ICMCTF2001 Session D1/D5-1: Synthesis, Characterization and Applications of Boron Nitride, Carbon Nitride and Fullerene Structures

Monday, April 30, 2001 10:30 AM in Room Town & Country

Monday Morning

Start	Invited?	Item
10:30 AM		D1/D5-1-1 Deposition Mechanism of Fullerene-Like Carbon (FLC) M. Chhowalla, N.L. Rupesinghe, D. Roy, I. Alexandrou, T.W. Clyne, G.A.J. Amaratunga (University of Cambridge, United Kingdom) Fullerene-like carbon (FLC) thin film is a predominantly sp2 bonded covalent material that has the unique properties of being hard and elastic. Fullerene-like structure can be obtained in carbon films deposited using magnetron sputtering, cathodic arc evaporation and mass selected ion beam deposition. Although the plasma characteristics of these techniques differ significantly, the fullerene-like phase can be obtained at the appropriate conditions. In this presentation, we will summarize the different conditions at which the fullerene-like phase can be deposited. FLC can be achieved by using high substrate temperature and nitrogen as is the case in magnetron sputtering, graphitic nanoparticles and high temperature as in arc discharge or very high ion energies (10keV) as in mass selected ion beam. In addition, annealing of amorphous carbon can also lead to fullerene-like structure. Here, we use visible Raman spectroscopy to study the evolution of the fullerene-like phase by monitoring the I(D)/I(G) ratio which indicates the clustering of sp2 sites. We have found that deposition parameters conducive for the nucleation of graphene planes is a necessary precursor for the formation of the FLC structure.
10:50 AM	Invited	D1/D5-1-2 Nano-Scale Property Measurments of Individual Carbon Nanotubes Z.L. Wang (Georgia Institute of Technology) Characterizing the physical properties of individual nanostructures is rather challenging because of the difficulty in manipulating the objects of sizes from nanometer to micrometer. Most of the nanomeasurements have been carried using STM and AFM. In this presentation, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements the mechanical and electrical properties of a single nanostructure, such as a carbon nanotube. Using a customer-built specimen holder, in-situ measurements on the mechanical properties of carbon nanotubes has been carried out using the resonance phenomenon induced by an externally applied alternating voltage [1,2]. The bending modulus of a carbon nanotube was obtained from the resonance frequency at a high precision. Alternatively, a nanotube was demonstrated as a "nanobalance" for measuring the mass of a single nanoparticle in the range of femtograms. The ballistic quantum conductance of a multi-walled carbon nanotube [3] was observed at room temperature using the set up in the TEM. Finally, the in-situ TEM technique has also been applied to measure the Young’s modulus of SiC - SiO2 composite nanowires [4].^[1] P. Poncharal, Z.L. Wang, D. Ugarte and W.A. de Heer, Science, 283 (1999) 1513. ^[2] R.P. Gao, Z.L. Wang, Z.G. Bai, W. de Heer, L. Dai and M. Gao, Phys. Rev. Letts., 85 (2000) 622; Z.L. Wang, P. Poncharal and W.A. De Heer, Pure Appl. Chem. Vol. 72 (2000) 209. ^[3] S. Frank, P. Poncharal, Z.L. Wang, and W.A. de Heer, Science, 280 (1998) 1744.^[4] Z.L. Wang, Z.R. Dai, Z.G. Bai, R.P. Gao and J.L. Gole, Appl. Phys. Letts., 77 (2000) 3349-3351; J.L. Gole, J.D. Scout, W.L. Rauch and Z.L. Wang, Appl. Phys. Letts., 76 (2000) 2346. [5] Research supported by NSF.
11:30 AM		D1/D5-1-4 Effects of Nitrogen on the Formation of Carbon Nanotubes R. Droppa Jr., P. Hammer, J.G. Huber, M.C. dos Santos, F. Alvarez (Universidade Estadual de Campinas, Brazil) Carbon nanotubes were generated by the arc discharge technique in a helium-nitrogen atmosphere. In order to observe the effects of nitrogen on the formation of the nanotubes the partial pressure of this gas is varied. The soot produced both on the cathode and the system internal walls is analyzed by X-ray Photoelectron Spectroscopy (XPS), Tunneling Electron Microscopy (TEM), Infrared and Raman spectroscopies. XPS data show that about 11 at. % of nitrogen was incorporated by the soot. The profile of the N1s peak clearly shows that the nitrogen atoms are at least in two distinct environments. In the soot generated in pure helium atmosphere TEM reveals that there are bundles of regular single-wall nanotubes (SWNT) with ~1.5 nm average diameter. On the other hand, tubes with irregular structure, larger diameters (~5 nm) and thick textured walls, as well as "worm"-like nanofibers are generated in presence of nitrogen. The Raman data indicate that some normal vibrational modes of the SWNT 1580 cm-1 as well as the so-called disorder D band around 1340 cm-1 are affected with nitrogen incorporation. Results on concentrated material and high resolution TEM will be also presented and discussed.
11:50 AM		D1/D5-1-5 Controlling Steps During Early Stages of the Aligned Growth of Carbon Nanotubes by Microwave Plasma Enhanced Chemical Vapor Deposition L.C. Chen, C.Y. Wen (National Taiwan University, Taipei, Taiwan, ROC); C.S. Shen (National Taiwan University, Taipei, Taiwan); Y.F. Chen (National Taiwan University, Taipei, Taiwan, ROC); K.H. Chan (Academia Sinica, Taipei, Taiwan, ROC) While it is now relatively easy to generate aligned carbon nanotubes (CNT), a form of tremendous interest in microelectronic applications, the key steps that control the aligned growth of the CNT is yet an open question. In the present study, well-aligned CNTs have been grown by microwave plasma enhanced chemical vapor deposition (MPECVD) on silicon substrates pre-coated with thin layers of transition metals, such as Fe, Co and Ni. Both high-resolution transmission electron microscopy and field emission scanning electron microscopy have been employed to study the structural evolution during the very early stages of CNT growth. Effects of processing gas composition as well as the pre-coating catalytic layer characteristics, such as the type of catalyst, crystallinity and layer thickness, have been investigated. It is observed that nucleation of CNTs can be significantly enhanced by adding nitrogen in the MPECVD process. Most interestingly, the very first key step toward growth of aligned CNTs is the formation of high-density fine carbon onion encapsulated metal (COEM) particles under hydrogen plasma. Furthermore, the formation and the size of the COEM particles were strongly affected by the crystallinity and the thickness of the catalytic layer, regardless of the type of the catalyst used. Some mechanisms of the aligned CNT growth could be proposed from these microscopic observations.
12:10 PM		D1/D5-1-6 Effect of NH₃ Environment Gas on the Growth of Aligned Carbon Nanotube in Catalytically Pyrolyzing C₂H₂ M. Jung (Korea Institute of Science and Technology and Hanyang University, Korea); K.-R. Lee (Korea Institute of Science and Technology, KOREA); J.W. Park (Hanyang University, Korea); K.Y. Eun (Korea Institute of Science and Technology, Korea) It has been well known that vertically aligned carbon nanotubes (CNTs) can be grown by thermal CVD in NH₃ environment. However, the mechanism of the vertically aligned CNT growth is yet to be clarified. In the present work, we investigated the effect of NH₃ gas on the growth of CNTs by changing the environment gas mixtures and catalysts. The prticles of Ni, Co and Fe of diameter ranging from 20 to 75nm were used as the catalyst. CNTs were grown at 950°C in various environments of mixture of H₂ and NH₃. We could show that the vertically aligned CNT growth is intimately related to the growth rate of CNT. The growth behavior of vertically aligned CNT was also dependent on the catalyst materials. Aligned CNT growth was significantly suppressed by H₂ addition to NH₃ environment when using Ni as the catalyst. However, the effect of H₂ addition was not siginificant for Co or Fe catalysts. This observation that the aligned CNT growth is dependent on the catalyst materials implies that the surface chemistry of the catalyst is an important factor to understand the growth behavior of CNT. We discussed the dependence in terms of the surface chemistry of catalyst caused by the environment gas.