Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D37: Focus Session: Carbon Nanotubes: Atom Mobility, Mechanical Response & Adsorption |
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Sponsoring Units: DMP Chair: Mercedes Calbi, University of Denver Room: 705/707 |
Monday, March 3, 2014 2:30PM - 3:06PM |
D37.00001: Controlling Atomic Movement on the Nanoscale Invited Speaker: Sinisa Coh Some of the grand challenges in nanoscience are the ability to control movement of atoms either to propel nanometer-sized machines, or to synthesize novel electronic devices and materials. To that end, electrical current can be used to move a wide range of metals (Fe, Cu, W, In, Ga) along the outside and inside of a carbon nanotube. In this talk I will present our finding of a peculiar way in which these metals move. For example, we find that an iron nanocrystal is able to pass through a constriction in the carbon nanotube with a smaller cross-sectional area than the nanocrystal itself. Remarkably, through in situ transmission electron imaging and diffraction, we find that, while passing through a constriction, the nanocrystal remains largely solid and crystalline and the carbon nanotube is unaffected. We account for this behavior by a pattern of iron atom motion and rearrangement on the surface of the nanocrystal. The nanocrystal motion can be described with a model whose parameters are nearly independent of the nanocrystal length, area, temperature, and electromigration force magnitude. I will also discuss implications of this work on synthesis of nanocomposite materials, and on the stability of carbon-based electronic devices. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D37.00002: Multi-Wall Carbon Nanotubes as Lithium Nanopipettes and SPM Probes Jonathan Larson, Satyaveda Bharath, William Cullen, Janice Reutt-Robey A multi-walled carbon nanotube (MWCNT) - terminated SPM cantilever, was utilized to perform nanolithography and surface diffusion measurements on a thin film of vapor-deposited lithium atop a silicon (111) substrate under ultra-high vacuum conditions. In these investigations the MWCNT tip was shown to act as both a lithium nanopipette and a probe for non-contact atomic force microscopy (NC-AFM) measurements. With the application of appropriate bias conditions, the MWCNT could site-selectively extract (expel) nano-scale amounts of lithium from (to) the sample surface. Depressions, mounds, and spikes were generated on the surface in this way and were azimuthally symmetric about the selected point of pipetting. Following lithium transfer to/from the substrate, the MWCNT pipette-induced features were sequentially imaged with NC-AFM using the MWCNT as the probe. Vacancy pits of ca. 300 nm diameter and 1.5 nm depth were observed to decay on a timescale of hours at room temperature, through diffusion-limited decay processes. A continuum model was utilized to simulate the island decay rates, and the lithium surface diffusion coefficient of D$=$7.5 ($\pm$1.3)*10$^{-15}$ cm$^{2}$/s was extracted. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D37.00003: Micro-tweezers for studying vibrating carbon nanotubes Arthur Barnard, Mian Zhang, Michal Lipson, Paul McEuen Vibrational modes in suspended carbon nanotubes (CNTs) are incredibly soft, which makes them sensitive to small forces and a prime candidate as force sensors. This same property, combined with the stiffness of the CNT to stretching, makes them an unusual mechanical system characterized both by large thermally-activated fluctuations and strong nonlinear interactions between the resonance modes. How do these thermal fluctuations manifest themselves in the resonance behavior? To address this question, we developed an electrically-contacted micro-tweezer platform that is capable of lifting a pristine CNT off of its growth substrate, directly applying strain to the free-standing doubly-clamped CNT, and controlling its proximity to electrical gates and optical ring (microdisk) resonators for sensing. We measure both the mechanical resonance frequencies and quality factors of the CNT as a function of strain and temperature and compare these to recent predictions that account for the entropic effects of fluctuations on CNTs. In addition, we use these tweezers to couple a CNT to a high-Q optical resonator and demonstrate remarkably strong optomechanical coupling. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D37.00004: Shape transitions in bistable carbon nanotubes coupled to encapsulated gas Oleg Shklyaev, Eric Mockensturm, Milton Cole, Vincent Crespi Large-diameter single-wall carbon nanotubes are bistable (i.e. can have inflated or collapsed cross-sections) and can be used to design nano-electromechanical systems such as engines, generators, and heat pumps. The underlying physical mechanism for these devices is the sensitivity of the tube's equilibrium shape to external stimuli such as temperature and applied voltage. Fixing one end in the inflated state and the other in the collapsed state creates a mobile transition region separating these states. Gas encapsulated inside the tube provides an additional means to control the tube shape by coupling its thermodynamic parameters to the equilibrium tube configuration. Depending on the conditions, the encapsulated gas can remain vapor or condense layer-by-layer on the inner wall surface. We analyze such a system with lattice-gas model and molecular dynamics simulations. Changing the gas temperature or number of gas atoms changes the relative fraction of collapsed and inflated regions, while external forces that change the tube shape also affect the phase of the encapsulated gas. Surprisingly, squashing an inflated tube that has gas condensed on its inner surface decreases the surface area available to the wetting layer, so that gas atoms are forced back into the vapor phase: a paradoxical effect where compression induces a transition from condensed to vapor phases. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D37.00005: Fermi Energy-Dependent Structural Deformation of Single-Wall Chiral Carbon Nanotubes Eduardo Barros, Bruno Vieira, Antonio Souza Filho, Mildred Dresselhaus In this work, we investigate structural deformation of single wall carbon nanotubes as a function of the Fermi Energy by calculating the structural and electronic properties of charged carbon nanotubes within an extended tight-binding approach. Density-Functional-Theory-based tight-binding parameters were used, following the procedure introduced by Vercosa \textit{et al}. [2] The total energy of the nanotube is calculated assuming that the electron population follows the Fermi-Dirac distribution for a given Fermi-Energy (E$_{\mathrm{F}})$. As the Fermi energy is varied, the total charge of the nanotube changes, thereby simulating a charging effect. Our results show that the relaxation of the electronic stress generated by an extra charge on the nanotube causes axial, radial and torsional strains which directly affect the electronic band structure of carbon nanotubes. The electron-electron Coulomb repulsion further increases this effect, leading to extremely high torsional strains and considerable changes to the electronic structure of the nanotubes. For example, torsional strains of up to 2{\%} were obtained for an (8,7) nanotube for a Fermi energy of about 1 eV, causing changes of more than 0.5 eV to the interband transition energies. \\[4pt] [1] Yang et al. PRL, 85(1), 2000. [2] Vercosa, et al. PRB, 81:165430, 2010. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D37.00006: Electrical conductance adsorption isotherms of rare gases on individual single-wall carbon nanotubes Oscar Vilches, Hao-Chun Lee, Boris Dzyubenko, David Cobden Simultaneous resonance frequency and electrical conductance isotherm measurements of inert gases adsorbed on the surface of a single suspended single-wall carbon nanotube have been performed to understand the relationship between the results of the two methods. The resonance frequency measurements determine the ratio between adsorbed mass and the mass of the nanotube. The conductance also varies with the amount of mass adsorbed, but its relationship with the adsorbed mass varies between different nanotubes. The conductance change is particularly dramatic in two cases: when transitions occur between two phases of different density, for example at the liquid-vapor transition of two-dimensional (2d) Ar in the 50 K range; and when Coulomb blockade oscillations are clearly visible, in particular for 2d $^{4}$He gas adsorption in the 5 to 10 K range. Current work on the connection between conductance and frequency isotherms with various gases will be presented. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D37.00007: Adsorption equilibration processes inside narrow pores Samantha Molnar, M. Mercedes Calbi Initially motivated by experimental results concerning gas adsorption in open-ended carbon nanotubes, we investigate the adsorption kinetics of a gas inside a nanopore by implementing a Kinetic Monte Carlo simulation of the gas dynamics. In addition to obtaining the change in coverage with time, we analyze the spatial configuration of the adsorbed phase inside the pore as it evolves towards equilibrium. We also identify blockage events near the ends of the pore, and determine the dependence of these processes on the length of the pore and the amount of gas adsorbed. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D37.00008: Observation of Henry's Law in Low-Density Measurements of Adsorption on Carbon Nanotubes Boris Dzyubenko, Denise Schmitz, Hao-Chun Lee, Oscar E. Vilches, David H. Cobden We have studied the adsorption of noble gases on pristine suspended single-walled carbon nanotubes at low temperatures in the limit of low density (coverage), as determined from the shift of the mechanical resonance frequency of the nanotube due to mass loading. The high homogeneity of the nanotube substrate and the sensitivity of the technique allow us to observe Henry's law, in which the coverage is proportional to the gas pressure. In this limit the adsorption isotherm is determined by single-atom effects, allowing unprecedentedly accurate ($\pm$ 2{\%}) determination of the single-particle binding energies to a nanotube. Also, by measuring the deviation from Henry's law as coverage increases we obtain information about the pairwise interactions between the adsorbed atoms using the virial expansion. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D37.00009: Curvature and nanoscale forces in controlling self-assembly of carbon nanotube-amphiphile complexes Jukka Maatta, Paul Van Tassel, Maria Sammalkorpi In aqueous solution, carbon nanotubes (CNTs) bundle strongly via hydrophobicity induced aggregation, yet the extraordinary properties are best realized when CNTs are dispersed as individual tubes. As a result, pure and well isolated individual CNTs are typically desired and extensive effort has been devoted to achieving good aqueous dispersion of CNTs through covalent or non-covalent functionalization. Here, we examine by molecular simulations the non-covalent solubilization of CNTs with a special focus on curvature effects. We employ molecular dynamics simulations and theoretical models to systematically study the amphiphile interactions at the CNT surface. We report that micelle-forming amphiphiles form hemimicellar structures whereas bilayer-forming lipids form tubular coatings. We characterize the energetics of the underlying physical components - the electrostatic, hydration, and geometric effects on CNT dispersion to examine the efficiency of the various CNT solubilization strategies. The observed differences in amphiphile absorption provide a microscopic understanding on the curvature-dependence in amphiphile-coated CNTs solubility in the aqueous phase and will facilitate the bottom-up design of soft nanoscale materials for nanotechnology. [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D37.00010: Ethane adsorbed on carbon nanohorns Brice Russell, Aldo Migone, Masako Yudasaka, Sumio Iijima We have measured adsorption isotherms for ethane adsorbed on as-produced single-walled carbon nanohorns. Measurements have been completed for five temperatures between 130 K and 195 K. The kinetics of adsorption will be compared to results previously obtained for ethane adsorption on purified HiPco single-walled carbon nanotubes. On nanotubes it was found that equilibration time for ethane decreased with increasing sorbent coverage; for adsorption on nanohorns, equilibration time increased with increasing sorbent coverage. The kinetic results for the fractional pressure change and sorbent mass loading were calculated under the assumption that the system was only subject to one rate-controlling mechanism. The point-B method was used to determine monolayer completion values at each temperature. Equilibrium results for ethane adsorbed on nanohorns will be compared to similar results on nanotubes. This work was supported by the NSF through grant DMR-1006428. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D37.00011: CO$_{\mathrm{2}}$ adsorption on carbon nanotubes Aldo Migone, Brice Russell, Shree Banjara We measured adsorption isotherms of CO2 on a 0.1106 g sample of purified HiPco SWNTs at six temperatures between 147 and 207 K. Plots of the amount of CO2 adsorbed as a function of the logarithm of the equilibrium pressure do not reveal any resolvable substeps in the adsorption data. We measured the effective monolayer capacity of the sample using the point B method. We found a specific surface area of 380 m2/g, significantly lower than that determined from a N2 isotherm measured on the same sample. We determined the isosteric heat of adsorption as a function of the amount of CO2 loaded onto the SWNTs. The values for the isosteric heat are lower than the latent heat of sublimation for most sorbent loading values below the saturated vapor pressure. Only for sorbent loadings in the lowest 5 {\%} (relative to the sorbent loading present when the saturated vapor pressure is reached) does the isosteric heat exceed the bulk sublimation value. Our results will be compared with others reported in the literature, as well as with results obtained for CO2 on related sorbents. This work was supported by the NSF through grant DMR-1006428. [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D37.00012: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 5:18PM - 5:30PM |
D37.00013: Role of defects in the physiological fate of carbon nanomaterials Aleksandr Kakinen, Ramakrishna Podila, Jingyi Zhu, Pooja Puneet, Anne Kahru, Apparao Rao Charged defects play an important role in not only materials properties (P. Puneet et al., Scientific Reports, 3, 3212 (2013)) but also in the determination of how materials interact at the nano-bio interface. Recently, it was shown that any physiological response, and hence the fate of carbon nanotubes (CNTs) in biological media, is dictated by the formation of protein-corona. Accordingly, we explored how defects in CNTs influence the biological interactions and protein corona formation using micro-Raman spectroscopy, electrochemistry, photoluminescence, and infrared absorption spectroscopy. Our results show that the interaction of CNTs and proteins (albumin, fibrinogen, and fetal serum) is strongly influenced by charge-transfer between defects and proteins ensuing in protein-unfolding which leads to a gain in conformational entropy. [Preview Abstract] |
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