Tesis
Estudo teórico das propriedades mecânicas e eletrônicas de sistemas bidimensionais do grupo IV sob deformações
Fecha
2018-08-02Autor
Vargas, Douglas Willian Duarte de
Institución
Resumen
In this work we study two dimensional materials compounds of group IV elements such as
graphene, silicene and germanene under biaxial and uniaxial strain. The aim of this study is
understand the mechanical properties of these materials and how the strain modify their electronic
properties. Using the density functional theory as implemented in the Quantum ESPRESSO (QE)
package, we determined the Lamé coefficients and using its coefficients we calculated the elastic
constants C11 and C12. The Young modulus in two dimension and the Poisson ratio was obtained
via uniaxial strain in two directions: armchair and zigzag. Using the Voigt approximattion we
estimated the Bulk modulus and the Shear modulus. All of those values are in good agreement
with the literature where graphene is characterized as a stiffness material. We analyzed the
stress-strain relation for all of three materials in the elastic region, where was observed an
asymmetric behavior in ultimate tensile strength, where the armchair direction is the more stiff.
The electronic properties was analyzed under uniaxial strain in three regions: linear (" = 0; 03),
harmonic (" = 0; 09), and near to ultimate tensile strength (" = 0; 15). Graphene under strain
does not show significant changes in its electronic properties. On the other hand, silicene and
germanene show the autodopping behavior, where electrons (tipe n conductivity) or/and holes
(tipe p conductivity) appear near to the Fermi level, in the vicinity of the Dirac cone greater
than 9%. This way, we showed that strain can control the conductivity properties of silicene and
germanene.