Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V24: Focus Session: Nanotube Related Hybrid Structures |
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Sponsoring Units: DMP Chair: Daniel Finkelstadt, Naval Research Laboratory Room: 326 |
Thursday, March 19, 2009 8:00AM - 8:36AM |
V24.00001: Broken Optical Symmetry in DNA-SWNT Hybrids: Spectroscopic Signaling of the Helical Wrap Invited Speaker: Functionalizing single-stranded DNA on a single-wall carbon nanotube (SWNT) has allowed isolating individual tubes, making them soluble, and separating SWNTs according to their chirality. Such strong technological impact motivated our study of the optical properties of the DNA-SWNT hybrids, commonly used now for the solution-based fabrication and experiments. The helicity of the DNA wrap may interfere with the intrinsic Hamiltonian of the SWNT and result in bandstructure modulation. Our modeling predicts a symmetry lowering in the hybrid due to the Coulomb potential of the regular helical wrap of the ionized backbone of the ssDNA, followed by the qualitative changes in the cross- or circularly polarized SWNT absorption spectrum (with no or little change in the parallel polarization). In particular, we predict the appearance of a new peak in the cross-polarized absorption of the ssDNA-SWNT at a frequency lower than that of all allowed transitions in the bare tube. Such effect can be used for optical identification of the wrap at sufficient ssDNA coverage. Wrap signaling happens also via another optical effect, a strong circular dichroism even in the complex with an achiral SWNT, and even at the frequencies where ss-DNA has no absorption features at all. Symmetry of the wrap is central to determine such a circular dichroism of the hybrid. Having in mind that the exact geometry of a DNA wrap for an arbitrary tube is not precisely known yet, we put forward a general model capable of tracking optical effects, varying the parameters of the wrap and/or tube diameter. For various ssDNA backbone helical angles and for various tubes we predict different absorption spectra, though a general qualitative feature of the helical symmetry breaking, the appearance of new van Hove singularities and circular dichroism, must be present. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V24.00002: Color Detection Using Chromophore-Nanotube Hybrid Devices Xinjian Zhou, Thomas Zifer, Bryan Wong, Karen Krafcik, Fran\c{c}ois L\'eonard , Andrew Vance In this talk, we will present a nanoscale color detector based on a single-walled carbon nanotube functionalized with azobenzene chromophores, where the chromophores serve as photoabsorbers and the nanotube as the electronic read-out. By synthesizing chromophores with specific absorption windows in the visible spectrum and anchoring them to the nanotube surface, we demonstrate the controlled detection of visible light of low intensity in narrow ranges of wavelengths. Our measurements suggest that upon photoabsorption, the chromophores isomerize from the ground state trans configuration to the excited state cis configuration, accompanied by a large change in dipole moment, changing the electrostatic environment of the nanotube. We will also present our all-electron ab initio calculations that are used to study the chromophore-nanotube hybrids and show that the chromophores bind strongly to the nanotubes without disturbing the electronic structure of either species. Calculated values of the dipole moments support the notion of dipole changes as the optical detection mechanism. [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V24.00003: Spectral Features of Carbon Nanotube Films Changeable With Increasing Thickness John H. Lehman, Katalin Kamar\'as, \'Aron Pekker, Katherine E. Hurst, D.B. Tanner We have investigated an apparent contradiction with respect to optical spectroscopy of carbon nanotube films. The measured absorbance shows ``inverted'' features: local maxima for dilute suspensions correspond to local minima for thick films. The inversion is reconciled by taking into account the saturation of absorption in thick films, when all the light is absorbed in the sample. In this case, the measured direct absorption is (1-R), and independent of thickness. Kramers-Kronig analysis of transmittance data, which provides a means to model absorbance for material ranging from nearly transparent to almost completely opaque, provides values of refractive index for a film of nanotubes. (Borondics et al., PRB 74, 045431 (2006)). From these values, we determined (1- R- T) at many values of the film thickness. This calculation is corroborated with measurements based on the spectral responsivity of a pyroelectric detector and the absolute absorbance of the films. These results are consistent with data on nanotube suspensions by Zhang et. al. (J. Phys. Chem B, 108, 8136 (2004)), representing the limiting case of transparent samples, as well as films by Lehman et. al. (J. Phys. Chem. C, 112, 11776--11778 (2008)) representing the other limiting case of completely opaque samples. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V24.00004: Light emitting peapods: A first-principles study Matus Milko, Tayebeh Movlarooy, Claudia Ambrosch-Draxl Nanohybrids i. e. single wall carbon nanotubes with encapsulated organic molecules have been proposed for opto-electronic devices as they combine the unique mechanical and electronic properties of nanotubes with the desired optical properties of $\pi$-conjugated molecules. We investigate structural, cohesive and optical properties of these hybrid systems using density functional theory. Including the contributions for the non-local dispersive interactions, we examine in a systematic manner the effect of tube diameter and chirality on the stability and bonding characteristics of the peapod as well as the position of the molecule inside the tube. We find that these systems are almost exclusively van-der-Waals bound. Based on a series of oligo-thiophenes encapsulated into zig-zag nanotubes, we explore how the presence of the molecules inside the cavity can alter the electronic and optical properties. In particular, we inspect new features in the dielectric and loss functions due to transitions between the states of the molecule and the nanotube. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V24.00005: Friction and Stability of Carbon Onions Films in Vacuum R.A. Al-Duhaileb, B.W. Jacobs, M.A. Crimp, V.M. Ayres, A. Hirata, M. Horikoshi, M.G.I. Galinato, N. Lehnert Planar graphite is a state-of-the-art low friction solid lubricant. However, in vacuum environments, graphite-based solid lubricants require potentially harmful heavy metal additives to maintain tribological performance. Recent experiments by our group indicate that carbon onions show excellent tribological performance ($\sim $0.03 friction coefficient) without the addition of heavy metal additives. They are therefore good candidates for environmentally benign solid lubricants for use in vacuum. Carbon onion film stability to prevent exposure of un-lubricated surfaces is also an important issue. Tribological performance assessed using ball-on-disk friction measurements equivalent to a 10 m sliding distance indicated that a 15 wt.{\%} solution at 80\r{ }C peroxide oxidation treatment improved the film stability. In the present work, carbon onion friction and film stability are correlated with fundamental structural and chemical properties investigated by high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and multi-wavelength micro-Raman spectroscopy at 77K. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V24.00006: Computational Study on the Structural and Electronic Properties of Various Fullerene Derivatives Sora Park, Jeung Sun Ahn, Young-Kyun Kwon Using $\em{ab~initio}$ density functional theory, we investigate the structural and electronic properties of various fullerene derivates. The equilibrium structures of various additives adsorbed on a fullerene molecule forming fullerene adducts are computed through the geometry relaxation. For a given fullerene adduct, we also calculate the optimum configuration with a different number of additives. In tandem with the structural studies, we calculate the dependence of the HOMO-LUMO gap of each fullerene adduct on the number of additives, and on their relative positions and orientations. Further, using the GW approximation, we also examine the quasiparticle electronic structure of various fullerene derivates. [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V24.00007: Diffusion of Various Molecules through Crystalline C$_{60}$ Solid and their Electronic and Vibrational Properties Young-Kyun Kwon First-principles density functional theory is used to study the diffusion of various molecules including diatomic molecules, inert gas molecules , and small metal atoms, and so on, through the C$_{60}$ solid. For each case, the energy surface of a diffusion path is calculated while performing full geometry relaxation of the whole system. Such studies are performed while changing the concentrations of diffusing molecules. The effects of these molecules on the electronic properties of C$_ {60}$ solid are also examined. Especially for diatomic molecules, such as H$_2$, N$_2$, and O$_2$, their frequency shifts are calculated relative to their corresponding counterparts. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V24.00008: Simulation of Fe$_{n}$-doped C$_{60}$ Monolayer on \textit{h}-BN/Ni (111) Lan Li, Hai-Ping Cheng We have performed first-principles calculations based on density functional theory to investigate the structure, electronic structure and magnetic properties of Fe$_{n}$-C$_{60}$ complexes. Interfaces that consist of a C$_{60}$ monolayer, a supporting h-BN/Ni (111) layers, and the transition metal Fe$_{n}$ ($n$ = 1-4 {\&} 15) have been thoroughly characterized. Electron transfer has been observed from the Fe ions to the C$_{60}$ molecules, which leads to the domination of ionic character on the Fe-C$_{60}$ bonding. Furthermore, the Fe$_{n}$-doped C$_{60}$ systems show strong hybridizations between s-, d- orbitals of Fe atoms and $p$-orbital (\textit{$\pi $}-like) of C atoms. The spin of the net transferred electrons from Fe$_{n}$ to C$_{60}$ is spin minority, which leads to a magnetic moment in C$_{60}$ opposite to the total magnetic moment of the system. All of the electronic structure calculations have been performed in generalized gradient approximation (GGA) and local density approximation (LDA). In Fe$_{4}$C$_{60}$ and Fe$_{15}$C$_{60}$ systems, we have also performed GGA+U and LDA+U calculations for comparison. [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V24.00009: Superatom states in an endohedral fullerene Tian Huang, Min Feng, Jin Zhao, Hrvoje Petek, Shangfeng Yang, Lothar Dunsch Motivated by the recent discovery of superatom states in C$_{60}$[1], we studied the electronic structures of an endohedral fullerene, Sc$_{3}$N@C$_{80}$, adsorbed on copper surface by LT-STM experiment and DFT calculation. Both experimental and calculated results show that superatom states also exist in Sc$_{3}$N@C$_{80}$. Different from the C$_{60}$, the encapsulated cluster (Sc$_{3}$N-) in Sc$_{3}$N@C$_{80}$ distorts the nearly-spherical potential of the carbon cage, making the atom-like orbitals look asymmetric in the STM images. The adsorbed molecules exhibit various shapes of superatom orbitals due to the different orientation of the Sc$_{3}$N@C$_{80}$ on the surface. When two molecules form a dimer, however, the strong intermolecular hybridization overcomes the perturbation induced by the inside clusters, making all the dimers to have similar H$_{2 }$like molecular orbitals with clear bonding and anti-bonding characteristics. [1] Min Feng, Jin Zhao, Hrvoje Petek Science, 320,359, 2008. [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V24.00010: Isotropic Wave Function Delocalization in C$_{60}$ Molecular Assemblies Min Feng, Jin Zhao, Hrvoje Petek Electronic wave function delocalization in a molecular material is highly surprising. Here, we describe a new paradigm of strong intermolecular hybridization of a hollow core-bound molecular state in C$_{60}$ assemblies. In 1D C$_{60}$ wire and 2D C$_{60}$ island, LT-STM revealed extensive, isotropic wave function delocalization at energy above 3.5eV, in contrast with the poor intermolecular wave function overlap of the $\pi $-molecular orbitals. DFT indicates that a new kind of molecular orbital, which is derived from the central potential of the hollow cage shape of C$_{60}$, is responsible for this NFE like wave function delocalization. This central potential derived from the screening interaction and gives rise to s, p, d, etc., symmetry atom-like orbitals, which we dub the superatom molecular orbitals (SAMOs). Studies show how these atomlike orbitals hybridize into H$_{2}$ molecule-like $\sigma $ and $\pi $ symmetry bonding/antibonding orbitals of C$_{60}$ dimmers, and for larger aggregates, with alkali atom-like NFE dispersions. As a common consequence of a hollow topology, we expect that similar SAMO states will exist in other molecules derived by wrapping and rolling molecular sheets into hollow cages and nanotubes. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V24.00011: First-principles calculation of electronic structures of new C$_{60}$ polymers Taichi Kosugi, Shinji Tsuneyuki C$_{60}$ fullerene molecules form fcc crystalline structure at an ambient pressure and temperature. It has been both theoretically and experimentally confirmed that this structure undergoes phase transitions into various structures at high temperatures and high pressures. Yamanaka et al. experimentally found that the individual C60 molecules in fcc structure, which are weakly bonded via van der Waals interactions, are connected to its neighbouring molecules under high temperature and high pressure, leading to the two-dimensional layered insulating rhombohedral polymer 2D-r, which is further polymerized under higher pressure and temperature into the three-dimensional polymer 3D-r. We searched for a new rhombohedral structure of C$_{60}$ polymer using ab initio calculations of the electronic structures and compared it with the experimentally observed data. In addition we quantitatively analyzed how the differenece between the chemical bondings in these structures affect their energetics. [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V24.00012: Role of OH Adsorption on the Properties of MRI contrast agent Gd$_{3}$N@C$_{80}$ Vince Ong, Shiv Khanna, Panos Fatouros Endohedral metallofullerenes Gd$_{3}$N@C$_{80}$ decorated with hydroxyl groups are now known to be excellent contrast enhancement agents for Magnetic Resonance Imaging (MRI) leading to strong relaxivity enhancements. One of the outstanding issues is the nature of OH adsorption and its effect on the properties of endohedral Gd$_{3}$N motif. We have carried out theoretical studies on the electronic structure and magnetic properties of the endohedral metallofullerenes functionalized with hydroxyl groups to demonstrate that the nature of OH can have significant effect on the magnetic spin density. The new findings may provide physical insight into the observed strong relaxivity enhancements. [Preview Abstract] |
Thursday, March 19, 2009 10:48AM - 11:00AM |
V24.00013: Imaging and Spectroscopy of Diamondoid-Fullerene Hybrid Molecules J.C. Randel, H.C. Manoharan Diamondoids have attracted attention as potential building blocks for nanometer-scale electronic and mechanical devices. The ability to functionalize diamondoids with various atomic and molecular groups enables customizable chemistry, as well as tunable electronic properties. Recently, the library of realizable functional groups has expanded beyond a few atoms, and now includes C$_{60}$ fullerenes. This addition provides a novel opportunity to study a material that combines the sp$^{2}$ and sp$^{3}$ forms of carbon bonding in one hybrid molecule. We investigate these molecules using scanning tunneling microscopy and spectroscopy. We find that thin films of the molecules pack in a well-ordered lattice on Au(111), and report on spectral measurements with single-molecule resolution. We comment on the connection between strong features in these electronic structure measurements and the nature of electron transport through single hybrid molecules. [Preview Abstract] |
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