Banca de DEFESA: GUILHERME RIBEIRO PORTUGAL

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : GUILHERME RIBEIRO PORTUGAL
DATE: 01/06/2023
TIME: 14:00
LOCAL: Universidade Federal do ABC
TITLE:

NaTaO3-BASED HETEROSTRUCTURES AND THIN FILMS FOR HETEROGENEOUS PHOTOCATALYSIS

PAGES: 184
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUBÁREA: Física da Matéria Condensada
SPECIALTY: Estruturas Eletrônicas e Propriedades Elétricas de Superfícies; Interf. e Partículas
SUMMARY:

Heterogeneous photocatalytic reactions are cited as the most promising solution for current environmental problems. Such reactions allow the reform of polluting gases such as CO₂ and the obtaining of environmentally friendly H₂ , aiming at its later redirection both for storage and use in a particular application. In the present project, ab initio theoretical methods based on the Density Functional Theory (DFT) are used to study how the formation of NaTaO -based heterostructures and thin films may change key properties of this well-known photocatalyst. We have first explored orthorhombic (100) NaTaO₃ monolayers, seeking deep insights of the one-layer limit impact on their physical properties. The monolayer is initially metallic and magnetic, in contrast to its semiconductor non-magnetic bulk. In-plane biaxial strain induces a charge disproportionation state in surface Ta atoms, taking the monolayer to its ground state through structural, electronic, and magnetic transitions. A monoclinic semiconductor non-magnetic monolayer is then obtained. Further hybrid calculations reveals anisotropic absorption peaks in the visible light region. Comparisons with multilayered films unveil that such a behavior is restricted to the monolayered system. The bilayered film, however, is characterized as a transition structure between the monolayer and the stable behavior observed for films with three or more layers. Biaxial compressive strain is able to trigger such transitions. When it comes to heterostructures, the sequential cations replacement in cubic NaNbO₃-NaTaO₃ superlattices results in an unexpected band gap reduction, charge separation, interface related absorption peaks nearer to the visible light spectrum, and a better band-edge alignment with water splitting and CO₂ photocatalytic potentials. Thereafter, calculations show that a monoclinic NaTaO₃-BaBiO₃ superlattice with 24 wt.% BaBiO₃ also displays most of the above-mentioned properties. Besides, a semiconductor-to-metal transition accompanied by the formation of a high-mobility two-dimensional electron gas (2DEG) confined at the interface is achieved should the number of BaBiO₃ layers be increased. Finally, hybrid DFT calculations unveiled that bulk-based scissors operator shifts are indeed capable of accurately correcting the band-edge positioning of different NaTaO₃ orthorhombic structures and can be powerful tools to obtain more accurate electronic properties, provided that the correct physical-mathematical treatment is considered. The results presented so far not only help to better understand the importance of low-dimensional NaTaO₃-based materials for an intrinsic boost of photocatalytic activity but also shed light towards new applications for such few-layer transition-metal-oxides in developing nanoelectronics.

COMMITTEE MEMBERS:
Presidente - Interno ao Programa - 1760410 - JEVERSON TEODORO ARANTES JUNIOR
Membro Titular - Examinador(a) Interno ao Programa - 1671298 - RENATO ALTOBELLI ANTUNES
Membro Titular - Examinador(a) Interno ao Programa - 2218228 - LUANA SUCUPIRA PEDROZA
Membro Titular - Examinador(a) Externo ao Programa - 3944999 - ROMARLY FERNANDES DA COSTA
Membro Titular - Examinador(a) Externo à Instituição - JAMES MORAES DE ALMEIDA - CNPEM
Membro Suplente - Examinador(a) Interno ao Programa - 1671275 - DERVAL DOS SANTOS ROSA
Membro Suplente - Examinador(a) Interno ao Programa - 1282172 - ROBERTO GOMES DE AGUIAR VEIGA
Membro Suplente - Examinador(a) Externo ao Programa - 1765425 - MARCIO GUSTAVO DI VERNIERI CUPPARI
Membro Suplente - Examinador(a) Externo à Instituição - ALVARO DAVID TÓRREZ BAPTISTA - USP