The study of bending properties of monolayer MoS2 in non-collinear electrodes using first principles theory

Bending deformation modulation of the optoelectronic properties of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, O): a first-principles study

CONTEXT

A first-principles approach based on density functional theory was used to explore the effect of bending deformation on the electrical structure of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, and O). The study included alternate doping of nonmetallic atoms, as well as a comparison of the effects of intrinsic bending deformation and nonmetallic doping deformation. The results demonstrate that boron atom doping raises the Fermi energy level. Examining the energy band structure indicates that the intrinsic molybdenum ditelluride is a direct band gap semiconductor, which is transformed from a direct band gap to an indirect band gap after doping. We selected boron-doped systems for bending deformation and compared them with the intrinsic systems. With increasing deformation, all systems start to shift from semiconductor to metal. When the deformation reaches 8°, the energy levels fill and the electron energy increases. The intrinsically bent systems transition from direct band gap to indirect band gap and eventually to metal. The indirect band gap semiconductor-to-metal transition process occurs after the bending deformation of the boron-doped atoms. The analytical results show that the absorption and reflection peaks of the molybdenum ditelluride system are blue-shifted after the bending deformation of the boron-doped atoms.

METHODS

Under fundamental principles, this research depends on the density functional theory framework (DFT) using the CASTEP module in the Materials-Studio software. The plane-wave pseudopotential approach with modified gradient approximation and the Perdew-Burke-Ernzerhof (PBE) generalized function is used for structure optimization and total energy calculations of the X-doped (X = B, C, N, O) MoTe2 system at different shape variables. Geometry optimization of the 27-atom superlattice MoTe2 was carried out, followed by alternative doping of tellurium atoms in the molybdenum ditelluride with B, C, N, and O. In this paper, the intrinsic bending deformation and B-doping of molybdenum ditelluride were selected for deformation analysis. Intrinsic bending deformations and boron-doped molybdenum ditelluride with bending angles ranging from 2° to 8° were employed for deformation investigation. In Fig. 1, pink is used to represent doped B atoms, orange is used to describe Te atoms, and green is used to represent Mo atoms. For the degree of deformation of molybdenum ditelluride, in this paper, it is expressed by the bending angle, i.e., the angle of the plane of molybdenum ditelluride after bending and deformation of a single layer of molybdenum ditelluride concerning the angle of the plane folded for the deformed plane. How to do it: For ease of presentation, the atomic chains are set to different colors. The purple part on both sides of the figure is bent and deformed, 3-5 atoms are fixed appropriately, and the middle part is deformed. On this basis, the bending deformation of intrinsically doped and boron-doped MoTe2 is comparatively analyzed. The effect of boron-doped atoms on the structure of MoTe2 is systematically investigated to study its structural stability and electronic structure. Fig. 1 a1 and a2 The main and side views of intrinsic MoTe2; b1 and (b2) the main and side views of MoTe2 doped with boron atoms bent by 8°.

Non-equilibrium spin-transport properties of Co/phosphorene/Co MTJ with non-collinear electrodes under mechanical bending

Monolayer phosphorene has outstanding mechanical flexibility, making it rather attractive in flexible spintronics that are based on 2D materials. Here, we report a first-principles study on non-equilibrium electronic-transport properties of the Co/phosphorene/Co magnetic tunnel junction (MTJ) with two α-Co electrodes. The magnetic moments of the two electrodes are considered in the parallel configuration (PC) and the anti-parallel configuration (APC). The tunneling current through the MTJ is investigated at a small bias from 0 to 40 mV when mechanical bending is applied on the MTJ with different central angle (θ) values. For both the PC and APC, the tunneling current increases evidently and monotonously with increasing mechanical bending for 25° < θ < 40°, as compared to that without bending, which is mainly due to the reduced tunnel barrier. In the PC, the spin-injection efficiency (SIE) of the current is largely increased at a small bias from 0 to 40 mV for 25° ≤ θ ≤ 30° with a maximum of 90%, while the SIE is overall increased under all mechanical bending angles for the APC. The tunnel magnetoresistance is decreased with an increasing bias voltage, which can be largely enhanced for θ ≥ 25°, especially at small bias. Our results indicate that the Co/phosphorene/Co MTJ has promising applications in flexible low-power spintronic devices.