Two-dimensional Janus X2STe (X = B, Al) monolayers: the effect of surface selectivity and adsorption of small gas molecules on electronic and optical properties.

This investigation delves into the adsorption characteristics of CO, NO, NO2, NH3, and O2 on two-dimensional (2D) Janus group-III materials, specifically Al2XY and B2XY. The examination covers adsorption energies and heights, diverse adsorption sites, and molecular orientations. Employing first-principles analysis, a comprehensive assessment of structural, electronic, and optical properties is conducted. The findings highlight NO2 as a prominent adsorbate, emphasizing the Te surface of 2D Al2STe and B2STe materials as particularly adept for NO2 detection, based on considerations of adsorption energy, height, and charge transfer. Additionally, the study underscores the heightened sensitivity of work function changes in the B2STe material. The adsorption properties of all gas molecules, except for NO2, on both materials were determined to be physical. Upon adsorption of the NO2 gas molecule onto the B2STe Janus material, it was observed that the material exhibited weak chemical adsorption behavior, which was confirmed by the adsorption energy, larger band gap change, electron localization function, work function changes and charge transfer from the material. This research provides valuable insights into the gas-sensing potential of 2D Janus materials.

An analysis of Schottky barrier in silicene/Ga2SeS heterostructures by employing electric field and strain.

Two-dimensional materials are leading the way in nanodevice applications thanks to their various advantages. Although two-dimensional materials show promise for many applications, they have certain limitations. In the last decade, the increasing demand for the applications of novel two-dimensional materials has accelerated heterostructure studies in this field. Hence, restoring the combination of two-dimensional heterostructured materials has been reported. In this paper, we show that the effect of the external electric field and biaxial strain on the silicene/Ga2SeS heterostructure has a critical impact on the tuning of the Schottky barrier height. The findings such as the variation of the electronic band gap, interlayer charge transfer, total dipole moment, and n-type/p-type Schottky barrier transitions of the silicene/Ga2SeS heterostructure under external effects imply that the device performance can be adjusted with Janus 2D materials.

Easy-axis rotation in ferromagnetic monolayer CrN induced by fluorine and chlorine functionalization.

On the basis of first-principles calculations, we investigate the absorption of fluorine and chlorine on ferromagnetic monolayer CrN focusing on the mechanism of spin reorientation. We use density functional theory in combination with the spin Hamiltonian approach to study the electronic and magnetic properties of monolayer CrN upon single-side adsorption of F and Cl atoms. While the electronic structure of ferromagnetic CrN remains half-metallic after functionalization, its preferred axis of magnetization is rotated toward the in-plane direction due to the orbital moment suppression. The half-coverage of CrN is found to be thermodynamically stable and ferromagnetically ordered at room temperature. Our findings demonstrate the possibility of altering the magnetic properties of a two-dimensional magnet after the adsorption of F and Cl, which opens a route to the detection of these gases using magnetic or optical measurements.

The effect of strain and functionalization on the optical properties of borophene.

Following its synthesis, borophene has drawn noticeable attention due to its remarkable intrinsic properties. Understanding and modifying these properties are crucial for implementation of borophene in high-technological applications. In this study, we employed ab initio techniques to examine the variation of the optoelectronic properties of buckled borophene by strain and surface functionalization. We find that the optical response can be tuned by applying compressive/tensile strain and covering the surface with hydrogen and fluorine atoms. It is shown that the variations in optical properties can be correlated with structural deformations and modifications in the electronic band structure. Revealing the tunability of the optical response of borophene can pave the way for its potential uses in various optoelectronic devices.

Electronic structure and optical properties of novel monolayer gallium nitride and boron phosphide heterobilayers.

Motivated by the increasing number of studies on optoelectronic applications of van der Waals (vdW) heterostructures, we have investigated the electronic and optical properties of monolayer gallium nitride (MGaN) and boron phosphide (MBP) heterobilayers by using first-principle calculations based on density functional theory. We have ensured the dynamical stability of the structures by considering their binding energies and phonon spectra. We show that the magnitude and status (direct or indirect) of the band gap are strongly dependent on the stacking pattern of the heterobilayers. Furthermore, we have investigated the band splittings in the presence of an external electric field which show the effect of the field on the band alignment of the structure. We have also shown the band gap, charge redistributions and work function of the structures are highly dependent on the magnitude and direction of the electric field such that its magnitude yields indirect to direct band gap transitions around |E⊥| ∼ 0.7 V Å-1 at the Γ point and the order of the band gap is varied according to the direction of the electric field. Moreover, we examine optical properties of MGaN/MBP heterobilayers as part of DFT calculations. The band gap and work function being tunable with changes in the external field together with the prominent absorption over the UV range make the MGaN/MBP heterobilayer a feasible candidate for optoelectronic applications.

The electronic, half-metallic, and magnetic properties of Ca1-xCrxS ternary alloys: Insights from the first-principle calculations.

The electronic, structural, and magnetic characteristics of Cr atom substituting Ca atom in rocksalt CaS have been investigated within the formalism of (GGA + PBE) and PBE with Hubbard correction (GGA + U). Our findings point out that the ternary alloys are dynamically stable depending on the obtained results of elastic constants. For structural properties, it is clear that the lattice constants decrease and bulk modulus increases with increasing concentration of chromium impurity. Interestingly, the perceived total magnetic moments increase with the Cr concentration and reaches the maximum for Ca0.25Cr0.75S, which is mainly composed of Cr atoms. Besides, it is found from PBE and PBE + U calculations that the Cr-substituted CaS gives half-metallic ferromagnetism (HMF). Finally, the deduced results of minority-spin bands demonstrate a half-metallic ferromagnetic gap and half-metallic (HM) gap. The predicted results confirmed that Ca1-xCrxS could be considered as a promising candidate material for spintronics applications.