Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B28: Focus Session: Carbon Nanotubes and Related Materials: Growth, Sorting and Properties |
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Sponsoring Units: DMP Chair: Ray Baughman, University of Texas at Dallas Room: C156 |
Monday, March 21, 2011 11:15AM - 11:51AM |
B28.00001: Fundamentals and applications of monodisperse carbon-based nanomaterials Invited Speaker: Carbon-based nanomaterials have attracted significant attention due to their potential to enable and/or improve applications such as transistors, transparent conductors, solar cells, batteries, water purification systems, infrastructure materials, drug delivery, and biosensors. This talk will delineate chemical strategies for tuning and enhancing the properties of these promising nanomaterials. For example, we have developed and commercialized a scalable technique for sorting single-walled carbon nanotubes (SWCNTs) by their physical and electronic structure using density gradient ultracentrifugation (DGU). The resulting monodisperse SWCNTs possess unprecedented uniformity in their electronic and optical properties, which enables the fabrication of high performance thin film field-effect transistors, optoelectronic devices, and transparent conductors. The DGU technique also enables multi-walled carbon nanotubes to be sorted by the number of walls, and solution phase graphene to be sorted by thickness, thus expanding the suite of monodisperse carbon-based nanomaterials. By recently extending our DGU efforts to SWCNTs and graphene dispersed in biocompatible polymers (e.g., DNA, poloxamers, etc.), new opportunities have emerged in biomedical applications. Ultimately, the ability to control structure and surface chemistry with sub-nanometer precision enables optimized properties for a diverse range of technologies that employ carbon-based nanomaterials. [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:03PM |
B28.00002: Electronic separation of dispersed carbon nanotubes in solution by Lorentz forces Charishma Subbaiah, Joshua Wood, Joseph Lyding Use of single-walled carbon nanotubes (SWNTs) in industry compatible device applications requires top-down control of SWNT electronic type. Therefore, we develop a technique for SWNT electronic separation, increasing the relative distribution of metallic SWNTs in solution by a magnetically induced Lorentz force. We take solutions of SWNTs in n-methylpyrrolidone and sonicate them, making a disperse solution on which we apply a non-uniform voltage waveform. This waveform generates a magnetic field that couples more strongly with metallic SWNTs than semiconducting SWNTs, due to a higher metallic SWNT magnetic moment, separating the tubes by Lorentz force. By conducting SWNT spectrophotometric measurements in the UV-vis-IR region, we assess the separation effectiveness. From the extracted supernatant solution, we observe a multi-fold absorbance enhancement in the metallic SWNT transition regions [1]. Additionally, the small full-width at half maximum in the absorbance peaks suggests that we are selecting a small number of metallic chiralities in our separation.\\[4pt] [1] Ausman et al., J. Phys. Chem. B. 104, 8911 (2000). [Preview Abstract] |
Monday, March 21, 2011 12:03PM - 12:15PM |
B28.00003: Horizontally Aligned Carbon Nanotube Growth: Defects and Film Density W.D. Tennyson, D. Shi, E.S. Sanchez, J.C. Keay, M.B. Johnson, D.E. Resasco Horizontally-aligned single-walled carbon nanotubes (SWNTs) were grown on ST-cut quartz by chemical vapor deposition (CVD). The 0.2-0.3 nm thick thermally evaporated Fe catalyst was patterned using standard liftoff processes both parallel and perpendicular to the $<2\bar{1}\bar{1}0>$ quartz surface (the SWNT alignment axis). Enhanced SWNT film density and improved film uniformity were observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM) when water was included with the carbon feed source (ethanol). For SWNT films without water, the SWNT linear density within 1 $\mu$m of the catalyst edge was 8 SWNT/$\mu$m and down to 2 SWNT/$\mu$m at 10 $\mu$m from the edge. However, films grown with water exhibited similar linear densities both near and far from the catalyst edge, 6 SWNT/$\mu$m. AFM observations suggest that tube-tube interactions during growth contribute to a reduced the linear SWNT density. Aligned SWNTs were observed to terminate when they intersected a non-aligned SWNT. Water-assisted growth reduced the concentration of unaligned SWNTs near the catalyst edge, resulting in a higher fraction of nanotubes extending from the catalyst. [Preview Abstract] |
Monday, March 21, 2011 12:15PM - 12:51PM |
B28.00004: Utilizing real time transmission electron microscopy to understand the mechanisms of nanotube nucleation, growth and growth termination Invited Speaker: In order for carbon nanotubes to find widespread application, we must have a deeper understanding of the mechanisms by which they nucleate, growth and cease growth, in an effort to fully control the resulting structures. Here we will describe how we can exploit the unique capabilities of in-situ environmental cell transmission electron microscopy to observe multiple aspects of these processes. With this approach we can directly visualize how the catalysts that mediate nanotube growth respond to various changes in the growth environment, and correlate these changes with the resulting nanotube structures. In the first part of the presentation, we will investigate how dynamic changes in the catalyst morphology are correlated with the termination of growth in vertically aligned SWNT arrays. In particular, we have investigate how the processes of catalyst coarsening, Ostwald ripening and diffusion into the catalyst support can lead to growth termination, and we will describe how changes in the growth feedstock - in particular the incorporation of controlled amounts of water vapor - can alter the catalyst evolution. In the second portion of the presentation, we will describe how altering other aspects of the growth feedstock - in this case the carrier gas, in combination with the water vapor content - can not only affect catalyst morphological evolution, but can also significantly bias the chiral distribution of the resulting nanotubes. We will correlate the changes in growth ambient with a faceting / defacting transition, as well as a resulting change in the rate of Ostwald ripening. [Preview Abstract] |
Monday, March 21, 2011 12:51PM - 1:03PM |
B28.00005: In situ diagnostics of the pulsed growth of graphene and carbon nanotubes David Geohegan, Alex Puretzky, Jason Readle, Christopher Rouleau, Murari Regmi, Gyula Eres, Gerd Duscher, Mina Yoon Non-equilibrium, pulsed gas delivery and pulsed heating synthesis approaches are used to explore and compare the kinetics and mechanisms of carbon nanotube and graphene growth on metal thin-films. Time-resolved, in situ optical reflectivity of growing nanotubes and graphene reveal the growth kinetics resulting from well-controlled, pulsed fluxes of acetylene by chemical vapor deposition. Alternatively, pulsed laser heating of substrates is used to provide well-defined transient growth temperature profiles for growth by chemical vapor deposition. Pulsed gas fluxes are shown to control the density and diameter of nanotubes in vertically-aligned nanotube arrays with nanoparticles of different size repeatedly nucleating, growing, and terminating growth in accordance with an empirical growth model. The pulsed processing approach is used to grow vertically aligned nanotube arrays with variable density. Research sponsored by the Materials Science and Engineering Division, Basic Energy Sciences, U.S. Department of Energy. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, U.S. Department of Energy. [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:15PM |
B28.00006: Growth of Ultra-High Density Vertically-Aligned Carbon Nanotube Forests John Robertson, Santiago Esconjauregui, Martin Fouquet, Bernhard Bayer, Stephan Hofmann We present a general catalyst design method to synthesise ultra-high density, aligned forests of carbon nanotubes by cyclic deposition and annealing of catalyst thin-films. This leads to nanotube forests with an area density of at least 10$^{13}$ cm$^{-2}$, over one order of magnitude higher than existing values (Hata 2004, Zhong 2006), and close to the limit of a fully dense forest. The technique consists of cycles of ultra-thin metal film deposition, annealing, and immobilisation. The nanotubes are then grown as normally by Chemical Vapor Deposition. These ultra-dense forests are needed to use carbon nanotubes as vias and interconnects in integrated circuits and as thermal interface materials. Further density increase to 10$^{14}$ cm$^{-2}$ by reducing nanotube diameter is possible. [Preview Abstract] |
Monday, March 21, 2011 1:15PM - 1:51PM |
B28.00007: Carbon Nanotubes with Temperature Invariant Viscoelasticity from -196$^{\circ}$C to 1000$^{\circ}$C Invited Speaker: Viscoelasticity describes the ability of a material to possess both elasticity and viscosity. Viscoelastic materials, such as rubbers, possess a limited operational temperature range, (e.g., for silicone rubber: -55 to 300$^{\circ}$C) above which the material breaks down and below which the material undergoes a glass transition and hardens. This is because molecular motion that is the origin of viscoelasticity is a thermally activated process. We created a viscoelastic material composed from a random network of long interconnected carbon nanotubes that exhibited an operational temperature range from -196$^{\circ}$C to 1000$^{\circ}$C [1]. The viscoelastic properties (storage modulus, loss modulus, and damping ratio) measured by DMA in N$_{2}$ ambient were nearly constant over an exceptionally wide temperature range (-140$^{\circ}$C$\sim $600$^{\circ}$C). As exemplified by the vibration isolator demonstration, the CNT material showed viscoelasticity beyond the DMA limitation at -190$^{\circ}$C (immersed in liquid nitrogen) and at $>$900$^{\circ}$C (exposed to butane torch). And we implemented impact tests at -196$^{\circ}$C, 25$^{\circ}$C and 1000$^{\circ}$C using a steel ball and analyzed the ball tracks. The ball tracks were identical for all cases as observed by SEM and 3-D mapping that suggested unvarying viscoelastic properties across this 1200$^{\circ}$C temperature range. We interpret that the thermal stability stems from energy dissipation through the zipping and unzipping of carbon nanotubes at contacts. Quantitatively, the viscoelastic properties by DMA showed that the CNT material possessed similar stiffness (storage modulus 1MPa), higher dissipation ability (loss modulus (0.3MPa) and damping ratio (0.3) than silicone rubber at room temperature. Further DMA characterization from -140$^{\circ}$C to 600$^{\circ}$C demonstrated temperature invariant frequency stability (0.1-100Hz), the same level of reversible deformation (critical strain 5{\%}) and fatigue resistance (1,000,000 cycles, 100Hz). \\[4pt] [1] Xu, M.; Futaba, D. N.; Yamada, T.; Yumura, M.; Hata, K. \textit{Science} (Accepted) [Preview Abstract] |
Monday, March 21, 2011 1:51PM - 2:03PM |
B28.00008: Understanding Chiral-Selective Growth of Carbon Nanotubes: In-Situ Raman Studies of Individual Single Walled Carbon Nanotube Growth Rahul Rao, David Liptak, Tonya Cherukuri, Daylond Hooper, Boris Yakobson, Benji Maruyama In-situ Raman scattering has been used to obtain growth kinetics of individual single-walled carbon nanotubes (SWNTs) using a custom designed cold-wall chemical vapor deposition (CVD) chamber coupled to a Raman spectrometer. Raman spectra are collected during SWNT growth and plots of the G band area versus time are fitted to self-exhausting exponential curves, from which we obtain SWNT growth rates and catalyst lifetimes (time constant). Chiral index assignments are made for several individual SWNTs via analysis of the radial breathing modes. The growth rate of the SWNTs is shown to be proportional to the chiral angle. In addition we find a positive correlation between SWNT length (obtained from SEM analysis) and the growth rate. This confirms the model put forth by Ding \textit{et al}. [1] which links SWNT growth rate to the chiral angle. A growth model based on our results illuminates an as-yet unexplained distribution in the chiral yield of typical CVD-grown nanotubes as being driven by chiral-selective growth kinetics. [1] Ding, F; Haturyunyan, A; Yakobson, B, I; Dislocation theory of chirality-controlled nanotube growth, Proc. Natl. Acad. Sci., 106, 2506, 2009 [Preview Abstract] |
Monday, March 21, 2011 2:03PM - 2:15PM |
B28.00009: Dislocation Dynamics in Multishell Carbon Nano-Onions Traian Dumitrica, Evgeniya Akatyeva, Jianyu Huang Graphite has long served as a model material to understand dislocations. An early work on natural graphite provided factual evidence for the existence of screw dislocations. Recently, synthetic carbon nanostructures began to be explored in order to understand dislocations at the nanoscale. Here we study the 1/2$<$0001$>$ edge dislocation in nested multishell carbon onions [1]. We report in situ electron microscopy observations of dislocation dissociation and annihilation processes in individual nanometer-sized carbon onions. Essential for these processes is the counterintuitive motion of the 1/2$<$0001$>$ edge from the outer surface to the inner region, which cross-links or unlinks a large number of shells. The correlation with atomistic simulations and analysis of the energy, which separates the strain and edge components, indicates that this inward glide originates in the reduction of edge with each inwards glide step, an effect specific to the spherical topology. \\[4pt] [1] E. Akatyeva, J. Y. Huang and T. Dumitrica, Phys. Rev. Lett. 105, 106102 (2010). [Preview Abstract] |
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