Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N27: Focus Session: Carbon Nanotubes: Functionalization I |
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Sponsoring Units: DMP Chair: Lars Ericson, NRL Room: LACC 501C |
Wednesday, March 23, 2005 8:00AM - 8:12AM |
N27.00001: Thermodynamic properties Ar films on the surface of a bundle of carbon nanotubes Milton Cole, Nathan Urban, Silvina Gatica, Jose Ricardo We employ canonical Monte Carlo simulations to explore the properties of an Argon film adsorbed on the external surface of a bundle of carbon nanotubes. The study is concerned primarily with three properties: specific heat, differential heat of adsorption, and Ar-Ar correlation functions. These measurable functions exhibit information about the dependence of film structure on coverage and temperature. Our results are intended to stimulate further experimental studies of this system and analogous systems involving other gases on nanotube bundles. One of the more interesting general results is that the specific heat is typically larger than might have been expected. Particularly remarkable outcome from the correlation function studies include the reduced longitudinal correlations in the groove and striped phases as T rises above 60 K. These results would be amenable to testing by diffraction experiments. [Preview Abstract] |
Wednesday, March 23, 2005 8:12AM - 8:24AM |
N27.00002: Neon adsorption isotherms on carbon nanohorns Vaiva Krungleviciute, Luke Heroux, Aldo Migone We will present results of neon adsorbed on unpurified carbon nanohorns. The nanohorn sample was obtained from Nanocraft, Inc. Our adsorption isotherm measurements were conducted at temperatures between 19 and 27 K. We determined the specific surface area for our sample, and studied adsorption at different coverages. Results for isosteric heat will also be presented. This work is supported by the NSF through grant DMR-0089713. [Preview Abstract] |
Wednesday, March 23, 2005 8:24AM - 8:36AM |
N27.00003: Adsorption of Xenon on Hipco Single Walled Carbon Nanotubes Dinesh Rawat, Luke Heroux, Vaiva Krungleviciute, Aldo Migone We have measured the adsorption of Xenon on purified HiPco SWCNTs for coverages in the first layer. We wanted to compare the results on this substrate to those we had obtained on lower purity arc-discharge produced nanotubes. In order to obtain an estimate for the binding energy. We measured six low-coverage isotherms for temperatures between 220K and 260K. We determined a value of 272 meV for the binding energy; this value is lower, by about 4{\%} than the value we had reported on arc discharge nanotubes$^{1}$. It is 1.67 times greater than the value for this quantity on planar graphite. We have measured five full isotherms at 150K, 155K, 160K, 165K, and 175K and have used these data to obtain the coverage dependence of the isosteric heat. The experimental values will be compared with computer simulation results for this quantity that have been conducted using different models for bundles$^{2}$. 1 A. J. Zambano, S. Talapatra, and A. D. Migone Physics Review B, 64, 2001. 2 Wei Shi, and J. Karl Johnson Physical Review Letters 91, 2003. * The present study was supported by the National Science Foundation through Grant {\#} DMR-0089713 [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 9:12AM |
N27.00004: Collisional-Induced Resistivity of Carbon Nanotubes Invited Speaker: A single-walled carbon nanotube (SWNT) is often mentioned as one of the strongest materials known. In tension along the tube axis, this statement is correct. However, the tube is ``soft'' in the radial direction, i.e., deformation or squash modes which give rise to an oscillating elliptical cross section have freq's in the range 20-30 cm$^{-1}$. Here, we present results of an \textit{in situ} electrical transport study (thermoelectric power (S) and resistivity ($\rho )$ ) of bundled SWNTs exposed to a series of gases (He, Ar,Ne,Kr,Xe;CH$_{4}$,N$_{2})$. Unusually strong and remarkably systematic changes in these transport properties are observed as the nanotubes undergo collisions with these atomic and molecular gases. At fixed pressure and temperature, the changes in the transport parameters, i.e., $\Delta $S and $\Delta \rho $, are observed experimentally to exhibit an $\sim $ M$^{1/3}$ behavior. At fixed temperature, $\Delta $S and $\Delta \rho $ saturate in the range 0.3-0.5 atm,, with the saturation pressure depending on M. Results of molecular dynamics that simulate the gas-nanotube collision show that the maximum deformation of the tube wall and the radial kinetic energy transfer to the tube wall also exhibit this M$^{1/3}$ behavior. It appears that the transient deformation or ``dent'' caused by the collisions may provide new scattering mechanism for itinerant electrons in the tube walls. These dents ring as the fundamental ``squash'' mode of the tube wall. The pressure p$_{sat}$ at which $\Delta $S and $\Delta \rho $ can be shown to be consistent with the tube pressure at which co-existing dents first begin to overlap. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:24AM |
N27.00005: Adsorption of Tetraflouromethane on HiPco Purified SWNTs Luke Heroux, Vaiva Krungleviciute, Dinesh Rawat, A.D. Migone We have studied the adsorption behavior of tetraflouromethane, CF4, on purified, single-walled HiPco nanotubes. Isotherms were performed between 100K and 125K. We find that there are two substeps in the first layer data for CF4 on the SWNTs; results will be compared to previous measurements on this system. Results for the isosteric heat as a function of coverage will also be presented. Long waiting times are necessary to ensure that equilibrium is reached in these experiments. This research supported by National Science Foundation grant {\#} DMR-0089713. [Preview Abstract] |
Wednesday, March 23, 2005 9:24AM - 9:36AM |
N27.00006: Adsorption of polar molecules on carbon nanotubes in transverse electric fields \c{S}.C. B\u{a}descu, T.L. Reinecke, E.S. Snow, F.K. Perkins, V.M. Bermudez Experiments in our laboratory show that capacitance measurements can be used for chemical sensing with arrays of single-wall carbon nanotubes (NTs). Molecular adsorption on NTs is affected by electrostatic gating that creates intense surface electric fields. The a.c. capacitance amplitude is found to be related to the intrinsic adsorbate dipole moment. To understand the details of the processes involved, \textit{ab-initio} calculations of molecular adsorption on graphene and on NTs with electric fields normal to the surfaces have been made. We study the dependence of adsorption energy, adsorption-induced polarizability and charge transfer on the field intensity and direction in the range 10$^{4}$-10$^{6}$ V/cm. We identify three groups of adsorbed molecules: (1) those with the dipole moment normal to the NT for which the observed capacitance depends $\sim $ linearly on dipole moment (e.g. C$_{3}$H$_{6}$O, CH$_{3}$Cl, NH$_{3}$, DMMP, CNH); (2) those with dipole moments parallel to the NT and that have little effect on the capacitance (e.g. C$_{6}$H$_{5}$Cl, C$_{6}$H$_{4}$Cl$_{2})$; (3) non-polar molecules (e.g. CH$_{4})$, polarized by the intense electric fields and by adsorption. The adsorption-induced dipole moment plays an important role in the total polarization. The results are consistent with the experiment, in particular with infrared spectroscopy data. [Preview Abstract] |
Wednesday, March 23, 2005 9:36AM - 9:48AM |
N27.00007: Adsorption of Aromatic Compounds on Carbon Nanotubes Lilia Woods, {\c{S}}tefan B{\u{a}}descu, Tom Reinecke The functionalization of carbon nanotubes (CNTs) by molecular adsorption is of scientific interest and also of importance in potential applications as sensors. We have studied theoretically the interactions between CNTs and organic aromatic molecules that are derived from benzene by addition of different functional groups (e.g. $CH_{3}$, $OH$, $NO_{2}$). We perform density functional ${\it ab}$ ${\it initio}$ calculations based on the plane-wave supercell method using the generalized gradient approximation. We explore the possible configurations of bonding to both zigzag and armchair CNTs. Two types of minimum energy configurations are distinguished: i) those where the benzene ring is parallel to the CNT surface and the coupling is dominated by $\pi-\pi$ interactions; ii) those where the functional groups of the molecules arrange normal to the CNT surface and bind stronger to the CNT. We discuss quantities related to experimental observables , such as adsorption energy, bonding, and changes induced on the CNT electronic structure. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N27.00008: Theoretical Study of Side Wall Ozonation of Single-Wall Carbon Nanotubes Brahim Akdim, Xiaofeng Duan, Tapas Kar, Ruth Pachter Oxidation of single-wall carbon nanotubes (SWCNTs) by ozone has been utilized extensively, for example, in the elimination of amorphous carbon in purification processes, for opening closed tips and sidewalls of nanotubes to maximize the rate of metal adsorption and hydrogen uptake, as well as to facilitate functionalization for achieving solubility. In this work, we present a density functional theory study, to investigate the adsorption mechanisms of O$_{3}$ on the sidewall of metallic C(5,5), and semiconducting C(10,0) SWCNTs, in the presence and absence of Stone-Wales defects with different morphologies. The energetics, electronic structures, and Raman modes shifts, upon adsorption, as compared to pristine tubes, will be discussed in detail. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N27.00009: Effects of Ion Beam Irradiation on Thermal Oxidation of Single Walled Carbon Nanotubes Ananta Adhikari, Hassaram Bakhru, Mengbing Huang, Pulickel Ajayan The properties of carbon nanotubes (CNTs) are closely dependent on their structures, and therefore may be tailored by controllably introducing defects in the nanotube systems. In this work, we investigate the effects of energetic ions (H$_{2}$, He and Ne) on the thermal stability of single wall nanotubes (SWNTs) against oxidation in air. SWNTs were irradiated with ions of energy in MeV to various doses in the range of 10$^{13 }$- 10 $^{16}$ cm$^{-2}$. Thermogravimetric analysis was used to determine the loss of CNT masses within 300-700 $^{o}$C as a result of oxidation processes. As opposed to the case of pristine SWNTs, the temperature (T$_{m})$ corresponding to maximum oxidation rate was increased by about 25 $^{o}$C for the SWNTs implanted with Hydrogen dose of 10$^{15}$ cm$^{-2}$, while He and Ne ion implantation resulting in decrease in T$_{m}$. The activation energies for thermal oxidation under various conditions were also extracted from TGA data, with values ranging from 1.13 eV (for pristine SWNTs) to 1.37 eV, depending on ion doses and species. Raman spectroscopy was used to determine the characteristics of the G band (C-C stretching mode) and D band (disorder induced mode) in CNTs. The work suggests that the bonding in CNTs could be strengthened or weakened depending on the amount of ion-beam- induced defects, leading to the enhanced or reduced thermal stability of CNTs against oxidation. [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N27.00010: Mechanism for bias-assisted mass transport of indium on carbon nanotube surfaces Filipe J. Ribeiro, J.B. Neaton, Steven G. Louie, Marvin L. Cohen We have preformed \emph{ab initio} pseudopotential density functional calculations to study the adsorption and diffusion of indium atoms on graphite-like and carbon nanotube surfaces. The adsorption energy was calculated as a function of In coverage, and it is shown that, for low surface densities, In becomes positively charged by donating one electron to the surface. This explains the experimental evidence that In deposited on carbon nanotubes migrates towards the cathode under an applied voltage. The effects of nanotube surface curvature on In adsorption are shown to be small. Based on the calculated energy barrier between two neighboring adsorption sites and the calculated vibrational frequencies of the adsorbate, the hopping rate for In adsorbed on graphene is estimated. Finally, In adsorption is shown to be stronger near a Stone-Wales defect, which could be linked to the nucleation of In nanocrystals. This work was supported by National Science Foundation Grant No. DMR04-39768 and by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S.Department of Energy under Contract No. DE-AC03-76SF00098. Computational resources have been provided by NPACI and NERSC. [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 10:36AM |
N27.00011: Morphological Evolution of Metal Nanoparticles in Metal-Carbon Nanotube Composites Jianxin Zhong, G. Malcolm Stocks Metal nanoparticle-carbon nanotube composites are new emerging nanomaterials with a variety of potential technological applications such as fuel cells, sensors, and nanocatalsyts. Currently, fabrication of these nanocomposite materials proceeds via trial and error due to the lack of fundamental understanding of their growth mechanisms. We propose a model to elucidate the morphological evolution of metal nanoparticles grown on surfaces of carbon nanotubes. The model is based on a novel concept, namely, bending-strain-induced self-organization of nanoparticles on curved surfaces. In the framework of continuum theory of elasticity, a criterion is derived to predict the size and shape of metal nanoparticles. Applications of the criterion to different metals show good agreement with experimental results. Our model is expected to be very fundamental. It has the potential to have important applications to understanding and controlling nanomaterials growth on any substrates with curved surfaces. [Preview Abstract] |
Wednesday, March 23, 2005 10:36AM - 10:48AM |
N27.00012: C60-Incorporated Carbon Nanohorns: Control of Filling and Releasing Ryota Yuge, Masako Yudasaka, Toshinari Ichihashi, Yoshimi Kubo, Sumio Iijima Single-wall carbon nanohorn (SWNH) has structures similar to single wall carbon nanotube, and nanometer-scaled holes were opened through the walls by heating in oxygen (SWNHox). Recently, we have succeeded in a large-scale preparation of C$_{60}$-incorporated SWNHox (C$_{60}$@SWNHox) at room temperature in liquid phase by our new method of ``nano-precipitation.'' In this report, we show that incorporation of C$_{60}$ inside SWNHox could be confirmed by TEM observation, Raman spectrum measurements, and X-ray diffraction measurements. Quantity of C$_{60}$ incorporated inside SWNHox was estimated from thermogravimetric analysis. The release rates of C$_{60}$ from C$_{60}$@SWNHox in solutions were able to be clarified by UV/Vis absorption measurements. Through these investigations, we found that the filling quantities and release rates of C$_{60}$ were able to be controlled easily for SWNHs. These are advantages of large-diameters of the tubes to which C$_{60}$ molecules are bound moderately. [Preview Abstract] |
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