In this work we present the study of CuO films produced by the DC magnetron sputtering technique and after thermal annealing. The structural, morphological, topography, vibrational, optical and electrical properties of the films were studied and characterized by the techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, spectroscopy UV-Visible (UV-Vis), electrical measurements and Hall effect. Firstly, copper films were deposited on a “borosilicate” glass substrate during 1 min using copper as a target. Films with different thicknesses were obtained by changing the sputtering source power (100, 150, 200, 250, 300, 350 and 400 W). Subsequently, these films were annealed at 500°C for 2 hours in air atmosphere to obtain CuO films.

The formation of the monoclinic phase was confirmed via XRD data analysis, without evidence of extra phases. Results indicates that the crystallite size increases from 39 nm to 54 nm as the film thickness increases. Furthermore, the residual strain is increased as the thickness decreases, which has been attributed to the structural disorder due to the strong film-substrate interaction. The unit cell volume varies in the range from 81.36 to 81.24 ų, with a slight tendency to decrease with the film thickness, being larger than the expected for bulk CuO (81.08 ų). Cross-sectional SEM images indicate that the film thickness ranges from 256 to 1450 nm, with a growth rate of (3.6 ± 0.2) nm/W. Raman spectroscopy measurements showed the presence of only canonical modes (Ag+2Bg) associated with the CuO crystalline phase. The positions of the Raman modes tend to shift to values expected for bulk CuO with the thickness increase. Furthermore, UV-Vis spectroscopy measurements revealed that the optical energy gap (Eg^opt) decreases from ~1.74eV to ~1.39 eV with the film thickness. The decreasing trends in both the band gap energy and Urbach energy (Eu) were attributed to the decrease of the tensile strain with the film thickness. Hall Effect measurements indicate that the CuO films are p-type, with a low concentration of charge carriers which varies in the range of 10¹⁴ - 10¹⁶ cm^-3 and with resistivity that varies from 22-35 Ωcm. Methane gas (CH₄) sensitivity tests carried out at different working temperatures (323-473 K) for the thinner film (256 nm) indicate an improvement in the sensitivity with the working temperature (until 473 K). Furthermore, sensitivity measurements for all CuO films at 473K indicate that the higher response is obtained for the thinner film (256 nm), which was associated with the smaller grain size determined for this film. These results suggest that CuO films are promising for gas sensing applications.

Carbon dots are a class of 0-dimensional nanomaterials important for many applications ranging from nanomaterials for industry nanosensors as optoelectronic components, in the medical field, and in energy storage. They have gained space in the scientific community for their easy and cost-effective synthesis, optical properties, and outstanding photoluminescence. For this matter, carbon dots with nitrogen enrichment have been shown to change the inner and surface structures of the carbon dots, characterizing the well-established nitrogen-rich carbon dots (N-CDs). In this work, the structure of the N-CDs while dispersed in an aqueous medium was investigated by using synchrotron Small-Angle X Ray Scattering (SAXS) and Dynamic Light Scattering (DLS), discussing the important phenomenon of aggregation that occurs in this system. The results show that the nitrogen content inside the N-CDs leads to two types of morphology: mass fractals for high nitrogen enrichment and surface fractals for low nitrogen enrichment. Furthermore, complex and hierarchical aggregates were identified in the dispersion of N-CDs that are all stable in the pHs considered here: 2, 7, and 12. The results were interpreted using the initial structure of the N-CDs powders, which were initially investigated using X Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), and SAXS, as well as the surface charge mechanism that these N-CDs have. The results found can be helpful in enhancing the N-CDs applications since the relationship between the structural and optical/electronic properties is still not clear.

It was determined the energy-momentum tensor for the electromagnetism with Lorentz breaking even term of the Standard Model Extended (SME) photon sector confined in a hyper torus. A generalized partition function method is used, following in parallel the thermofield dynamics formalism written in N-dimensional toroidal manifold. After considering general aspects of the SME photon sector in a toroydal manifold, the influence of the isotropic CPT-even electromagnetic sector of the SME is analysed. The approach is then applied to the Casimir effect at finite temperature, corresponding to a topology (S 1 ) r ×R N−r , where N is the dimension of the Minkowski space-time, and r is the number of compactified dimensions influence of the isotropic CPT-even electromagnetic sector of the SME is analysed.

In this work, the qubit-excitonic dynamics in three different quantum systems will be analyzed which will allow us to extract various relevant information, such as the concurrence, which it is the means by which it is possible to calculate how entangled a quantum system is. First we study the open quantum system composed by two valleys populated by bright excitons, where it was shown that competition as a function of time always decays, that is, it always reached zero steady states. In the second study, we introduced to the first system a bimodal microcavity, where two initial states di- ferents: The first with the qubit-excitons in an uncorrelated state (non-correlated state). entangled) and the cavity photons in a Bell state (maximally entangled state). in the second initial state, we leave the qubit-excitons in a Bell state and the cavity photons in an uncorrelated state. Calculations were then carried out post-dynamics, such as the separation of the density matrices of the composite system, and finally we calculated the concurrence for the excitonic system. This analysis showed that the concurrence presented satisfactory stationary values for its use in Computing Quantum, showing that the cavity introduced to the system benefited entanglement of qubit-excitons. In the third, we worked with a system of three levels located in a single valley, populated by bright and dark qubit-excitons, where the objective was to find analytical stationary solutions, as well as comparing the equations of motion obtained through the Linblad Master Equation with the equations obtained using the formalism of the rate equations.

Photosynthetic organisms are responsible for the most abundant form of energy con-
version in nature. Therefore, it is important to understand how charge transport between the mo-
lecules involved in this process works. According to Marcus theory, this transport depends on
certain properties of these molecules, such as reorganization energy (λ) and Gibbs free energy.
These properties can be quantitatively estimated by applying density functional theory (DFT).
However, most pigments in photosynthesis have conjugated bonds. Thus, the alternation of
single and double bonds increases the overlap of electronic orbitals. Therefore, orbital deloca-
lization and vibrational effects are even more relevant for these molecules. Here, we calculated
the reorganization energies of 15 important molecules for photosynthesis using a reliable DFT-
based approach. The fitting of the long-range parameter of the functional reduces the effects
of orbital delocalization, while molecular vibrations are accounted for by the method of nu-
clear ensembles. The results show that the functional fitting reduces the reorganization energy,
while the vibrational effects produce distributions of this quantity, affecting charge transfer rates
between the molecules involved by up to an order of magnitude.

This study reports on the isotopic effect controlling the conformation rearrangement rates, as a function of the temperature, of isolated hydrogen peroxide (H2O2), the simplest chiral molecule exhibiting enantiomeric configurations, and of the same molecule in weakly bound complexes formed with noble gases (He, Ne, Ar, Kr, Xe, and Rn), as both H atoms are replaced by the muonium (the lightest isotope of the hydrogen atom), deuterium, and tritium (the heaviest isotopes of the hydrogen atom). The thermal chiral rate calculations, with and without tunneling corrections, were performed exploiting the theory of transition state by using geometries, energies, and frequencies of relevance calculated at MP2(full)/aug-cc-pVTZ level and with Counterpoise correction of basis set superposition error. Through this study, we understood how isotopes and noble gases affect the transition rates between chiral conformations of hydrogen peroxide. The findings indicate that muonium acts as a ”catalyst” for chiral transition, providing an important anti-Arrhenius behavior controlled by the tunneling through barriers, whereas deuterium and tritium have a preserving effect, that is their rates follow the canonical Arrhenius behavior. Furthermore, heavier noble gases significantly alter the chiral conformational rate.

Since the 1950s, theoretical researchers in the field of nanomaterials have focused their attention on developing computational methods capable of creating nanotube structures that can be recreated in nature with the aim of contributing to the technological market. From this perspective, this research proposes the creation and analysis of nanoring and nanobelt structures that can contribute to the construction and physical characterization of nanotubes. In this work, 19 nanoring structures were developed, theorized and calculated using Density Functional Theory (DFT), which proved to be stable and promising to be synthesized. Their computational calculations presented relevant results based on the analysis of convergence criteria, such as: analysis of structural, electronic and optical properties. However, some of these structures showed significant results electronically: three of them showed superconducting properties and one structure showed insulating properties. All of these electronic properties have promising applications in the cosmetic and energy industries, which means that this research can indirectly contribute to the well-being of society. Furthermore, a nanobelt structure was developed, the Boron Nitride nanobelts. It was calculated using DFT and Time-Dependent Density Functional Theory (TDFT) and it was identified that it could be a possible replacement for [12]cyclofenacene as it is more stable and less energetic, which contributes to the detection of ultraviolet radiation (UV).

The study presented in this doctoral thesis work is important for us to understand the elec-tronic properties of a group of organic molecules, such as the amino acid cysteine and aromatic molecules (benzene, aniline, and o-, m-, and p-nitroaniline), in their forms of neutral and singly charged ions, which has great interest in the field of atomic molecular physics, quantum chemistry, pharmacy, biochemistry, and industrial chemistry. Five conformations of the cysteine amino acid (Cys01, Cys02, Cys03, Cys04, and Cys05) were calculated, with five neutral molecules and from these structures, five cationic conformations were calculated. The calculation results showed that there are structural modifications in the cysteine amino acid conformations, which are evident in the lengths of chemical bonds, bond orders (BOs), and charge distribution, when comparing the differ-ent singly charged conformations with the neutral ones. Our results indicate that the alpha carbon is the most favorable fragmentation point for the CH2SH and COOH radicals, after a single ionization of the cysteine molecule. The possibility of finding fragmentation routes, by theoretical methods, led us to compare molecular ions between neutral benzene, aniline, and o-, m-, and p-nitroaniline molecules, using Density Functional Theory (DFT), under an aug-cc-pVDZ basis set and a B3LYP ex-change correlation functional. After determining the structure and electronic energy of the neutral and doubly charged species, we also used the same methods used for the cysteine amino acid cal-culations such as: Wiberg bond indices and Bader's quantum theory of atoms in molecules (QTAIM). Where it was possible to observe the charge transfer and electronic distribution in each monomer, making it possible to observe possible locations for fragment formation in at least two pairs of car-bon-carbon (CC) atoms of the aromatic ring, which indicates the possible loss of the -CNH2 and -NO2 groups in the doubly charged aniline and nitroaniline molecules.

Magnetite (Fe3O4) nanoparticles coated with organic material are of considerable importance in various areas of engineering, as well as in biomedicine. Several papers show drastic changes in the magnetic properties related to the surface effects and the particle-particle interactions strength. However, there is no consensus about the origin or mechanisms that produce these changes, which could be different depending on the particle size and shape, coating efficiency and particle-particle interaction strength. Aiming to shed light on these issues, oleic acid (OA) coated Fe3O4 nanoparticles with sizes 4, 6 and 9 nm were synthesized by a thermal decomposition method using phenyl ether, benzyl ether and octadecene as organic solvents. These samples were additionally coated with essential oil ((Fe3O4@AO/OE). Structural and microscopic Fe3O4@AO nanoparticles results revealed Fe3O4 nanoparticles with good crystallinity and almostspherical or polyhedral shapes depending on the solvent used for the synthesis. Infrared (FTIR) spectroscopy indicated OA molecules attached to the surface of Fe3O4 NPs via bidentate (chelating and/or bridging) bonds. Thermogravimetric analysis (TGA) confirmed the presence of weakly and strongly bound AO molecules in the Fe3O4@AO samples, suggesting a successful coating of the Fe3O NPs. Magnetization (M) vs. magnetic field (H) curves are consistent with a core/shell structure formed by magnetite/maghemite phases, in consistency with FTIR spectroscopy. Lower than expected saturation magnetization values were determined for bulk magnetite, which was attributed to the probable presence of a fraction of low-spin (LS) iron ions in the maghemite layer on the surface of the particles. In that regard, the analysis by Mössbauer spectroscopy confirmed these results, as well as the better crystalline quality in the samples synthesized with benzyl ether used as the synthesis solvent. The magnetic results show that depending on the amount of AO coating, it is possible to adjust the particleparticle separation distance, avoiding nanoparticle agglomeration and particle-particle interactions. Dependence of magnetization on temperature reveals the presence of interacting and non-interacting NPs. AC magnetic susceptibility measurements are consistent with these results and confirm a superparamagnetic behavior (SPM), attributed to non-interacting NPs, and interacting SPM, attributed to interacting NPs and whose interaction strength is not sufficient to lead to behavior similar to that of spin glass. On the other hand, the FTIR results of the Fe3O4@AO/EO samples indicate the presence of EO without direct connection with the AO or with the metal ions on the surface of the Fe3O4 NPs. These results are consistent with those obtained from the analysis of thermogravimetric curves, where the intermediate-sized sample showed a higher amount of EO. Also, the EO coating had changes in the magnetic response. A reduction in the saturation magnetization and variation in the ZFC and FC curves was observed with lower blocking temperatures and lower activation energies in relation to Fe3O4@AO samples. These results were confirmed by measurements of AC susceptibility as a function of temperature. This suggests a lower degree of particle agglomeration and the weakening of particle-particle interactions as a function of the amount of EO in the Fe3O4@AO/EO samples.

This thesis aims to address new properties and behaviors in low-dimensional systems, which can be divided into two branches: (i) new topological properties found in a one-dimensional electron system with Rashba and Dresselhaus spinorbit interaction, periodically modulated in space, and (ii) manipulation of the valley degree of freedom in two-dimensional materials with inversion asymmetry and potential use as a carrier of quantum information. In the first work we have investigated the phase diagram of a one-dimensional band insulator with spin-orbit coupled electrons, supporting trivial, and topological gapped phases separated by intersecting critical surfaces. The intersections define multicritical lines across which the ground-state energy becomes nonanalytical, concurrent with a closing of the band gap, but with no phase transition taking place. This finding challenges the standard theory of quantum phase transitions according to which a nonanalyticity in the ground-state energy implies a quantum phase transition. Regarding quantum information, we studied a two-level exciton qubit that takes into account the valley degree of freedom. In this scenario, the two valley states are mixed by the intervalley exchange Coulomb interaction and can be tuned by an external magnetic field. We observed that the intensity and sign of the external magnetic field affect the valley pseudospin for different exciton momentum. Finally, We have worked with optical excitonic and valleytronics in two dimensional (2D) materials. We have so far obtained results for the dynamics and scatterings of excitons between excitonic states in 2D van der Walls transition metal dichalchogenides heterostructures MoS2/WS2. We have also investigated the magnetic proximity effect by tuning the valley polarization, as well as the photoluminescence of interlayer excitons, singlets, and long-living triplets. We found that crossing their energies for certain exchange field values gives rise to a photoluminescence peak signature near this critical field. The large valleysplitting energy plays an important role in the valley polarization.

In recent years, organic molecules known as carbon nanobelts have been the subject of much research. Recently, one of these molecules - called (12)cyclophenacene - was synthesized. This synthesis marked a great advance in synthesis technologies since this molecule has been studied since the 1950s. In this work, two new molecules derived from (12)cyclophenacene are proposed, which are called silicon carbide nanobelt or SiC-nanobelt (C24Si24H24) and boron nitride nanobelt or BN-nanobelt (B24N24H24). To verify stability and possible applications of these molecules, the electronic, optical, and thermodynamic properties of SiC and BN-nanobelts were determined. These properties were calculated using the DFT method with the PWC and PBE functionals, with the Double Numerical Plus Polarization (DNP) basis set. It was verified, through electronic structure calculations, that the BN-nanobelt is more stable (-14.11 hartrees) than the SiC-nanobelt (-12.21 hartrees). It was also observed that the SiC-nanobelt has characteristics of a semiconductor (GAP estimated at 2.13 eV), and the BN-nanobelt has characteristics of an insulator (GAP estimated at 4.62 eV). Optical properties revealed that SiC-nanobelt absorbs in the visible region, while BNnanobelt absorbs in the ultraviolet region. From the point of view of thermodynamic properties, it was observed through the Gibbs free energy that for a temperature above 718 K a spontaneous reaction occurs for SiC-nanobelt. Furthermore, quantum dynamics calculations showed that both proposed nanobelts are thermally stable, with the bonds of BN-nanobelt and SiC-nanobelt breaking at temperatures of 3000 K and 2500 K respectively. Based on the results obtained for the electronic, optical, thermodynamic, and dynamic properties, it is possible to infer that the new inorganic nanobelts are stable systems (their syntheses are viable) and have potential technological applications

 Machine learning (ML) has become an important computational tool in the study of physical systems, providing important advancements in the study and description of po- tential energy surfaces (PESs). However, little has been investigated about the behavior of these algorithms in weakly bound systems, such as molecules present in the terrestrial atmosphere and in the interstellar medium. The present study aims to analyze the perfor- mance of kernel methods - a type of ML algorithm - in the description of the SEPs of the ^H₂^O_2 — Kr system through a topographic study of it. We will also analyze the learning curves and predictive capabilities of this model in terms of interpolating points on the surface.

Abstract: In this work, the binding characteristics of the adducts formed by a noble gas atom (Ng = He, Ne, Ar, Kr, Xe and Rn) and the oxygen molecule (O$_2$) in its ground state $^3\Sigma_g^-$, subject of several experimental studies, were characterized from different theoretical points of view to clarify basic aspects of intermolecular bond. For the most stable configuration of all O$_2$-Ng systems, equilibrium distance and binding energy were calculated at CCSD(T)/aug-cc-pVDZ and CCSD(T)/aug-cc-pVTZ levels, respectively, and compared with the experimental data. Rovibrational energies, spectroscopic constants and lifetime as a function of temperature were also evaluated by adopting properly formulated potential energy curves. Using charge displacement analysis, symmetry-adapted perturbation theory (SAPT) and natural bond orbital (NBO) methods, the nature of the interaction involved was thoroughly investigated. In all adducts, charge transfer was found to play a minor role, although the O$_2$ molecule is an open-shell specie exhibiting a positive electron affinity. The obtained results also indicate that the dispersion attraction contribution is the main responsible for the stability of the complexes.

The non-linear gravitational waves are exact solutions to Einstein’s equations, geometrically corresponding to a null geodesic congruence in spacetime, with the perpendicular surfaces representing the two-dimensional flat spacetime. Physically, these solutions represent progressive waves propagating at the speed of light. In this thesis, the metric tensor corresponding to such waves is obtained from physical impositions on a general spacetime. The interaction between the waves and the particles is analyzed from the energy transfer between the waves and the particles. By modeling pulse-polarized waves, it is discovered that gravitational waves can give or remove energy from a particle, depending on the initial conditions of the particle and the wave parameters. Discrete values for the wave parameter, related to the pulse length, are found for which a maximum energy transfer occurs. A relation is found between the inertial accelerations of the spacetime, calculated from the expressions of the Teleparallel Equivalent of the General Relativity (TEGR). Ergo, a generalization of the classical work-energy relation is proposed to describe the energy transfer, and its validity is numerically corroborated. By extending the investigation to more general gravitational waves, the energy and angular momentum of the gyratonic waves are calculated within TEGR. The interaction between the gyratonic waves and particles is also investigated, and some relations conserved quantities of the gravitational field and particles are related. From the results obtained, it is specula

In this work we report the effects of electron-phonon coupling on the density distribution of charges in silicene nanoribbons by the using the extended tight-binding model with lattice relaxation. The results show that the charge distribution on the silicon nanoribbons is analogous to that of graphene and that the charge location increases when the intensity of the electron-phonon coupling also increases. We also show that silicon nanoribbons can be a conductive or semiconducting material, depending on the width of the nanoribbons. We evaluated the kinematic behavior of the charge center associated with the polaron for different electric field strengths implemented in the system in an adiabatic way. We considered three values of electron-phonon coupling in order to verify the degree of charge stability along the length nanoribbons. In this way, we show that fluctuations in the values of the average polaron velocities occur as the quasi-particle velocity approaches a saturation value. We verified that the average density of charge distribution is strongly modified due to the presence of a more intense electric field. We also verified that electron-phonon coupling is a fundamental parameter in the description of polaron transport in armchair silicene nanoribbons, since it significantly alters the time in which the charge disperses along the lattice. In addition to contributing intensely to the increase or reduction in the average speed of charge carriers in armchair silicene nanoribbons, system of the great nanoscientific and nanotechnological interest.

SUMMARY
After the isolation of graphene in 2004, scientists quickly showed that it has remarkable properties.
However, as the scientific understanding of graphene has matured, it has become clear that it also has
limitations: for example, graphene does not have a bandgap, making it unsuitable for use in optical -
electronic devices. This motivated explorations of materials in the form of monolayers beyond
graphene, which could incorporate functionality that graphene lacks. Transition metal dichalogenides
(TMDs) are prime candidates in this field. TMDs have a wide variety of properties accessible through
the choice of chalcogen atom, metal atom and atomic configuration (1H, 1T and 1T'). Similar to
graphene, monolayer TMDs can be produced through mechanical exfoliation, however useful
applications will require the development of reliable methods for the synthesis and growth of
monolayers. In this work, I present a theoretical study, through DFT calculations, of the OsSe2
monolayers in the 1T' phase. Among other things, we sought to verify the stability of the material,
which was confirmed when studying the dispersion of phonons. The graph presents the acoustic and
optical branches well defined and with positive values defined which is a strong point in the sense of
verifying the stability of osmium diselenide. We studied the band structure where it was found that
the material has an indirect gap. Another analysis that was carried out is associated with the
thermodynamic properties, where so many quantities enter, it was found that the heat capacity
increases rapidly as the temperature increases in the range from 0 to 200K, reaching the Dulong-Petit
limit around 600K.

In the last decades, magnetic nanoparticles have been the object of increasing scientific
research, due to their unique properties, not observed in bulk materials, which allow their use
in biomedical, environmental, and energy applications. In this context, the objective of this
thesis is to investigate the intraparticle and interparticle characteristics in exchange bias and
training effects observed in dispersions of bimagnetic nanoparticles. Thus, we synthesized
magnetic fluids based on cobalt ferrite nanoparticles, covered with a shell of maghemite, with
sizes of 3.5 nm, 4.2 nm, 4.7 nm, and 6.0 nm. Samples with different states of interaction
between particles were obtained, by varying the volumetric fraction of the colloidal
dispersions φ between 0.10% and 2.65% and also in powder. The structural characterization of
the nanoparticles was performed using X-Ray Diffraction measurements and indicate a spinellike
cubic structure. Transmission Electron Microscopy results confirmed the formation of
approximately spherical particles with low polydispersion. Using Atomic Absorption
Spectroscopy measurements, the stoichiometry and morphochemical characteristics of the
particles were extracted, as well as the volumetric fraction of particles in the dispersions.
Measurements of high field DC magnetization as a function of temperature showed the
existence of an intraparticle interface between a ferrimagnetically ordered core (FI) and a spin
glass disordered shell (SGL). From this type of bimagnetic structure, the phenomenon of
exchange bias arises, when magnetization measurements are performed after cooling with an
applied field (field cooling - FC). In a dilute fluid regime, in which the individual behavior stands
out, it was observed that the particles of smaller diameter and with a higher fraction of spins
frozen in the SGL shell present a more intense exchange bias when compared to particles of
larger diameter and with smaller proportion of disordered spins. Thamm-Hesse analysis
showed, both in concentrated dispersions and powder sample, a demagnetizing contribution,
in which interparticle dipolar interactions predominated, which intensifies when the
interparticle distance decreases. Over the entire range of the investigated cooling field, the
exchange bias is greater when the dipole interactions are more intense. The investigation of
the training effect indicates two populations of disordered spins. Rotatable spins always
reorganize faster than frozen ones and this is enhanced by dipole interactions. However, in
powder regime, interparticle exchange interactions make more difficult to rearrange
disordered surface spins.