Banca de DEFESA: MÁRIO ROCHA DOS SANTOS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE: MÁRIO ROCHA DOS SANTOS
DATA: 25/04/2023
HORA: 14:00
LOCAL: Presencial - Auditório do Departamento de Fisica/UFPI
TÍTULO: Estudo das propriedades eletrônicas de alótropos de carbono exóticos à base de anéis tetragonais
PALAVRAS-CHAVES: Estruturas exóticas à base de carbono. Nanotubos de carbono. Estrutura eletrônica. Polarização de Spin.
PÁGINAS: 150
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

With the emergence of nanomaterials, vast technological applications
and the great possibility of synthesizing exotic structures, we study the
structural and electronic properties of 2D and 1D carbon-based structures that
include tetragonal rings in their networks. Were studied structures already
reported in the literature by other authors, such as Biphenylene and
Naphthylene-β. Was also proposed a new exotic structure based on the
concatenation of triphenylene blocks. To describe these properties, calculations
of first principles were used within an approach, mainly, of the DFT. We found
for these structures spin-polarized states, AFM states, since with the tetragonal
rings in these structures open a possibility to find such materials, however, only
is possible find these states by DFT from of the organization of the up and down
spins of these structures, at the beginning of the calculation. For Biphenylene
2D structures in the AFM state, were found an zero-gap semiconductor,
different from the NP case, metallic. For 1D structures, such as nanoribbons,
AFM structures were found only for large widths. In the case of nanotubes, they
present semiconductor properties. We found AFM states for the 2D structure of
Naphthylene-β with properties of a semiconductor material, presenting a gap of
0.38 eV in the GGA functional and 0.69 eV in the HSE functional. For
nanotubes, we found metallic structures in the NP state and semiconductors in
the AFMstate. For this family, we used a ZF approach to better understand the
electronic properties of nanotubes. Applying electric field in these nanotubes,
we observed a gap closure of the AFM structures. We also observed greater
radial deformation for larger diameter nanotubes. Finally, for family of the
Triphenylene, the electronic properties of the AFM and NP structures are similar
to the 2D structures of Naphthylene-β, presenting a gap of 0.26 in the AFM
state. The triphenylene nanoribbons narrow, in the NP case, have a
semiconductor character, with a gap of up to 1.06 eV, due quantum
confinement effects. Ribbons with widths greater than 30.80 Å become metallic
as their 2D structure. The electronic properties of nanoribbons do not depend
on chirality. For nanotubes, we found similar behavior. For AFM case, the tapes
present a gap varying around value of the 2D system in the spin-polarized
configuration. For all systems, the AFM states have lower energy.

MEMBROS DA BANCA:
Interno - 1623821 - ACRISIO LINS DE AGUIAR
Externo ao Programa - 541.512.873-53 - ANTONIO GOMES DE SOUZA FILHO - UFC
Presidente - 1548848 - EDUARDO COSTA GIRAO
Interno - 2643659 - IRISMAR GONCALVES DA PAZ
Externo ao Programa - 659.871.100-25 - JORDAN DEL NERO - UFPA
Interno - 423297 - JOSE PIMENTEL DE LIMA
Interno - 1250015 - PALOMA VIEIRA DA SILVA