AVS2001 Session NT+EL+NS-TuM: Nanotubes: Growth and Characterization

Tuesday, October 30, 2001 8:20 AM in Room 133

Tuesday Morning

Start	Invited?	Item
8:20 AM	Invited	NT+EL+NS-TuM-1 Modification of Single wall Carbon Nanotubes S. Iijima (NEC Corporation, JST-ICORP and Meijo University, Japan) This talk will discuss hybrid structures of SWNTS with other materials such as various types of fullerenes and other molecules which are incorporated into the interior spaces of nanotubes. It will also cover discussion on chemical modification of SWNTs with organic materials.
9:00 AM		NT+EL+NS-TuM-3 Patterned Growth of Vertically Aligned Carbon Nanofibers by High Density Plasma Enhanced Chemical Vapor Deposition J.B.O. Caughman, V.I. Merkulov, D.H. Lowndes, E.D. Ellis, L.R. Baylor, M.A. Guillorn (Oak Ridge National Laboratory) Vertically aligned carbon nanofibers (VACNFs) are being studied for use as field emitters. The VACNFs have been grown on a nickel catalyst layer using a high density inductively coupled plasma source. The source operates at 13.56 MHz and couples power to the plasma via a flat spiral coil. A hydrogen and acetylene plasma is used to produce the precursors needed for growth. The aligned VACNFs are grown on a heated substrate located downstream from the ionization zone. The energy of the ions impacting the growth surface is controlled with radio frequency bias. Self-bias voltages are typically in the range of -50 to -300 V. Operating pressures are in the range of 50 to 200 mTorr and growth temperature is typically around 700 degrees C. Results show that the diameter of the VACNFs depends on the size of the nickel catalyst particle and are typically 25-100 nm in diameter. The height of the VACNFs depends on the growth time and bias conditions, with typical lengths of around 1 micron. The VACNFs have been grown on nickel patterns on silicon to form arrays of isolated emitters. The relationship between growth conditions and field emission will be presented.¹ ¹ Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725.
9:20 AM		NT+EL+NS-TuM-4 Large-Area Growth of Well-Aligned Carbon Nanotubes by Hot-Filament-Assisted DC Plasma Chemical Vapor Deposition T. Negishi, Y. Hayashi, S. Nishino (Kyoto Institute of Technology, Japan) For the realization of field emission displays (FED) using carbon nanotubes (CNT), the efficient production method of CNT suitable for them should be developed. In order to obtain aligned CNT perpendicular to substrates for the application, direct growth on catalyst metal plates is desirable. It was reported that well-aligned carbon nanotubes were grown by plasma chemical vapor deposition (CVD). However the growth area was less than 1 inch in diameter. We have succeeded in carrying out the growth of well-aligned CNT with high density on a 5 cm x 5 cm nickel plate by hot-filament-assisted DC plasma (HF-DCP) CVD in the gas of CH₄/H₂. The growth method and conditions were as follow. DC voltage of -500V was impressed on the substrate with hot-filaments grounded. The filaments not only raise the temperature of a substrate, but stabilize a DC plasma. A luminous region was observed just above the substrate. By the optical emission spectroscopy, it was confirmed that the luminescence was derived from exited hydrogen and hydrocarbon radicals. Therefore the process is called HF-DCP CVD. Nickel substrates were heated by the filaments to 450-600 °C. The substrates were pretreated in pure hydrogen plasma before the growth of carbon nanotubes. Well-algined CNT about 50 nm in diameter and about 10 microns in length were observed by scanning electron microscopy in the density of about 10⁹ cm^-2 on the surface of the treated substrate. Field-emission properties of CNT were evaluated and a current density of 1.2 mA/cm² was obtained for -1500V bias between the substrate and the counter electrode with a distance of 300 um. By this method, the growth of well-aligned CNT in an even larger area is expected.
9:40 AM		NT+EL+NS-TuM-5 Tailoring Growth and Properties of Nanotube Networks for Applications B.-Q. Wei, Y.-P. Zhao, P.M. Ajayan, G. Ramanath (Rensselaer Polytechnic Institute) We present strategies for obtaining aligned nanotube architectures, and locally modifying their nanotube properties, to enable their use for applications such as interconnects in future devices. We demonstrate various methodologies such as substrate templating, using gas-phase catalysts delivery, and interfacial reactions, to obtain substrate-selective growth, vertical as well as horizontal alignment, and metal-nanotube-substrate connection formation by chemical vapor deposition (CVD). We describe the use of focused ion beam (FIB) to modify the nanotube structure after deposition. We show that by controlling ion energy and dose, one can either tailor the electrical properties of nanotubes and/or micromachine them. We also report, for the first time, a nanotube-length-independent piezoelectric-like resonance in the impedance spectrum at ~ 37.6 kHz during AC probing of single-walled nanotubes. These will be relevant from the viewpoint of building devices such as ultrasonic nanotransducers, quantum well devices and nano-electromechanical actuators.
10:00 AM	Invited	NT+EL+NS-TuM-6 Growth of Carbon Nanotubes and Applications in Microscopy L. Delzeit, C. Nguyen, R. Stevens, B. Chen, J. Han, M. Meyyappan (NASA Ames Research Center)
11:20 AM		NT+EL+NS-TuM-10 The Effect of Photon Energy, Average Power, and Repetition Rate on Nanotube Synthesis Using a Free Electron Laser B.C. Holloway, A.D. Friedman (College of William & Mary); M.W. Smith (NASA Langley Research Center); C.K.W. Adu, A.L. Loper, B.K. Pradham, G. Chen, S. Bhattacharyya, P.C. Eklund (Pennsylvania State University); J.E. Fisher (University of Pennsylvania) The free electron laser (FEL) located at Thomas Jefferson National Accelerator Facility (Jlab) was used to produce single-walled carbon nanotubes (SWNTs) by laser vaporization of a catalyzed carbon target. The Jlab FEL offers the advantage of a high power (~1000 Watts maximum average power), tunable (~2-7 micron), high repetition rate (MHz) photon source where parameters can be varied rather easily compared to tabletop systems. Initial experiments with the FEL show that, under the appropriate conditions, large soot generation rates (>10 mg/min) with high SWNT yield are possible . In addition raman scattering and high resolution transmission electron microscopy (HRTEM) of the FEL-produced material shows novel properties such as larger tube diameters, smaller bundle sizes, and interesting variations with carbon target catalyst composition. While the FEL operating conditions and synthesis system design have not yet been optimized, the potential for large scale production of SWNTS and/or "diameter tuning" using an FEL will also be discussed. Work supported by DARPA, ARO, NSF, and NASA.
11:40 AM		NT+EL+NS-TuM-11 Energy-Filtered Reflection High-Energy Electron Diffraction from Carbon Nanotubes J.T. Drotar, B.-Q. Wei, Y.-P. Zhao, G. Ramanath, P.M. Ajayan, T.-M. Lu, G.-C. Wang (Rensselaer Polytechnic Institute) Using reflection high-energy electron diffraction (RHEED), we have observed energy-filtered diffraction patterns from both vertically aligned and randomly oriented multi-walled carbon nanotube samples. The diffraction patterns show a ring structure that roughly corresponds to powder diffraction from graphite. Using a simple kinematic treatment, we were able to obtain information on the crystal structure of the individual nanotubes from the radial profiles of the rings. The interlayer spacing is significantly higher than in graphite, and there is almost no evidence of interlayer correlation. This is consistent with previous x-ray diffraction studies of multi-walled carbon nanotubes. We were also able to obtain information on the alignment and spacing of nanotubes. For the vertically aligned sample, the center to center spacing of the nanotubes was found, from reflection electron energy-loss spectra (REELS), to be 52 ± 12 nm. To the best of our knowledge, this study constitutes the first observation of RHEED patterns from multi-walled nanotubes. This work was supported by NSF and the Interconnects Focus Center New York.