Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A24: Focus Session: Nanotube Synthesis |
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Sponsoring Units: DMP Chair: Avetik Harutyunyan, Honda Research Room: 326 |
Monday, March 16, 2009 8:00AM - 8:36AM |
A24.00001: Thermodynamic instabilities in nano-catalysts and their effects on the diameter of grown nanotubes Invited Speaker: Fe and Fe:Mo nanoclusters are becoming the standard catalysts for growing single-walled carbon nanotubes (SWCNTs) via chemical vapor decomposition (CVD). Contrary to the Gibbs-Thomson formalism, experimental results show that reducing the size of the catalyst beyond a certain limit requires increasing the (minimum) growth temperature. This apparent paradox is addressed in terms of solubility of C in Fe nanoclusters. By using first principles calculations, an innovative thermodynamic model is constructed to determine the behavior of the phases competing for stability. As a function of particle size, there are three scenarios: steady state-, limited-, or no-growth of SWCNTs, corresponding to unaffected, reduced, and zero solubility of C in the clusters. The results are extended to Fe-Mo binary catalysts. The 15+ year long-standing question about the effects of Mo concentration on the growth capability is finally answered. Phys. Rev. Lett. {\bf 100}, 195502 (2008), Phys. Rev. B, {\bf 77}, 115450 (2008), Phys. Rev. B {\bf 75}, 205426 (2007). [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 8:48AM |
A24.00002: CVD grown SWCNTs on Si substrate from DPN patterned catalyst precursor. Irma Kuljanishvili, Rachel Koltun, Scott Mayle, Venkat Chandrasekhar, Dmitriy Dikin , Sergey Rozhok Much interest has been generated around patterning and synthesis of high quality single wall carbon nanotubes (SWCNTs) into desired architectures. Here we report our work, undertaken to elucidate a simple method for delivering catalyst nanoparticles on defined locations on Si substrate via direct writing approach. We applied the Dip Pen Nanolithography (DPN) approach to pattern catalyst nanoparticles in selective locations on the substrate and developed a successful recipe for the subsequent CVD growth to produce high quality SWCNTs into scalable array geometries. Key parameters for successful implementation of this technology into devices or circuit architectures will be discussed. We will present our results on patterning, synthesis and characterization of SWCNTs as-grown on the substrate. Raman spectroscopy analysis, electrical and thermal properties of individual SWCNTs prepared into complex nanodevices will be presented in progress. [Preview Abstract] |
Monday, March 16, 2009 8:48AM - 9:00AM |
A24.00003: Effective Growth of Boron Nitride Nanotubes by Thermal-CVD Chee Huei Lee, Ming Xie, Derek Meyers, Jiesheng Wang, Yoke Khin Yap The synthesis of boron nitride nanotubes (BNNTs) are challenging as compared to the growth of carbon nanotubes (CNTs). Most of reported techniques required unique setup and temperatures $>$1300 $^{\circ}$C. Here we show that clean and long multiwalled BNNTs can be grown by simple catalytic thermal CVD. This was obtained by a growth vapor trapping approach inspired by the whisker nucleation theory. Based on our new findings, we have achieved patterned growth of BNNTs at desired locations. High resolution TEM shows that these BNNTs are highly crystallized. Besides, the tangential vibrational mode predicted by theory was detected in our BNNTs. This vibration mode could be the fingerprint for BNNTs with high crystallinity. [Preview Abstract] |
Monday, March 16, 2009 9:00AM - 9:12AM |
A24.00004: Co-optimizing carbon nanotube synthesis: control of diameter, structural quality, and growth kinetics along with simultaneous cost minimization Eric R. Meshot, Desire\'e L. Plata, Christopher M. Reddy, Philip M. Gschwend, A. John Hart We employ a decoupled CVD method that not only facilitates control of mean diameter and structural quality of vertically aligned CNTs, but also co-optimization of kinetics for efficient growth to ``forest'' heights of several millimeters. The growth substrate temperature (Ts) governs agglomeration of the catalyst film which primarily determines CNT diameter, while structural quality monotonically increases with Ts. Independent heating (Tp) of the reactant mixture generates a strikingly diverse population of active hydrocarbons. These analyses, in concert with real-time laser measurements of forest growth rate and height suggest that select products of gas treatment promote growth, while excessive gas-phase pyrolysis of hydrocarbons adversely affects the CNT structure. Further, we directly inject select compounds in the absence of thermal treatment, thus minimizing energetic costs. [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:24AM |
A24.00005: Diameter and Geometry Control of Vertically Aligned SWNTs through Catalyst Manipulation Rong Xiang, Erik Einarsson, Jun Okawa, Yoichi Murakami, Shigeo Maruyama We present our recent progress on manipulating our liquid-based catalyst loading process, which possesses greater potential than conventional deposition in terms of cost and scalability, to control the diameter and morphology of single-walled carbon nanotubes (SWNTs). We demonstrate that the diameter of aligned SWNTs synthesized by alcohol catalytic CVD can be tailored over a wide range by modifying the catalyst recipe. SWNT arrays with an average diameter as small as 1.2 nm were obtained by this method. Additionally, owing to the alignment of the array, the continuous change of the SWNT diameter during a single CVD process can be clearly observed and quantitatively characterized. We have also developed a versatile wet chemistry method to localize the growth of SWNTs to desired regions via surface modification. By functionalizing the silicon surface using a classic self-assembled monolayer, the catalyst can be selectively dip-coated onto hydrophilic areas of the substrate. This technique was successful in producing both random and aligned SWNTs with various patterns. The precise control of the diameter and morphology of SWNTs, achieved by simple and scalable liquid-based surface chemistry, could greatly facilitate the application of SWNTs as the building blocks of future nano-devices. [Preview Abstract] |
Monday, March 16, 2009 9:24AM - 9:36AM |
A24.00006: Ethanol-promoted growth of dense vertically aligned small-diameter carbon nanotubes Yongyi Zhang, John Gregoire, John Hart We report the use of a small concentration of ethanol in addition to ethylene as the carbon source for growth of vertically aligned CNT ``forests.'' In our system, adding ethanol promotes the catalyst lifetime from approximately 20 minutes to nearly 60 minutes, and accordingly increases the forest height from 2.5 mm to over 5 mm, with CNT diameters of approximately 5 nm (2-3 walls). Spread composition films deposited by gradient sputtering, combined with non-destructive mapping of CNT diameter and alignment by small-angle X-ray scattering, enable high-throughput discovery of necessary and sufficient conditions for growth of small-diameter CNTs. Compared with the widely known water-assisted ``super growth'' process, we find that ethanol enables much finer control of the dewpoint and thus offers more consistent and tunable results. Also, ethanol is a weaker oxidant than water and therefore creates fewer structural defects due to unwanted etching of the CNT walls. [Preview Abstract] |
Monday, March 16, 2009 9:36AM - 9:48AM |
A24.00007: Manufacturing thin films of densely packed horizontally aligned carbon nanotubes Sameh Tawfick, A. John Hart Dense packing of carbon nanotubes (CNTs) over long-range dimensions is necessary to replicate their outstanding properties in functional thin films. We present a continuous method for transforming pillars of vertically aligned (VA) CNTs into densely packed, horizontally aligned (HA) CNT ribbons and sheets, which can be directly used on wafer-scale dimensions and/or patterned by photolithography and plasma etching to achieve feature dimensions down to the micron scale. In this process, a small roller is used to ``topple'' millimeter-tall VA-CNT microstructures and to simultaneously compress them, thus increasing the packing fraction of CNTs from 2{\%} to 60{\%}. We formulate design guidelines for selection of pattern geometry, roller diameter and material, and the kinetics of the rolling motion. This enables precise control of the HA-CNT film topography and thickness, and the packing density and orientation of the CNTs. Nanoindentation of the HA-CNT films reveals that the initial tortuosity of the VA-CNT forest determines the ultimate achievable densification. Electrical conductivity of ribbons is characterized using dc-four-point testing of lithographically-patterned CNT ribbons with Au contacts. The HA-CNT structures are easily transferred to other substrates, enabling integration with CMOS and MEMS fabrication, and with alternative substrates such as flexible plastics. [Preview Abstract] |
Monday, March 16, 2009 9:48AM - 10:00AM |
A24.00008: Incremental Growth of Single-Wall Carbon Nanotube Arrays Explored by Pulsed CVD Jeremy Jackson, Alex Puretzky, Igor Merkulov, Christopher Rouleau, Karren More, Norbert Thonnard, Gyula Eres, David Geohegan Gas pulses of variable duration and peak flux were used to explore the incremental growth and evolution of alignment of vertically-aligned carbon nanotubes arrays (VANTAs) by typical chemical vapor deposition within a tube furnace. Time-resolved reflectivity from Fe/Al catalyst-coated Si substrates was used to follow the growth of the arrays after the arrival of successive acetylene gas pulses injected into fast argon-hydrogen flows at 6 Torr total pressure. The evolution of alignment of the arrays measured with the in situ optical reflectivity data was correlated with SEM images for growth resulting from single- and multiple-pulse growth. The incremental length per pulse was varied from 20 nm to several microns in less than a second, corresponding to growth rates ranging up to 7 microns/second. Effects of repeated renucleation of growth along the nanotube wall structure were measured by HRTEM and Raman spectroscopy. [Preview Abstract] |
Monday, March 16, 2009 10:00AM - 10:12AM |
A24.00009: A model of dry-drawing of multiwall carbon nanotube forest into self-assembled sheets and yarns Alexander Kuznetsov, Alexandre Fonseca, Ray Baughman, Anvar Zakhidov A dry-state technique to produce highly-oriented, free-standing multiwalled carbon nanotube (MWNT) sheets and yarns which are mechanically strong, transparent, and highly oriented has been developed recently [1,2]. A model which allows to describe the main features of the process of dry-drawing self-assembly of vertically oriented multiwall carbon nanotube (MWCNT) forest into horizontal MWCNT sheets or yarns is developed in this presentation. The model is based on two main concepts: 1. self-strengthening of nanotube bundle interconnects during the bending-pulling process; 2. rearrangement of bundles by accordion-type stretching motion accompanied by detachment of bundles (at the top and bottom of the forest). This detachment occurs due to unzipping and self-strengthening of interconnects beyond a critical force, which permits to pull the next bundle from the forest, keeping the process of dry-drawing continuous. Developed model determines the parameters of CNT forest for which the dry-drawing is possible. It also allows to estimate such properties of the produced sheets and yarns as length, density, strength and electrical conductivity. [1] M. Zhang et al., Science \textbf{2005}, 309, 1215. [2] M. Zhang et al., Science \textbf{2004}, 306, 1358. [Preview Abstract] |
Monday, March 16, 2009 10:12AM - 10:24AM |
A24.00010: Termination mechanism of carbon nanotube forest growth Mostafa Bedewy, Eric R. Meshot, Yongyi Zhang, Haicheng Guo, Eric Verploegen, Wei Lu, A. John Hart Understanding the termination event in the growth of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) is a roadblock in the pursuit of ultra-long CNTs, which would be useful for many of applications. Our previous in situ measurements show that vertically-aligned CNT ``forest'' growth terminates abruptly, which is not predicted by widely suggested models of diffusion-limited growth. In this work, we complement forest height measurements with mass and density measurements, and with spatial mapping of CNT diameter, alignment, and spacing along the forest sidewall by small-angle and ultra-small-angle synchrotron X-ray scattering (SAXS, USAXS). Accordingly, we reveal that the areal density of growing CNTs begins to decay long before the forest height terminates, indicating that gradual deactivation of catalyst particles is collectively responsible for the limitation to CNT forest height. Considering that mechanical and surface interactions among CNTs create the self-supporting forest structure, a gradual decay of CNT density can lead to an abrupt loss of CNT alignment at the forest base when the CNT-CNT spacing increases sufficiently. This proposed mechanism is supported by finite element models of CNT-CNT buckling and contact. [Preview Abstract] |
Monday, March 16, 2009 10:24AM - 10:36AM |
A24.00011: Clarifying the Rules for the Highly Efficient Growth of Carbon Nanotubes Don Futaba, Jundai Gotou, Satoshi Yasuda, Takeo Yamada, Motoo Yumura, Kenji Hata In water-assisted chemical vapor deposition (CVD), the addition of a growth enhancer, e.g. water, to the ambient of normal hydrocarbon dramatically improves growth efficiency resulting in vertically aligned forests [1]. Here, we present a generalized picture of water-assisted CVD (Super-growth) by demonstrating that highly efficient growth of carbon nanotubes (CNTs) is possible by, essentially, a countless number of growth enhancers exemplified here by alcohols ethers, esters, ketones, aldehydes, and even carbon dioxide. From an extensive investigation, we found that the key for highly efficient growth is to use two essential ingredients: 1) a carbon source not containing oxygen, and 2) a growth enhancer containing oxygen. We believe that this new understanding of CNT synthesis further cultivates and expands the world of CVD where innumerable new and completely unexplored growth ambients can emerge that would lead to further scientific discovery [1] K. Hata \textit{et al}, Science, \textbf{306}, 1241 (2004). [Preview Abstract] |
Monday, March 16, 2009 10:36AM - 10:48AM |
A24.00012: ABSTRACT WITHDRAWN |
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