Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F5: Focus Session: Computational Discovery and Design of New Two-dimensional Materials beyond Graphene |
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Sponsoring Units: DMP DCOMP Chair: Richard Hennig, Cornell University Room: 301 |
Tuesday, March 19, 2013 8:00AM - 8:36AM |
F5.00001: Electronic and magnetic properties of 2D BCN nanostructures Invited Speaker: Hyoungki Park Recent developments of two-dimensional (2D) nanomaterials hold great promises for future electronics, optics and spintronics. Since the isolation and electronic characterization of graphene, other layered 2D crystals also have been synthesized. In particular, carbon can be combined with its neighboring atoms in the periodic table, boron and nitrogen as hexagonal BN (h-BN), to obtain hybrid BCN configurations. These BCN 2D nanostructures show a rich variety of physical properties, distinct from parent materials. Their electronic properties can in principle be tuned by varying the concentration of each of the three elements. We study electronic structures of a variety of 2D BCN nanostructures using hybrid functional HSE in density functional theory (DFT). We show that their electronic properties can be gradually tuned by composition and the atomic configuration of three elements. We demonstrate that the substitution-induced impurity states, associated with carbon atoms, and their interactions dictate the electronic structure and properties of C-doped h-BN. Stacking of localized impurity states in small C clusters embedded in h-BN forms a set of discrete energy levels in the wide gap of h-BN, leading to electronic structures of quantum dots made of carbon nano-domains for applications in optics and opto-electronics. We also show that half-metallic electron transport can be achieved by low concentration substitutional doping of only one sublattice of graphene by nitrogen or boron atoms. The delocalized spin-densities induced by the unpaired electrons at substitutional sites permeate only through the sublattice where the nitrogen (boron) atoms belong. For interacting nitrogen (boron) atoms located along the ``zigzag'' direction and in the same sublattice the ferro-magnetic spin-ordering is energetically favored, and substitution-induced impurity states selectively disturb the spin-polarized $\pi$-orbital of that same sublattice. [Preview Abstract] |
Tuesday, March 19, 2013 8:36AM - 8:48AM |
F5.00002: Electronic Structures of Single-Layer Boron Pnictides Houlong L. Zhuang, Richard G. Hennig Single layered materials such as graphene and boron nitride promise alternative routes to electronic devices. We use density-functional calculations to identify potential novel 2D materials in the boron pnictide family and determine their stability and electronic properties.\footnote{H. L. Zhuang and R. G. Hennig. Appl. Phys. Lett., \textbf{101}, 153109 (2012)}Hybrid density functional calculations show that BN, BP, BAs and BSb in this family exhibit a direct bandgap of 6.1, 1.4, 1.2 and 0.6 eV, respectively, that originates from the energy difference of the $p_z$ orbitals of the species and is tunable by strain. The bandgap linearly decreases with strain for BN, while it increases non-linearly for BP, BAs, and BSb. The calculated natural band offsets between the various boron pnictides are all of type I. We expect that these results will provide valuable guidance in designing electronic devices based on single-layer boron pnictides. [Preview Abstract] |
Tuesday, March 19, 2013 8:48AM - 9:00AM |
F5.00003: Impurity induced states in monolayer hexagonal BN Susumu Saito, Yoshitaka Fujimoto, Takashi Koretsune Ever since the experimental production of graphene, it has attracted much attention as a future device material with monoatomic-layer thickness although the material has metallic electronic transport properties. In this respect, a monoatomic layer of hexagonal boron nitride (hBN) can be even more interesting device material to be used in the future since it possesses semiconducting electronic properties with the fundamental energy gap. We study the electronic properties of the hBN monolayer in the framework of the density-functional theory and the many-body theory with Hedin's GW approximation. Both donor and acceptor-type states induced by the substitutional C impurity atom at B and N sites respectively are studied in detail. In addition, we also study the impurity states induced by the substitution of the cluster of atoms in hBN by the graphene flake. These impurity states are found to be generally rather deep, and therefore we discuss the possible methods to change the ionization energies of these impurity-induced states [1]. \\[4pt] [1] Y. Fujimoto, T. Koretsune, and S. Saito, to be published. [Preview Abstract] |
Tuesday, March 19, 2013 9:00AM - 9:12AM |
F5.00004: Ab initio study of the buckling on silicene and germanene Edgar Martinez-Guerra, Karla Hern\'andez, Eduardo Cifuentes-Quintal, Romeo de Coss Recently, a new graphene-like silicon structure was discovered: silicene. Since its discovery, silicene has been more exciting than graphene because this is a semiconductor and it should be compatible with silicon-based electronic. Silicon and germanium atoms have similar electronic configurations as those of carbon and this the reason that the bandstructure of silicene and germacene exhibits the Dirac cones at K point, with a very similar linear dispersion around it, like in graphene. The disvintage is that sp$^{\mathrm{2}}$ bonded Si is much less stable than for carbon resulting that to be stable in the planar layer their atoms must buckle. In this work, we calculated the sp character on silicene and germacene to correlate its hibridization with the velocity of electrons and holes at Dirac cones. The calculations were performed using the pseudopotential LCAO method with GGA for the exchange-correlation energy functional. The buckling of silicene and germacene layer was 0.50 and 0.69 {\AA}, respectively. In addition, the sp- character of silicene and germacene buckled was 2.33 and 2.64, respectively. Thus, a detailed analysis on the electronic band structure of these system show that as sp character goes from sp2 to sp3 it is correlated with a decrease of velocity of electrons and holes at Dirac cones. This study is primarly important and it could address a new future to modulate carrier velocities on bidimensional systems. This research was supported by Conacyt under Grant No. 133022. [Preview Abstract] |
Tuesday, March 19, 2013 9:12AM - 9:24AM |
F5.00005: Properties of silicene on graphene Lok Lew Yan Voon, Ruiping Zhou, Yan Zhuang Silicene, the silicon analog of graphene, was first shown by one of the authors in 2007 to have similar properties to graphene. Three groups have reported the fabrication of silicene on metal in Phys. Rev. Lett. in 2012. In this talk, we will present results on the structure and properties of silicene on graphene obtained from ab initio calculations. A new structure of bilayer silicene on graphene is obtained. The band structure reveals a phenomenon of self-doping. Finally, the application of a transverse electric field and I-V characteristics will be presented. [Preview Abstract] |
Tuesday, March 19, 2013 9:24AM - 9:36AM |
F5.00006: Gated Silicene as a tunable source of nearly 100\% spin-polarized electrons Wei-Feng Tsai, Cheng-Yi Huang, Tay-Rong Chang, Hsin Lin, Horng-Tay Jeng, Arun Bansil We demonstrate, via first-principles calculations, that gated silicene with a low-buckled honeycomb structure posseses two gapped Dirac cones with nearly full spin-polarization at the corners of the Brillouin zone. By using this key finding, we further propose a design of a silicene-based spin-filter to switch the output spin current simply by gating without the need to switch magnetic domains. Quantum transport calculations indicate that such designs will be highly efficient (nearly 100\% spin-polarized) and robust against weak disorder and edge imperfections. We also propose a Y-shaped spin/valley separator that produces spin-polarized current at two output terminals with opposite spins. [Preview Abstract] |
Tuesday, March 19, 2013 9:36AM - 9:48AM |
F5.00007: Density functional investigation of epitaxial silicene on semiconducting substrates G.P. Das, A. Bhattacharya, S. Bhattacharya In spite of the uniqueness of carbon to form pristine fullerene, nanotube and graphene, there have been attempts to replicate these nanostructures with silicon. Most recently, the free-standing quasi-2D honeycomb structure of silicene has been predicted to be stable with linear band dispersion and Dirac cone feature similar to graphene. Epitaxial silicene on Ag(110) and on ZrB$_{2}$(0001) substrates have already been reported [1,2]. We have carried out first principles density functional investigation of the structural and electronic properties of silicene monolayer on various wurzite structured III-V and II-VI semiconducting substrates, with metal terminated (MT) as well as non-metal terminated (NMT) top surface [3]. The binding energies of silicene on MT semiconductors are in the range 0.5 - 0.7 eV/atom and their behavior can be metallic, semi-metallic or even magnetic, depending on the choice of substrates. The silicene overlayer undergoes n-/p-type doping on MT/NMT semiconductor surface, depending upon the direction of the charge transfer. [1] P. Vogt, et al, Phys. Rev. Lett. \textbf{108} (2012) 155501. [2] A. Fleurence et al, Phys. Rev. Lett. \textbf{108} (2012) 245501 [3] A. Bhattacharya et al,, to be published. [Preview Abstract] |
Tuesday, March 19, 2013 9:48AM - 10:00AM |
F5.00008: Physisorption of nucleobases on silicene and applications for DNA sequencing Rodrigo Amorim, Ralph Scheicher We have used density functional theory including van der Waals corrections combined with the non-equilibrium Green's function (NEGF) method to study the adsorption of individual nucleobases on top of a 2-D allotrope of silicon, known as silicene, which was experimentally discovered to exist in a hexagonal buckled form. Our study focused on the stability, electronic properties and transverse electronic transport, i.e., changes in the transmission and the conductance caused by each base (A, C, G, T) in silicene compared to its pristine form. Intriguingly, despite the weak interaction between nucleobases and silicene, considerable changes in the transmittance at zero bias are predicted by us. This opens up the possibility to utilize silicene as an integrated-circuit biosensor as part of a lab-on-a-chip device. [Preview Abstract] |
Tuesday, March 19, 2013 10:00AM - 10:12AM |
F5.00009: Normal Compressive Strain Induced Metallic Transition of Semiconducting Bilayer Transition Metal Dichalcogenides Abhishek Singh, Swastibrata Bhattacharyya First principle density functional theory based calculation was carried out to investigate the effect of strain on the band gap of bilayer semiconducting transition metal dichalcogenides (TMDs). The band gap of these materials was observed to decrease smoothly with the application of normal compressive strain. Most importantly, the materials exhibit semiconductor to metal (S-M) transition after a critical pressure (inter-layer distance) is reached. This critical pressure varies with the type and stacking pattern of the material. The S-M transition is attributed to lifting of degeneracy of the bands at the fermi level caused by inter-layer interactions via charge transfer from metal to chalcogens. The GGA result was validated by incorporating the band gap corrections using hybrid functionals and GW method. The tuning of band gap of TMDs by applying normal compressive strain opens a possibility to use these materials in various applications of nanoelectronics such as electromechanical sensors, switches etc. [Preview Abstract] |
Tuesday, March 19, 2013 10:12AM - 10:24AM |
F5.00010: First-principles study of electric field effect on GaN bi- and trilayers Dongwei Xu, Haiying He, Ravindra Pandey, Shashi P. Karna First-principles calculations based on density functional theory (DFT) are performed to study bilayers and trilayers of GaN. The calculated results suggest that the bi- and trilayer systems both prefer planar graphene-like configurations rather than buckled bulk-like configurations in their ground states. The most stable configurations are predicted to be the so-called AA$'$ stacking for the bilayer and the AA$'$A stacking for the trilayer at the GGA-DFT level of theory. By appling an external perpendicular electric field to the AB-stacked bilayer, its band gap increases monotonically. However, this is not case for the symmetric AA$'$ stacked bilayer, ABA or AA$'$A stacked trilayer where the applied electric field reduces the band gap. Furthermore, a semiconductor-metal transition is predicted for the ABA stacked GaN trilayer at about 0.4 V/ {\AA}. [Preview Abstract] |
Tuesday, March 19, 2013 10:24AM - 10:36AM |
F5.00011: Interfaces between buckling phases in Silicene Matheus P. Lima, Ant\^onio J.R. da Silva, Adalberto Fazzio Silicene has a honeycomb buckled lattice, with two energetically degenerate geometric phases ($\alpha$ and $\beta$). The $\alpha$ phase has one atom shifted up, and its neighbors shifted down, whereas the $\beta$ phase the shifts are reversed. Some consequences of this buckling pattern are: i) the increase of spin-orbit coupling, thus enhancing the Quantum Spin Hall Effect; ii) potential to tune several properties with the application of an external electric field. Therefore, the understanding of the effects caused by this buckling is crucial to fully explore the potential of this material. In this work we performed simulations based on Density Functional Theory to investigate the co-existence of the $\alpha$ and $\beta$ phases in the same sample. We show that: i) This phase inversion is stable in the zigzag and armchair directions, and can make curves, allowing the formation of islands; ii) The formation energy per unit length is approximately $0.02~eV/$Ang; iii) The modifications caused in the Density of States (DOS) are small, and appear $0.5~eV$ below the Fermi energy. Finely, we show how these linear defect will appear in Scanning Tunneling Microscopy (STM) experiments. [Preview Abstract] |
Tuesday, March 19, 2013 10:36AM - 10:48AM |
F5.00012: Electron-Phonon Coupling in Two-Dimensional Germanene Ryan Stein, David Schaefer, Jia-An Yan The phonon properties of the two-dimensional honeycomb allotrope of germanium, germanene, were studied by first-principles calculations. We found that the highest optical branches on the phonon dispersions at $\Gamma$ and K symmetry points of the first Brillouin zone exhibit similar behavior as in graphene and graphite, indicating possible Kohn anomalies in germanene. Electron-Phonon coupling for the high symmetric modes will be discussed. [Preview Abstract] |
Tuesday, March 19, 2013 10:48AM - 11:00AM |
F5.00013: Optical signatures of valley-spin coupling in graphene-like materials: silicene and germanene E.J. Nicol, C.J. Tabert, L. Stille With the success of graphene and the development of the field of two-dimensional crystals, other graphene-like materials are now of interest, such as, monolayers of silicon (silicene) and germanium (germanene). The interplay of spin orbit coupling, due to the buckled structure of these materials, and a perpendicular electric field is predicted to give rise to a rich variety of phases via an electrically tunable band gap [1,2]. These span a topological or quantum spin Hall insulator, a valley-spin-polarized metal and a band insulator [2]. We have calculated the dynamical conductivity [3] and show that it should reveal signatures of these different phases which would allow for their identification along with the determination of parameters such as the spin orbit energy gap. Furthermore, the effect of spin-valley coupling can be seen in the response to circularly polarized light as a function of frequency. Using right- and left-handed circular polarization it is possible to select a particular combination of spin and valley index. The frequency for this effect can be varied by tuning the band gap.\\[4pt] [1] N.D. Drummond, V. Zolyomi, V.I. Fal'ko, PRB 85, 075423 (2012).\\[0pt] [2] M. Ezawa, New J. Phys. 14, 033003 (2012).\\[0pt] [3] L. Stille, C.J. Tabert, E.J. Nicol, PRB 86, 195405 (2012). [Preview Abstract] |
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