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In this work, the physical properties of the rare earth modified BaTiO3 system, specifically with the Sm3+ ion, have been investigated. The structural, micro-structural, ferroelectric, dielectric and electric properties were analyzed as a function of the samarium content by considering the Ba1-xSmxTiO3 chemical formula (x = 0, 0.001, 0.002, 0.003 e 0.005). The materials were obtained from the Pechini´s method (or polymeric precursors method), well known in the current literature for its efficiency, when compared to conventional methods commonly used for obtaining ceramic materials. In this way, the Pechini´s method shows several advantages such as low synthesis temperatures, low levels of contaminations, high stoichiometric control and homogenization, and the possibility for obtaining nano-metric scaled powders. All of these characteristics allow to obtain high density ceramics. The study of the structural and micro-structural properties were performed in order to confirm the desired ferroelectric phases, from the x-ray diffraction and scanning electronic microscopy techniques, respectively. For all the cases, the dielectric and electric properties were investigated in a wide frequency and temperature range. The obtained results have been discussed according the current theories reported in the literature. In particular, it was analyzed the conductive effects provided from the rare earth doping, viewing to better understand the factors, which influence and determine the semiconductor characteristics of such materials. These factors allow to focuses the response of the studied materials for furthers applications in the electro-electronic industry.

The present work represents a theorical study of the GaSb-(2x6) surface reconstructions. The surface atomic geometry and the electronic structures of three surface reconstruction models were investigated and the energetically more stable model was determined. One of the model studed was proposed by Sieger, from experimental results and shows a liberations of two electrons per (2x6) unit cell. The other two models were proposed by us as modifications of Sieger model. The first model proposed by us was denominated Model I (M-I) and obeys the el ectron couting model. The second model proposed by s was called Model II (M-II) and shows the absence of two electrons per (2x6) unit cell. The computacional pach fhi98md [2] was used to carried out ab initio self-consistent calculations within the Density Functional Theory (DFT). The Kohn-Sham equations were solved by employing fully separable norm-conserving pseudopotentials as proposed by Kleinman and Bylander. The exchange-correlation term was treate whitin Generalized Approximation (GGA). From our results, we concluded that Sieger model is energetically more stable than the M-I model by 0,82 eV and is energetically more stable than the M-II model by 0,86 eV. Total charge density analisys show that the formation of the Sb double-layer at the GaSb(001)-(2x6) surface can be suported by the covalent character of the bondings between superficial Sb atoms and subsuperficial atoms, as strong as the covalent bonding between the Sb dimers.

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In this work were studied optical properties of polymeric blends of luminescent conjugated polymer poly (9,9 n-dihexyl-2,7-fluorenodiilvinileno-alt-1,4-henylenevinylene) (LAPPS16) in atactic polymeric matrix: poly (methyl methacrylate) (PMMA) (75,000 MW), poly (ethyl methacrylate) (PEMA) (MW 350,000) and poly(isopropyl methacrylate) (PiPMA) (MW 100,000) were studied. The blends are self-standing films were made by co-precipitation process and these properties were then investigated by optical absorbance, photoluminescence (PL), photoluminescence of excitation(PLE), emission ellipsometry (EE) and photoluminescence in situ temperature. The samples were structurally characterized by x-ray diffraction and measurements showed that does not structural changes in the matrices of methacrylates. The optical absorbance and emission ellipsometry showed that the luminescent polymer LAPPS16 is highly diluted with low aggregates on the samples studied. The states of polarized emitted light by films were studied by emission ellipsometry technique. The samples were excited by linear vertically polarized light and the measured emission is more polarized when conjugated segments smaller gap of energy, i.e. higher length of conjugated. This result is related to the process of transfer energy inter and intramolecular. The relaxation temperature of atactic polymers PMMA, PEMA and PIPMA were verified by variation of photoluminescence intensity and wavelength of excitation, which was performed on the temperature range from 35K to 410K. This study showed that luminescent polymeric probe, LAPPS 16, suffer influence of relaxation temperatures α, β, γ and δ of methacrylate, meanly when there is an energy transfer on LAPPS16 excited with high energy. Finally, this worked showed the luminescent polymer, how LAPPS16, could be used for study dynamics properties in system matrix guest-host.

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In this work we studied the effects of coherent laser in a system formed by a quantum dot (QD) in a nanocavity. Initially we investigated the case where the energy of an éxciton are in resonance with the cavity mode and we vary the frequency of the laser. During our simulation we have used pulsed and continuos laser. We consider only the éxciton state of the QD, and in situations where both the laser and the cavity mode are close to resonance, allowing us to use the rotating wave approximation. The QD was treated as a two-level system and the cavity containing a maximum of four photons. For this study we used the Jaynes-Cummings model with an extra term related to the external pulse, which was used to manipulate quantum states. This was done with the help of diagonalization of the approximated Hamiltonian and searching for anticrossings in its energy spectrum. Then we use a continuous laser and the technique of calculating the average occupational each state to do a better mapping of the parameter values required to make the manipulation of quantum states. We found that the system can be manipulated using the process of two or more photons, and the energies of these photons could be estimated using a mapping procedure developed in this dissertation.

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The material host, considered in this research, for ions of Neodymium was glass matrix SNPZ (40SiO2 . 30Na2CO3 . 20PbO . 10ZnO (%mol)) doped with XNd2O3 (%wt), where X = 0.1; 0.3; 0.5; 0.7; 0.9; 1.1; 1.3; 1.5; 1.7; 1.9. The specters of optic absorption of doped matrix glass SNPZ with ions Nd3+ had presented bands of optic absorption (OA) centered around 431, 474, 514, 530, 586, 630, 685, 739, 804, 876 and 1598 nm, gotten ambient temperature. Already the photoluminescence specters (PL) had presented bands centered around 811, 880, 1060, 1330 nm, gotten, also, to the ambient temperature, using the line of excitement of 514.5 nm (19436 cm-1) of an argon laser, for pump of electrons of the 4I9/2 state for 4G9/2 + 4G7/2 + 2K13/2 of ions of Neodymium inserted in glass matrix SNPZ, where 4F3/2 occurred a nonradiative decline until the state. The difference of energy of the intermediate states between 4G9/2 + 4G7/2 + 2K13/2 and 4F3/2 is of the order of the corresponding energy to the ways of vibration of glass matrix SNPZ, that are of 421, 515 and 851 cm-1 in agreement the Raman specters, gotten to the ambient temperature. To get the spectroscopic parameters one used the calculations of the Theory of Judd-Ofelt, where presented a maximum quantum efficiency of 97.8 % glass doped in matrix SNPZ with 0.7 Nd2O3 (%wt), correspondent the 9.490 x 1019 ions/cm3 and verified an experimental lifetime of 302 µs for the state 4F3/2. Ahead of this, it can be concluded that glass matrix SNPZ makes possible to be an ideal host for ions of Neodymium in relation to the excessively material ones. In this work of research it was verified that the length of migration of the photon is maximum for doped glass matrix SNPZ with 1.1 Nd2O3 (%wt), correspondent 1.22 x 1020 ions/cm3. At last, for the fact of the ion of Nd3+ to present emission and absorption around 880 nm can be used doped glass matrix SNPZ with ions of Nd3+ as amplifying optic. Being able to conclude that it exists a distance it criticizes that it favors the diffusion of photons, a time that the concentration is related with distance between ions.

In this work, the thermal and optical properties is of the system P2O5 - ZnO - Al2O3 - AO - PbO - La2O3 (mol %) + XEr2O3 [A = Ba; Mg; X = 0; 1; 2; 3; 4; 5 (wt %)] was studied aiming at applications in optical fibres and planar waves-guides, as optical amplifiers. Such system is unknown and of low cost if compared with others, for example, those made with tellurium oxide, aiming production in the industrial scale. This research was developed in three consecutive stages, where in the first one the concentration of La2O3 was varied considering to get systems with reasonable thermal stability and optical properties. In the second stage, chosen the best composition with fixed La2O3 (mol%), looking for change the concentration of PbO and verify the change in the refractive index. Already in the third and last stage one searched to elaborate a glass from increasing concentrations of Er2O3 (wt %) aiming an optical amplification around 1530 nm. Therefore, ahead of the general objective of this research, it is of basic importance to study thermal and optical properties, such as transmittance, refractive index and differential scanning calorimetry, of the glasses resultants in each of these three stages. It was observed, in the first stage, that this system presents greater glass stability (GS - glass stability) and reasonable optical properties, when the composition contains 10La2O3 (mol %). Already in the second stage, keeping fixed 10La2O3 (mol %), this system presents greater index of refraction, when in its composition contains 10PbO (mol %) and A = Ba. Finally, in the third stage, it was observed that the biggest value of life time of the state 4I13/2 of Er3+ is 1,2 ms, for a 1Er2O3 (wt%) concentration. Ahead of this value of the life time and the thermal and optical properties, observed in all the three stages, one concludes that considered unknown systems in this research, with its compositions, suggested for the construction of the cladding and the core of a possible optical fibre are 63P2O5 . 14ZnO . 1Al2O3 . 10MgO. 2PbO. 10La2O3 (mol%) and 55P2O5. 14ZnO. 1Al2O3 . 10BaO. 10PbO. 10La2O3 (mol%) + 1Er2O3 (wt%), exactly not being these concentrations that had presented greater width of the half height of the emission band of the transition 4I13/2 → 4I15/2.

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In present work we studied the processes of phase transition of five luminescent liquid-crystals by using emission ellipsometry technique. The samples studied present different mesophases liquid crystalline between the solid crystalline and liquid isotropic phases. The samples were characterized by optical absorption, photoluminescence, and emission ellipsometry technique (EE) in function of sample temperature. The EE measurement allowed us obtain the Stokes parameters, the degree of polarization of emitted light, and ellipticity and rotation angle of the polarization ellipse. In addition, we founded that the degree polarization, the ellipticity, and the rotation angle of polarization ellipse of emitted light change when the sample temperature increase. It was possible to correlate those changes with the phase transition temperature for each sample in concordance with the literature data. Finally, we propose empirical model to explain our results using the emission ellipsometry technique to determine the phase transition temperature of luminescent liquid crystal systems.

In the present work we investigate theoretically the quantum transport in both, stationary and transient regimes of system composed of the two quantum dots coupled to each other via hopping and to reservoirs. Using nonequilibrium Green function technique we calculate spinresolved current and ocupation in the presence of ferromagnetic leads. The analysis of the shot noise was also carried out, observing effects on both zero frequency and also finite frequency. In particular, for the system of two quantum dots, the dynamics reveal coherent Rabi oscillations, which one suppressed as time evolves due to the incoherent tunneling to the reservoirs. Both the Rabi frequency and the coherence time are strongly affected by the external source-drain voltage. This coherence is emphasized by the shot-noise signal, which presents a characteristic behavior at the Rabi frequency, being more pronounced when the two levels are in resonance. We also note that the Rabi oscillations are amplified when the interdot hopping is higher than the incoherent tunneling rate. Additionally, we investigated electronic transport of an ensemble of coupled sites that simulates an array of quantum dots or a molecule. An external bias voltage is applied along the structure in order to study the tunneling current, the transmission coefficient, shot noise and Fano factor. While in the linear case the characteristic I-V curve reveals no current rectification, in the disordered configuration a robust rectification is found, thus indicating an operation regime typical of a molecular diode. The negative differential resistance (NDR) is also observed due to the drop of the bias voltage along the structure, that decreases the probability of transmission between the orbital neighbors. We note that when the system becomes disordered the spin correlation tends to increase, with Fano factor reaching values close to 0.4.

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The Raman Optical Activity (ROA) has been offered numerous information about the conformation of chiral molecules, an these, has great relevance in many areas, including Biology and Medicine. In present work we investigated a new technique to measure the Raman Optical Activity of chiral molecules: the Raman Spectroscopy by Ellipsoetry (RaSE). The technique ROA quantifies the vibrational optical activity through measurement of a small difference in the intensity of Raman scattering for chiral molecules in incidence of polarized circularly right and left laser light. The RaSE is the application of ellipsometry to measure the Raman scattering, that means, through the technique of ellipsometry we can measure the Stoke parameters, which describe the polarization state of light. The exciting source in RaSE is a laser light beam which can be decomposed into two polarizations: a beam of circularly polarized light right or left. Therefore, the parameter S3 describes the amount of light and when normalized ROA is the acquired signal, therefore provide the difference of intensity of Raman scattering. With this concepts, we performed measurements of RaSE using alcohol (S)-(−)-1-phenylethanol (1-PhEtOH), that was the first chiral substance been characterized using the Raman Optical Activity. The spectrum ROA of 1-PhEtOH using the RaSE is fully agreement with the literature and proves the veracity of the results of RaSE.

The main objective of this work is to research and obtain surface protected topological states in nano-ribbons created from the leaves of Germanene and Silicene. These sheets belong to the class of Topological Insulators and correspond to monolayers of germanium and silicon atoms in a hexagonal arrangement that is similar to the graphene sheet. For this investigation, we conducted a study of the electronic and structural properties of these sheets, as well as their respective nano-ribbons through first-principles calculations based on density functional theory (DFT). In this methodology we use the generalized gradient approximation (GGA) for estimating the exchange and correlation term, and the PAW method for the effective potential and the expansion of plane waves of the Kohn-Sham. We conducted a computer simulation with the aid of the package VASP (Vienna ab-initio Simulation Package). As a starting point for our research, we used the methodology of solid state physics in order to describe the crystalline structure of the leaves as well as their mutual space. Subsequently we analyze the band structure, from which many of its properties can be visualized. For this task, we initially proceeded to investigate the stability of these systems via total energy calculations, in turn obtaining the network parameters that minimizes the energy of the system. We also obtained the energy cutoff, ECUT used in our calculations, or in other words, determining the number of plane waves needed to expand the electronic wave functions on the DFT formalism. We continued our study, with the creation and analysis of two different configurations of nano-ribbons, one that corresponds to a straightforward cut of the sheet with the armchair termination pattern, and the other based on a reconstruction of those edges, which provide an energetically more stable system. Subsequently we obtained electronic structures, and conducted a study of its variation due to the change of the width of the nano-ribbon and ionic relaxation of its edges. In a way, we modified the above parameters in order to obtain a system that would give us a zero gap, or at least insignificant, as well as a specific configuration for the spin texture, in order to verify the evidence of surface protected topological states in these nano-ribbons.

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