Estudo por primeiros princípios de propriedades eletrônicas e estruturais de talco e calcogenetos de molibdênio

Abstract

In this work, we performed first-principles calculations based on the Density Functional Theory to investigate properties of two-dimensional (2D) materials. We consider the following 2D materials: talc (Mg3Si4O10(OH)2), and molybdenum chalcogenides MoS2, MoSe2, and MoSSe alloys. The investigation on talc was divided into two parts: the study of mechanical properties, where we evaluated the cohesive energy, the bulk modulus, the energy barrier that has to be overcome to initiate the lateral sliding, the breaking strength and the flexural rigidity, and thestudy of the electronic properties of talc/graphene heterostructures. In the study of chalcogenides, we investigated the behavior of those materials when subjected to high levels of tensile strain. We show that talc presents small values of interlayer cohesive energy and small values ofthe energy barrier that has to be overcame to initiate the lateral sliding, as well as a high value of flexural rigidity for the talc monolayer. These results, together with the high value of monolayer breaking strength, allowed us to predict that talc can be mechanically exfoliated. This is consistent with experimental results by co-workers, which found that natural talc can be mechanically exfoliated down to monolayer and few-layers flakes. In the case of talc/graphene heterostructures, we investigated whether talc could produce any changes in the electronic properties of graphene. We found that intrinsic, non-defective talc behaves as a good substrate for graphene, not modifying its properties. However, the presence of impurities in talc monolayer can lead toheavy doping of graphene, which can be either p-type or n-type. In the case of the chalcogenides, we found that when subjected to tensile uniaxial stress, next to breaking strength, they exhibit an anomalous behavior characterized by the reorientation of the zig-zag direction to thearmchair direction. This behavior was also observed in ab-initio molecular dynamics in a range of values of stress and temperature.