Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session N29: Focus Session: Carbon Nanotubes: Synthesis |
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Sponsoring Units: DMP Chair: John Cumings, University of Maryland Room: Colorado Convention Center 303 |
Wednesday, March 7, 2007 8:00AM - 8:36AM |
N29.00001: HRTEM studies of various carbon nanotubes Invited Speaker: Among various synthesis methods of carbon nanotubes (CNT), catalytic CVD method has gained its majority. There are several reasons for the popularity of CCVD method, which is the simplicity of the instrumental setup, ease of varying the CNT growth condition, and relatively simple control over the number of layers. We have been working with the CCVD method for producing high quality nanotubes, and by finding the right synthesis condition, succeeded in obtaining highly homogeneous double-wall carbon nanotubes (DWCNT). In the heat-treated DWCNT sample, we were able to find various coalesced tubes with interesting morphologies. In the present talk, the process of producing high quality DWCNT and its morphological changes by various treatments will be shown. In collaboration with Hiroyuki Muramatsu, Yoong Ahm Kim, and Morinobu Endo, Shinshu University and the Endo Lab Team. [Preview Abstract] |
Wednesday, March 7, 2007 8:36AM - 8:48AM |
N29.00002: Growth Characteristics of Long, Gas Flow Aligned Carbon Nanotubes (CNT) by Chemical Vapor Deposition (CVD) Alfonso Reina, Mario Hofmann, David Zhu, Jing Kong An investigation is undertaken to elucidate differences in the growth of long, gas flow aligned nanotubes and short, randomly oriented nanotubes. The synthesis is carried under ambient pressure ethanol and methane CVD from iron-based nanoparticles on SiO$_2$ substrates. The two CNT morphologies are controlled by tuning chemical parameters such as catalyst pre-treatment. The growth of long, aligned CNTs presents two main differences over the growth of short, randomly aligned CNTs. The growth lifetime is significantly higher (15 minutes vs. 10 seconds) and alignment with the gas flow occurs only when a nanotube achieves a length of 40 $\mu$m, suggesting that short growth lifetimes limit not only the length of CNTs but also their alignment with the gas flow. Finally, a series of studies were done to explore possible mechanisms of CNT growth death. Differences in the nanoparticles catalytic lifetime and/or CNT growth rate are the most probable factors determining alignment. [Preview Abstract] |
Wednesday, March 7, 2007 8:48AM - 9:00AM |
N29.00003: Distribution and stability of Carbon in Fe-C nanoparticles. Neha Awasthi, Aiqin Jiang, Aleksey Kolmogorov, Wahyu Setyawan, Kim Bolton, Stefano Curtarolo Catalytic Chemical Vapor deposition (CVD) method is widely used to produce carbon nanotubes. To improve our understanding of the CVD growth mechanism, we focus on the thermodynamics and the phase stability of catalyst Fe-C nanoparticles. Using \textit{ab initio} methods and classical molecular dynamics simulations, we investigate 1) the diffusion and solubility of carbon atoms in nanoparticles by calculating the distribution of carbon atoms inside the clusters, 2) the formation and stability of carbides at nanoscale, and 3) the effect of substrates on such structures. We address the implications of these results on NT growth, and give possible strategies to mitigate the problems. [Preview Abstract] |
Wednesday, March 7, 2007 9:00AM - 9:12AM |
N29.00004: Challenges for Growth of Smallest Diameter Single-Walled Carbon Nanotubes by Catalytic Method Oleg Kuznetsov, Elena Mora, Toshio Tokune, Stefano Curtarolo, Kim Bolton, Avetik Harutyunyan We investigate the viability of formation of very small diameter ($<$ 0.5nm) freestanding SWNTs by CVD based on concept of carbon diffusion through the catalyst particle, originated from the vapor-liquid-solid growth mechanism. We found that the decrease of particle size required for nucleation of small diameter tubes results in a significant increase of catalytic decomposition temperature of hydrocarbon and, accordingly, the temperature required for nucleation and growth of nanotubes. However, high temperature increases the mobility of particles and endorses their agglomeration with formation of bigger particles, as well as leads to deactivation of catalyst by formation of intermetallic compounds with support material. The results of Raman spectroscopy, (n,m) assignments of the grown tubes and TEM studies for the smallest diameter tubes are presented. Performed \textit{ab-inito} and molecular dynamics simulations qualitatively explain the experimental finding based on size dependent carbon solubility of catalyst, by analyzing supported nanocatalyst-carbon binary phase diagram. [Preview Abstract] |
Wednesday, March 7, 2007 9:12AM - 9:24AM |
N29.00005: Growth of carbon nanotubes by the pyrolysis of thiophene Gaohui Du, Wenzhi Li Branched carbon nanotubes have been reported and produced by the pyrolysis of metallocene-thiophence mixture. In our experiments, we prepared the carbon nanotubes (CNTs) by the pyrolysis of thiophene as the carbon source over cobalt catalysts. The lengths of carbon nanotubes can reach 0.5-1 mm for the growth time of 15 min. The effects of flow rate and temperature on the growth of CNTs have been investigated. The branched carbon nanotubes were also found in the experiments, showing Y-junction or T-junction, even connecting each other to form a web. The growth mechanism of the branched CNTs was studied using transmission electron microscopy. The electron transportation properties along these branched CNTs are under investigation. [Preview Abstract] |
Wednesday, March 7, 2007 9:24AM - 9:36AM |
N29.00006: Initial Stage of Growth of Single-Wall Carbon Nanotubes: Modeling and Simulations I. Chaudhuri, M. Yu, C. S. Jayanthi, S. Y. Wu Through a careful modeling of interactions, collisions, and the catalytic behavior, one can obtain important information about the initial stage of growth of single-wall carbon nanotubes (SWCNTs), where a state-of-the-art semi-empirical Hamiltonian [Phys. Rev. B,\textbf{ 74}, 155408 (2006)] is used to model the interaction between carbon atoms. The metal catalyst forming a supersaturated metal-alloy droplet is represented by a jellium, and the effect of collisions between the carbon atoms and the catalyst is captured by charge transfers between the jellium and the carbon. Starting from carbon clusters in different initial configurations ($e.g$., random structures, cage structures, bulk-cut spherical clusters, \textit{etc}.), we anneal them to different temperatures. These simulations are performed with clusters placed in the jellium as well as in vacuum. We find that, in the presence of jellium, and for an optimal charge transfer of $\sim \quad 0.2 e,$ open cage structures (and some elongated cage structures) are formed, which may be viewed as precursors to the growth of SWCNTs. We will also discuss the implications of a spherical boundary on the nucleation of a SWCNT. [Preview Abstract] |
Wednesday, March 7, 2007 9:36AM - 9:48AM |
N29.00007: Universal Template Technique for Patterned Growth of Carbon Nanotubes Ying Chen, Hua Chen, Jun Yu, Bill Li, Vince Creig, James Williams A new template technique has been developed to help patterned growth of carbon nanotubes on Si surface without predeposition of metal catalysts. Focused ion beam (FIB) milling system was used to create nanosized patterns on Si wafer surface as the template. Under a controlled pyrolysis of iron phthalocyanine at 1000 $^{o}$C, carbon nanotubes only nucleate and grow in the template. The selective growth is due to the special surface morphology and crystalline structure created by FIB. This template technique can be used to help patterned growth of other nanotubes and nanowires on any substrates. [Preview Abstract] |
Wednesday, March 7, 2007 9:48AM - 10:00AM |
N29.00008: Synthesis of Narrow Chirality Distributions of Single-Walled Carbon Nanotubes using Catalyst Particle Templates Produced by Nanosphere Lithography Noureddine Tayebi, Joseph Lyding We report a simple and inexpensive technique based on nanosphere lithography [1], which allows for the fabrication of periodically-spaced and monodispersed metal particles from which the chemical-vapor-deposition synthesis of single-walled carbon nanotubes (SWNTs) is achieved. We have controlled the diameter of these metal particles, and thus that of the SWNTs, from 1 nm down to 0.7 nm, with an interparticle spacing varying from 50 nm down to 5 nm. Raman spectroscopy analysis reveals that a narrow chirality distribution is achieved. We are currently confirming the chirality results using fluorescence spectroscopy and scanning tunneling microscopy. Transmission electron microscopy analysis reveals that the 0.7 nm particles are crystallographically identical, which could be the origin of such a narrow distribution. Furthermore, the current technique was used to grow aligned SWNTs on single-crystal quartz substrates [2]. [1] J. C. Hulteen et al., J Vac Sci Technol A, 13, 1553 (1995) [2] C. Kocabas et al., J Am Chem Soc, 128, 4540 (2006) [Preview Abstract] |
Wednesday, March 7, 2007 10:00AM - 10:12AM |
N29.00009: Synthesis and characterization of dense, vertically-aligned carbon nanotube forests from 10nm colloidal iron oxide nanoparticles David Hutchison, Brendan Turner, Richard Vanfleet, Robert Davis, Brian Woodfield, Juliana Boerio-Goates We report growth of vertically-aligned carbon nanotubes (VACNTs) on alumina using 10nm iron oxide nanoparticles dried from a colloid. VACNTs were grown by chemical vapor deposition using ethylene, hydrogen and argon, and found to be dense forests with height, number of walls, and density dependent on the catalyst concentration. Comparison between VACNTs produced from nanoparticles and those from more traditional sputtered or evaporated iron films will be made. The forests have been characterized by Raman, TEM, and SEM, and the iron catalyst particles by AFM and TEM. Growth directly from pre-prepared nanoparticles of uniform size offers insight into how the catalyst particles seed carbon nanotube growth and is easier to prepare and faster than iron film deposition by sputtering. [Preview Abstract] |
Wednesday, March 7, 2007 10:12AM - 10:24AM |
N29.00010: Synthesis and Structure of Carbon Nanotube Y-junctions Bimal Pandey, Wenzhi Li The effect of catalyst and carbon source on the synthesis and structure of carbon nanotube Y-junctions (CNTYs) using chemical vapor deposition has been investigated. Three different nitrates, including cobalt nitrate, calcium nitrate, and magnesium nitrate, are used as catalyst precursors and thiophene (C$_{4}$H$_{4}$S) is used as carbon source to synthesize CNTYs. CNTYs with straight branches are synthesized by using mixture of cobalt/magnesium nitrates or cobalt/calcium nitrates while individual cobalt nitrate, magnesium nitrate, calcium nitrate, or mixture of magnesium/calcium nitrates doesn't grow any CNTYs, indicating that cobalt/magnesium or cobalt/calcium facilitates the formation of CNTYs. Experimental result shows that the diameter and yield of CNTYs are affected by the ratio of cobalt/magnesium or cobalt/calcium nitrates. In addition, carbon sources such as methane (CH$_{4})$ and acetylene (C$_{2}$H$_{2})$ have also been used as carbon source to grow CNTYs. It is found that linear nanotubes rather than CNTYs can be formed. The result shows both the catalyst and the carbon source affect the formation of CNTYs. [Preview Abstract] |
Wednesday, March 7, 2007 10:24AM - 10:36AM |
N29.00011: Melting and Premelting of Carbon Nanotubes Kaiwang Zhang, G. Malcolm Stocks, Jianxin Zhong We report results of molecular dynamics simulations of melting and premelting of single-walled carbon nanotubes (SWNTs). We found that the traditional critical Lindemann parameter for melting of bulk crystals is not valid for SWNTs. Using the much smaller critical Lindemann parameter developed for melting of nanoparticles as a criterion, we show that the melting temperature of perfect SWNTs is 4800K. We further show that Stone-Wales defects in a SWNT significantly reduce the melting temperature of atoms close the defects, resulting in premelting of SWNTs around the defects at 2600K. [Preview Abstract] |
Wednesday, March 7, 2007 10:36AM - 10:48AM |
N29.00012: Direct growth of carbon nanotubes on BaTiO$_3$ thin films for ferroelectric field effect devices Patrycja Paruch, Agham-Bayam Posadas, Charles H. Ahn, Paul L. McEuen Carbon nanotube field effect transistors have been extensively investigated using a variety of gate dielectrics. We propose instead to use {\it ferroelectric} (FE) field effect, replacing the dielectric by a thin FE film on a conducting substrate. The remanent FE polarization can provide reversible, locally-controlled, and non-volatile electronic doping of up to $\sim$ 5 x 10$^{14}$ charges/cm$^2$, over 10 times greater than that available with SiO$_2$ at breakdown fields. However, many FE materials cannot withstand the high temperatures and reducing atmosphere required for CNT growth. We subjected different perovskite FEs to CNT growth conditions, and from subsequent local and macroscopic measurements of their polarization we have identified BaTiO$_3$ as a good device material. Single walled CNTs grown on BaTiO$_3$ were characterized using the Nb:SrTiO$_3$ substrate as a gate electrode. The effects of FE polarization on the CNT electronic properties are currently being studied. [Preview Abstract] |
Wednesday, March 7, 2007 10:48AM - 11:00AM |
N29.00013: Replicating carbon nanotubes with molybdenum chalcogenide nanowires Teng Yang, David Tomanek, Igor Popov, Gotthard Seifert In an attempt to design chemically stable and easily separable one-dimensional conductors, we performed {\em ab initio} Density Functional calculations for Mo$_6$S$_{6-x}$I$_x$ nanowires with a varying concentration of iodine. Such Chevrel like systems have been synthesized before, but had necessitated alkali counter-ions for stabilization. The backbone of our nanowires consists of Mo$_6$ octahedra structures, covered by I and S atoms. We find the stoichiometry with $x=2$ to be preferred on energy grounds. Our results suggest these nanowires to be not only structurally rigid, but also to be rather easily separable. The electronic structure of these nanowires strongly resembles that of semi-metallic carbon nanotubes, with two crossing bands giving rise to a constant density of states, flanked by a pair of van Hove singularities near the Fermi level. Since the semi-metallic nature of these nanowires is robust, these systems may offer a viable alternative to carbon nanotubes, where conductivity strongly depends on chirality. [Preview Abstract] |
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