Konstantina Iordanidou

Impact of point defects on the electronic and transport properties of silicene nanoribbons

We study the impact of various point defects on the structural, electronic and ballistic transport properties of armchair silicene nanoribbons, using the density functional theory and the non equilibrium Greens function method. The effect of a Stone-Wales defect, an interior/edge vacancy and an edge dangling bond is examined. Our results show that structural imperfections can alter the electronic structure (energy band structure and density of states) of the nanoribbons and can either increase or decrease the ballistic current. The dependence of the transport properties on the position of the defects (sublattice A or B) and on their distance from the contact is also investigated.

Functional silicene and stanene nanoribbons compared to graphene: electronic structure and transport

Since the advent of graphene, other 2D materials have garnered interest; notably the single element materials silicene, germanene, and stanene. We investigate the ballistic current–voltage (I–V) characteristics of armchair silicene and stanene armchair nanoribbons (AXNRs with X = Si, Sn) using a combination of density functional theory and non-equilibrium Greens functions. The impact of out-of-plane electric field and in-plane uniaxial strain on the ribbon geometries, electronic structure, and (I–V)s are considered and contrasted with graphene. Since silicene and stanene are sp2/sp3 buckled layers, the electronic structure can be tuned by an electric field that breaks the sublattice symmetry, an effect absent in graphene. This decreases the current by ~50% for Sn, since it has the largest buckling. Uniaxial straining of the ballistic channel affects the AXNR electronic structure in multiple ways: it changes the bandgap and associated effective carrier mass, and creates a local buckling distortion at the lead-channel interface which induces a interface dipole. Due to the increasing sp3 hybridization character with increasing element mass, large reconstructions rectify the strained systems, an effect absent in sp2 bonded graphene. This results in a smaller strain effect on the current: a decrease of 20% for Sn at 15% tensile strain compared to a ~75% decrease for C.

Topological to trivial insulating phase transition in stanene

Electronic properties of stanene, the Sn counterpart of graphene are theoretically studied using first-principles simulations. The topological to trivial insulating phase transition induced by an out-of-plane electric field or by quantum confinement effects is predicted. The results highlight the potential to use stanene nanoribbons in gate-voltage controlled dissipationless spin-based devices and are used to set the minimal nanoribbon width for such devices, which is typically approximately 5 nm.

Silicene on non-metallic substrates: Recent theoretical and experimental advances

Silicene, the silicon counterpart of graphene, has been successfully grown on metallic substrates such as Ag(111), ZrB2(0001), and Ir(111) surfaces. However, characterization of its electronic structure is hampered by the metallic substrate. In addition, potential applications of silicene in nanoelectronic devices will require its growth on or integration with semiconducting and insulating substrates. We herein present a review of recent theoretical works regarding the interaction of silicene with non-metallic templates, distinguishing between the weak van-der-Waals-like interactions of silicene with, for example, layered metal (di)chalcogenides, and the stronger covalent bonding between silicene and, for example, ZnS surfaces. We then present a methodology to effectively compare the stability of diverse silicene structures using thermodynamics and molecular dynamics density functional theory calculations. Recent experimental results on the growth of silicene on MoS2 are also reported and compared to the theoretical predictions.

Erratum to: Silicene on non-metallic substrates: Recent theoretical and experimental advances

The name of the second author in the original version of this article was unfortunately wrongly written on page 1169.Instead ofKostantina IordanidouIt should readKonstantina Iordanidou

Ferromagnetism in two-dimensional hole-doped SnO

Hole-doped monolayer SnO has been recently predicted to be a ferromagnetic material, for a hole density typically above 5x1013/cm2. The possibility to induce a hole-doped stable ferromagnetic order in this two-dimensional material, either by intrinsic or extrinsic defects, is theoretically studied, using first-principles simulations. Sn vacancies and Sn vacancy-hydrogen complexes are predicted to be shallow acceptors, with relatively low formation energies in SnO monolayers grown under O-rich conditions. These defects produce spin-polarized gap states near the valence band-edge, potentially stabilizing the ferromagnetic order in 2D SnO. Hole-doping resulting from substitutional doping is also investigated. Among the considered possible dopants, As, substituting O, is predicted to produce shallow spin-polarized gap states near the valence band edge, also potentially resulting in a stable ferromagnetic order in SnO monolayers.