Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session B28: Focus Session: Optical Properties of Nanostructures II: Graphene, Graphite and Related Materials |
Hide Abstracts |
Sponsoring Units: DMP Chair: Shigeo Maruyama, University of Tokyo Room: Morial Convention Center 220 |
Monday, March 10, 2008 11:15AM - 11:27AM |
B28.00001: Optical studies of multilayer graphene in magnetic fields Hsiang-Lin Liu, G. L. Carr, K. A. Worsley, M. E. Itkis, E. Bekyarova, R. C. Haddon, A. N. Caruso We report the optical properties of multilayer graphene thin films grown on silicon substrate. The room-temperature reflectance and transmittance of the samples were measured over the energy range from the far-infrared to near-infrared. To extract the optical constants of the films, we analyzed all of the layers of this thin-film structure using a Drude-Lorentz model. From the parameters obtained, we compute the optical constants. With decreasing temperature, the far-infrared transmittance of the samples is increasing up to 4 {\%} down to 2 K. Interestingly, in an applied magnetic field of up to 10 Tesla, the giant positive magneto-optical effects over 20 {\%} are observed in the far-infrared region from 2 K to 300 K. Possible origin of these will be discussed. [Preview Abstract] |
Monday, March 10, 2008 11:27AM - 11:39AM |
B28.00002: Edge states and optical transition energies in carbon nanoribbons Jie Jiang, Wenchang Lu, Jerry Bernholc The local density of states (LDOS) of edge states and optical transition energies in carbon nanoribbons are investigated with density-functional calculations. The LDOS in either magnetic or non magnetic phases show peaks both below and above the Fermi level. The peaks in the two phases are localized in different energy ranges. Moreover, the LDOS in the two phases have the same decay shapes. The defects at zigzag edges are found to destroy spin-polarization in edge states. They also tend to increase the decay length in edge states by mixing defect and edge states. Thus, the LDOS measured by scanning tunneling spectroscopy shows different features depending on the edge quality. We also find that the optical transition energies $E_{ii}$ are not affected by the spin-polarization. However, edge effects tend to increase $E_{ii}$ values by 1.25/W, where W is the ribbon width. Therefore, the ratios of $E_{ii}$ in nanoribbons for different i are changed from those observed in single-wall carbon nanotubes. [Preview Abstract] |
Monday, March 10, 2008 11:39AM - 11:51AM |
B28.00003: Raman Studies of Electron-Phonon Coupling in Graphene and Graphite Intercalated Compounds J. Camacho, M. Y. Sfeir, A. T. Bollinger, A. C. Walters, C. A. Howard, M. Ellerby, J. A. Misewich, T. Valla Effects of the electron-phonon interaction in carbon-based materials can be seen in many physical properties, ranging from relatively high-Tc superconductivity in doped fullerenes and graphite intercalated compounds to being a limiting factor on the mobility of carriers in carbon nano-tubes. Despite the intensive research, these effects are not completely understood. Here we present Raman scattering studies of several long wavelength optical phonons in different graphene-based materials. We find that the frequency and line-width of some modes are very sensitive to electric field doping and to chemical doping of graphene sheets, reflecting the changes in interactions of these modes with charge carriers in the system. [Preview Abstract] |
Monday, March 10, 2008 11:51AM - 12:03PM |
B28.00004: Optical Selection Rule from Inversion Symmetry Breaking and Valley Optoelectronics in Graphene Wang Yao, Di Xiao, Qian Niu Inversion symmetry breaking allows contrasted circular dichroism in different $k$-space regions, which takes the extreme form of optical selection rules for interband transitions at high symmetry points. In graphene systems with broken inversion symmetry, this enables valley dependent interplay of electrons with light of different circular polarizations, in analogy to spin dependent optical activities in semiconductors. We discuss graphene based valley optoelectronics applications where light polarization information can be interconverted with electronic information. [Preview Abstract] |
Monday, March 10, 2008 12:03PM - 12:15PM |
B28.00005: Gate-Variable Optical Transitions in Graphene Feng Wang, Yuanbo Zhang, Chuanshan Tian, Caglar Girit, Alex Zettl, Michael Crommie, Y. Ron Shen Two-dimensional graphene monolayers and bilayers exhibit fascinating electrical transport behaviors. Using infrared spectroscopy we find that they also have strong interband transitions and, remarkably, their optical transitions can be significantly modified through electrical gating. This unique gate-dependence of interband transitions adds a valuable dimension for optically probing graphene bandstructure. For a graphene monolayer, it yields directly the linear band dispersion of Dirac fermions, while in a bilayer it reveals a dominating van-Hove singularity arising from interlayer coupling. [Preview Abstract] |
Monday, March 10, 2008 12:15PM - 12:27PM |
B28.00006: Filling-Factor-Dependent Magnetophonon Resonance in Graphene Kostyantyn Kechedzhi, Mark Goerbig, Jean-Noel Fuchs, Vladimir Falko We describe a peculiar fine structure acquired by the in-plane optical phonon at the $\Gamma$-point in graphene when it is brought into resonance with one of the inter-Landau-level transitions in the material. The effect is most pronounced when this lattice mode is in resonance with inter-Landau-level transitions $-,1\Rightarrow 0 $ and $0\Rightarrow+,1$ at a magnetic field $B_0 \approx 30$ T. The predicted mode splitting may be used to measure directly the strength of the electron-phonon coupling, and also to distinguish between circularly (left- and right-hand) polarized lattice modes. A similar effect is predicted in bilayer graphene in lower magnetic fields. \newline \newline [1] M.O. Goerbig, J.-N. Fuchs, K. Kechedzhi, V. I. Fal'ko, PRL 98, 087402 (2007). [Preview Abstract] |
Monday, March 10, 2008 12:27PM - 12:39PM |
B28.00007: Raman Spectrum of Strained Single Layer Graphene Minsheng Wang, Song Han, Kang L. Wang Two-dimensional single layer graphene (SLG) films are very attractive due to their unique electrical and optical properties. In this work, silicon nitride, silicon oxide and polyimide are used to induce strain in SLG sheets. Micro-Raman spectra reveal the evolution of graphene feature peaks under various stress conditions. Different peak position, width and shape are observed due to different stress type, level and direction. Changes of the second order D peaks show that strain affects not only the phonon spectrum but also the electron band through a double resonant Raman process. Relative intensity changes between D and G bands indicate that defects are introduced into graphene during some of the deposition processes, which usually are not observed in spin-coated SLG samples. Strain effects also can be utilized to further modify the electron band structure of graphene. [Preview Abstract] |
Monday, March 10, 2008 12:39PM - 12:51PM |
B28.00008: Infrared probe of charge dynamics in graphene transistors Zhiqiang Li, Erik Henriksen, Zhigang Jiang, Zhao Hao, Michael Martin, Philip Kim, Horst Stormer, Dimitri Basov We report on infrared (IR) spectroscopy of charge dynamics in monolayer graphene. IR reflectance and transmission measurements were performed on graphene transistors as a function of gate voltage. From these data, we obtained the optical conductivity of graphene at various carrier densities. The dominant feature of the optical conductivity is an interband transition with the onset at twice the Fermi energy, which evolves systematically with gate voltage. Similar behavior was observed with the Fermi level on either side of the Dirac point. We will compare these results with theoretical predictions and discuss several new aspects of the charge dynamics in graphene uncovered by this work. [Preview Abstract] |
Monday, March 10, 2008 12:51PM - 1:03PM |
B28.00009: The G-band phonon frequency in single layer graphene Hyungbin Son, Alfonso Reina, Mildred Dresselhaus, Jing Kong Recent experimental studies on the high-frequency phonon modes of as-deposited n-graphene layer (nGL) films report that the frequency of the G-band in single graphene layer is generally higher than that in nGL films (n>2) and highly ordered pyrolytic graphite (HOPG). However, our results show that the frequency of the G-band in single graphene layer approaches that in HOPG when the single graphene layer transfered to different substrate, sonicated, or exposed to NaOH. These results suggest that the difference in the frequency of the G-band in single graphene layer and HOPG is due to the strain generated in the deposition process. [Preview Abstract] |
Monday, March 10, 2008 1:03PM - 1:15PM |
B28.00010: Spatially resolved and polarized Raman spectroscopy of graphene Duhee Yoon, Hyerim Moon, Hyeonsik Cheong Graphene samples were prepared by micromechanical cleavage of graphite flakes on silicon wafer, which was covered with a 300-nm silicon oxide layer. Raman spectra of a single-layer graphene were clearly differentiated from those of a few layers of graphene sheets. We compared the spatially resolved micro-Raman spectra with atomic force microscopy to determine the number of layers for each sample, and variations of Raman spectra, which intensity and shift of Raman peak, were observed through the Raman image. The Raman G peak, corresponding to Raman active mode E$_{2g}$, was observed at $\sim $1590 cm$^{-1}$, and G' peak due to double resonance Raman scattering was observed at $\sim $2700 cm$^{-1}$. We performed polarized Raman spectroscopy of a single-layer graphene. The intensity of G peak was independent of polarization, in agreement with Raman tensor calculation. The variation of Raman intensity of G' peak was measured as a function of the analyzer angle. The intensity was maximum for parallel polarization and was minimum for perpendicular polarization. The depolarization ratio was 1/3. [Preview Abstract] |
Monday, March 10, 2008 1:15PM - 1:27PM |
B28.00011: Probing Edge defects in \textit{n} (\textit{n}=1,2..) Graphene Layer system via Raman Scattering Humberto Gutierrez, Awnish Gupta, Peter Eklund Results of a microRaman study (spot size $\sim $0.7 microns; 514.5 nm excitation) of an edge (or boundary) of n- layer graphene films is presented. Graphene (n=1 layer) exhibits a very narrow Lorentzian D-band at $\sim $1344 cm$^{-1}$ with FWHM $\sim $15 cm$^{-1}$. For 2$<$n$<$5, this narrow peak is found to split into four bands. Interestingly, the D band intensity of the edge is quite strong (1/4 of the G-band) If te defects are truly localized on the edge, this implies a better resonance than found for defects at the interior, or, on the other hand, the range of the defects may extend a long distance into the interior of the films and involve many sites. Polarized Raman studies on this D band were made with the incident field at an angle $\theta $ with the respect to the average direction of the edge. The scattered light was collected either parallel (H) or perpendicular (V) to the edge. The polar intensity plots I$_{V}(\theta )$ and I$_{H}(\theta )$ were found to exhibit a quadrupolar and dipolar pattern, respectively. [Preview Abstract] |
Monday, March 10, 2008 1:27PM - 1:39PM |
B28.00012: X-ray absorption spectroscopy of graphite oxides Hae-Kyung Jeong, Leyla Colakerol, Han-Jin Noh, Yun Pyo Lee, Mei Hua Jin, Per-Anders Glans, Jae-Young Kim, Kevin E. Smith, Chong Yun Park, Young Hee Lee We have investigated electronic structures of graphite oxide using x-ray absorption spectroscopy at carbon and oxygen K-edges. Unoccupied states such as $\pi ^{\ast }$ and $\sigma ^{\ast }$ states originating from sp$^{2}$ hybridization in graphite are also visible in the graphite oxide, even though the graphite oxide experiences a severe oxidation. Additional electronic states of the graphite oxide compared to that of pure graphite are ascribed to the functional groups such as epoxide, carboxyl, and hydroxyl groups that are present in the graphite oxide. [Preview Abstract] |
Monday, March 10, 2008 1:39PM - 1:51PM |
B28.00013: Symmetry breaking in epitaxial graphene probed by ARPES Aaron Bostwick, Taisuke Ohta, Jessica McChesney, K. V. Emtsev, Th. Seyller, Karsten Horn, Eli Rotenberg The energy bands of $n$-doped graphene on SiC(0001) have been observed to deviate significantly from the expected conical shape near the Dirac crossing[Bostwick et al 2007, Zhou et al 2007]. Two scenarios have been proposed to explain these deviations, either as originated from the real part of the electronic self-energy due to many body interactions[Bostwick et al], or from ``A-B'' symmetry-breaking due to chemical interactions between the graphene and the underlying layer[Zhou et al]. In this talk we present a number of arguments against the A-B symmetry breaking scenario, among which is the observed \textbf{k}-dependent intensity of the Fermi surface as measured by ARPES. We show that the observed intensity distribution is directly sensitive to the degree of A-B symmetry breaking and show that the upper limit for an energy gap in graphene on SiC is much smaller than the observed deviations in the band structure. [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