Doutorado em Física

URI Permanente para esta coleção

http://repositorio.ufes.br/handle/10/17493

Nível: Doutorado
Ano de início: 2003
Conceito atual na CAPES: 4
Ato normativo: Parecer CES/CNE nº 487/2018, homologado pela Port. MEC 609, publicado no DOU em 18/03/2019.
Periodicidade de seleção: Semestral
Área(s) de concentração: Física
Url do curso: https://fisica.ufes.br/pt-br/pos-graduacao/PPGFis/detalhes-do-curso?id=1509

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Bases gaussianas geradas com os métodos Monte Carlo Simulated Annealing e Particle Swarm Optimization.
(Universidade Federal do Espírito Santo, 2017-10-03) Reis, Thiago Mello dos; Alfonso, Jorge Luis Gonzalez; Caetano, Edson Passamani; Continentino, Mucio Amado; Nascimento, Valberto Pedruzzi; Macedo, Waldemar Augusto de Almeida
The Monte Carlo Simulated Annealing and Particle Swarm Optimization methods were used to generate adapted Gaussian basis set for the atoms from H to Ar, in the ground state. A study about the e ciency and the reliability of each method was performed. In order to check the reliability of the proposed methods, we perform an speci c study considering a training set of 15 atoms, namely: N, Mg, Al, Cl, T i, N i, Br, Sr, Ru, P d, Sb, Cs, Ir, Tl, At. First of all, the Improved Generator Coordinate Hartree-Fock Method was applied to generate adapted basis which was used as start point to generate new Gaussian basis sets. After that, the Monte Carlo Simulated Annealing and Particle Swarm Optimization methods were developed from parallel studies, however following the same procedure so as we could have the possibility to compare them. Previously applying of the developed methods we perform some calibrations in order to de ne the values of the parameters of the algorithms; we perform studies about annealing schedules (for the Monte Carlo Simulated Annealing method), the total of swarm's particle (for the Particle Swarm Optimization method), and the total of steps for each algorithm. After the calibration procedure, both methods were applied, with the variational principle, to the Hartree-Fock wave function to give us the fully optimized Gaussian basis sets. Next, the basis sets were contracted by considering the lowest total energy loss, prioritizing the contraction of the most internal exponents. The last two steps of our procedure were the addition of polarized and di use functions, respectively. These procedures were performed by using the methods which we developed in this work through calculations to the MP2 level. The basis sets that have been generated in this work were used in some atomic and molecular calculations; we compare such results with relevant results from literature. We veri ed that, if we consider the same computational e ciency for both Monte Carlo Simulated Annealing and Particle Swarm Optimization methods, there is a vi small di erence between them as regards the accuracy, so that by using the Monte Carlo Simulated Annealing method we obtain best results. When we compare the results of this work with those from literature we note similar results for the properties that were studied, however the proposed methods in this work are more e cient, and we can de ne a single total numbers of steps for the algorithms even though we are treating with di erent atomic systems. In addition, we verify that the proposed methods in this work are more accurate than other similar methods presented in the literature, in the task of nding the global minima of the uncontracted basis sets to HF level of theory. It will be necessary to perform additional studies to check the real relationship between the accuracy of the methods. We do not verify the in uence of several parameters of the Particle Swarm Optimization algorithm in this work. The fact that the developed methods in this work have been constructed through Double Zeta basis does not prevent them to be used for larger basis sets, the two methods are able to be applied to generate Gaussian basis sets in the atomic environment for Gaussian basis sets with di erent qualities
Espectroscopia de RMN no estado sólido aplicada em estudos de biocarvões e hidrocarvões contendo fósforo
(Universidade Federal do Espírito Santo, 2023-12-11) Santoro, Mariana Coelho; Freitas, Jair Carlos Checon de; https://orcid.org/0000000244742474; http://lattes.cnpq.br/3074997830683878; https://orcid.org/0000000214072203; http://lattes.cnpq.br/8895787167310666; Emmerich, Francisco Guilherme; http://lattes.cnpq.br/0914292768585767; Silva, André Romero da; https://orcid.org/0000000214976093; http://lattes.cnpq.br/3079774974302460; Alfonso, Jorge Luis Gonzalez; http://lattes.cnpq.br/9030024304752445; Trubetskaya, Anna
This work deals with the preparation and characterization of different biochars and hydrochars obtained through slow pyrolysis and hydrothermal carbonization (HTC) of organic precursors, aiming applications in soils as sources of phosphorus (P). In the first part of the work, a set of hydrochar samples obtained from the HTC of poultry litter, synthesized at different temperatures, residence times and initial pH, were studied. In a second part, hydrochar samples were synthesized through the HTC of microalgae cultivated in a wastewater treatment plant, and the effects of different temperatures, residence times and MgO addition to the raw material were studied, focusing on the speciation of P. The main tools used to understand the chemical nature and the modifications that occurred during the hydrothermal process of these two sets of samples were the standard protocol of measurements for fractionation of P species and solid-state 13C and 31P nuclear magnetic resonance (NMR) spectroscopy. The 13C NMR spectra of the hydrochars showed that the structural changes of the precursors during the HTC depend mainly on the heat treatment temperature and that, in the range of investigated temperatures, the hydrochars obtained are composed mostly of aromatic and alkyl groups, regardless of the residence time. In addition, the results showed that HTC altered the physical state and solubility of different P species, with the increase in temperature and residence times causing an increase in the amount of total phosphorus in the hydrochars. The addition of MgO in the hydrothermal treatment of microalgae has proven to be a viable way to significantly reduce losses and increase the total and water-soluble amounts of phosphorus in the hydrochars. In another branch of the work, biochar samples obtained from two types of lignocellulosic residues - coffee husk and coconut shells - were studied. The samples were physically activated with steam and modified with Ca or Mg to be used in phosphate adsorption experiments from aqueous solutions of ammonium phosphate or human urine as sources of P. Solid-state 31P NMR was used in conjunction with thermogravimetry and X-ray diffraction to characterize these biochars. The Mg-modified samples showed adsorption of 96% of the phosphates present in human urine, with precipitation of struvite and other disordered Mg phosphates. Thus, the chemical modification of biochars with Mg compounds proved to be a viable route to produce phosphate adsorbents that can be used as slow-release phosphate fertilizers.
Espectroscopia e relaxometria de RMN aplicadas em estudos envolvendo a síntese de biodiesel por catálise heterogênea
(Universidade Federal do Espírito Santo, 2023-03-28) Fernandez, Joycel Verde; Alfonso, Jorge Luis Gonzalez; https://orcid.org/0000-0001-5841-8731; http://lattes.cnpq.br/9030024304752445; https://orcid.org/000000022465811X; http://lattes.cnpq.br/9965613684540239; Novotny, Etelvino Henrique; https://orcid.org/0000-0001-9575-1779; http://lattes.cnpq.br/3604285557454730; Nascimento, Valberto Pedruzzi; https://orcid.org/0000000295435335; http://lattes.cnpq.br/9908042258225541; Santos, Reginaldo Bezerra dos; https://orcid.org/0000-0003-2966-7231; http://lattes.cnpq.br/6265396050660132; Lopes, Thierry Ramos
This work describes the use of NMR spectroscopy and relaxometry methods in research involving the synthesis of biodiesel from oils of vegetable origin. In the first part of the work, solid state 13C and 31P NMR methods were used to characterize biochars and ash from coffee husk, which were used as heterogeneous catalysts to produce biodiesel from the transesterification reaction between methanol and. commercial and fried soybeans oils. The results showed the presence of different inorganic compounds, mostly phases containing Ca and K, several carbonates, and specifically the compound K2Ca(CO3)2, which was identified in all catalysts. Biodiesel conversions obtained using the biochars samples had values above 66 % and for the activated biochar sample (PC700_CA) the value was 74 %. However, ash catalysts had conversions to biodiesel above 90 %. This effect was related to the high concentrations of K and Ca salts (fairchildite and buetschliite) in the ashes. Reuse tests conducted with the ash catalyst showed a significant reduction in efficiency after the second cycle, due to the partial removal of active phases containing mainly K. Calibration methods, using DTG and NMR-TD techniques, were constructed to quantify the biodiesel concentrations obtained by the catalysts. The efficiencies of the calibration methods showed better performances for the ash catalysts. In conclusion, coffee husk represents a cheap and viable source with regard to the preservation of the environment for the production of biodiesel via heterogeneous catalysis, without the need for chemical modifications. Such methods proved to be efficient for the quantification of biodiesel concentrations in liquid solutions, allowing the detection and quantification of contamination or adulteration of vegetable oil in biodiesel samples. These methods are recommended for use with other sources of oils.
Estudo teórico de heteroestruturas baseadas em materiais bidimensionais
(Universidade Federal do Espírito Santo, 2018-10-26) Souza, Everson dos Santos; Scopel, Wanderlã Luis; Scopel, Wanderlã Luis; Amorim, Rodrigo Garcia; Souza, Fábio Arthur Leão de Souza; Canal Neto, Antônio; Alfonso, Jorge Luis Gonzalez; Caetano, Edson Passamani
This thesis presents a theoretical investigation of two heterostructures based on 2D materials: (i) substitutionally cobalt-doped graphene bilayer (Co/GBL) on the Cu(111) surface [Co/GBL/Cu(111)] and (ii) a graphene-MoSe2 in-plane lateral heterostructure. The properties of these systems were studied through simulations of X-ray Absorption NearEdge Structure (XANES) spectroscopy and/or electronic structure methods based on Density Functional Theory (DFT). Our results indicate a magnetic switching phenomenon in the Co/GBL/Cu(111) system, that is, the capability of switch on and off the magnetization of the Co-doped graphene bilayer on Cu(111). This phenomenon is based on control of Co/GBL Cu(111) electronic charge transfer by an external electric field; which adjust the electronic occupation of the Co-3dz 2 and C-2pz orbitals near the Fermi level and, as a consequence, the magnetic properties of Co-doped graphene bilayer. In the graphene-MoSe2 system, based on energetic stability criteria for different structural models, we found that zigzag and Klein edges of graphene can serve as a nucleation site for the formation of energetically stable graphene-MoSe2 interfaces, where different structural morphologies are possible. For the energetically more likely interface geometries, were carried out additional characterizations of electronic and structural properties through simulations of XANES spectroscopy at the C K-edge. The analysis of the absorption spectra indicated the feasibility of identifying different interface geometries in the graphene-MoSe2 hybrid system from XANES spectroscopy measurements. The results also revealed that the local electronic and magnetic properties depend on the interface atomic structure. In particular, we found half-metallicity characteristic (conduction in only one of the two spin channels) at certain interface geometries, which has great potential for spintronics applications.
Filmes finos supercondutores de Nb e híbridos Nb/[Co/Pd]: nanoestruturação e caracterização estrutural, magnética e transporte elétrico.
(Universidade Federal do Espírito Santo, 2017-03-10) Freitas, Tales Costa de; Alfonso, Jorge Luis Gonzalez; Caetano, Edson Passamani; Continentino, Mucio Amado; Nascimento, Valberto Pedruzzi; Macedo, Waldemar Augusto de Almeida
This thesis deals with the studies of structural, magnetic and electric transport properties of Nb thin films grown directly on Si (100) substrates, by Magnetron Sputtering, and under different substrate temperatures TS and Nb thicknesses tNb and also in their hybrid S/F superconductor/ferromagnetic systems such as Si(100)/Nb(tNb nm)/Pd(1.1 nm)/[Co(0.3 nm)Pd(1.1 nm)]12 and Si(100)/Nb(100 nm)/Pd(tP d nm)/[Co(0.3 nm)Pd(3 nm)]12, where the tNb value is of 15, 20, 50 and 100 nm, and Pd thickness tP d is of 1, 3 ,5 e 10 nm. In the case of the Nb thin films, the main results show: (i) the dependence of the critical density current JC(T) with the substrate temperature TS, where it was demonstrated the optimum value for the TS (responsible for the highest JC value). The JC(T) values were estimated by mean of magnetic hysteresis loops, assuming the granular character of the Nb films experimentally observed by atomic force microscopy; (ii) the influence of the Nb thickness tNb on the granular features of Nb films; a characteristic that determines the significant reduction of the superconducting critical temperature TC, due to the finite grain size effect; (iii) the semiconducting and negative magnetorresistance behaviors of Nb films around the superconducting transition; properties that were determined, in a small temperature range, by measuring the electrical resistance of granular Nb thinner films (20 e 50 nm); (iv) the dependence of µ0HC2(T) for the 100 nm thick Nb films that present 3D-like behavior (except for their lower TC values), according to empirical models applied to analyze the experimental data of this work. In the case of the hybrid S/F system, the main results demonstrate (I) that the S/F system behaves within an intermediate stage between 2D-3D transition; (II) the influence of proximity effect of the ferromagnetic F material on the Nb superconducting properties, which causes a reduction and “oscillation” of the critical temperature TC. Empirical models, reported in the literature, help to establish parameter of control of the action of external agents on the dynamic orientation of the Co/Pd multilayers and the nucleation of Nb superconductor films, establishing, for example, intensities and regions (temperature and magnetic field ranges) for technological applications of the Si/Nb/Pd/[Co/Pd] heterostructures here studied. The films, here studied, were prepared more than one time and their results are reasonable reproducible, indicating that the discussed properties are related to the system and do not to specific samples.
Investigação de materiais carbonosos e lignocelulósicos por ressonância magnética nuclear de 13C no estado sólido.
(Universidade Federal do Espírito Santo, 2019-12-03) Cipriano, Daniel Fernandes; Freitas, Jair Carlos Checon de; https://orcid.org/0000000244742474; http://lattes.cnpq.br/3074997830683878; https://orcid.org/; http://lattes.cnpq.br/; Bonagamba, Tito Jose; https://orcid.org/; http://lattes.cnpq.br/; Filgueiras, Paulo Roberto; https://orcid.org/0000000326171601; http://lattes.cnpq.br/1907915547207861; Romao, Wanderson; https://orcid.org/0000000222546683; http://lattes.cnpq.br/9121022613112821; Alfonso, Jorge Luis Gonzalez; http://lattes.cnpq.br/9030024304752445
Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used in investigations of different biomass materials from Brazil, as well as in studies of the structural properties of carbon materials such as chars derived from phenolic resin, graphite
O Modelo Anisotrópico Ginzburg-Landau e a Determinação de Campos Magnéticos Dispersos em Nanoestruturas Híbridas Supercondutoras-Ferromagnéticas.
(Universidade Federal do Espírito Santo, 2020-11-26) Paschoa, Anderson dos Santos; Caetano, Edson Passamani; https://orcid.org/0000000213102749; http://lattes.cnpq.br/9401385573887851; https://orcid.org/; http://lattes.cnpq.br/; Continentino, Mucio Amado; https://orcid.org/; http://lattes.cnpq.br/; Nascimento, Valberto Pedruzzi; https://orcid.org/0000000295435335; http://lattes.cnpq.br/9908042258225541; Passos, Carlos Augusto Cardoso; https://orcid.org/; http://lattes.cnpq.br/2528679879816545; Candela, Dalber Ruben Sanchez; Alfonso, Jorge Luis Gonzalez; http://lattes.cnpq.br/9030024304752445; Rodriguez, Victor Antonio Pena
In this doctorate thesis, the Ginzburg-Landau anisotropic model was experimentally tested. The physical parameter Δ𝑻𝑪=𝑻𝑪
Relação entre o transporte elétrico e a estrutura de poros no sistema YBa2Cu3O7
(Universidade Federal do Espírito Santo, 2013-01-29) Piumbini, Cleiton Kenup; Alfonso, Jorge Luis Gonzalez; Cunha, Alfredo Gonçalves; Rodrigues Junior, Durval; Ferreira, Letície Mendonça; Freitas, Jair Carlos Checon; Caetano, Edson Passamani
The principal objective of this thesis is the study of the relationship between the transport critical current density and the pore structure in YBa2Cu3O7-y bulk samples. In order to perform the experimental work samples of two different systems were prepared. The first sintered system was (YBa2Cu3O7-y)1-x(Sb2O3)xwhile the second one was obtained through the use of different sintering conditions. The samples were characterized through X-ray, magnetic and transport critical current density measurements, besides N2 sorption analysis. In both systems, the doping and the different sintering conditions modified the pore structure of the samples. For the (YBa2Cu3O7-y)1-x(Sb2O3)x system the transport critical current density did not depend on the pore structure, while in the second system this parameter showed a strong correlation with the principal features of the pore structure. In order to better understand the correlation between the electric transport and the structural properties of the specimens, it was developed a computational simulation aiming to incorporate the principal elements of the granular structure of ceramic samples. To this end, the granular simulated granular structure was obtained by a tessellation of the space through the Voronoi technique. The results of computer simulations show that it is possible to capture the dependence of the critical current density of transport with the relevant quantities to different systems studied in this thesis. Finally, this work shows the importance of controlling the pore structure in order to optimize the electrical properties of ceramic superconductors cuprates, which is transcendent to possible technological applications of these systems.
Simulações atomísticas e previsão de espectros de RMN em materiais carbonosos
(Universidade Federal do Espírito Santo, 2018-07-13) Ambrozio, Alan Johnny Romanel; Scopel, Wanderlã Luis; Scopel, Wanderlã Luis; Paz, Wendel Silva; Freitas, Jair Carlos Checon de; Leitão, Alexandre Amaral; Gonçalves, Arlan da Silva; Mota, Vinícius Cândido; Alfonso, Jorge Luis Gonzalez
In this work, the 13C NMR spectral parameters of both ordered and disordered carbon materials were calculated using computational simulations. The 13C NMR shielding in a single graphene sheet was calculated using density functional theory (DFT) via the gauge-including projector augmented plane wave (GIPAW) method. After performing convergence tests involving changes of k-sampling and supercell size, the calculations were extended to graphene-based systems, including graphene bilayer and stacked graphene sheets, finally leading to hexagonal graphite. Regarding the disordered carbon materials, the 13C NMR chemical shifts corresponding to different sites in atomistic models of amorphous hydrogenated carbons were also computed at different H contents by employing molecular dynamics and firstprinciples methods. The models were validated by the pair distribution functions and further bonding analyses were carried out to determine the amounts of sp3 and sp2 carbons in the structures. Specifically, the obtained results allowed the distinction of the chemical shifts associated with different types of carbon sites, with different hybridization states and bonded or not to a hydrogen atom. The calculated results showed good agreement with experimental 13C NMR spectra of different types of carbon materials, evidencing the power of the DFT calculations to predict NMR parameters in graphene-based nanocarbons and to identify local structural features of disordered carbon materials.
Utilização de RMN no estado sólido em uma abordagem multinuclear para estudo de materiais carbonosos porosos.
(Universidade Federal do Espírito Santo, 2017-09-06) Lopes, Thierry Ramos; Freitas, Jair Carlos Checon de; Scopel, Wanderlã Luis; Bueno, Thiago Eduardo Pedreira; Alfonso, Jorge Luis Gonzalez; Bonagamba Tito José; Gontijo, Leonardo Cabral
This work is concerned with a study of activated carbons prepared by physical and chemical activation, using solid-state nuclear magnetic resonance (NMR) spectroscopy in a multinuclear approach. The activated carbons were obtained starting from the endocarp of babassu coconut (EB), either by physical activation (with steam named as EBF samples) or by chemical activation (using H3P O4 named as EBP samples). The activated carbons exhibited high speci c surface area, with values depending on the experimental conditions used in each synthesis. The 1H NMR spectra of the EBF samples showed two major peaks with chemical shifts changing as a function of the activation temperature. The broader peak was associated with 1H nuclei in aromatic groups, the other being associated with adsorbed water. In order to better understand these results, hydrated samples of milled graphites were also studied by 1H NMR, allowing the identi cation of a signi cant variation of the chemical shift of the peak due to adsorbed water as a function of the increase in the milling time (which caused structural changes in the milled graphites). The chemical nature of the phosphorus-containing species in the EBP samples was studied by 1H, 13C and 31P solid-state NMR spectroscopy, including 2D 1H -31 P correlation experiments, which allowed the detection of the formation of di erent phosphorus compounds (mostly containing phosphate groups) embedded into the porous carbon network. Due to the natural occurrence of silicon compounds in the endocarp of babassu coconut, the chemical activation with H3P O4 was found to produce silicon pyrophosphate nanocrystals. Nanocomposites containing nanostructured Al compounds were obtained by impregnation of EBF and EBP samples with Al(NO3)9H2O, followed by heat treatments at di erent temperatures; 27Al NMR spectra were used to analyze the coordination type of the Al3+ cations present in each sample, which was changed depending on the heat treatment temperature.

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