Synthesis of the Bi2Se3 topological insulator using the TBDTA isochoric analyzer

Name: Messias Bicalho Cevolani
Type: PhD thesis
Publication date: 30/03/2022
Advisor:

Name Rolesort descending
Alfredo Gonçalves Cunha Advisor *

Examining board:

Name Rolesort descending
Alfredo Gonçalves Cunha Advisor *
Jonder Morais External Examiner *
Cleocir José Dalmaschio External Examiner *
Vagner Eustáquio de Carvalho External Examiner *
Thiago Eduardo Pedreira Bueno External Examiner *
Wendel Silva Paz Internal Examiner *
Wanderlã Luis Scopel Internal Examiner *

Summary: Several studies were carried out on the constant volume synthesis of the topological insulator Bi2Se3, using the TBDTA device, and it was developed by improvements on the Thermobarometric Analyser (TBA). This device performs monitoring of pressure, absolute and differential temperature during experiments of synthesis, decomposition, and evaporation of substances, at constant volume processes. The monitoring of thermodynamic parameters during the synthesis made it possible to verify the influence of the element selenium quantity inside the reaction ampoule on the crystalline quality and on the Bi2Se3 band structure properties, including the emergence of surface topological states verified from ARPES measurements. The observations made allowed the elaboration of a synthesis route, with four heat treatments, to promote the homogenization and crystallization of the sample. The selenium evaporation was also studied to compare the pure selenium and the Bi2Se3 compound equilibrium pressures. For pure selenium, it was verified that the liquid/gas transition is not like an ideal gas. Initially, the liquid selenium evaporates forming gaseous molecules with several selenium atoms, then decomposition into smaller molecules occur as the temperature increases. This indicates that the number of gaseous particles increases with temperature. Bi2Se3 samples were produced with metallic doping. ARPES measurements showed the emergence of surface topological states and that 1% of aluminum downshifts the Fermi level towards the valence band.

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