiol-based ligand to influence the chemistry in post-processing and application. A wide range of tools have been used to characterize the spectral and physical properties of the QDs. We have successfully immobilized QDs on a variety of substrates including glass coverslips, silicon and indium tin oxide coated glass. Immobilization is achieved with even and consistent distributions of QDs on the substrate by using self-assembly of the colloidal particles onto substrates functionalized with N1-(3-Trimethoxysilylpropyl)diethylenetriamine (DETA) silane.Using fluorescence microscopy we have successfully demonstrated the detection of interactions between QDs and other nano-materials including green fluorescent protein and gold seed particles, demonstrating that QDs may, in principle, be used in a wide field microscopy technique to sense nano-materials with high resolution.

In this thesis investigations into chemically modified graphene structures are presented. Chemical functionalization of graphene is the chemical attachment of molecules or atoms to the graphene surface via covalent or Van der Waals bonds, this process offers a unique way to tailor the properties of graphene to make it useful for a wide range of device applications. One type of chemical functionalization presented in this thesis is fluorination of graphene which is the covalent attachment of fluorine to the carbon atoms of graphene and the resultant material is fluorographene which is a wide band-gap semiconductor. For low fluorine coverage the low temperature electron transport is through localized states due to the presence of disorder induced sub-gap states. For high fluorine coverage the electron transport can be explained by a lightly doped semiconductor model where transport is through thermal activation across an energy gap between an impurity and conduction bands. On the other hand, at low temperatures the disorder induced sub-gap density of states dominates the electrical properties, and the conduction takes place via hopping through these localized states. In this thesis it is also shown that electron beam irradiation can be used to tune the coverage of fluorine adatoms and therefore control energy gap between the impurity and conduction bands. Futhermore, electron beam irradiation also offers a valuable way to pattern conductive structures in fluorinated graphene \textit{via} the irradiation-induced dissociation of fluorine from the fluorinated graphene. This technique can be extended to the patterning of semiconducting nano-ribbons in fluorinated graphene where the spatial localization of electrons is just a few nm. The second type of chemical functionalization presented in this thesis is the intercalation of few layer graphene with ferric chloride which greatly enhances the electrical conductivity of few layer graphene materials making them the best known transparent conductors.

This thesis is an investigation of infrared electro-absorption at room temperature in electrochemically self assembled Cadmium Sulfide quantum dots produced by electrodepositing the semiconductor in 50nm pores of an anodic alumina film. Infrared absorption in these systems is associated with real space transitions of electrons between electronic states in the Cadmium Sulfide quantum dots and trap states in the surrounding alumina. When an electric field is applied on a quantum dot, it modulates the absorption by altering the overlap between the wavefunctions of dot states and the trap states in the alumina. This results in a change in the matrix element for absorption. Such a phenomenon is reminiscent of the quantum confined Stark effect. The ability to electrically modulate absorption in these structures can result in inexpensive infrared signal processing devices operating at room temperature.

CdSe semiconductor nanocrystals (quantum dots--QDs) with diameters ranging between 1.5 and 8 nm exhibit strong, tunable luminescence [1-5]. They have been widely investigated for their size-dependent optoelectronic properties [6], and for their potential use in optical devices [7], biological labels [8] and sensors [9]. Luminescent quantum dots (QDs) show higher photostability and narrower emission peaks compared to organic fluorophores [8]. The objective of my project was to apply QDs magnetic/luminescent nanoparticle as biological labels in cells. Luminescent CdSe QDs emit bright visible light with high quantum yield and sharp emission peak. The CdSe QDs were capped with a ZnS layer. This increased their emission efficiency and photostability due to the larger band gap of ZnS. The QDs were transferred from organic solvent (e.g. chloroform, hexane) to water by exchanging the capping group (Trioctylphosphine Oxide—TOPO) with mercaptoacetic acid. To develop a separation and detection tool for cells, we combined γ-Fe2O3 magnetic particles with CdSe/ZnS QDs in core-shell composite. The composite nanoparticles showed strong fluorescence emission and high water solubility. Different antibodies were attached to the particles through EDAC coupling. The antibody-coated particles were used to successfully separate and detect breast cancer cells in blood cells.

The first project focused on the preparation, characterization, and application of dual emission quantum dot encoded mesoporous silica microparticles. The quantum dots were added in precisely controlled ratios and were stably encapsulated within the pores of the silica. Several experiments were performed to test the superior stability of the quantum dot-silica composites over dye-loaded silica particles. The composite particles exhibited very high fluorescence, were functionalized with antibodies, and were used as signal transducers for the detection of a protein expressed by breast cancer cells. The second project focused in more detail on the detection capabilities of the quantum dot-silica composites. Three different types of quantum dot-silica composites were prepared. Each type was loaded with a separate type of quantum dot with distinct emission wavelengths and was functionalized with separate antibodies for detection of three different breast cancer biomarkers. These three composite sensors were used together for the simultaneous detection of each of the breast cancer markers. The initial strategy utilized the direct detection method in which the antigen is nonspecifically adsorbed to a glass plate. An improved second strategy was more sensitive and used a capture antibody which was covalently bound to a glass plate to immobilize the antigen. The third project focused on the preparation and application of magnetic, fluorescent human serum albumin nanoparticle composites. A fluorescent drug analogue and iron oxide nanoparticles were encapsulated into 100 nm human serum albumin nanoparticles. The advantage of these composite particles is that they could be used as a theranostic tool which could target, detect, and treat diseased tissue in a single application. Release of the drug analogue from the nanocomposites was achieved by addition of proteolytic enzymes that are expressed or overexpressed in cancer cells. The temporal release of the fluorescent drug analogue was measured as a function of enzyme concentration. The amount of drug released was directly proportional to enzyme concentration.

A plasmônica tem chamado atenção nos últimos anos como um candidato viável para substituir a indústria eletrônica, assim como interação dos plásmons com a matéria devido a suas propriedades exóticas. O confinamento destes plásmons de superfície em nanoestruturas metálicas fabricadas com técnicas de litografia óptica, eletrônica e de íons cada vez mais avançadas, abriu a possibilidade de desenvolver vários modelos de dispositivos ópticos que trabalham na região do visível. Além disso, o estudo da interação de plásmons poláritons de superfície com emissores quânticos nas proximidades de nanoestruturas metálicas permite manipular as propriedades tanto dos plásmons como dos emissores quânticos. Tanto a preparação como a análise de amostras em plasmônica necessitam de técnicas capazes de investigar sistemas em nanoescala. Neste trabalho, investigamos a interação de plásmon poláritons confinados numa superfície de ouro com átomos artificiais, i.e. os emissores quânticos são pontos quânticos numa matriz de InAs/GaAs. Para isso, empregamos a análise da interação dos plásmons confinados numa grade metálica, com dimensões características abaixo do comprimento de onda da luz utilizada, assim como um sistema simples composto por uma na camada de ouro capaz de confinar plásmons em duas dimensões. A análise da interação com os estados de energia dos éxcitons nos pontos quânticos foi feita empregando medidas de micro-fotoluminescência a 77K e medidas de tempo de vida. Nos sistemas compostos pelas grades metálicas, observamos que é possível manipular a relação do espectro de luminescência correspondente a cada estado de energia do éxciton. Já no sistema composto pelo filme metálico simples, foi possível modificar o tempo de vida do estado fundamental do éxciton apenas modificando o cap layer da camada de pontos quânticos. / Plasmonics has drawn attention in recent years as a viable candidate to replace the electronics industry, as well as the interaction of plasmons with matter due to its exotic properties. The confinement of these surface plasmons in metal nanostructures made of increasingly advanced optical, electronic and ionic lithography techniques, opened the possibility of developing various models of optical devices working in the visible spectrum. Moreover, the study of interaction of surface plasmon polaritons with quantum emitters nearby metallic nanostructures opens a path to manipulate the properties of both plasmons and the quantum emitters. Both the preparation and analysis of samples in plasmonics require techniques capable of investigating nanoscale systems. In this thesis, we investigate the interaction of plasmon polaritons confined to a golden metallic surface with artificial atoms, i.e. quantum emitters consisting of quantum dots in a matrix of InAs/GaAs. For this, we used the analysis of the interaction of plasmons confined in a metallic grating with characteristic dimensions below the wavelength of light used, as well as a simple system composed of a thin gold layer which can confine plasmons in two dimensions. The analysis of the interaction with the exciton energy states in quantum dots was made using micro-photoluminescence measurements at 77 K and lifetime measurements. In systems composed by metal gratings, we note that it is possible to manipulate the relationship of the corresponding luminescence spectrum for each exciton energy state. In the system composed of the simple metal lm, it was possible to modify the ground state lifetime of the exciton only modifying the cap layer of the quantum dot layer.

Orientadores: Mônica Alonso Cotta, Peter Alexander Bleinroth Schulz / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T17:54:43Z (GMT). No. of bitstreams: 1 Vicaro_KlausOrian_D.pdf: 6412839 bytes, checksum: d994f5b0a67263a799df2b77a074f96b (MD5) Previous issue date: 2008 / Resumo: Neste trabalho caracterizamos as propriedades elétricas de nanoestruturas semicondutoras de InAs/InP, principalmente quantum dots e quantum wires, obtidas pelo modo de crescimento Stranski-Krastanov com epitaxia por feixe químico (CBE). Medidas de topografia, de condutância elétrica e corrente-voltagem com resolução espacial foram realizadas nas estruturas crescidas utilizando microscopia de força atômica em modo condutivo (C-AFM) com ponta metalizada. Estruturas tipo mesa foram processadas nas amostras usadas em C-AFM e medidas elétricas a temperaturas mais baixas que 273 K foram adquiridas. Transporte por emissão termiônica tridimensional (não-homogêneo) foi observado entre a ponta condutora e as nanoestruturas de InAs. Isso sugere que as vizinhanças da nanoestrutura, formada pela wetting layer (WL), alteram a configuração da altura da barreira, tornando-a dependente da voltagem aplicada na junção metal-semicondutor. Por outro lado, a voltagem de limiar, definida como a voltagem necessária para obter a menor corrente elétrica detetável, varia com o tamanho e forma da nanoestrutura; ela está relacionada com o estado eletrônico da nanoestrutura e também com o gap eletrônico do semicondutor, que é menor nas nanoestruturas maiores. Condução elétrica por hopping e ruído telegráfico aleatório (RTN) foram observados a baixas temperaturas nos dispositivos fabricados via e-beam com dezenas ou centenas de nanoestruturas de InAs/InP. O transporte tipo hopping de Éfros-Shklovskii ocorre a temperaturas mais altas (> 70 K) e polarizações baixas onde a densidade de portadores no dispositivo é baixa e a interação coulombiana forte. Com o aumento da polarização o hopping muda para intervalo variável de Mott em sistemas 2D, e correlacionado com a dimensionalidade da WL ¿o canal de condução. O RTN aparece em temperaturas mais baixas (< 40 K) mas somente nos dispositivos contendo nanoestruturas que permitem o aprisionamento de portadores. Simulações numéricas usando um modelo heurístico mostraram que poucas nanoestruturas podem alterar o transporte elétrico num ensemble com centenas delas / Abstract: In this work we characterized the electrical properties of InAs/InP semiconductor nanostructures, mainly quantum dots e quantum wires, obtained by Stranski-Krastanov growth mode using chemical beam epitaxy (CBE). Topography, electrical conductance, and current-voltage measurements with spatial resolution were performed on the grown structures using atomic force microscopy in conductive mode (C-AFM) with metalized tip. Mesa-like structures were processed on the samples used in C-AFM; electrical measurements at temperatures lower than 273 K were then acquired. Three-dimensional thermionic emission (non-homogeneous) transport was observed between the conductive tip and the InAs nanostructures. This suggests that the nanostructure neighborhood, formed by the wetting layer (WL), changes the barrier height configuration and makes it dependent on the voltage applied to the metal-semiconductor junction. On the other hand, the threshold voltage, defined as the voltage necessary to detect the lowest current level, varies with nanostructure size and shape; it is related to the nanostructure electronic state and also to the semiconductor electronic gap that is smaller for the larger nanostructures. Electrical conductance via hopping and random telegraphic noise (RTN) were observed at low temperatures on the devices fabricated via e-beam with dozens or hundreds of InAs/InP nanostructures. The Éfros-Shklovskii hopping transport occurs at higher temperatures (> 70 K) and low polarizations where the device carrier density is low and the coulombian interaction is strong. Increasing the polarization the hopping changes to the Mott variable range on 2D system, which correlates to the WL dimensionality ¿the conduction channel. The RTN appears in low temperatures (< 40 K) but only in those devices with nanostructures that allow carrier trapping. Numerical simulations using a heuristic model showed that few nanostructures can change the electrical transport in an ensemble with hundreds of them / Doutorado / Física / Doutor em Ciências / 01/13463-1 / FAPESP

Fluorescent carbon dots are a new class of carbon nanomaterials that have emerged recently, and have created a lot of interest as a potential competitor to classical semiconductor quantum dots. Carbon dots possess low toxicity, biocompatibility, easy and low-cost synthesis, and good optical properties. They show huge potential as novel and versatile nanomaterials for a wide range of applications such as bioimaging, drug delivery, chemical sensing, photocatalysis, and as sensitizers for photovoltaic solar cells. The main motivation for this research was the need to produce non-toxic, low-cost nanomaterials with good optical and electrical properties for the use in the fabrication of sustainable, inexpensive nanostructured solar cells with good efficiency. The main aims and objectives of this PhD research were: to synthesize fluorescent carbon dots from biomass-derived precursors by using the hydrothermal synthesis method, to understand and explain structural and optical properties of the as-synthesized carbon dots, and to use the carbon dots as sensitizers for nanostructured solar cells. Carbon dots (CDs) were synthesized using hydrothermal synthesis method from polysaccharides (chitosan and chitin), monosaccharide (D-glucose), amino acids (L-arginine and L-cysteine), and from real food waste in the form of lobster shells. Carbon dots were thoroughly characterized to obtain the information about their structural and optical properties. The as-synthesized carbon dots showed polydispersity and quasi-spherical morphology, with particle sizes ranging from 5-17 nm. Carbon dots showed predominantly amorphous nature, and the functional groups from the starting precursors were successfully incorporated into the as-synthesized carbon dots. Diluted solutions of carbon dots were transparent under daylight and showed blue-green photoluminescence emission under UV excitation. All carbon dots showed excitation-dependent photoluminescence emission which was more pronounced for excitation wavelengths larger than 320 nm. Chitosan CDs, L-cysteine CDs and lobster CDs also showed excitation-independent emission for excitation wavelength in the range of 200 - 320 nm. The highest fluorescence quantum yield of (43.3 ± 2.1) % was calculated for L-arginine CDs. It was concluded that the origin of light emission in carbon dots must be governed by the interplay between the absorption due to the carbon cores and the surface functional groups. Considering the application of the as-synthesized carbon dots, two types of solar cells were fabricated. Carbon dots were used as sensitizers for ZnO-nanorod-based and for TiO2-based nanostructured solar cells. Three types of carbon dots (chitosan CDs, chitin CDs and D-glucose CDs) were used as sensitizers for ZnO-nanorod-based solar cells. ZnO nanorods were successfully coated with carbon dots, and the chitosan-CDs-sensitized solar cells showed the efficiency of 0.061 %. When using layer-by-layer coating method, solar cells with combination of chitosan- and chitin-CDs as sensitizers showed the efficiency of 0.077 %. All six types of carbon dots (chitosan CDs, chitin CDs, D-glucose CDs, L-arginine CDs, L-cysteine CDs, and lobster CDs) were used as sensitizers for TiO2-based nanostructured solar cells. TiO2-based solar cells sensitized with carbon dots showed much higher efficiency compared to the ZnO-nanorod-based solar cells. L-arginine-CDs sensitized TiO2-based solar cells showed the highest efficiency of (0.362 ± 0.007) %, which was the best efficiency of all fabricated solar cells. By surveying a range of biomass-derived carbon dots, and demonstrating a clear link between functionalisation and solar cell performance, this PhD research project provides a guide to direct future development of low-cost, biomass-derived sensitizers for nanostructured solar cells.