Ab initio study by DFT+U of Sn(1-x)SeAg(x), SnSe(1-x)Ag(x) and ZnX (X = O, S, Se, Te) monolayers

Autor: Monteiro, Joziano Rony de Miranda, https://orcid.org/0000-0003-0786-8235
Přispěvatelé: Frota, Hidembergue Ordozgoith da, Rego, Celso Ricardo Caldeira, Ghosh, Angsula, Cavalcante, Cicero Augusto Mota, Gusm??o, Marta Silva dos Santos
Jazyk: portugalština
Rok vydání: 2021
Předmět:
Zdroj: Biblioteca Digital de Teses e Dissertações da UFAM
Universidade Federal do Amazonas (UFAM)
instacron:UFAM
Popis: Submitted by Joziano Monteiro (joziano.miranda@ufam.edu.br) on 2021-04-06T23:42:19Z No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_Joziano_Rony_de_Miranda_Monteiro.pdf: 101894965 bytes, checksum: 2d7c3d7a2b9847bd71f22fcdc1bed2e2 (MD5) CartaEncaminhamentoAutodep??sito.pdf: 144875 bytes, checksum: 9223ba390b976b1f0b21eb2ca02b6387 (MD5) ata.pdf: 478647 bytes, checksum: 772530c2165ceb61d94ebd67df70c3e7 (MD5) Approved for entry into archive by PPGFIS F??sica (ppgfisufam.sec@gmail.com) on 2021-04-09T15:50:55Z (GMT) No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_Joziano_Rony_de_Miranda_Monteiro.pdf: 101894965 bytes, checksum: 2d7c3d7a2b9847bd71f22fcdc1bed2e2 (MD5) CartaEncaminhamentoAutodep??sito.pdf: 144875 bytes, checksum: 9223ba390b976b1f0b21eb2ca02b6387 (MD5) ata.pdf: 478647 bytes, checksum: 772530c2165ceb61d94ebd67df70c3e7 (MD5) Approved for entry into archive by Divis??o de Documenta????o/BC Biblioteca Central (ddbc@ufam.edu.br) on 2021-04-09T16:55:38Z (GMT) No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_Joziano_Rony_de_Miranda_Monteiro.pdf: 101894965 bytes, checksum: 2d7c3d7a2b9847bd71f22fcdc1bed2e2 (MD5) CartaEncaminhamentoAutodep??sito.pdf: 144875 bytes, checksum: 9223ba390b976b1f0b21eb2ca02b6387 (MD5) ata.pdf: 478647 bytes, checksum: 772530c2165ceb61d94ebd67df70c3e7 (MD5) Made available in DSpace on 2021-04-09T16:55:52Z (GMT). No. of bitstreams: 4 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_Joziano_Rony_de_Miranda_Monteiro.pdf: 101894965 bytes, checksum: 2d7c3d7a2b9847bd71f22fcdc1bed2e2 (MD5) CartaEncaminhamentoAutodep??sito.pdf: 144875 bytes, checksum: 9223ba390b976b1f0b21eb2ca02b6387 (MD5) ata.pdf: 478647 bytes, checksum: 772530c2165ceb61d94ebd67df70c3e7 (MD5) Previous issue date: 2021-02-26 CAPES - Coordena????o de Aperfei??oamento de Pessoal de N??vel Superior The present thesis addresses two types of theoretical studies for two-dimensional crystalline systems. Initially, the Hamiltonian model approach has been used to study a system composed of graphene deposited on a hexagonal lattice substrate taking into account the Hubbard interaction. The prinicipal objective is to understand the mechanisms that could induce a gap in the dispersion relation of the system. A comparison between the results of the above model and the ab initio approach, via Density Functional Theory - DFT, shows a good agreement, inspite od having different philosophies. The gap in this system could be induced by the inhomogeneity of Hubbard's interaction in the substrate sublattices or by the strong hybridization between the monolayers. The second part of our work involves the use ab initio approach via DFT with Hubbard's interaction, a method known as DFT+U to study the electronic and thermoelectric properties of SnSe monolayer and its derivatives. Pristine structure (M-SnSe) along with that modified by vacancy (M-SnSe(1-x), M-Sn(1-x)Se) and also doped by substitution of Ag atoms (M-SnSe(1-x)Ag(x), M-Sn(1-x)SeAg(x)) were considered. In this work, x corresponds to the proportions of 25% and 12.5%. The effects of vacancies and Ag doping on the thermoelectric performance of the materials are considered. The results show that the Sn[Se] vacancies and the substitutional doping by Ag, reduce the thermoelectric performance when compared to that of the pure structure. Sn vacancies were more detrimental to thermoelectric performance than Se vacancies. Using the same method, the elastic and dynamic stability, as well as the electronic, thermoelectric and optical properties of the ZnX monolayers (X = O, S, Se, Te) are also studied. The results show that the structures are dynamically stable, have a direct gap at the Gamma point symmetry. They have low lattice thermal conductivity and their thermoelectric performance is approximately 1. ZnO and ZnS are transparent to visible light where ZnSe and ZnTe have orange and blue colors, respectively. The observed shift in the energy from the absorption threshold to the ultraviolet region governed by selection rules appears when the polarization is perpendicular to the plane of the monolayers. The absorption spectra are displaced to the ultraviolet region by 1.96 eV (ZnO), 1.46 eV (ZnS), 1.51 eV (ZnSe) and 1.88 eV (ZnTe). Sistemas cristalinos bidimensionais s??o estudados na presente tese. Inicialmente, utiliza-se a abordagem do Hamiltoniano modelo para estudar um sistema composto por grafeno depositado sobre um substrato de rede hexagonal, levando em considera????o a intera????o de Hubbard. Neste estudo, busca-se compreender, do ponto de vista da modelagem proposta, os mecanismos que podem induzir a uma abertura de gap na rela????o de dispers??o do sistema. Os resultados mostraram que a abertura de gap pode ser induzida pela n??o homogeneidade da intera????o de Hubbard nas sub-redes do substrato ou pela forte hibridiza????o entre as monocamadas. As estruturas de bandas obtidas atrav??s do modelo e as obtidas atrav??s da abordagem ab initio, via Teoria do Funcional de Densidade, mostram-se estar, qualitativamente, em bom acordo, apesar de as duas abordagens terem filosofias distintas. Na sequ??ncia, utiliza-se a abordagem ab initio, via Teoria do Funcional de Densidade, levando em conta a intera????o de Hubbard, m??todo conhecido como DFT+U, para estudar as propriedades eletr??nicas e termoel??tricas das monocamadas de SnSe com estrutura pura (M-SnSe), modificada por vac??ncia (M-SnSe(1-x), M-Sn(1-x)Se) e dopada por substitui????o por ??tomos de Ag (M-SnSe(1-x)Ag(x), M-Sn(1-x)SeAg(x)), onde x corresponde as propor????es de 25% e 12,5%, afim de investigar os efeitos das vac??ncias e dopagem por Ag no desempenho termoel??trico do material. Os resultados mostram que as vac??ncias de Sn[Se] e a dopagem substitucional por Ag, nas propor????es estudadas, reduzem o desempenho termoel??trico quando comparado a estrutura pura. As vac??ncias de Sn se mostraram mais prejudiciais ao desempenho termoel??trico do que as vac??ncias de Se. Utilizando o mesmo m??todo, estuda-se a estabilidade el??stica e din??mica, bem como das propriedades eletr??nicas, termoel??tricas e ??ticas das monocamadas ZnX(X=O, S, Se, Te). Os resultados mostram que as estruturas s??o dinamicamente est??veis, possuem gap direto no ponto de simetria Gama, t??m baixa condutividade t??rmica da rede, seu desempenho termoel??trico ?? de aproximadamente 1, o ZnO e ZnS s??o transparentes ?? luz vis??vel, o ZnSe tem cor laranja e o ZnTe cor azul. Existe um deslocamento, regido por regras de sele????o, da energia do limiar de absor????o para o ultravioleta, que aparece quando a polariza????o ?? perpendicular ao plano das monocamadas, onde os espectros de absor????o est??o deslocados para o ultravioleta de: 1,96 eV (ZnO), 1,46 eV (ZnS), 1,51 eV (ZnSe) e 1,88 eV (ZnTe).
Databáze: OpenAIRE
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