Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y8: Ultrathin and Layered Materials |
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Sponsoring Units: DCMP Chair: Yuan Huang, Brookhaven National Laboratory Room: 006C |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y8.00001: Sliding friction of adsorbed films on fullerene substrates with tunable conductivity Samuel Kenny, Jacqueline Krim Friction at the nanoscale is known to encompass phononic, electrostatic, conduction electronic and magnetic effects [1], with electronic contributions being less well characterized than phononic contributions. Experiments measuring friction and diffusion of adsorbed gases on superconductors, for example, have revealed a decrease in resistance of the film concomitant with a decrease in sliding friction, but the electrical properties were difficult to fine tune.[2] Since their discovery nearly thirty years ago, C$_{60}$ and related compounds have been widely studied in the context of photovoltaic research and related photoconductive properties. As such, they constitute ideal systems for studies of sliding friction on substrates with variable electrical resistivity.[3] We report here our quartz crystal microbalance studies of the frictional properties of adsorbate molecules sliding on fullerene films irradiated by visible laser light so as to tune the electrical resistivity of the substrate. [1] J. Krim, Advances in Physics, 61 (2012) pp. 155-323. [2] M. Highland et al., PRL (2006). [3] A. Hamed \textit{et al.}, PRB 47 (1993) pp. 10873-10880. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y8.00002: Water Interaction with Pristine and Nanopatterned Graphite Surfaces Dinko Chakarov We used number of surface sensitive techniques to study and compare the interaction of water with pristine surface of highly oriented pyrolytic graphite and model nanostructured surfaces fabricated by hole-mask colloidal lithography and oxygen plasma etching. Surface morphology and concentration of defects play important role and determine the amount of water bound in two- and three-dimensional hydrogen-bonded networks and thus the structure of ice films. Similarly, the amount and concentration of intersheet openings control the rate of water intercalation into graphite structures. The new findings are of particular interest for development of graphene exfoliation methods and for better understanding of graphene functionalization. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y8.00003: Quantum tunneling effects of 2-dimensional materials and their application for fast time response of deep UV detectors Peter Xianping Feng, Ali Aldalbahi We report on our approach to low substrate temperature, digital control, fast ($\sim$ 1 minute) synthesis of 2D single crystalline BNNSs. We focus our experiments on studies of various effects (temperature, tunneling, breakdown, polarization, subtract, thickness) on electrical and electronic properties, as well as on sensitivity, response and recovery times, repeatability, lifetime of BNNSs-based deep UV detectors. Raman scattering spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), Transmission electron microscopy (TEM) and electrometer were used to characterize the BNNSs. SEM and TEM measurements clearly indicate that each sample/membrane consists of a large amount of ultra-thin, high-quality BNNSs with distribution over entire surfaces of substrates (3x3 cm$^{2})$. Electrical characterization reveals the effects of temperature on the electrical \textbf{c}onductivity of transparent BNNSs highly depend on the directions of observations in the 2D case but vanished from the 3D bulk materials or thick films. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 8:48AM |
Y8.00004: Observation of Single and Degenerated Charge Ordering in IrTe$_{\mathrm{2}}$ Hyo Sung Kim, Tae-Hwan Kim, Sooran Kim, Kyoo Kim, Byung Il Min, Yong-Heum Cho, Jun Jie Yang, Sang-Wook Cheong, Han Woong Yeom We investigate the intriguing broken symmetry low temperature phases of IrTe$_{\mathrm{2}}$ using high-resolution scanning tunneling microscopy and spectroscopy. We experimentally separate the structural and electronic modulations of the stripe phase reported previously. This result clearly indicate the charge ordering in the surface Te layer, which is consistent with the expectation of the It dimerization and charge ordering model but unambiguously denies the charge-density-wave-and-soliton model. In addition, we observe a metastable honeycomb charge-ordered phase. This phase is thought to be a 3$q$ state of the stripe phase in analogy with the 2$q$ (3$q)$ state description of the checkerboard charge order (the skyrmion spin order). [Preview Abstract] |
Friday, March 6, 2015 8:48AM - 9:00AM |
Y8.00005: Surface X-Ray Scattering Studies of TiSe$_2$ Thin Films Grown on Se-Terminated GaAs(111)B Xinyue Fang, Hawoong Hong, Yang Liu, Shih-Chang Weng, T.-C Chiang Titanium Diselenide (TiSe$_2$) is a prototypical charge density wave (CDW) compound which transforms into a commensurate (2$\times$2$\times$2) superstructure upon cooling to below about 200 K. This transition is marked by substantial changes in the transport properties. Although this systems has been studied extensively, the underlying physical mechanism for the structural distortion is still under debate. Studying thin films of TiSe$_2$ provides a means to tune the electronic interactions through reduced dimension, and the effects on the CDW transition could provide valuable information about the mechanism. We have successfully grown TiSe$_2$ epitaxial films on Se-terminated GaAs(111)B substrates via MBE. The optimum growth condition has been determined, and the CDW order parameter has been measured as a function of temperature for different film thicknesses. [Preview Abstract] |
(Author Not Attending)
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Y8.00006: Ag(111)-$\surd $3$\times$$\surd $3-Silicene Versus Si(111)-$\surd $3$\times$$\surd $3-Ag surface Hui Li Since 2012, silicene has been successfully grown on Ag(111) surface. We have provided reasonable atomic models of $\surd $3$\times$$\surd $3 silicene. However, the atomic and electronic structures of $\surd $3$\times$$\surd $3 silicene are still heavily debating, especially, it is easily to be confused to the Si(111)-$\surd $3$\times$$\surd $3-Ag surface. Here, I give a report of our recent works on silicene. With first-principles calculations combined with STM observations, we studied the structures of multilayer silicene on Ag(111) substrates, which all have $\surd $3$\times$$\surd $3 relaxed surfaces, and diamond-like stacking mode. Both calculations and STS show such silicon surface has strong Dirac-cone-like surface state, indicating the multilayer silicene possesses a new kind of silicon surface. The Si(111)-$\surd $3$\times$$\surd $3Ag surface is further compared to epitaxial silicene. It is found that the simulated STM images of both surfaces are similar, the there is also strong surface state for Si(111)-$\surd $3$\times$$\surd $3-Ag surface. However, the different temperatures for symmetry-breaking phase transitions and different H-adsorption structures can be used for distinguishing such two surfaces. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y8.00007: Growth and Characterization of Silicon at the 2D Limit Andrew Mannix, Brian Kiraly, Mark Hersam, Nathan Guisinger Because bulk silicon has dominated the development of microelectronics over the past 50 years, the recent interest in two-dimensional (2D) materials (e.g., graphene, MoS$_{\mathrm{2}}$, phosphorene, etc.) naturally raises questions regarding the growth and properties of silicon at the 2D limit. Utilizing atomic-scale, ultra-high vacuum (UHV) scanning tunneling microscopy (STM), we have investigated the 2D limits of silicon growth on Ag(111). In agreement with previous reports of \textit{sp}$^{2}$-bonded silicene phases, we observe the temperature-dependent evolution of ordered 2D phases. However, we attribute these to apparent Ag-Si surface alloys. At sufficiently high silicon coverage, we observe the precipitation of crystalline, \textit{sp}$^{3}$-bonded Si(111) domains. These domains are capped with a $\surd $3 honeycomb phase that is indistinguishable from the silver-induced $\surd $3 honeycomb-chained-trimer reconstruction on bulk Si(111). Further \textit{ex-situ }characterization with Raman spectroscopy, atomic force microscopy, cross-sectional transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy reveals that these sheets are ultrathin sheets of bulk-like, (111) oriented, \textit{sp}$^{3}$ silicon. Even at the 2D limit, scanning tunneling spectroscopy shows that these silicon nanosheets exhibit semiconducting electronic characteristics. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y8.00008: Growth of Si thin film on 6H-SiC(0001) Hsin-Ju Wu, M. Tien Hoang, Yuntao Li, Phillip N. First Graphene is much studied for its unusual electronic properties. Other carbon group elements such as silicon (Si) and germanium (Ge) also are predicted to have stable 2D phases for which the electronic structure and properties could be still more interesting. Silicon carbide, already an excellent insulating substrate for epitaxial graphene, could potentially play a similar role for silicene. Commonalities in the substrate and processing may lead to the integration of carbon and silicon technologies. Here, we use surface analysis techniques (LEED, AES, STM) to investigate the formation of 2D Si on SiC(0001), under low pressures of silane or silicon. Similar methods allow control of surface graphene growth by compensating Si desorption from SiC. Among several Si-rich reconstructions, we find a single stable hexagonal phase, at a coverage close to twice the Si density predicted for silicene, and with a unit cell consistent with a commensurate layer of silicene or silicane. For a graphitized SiC starting surface, silane is shown to etch graphene, reforming SiC. [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y8.00009: Layering-induced Superlubricity: Gold on Graphite Andrea Vanossi, Roberto Guerra, Erio Tosatti By means of realistic MD simulations, we explore the static friction trend as a function of the true contact area and the model dimensionality for 2D gold nanoislands and 3D gold nanoclusters deposited on graphite, interesting tribological systems whose slow and fast dynamics have been previously investigated [1]. For increasing island size, because of the relative gold-graphite lattice mismatch, the interface stress energy has the chance to pile up by forming frustrated unmatched (i.e., incommensurate) regions and to develop a continuous solitonic pathway, foreshadowing a possible condition for the occurrence of ultra-low friction regimes. The significant reduction of the depinning threshold, towards superlubricity, with the system dimensionality can be ascribed to a layering-induced effective stiffness of the interface contact, favoring the natural Au-C lattice incommensurability. \\[4pt] [1] R. Guerra, U. Tartaglino, A. Vanossi, and E. Tosatti, Nature Materials 9, 634 (2010). [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y8.00010: Electrostatic Manipulation Of Graphene On Graphite Carlos Untiedt, Carmen Rubio-Verdu, Giovanni Saenz-Arce, Jes\'us Martinez-Asencio, David C. Milan, Mohamed Moaied, Juan J. Palacios, Maria Jose Caturla Here we report the use of a Scanning Tunneling Microscope (STM) under ambient and vacuum conditions to study the controlled exfoliation of the last layer of a graphite surface when an electrostatic force is applied from a STM tip. In this work we have focused on the study of two parameters: the applied voltage needed to compensate the graphite interlayer attractive force and the one needed to break atomic bonds to produce folded structures. Additionally, we have studied the influence of edge structure in the breaking geometry. Independently of the edge orientation the graphite layer is found to tear through the zig-zag direction and the lifled layer shows a zig-zag folding direction. Molecular Dinamics simulations and DFT calculations have been performed to understand our results, showing a strong correlation with the experiments. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y8.00011: A combined experimental and theoretical study of Rashba-split surface states on the $(\sqrt{3}\times \sqrt{3})$ Pb/Ag(111)$R30^{\circ}$ surface Matthias Bode, Lydia El-Kareh, Arne Buchter, Hendrik Bentmann, Friedrich Reinert, Stefan Bl{\"u}gel, Gustav Bihlmayer We report on a combined low-temperature scanning tunneling spectroscopy (STS), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) investigation of the $(\sqrt{3}\times \sqrt{3})R30^{\circ}$ Pb/Ag(111) surface alloy which provides a giant Rashba-type spin-splitting. With STS we observed spectroscopic features that are assigned to two hole-like Rashba-split bands in the unoccupied energy range. By means of STS and quantum interference mapping we determine the band onsets, splitting strengths, and dispersions for both bands. The unambiguous assignment of scattering vectors is achieved by comparison to ARPES measurements. While intra-band scattering is found for both Rashba bands, inter-band scattering is only observed in the occupied energy range. Spin- and orbitally-resolved band structures were obtained by DFT calculations. Considering the scattering between states of different spin- and orbital character, the apparent deviation between experimentally observed scattering events and the theoretically predicted spin polarization could be resolved. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y8.00012: Effects of Surface Roughness and Electron-Phonon Interaction on Electron Transport of Ultrathin Epitaxial Copper Films Yukta Timalsina, Andrew Horning, Robert Spivey, Kim Lewis, Gwo-Ching Wang, Toh-Ming Lu We report effects of surface roughness and electron-phonon interaction on transport properties of electrons in ultrathin epitaxial copper films of thickness ranging from 5 nm to 500 nm grown on Si(100) substrates. The transport of electrons in the film was examined by measuring the temperature dependent resistivity in the temperature range of 5 K to 300 K. We demonstrate that the temperature independent component of resistivity can be described by the root-mean-square-surface roughness and lateral correlation length with no adjustable parameter, using a recent quasi-classical model developed by Chatterjee and Meyerovich [1]. However, the temperature dependent component of the resistivity can be described using the Bloch-Gr\"{u}neisen formula with a thickness dependent electron-phonon coupling constant and a thickness dependent Debye temperature. We show that the increase of the electron-phonon coupling constant with the decrease of film thickness gives rise to an enhancement of the temperature dependent component of the resistivity.\\[4pt] [1] Chatterjee S and Meyerovich A E 2010 Interference between bulk and boundary scattering in high quality films \textit{Phys. Rev. B} \textbf{81} 245409--10 [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y8.00013: Interplay between Electromagnetic and Coulomb Coupling Danhong Huang, Godfrey Gumbs, Alexei Maradudin, Bo Gao Both the transverse electromagnetic and longitudinal coulomb couplings of the surface-plasmon mode to the collective excitation of Dirac electrons are investigated. The unique features of coupled quantum-plasmon modes are demonstrated. The predicted dispersion relations of these quantum-plasmon modes should be experimentally observable. For a double-layer graphene structure, the interplay between the interlayer Coulomb forces and the electromagnetic coupling to each layer is calculated. The effective polarizability matrix for coupled double-layer graphene and a semi-infinite conductor is obtained for constructing an effective-medium theory, which includes correlation effects from the Coulomb interaction between electrons in graphene and the conductor as well as the electromagnetic field between them. [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y8.00014: Semiconductor- to Metallic-like Behavior in Bi Thin Films Deposited on (100) KCl Substrate Thanh Nhan Bui, Jean-Pierre Raskin, Benoit Hackens Bi thin films, with a thickness of 100 nm, are deposited by electron-beam evaporation on a freshly cleaved (100) KCl substrate. The deposition temperature ranges from room temperature up to 170 $^{\circ}$C. Scanning electron microscopy reveals that films deposited at room temperature present a maze-like microstructure on its surface typical of the rhombohedral (110) texture as confirmed by X-ray diffraction. By heating the substrate to a temperature above 80 $^{\circ}$C during the deposition, another microstructure appears characterized by concentric triangular shapes corresponding to the trigonal texture. Temperature dependence of the resistivity from room temperature down to 10K shows a semiconductor-like behavior for films deposited at room temperature and a metallic-like behavior for films deposited above 80 $^{\circ}$C. From low temperature magnetoresistance measurements (at 10K and up to 6 T), we extract the electronic transport parameters (mobility and charge carrier concentration). These data, together with the average grain size, help us provide an explanation for the transition between both behaviors. [Preview Abstract] |
Friday, March 6, 2015 10:48AM - 11:00AM |
Y8.00015: Synthesis of Ultra-Thin Single Crystal MgO/Ag/MgO Multilayer for Controlled Photocathode Emissive Properties Daniel Velazquez, Rachel Seibert, Zikri Yusof, Jeff Terry, Linda Spentzouris Developments of new accelerator technologies such as free-electron lasers and high-energy accelerators, among others, continuously set requirements for particle sources to produce higher beam flux. The emissive properties of these photocathodes directly influence the accelerator beam flux and thus the performance of the accelerator as a whole. The objective of this project is to test the possibility of engineering the photoemissive properties of materials for potential use as photocathodes. For this purpose we use a Density Functional Theory calculations by collaborator Karoly Nemeth et al. [Phys. Rev. Lett. 104, 046801, 2010], which predict a thickness dependent change in the band structure that results in a change in the work function and dispersion of occupied states at the Fermi level. Multilayered MgO/Ag/MgO in the crystallographic orientations (001) and (111) were grown on Ag/MgO(001) and Ag/Si(111), respectively using pulsed laser deposition (PLD). A series of surface probing techniques were used to characterize physical, chemical and photoemissive properties of the films. [Preview Abstract] |
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