A First-Principles Study of Nonlinear Elastic Behavior and Anisotropic Electronic Properties of Two-Dimensional HfS2.

We utilize first principles calculations to investigate the mechanical properties and strain-dependent electronic band structure of the hexagonal phase of two dimensional (2D) HfS2. We apply three different deformation modes within -10% to 30% range of two uniaxial (D1, D2) and one biaxial (D3) strains along x, y, and x-y directions, respectively. The harmonic regions are identified in each deformation mode. The ultimate stress for D1, D2, and D3 deformations is obtained as 0.037, 0.038 and 0.044 (eV/Ang3), respectively. Additionally, the ultimate strain for D1, D2, and D3 deformation is obtained as 17.2, 17.51, and 21.17 (eV/Ang3), respectively. In the next step, we determine the second-, third-, and fourth-order elastic constants and the electronic properties of both unstrained and strained HfS2 monolayers are investigated. Our findings reveal that the unstrained HfS2 monolayer is a semiconductor with an indirect bandgap of 1.12 eV. We then tune the bandgap of HfS2 with strain engineering. Our findings reveal how to tune and control the electronic properties of HfS2 monolayer with strain engineering, and make it a potential candidate for a wide range of applications including photovoltaics, electronics and optoelectronics.

Hydrogenated Ψ-graphene as an ultraviolet optomechanical sensor.

PSI (ψ)-graphene is a dynamically and thermally stable two-dimensional (2D) allotrope of carbon composed of 5-6-7 carbon rings. Herein, we study the opto/mechanical behavior of two graphene allotropes, Ψ-graphene and its hydrogenated form, Ψ-graphane under uniaxial and biaxial strain using density functional theory (DFT) calculations. We calculated the elastic constants and second Piola-Kirchhoff (PK2) stresses, in which both nanostructures indicate a similar elasticity behavior to graphene. Also, the plasmonic behavior of these structures in response to various strains has been studied. As a result, plasmonic peaks varied up to about 2 eV under strain. Our findings reveal that these two structures have a large peak in the ultraviolet (UV) region and can be tuned by different applied strain. In addition, Ψ-graphene has smaller peaks in the IR and UV regions. Therefore, both Ψ-graphene and Ψ-graphane can be used as UV optomechanical sensors, whereas Ψ-graphene could be used as an infrared (IR) and visible sensor.