Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W1: Focus Sesson: Graphene: Nanostructures |
Hide Abstracts |
Sponsoring Units: DMP Chair: An-Ping Li, Oak Ridge National Laboratory Room: 001A |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W1.00001: Semiconductor–half-metal transition in zigzag-graphene-nanoribbons/graphene Mingxing Chen, Michael Weinert Magnetic and electronic properties of H-terminated zigzag graphene nanoribbons supported by graphene substrate are investigated using first-principles calculations. A critical width of 3 nm is found for the onset of electron-electron interactions between the edges. Weak edge magnetism of the nanoribbons is well preserved upon the presence of the graphene substrate due to the weak interaction between them, which on the other hand drives a size-dependent spin splitting of the edge states. As a result of the interaction, a semiconductor-halfmetal transition is observed. Our findings not only are of fundamental interest but also have practical implications in potential applications of graphene-based nanoelectronics. [Preview Abstract] |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W1.00002: Observations of superlattice Dirac points in one-dimensionally-rippled graphene on hexagonal BN using scanning tunneling spectroscopy Won-Jun Jang, Min Wook Lee, Soon-Hyeong Lee, Min Wang, Sung Kyu Jang, Minwoo Kim, Sungjoo Lee, Sang-Woo Kim, Young Jae Song, Se-Jong Kahng It has been predicted that superlattice potentials in graphene would induce new Dirac points due to lattice-induced chirality of charge carriers. In this talk, we present our experimental observations of new Dirac points in one-dimensionally-rippled graphene on hexagonal BN using scanning tunneling microscopy and spectroscopy. The ripples, formed by thermal cycles, showed two new Dirac points of which energy levels were proportional to 1/L, where L was the period of a ripple, in agreement with theoretical predictions. Our study shows that one-dimensional periodic potential is an accessible component for controlling electronic properties of graphene. [Preview Abstract] |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W1.00003: Imaging coherent transport in a mesoscopic graphene ring Damien Cabosart, Sebastien Faniel, Frederico R. Martins, Boris Brun, Alexandre Felten, Vincent Bayot, Benoit Hackens Mesoscopic graphene devices often exhibit complex transport properties, stemming both from the peculiar electronic band structure of graphene, and from the high sensitivity of transport to local disorder in this two-dimensional crystal. To disentangle contributions of disorder in the different transport phenomena at play in such devices, it is necessary to devise new local-probe methods, and to establish links between transport and the microscopic structure of the devices. Here, we present a spatially-resolved investigation of coherent transport inside a graphene quantum ring (QR), where Aharonov-Bohm conductance oscillations are observed. Thanks to scanning gate microscopy, we first identify spatial signatures of Coulomb blockade, associated with disorder-induced localized states. We then image resonant states which decorate the QR local density of states (LDOS). Simulations of the LDOS in a model disorder graphene QR confirm the presence of such scarred states. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W1.00004: Electronic Transport in Hexagonal Boron Nitride Encapsulated Graphene Nanoribbon Won Jong Yoo, Daeyeong Lee, Euyheon Hwang, Philip Kim The electronic transport properties of the hexagonal boron nitride (hBN) encapsulated graphene nanoribbon (GNR) are studied. We find that the transport gap of the hBN encapsulated GNR is almost identical to that of the same size GNR on the silicon dioxide (SiO$_2$) substrate in spite of their quantitatively different physical parameters, indicating that the transport gap of the hBN encapsulated GNR is affected mainly by edge disorders rather than surface disorders. The relatively lower density of Coulomb diamonds (20/V$\mu$m), larger charge island diameter (80 nm), longer hopping length (200 nm), and other results obtained from electrical and temperature dependent measurements show that the hBN encapsulated GNR has the less degree of disorder because of the less surface disorder. The insulating behavior within the transport gap can be understood through the one-dimensional variable range hopping (VRH) and it is maintained up to $\sim$50 K which is higher than that of the GNR on SiO$_2$. However, with increasing temperature the VRH transport behavior crosses over to the thermally activated insulating behavior. Moreover, the transport gap of the hBN encapsulated GNR shows clearer band edges and fewer impurity states within the band gap as compared with that of the GNR on SiO$_2$. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W1.00005: Semiconducting Graphene Ribbons Grown on Nitrogen-Seeded SiC Feng Wang, Gang Liu, Sara Rothwell, Meredith Nevius, Matthew Conrad, Philip Cohen, Leonard Feldman, Edward Conrad A wide band gap semiconducting form of graphene can be produced by growing a buckled form of graphene from a SiC$(000\bar{1})$ surface randomly seeded with nitrogen. In this work, we show that the disorder observed in this form of graphene can be substantially reduced by pre-patterning the nitrogen seeded SiC surface into trenches. The result of the patterning is highly improved film thickness variations, orientational epitaxy, domain size, and electronic structure. In addition, the ordering induced by this patterned growth offers a way to take advantage of the extremely high mobilities and switching speeds in C-face graphene devices while having the thickness uniformity and fabrication scalability normally only achievable for graphene grown on the SiC(0001) Si-face. [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W1.00006: Surface-assisted formation of graphene nanoribbons on Au surfaces Claudia Cardoso, Deborah Prezzi, Elisa Molinari, Andrea Ferretti The formation of graphene nanoribbons (GNRs) on Au(110) and Au(111), as based on the surface-mediated reaction of 10,10$'$-dibromo-9,9$'$ bianthracene (DBBA) molecules was investigated by means of first-principles calculations. The study was done in direct collaboration with experimental groups performing structural and spectroscopic characterization by means of STM, XPS/UPS, NEXAFS. Comparison between the Au(110) and Au(111) surfaces unveils the delicate interplay between surface atomic corrugation, molecular mobility, and adsorption energies, that drive the GNR growth. Concerning the Au(110) surface, we have studied the molecule/surface interaction at different stages of the GNR formation. The role of different reconstructions has been investigated, showing that both precursors and GNRs interact differently with different surfaces. Calculations for the precursor molecules showed that initial stages of the reaction crucially determine the final configuration and orientation of the GNRs. In the specific case of Au(111) we have also studied the evolution of the Au Shockley surface state as a function of GNR growth. We show that the GNR/Au interaction results in an upshift of the Shockley surface state of Au(111) by 0.2 eV, together with an increased electron effective mass. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 4:18PM |
W1.00007: Ballistic nanostructures for epitaxial graphene nanoelectronics Invited Speaker: Walt de Heer Graphene nanoelectronics [1] was inspired by carbon nanotube electronics. While carbon nanotubes demonstrated advantageous electronic properties, like room temperature ballistic transport, immunity to electromigration and significant bandgaps, manufacturability remains a problem. Independent of other graphene work research at Georgia Tech evolved from the premise that epitaxial graphene on silicon carbide could serve as viable platform for graphene based electronics. Epitaxial graphene (EG), known since the 1970's, is produced by sublimation of Si from the SiC surface. The 2D electronic and structural properties of EG are significantly superior to transferred graphene and, in contrast to transferred graphene, EG is scalable[2]. Nanopatterning is achieved by selective high temperature graphene growth on the sidewalls of structures that are etched in the SiC. These annealed graphene nanostructures demonstrate a host of remarkable properties. Recently 10 $\mu$m scale single channel room temperature ballistic transport (R$=$h/e$^{2}\approx $26 kOhm) has been observed in neutral graphene sidewall nanoribbons [3] (in contrast, similarly sized exfoliated graphene ribbons are insulators due to disorder). These ballistic nanoribbons, as well as other nanostructures are readily and reliably produced using optical lithography. Remarkably, the ballistic transport does not depend on the microstructure of the ribbon edges, thereby precluding current models for the effect. These ballistic ribbons can be used as quantum wires in graphene nanoelectronics. This breakthrough discovery has revitalized efforts towards the development of high-performance graphene nanoelectronics. In this talk I will present the status quo of this effort. The experiments that demonstrate ballistic transport will be discussed, include recent development of EG transistors with room temperature on-off ratios exceeding 10$^{6}$ and the development of semiconducting EG [4]. \\[4pt] [1] C. Berger, et al, Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics, J Phys Chem B 108, 19912-19916 (2004).\\[0pt] [2] M. Sprinkle, et al. Scalable templated growth of graphene nanoribbons on SiC, Nat Nanotechnol 5, 727-731 (2010).\\[0pt] [3] J. Baringhaus, et al Exceptional ballistic transport in epitaxial graphene nanoribbons, Nature 506, 349-354 (2014).\\[0pt] [4] J. Kunc, et al. Planar Edge Schottky Barrier-Tunneling Transistors Using Epitaxial Graphene/SiC Junctions, Nano Letters 14, 5170$-$5175 (2014). [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W1.00008: Atomically precise nitrogen-doped graphene nanoribbons Alexander Sinitskii There is a considerable interest in graphene nanoribbons (GNRs), few-nm-wide strips of graphene with high aspect ratios, because of their intriguing physical properties. For example, GNRs with zigzag edges are predicted to exhibit low-dimensional magnetism, while GNRs with armchair edges can possess large energy band gaps, making them promising materials for future electronics and photovoltaics. The ability to control structural parameters of GNRs, such as their width, edge structure and termination, with atomic precision is the key for practical realization of these intriguing nanoscale properties. Physical properties of GNRs can also be modified by their doping with heteroatoms, such nitrogen, resulting in nitrogen-doped GNRs or N-GNRs. In this talk I will demonstrate that large quantities of narrow atomically precise N-GNRs can be synthesized via Yamamoto coupling of molecular precursors containing nitrogen atoms followed by cyclodehydrogenation using Scholl reaction. Several types of N-GNRs with different doping levels have been synthesized and systematically studied by spectroscopic, microscopic and transport methods. Incorporation of nitrogen atoms in graphene lattice is shown to be an effective route to affect GNRs' band gap, doping level as well as aggregation behavior. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W1.00009: Superconducting Proximity Effect in Sidewall Graphene Nanoribbons Owen Vail, John Hankinson, Clement Bouvier, Claire Berger, Walt De Heer, Zhigang Jiang Epitaxial graphene nanoribbons (EGNRs) grown on sidewall SiC have recently emerged as a novel material system enabling single channel room temperature ballistic transport over micrometer distance. In this work, we fabricate Al-EGNR-Al junctions and study the electronic transport as a function of bias voltage, temperature, and magnetic field. We show that although the measured resistance across the junction is dominated by the EGNR, spectral features associated with superconductivity of Al electrodes are evident. These features are fully developed at low temperatures and evolve with magnetic field. We comment on the implication of our observations with respect to the electronic properties of sidewall EGNRs. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W1.00010: Spin orbit coupling and electron pairing instabilities in superconductors Armen Kocharian, Gayanath Fernando, Kun Fang, Alexander Balatsky Exact diagonalization, Lanczos and variational cluster approximation (VCA) have been used for accurate studies of Rashba spin-orbit effects in the presence of electron correlations. These have been carried out in order to address current challenging problems in superconductivity, magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures. The modeled spin-orbit coupling in assembled nano-ribbons (as arrays of clusters) in various two-dimensional square and topological honeycomb structures (generated by periodically repeated Betts lattices) provide an ideal playground for understanding various competing phases, electron pairing and phase separation instabilities in conventional and unconventional superconductors. Our models allow us to calculate the spectral functions and accurately extract electronic, magnetic properties including spin transport and electron pairing in these systems. The results also highlight important aspects of the interplay of the spin-orbit coupling with magnetic fields in graphene-like systems and unconventional superconductors induced by weak, moderate and strong electron interactions. [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W1.00011: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W1.00012: Bound states in single and bilayer graphenes by a one-dimensional potential well: continuum model versus lattice model Akihiro Okamoto, Takehito Yokoyama, Shuichi Murakami Edges of a graphene show characteristic edge states depending on its edge shapes such as zigzag or armchair. Instead of these edge states, we consider bound states on a graphene with a one-dimensional potential well. We set the potential well which has a finite width in one direction and is infinitely extended in the other direction. We consider both the single layer and bilayer graphenes. In the continuum model of Dirac cones, we can analytically calculate the bound states, and discuss their properties. Then we also calculate analytically the bound states, also for the tight-binding model for single-layer graphene. It reproduces the results for the continuum model, such as a linear dispersion of bound states near K and K$'$ points. We discuss how the bound states dispersion change for various potential profiles. [Preview Abstract] |
Thursday, March 5, 2015 5:18PM - 5:30PM |
W1.00013: Graphene nanopatterning with 2.5 nm precision: combining bottom-up and top-down techniques Jose M. Gomez-Rodriguez, Antonio J. Martinez-Galera, Ivan Brihuega, Angel Gutierrez-Rubio, Tobias Stauber The selective modification of pristine graphene represents an essential step to fully exploit its potential. Here we merge bottom-up and top-down strategies to tailor graphene with nanometer accuracy. In a first step, graphene electronic properties are macroscopically modified using the periodic potential generated by the self assembly of metal cluster superlattices on a graphene/Ir(111) surface. Then, we show that individual metal clusters can be selectively removed at room temperature by a STM tip with perfect reproducibility, which enables one to nanopattern the system down to the 2.5 nm limit given by the distance between neighbouring clusters, i.e., the periodicity of the moire-pattern. The method can be carried out on micrometer sized regions, with clusters of different materials -which allows tuning the strength of the periodic potential- and the structures so created are stable even at room temperature. As a result, we can strategically combine graphene regions that should present large differences in their electronic structure to design graphene nanostructures with specific functionalities. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700