Banca de DEFESA: CYNTHIA MARINA RIVALDO GOMEZ
Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.DISCENTE : CYNTHIA MARINA RIVALDO GOMEZ
DATA : 31/10/2019
HORA: 14:00
LOCAL: santo andre
TÍTULO:
Synthesis and Physical Properties of Halide Quantum Dots and local Nano-heterostructures on Semiconducting Microtubes
PÁGINAS: 100
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
ESPECIALIDADE: Prop. Óticas e Espectrosc. da Mat. Condens; Outras Inter. da Mat. com Rad. e Part.
RESUMO:
The study of novel strategy for fabrication and physical properties of nano and microstructures is very important for both fundamental science and technological applications. Semiconducting nano-heterostructured systems based on transition metal oxides and halide perovskites have attracted great interest due to their unique physical properties and potential applications. In this work, we have synthesized and studied the physical properties of both halide perovskite CsPbX3(X=Br, I, and Cl) quantum dots (QDs) and micro/nanostructures (microtube and nanowires) of TiO2and ZnO. In addition, we have combined both families of semiconductors by decorating TiO2microtube with quantum dots forming local nano-heterostructures.
First, the synthesis of perovskite QDs for the three-halide ions was carried out viahot injection method and supersaturated recrystallization process. HRTEM images show a cubic shape morphology of CsPbBr3NCs with a size around 12 nm and a crystalline structure with an interplanar spacing of 2.45 Å corresponding to the (012) crystal plane. Optical property characterization reveals the presence of two band gap energies corresponding to CsPbBr3(2.34 eV)and rutile-TiO2(2.97 eV).
On the other hand, tubular micro/nanostructures of TiO2and ZnO with different designs (microtubes, nanowires, and core-shell structures) have been obtained. Hollow microstructures were obtained by using thermal oxidation process with the presence of electrical current. We have reported a new route to fabricate hollow materials. The synthesis route consists ina combination of thermal oxidation process, application of electric current, and structural phase transition. Furthermore, our resultsrevealed an important physical phenomenon based ona colossal mass transfer by lattice, grain, and surface diffusion of Ti ions forming TiO2microtubes. The structural phase transition in the metallic Ti occurring at high temperature boosts the mobility of Ti ions creating vacanciesto the system. The electric current would drive these vacancies to inward direction and condensing into voids. In addition to the TiO2 system, other hierarchical ZnO nanostructures were studied by using the same approach. Synthesis of hierarchically structured nanowires on and nanosticks in ZnO microtubes is obtained. They were produced by the thermal oxidation method at temperatures above the melting point of the metallic Zn (TF= 420 ° C). Throughout the synthesis process, in situmeasurements of electrical resistivity as a function of temperature were performed for both systems. We suggest a mechanism for the formation of these micro /nanostructures combining ionic diffusion and stress-induced migration of Zn ions due to compressive stress.
Finally, we have produced and studied the physical properties of local nano-heterostructures by coupling the perovskite CsPbBr3quantum dots on the surface of our semiconducting TiO2microtube. We have observed a coalescence process when the QDs are on the surface of the microtube which increases to around 40 nm. The red shift optical properties confirm the increasing in size. Time-resolved photoluminescence decay measurements suggest difference in charge dynamics when comparing both samples, revealing the interaction of CsPbBr3QDs with the microtube surface, which confirms the formation of local heterostructures. The TiO2 microtube decorated with quantum dots exhibits a large decreasing in electrical resistivity reaching almost 95% when compared with the pristine TiO2microtube.This significant increasing in the electrical conductivity is associated with charge transfer from perovskite nanocrystals into the semiconductor microtube which can be used to fine tune in its electronic properties.
MEMBROS DA BANCA:
Presidente - Interno ao Programa - 2605463 - JOSE ANTONIO SOUZA
Membro Titular - Examinador(a) Externo ao Programa - 1707133 - ISELI LOURENCO NANTES CARDOSO
Membro Titular - Examinador(a) Externo ao Programa - 1552290 - ANDRE SANTAROSA FERLAUTO
Membro Titular - Examinador(a) Externo à Instituição - MURILO SANTHIAGO
Membro Titular - Examinador(a) Externo à Instituição - VALMIR A. CHITTA - USP
Membro Suplente - Examinador(a) Interno ao Programa - 1544408 - GUSTAVO MARTINI DALPIAN
Membro Suplente - Examinador(a) Externo ao Programa - 1545089 - DANIEL ZANETTI DE FLORIO
Membro Suplente - Examinador(a) Externo ao Programa - 1671292 - SYDNEY FERREIRA SANTOS