RESUMEN
Due to the breaking of the mirror symmetry, two-dimensional layered Janus materials possess many extraordinary mechanical and electronic properties that cannot exist in symmetric structures. In this paper, we propose and investigate the structural and electronic properties of Janus T'-RuXY (X/Y = S, Se, and Te) monolayers using the first-principles simulations. Our calculated results indicate that the T'-RuXY is found to be dynamically and mechanically stable through the phonon dispersion analysis and examination of elastic properties. The T'-RuXY exhibits high anisotropic elastic characteristics due to its in-plane anisotropic atomic structure. Besides, the vertical asymmetry of T'-RuXY leads to the appearance of a difference in the vacuum level between its two different surfaces. At the ground state, all three structures of the Janus T'-RuXY are semiconductors with indirect bandgaps. The bandgaps of T'-RuXY can be modulated by a biaxial strain. Particularly, the semiconductor-to-metal phase transitions are observed in all studied structures at a large compressive strain. Our calculation results not only provide important structural and electronic features of the Janus T'-RuXY monolayers but also show the prospect of their application in nanoelectromechanical devices.
RESUMEN
Although O is an element of chalcogen group, the study of two-dimensional (2D) O-based Janus dichalcogenides/monochalcogenides, especially their 1T-phase, has not been given sufficient attention. In this work, we systematically investigate the structural, electronic, and optical properties of 1T Janus GeSO monolayer by using the density functional theory. Via the analysis of phonon spectrum and evaluation of elastic constants, the GeSO monolayer is confirmed to be dynamically and mechanically stable. Calculated results for the elastic constants demonstrate that the Janus GeSO monolayer is much mechanically flexible than other 2D materials due to its small Young's modulus. At the ground state, while both GeS2 and GeO2 monolayers are indirect semiconductors, the Janus GeSO monolayer is found to be a direct band gap semiconductor. Further, effective masses of both electrons and holes are predicted to be directionally isotropic. The Janus GeSO monolayer has a broad absorption spectrum, which is activated from the visible light region and its absorption intensity is very high in the near-ultraviolet region. The calculated results not only systematically provide the fundamental physical properties of GeSO monolayer, but also stimulate scientists to further studying its importance both theoretically and experimentally.
RESUMEN
We theoretically address the electronic structure of mono- and simple bi-layer armchair graphene nanoribbons (AGNRs) when they are infected by extrinsic charged dilute impurity. This is done with the aid of the modified tight-binding method considering the edge effects and the Green's function approach. Also, the interplay of host and guest electrons are studied within the full self-consistent Born approximation. Given that the main basic electronic features can be captured from the electronic density of states (DOS), we focus on the perturbed DOS of lattices corresponding to the different widths. The modified model says that there is no metallic phase due to the edge states. We found that the impurity effects lead to the emergence of midgap states in DOS of both systems so that a semiconductor-to-semimetal phase transition occurs at strong enough impurity concentrations and/or impurity scattering potentials. The intensity of semiconductor-to-semimetal phase transition in monolayer (bilayer) ultra-narrow (realistic) ribbons is sharper than bilayers (monolayers). In both lattices, electron-hole symmetry breaks down as a result of induced-impurity states. The findings of this research would provide a base for future experimental studies and improve the applications of AGNRs in logic semiconductor devices in industry.