Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session X22: Focus Session: Carbon Nanotubes: Absorption and Defects |
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Sponsoring Units: DMP Chair: Jerome Lagoute, CNRS Room: Portland Ballroom 252 |
Thursday, March 18, 2010 2:30PM - 2:42PM |
X22.00001: The chlorination of carbon nanotubes Dogan Erbahar, Savas Berber We use {\it ab initio} density functional calculations to study the chlorination of pure and defective carbon nanotubes. We first focus on the adsorption of a second Cl after the adsorption of the first Cl atom. We find that the second Cl prefers to adsorb closer to the first adsorption site. We then search for the clustering tendency of the adsorbates, and determine the optimum adsorption configurations for different Cl coverages. Unlike for adsorption outside the nanotube, the adsorption inside the nanotube is only physisorption, and the atomic structure is governed by the charge transfer. We observe that the chemisorption is energetically more favorable in small diameters while the energy difference for large diameters is not significant. Therefore, the residual Cl left after the halogen gas treatment of the nanotubes can be removed without damaging the nanotube walls. Note that the halogens are viable alternatives to harsher chemicals in the purification. However, we find that the Cl atoms adsorb on defects more strongly, and the adsorbates may initiate significant structural reconstructions of the defects. Last, we obtained activation energies during the adsorption of a Cl pair on a carbon nanotube. [Preview Abstract] |
Thursday, March 18, 2010 2:42PM - 2:54PM |
X22.00002: Fe-Porphyrin adsorbed on single-wall carbon nanotubes for heterogeneous catalysis Walter Orellana, Igor Ruiz-Tagle We study the stability and electronic properties of Fe-Porphyrin (FeP) attached on pristine and defective (with a vacancy) single-wall carbon nanotubes (CNTs) by density functional theory calculations and molecular dynamic simulations. We investigate the CNT-FeP systems as a catalyst for the oxygen reduction reaction. Different configurations for the attached FeP were analyzed considering both physisorption and chemisorption. Metallic and semiconducting CNTs of about 1.1-nm in diameter are our model systems. Our results show that on pristine CNTs, FeP is physisorbed with binding energies of about 1.7~eV. Whereas, chemisorbed FeP ($sp^3$ and $sp^2$ hybridizations) have binding energies within 2.3-4.7 eV. Our molecular dynamic simulations show that these binding energies increase slightly at room temperature. The electronic band structures of the CNT-FeP systems preserve the CNT electronic characters, however, in (14,0)-FeP the band gap is reduced up to 0.03~eV, suggesting that this system behaves as an electron acceptor. The interaction between the O$_2$ molecule and the Fe atom of the FeP-CNT systems is also discussed. [Preview Abstract] |
Thursday, March 18, 2010 2:54PM - 3:06PM |
X22.00003: CO$_{2}$ adsorption on single-walled dahlia-like carbon nanohorns Jaime Bohorquez, Vaiva Krungleviciute, Aldo Migone, Masako Yudasaka, Sumio Iijima The adsorption of CO$_{2}$ on spherical aggregates of as-produced (i.e., closed) dahlia-like single-walled carbon nanohorns was investigated. We conducted volumetric adsorption measurements at five temperatures between 147 and 180 K. The shape of the isotherms for CO$_{2}$ is very different from those measured with neon and CF$_{4}$. For CO$_{2}$ there is a single, smeared step in the adsorption data between the lowest coverages and saturation. By contrast, Ne and CF$_{4}$ show two distinct substeps on the same substrate. The isosteric heat was also obtained and its dependence on coverage also showed an usual behavior: it increased with increasing coverage. The isosteric heat decreases with coverage both for Ne and CF$_{4}$. The stronger intermolecular interactions present for CO$_{2}$ probably are responsible for this adsorbate's unusual behavior. Comparisons with the behavior reported in the literature for CO$_{2}$ on SWNTs, which shows similar unusual characteristics, will also be made. [Preview Abstract] |
Thursday, March 18, 2010 3:06PM - 3:18PM |
X22.00004: Dependence of adsorption kinetics on the length of the alkane adsorbate Dinesh Rawat, Toyo Furuhashi, Aldo Migone We present the results of an adsorption kinetics study of methane, ethane, propane, butane and pentane films on purified HiPco SWNTs. These studies consisted of monitoring the time evolution of the adsorbate gas pressure, for different fractional coverages, along adsorption isotherms. For methane and ethane, the times for the pressure to equilibrate were found to decrease as the fractional coverage increased. However, for propane, butane and pentane, a reverse trend was observed. We speculate that the observed increase in the equilibration time with coverage for the longer alkanes is due to rearrangement of molecules in the adsorbed film. Results for the adsorption kinetics of butane on a cell containing no substrate will also be presented, and compared to those observed for adsorption on the nanotubes. The observed differences in adsorption kinetics suggest the possibility of using adsorption as a means to achieve the separation of gaseous alkane mixtures. [Preview Abstract] |
Thursday, March 18, 2010 3:18PM - 3:30PM |
X22.00005: Effects of surface heterogeneity on TPD spectra: a computer simulation study Nayeli Zuniga-Hansen, Mercedes Calbi We study gas desorption from external surfaces of carbon nanotube bundles by using a Kinetic Monte Carlo scheme. We focus on desorption of quasi-spherical molecules that form monolayers comprised by three or five lines of molecules along the tubes. Each line is characterized by a particular binding energy. By varying the initial coverage, we observe the effects of this energy heterogeneity of the surface on the Temperature Programmed Desorption Spectra. In particular, by keeping track of the individual coverage on these lines, we investigate the diffusion processes across the lattice and its effect on the spectra. We also discuss implications for available and prospective experimental results. [Preview Abstract] |
Thursday, March 18, 2010 3:30PM - 3:42PM |
X22.00006: Study of Ethylene film adsorbed on purified HiPco Single-walled carbon nanotubes Toyo Furuhashi, Dinesh Rawat, Aldo Migone We have measured adsorption isotherms for ethylene on purified HiPco SWNTs for coverages in the first and second layers. The isotherms were performed at 110, 120,130 and 140 K. Consistent with what is found for a number of other adsorbates, two distinct groups of binding energy sites were found for ethylene adsorbed on purified HiPco SWNTs. Additional features present in the isotherm data (namely, the presence of a possible substep) suggest the possibility of a phase transition occurring in the film when the film coverage is near the completion of the first layer. We have also determined the coverage dependence of isosteric heat of adsorption for ethylene using the results for isotherms obtained at the above-mentioned temperatures. The results will be compared to ethylene films on graphite and ethane on nanotubes. [Preview Abstract] |
Thursday, March 18, 2010 3:42PM - 3:54PM |
X22.00007: Coupling between electrons and an adsorbed atomic monolayer on the surface of a single nanotube. Zenghui Wang, Erik Fredrickson, Oscar Vilches, David Cobden Two-dimensional phase transitions within an atomic monolayer adsorbed on the surface of a single suspended carbon nanotube can be detected by using the nanotube as a vibrating nanobalance. Here we report that such phase transitions can also be detected and studied by measuring the electrical conductance of the nanotube. In addition, the behavior of the monolayer is affected by the electric current through the nanotube, which produces heating, and by a dc gate voltage, which controls the electric field at the nanotube surface. As a result, new kinds of adsorption experiments are possible in which the coupling between the adsorbates and substrate electrons can be quantified and parameters of the monolayer can be tuned. [Preview Abstract] |
Thursday, March 18, 2010 3:54PM - 4:06PM |
X22.00008: Specific heat and anomalous effective dimensionality of quantum gases adsorbed near nanopores Mamadou Mbaye, Steven Full, Jessica McNutt, Milton Cole, Silvina Gatica Three problems involving quasi-one-dimensional (1D) ideal gases are discussed: quantum particles localized within the ``groove'' between nanotubes, between two nearly parallel, coplanar nanotubes and confined in the interstitial region between four square parallel pores. The low T behavior found in most cases differs qualitatively from naive expectations. [Preview Abstract] |
Thursday, March 18, 2010 4:06PM - 4:18PM |
X22.00009: Formation of defect structures on graphene and CNTs: Effect of sulphur insertion Oguz Gulseren, Rasim Ovali, Gokce Kucukayan, Erman Bengu Motivated from the possible mechanisms behind the junction formation on carbon nanotubes (CNTs), we investigated various defect structures of graphene by using planewave pseudopotential calculations based on density functional theory. The investigated defect structures, single or double vacancies, Stone-Wales defects, 4-5-7-8 rings of carbon, and combinations of these rings, are formed within large graphene nanoribbons where edges are satured by hydrogen atoms. After geometry optimization, the cohesive and formation energies are calculated from corresponding total energies. For point defects, Stones Wales, single 8-ring and single 7-ring type defect structures, the relaxed structures remain almost planar with a little local distortion; therefore, these structures might not be an appropriate initial structure for Y- junction formation on CNTs. However, the single 4-ring or various 5-ring (single, double and triple 5-rings) defects have highly curved final geometries and it becomes sharper from single to triple ring structures. Hence, these type of defect structures are good initial structure candidates for junction formation on CNTs. Then, the effects like insertion of sulphur that might lead such defect structures on graphene are investigated and discussed in detail. [Preview Abstract] |
Thursday, March 18, 2010 4:18PM - 4:30PM |
X22.00010: Potassium doped carbon nanotubes: theory and experiment Aldo Romero, Alejandra Garcia, Lina Hoyos, Francisco Perez, Sinhu\'e Lopez, Hugo Ponce, Camilo Espejo It has been demonstrated that some of the properties of carbon nanotubes can be manipulated by doping them with different set of atoms. In this work, we present a series of experiments as well as theoretical calculations in that respect. We demonstrate our experimental procedure by doping the nanotubes with potassium and characterize them by different experimental techniques such as SEM, Raman, X-ray, etc. We observe a large change on the nanotubes curvature and the appearance of nanostructures such as helicoids and toroids. The density of those nanostructures depends on the doping concentration. We rationalize our findings by using density functional theory calculations and conclude by showing how doping can be use to increase reactivity and the presence of heptagons and pentagons, responsible for the appearance of curvature. [Preview Abstract] |
Thursday, March 18, 2010 4:30PM - 4:42PM |
X22.00011: The Role of Point Defects and Functionalizations in the Cyclic Voltammetry of Single-Walled Carbon Nanotubes Vaikunth Khalap, Tatyana Sheps, Alexander Kane, Philip G. Collins The use of carbon electrodes in electrochemistry is usually preceded by extensive surface functionalization or oxidative pretreatments to ``activate'' the carbon surface. Precise and quantitative determination of the role of this functionalization is exceedingly difficult. To understand the exact role of different surface groups, we utilize individual, single-walled carbon nanotubes (SWCNTs) as unique, nanoscale working electrodes. Cyclic voltammetry on pristine single SWCNTs quantitatively determines electron transfer rates for a perfect, defect-free graphitic surface of known area. Furthermore, the incorporation of single point defects in the SWCNT sidewall allows kinetic rates to be probed as a function of disorder. Cyclic voltammetry of the same SWCNT before and after the production of a point defect shows a pronounced enhancement of electrochemical activity that can be unambiguously ascribed to the presence of the functionalization. This research is partly supported by NSF (CBET-0729630) and a GAANN fellowship (VRK). [Preview Abstract] |
Thursday, March 18, 2010 4:42PM - 4:54PM |
X22.00012: Nitrogen doped carbon nanotubes for dioxygen reduction from ab initio simulation Shizhong Yang, Guang-Lin Zhao, Ebrahim Khosravi Nitrogen substitutionally doped short carbon nanotubes (CNTs) has potential application for metal-free efficient oxygen reduction reactions(ORRs). We have performed \textit{ab initio} density-functional-theory (DFT) calculations to simulate nitrogen substitutionally doped short (10, 0) CNTs. Our calculated results show that nitrogen prefers to stay at the open-edge of the short CNTs. Dioxygen O$_{2}$ can adsorb and partially reduce on the carbon-nitrogen complex site (Pauling site) and on carbon-carbon long bridge sites at the open-edge of the CNTs. The results of the spin polarization calculations show that the carbon atoms on the open-edge of the CNT can possess a magnetic moment of about 0.59 $\mu $B/atom, while those carbon atoms in the inner wall of the CNT do not have a magnetic moment. The doped nitrogen in the CNT does not have a magnetic moment. The chemisorption of dioxygen O$_{2}$ on the open-edge of the short CNT reduces the magnetic moments of the carbon atoms to nearly zero. [Preview Abstract] |
Thursday, March 18, 2010 4:54PM - 5:06PM |
X22.00013: Evaluating defects in solution processed carbon nanotube devices by low temperature transport spectroscopy Paul Stokes, Saiful I. Khondaker We evaluate defects in solution processed dielectrophoreticly assembled single-walled carbon nanotube (SWNT) devices via low temperature electron transport spectroscopy. In contrast to the general belief that solution processing introduces many defects in SWNTs, we show that devices assembled from stable solutions can give rise to relatively clean quantum dot behavior. This is a strong indication that there are no or few intrinsic defects in the SWNTs. The individual, 1 um long SWNT devices were fabricated by dielectrophoresis from a surfactant free commercially available SWNT solution. Measurements on a number of semi-metallic SWNT devices at low temperature show periodic Coulomb Blockade oscillations as a function of gate voltage along with well defined Coulomb diamonds. The Coulomb diamonds were further modeled to elucidate number of quantum dots in the transport channel. Our observation is a significant step forward for the use of solution processed SWNTs for high yield and high quality devices in nanoelectronics. [Preview Abstract] |
Thursday, March 18, 2010 5:06PM - 5:18PM |
X22.00014: Controlling the kink angle of intramolecular carbon nanotube junctions: A combined experimental and theoretical study Jan Blueher, Jens Kunstmann, Imad Ibrahim, Alicja Bachmatiuk, Felix Boerrnert, Mark Ruemmeli, Gianaurelio Cuniberti Intramolecular carbon nanotube (CNT) junctions are nanotubes with kinks generated by heptagon-pentagon defect pairs. They are very attractive functional building blocks for future electronics, as they can be used as diodes and transistors. Usually CNT junctions are synthesized incidentally [1]. Using chemical vapor deposition techniques we are trying to grow CNT junctions in a more controlled way. In particular, we want to control the kink angle in order to produce junctions with well defined electronic properties. Our approach raises the question: Are there special kink angles that induce a certain change in electronic properties? In order to answer this question we developed a scheme that allows generating the atomic structure of CNT junctions with an arbitrary number of heptagon-pentagon defects. To break down the large number of different geometrical possibilities to achieve a CNT junction with a specific angle we study the energetics of different defect combinations and discuss the implication of these results for the experimental realization of well defined CNT junctions. [1] Wei et al., Adv. Mater. 20, 2815 (2008). [Preview Abstract] |
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