Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D53: Surfaces, Interfaces, and Thin Films: 2D Materials |
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Sponsoring Units: DCMP Chair: Kenan Gundogdu, North Carolina State University Room: Mile High Ballroom 2C |
Monday, March 3, 2014 2:30PM - 2:42PM |
D53.00001: Crystal Symmetry and Surface States Huiping Wang, Ruibao Tao This work reports a rigorous criterion for the non-existence of surface states in a semi-infinite crystal with the (hkl) cut surface. We have proved that a (hkl) cut crystal will not induce any surface state if any (hkl) plane has the reflection symmetry in an infinite crystal constructed by an infinite number of parallel (hkl) crystal planes which are periodically arranged one by one by coupling. The conclusion is valid for any 3D and 2D structure crystal and any multiple neighbor hopping among crystal planes. The spin-orbit coupling breaks the chiral symmetry, resulting in the reflection symmetry breaking, surface states will emerge in the crystal. [Preview Abstract] |
Monday, March 3, 2014 2:42PM - 2:54PM |
D53.00002: Mechanism for asymmetric charge distribution in Rashba-type surface states and the origin of the energy splitting scale Beomyoung Kim, Wonsig Jung, Yeongkwan Kim, Yoonyoung Koh, Wonshik Kyung, Changyoung Kim, Panjin Kim, Jung Hoon Han, Joonbum Park, Jun Sung Kim, Masaharu Matsunami, Shin-ichi Kimura The mechanism for Rashba-type band splitting is examined in detail. We show how an asymmetric charge distribution is formed when the local orbital angular momentum (OAM) and crystal momentum get interlocked due to surface effects. An electrostatic energy term in the Hamiltonian appears when such an OAM- and crystal-momentum-dependent asymmetric charge distribution is placed in an electric field produced by inversion-symmetry breaking. Analysis by using an effective Hamiltonian shows that, as the atomic spin-orbit coupling (SOC) strength increases from weak to strong, the originally OAM-quenched states evolve into well-defined chiral OAM states and then to states of total angular momentum $J$. In addition, the energy scale of the band splitting changes from the atomic SOC energy to electrostatic energy. To confirm the validity of the model, we performed circular dichroism angle-resolved photoemission spectroscopy experiments as well as first-principles calculations. We find that the effective model can explain various aspects of the spin and OAM structures of the system. [Preview Abstract] |
Monday, March 3, 2014 2:54PM - 3:06PM |
D53.00003: Bonding instability induced Surface Insulating State in IrTe$_{2}$ A.G. Gianfrancesco, Q. Li, J.Q. Yan, X. Chen, W. Lin, S. Kalinin, D.J. Singh, D. Mandrus, M. Pan Using STM/S and DFT calculations, we find that the surface of in-situ cleaved IrTe2 undergoes a structural transition from trigonal to triclinic lattice below transition temperature, accompanied by formation of unidirectional structural modulations with distinct wavelengths. As temperature approaches 4 K, the system changes into a phase with formation of a single modulated structure with a fully-developed insulating gap. DFT rules out the CDW instability as the origin of this transition, confirming local structural distortion induced orbital degeneracy leading to strong-repulsion between Te p-band, therefore producing an insulting Te surface layer while the bulk stays metallic. This research was conducted (QL, WL, MP) at the CNMS, sponsored at ORNL by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE. Research was supported (WL, SVK) by MSED, Basic Energy Sciences, the U.S. DOE. Fellowship support (AG) from the UT/ORNL Bredesen Center for Interdisciplinary Research and Graduate Education. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D53.00004: Topological conduction of Sb films on boron-doped graphene Chih-Kai Yang, Chi-Hsuan Lee It has been shown that thin antimony films can have topological surface states by adsorption of non-magnetic impurity atoms. Using density functional calculations, we show that Sb films placed on boron-doped graphene also have Dirac cones and can provide spin-polarized transport. The calculated binding energy indicates that it is a robust structure and thus a viable conduit for topological conduction. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D53.00005: Observation of electronic structure of silicene by scanning tunneling microscopy Youngtek Oh, Wonhee Ko, Insu Jeon, Hyo Won Kim, Hyeokshin Kwon, JiYeon Ku, Sung Woo Hwang, Hwansoo Suh Silicene, an atomic monolayer of silicon atoms, has a hexagonal symmetry and is expected to have Dirac fermions. Recently, silicene has been intensively investigated in various substrates such as Ag(111), ZrB2 (0001), and Ir(111). We grew a monolayer of silicene on the Ag(111) surface by ultrahigh vacuum deposition and annealing of silicon atoms. The geometric and electronic properties of silicene grown on the Ag(111) were investigated by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The (4x4) structures of silicene were observed in LEED patterns and STM images. We observed domains formed inside the silicene. The electronic properties of silicene were measured by scanning tunneling spectroscopy (STS). [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D53.00006: Epitaxial Co-Deposition Growth of CaGe$_{2}$ Films by Molecular Beam Epitaxy for Large Area Germanane Patrick Odenthal, Igor Pinchuk, Adam Ahmen, Walid Amamou, Josh Goldberger, Roland Kawakami Here, we report the successful co-deposition growth of CaGe$_{2}$ films on Ge(111) substrates by molecular beam epitaxy and their subsequent conversion to germanane by immersion in hydrochloric acid. We find that the growth of CaGe$_{2}$ occurs within an adsorption-limited growth regime, which ensures stoichiometry of the film. We utilize \textit{in situ} reflection high energy electron diffraction (RHEED) to explore the growth temperature window and find the best RHEED patterns at 750 $^{\circ}$C. Finally, the CaGe$_{2}$ films are immersed in hydrochloric acid to convert the films to germanane. Auger electron spectroscopy of the resulting film indicates the removal of Ca and RHEED patterns indicate a single-crystal film with in-plane orientation dictated by the underlying Ge(111) substrate. X-ray diffraction and Raman spectroscopy indicate that the resulting films are indeed germanane. \textit{Ex situ} atomic force microscopy shows that the grain size of the germanane is on the order of a few micrometers, being primarily limited by terraces induced by the miscut of the Ge substrate. Thus, optimization of the substrate could lead to the long-term goal of large area germanane films. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D53.00007: Tune the electronic and phonon properties of silicene and germanene through biaxial strain and electric field Jia-An Yan, Ryan Stein, Gregory Coard We presented a density-functional study of the effects of biaxial strain and perpendicular electric field on the electronic and phonon properties of the two-dimensional (2D) silicene and germanene sheets. The two factors can be applied along the parallel and perpendicular directions independently, and therefore increase the tunability on the electronic band structure and phonon properties in these 2D systems. Important quantities such as the Gr\"{u}neisen parameters will be calculated. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D53.00008: STM study of monolayer MoS$_{2}$ synthesized by Chemical Vapor Deposition Adam Mills, Chuanhui Chen, Yifei Yu, Linyui Cao, Changgang Tao Monolayer molybdenum disulfide (MoS$_{2})$, an atomically thin transition-metal dichalcogenide semiconductor with a direct band gap, as opposed to an indirect band gap in bulk MoS$_{2}$, has recently captured a lot of research interest for its distinctive optical and electronic properties, and potential applications such as field effect transistors, optoelectronic devices and chemical sensors. Using scanning tunneling microscopy, we have investigated monolayer MoS$_{2}$ synthesized by chemical vapor deposition. The structural and electronic properties of monolayer MoS$_{2}$ grown on glassy carbon and other substrates will be presented. We will also discuss our preliminary scanning tunneling spectroscopy measurements on these samples. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D53.00009: First Principles Study of Bismuth Films at Transition Metal Grain Boundaries Qin Gao, Michael Widom Recent experiments suggest that Bi impurities segregate to form bilayer films on Ni and Cu grain boundaries but do not segregate in Fe. To explain these phenomena, we study the total energies of Bi films on transition metal (TM) $\Sigma$3(111) and $\Sigma$5(012) grain boundaries (GBs) using density functional theory. Our results agree with the observed stabilities. We propose a model to predict Bi bilayer stability at Ni GBs which suggests that Bi bilayer is not thermodynamically stable on low energy (111) twist CSL GBs but is stable in most (100) twist CSL GBs. We investigated the interaction and bonding character between Bi and TMs to explain the differences among TMs based on localization of orbitals and magnetism. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D53.00010: Transfer of Epitaxial Thin Films to Carrier Substrates Carley Miki, Gabriel A. Devenyi, Stephen Jovanovic, Kristoffer Meinander, Jessica Carvalho, Guozhen Zhu, John S. Preston CdTe and ZnTe are important materials in the semiconductor industry and are currently being used in many devices such as solar cells, laser diodes, detectors, and LEDs. Sapphire substrates (Al$_2$O$_3$) have been found to yield high quality epitaxial films of these materials, but the cost of this substrate makes large scale growths unrealistic. Recently, a novel technique developed at McMaster University has been successful in transferring large areas of CdTe and ZnTe films grown by pulsed laser deposition from sapphire to a wide variety of carriers without altering the film or substrate. This allows the sapphire to be reused for an indefinite number of growths without extensive treatment, and films to be transferred to various carriers while maintaining their quality. The physics of this technique is currently not well understood, prompting an investigation of the interface between the film and substrate to characterize the atomic structure in this region. Results from this study will help to refine this technique and identify potential for new applications. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D53.00011: Is graphene more conductive than h-BN? Xiaoliang Zhong, Rodrigo Amorim, Alexandre Rocha, Ravindra Pandey Electronic tunneling through multilayers of graphene and h-BN sandwiched between gold electrodes is investigated by density functional theory together with the non-equilibrium Green's Function method. The calculated results predict similar transmittance characteristics for the device configuration consisted of graphene and h-BN monolayers, though the pristine graphene and h-BN layers are semimetal and semiconductor, respectively. The h-BN monolayer exhibits a higher degree of p-type doping due to electron transfer from boron to the contact gold atoms relative to that predicted for graphene. A strong coupling of electrode-monolayer at the device interface is therefore likely to be the cause of similar vertical electron tunneling characteristics of the device configurations considered. For the multilayer cases, h-BN shows an exponential dependency of transmission function on the number of layers, whereas multilayer graphene exhibits relatively high tunneling probability due to a stronger interlayer coupling between adjacent layers of graphene. [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D53.00012: Hydrogen Trapping in Carbon-Doped $h$-BN/Rh(111) Nanomesh Jarvis Loh, Sandeep Nigam, Ravindra Pandey, Govinda Mallick Atomic or molecular preferential adsorption on surface nanotemplates provides a facile and feasible means of fabricating ordered low-dimensional nanostructures with tailored functionality. In this study, by employing density-functional theory calculations, we demonstrate (1) the carbon doping of the (B,N)$=$(fcc$_{\mathrm{Rh}}$,top$_{\mathrm{Rh}}) h$-BN/Rh(111) nanomesh, and (2) the selective trapping of hydrogen atoms on these dopants at various sites of the nanomesh -- within the pore, on the wire, and at an intermediate site. Contrary to carbon-doped boron nitride sheets, it is energetically more favorable for a carbon impurity to replace a nitrogen atom as compared to a boron atom at all three sites of the nanomesh. In addition, the adsorption energy of hydrogen adsorbates is greater at the wire of a nitrogen-substituted nanomesh relative to that in its pore, while this adsorption energy is invariant at different sites in a boron-substituted nanomesh. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D53.00013: Spatial dependent van der Waals energy between graphene and boron-nitride Mehdi Neek-Amal, Francois Peeters The small mismatch between the honeycomb lattices of graphene (GE) and boron nitrate (h-BN) leads to long wavelength Moir\'{e} patterns. In order to describe such patterns it will require large size unit cells that are unattainable with \textit{ab-initio} calculations. Earlier density functional theory calculations imposed lattice matching between graphene and h-BN which induces strain and opens a gap of 4 meV [1]. In previous works the Moir\'{e} pattern in GE/h-BN was connected to the van der Waals interaction [2], but a clear theoretical microscopic analysis is still missing. We used atomistic simulations [3] with very large unit cells to investigate quantitative aspects of the connection between the vdW interaction and the Moir\'{e} patterns. The value and symmetry of the spatial dependent vdW energy is obtained which agrees with the recently reported Moir\'{e} patterns. \textit{Acknowledgement}: This work was supported by FWO-Vl, EU-Marie Curie and the Methusalem foundation. [1] B. Sachs \textit{et al}, Phys. Rev. B \textbf{84}, 195414 (2011); M. Zarenia \textit{et al}, Phys. Rev. B \textbf{86}, 085451 (2012). [2] C.R. Dean \textit{et al}, Nat. Nanotech. \textbf{5}, 722 (2010); J.H. Chen \textit{et al}, Nat. Nanotech. \textbf{3}, 206 (2008). [3] M. Neek-Amal and A. Lajevardipour, Comp. Mat. Sc. \textbf{49}, 839 (2010). [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D53.00014: Thermodynamic Studies of Decane on Boron Nitride and Graphite Substrates Using Synchrotron Radiation and Molecular Dynamics Simulations Nicholas Strange, Thomas Arnold, Matthew Forster, Julia Parker, J.Z. Larese Hexagonal boron nitride (hBN) has a lattice structure similar to that of graphite with a slightly larger lattice parameter in the basal plane. This, among other properties, makes it an excellent substrate in place of graphite, eliciting some important differences. This work is part of a larger effort to examine the interaction of alkanes with magnesium oxide, graphite, and boron nitride surfaces. In our current presentation, we will discuss the interaction of decane with these surfaces. Decane exhibits a fully commensurate structure on graphite and hBN at monolayer coverages. In this particular experiment, we have examined the monolayer structure of decane adsorbed on the basal plane of hBN using synchrotron x-ray radiation at Diamond Light Source. Additionally, we have examined the system experimentally with volumetric isotherms as well as computationally using molecular dynamics simulations. The volumetric isotherms allow us to calculate properties which provide important information about the adsorbate's interaction with not only neighboring molecules, but also the interaction with the adsorbent boron nitride. [Preview Abstract] |
Monday, March 3, 2014 5:18PM - 5:30PM |
D53.00015: Carrier Density Modulation in the Graphene/Ferroelectric Interface Diomedes Saldana-Greco, Christoph Baeumer, Moonsub Shim, Lane W. Martin, Andrew M. Rappe Atomic and electronic structure insights of the graphene/ferroelectric interface via density functional theory (DFT) calculations elucidate the yet unexplored theoretically anticipated strong coupling between graphene transport properties and the exposed ferroelectric polarization. A model system consisting of ferroelectric LiNbO$_{3}$ (0001) slab with graphene facing both up- and down-polarized surfaces has been constructed to investigate the nature of the interfacial interaction. Our DFT calculations predict that the electronic structure of graphene facing either polar surface is preserved with neat Dirac cones at the \emph{K} points in the Brillouin zone. We observed that the Dirac cone of the graphene in close contact with the up-polarized (down-polarized) LiNbO$_{3}$ surface is shifted below (above) the Fermi energy. Here, we demonstrate experimentally and theoretically that the doping levels of graphene can be modulated based on the ferroelectric polarization, temperature-induced potential inversion and surface reconstructions leading to increased and decreased electron concentration in graphene on up-polarized and down-polarized LiNbO$_{3}$ surfaces, respectively. [Preview Abstract] |
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