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    Öğe
    Can Stable MoS2 Monolayers and Multilayers Be Constituted in the Biphenylene Network?
    (Amer Chemical Soc, 2023) Gorkan, Taylan; Demirci, Salih; V. Barth, Johannes; Aktürk, Ethem; Çıracı, Salim
    Based on the first-principles calculations, we predict that the well-known 2H-MoS2 monolayer of the trigonal prismatic phase appearing in a hexagonal network can also constitute another stable phase in the biphenylene network (B-MoS2). It consists of the connected octagon, hexagon and square rings and hence maintains the same numbers of neighbors of the constituent atoms, but its bonds between transition metal and chalcogen atoms are deformed to construct a direct but narrow band gap semiconductor with directional electronic conduction and optical properties with strong absorption in the near-infrared region. It has softer mechanical properties and site specific chemical activities of the same kind of constituent atoms. In the same way, vacancies of different chalcogen atoms in the cell attain different defect states in the band gap. This phase can remain stable above the room temperature and has a cohesive energy comparable to all the other 2D phases of the same compound. In fact, transitions from the 2H-phase to the B-phase can be possible. The B-phase can form multilayers and also a metallic 3D layered, van der Waals crystal with weak interlayer coupling. The narrow band gap of the monolayer is reduced in the bilayer but diminishes in multilayers and 3D layered crystals to change the semiconductor to a metal. Even more interesting is that B-MoS2 is versatile for the modulation of the band gap, even for the metal-insulator transition under applied strains.
  • Küçük Resim
    Öğe
    Stability and electronic properties of monolayer and multilayer structures of group-IV elements and compounds of complementary groups in biphenylene network
    (Amer Physical Soc, 2022) Demirci, Salih; Çallıoğlu, Şafak; Gorkan, Taylan; Aktürk, Ethem; Çıracı, Salim
    We predict that specific group-IV elements and IV-IV, III-V, and II-VI compounds can form stable, free-standing two-dimensional (2D) monolayers consisting of octagon, hexagon, and square rings (ohs), in which the threefold coordination of atoms is preserved to allow sp(2)-type hybridization. These monolayers can also construct bilayers, multilayers, three-dimensional (3D) layered van der Waals solids, and 3D crystals with strong vertical bonds between layers as well as quasi-one-dimensional nanotubes and nanoribbons with diverse edge geometries. All these ohs structures can constitute a large class of 2D materials ranging from good metals to wide bandgap semiconductors and display physical and chemical properties rather different from those of their counterparts in the hexagonal (honeycomb) network. The metallic state of freestanding 2D C, Si, and Ge ohs monolayers and 3D C ohs bulk contrast, respectively, with graphene, silicene, germanene, and graphite.
  • [ X ]
    Öğe
    Two dimensional ruthenium carbide: structural and electronic features
    (ROYAL SOC CHEMISTRY, 2020) Görkan, Taylan; Demirci, Salih; Jahangirov, S.; Gokoglu, Gökhan; Aktürk, Ethem
    The design and realization of novel 2D materials and their functionalities have been a focus of research inspired by the successful synthesis of graphene and many other 2D materials. In this study, in view of first principles calculations, we predict a novel 2D material ruthenium carbide (RuC) in graphene-like honeycomb hexagonal lattice with planar geometry. Phonon dispersion spectra display a dynamically stable structure. Comprehensive molecular dynamics calculations confirm the stability of the structure up to high temperatures as approximate to 1000 K. The system is a narrow gap semiconductor with a band gap of 53 meV (345 meV) due to GGA-PBE (HSE) calculations. Band gap exhibits significant changes by applied strain. Elastic and optical properties of the system are examined in monolayer form. RuC/RuC bilayer, RuC/graphene and RuC/h-BN heterostructures are also investigated. By calculating the phonon dispersion it is verified that RuC bilayer is the most stable in AA type-stacking configuration where Ru and C atoms of both layers have identical lateral coordinates. The effects of atomic substitutions on electronic band structures, acting as p-type and n-type doping, are revealed. A novel 3D RuCLi structure is also predicted to be stable and the isolation of its monolayer forms are discussed. Ruthenium carbide, as a 2D material which is dynamically and thermally stable, holds promise for applications in nanoelectronics.