Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session T31: Novel Structural Chemistry & Materials |
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Sponsoring Units: DCMP Chair: Daniel Finkenstadt, U.S. Naval Academy Room: C145 |
Wednesday, March 23, 2011 2:30PM - 2:42PM |
T31.00001: Theoretical studies of the caged hydrocarbon, octahedrane (C$_{12}$H$_{12}$, D$_{3d}$) Steven Richardson, Daniel Finkenstadt, Michael Mehl, Mark Pederson Polyhedral hydrocarbon cages provide an interesting class of molecules for experimental and theoretical study because of their unique shapes. One such molecule is octahedrane (C$_{12}$H$_{12}$, D$_{3d}$) which was first synthesized by Lee {\it et al.} in 1993.\footnote{C-H Lee, S. Liang, T. Haumann, R. Boese, and A. de Meijere, {\it Angew. Chem. Int. Ed. Engl.} {\bf 1993,} 32, 559.} Octahedrane contains two fused three-membered rings and six five-membered rings. Theoretical work by de Meijere {\it et al.}\footnote{A. de Meijere, C-H Lee, M. A. Kuznetsov, D. V. Gusev, S. I. Kozhushkov, A. A. Fokin, and P. R. Schreiner, {\it Chem. Eur. J.} {\bf 2005,} 11, 6175.} using density-functional theory (DFT) has shown that octahedrane is more strained than the structurally related molecules decahedrane (C$_{16}$H$_{16}$, D$_{4d}$), which has two fused four-membered rings and eight five-membered rings, and dodecahedrane (C$_{20}$H$_{20}$, I$_{h}$), which has two fused-membered rings and ten five- membered rings. In this work we report the first DFT calculations of the infrared and Raman vibrational spectra for octahedrane which will be of importance for future efforts in characterizing this unique caged hydrocarbon. [Preview Abstract] |
Wednesday, March 23, 2011 2:42PM - 2:54PM |
T31.00002: Golcondane (C20H24): Theoretical studies of a novel strained, caged hydrocarbon molecule Daniel Finkenstadt, Michael Mehl, Mark Pederson, Steven Richardson In 1993 Mehta and Reddy reported the synthesis of a new C$_{20}$ polyhedrane, which they named golcondane (C$_{20}$H$_{24}$, D$_{2d}$) in honor of the 400$^{th}$ anniversary of the founding of the Indian city of Hyderabad, whose original name was Golconda. Golcondane is a caged, nonacyclic hydrocarbon that has two fused four-membered rings, four fused five-membered rings, and two fused seven-membered rings. Its chemical structure was determined by $^{13}$C NMR spectroscopy and unpublished X-ray crystal diffraction studies. Motivated by our previous success in using density-functional theory (DFT) to compute the structural, electronic, and vibrational properties of other hydrocarbons such as cubane, octanitrocubane, the medium-sized diamondoid molecule cyclohexamantane, as well as the novel class of materials known as {\it sila-}diamondoids, we have used DFT and tight- binding molecular dynamics (TBMD) to compute from first- principles similar properties for golcondane. Our work is especially significant with the lack of other theoretical or experimental studies on this interesting molecule in the published literature. [Preview Abstract] |
Wednesday, March 23, 2011 2:54PM - 3:06PM |
T31.00003: Spectroscopic identification of bond strain and pi interactions in a series of saturated carbon-cage molecules: adamantane, twistane, octahedrane, and cubane Trevor M. Willey, J.R.I. Lee, T. van Buuren, L. Landt, P.R. Schreiner, A.A. Fokin, B.A. Tkachenko, N.A. Fokina, D. Brehmer Novel nanocarbons such as fullerenes, nanotubes, graphene, and nanodiamond reside at the cutting edge of nanoscience and technology. Along with chemical functionalization, geometrical constraints such as extreme curvature or defects in crystallites can modify the electronic properties. This paper presents a fundamental study of how bond strain affects electronic structure in a benchmark series of novel saturated carbon cage compounds. Adamantane, the smallest diamondoid, has carbon atoms commensurate with the diamond lattice. Twistane has the same stoichiometry (C$_{10}$H$_{16})$, but introduces some bond strain into the cage. Octahedrane (C$_{12}$H$_{12})$ and cubane (C$_{8}$H$_{8})$ have increasing strain, culminating in cubane where C-C bonds lie either parallel, or orthogonal to one another. Using gas-phase NEXAFS spectroscopy, we observe the broad C-C $\sigma $* splits into two more narrow and intense resonances with increasing strain. Also, LUMO states associated with tertiary C-H $\sigma $* broaden and shift to lower energy, and are 3X more intense in cubane than octadedrane. The differences are entirely due to the shape rather than stoichiometry, and indicate, we believe, some $\pi $ interaction between parallel C-C bonds in the cubane. [Preview Abstract] |
Wednesday, March 23, 2011 3:06PM - 3:18PM |
T31.00004: Spectroscopy and Structure of Diamondoid-Fullerene Hybrid Molecules at the Single-Molecule Level Jason C. Randel, Georges Ndabashimiye, Hari C. Manoharan Diamondoids---a nanometer-scale form of carbon sharing the \textit{sp}$^{3}$ bonding structure of bulk diamond---are promising new electronic and mechanical device elements and have recently become accessible to experiments. While new fields of research have also sprouted from carbon's \textit{sp}$^{2}$ forms (such as graphene, fullerenes, and carbon nanotubes), materials representing the intersection of \textit{sp}$^{2}$ and \textit{sp}$^{3}$ bonding structures are an exciting new arena for nanoscale science and technology. In this study, we investigate hybrid molecules fusing \textit{sp}$^{2}$ and \textit{sp}$^{3}$ allotropes of carbon (in the form of C$_{60}$ fullerenes and molecular diamondoids, respectively) into one well-defined system. We use low-temperature scanning tunneling microscopy to characterize monolayers and single molecules with sub-molecular resolution. We show the degree to which the electronic properties of the hybrid molecules differ from their single-allotrope components, and highlight the intriguing electronic features that emerge which have no analog in either of the separate molecular constituents. [Preview Abstract] |
Wednesday, March 23, 2011 3:18PM - 3:30PM |
T31.00005: The Study of Hypothetical Carbon Allotropes Using Hartree Fock and Density Functional Computational Methods P.A. Ecton, C.J. Morris, J.M. Perez, S.G. Srivilliputhur, G.F. Verbeck We have investigated the possibility of hypothetical alternative carbon allotropes using computational methodologies using Gaussian and VASP molecular simulation programs. We investigate the possible existence of carbon based balls, nanotubes and sheets composed of hexagonal rings, cyclobutane rings or pentagonal rings. The possibility of the existence of a hypothetical allotrope is determined by the convergence of the given allotrope under geometric optimization. The theories used to compute such convergence are Hartree-Fock theory and density functional theory. The theoretical Raman spectra of each allotrope can also be computed using Gaussian. The results concerning the reality of the substances under investigation are inconclusive except for a C$_{24}$ ball, which has been shown to converge to graphene and is therefore an unstable molecule. [Preview Abstract] |
Wednesday, March 23, 2011 3:30PM - 3:42PM |
T31.00006: Electron Beam Stimulated Molecular Motions of C$_{60}$s inside Single-Walled Carbon Nanotubes Ke Ran Electron beam irradiation stimulated motions of carbon nanostructures from single C$_{60}$ to C$_{60}$s chain inside single-walled carbon nanotubes (CNTs) were investigated by low voltage and high resolution TEM. Single C$_{60}$'s jump in a defective zigzag C$_{60}$s molecular chain inside host CNT was observed. A cluster of C$_{60}$s inside an isolated partially filled CNT can translate back and forth within the hollow space for several times. Intermediate states of these translations were recorded as well, together with pickup of additional C$_ {60}$s when the moving cluster reached either end of the hollow space. Continuous rotation of a zigzag C$_{60}$ molecular chain inside an overloaded CNT resulted in alternate expansion and contraction of the projected width of the host CNT in the TEM images. The maximum expansion was up to 29\%. Potential calculation for the molecular motion was performed based on the van der Waals interaction among C$_{60}$s and CNT. Activation energies ranging from 0.3 eV to 0.7 eV were estimated. The molecular motion was attributed to momentum transfer during elastic scattering of electrons by the molecules, instead of thermal energy or thermal gradient. Our study demonstrates the potential of driving molecular motion by electron irradiation. [Preview Abstract] |
Wednesday, March 23, 2011 3:42PM - 3:54PM |
T31.00007: First-Principles Calculations of Graphene Nanomesh William Oswald, Zhigang Wu Graphene has recently attracted intensive attentions owing to its remarkable structural and electronic properties and its significant potential for applications in electronic and optoelectronic devices for size miniaturization and fast electron transportation. However, bulk graphene is a semi-metal with zero bandgap $E_{g}$, and opening a sizable $E_{g}$ is critical for building operational graphene-based transistors. Recently, a new scheme of opening bandgap through punching nanoscale holes in graphene sheet, the graphene nanomesh, was proposed and verified experimentally [1]. However, the mechanism leading to the bandgap opening remains unknown. We have carried out first-principles calculations based on density functional theory (DFT) to study the bandgap opening mechanism and $E_{g}$ as functions of structural parameters, including the hole size, the hole shape, and the hole-hole distances. Our results suggest that the bandgap opening is a result of quantum confinement at nanomesh necks, while the value of $E_{g}$ depends not only on the width of nanomesh necks, but also on the chirality of the hole edge. This work was supported by the start-up research funds from Colorado School of Mines. \\[4pt] [1] J. Bai, X. Zhong, S. Jiang, Y. Huang, and X. Duan, Nature Nanotech. \textbf{5}, 190 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 3:54PM - 4:06PM |
T31.00008: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 4:06PM - 4:18PM |
T31.00009: Effects of shape and edge-passivation on magnetic moments in graphene nanomesh by first-principles investigation Hongxin Yang, Mairbek Chshiev First-principles calculations of electronic and magnetic properties of pure and H-terminated graphene nanomesh (GNM) are presented. We found stable antiferromagnetic and non-magnetic ground state for GNM with balanced zigzag and armchair-type edge structures, respectively. At the same time, a band gap opening in the balanced zigzag edge GNMs which can reach up to 0.40 eV is also found. Interestingly, GNM with unbalanced edge structure shows stable ferrimagnetic state giving rise to a net moment up to 4 Bohr magnetons per unit cell, and the exchange energy between ferrimagnetic state and paramagnetic state is larger than 1 eV per unit cell providing potential for high Curie temperature in this material. Furthermore, we found that the ground states for H-terminated GNM strongly depend on the hole symmetry: large spin polarization ground state is found for GNMs with triangle and pentagon hole shapes, while for GNMs with parallelogram and hexagon shaped holes the ground states are paramagnetic. Finally, we found that the magnetization of the GNM structure is strongly affected by the hole size: the larger hole size attains large moments, while small one may even kill all the moments. [Preview Abstract] |
Wednesday, March 23, 2011 4:18PM - 4:30PM |
T31.00010: Sensing gas molecules using graphitic nanoribbon films and networks Yanbin An, Jason L. Johnson, Ashkan Behnam, S.J. Pearton, Ant Ural We fabricate and study the gas sensing properties of graphitic nanoribbon (GNR) films and networks consisting of multi-layer graphene nanoribbons with an average width of 7 nm. We experimentally demonstrate the high sensitivity of these films and networks for sensing gas molecules at the parts-per-million (ppm) level, in particular hydrogen and ammonia. The sensing response exhibits excellent repeatability and full recovery in air. Furthermore, our results show that functionalization by metal nanoparticles could significantly improve the sensitivity. We characterize the sensing response at various temperatures, gas concentrations, recovery ambients, and film thicknesses. We find that the relative resistance response of the GNR films shows a power-law dependence on the gas concentration, which can be explained by the Freundlich isotherm. The activation energy obtained from the sensing experiments is consistent with the theoretical calculations of the adsorption energies of gas molecules on graphene sheets and nanoribbons. Their simple and low-cost fabrication process and good sensing response open up the possibility of using graphitic nanoribbon films and networks for large-scale sensing applications. [Preview Abstract] |
Wednesday, March 23, 2011 4:30PM - 4:42PM |
T31.00011: Opening of slit-shaped pores from bending of graphene walls Matthew Connolly, Carlos Wexler Graphene has gained particular interest in many areas of research including adsorption. Recent studies have shown deformations in graphene resulting from the pressure of intercalants or edge bonds. In this talk, the opening of slit shaped pores from uniaxial bending of the graphene walls of the pore is examined. The energy functional associated with the deformation from equilibrium shape is minimized to obtain an optimal shape. The minimization is done analytically for a simple model and numerically for various graphene-graphene interaction potentials. The strain induced from bending has been shown to effect the hybridization of carbon bonds within the graphene sheet. The effect of any increase in the number of binding sites due to bending as well as hybridization effects on excess adsorption are studied by Molecular Dynamics simulations. [Preview Abstract] |
Wednesday, March 23, 2011 4:42PM - 4:54PM |
T31.00012: Magneto-reflectance studies of graphite in intense magnetic field Li-Chun Tung, Paul Cadden-Zimansky, Jinbo Qi, Zhigang Jiang, Dmitry Smirnov Magnetic subbands of Kish graphite have been investigated by the magneto-infrared reflectance spectroscopy at 4K up to 31T. Both of the Schr\"{o}dinger- (K-point) and Dirac-like (H-point) Landau level transitions have been observed. The intense magnetic field resolves the transitions caused by the symmetry breaking of the doubly degenerate E3 band near the charge-neutrality point and the splitting of interband transitions due to electron-hole asymmetry. These transitions were not evident in the recent magneto-transmittance studies at high magnetic fields and are important in understanding electron-hole asymmetry and the opening of the energy gap between electron and hole bands. From the SWMC model, we derived a new formula to describe the magnetic field dispersion of the K-point transitions and a good agreement is achieved with a set of band parameters consistent with the ones reported in the literature. [Preview Abstract] |
Wednesday, March 23, 2011 4:54PM - 5:06PM |
T31.00013: Size-dependence of electronic and optical properties of armchair graphene nanoislands Jonathan Moussa, James Chelikowsky Atomicly precise armchair graphene nanoislands (benzenoid polycyclic aromatic hydrocarbons) have been produced by organic synthesis and to-date have attained sizes up to 222 carbon atoms. The electronic and optical properties of these nanoislands are studied using a combination of semi-empirical methods, time-dependent density functional theory, and the GW/Bethe-Salpeter formalism. Comparisons are made with experimental measurements where available. For this class of materials, theory is able to predict the necessary nanoisland sizes required for potential photovoltaic and light-emitting applications. The study of large nanoislands is focused on parallelogram-shaped islands, which should be particularly amenable to synthesis over a wide range of sizes. [Preview Abstract] |
Wednesday, March 23, 2011 5:06PM - 5:18PM |
T31.00014: Modifying Electronic and Magnetic Properties of BCN sheets by Boron Nitride Domain Size and Tensile Strain Chun Tang, Changfeng Chen Recent experiments have successfully synthesized atomic thin BCN hybrid composites with controllable BN domain concentration. Using first principles calculations, we report the scaling law of electronic and magnetic properties of this novel structures with respect to BN domain size and geometry. We find due to the BN domain induced internal electric field, the magnetic moment can be effectively modified. External tensile strain engineering can also be applied as an efficient tool to modify the electronic and magnetic properties. Our results may have important applications in semiconducting devices. [Preview Abstract] |
Wednesday, March 23, 2011 5:18PM - 5:30PM |
T31.00015: Functionalized 2D atomic sheets with new properties Qiang Sun, Jian Zhou, Qian Wang, Puru Jena Due to the unique atomic structure and novel physical and chemical properties, graphene has sparked tremendous theoretical and experimental efforts to explore other 2D atomic sheets like B-N, Al-N, and Zn-O, where the two components offer much more complexities and flexibilities in surface modifications. Using First principles calculations based on density functional theory, we have systematically studied the semi- and fully-decorated 2D sheets with H and F and Cl. We have found that the electronic structures and magnetic properties can be effectively tuned, and the system can be a direct or an indirect semiconductor or even a half-metal, and the system can be made ferromagnetic, antiferromagnetic, or magnetically degenerate depending upon how the surface is functionalized. Discussions are made for the possible device applications. [Preview Abstract] |
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