Metal to semiconductor switching in the AgTe monolayer via decoration with alkali metal and alkaline earth metal atoms: a first-principles perspective.

In this work, employing first-principles calculations, we systematically investigate the atomic structure and electronic and optical properties of the AgTe monolayer, as well as the impact of alkali metal (Li, Na, K) and alkaline earth metal (Be, Mg, Ca) atoms decoration. The AgTe monolayer exhibits metallic characteristics. When Li, Na, K, and Mg atoms are decorated on the AgTe monolayer, the decorated AgTe monolayers are dynamically stable. In contrast, with Be and Ca atoms, the decorated structures are found to be dynamically unstable. Interestingly, the decoration of Li, Na, and K atoms into the AgTe monolayer can open the band gaps in the decorated Li-, Na- and K-AgTe monolayers around the Fermi level, leading to the actualization of metal-to-semiconductor transitions. In contrast, the decorated Mg-AgTe monolayer maintains its metallic characteristic. The highest electron and hole mobilities are achieved in the Na-AgTe monolayer among the decorated structures, suggesting the applicability of this structure in photovoltaic applications. The optical study shows that Li-, Na- and K-decorated AgTe monolayers have improved light absorption in the visible light region. Consequently, our findings shed light on the decoration of these 2D material monolayers and can potentially enhance and motivate studies in producing these monolayers for current nanodevices and future applications.

Theoretical prediction of two-dimensional BC2X (X = N, P, As) monolayers: ab initio investigations.

In this work, novel two-dimensional BC[Formula: see text]X (X = N, P, As) monolayers with X atoms out of the B-C plane, are predicted by means of the density functional theory. The structural, electronic, optical, photocatalytic and thermoelectric properties of the BC[Formula: see text]X monolayers have been investigated. Stability evaluation of the BC[Formula: see text]X single-layers is carried out by phonon dispersion, ab-initio molecular dynamics (AIMD) simulation, elastic stability, and cohesive energies study. The mechanical properties reveal all monolayers considered are stable and have brittle nature. The band structure calculations using the HSE06 functional reveal that the BC[Formula: see text]N, BC[Formula: see text]P and BC[Formula: see text]As are semiconducting monolayers with indirect bandgaps of 2.68 eV, 1.77 eV and 1.21 eV, respectively. The absorption spectra demonstrate large absorption coefficients of the BC[Formula: see text]X monolayers in the ultraviolet range of electromagnetic spectrum. Furthermore, we disclose the BC[Formula: see text]N and BC[Formula: see text]P monolayers are potentially good candidates for photocatalytic water splitting. The electrical conductivity of BC[Formula: see text]X is very small and slightly increases by raising the temperature. Electron doping may yield greater electric productivity of the studied monolayers than hole doping, as indicated by the larger power factor in the n-doped region compared to the p-type region. These results suggest that BC[Formula: see text]X (X = N, P, As) monolayers represent a new promising class of 2DMs for electronic, optical and energy conversion systems.

Two-dimensional penta-like PdPSe with a puckered pentagonal structure: a first-principles study.

Low-symmetry penta-PdPSe (Pd4P4Se4) with intrinsic in-plane anisotropy was synthesized successfully [P. Li et al., Adv. Mater., 2021, 2102541]. Motivated by this experimental discovery, we investigate the structural, mechanical, electronic, optical and thermoelectric properties of PdPSe nanosheets via density functional theory calculations. The phonon dispersion, molecular dynamics simulation, and cohesive energy mechanical properties of the penta-PdPSe are verified to confirm its stability. The phonon spectrum represents a striking gap between the high-frequency and the low-frequency optical branches and an out-of-plane flexure mode with a quadratic dispersion in the long-wavelength limit. The Poisson's ratio indicates that penta-PdPSe is a brittle nanosheet. The penta-PdPSe is a semiconductor with an indirect bandgap of 1.40 (2.07) eV using the PBE functional (HSE06 hybrid functional). Optical properties simulation suggests that PdPSe is capable of absorbing a substantial range of visible to ultraviolet light. Band alignment analysis also reveals the compatibility of PdPSe for water splitting photocatalysis application. By combining the electrical and thermal transport properties of PdPSe, we show that a high power factor is achievable at room temperature, thus making PdPSe a candidate material for thermoelectric applications. Our findings reveal the strong potential of penta-PdPSe nanosheets for a wide array of applications, including optoelectronic, water splitting and thermoelectric device applications.

Electronic, optical and thermoelectric properties of a novel two-dimensional SbXY (X = Se, Te; Y = Br, I) family: ab initio perspective.

Recent developments in the synthesis of highly crystalline ultrathin BiTeX (X = Br, Cl) structures [Debarati Hajra et al., ACS Nano 14, 15626 (2020)] have led to the exploration of the atomic structure, dynamical stability, and electronic, optical, and thermoelectric properties of SbXY (X = Se, Te; Y = Br, I) monolayers via density functional calculations. The calculated phonon spectrum, elastic stability conditions, and cohesive energy verified the stability of the studied SbXY monolayers. The mechanical properties reveal that all studied monolayers are stable and brittle. Based on PBE (PBE + SOC) functional calculations, the SbXY monolayers are semiconductors with indirect bandgaps. The calculated bandgaps using HSE (HSE + SOC) for SbSeBr, SbSeI, SbTeBr, and SbTeI monolayers are between 1.45 and 1.91 eV, which are appealing for applications in nanoelectronic devices. The signature of the Rashba effect appears in the SbXY monolayer. The SbXY monolayers are visible-light active. Hole doping can be an efficient way to increase the electricity production of SbXY monolayers from waste heat energy. This study suggests that SbXY (X = Se, Te; Y = Br, I) monolayers represent promising new electronic, optical, and energy conversion systems.

Effect of adsorption and substitutional B doping at different concentrations on the electronic and magnetic properties of a BeO monolayer: a first-principles study.

The 2D form of the BeO sheet has been successfully prepared (Hui Zhang et al., ACS Nano, 2021, 15, 2497). Motivated by these exciting experimental results on the 2D layered BeO structure, we studied the effect of the adsorption of B atoms on BeO (B@BeO) and substitutional B atoms (B-BeO) at the Be site at different B concentrations. We investigated the structural stability and the mechanical, electronic, magnetic, and optical properties of the mentioned structures using first-principles calculations. We found out that hexagonal BeO monolayers with adsorbed and dopant B atoms have different mechanical stabilities at different concentrations. B@BeO and B-BeO monolayers are brittle structures, and B@BeO structures are more rigid than B-BeO monolayers (at the same B concentration). The adsorption and the formation energy per B atom decrease as the B concentration increases. In comparison, the work function increases when increasing the B concentration. The work function of B@BeO is higher than the corresponding value of B-BeO (at the same B concentration). The magnetic moment linearly increases as the B concentration increases. BeO is a semiconductor with an indirect bandgap of 5.3 eV. The B@BeO and B-BeO structures are semiconductors, except for 3B-BeO (14.2% doped concentration), which is a metal. The bandgap is 1.25 eV for most of the adsorbed atom concentrations. For B-BeO, the bandgap decreases to zero at a concentration of 14.2%. The bandgap of the B-BeO monolayer at different B concentrations is smaller than the corresponding values of the B@BeO monolayer, which indicates that B substitutional doping has a greater effect on the electronic structure of the BeO monolayer than B adsorption doping. We investigated the optical properties, including the dielectric function and absorption coefficient. The results indicate good optical absorption in the range of infrared and ultraviolet energies for the B adsorbed and doped BeO monolayer.

Novel two-dimensional AlSb and InSb monolayers with a double-layer honeycomb structure: a first-principles study.

In this work, motivated by the fabrication of an AlSb monolayer, we have focused on the electronic, mechanical and optical properties of AlSb and InSb monolayers with double-layer honeycomb structures, employing the density functional theory approach. The phonon band structure and cohesive energy confirm the stability of the XSb (X = Al and In) monolayers. The mechanical properties reveal that the XSb monolayers have a brittle nature. Using the GGA + SOC (HSE + SOC) functionals, the bandgap of the AlSb monolayer is predicted to be direct, while InSb has a metallic character using both functionals. We find that XSb (X = Al, In) two-dimensional bodies can absorb ultraviolet light. The present findings suggest several applications of AlSb and InSb monolayers in novel optical and electronic usages.

Biphenylene monolayer as a two-dimensional nonbenzenoid carbon allotrope: a first-principles study.

In a very recent accomplishment, the two-dimensional form of biphenylene network (BPN) has been fabricated. Motivated by this exciting experimental result on 2D layered BPN structure, herein we perform detailed density-functional theory-based first-principles calculations, in order to gain insight into the structural, mechanical, electronic and optical properties of this promising nanomaterial. Our theoretical results reveal the BPN structure is constructed from three rings of tetragon, hexagon and octagon, meanwhile the electron localization function shows very strong bonds between the C atoms in the structure. The dynamical stability of BPN is verified via the phonon band dispersion calculations. The mechanical properties reveal the brittle behavior of BPN monolayer. The Young's modulus has been computed as 0.1 TPa, which is smaller than the corresponding value of graphene, while the Poisson's ratio determined to be 0.26 is larger than that of graphene. The band structure is evaluated to show the electronic features of the material; determining the BPN monolayer as metallic with a band gap of zero. The optical properties (real and imaginary parts of the dielectric function, and the absorption spectrum) uncover BPN as an insulator along thezzdirection, while owning metallic properties inxxandyydirections. We anticipate that our discoveries will pave the way to the successful implementation of this 2D allotrope of carbon in advanced nanoelectronics.

Surface modification of titanium carbide MXene monolayers (Ti2C and Ti3C2) via chalcogenide and halogenide atoms.

Inspired by the recent successful growth of Ti2C and Ti3C2 monolayers, here, we investigate the structural, electronic, and mechanical properties of functionalized Ti2C and Ti3C2 monolayers by means of density functional theory calculations. The results reveal that monolayers of Ti2C and Ti3C2 are dynamically stable metals. Phonon band dispersion calculations demonstrate that two-surface functionalization of Ti2C and Ti3C2via chalcogenides (S, Se, and Te), halides (F, Cl, Br, and I), and oxygen atoms results in dynamically stable novel functionalized monolayer materials. Electronic band dispersions and density of states calculations reveal that all functionalized monolayer structures preserve the metallic nature of both Ti2C and Ti3C2 except Ti2C-O2, which possesses the behavior of an indirect semiconductor via full-surface oxygen passivation. In addition, it is shown that although halide passivated Ti3C2 structures are still metallic, there exist multiple Dirac-like cones around the Fermi energy level, which indicates that semi-metallic behavior can be obtained upon external effects by tuning the energy of the Dirac cones. In addition, the computed linear-elastic parameters prove that functionalization is a powerful tool in tuning the mechanical properties of stiff monolayers of bare Ti2C and Ti3C2. Our study discloses that the electronic and structural properties of Ti2C and Ti3C2 MXene monolayers are suitable for surface modification, which is highly desirable for material property engineering and device integration.

Electronic transport calculations for rough interfaces in Al, Cu, Ag, and Au.

We present results of electronic structure and transport calculations for metallic interfaces, based on density functional theory and the non-equilibrium Green's function method. Starting from the electronic structure of smooth Al, Cu, Ag, and Au interfaces, we study the effects of different kinds of interface roughness on the transmission coefficient and the I-V characteristic. In particular, we compare prototypical interface distortions, including vacancies and metallic impurities.