ICMCTF2007 Session D3: Carbon Nanotubes and Related Materials

Thursday, April 26, 2007 1:30 PM in Room Sunset

Thursday Afternoon

Start	Invited?	Item
1:30 PM	Invited	D3-1 Nanelectronics using Carbon Nanotubes G. Amaratunga (Cambridge University, United Kingdom) The availability of carbon in tubular form with aspect ratios as high as a 1000, having diameters as low as 0.5nm raises the possibility of exploring whole new classes of electronic devices. When coupled with technologies which allow for precision placement of carbon nanotubes (CNT) as well as control of tube dimensions through deterministic growth, scaling to form practical circuits becomes feasible. Such technologies are reviewed and shown to be now ‘mature’ for multiwall CNTs having diameters down to 50nm. Some new devices which take advantage of very high aspect ratio graphite are presented. These include nanoelectromechanical switches and memory. There are no special physical or chemical advantages which are exploited. However, when the diameter of the nanotubes approach 5nm they start to have unique properties not seen in graphite. Technologies for controlled and deterministic growth of these single ( double) wall CNTs are not well developed. Some approaches which hold promise in terms of SWCNT device scalability for circuits are reviewed. The transistor characteristics available from SWCNTs are not at first sight superior to those available from Si nanotransistors when one considers total transconductance ( as opposed to specific transconductance which is a non-scalable quantity in CNT transistors). The details of device scaling in ULSI ICs which limit performance are examined to understand the potential of CNTs as replacements for the Si channel in MOSFETs. The use of a hetero-transistor system based on SWCNTs and ZnO nanowires to achieve complementary (CMOS) conduction is also presented. Will this be the basis for the replacement of Si channelled devices in ICs in 20 years?
2:10 PM	Invited	D3-3 Novel Displays and Electronics with Carbon Nanotube I.T. Han, Y.W. Jin, J.M. Kim (Samsung Advanced Institute of Technology, Korea) Carbon nanotube made lots of new business area through its outstanding physical and chemical properties for past decade. The devices using high aspect ratio and electric property of CNT have been mostly researched. Here, I will introduce novel device concenpts for light sources and electromechanical swithes. The use of CNT in the conventional devices showed promising results to overcome the present technical barriers of those devices. The liquid crystal display (LCD), Plasma dischage display (PDP), inorganic electroluminescent display (ILED) and memory divices may get enhanced performance with the use of CNT.
2:50 PM		D3-5 Functionalization of Vertically Aligned Carbon Nanotubes via Radio-Frequency Nitrogen Plasma G. Abbas, P Papakonstantinou, S. Iyer (University of Ulster, United Kingdom); I. Kirkman (SERC, Daresbury Laboratory, United Kingdom); L.C. Chen (National Taiwan University, Taiwan) Knowing the details of the interaction of N impurities with CNTs is very important for understanding and optimising the nanotube doping process. Several methods based on arc discharge, CVD and pyrolysis are used nowadays to produce nitrogen doped CNTs. In most of these directly grown CN_x nanotubes the local environment of N within the carbon network mainly consists of N-C structures arranged in a pyridine like configuration, which explains the metallic structure observed in these nanostructures. Although there are many reports on the nitrogen doping of MWNTs during growth in nitrogen atmosphere, post-deposition nitrogenation of pre-formed CNTs is less explored. Only a handfull of experiments have been done on post deposition plasma processing of CNTS thus far, with very limited information on the local atomic environment. In this study we have investigated the post-growth N-doping process using inductive coupled rf-plasma at 13.56 MHz at room temperature. The electronic structure of nitrogen-incorporated vertically aligned multiwalled carbon nanotubes (CN_x-nanotubes) has been examined by angle-dependent near-edge x-ray absorption fine structure (NEXAFS) spectroscopy at the C, N and O K-edges. Angle dependent NEXAFS studies show evidence for the formation of planar CN phase in the CN_x-nanotubes films. The NEXAFS data of in-situ annealing process confirmed the development of a substitutional graphitic nitrogen in the CNT structure. The O K-edge spectra of the CNx nanotubes highlight the presence of significant oxygen containing functional groups. Thermal gravimetric analysis (TGA) measurements established a lower decomposition temperature for the plasma treated CNTs. This has its origin in the presence of a large fraction of active sites induced by N-plasma treatment that accelerates the oxidation rate of CN_x nanotubes.
3:10 PM		D3-6 Influence of CO₂ / N₂ on the Growth of Carbon Nanotubes in Methane by using Thermal Chemical Vapor Deposition M. Chen, H.W. Yu (Ming-Hsin University, Taiwan) Carbon nanotubes(CNTs) were efficiently grown on the substrates via thermal chemical vapor deposition by using CH₄ and CO₂ gas mixtures. Fe catalytic nanoparticles were deposited Si and carbon cloth substrates and facilitate the formation of high-quality carbon nanotubes. This is apparently different from the conventional reaction in gas mixtures of H₂/CH₄, H₂/C₂H₂, NH₃/CH₄, H₂/C₆H₆ and so on. Carbon dioxide is used to replace the harmful gases of H₂ and NH₃ and the addition of N₂ in the mixture gas of CH₄ and CO₂ obviously improve the growth and quality of CNTs, and benefit to observe the reaction growth of CNTs in a different atmosphere condition. This paper demonstrates the effects of compositional ratio of CH₄, CO₂ and N₂ in the mixture gas on the growth of carbon nanotubes in novel atmospheric condition. Various substrates of Si and carbon cloth were used to synthesize and grow the homogenous layer of CNTs by using CH₄-CO₂-N₂ gas sources. A significant difference in morphological structure was observed and analyzed on the different substrates of Si and carbon cloth. By proper adjusting growth parameters, a high quality CNTs can be observed on Fe-deposited substrates. The characteristics of the as-grown carbon nanotubes on different substrates were analyzed by SEM, TEM and Raman spectroscopy.
3:30 PM		D3-10 Microfabrication of Carbon Nanotubes on Microfluidic Channels H. Wu, D. Mishra, J. Ting, S. Chen (National Cheng Kung University, Taiwan) Nanosubjects bear tremendous potential for microfluidics in creating smart functions such as fabricating functional components in microchannels. Traditional microfabrication methods using photolithographic techniques, however, require many complicated steps and sometimes difficult to implement. In an attempt to build trapping components for proteins, in this study, aligned carbon nanotubes (CNTs) were grown on microchannels with a width of ? at the bottom, 140m at the top and a depth of 20m using microwave plasma enhanced chemical vapor deposition (MPCVD) at a temperature near 370. The microchannels were made on soda-lime glass substrate and for comparison, CNTs were also grown on the flat glass substrate. Fe-Si thin films were used as the catalyst for the growth of CNTs. The Fe-Si thin films were prepared using rf magnetron sputter deposition. CNTs grown on both types of substrates were first characterized for their morphologies, dimensions, microstructures, and surface chemistry. The results show CNTs obtained on both flat substrate and microchannels exhibit different characteristics. The CNTs grown on the microchips were also evaluated for protein absorption efficiency under different pH values. More adsorption was observed at lower pH values, under which most proteins bear positive charges and are more likely to be trapped by the carboxylated carbon nanotubes.