Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S37: Focus Session: Carbon Nanotubes: Diameter, Wall & Chirality Control |
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Sponsoring Units: DMP Room: 705/707 |
Thursday, March 6, 2014 8:00AM - 8:36AM |
S37.00001: Recent studies on double wall and triple wall carbon nanotubes Invited Speaker: Mildred Dresselhaus Recent progress is reported in studying 1) metallicity effects in double wall and triple wall carbon nanotubes, and 2) self healing effects in bundles due to ruptures in current flow due to Joule heating in carbon nanotube bundles. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S37.00002: Diameter-Selective Alignment of Carbon Nanotubes on Si (001) Stepped Surfaces Batnyam Enkhtaivan, Masahide Yoshimura, Jun-Ichi Iwata, Atsushi Oshiyama The necessity of aligning carbon nanotube (CNT) raises important questions of whether the alignment is energetically feasible and of whether the electronic properties of CNTs are modified on the substrate surface. We report total-energy electronic-structure calculations based on the DFT that provide stable adsorption sites, structural characteristics, and energy bands of CNTs adsorbed on the Si(001) stepped surfaces. We choose (5,5), (9,9) and (13,13) armchair CNTs with the diameters of 6.8 {\AA}, 12.2 {\AA} and 17.6 {\AA} and explore all the possible adsorption sites either on the terrace or at step edges. We find that the (9,9) CNT is most favorably adsorbed at the edge of the double-layer step D$_{B}$ along the $<$110$>$ direction, whereas the (5,5) and (13,13) CNTs favor the terrace site where the CNTs are perpendicular to the Si dimer rows. This finding is indicative of the diameter-selective self-organized alignment of CNTs by exploiting the Si surface steps. We also find that the electronic structure of each CNT is modified upon adsorption depending on the adsorption site and the diameter of the CNTs. In particular, the (9,9) CNT at the most stable step edge site becomes semiconducting and also an interesting flat band appears at Fermi level. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S37.00003: Chirality, Metallicity, and Transition Dependent Asymmetries in Resonance Raman Excitation Profiles of Chirality-Enriched Carbon Nanotubes Stephen Doorn, Juan Duque, Hagen Telg, Erik Haroz, Xiaomin Tu, Ming Zheng Access to carbon nanotube samples enriched in single chiralities allows the observation of new photophysical behaviors obscured or difficult to demonstrate in mixed-chirality ensembles. Recent examples include the observation of strongly asymmetric G-band excitation profiles resulting from non-Condon effects$^{1}$ and the unambiguous demonstration of Raman interference effects.$^{2}$ We present here our most recent results demonstrating the generality of the non-Condon behavior to include metallic species (specifically several armchair chiralities). Additionally, the E$_{ii}$ dependence in non-Condon behavior with excitations from E$_{11}$ thru E$_{44}$ for both RBM and G modes will be discussed. 1. J.G. Duque, et. al., ACS Nano, 5, 5233 (2011). 2. J.G. Duque, et. al., Phys. Rev. Lett. 108, 117404 (2012). [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S37.00004: Resonance Raman Spectroscopy of Single-Wall Carbon Nanotubes Separated via Aqueous Two-Phase Extraction J.R. Simpson, J.A. Fagan, A.R. Hight Walker We report Resonance Raman Spectroscopy (RRS) measurements of single-wall carbon nanotube (SWCNT) samples dispersed in aqueous solutions via surfactant wrapping and separated using aqueous two-phase extraction (ATPE) into chirality-enriched semiconducting and metallic SWCNT species. ATPE provides a rapid, robust, and remarkably tunable separation technique that allows isolation of high-purity, individual SWCNT chiralities via modification of the surfactant environment. We report RRS measurements of individual SWCNT species of various chiral index including, armchair and zigzag metals. Raman provides a powerful technique to quantify the metallic SWCNTs in ATPE fractions separated for metallicity. We measure Raman spectra over a wide range of excitation wavelengths from 457\,nm to 850\,nm using a series of discrete and continuously tunable laser sources coupled to a triple-grating spectrometer with a liquid-nitrogen-cooled detector. The spectra reveal Raman-active vibrational modes, including the low-frequency radial breathing mode (RBM) and higher-order modes. SWCNT chiral vectors are determined from the Raman spectra, specifically the RBM frequencies and corresponding energy excitation profiles, together with input from theoretical models. [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S37.00005: Chirality Separation of Single-Wall Carbon Nanotubes using Aqueous Two-Phase Extraction Jeffrey Fagan Aqueous two-phase extraction (ATPE) was recently demonstrated to enable the separation of individual species of single-wall carbon nanotubes (SWCNTs) across the separated phases. In this presentation I will describe the use of a dextran - polyethylene glycol aqueous two-phase system along with a separation scheme of varying surfactant concentrations to enable isolation at high purity of specific small diameter SWCNT species. Separation by ATPE is rapid and robust, with a remarkable tunability that allows isolation of most single nanotube chiralities at high purity. Choice of surfactant(s), temperature, polymer concentrations, and the addition of small molecule salts can all be used to tune the exact partitioning of single SWCNT species between the two phases. [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S37.00006: Chirally - Selective Growth of Single Walled Carbon Nanotube on Fe$_{13}$ Nanocatalyst Anteneh Tefera, Mogus Mochena Controlled growth of single - walled carbon nanotubes with desired chiral indices remains the holy grail of single walled carbon nanotube synthesis. We performed ab initio molecular dynamics calculation of the nucleation and early stage growth of (5,0) SWCNT in the low temperature range where the nanocatalyst is a solid. We show that a zigzag formation of carbon atoms is possible when the surface of the pentagonal pyramid of Fe$_{13}$ icosahedron is exposed to ambient carbon atoms or carbon atoms and dimers or a ring of ten carbon atoms. The possibility of anomalous cap formation resulting from competing repulsive and attractive forces is presented. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S37.00007: Why do carbon nanotubes grow chiral? Evgeni Penev, Vasilii Artyukhov, Boris Yakobson Carbon nanotubes (CNT) hold enormous technological promise. It can turn into reality only if one can control in a practical way the CNT chirality---the geometric feature of the tubular carbon topology that governs the CNT electronic properties. Experimental efforts over the last decade have consistently revealed a puzzling strong preference towards specific chiral CNT grown via catalytic chemical vapor deposition, challenging any existing hypotheses and turning chirality control even more elusive. Here we investigate the roles of different factors in shaping the chirality distribution of CNT yield, including nanotube-catalyst interface [1], the energetic landscape of CNT caps [2], or growth kinetics [3], building upon our ``Nanoreactor'' framework developed for graphene synthesis [4]. Our theory shows promise in explaining narrow chirality distributions seen in multiple recent experimental studies.\\[4pt] [1] Y. Liu, A. Dobrinsky, B. I. Yakobson, Phys. Rev. Lett. \textbf{105}, 235502 (2010).\newline [2] E. S. Penev, V. I. Artyukhov, and B. I. Yakobson (submitted).\newline [3] F. Ding, A. R. Harutyunyan, B. I. Yakobson, Proc. Natl. Acad. Sci. U.S.A. \textbf{106}, 2506 (2009).\newline [4] V. I. Artyukhov, Y. Liu, B. I. Yakobson, Proc. Natl. Acad. Sci. U.S. [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S37.00008: Energy landscape of carbon nanotube caps: lack of intrinsic chirality bias and consequences for selective growth Vasilii Artyukhov, Evgeni Penev, Boris Yakobson In the initial stages of carbon nanotube (CNT) growth, a fixed pattern of six pentagons encodes what unique $(n,m)$ chirality a nascent CNT would inherit and can be viewed as its ``inorganic gene''. We shall present the results from a large-scale computational effort designed to establish a quantitative structure--property (intrinsic elastic energy) relation for a set of more than 4500~caps, including all isomers that obey the isolated pentagon rule, corresponding to tube diameters $d \leq 1$~nm. Our analysis shows that the energy scale associated with the CNT caps is small, compared to that of the CNT/catalyst interface. Such a flat energy landscape is irrelevant to chiral selectivity and lends further credibility to interface-controlled scenarios for selective growth of single-walled CNTs. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S37.00009: Chirality-Dependent Vapor-Phase Epitaxial Growth and Termination of Single-Wall Carbon Nanotubes Bilu Liu, Jia Liu, Chongwu Zhou Chirality-pure single-wall carbon nanotubes are highly desired for both fundamental study and many of their technological applications. Recently, we have shown that chirality-pure short nanotubes can be used as seeds for vapor-phase epitaxial cloning growth, opening up a new route toward chirality-controlled carbon nanotube synthesis. Nevertheless, the yield of vapor-phase epitaxial growth is rather limited at the present stage, due to the lack of mechanistic understanding of the process. Here we report chirality-dependent growth kinetics and termination mechanism for the vapor-phase epitaxial growth of seven single- chirality nanotubes of (9, 1), (6, 5), (8, 3), (7, 6), (10, 2), (6, 6), and (7, 7), covering near zigzag, medium chiral angle, and near armchair semiconductors, as well as armchair metallic nanotubes. Our results reveal that the growth rates of nanotubes increase with their chiral angles while the active lifetimes of the growth hold opposite trend. Consequently, the chirality distribution of a nanotube ensemble is jointly determined by both growth rates and lifetimes. These results correlate nanotube structures and properties with their growth behaviors and deepen our understanding of chirality-controlled growth of nanotubes. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S37.00010: A Molecular Dynamics Study of Single-Walled Carbon Nanotubes (SWCNTs) Dispersed in Bile Salt Surfactants Frederick Phelan Jr., Huai Sun Single-walled carbon nanotubes (SWNCTs) are materials with structural, electronic and optical properties that make them attractive for a myriad of advanced technology applications. A practical barrier to their use is that SWCNT synthesis techniques produce heterogeneous mixtures of varying lengths and chirality, whereas applications generally require tubes with narrow size distributions and individual type. Most separation techniques currently in use to obtain monodisperse tube fractions rely on dispersion of these materials in aqueous solution using surfactants. The dispersion process results in a mixture of colloidal structures in which individual tubes are dispersed and contained in a surfactant shell. Understanding the structure and properties of the SWCNT-surfactant complex at the molecular level, and how this is affected by chirality, is key to understanding and improving separations processes. In this study, we use molecular dynamics (MD) simulations to study the structure~and properties of SWCNT-surfactant colloidal complexes. We tested a number of methods and protocols in order to build an accurate model for simulating SWCNT systems for a variety of bile salt surfactants as well as anionic co-surfactants, components that are widely used and important in experimental separation studies at NIST. The custom force field parameters used here will be stored in WebFF, a Web-hosted smart force-field repository for polymeric and organic materials being developed at NIST for the Materials Genome Initiative. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S37.00011: Chiral Selection of Single-Wall Carbon Nanotubes in Murine Organs John Heddleston, Ashwin Bhirde, Zhe Wang, Constantine Khripin, Jeffrey Fagan, Ming Zheng, Xiaoyuan Chen, Angela Hight Walker Single-wall carbon nanotubes (SWCNTs) have garnered significant interest as innovative tools for biomedical applications. They are being used for a variety of purposes, e.g. to deliver drug payloads, monitor cellular activity, or as in vivo imaging tools. However our current understanding of how SWCNTs behave in biological systems is limited. In this work we use Raman spectroscopy to measure the radial breathing modes (RBMs) of SWCNTs in murine organs following intravenous administration. We identify RBMs in multiple homogenized organs and can additionally measure the less SWCNT-specific carbon Raman peaks in others. Further, we quantify significant changes in the relative contribution of different SWCNTs chiralities to the overall RBM distribution. We observe this change in SWCNTs with a smaller diameter (7.6 A) but not in larger diameter tubes (14 A). These data are among the first to measure RBMs in organs and suggest that chiral selection can occur in biological systems with susceptibility for selection dependent on SWCNT diameter. [Preview Abstract] |
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