Synthesis, Characterization and Applications of Boron Nitride, Carbon Nitride and Fullerene Like Structures

Monday, April 10, 2000 1:30 PM in Room Royal Palm Salon 4-6

Start Invited? Item
1:30 PM D1-2-1 Plasma-assisted Si and N Incorporation in Quasi-aligned Carbon Nanotubes
P.D. Kichambare, C.Y. Wen (National Taiwan University, Taipei, Taiwan, Taiwan, R. O. C.); L.C. Chen (National Taiwan University, Taipei, Taiwan., Taiwan, R. O. C.); F.-G. Tarntair (National Chiao Tung University, Hsinchu, Taiwan, R. O. C.); C.H. Shen (National Taiwan University, Taiwan,ROC); Y.F. Chen (National Taiwan University, Taipei, Taiwan, R. O. C.)
Recently nanorods of SiCN with superior emission current stability than pure carbon nanotubes have been reported by our group. These nanorods preserved the same hexagonal symmetry like SiCN crystals and exhibited very high aspect ratio. The high aspect ratio of SiCN nanorod gives a large field enhancement effect comparable to that of carbon nanotube (CNT). Obviously, the electron affinity or work function of SiCN is different from that of CNT. In addition, the improved stability in electron emission is likely due to the structural stability of SiCN nanorod. Within this context, it is thought worthwhile to incorporate Si and N in carbon nanotubes and investigate systematically the effect of Si and N addition on the morphological transformation as well as the interdependence between the morphology and electron emission properties in Si and N incorporated carbon nanotubes. Carbon nanotubes containing Si and N are grown on large area over pretreated Si (100) substrates by microwave plasma enhanced chemical vapor deposition (MWPCVD) technique. These silicon substrates were first coated with transition metal (Fe, Co and Ni) nitrates solution and further reduced to metal particles. Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) show that the nanotubes still retain tubular structure up to silicon and nitrogen concentration of 10 at. %. At higher silicon and nitrogen content pronounced structural transformation are observed. The effect of incorporation of Si and N in carbon nanotubes, role of transition metal catalyst on growth and morphology as well as field emission behavior of these nanotubes will be discussed.
1:50 PM D1-2-2 Nanocomposite Carbon Films: Growth Mechanism and Practical Applications
I. Alexandrou, M. Chhowalla, M. Baxendale, G.A.J. Amaratunga (University of Cambridge, United Kingdom); C.J. Kiely (University of Liverpool, United Kingdom)
A new carbon arc technique is introduced for the growth of carbon based thin film materials. The films are characterized using high resolution electron microscopy (HREM), electron energy loss spectroscopy (EELS) and field emission measurements. The HREM images show that the material consists of a matrix with agglomerates of multi-walled carbon nanoparticles embedded in it. Although the matrix first appears to be amorphous close inspection shows that it consists of a mixture of amorphous material and graphene layers. The existence of graphene sheets in the matrix is also suggested by the similarity between the C K-edge spectra from the deposited material and that from a C@sub 60@ fullerite reference crystal. The formation and the incorporation in the film of the agglomerates of carbon nanoparticles is discussed based on a series of HREM images from films grown by systematically varying the gas pressure from zero to 10@super -2@ mbar. The use of the deposited material and particularly the role of the nanoparticle agglomerates in field emission is also discussed.
2:10 PM D1-2-3 Intermolecular Bonds in Fullerene and Fullerene Like Compounds
S. Stafström (Linköping University, Sweden)
Intermolecular bonds can be created in C@sub 60@ by chemical processes, such as doping, by radiation, or by high pressure treatment at high temperatures. The resulting polymeric phases have physical properties that differ significantly from those of pristine C@sub 60@. In this work we review the physical properties of these polymerized phases, in particular the stability of the two- and one-dimensional C@sub 60@ polymers are discussed. A calculation scheme is presented that in a very simple way explains the relation between doping level and dimensionality of the polymerized phases. The electronic properties of the doping induced polymerized phases are also discussed. @paragraph@ Similar to doping induced polymerization, intermolecular bond formation also occurs spontaneously between C@sub 59@N molecules. The role of nitrogen in this bond formation is analyzed, in particular in relation with the stability of the C@sub 59@N dimer. Based on this study, we also discuss the role of nitrogen in fullerene like CN@sub x@ structures and present some possible mechanism for the formation of interlayer bonds between curved graphite layers.
2:50 PM D1-2-5 Nanostructured Carbon Films
B. Schultrich, H.J. Scheibe (Fraunhofer Institute Material and Beam Technology, Germany); C.F. Meyer (Fraunhofer Institute Material and Beam Technology)
Amorphous carbon films allow the simultaneous realization of sp3 (diamond) bonds and sp2 (graphite) bonds. By adjusting the sp3 : sp2 ratio and by structurization on the nanometer scale, the film properties may be varied over a broad range and in this way adapted to the special demands of applications. Pulsed laser and arc techniques have proved to be very suitable tools for the preparation of such films. By periodic alteration of the deposition conditions the sp3 : sp2 ratio (and hence density, stiffness and so on) may be changed from layer to layer. In this way the very high intrinsic stresses in superhard carbon films can be relaxed to an acceptable level. Under slightly modified deposition conditions a lateral structurization on the nanometer level was found consisting of fullerenelike nanoparticles (nanoonions or nanotubes) dispersed in an amorphous matrix. The large interest in such structures stems from their possible application as electron emitters in flat panel displays. For clarifying the nature of the nanostructure the TEM investigations have been supported by extensive computer simulations. The correlation of nanostructurization and mechanical, optical and electrical properties is discussed.
3:10 PM D1-2-6 Invited - Missing - Suenaga
K. Suenega (Japan Science and Technology Corporatio, Meijo University, Japan)
Since the discovery of pure carbon nano-particles with tubular or onion shapes, researches for generating similar nanostructures involving non-carbon elements have been stimulated. The predicted electronic structure of the multi-element nanostructure form is variable and essentially determinable by its chemical composition. Therefore the controlled production of hetero-junctions of such nanoparticles can lead to the creation of a nanometer scale device with tailored electronic properties. A characterization tool with high spatial resolution is indispensable for the successful realization of such devices with anticipated geometry. Spatially resolved electron energy loss spectroscopy (EELS) is quite well-suited to such kinds of analysis: using an incident probe generated by a field emission scanning transmission electron microscope (STEM), one is able to simultaneously perform elemental mapping and chemical state assignment at sub-nanometer resolution. @paragraph@The present contribution describes how the nano-EELS techniques have been applied to characterize various multi-element B-C-N nanostructures. Studies for (a) CNx nanotubulite (0.01