Orientador: Wagner de Campos / Co-orientador: Luiz Cláudio Fernandes / Inclui apêndice / Dissertaçao (mestrado) - Universidade Federal do Paraná, Setor de Ciencias Biológicas, Programa de Pós-Graduaçao em Educaçao Física. Defesa: Curitiba, 2007 / Inclui bibliografia e anexos / Área de concentraçao: Exercício e esporte

O presente trabalho encontra-se dividido nas seguintes etapas: primeiramente são expostas algumas limitações presentes nas equações dinâmicas dos plasmas não-colisionais. A seguir obtem-se, de maneira heurística, algumas correções elementares às teorias lineares, correções estas que conduzem diretamente as assim chamadas quase-lienares em suas formas não relavística e relavística. Examina-se então o efeito da variação relativística da girofrequência sobre o coeficiente de difusão, numa aproximação tipicamente perturbativa. / The present work is divided in the following parts: firstly some limitations which are present in the dynamical equations for collisionless plasmas are discussed. Then we obtain, in a heuristic form, some elementary corrections to the linear theories, which directly lead to the so-called quasi-linear theories in its non-relativistic and relativistic forms. The effect of the relativistic variation of the gyrofrequency on the diffusion coefficient is examined in a typically perturbative approximation.

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No. of bitstreams: 2 Tese - Marcus Carrião dos Santos - 2016.pdf: 18819776 bytes, checksum: c30d69dcb666acd99ab25efc73f7a96e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-05-04 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. The scientific community has endeavored to identify the properties that lead to maximum efficiency dissipation of magnetic nanoparticles. However, the diameter in which this efficiency reaches maximum is sometimes bigger than 10 nm, presenting several incompatibilities with biomedical aplications. On the other hand, small nanoparticles (< 8 nm}) do not suffer from the same disadvantages. On the contrary, they benefit from a biodistribution convenient for cancer treatment, affinity for the lymphatic system, further penetration of tumor tissue and renal clearance. However, the use of small nanostructures as heat centers never received much attention, in part because the model most used to describe the magnetic hyperthermia phenomenon, the linear response theory (LRT), provides a very small dissipation in these systems. Recently, experimental results have questioned this inefficiency and evidences that it is possible to produce a biological response (including cell death) without necessarily measuring a temperature variation opened up new possibilities for small nanostructures. This research, therefore, proposes a change in magnetic nanostructure tailoring strategy for biomedical applications of hyperthermia: to make more efficient dissipation in small nanoparticles. Therefore, it is necessary to rebuild the theoretical framework of hyperthermia, making the description of these small systems more accurate. This thesis deals with the development of modeling tools to enable a distinction between the most superficial and internal region of the nanoparticle, recognizing that many of the properties at the nanoscale has its origin in surface effects and the surface-to-volume ratio. A model for the description of core-shell system magnetization was developed, based on the Heisenberg Hamiltonian and a mean field theory in which different parameters may be assigned to each region. The combination of this model with the LRT has given rise to a new description of hyperthermia phenomenon in which the importance of surface effects and can be explicitly considered, making also possible the description of heterogeneous systems. The model was compared with original (homogeneous nanoparticles) and literature (heterogeneous nanoparticles) experimental data, with good qualitative agreement with the results. In an attempt to verify the influence of effects of nonlinearity in these systems, a non-linear response theory was developed from the generalization of the LRT, and applied to core-shell systems. The fundamental role of these theoretical tools is to point the direction in which the nanomaterials tailoring should advance to make viable the proposed hyperthermia with small nanostructures. The models proposed here suggest that a higher dissipation efficiency in small systems is obtained with a combination of materials which lead to the reduction ratio of shell-to-core damping factors, increasing of the exchange constant in the interface and maximizing the shell-to-core anisotropy constants, indicating that better results should be found in Soft@Hard systems. / O fenômeno de dissipação de calor por materiais magnéticos que interagem com um campo magnético alternado, conhecido como hipertermia magnética, é uma emergente e promissora terapia para muitas doenças, principalmente o câncer. A comunidade científica tem se esforçado para identificar as propriedades que levam à eficiência máxima de dissipação em nanopartículas magnéticas. Entretanto, muitas vezes, o diâmetro para o qual essa eficiência é máxima supera 10 nm, apresentando diversas incompatibilidades com as aplicações biomédicas. Por outro lado, nanopartículas pequenas (< 8 nm) não sofrem das mesmas desvantagens, pelo contrário, se beneficiam de uma biodistribuição conveniente para o tratamento oncológico, afinidade com o sistema linfático, maior penetração no tecido tumoral e excreção via depuração renal. Entretanto, o uso de nanoestruturas pequenas como centros de calor nunca recebeu muita atenção, em parte, porque o modelo mais utilizado para descrever o fenômeno de hipertermia magnética, a teoria de resposta linear (LRT), prevê uma dissipação muito pequena nesses sistemas. Recentemente, resultados experimentais colocaram em dúvida essa ineficiência e evidências de que é possível produzir uma resposta biológica (inclusive morte celular) sem necessariamente elevar a temperatura de forma mensurável abriram novas possibilidades para as nanoestruturas pequenas. Esse trabalho propõe, então, uma mudança na estratégia de engenharia de nanoestruturas magnéticas para aplicações biomédicas de hipertermia: que se busque tornar mais eficiente a dissipação em nanopartículas pequenas. Para tanto, é necessário reconstruir o arcabouço teórico de hipertermia, para tornar a descrição desses sistemas pequenos mais precisa. Esta tese ocupa-se do desenvolvimento de ferramentas de modelagem que permitam uma diferenciação entre a região mais superficial e interna da nanopartícula, reconhecendo que grande parte das propriedades em escala nanométrica tem sua origem nos efeitos de superfície e na relação superfície-volume. Um modelo de descrição da magnetização de sistemas core-shell foi desenvolvido, com base na hamiltoniana de Heisenberg e em uma teoria de campo médio, no qual podem ser atribuídos diferentes parâmetros para cada uma dessas regiões. A combinação desse modelo com a LRT deu origem a uma nova descrição do fenômeno de hipertermia no qual a importância de efeitos de superfície podem ser explicitamente considerados, tornando possível também a descrição de sistemas heterogêneos. O modelo foi comparado com dados experimentais originais (nanopartículas homogêneas) e da literatura (nanopartículas heterogêneas), apresentando boa concordância qualitativa com os resultados. Na tentativa de verificar a influência de efeitos de não-linearidade nesses sistemas, desenvolveu-se uma teoria de resposta não-linear a partir da generalização da LRT, aplicando-a a sistemas core-shell. O papel fundamental dessas ferramentas teóricas é apontar a direção para qual a engenharia de nanomateriais deve avançar para tornar a proposta de hipertermia com nanoestruturas pequenas viável. Os modelos propostos aqui sugerem que a maior eficiência de dissipação em sistemas pequenos será obtida com a combinação de materiais que levem à redução da razão entre os fatores de damping da shell com relação ao core, o aumento da constante de exchange na interface e a maximização da razão entre as constantes de anisotropia da shell com relação ao core, indicando melhores resultados para sistemas Soft@Hard.

This work reports on the study of the products obtained by the plasma treatment of methane mixtures or benzene mixtures in a coaxial cylindrical dielectric barrier discharge reactor at atmospheric pressure. The plasma products have been analyzed by spectroscopic and mass spectrometric techniques (GC-MS, FT-IR, NMR, MALDI-TOF MS). Moreover, in this work we report the plasma phase characterization in a parallel plate DBD reactor by using OES and LIF tecniques.

This thesis presents experimental studies, based on guided ion beam mass spectrometric techniques and coupled to theoretical interpretations by quantum chemistry, on ionic mechanisms for the molecular growth of aromatic hydrocarbons with a particular relevance for understanding the formation of large molecules in ionized gases such as planetary iono-spheres, plasmas and combustion systems. The starting point of this dissertation is a study of the reactivity of naphthyl cation C10H7+ with benzene. Ion-molecule reactions leading to hydrocarbon growth via the formation of new C-C bond are studied with special reference to the association product C16H13+. Another experiment in this dissertation concerns the reactivity of the C12H9+ ion with benzene. The growth of hydrocarbon ions up to C18H15+ species via C–C bond forming reactions is observed. The adduct formation route is found to be exothermic and barrierless, while other products are found to have energy barriers. The last topic addressed in this thesis is the experimental investigation of the possible formation mechanisms of the ion C12H10O+, observed in benzene/air plasma corona discharges at atmospheric pressure.

Collisions with He+ are an important pathway for the destruction of complex organic molecules in the interstellar medium (ISM). We have carried out dissociative charge transfer reactions of He+ with two oxygen containing organic molecules, ubiquitous in ISM: dimethyl ether (DME, CH3OCH3 ) and methyl formate (MF, HCOOCH3). Since they have a prebiotic relevance, several models were developed to explain how these molecules are formed and destroyed in the ISM. The reactions have been investigated by using the home-built Guided-Ion Beam Mass Spectrometer (GIB-MS) apparatus. Absolute cross sections and branching ratios of the products have been measured as a function of the collision energy in the hyperthermal energy range (i.e. from about 0.1 eV to 7 eV). The presence of the molecular ion was not observed among the products for these reactions, which means that the nascent DME and MF radical cations are formed in a dissociative state. Insights on both the charge transfer processes have been obtained by investigating the nature of the non-adiabatic transitions between the reactant and product potential energy surfaces (PES). The PES has been represented by using a semi-empirical method to model the inter-molecular interactions. To explain the experimental evidence, two excited states of DME and MF radical cations have been invoked: He+ captures an electron from inner valence orbitals of both the organic molecules, having binding energies ~10 eV higher than the HOMO. An improved Landau-Zener-StÃ1⁄4ckelberg model has been developed to obtain the total integral cross-section to be compared with the experimental results. Inter-molecular interaction and electron densities of the orbitals involved in the reaction turned out to be key points to describe the dynamics of the two studied dissociative charge transfers. A very good agreement is obtained between the experimental and calculated total cross-sections at low collision energy, which is the most relevant range for the interstellar environment. These results represent a significant starting point to estimate rate constants for the total dissociation of DME and MF by collisions with He+ ions in the ISM at low temperatures.

The present thesis is focused on the study of Organic Semiconducting Single Crystals (OSSCs) and crystalline thin films. In particular solution-grown OSSC, e.g. 4-hdroxycyanobenzene (4HCB) have been characterized in view of their applications as novel sensors of X-rays, gamma-rays, alpha particles radiations and chemical sensors. In the field of ionizing radiation detection, organic semiconductors have been proposed so far mainly as indirect detectors, i.e. as scintillators or as photodiodes. I first study the performance of 4HCB single crystals as direct X-ray detector i.e. the direct photon conversion into an electrical signal, assessing that they can operate at room temperature and in atmosphere, showing a stable and linear response with increasing dose rate. A dedicated study of the collecting electrodes geometry, crystal thickness and interaction volume allowed us to maximize the charge collection efficiency and sensitivity, thus assessing how OSSCs perform at low operating voltages and offer a great potential in the development of novel ionizing radiation sensors. To better understand the processes generating the observed X-ray signal, a comparative study is presented on OSSCs based on several small-molecules: 1,5-dinitronaphthalene (DNN), 1,8-naphthaleneimide (NTI), Rubrene and TIPS-pentacene. In addition, the proof of principle of gamma-rays and alpha particles has been assessed for 4HCB single crystals. I have also carried out an investigation of the electrical response of OSSCs exposed to vapour of volatile molecules, polar and non-polar. The last chapter deals with rubrene, the highest performing molecular crystals for electronic applications. We present an investigation on high quality, millimeter-sized, crystalline thin films (10 – 100 nm thick) realized by exploiting organic molecular beam epitaxy on water-soluble substrates. Space-Charge-Limited Current (SCLC) and photocurrent spectroscopy measurements have been carried out. A thin film transistor was fabricated onto a Cytop® dielectric layer. The FET mobility exceeding 2 cm2/Vs, definitely assess the quality of RUB films.

This thesis work is focused on the use of selected core-level x-ray spectroscopies to study semiconductor materials of great technological interest and on the development of a new implementation of appearance potential spectroscopy. Core-level spectroscopies can be exploited to study these materials with a local approach since they are sensitive to the electronic structure localized on a chemical species present in the sample examined. This approach, in fact, provides important micro-structural information that is difficult to obtain with techniques sensitive to the average properties of materials. In this thesis work we present a novel approach to the study of semiconductors with core-level spectroscopies based on an original analysis procedure that leads to an insightful understanding of the correlation between the local micro-structure and the spectral features observed. In particular, we studied the micro-structure of Hydrogen induced defects in nitride semiconductors, since the analysed materials show substantial variations of optical and electronic properties as a consequence of H incorporation. Finally, we present a novel implementation of soft x-ray appearance potential spectroscopy, a core-level spectroscopy that uses electrons as a source of excitation and has the great advantage of being an in-house technique. The original set-up illustrated was designed to reach a high signal-to-noise ratio for the acquisition of good quality spectra that can then be analyzed in the framework of the real space full multiple scattering theory. This technique has never been coupled with this analysis approach and therefore our work unite a novel implementation with an original data analysis method, enlarging the field of application of this technique.

III-nitride materials are very promising for high speed electronics/optical applications but still suffer in performance due to problems during high quality epitaxial growth, evolution of dislocation and defects, less understanding of fundamental physics of materials/processing of devices etc. This thesis mainly focus on GaN based heterostructures to understand the metal-semiconductor interface properties, 2DE(H)G influence on electrical and optical properties, and deep level states in GaN and InAlN, InGaN materials. The detailed electrical characterizations have been employed on Schottky diodes at GaN and InAl(Ga)N/GaN heterostructures in order to understand the metal-semiconductor interface related properties in these materials. I have observed the occurrence of Schottky barrier inhomogenity, role of dislocations in terms of leakage and creating electrically active defect states within energy gap of materials. Deep level transient spectroscopy method is employed on GaN, InAlN and InGaN materials and several defect levels have been observed related to majority and minority carriers. In fact, some defects have been found common in characteristics in ternary layers and GaN layer which indicates that those defect levels are from similar origin, most probably due to Ga/N vacancy in GaN/heterostructures. The role of structural defects, roughness has been extensively understood in terms of enhancing the reverse leakage current, suppressing the mobility in InAlN/AlN/GaN based high electron mobility transistor (HEMT) structures which are identified as key issues for GaN technology. Optical spectroscopy methods have been employed to understand materials quality, sub band and defect related transitions and compared with electrical characterizations. The observation of 2DEG sub band related absorption/emission in optical spectra have been identified and proposed for first time in nitride based polar heterostructures, which is well supported with simulation results. In addition, metal-semiconductor-metal (MSM)-InAl(Ga)N/GaN based photodetector structures have been fabricated and proposed for achieving high efficient optoelectronics devices in future.

III-nitrides are wide-band gap materials that have applications in both electronics and optoelectronic devices. Because to their inherent strong polarization properties, thermal stability and higher breakdown voltage in Al(Ga,In)N/GaN heterostructures, they have emerged as strong candidates for high power high frequency transistors. Nonetheless, the use of (Al,In)GaN/GaN in solid state lighting has already proved its success by the commercialization of light-emitting diodes and lasers in blue to UV-range. However, devices based on these heterostructures suffer problems associated to structural defects. This thesis primarily focuses on the nanoscale electrical characterization and the identification of these defects, their physical origin and their effect on the electrical and optical properties of the material. Since, these defects are nano-sized, the thesis deals with the understanding of the results obtained by nano and micro-characterization techniques such as atomic force microscopy(AFM), current-AFM, scanning kelvin probe microscopy (SKPM), electron beam induced current (EBIC) and scanning tunneling microscopy (STM). This allowed us to probe individual defects (dislocations and cracks) and unveil their electrical properties. Taking further advantage of these techniques,conduction mechanism in two-dimensional electron gas heterostructures was well understood and modeled. Secondarily, origin of photoluminescence was deeply investigated. Radiative transition related to confined electrons and photoexcited holes in 2DEG heterostructures was identified and many body effects in nitrides under strong optical excitations were comprehended.