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    Lateral Composite Structures of Graphene/Graphane/Graphone: Electronic Confinement, Heterostructures with Tunable Band Alignment, and Magnetic State
    (Amer Chemical Soc, 2023) Demirci, Salih; Gorkan, Taylan; Akturk, Ethem; Ciraci, Salim
    Graphene can be hydrogenated fully on both sides andalso semihydrogenatedon one side to constitute graphane and graphone, respectively. Whileboth are wide band gap semiconductors, graphone also acquires a magneticground state originating from unpaired & pi;-bonds. We predict thatlateral composite structures/heterostructures can be constructed bythe patterned dehydrogenation of graphane or graphone with commensurateinterfaces, which display diverse physical properties depending ontheir constituents, interface geometry, and size. When constructedby consecutive graphane and graphene strips of very narrow width,they can attain exclusive electronic and magnetic properties in 2D,which are different from those of both parent materials. However,periodic and commensurate semiconductor-semiconductor heterostructureswith straddling band alignment and tunable band gaps can form, ifthe widths of strips with the armchair interface are wide enough toentail confinements of electronic states and hence to change the dimensionalityof the system from 2D to 1D. Depending on the type of zigzag interface,periodic heterostructures attain spin polarized straddling band alignments.Composite structures patterned on graphone can form magnetic semiconductor-semiconductorheterostructures, which have different staggered band alignments fordifferent spin polarization. Specifically, under the in-plane electricfield, a single heterostructure constructed on zigzag nanoribbonscan change its magnetic state and start to operate as a magnetic diodefor one spin direction. All of these composite structures, which allowelectronic confinement followed by a change of dimensionality, offervarious quantum structures and functionalities with potential applicationsin spintronics.
  • [ X ]
    Öğe
    Magnetization of silicene via coverage with gadolinium: Effects of thickness, symmetry, strain, and coverage
    (Amer Physical Soc, 2021) Demirci, Salih; Gorkan, Taylan; Callioglu, Safak; Yuksel, Yusuf; Akinci, Umit; Akturk, Ethem; Ciraci, Salim
    When covered by gadolinium (Gd) atoms, silicene, a freestanding monolayer of Si atoms in a honeycomb network, remains stable above the room temperature and becomes a two-dimensional (2D) ferromagnetic semiconductor, despite the antiferromagnetic ground state of three-dimensional bulk GdSi2 crystal. In thin GdSi2 multilayers, even if magnetic moments are ordered parallel in the same Gd atomic planes, they are antiparallel between nearest Gd planes; hence they exhibit a ferrimagnetic behavior. In contrast, a freestanding Gd2Si2 monolayer constructed by covering silicene from both sides by Gd atoms is a stable antiferromagnetic metal due to the mirror symmetry. While multilayers covered by Gd from both sides having an odd number of Gd planes have a ferrimagneticlike ground state, even-numbered ones have antiferromagnetic ground state, but none of them is ferromagnetic. Silicon atoms intervening between Gd planes are responsible for these intriguing magnetic orders conforming with the recent experiments performed on Si(111) surface. Additionally, the magnetic states of these 2D gadolinium disilicide monolayers can be monitored by applied tensile strain and by the coverage/decoration of Gd. These predictions obtained by using first-principles, spin-polarized, density functional theory calculations combined with Monte Carlo simulations herald that C, B, Si, Ge, Sn, and their compounds functionalized by rare-earth atoms can lead to novel nanostructures in 2D spintronics.
  • Küçük Resim
    Öğe
    Modification of electronic structure, magnetic structure, and topological phase of bismuthene by point defects
    (Amer Physical Soc, 2017) Kadioglu, Yelda; Kilic, Sevket Berkay; Demirci, Salih; Akturk, O. Uzengi; Akturk, Ethem; Ciraci, Salim
    This paper reveals how the electronic structure, magnetic structure, and topological phase of two-dimensional (2D), single-layer structures of bismuth are modified by point defects. We first showed that a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology. We then investigated interactions between single foreign adatoms and bismuthene structures, which comprise stability, bonding, electronic structure, and magnetic structures. Localized states in diverse locations of the band gap and resonant states in band continua of bismuthene are induced upon the adsorption of different adatoms, which modify electronic and magnetic properties. Specific adatoms result in reconstruction around the adsorption site. Single vacancies and divacancies can form readily in bismuthene structures and remain stable at high temperatures. Through rebondings, Stone-Whales-type defects are constructed by divacancies, which transform into a large hole at high temperature. Like adsorbed adatoms, vacancies induce also localized gap states, which can be eliminated through rebondings in divacancies. We also showed that not only the optical and magnetic properties, but also the topological features of pristine h-bismuthene can be modified by point defects. The modification of the topological features depends on the energies of localized states and also on the strength of coupling between point defects.
  • [ X ]
    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; Callioglu, Safak; Gorkan, Taylan; Akturk, Ethem; Ciraci, 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.