AVS 53rd International Symposium
    Nanometer-scale Science and Technology Friday Sessions
       Session NS-FrM

Paper NS-FrM12
Atomic Level Analysis of Carbon Nanotubes and Graphite Nanofibers by the Scanning Atom Probe

Friday, November 17, 2006, 11:40 am, Room 2016

Session: Nanowires
Presenter: O. Nishikawa, Kanazawa Institute of Technology, Japan
Authors: O. Nishikawa, Kanazawa Institute of Technology, Japan
M. Taniguchi, Kanazawa Institute of Technology, Japan
Correspondent: Click to Email
Utilizing the unique capability of the scanning atom probe (SAP) carbon nanotubes (CNT) and graphite nanofibers (GNF) are mass analyzed detecting individual field evaporated ions. The analyzed CNTs are the mixture of single and multiple wall nanotubes (SWCNT and MWCNT). A minute lump of densely intertwined CNT was mounted at the apex of a tungsten tip with silver paste. The GNFs are grown on a nickel substrate. The mass analysis of the CNT and GNF by the SAP was conducted by applying DC and pulsed voltages to the specimen at room temperature. The mass resolution of the SAP is better than 1000. It has been reported that most CNTs and graphite contain a significant amount of hydrogen and oxygen. In this study we focused at the correlation between the C-C binding and the local concentration of hydrogen and oxygen in CNTs and GNFs. Field evaporation of metal proceeds atom-by-atom base because the metallic binding is uniform and non-directional. On the other hand the covalent bonds are directional and non-uniform. Accordingly, non-metallic specimens are mostly field evaporated as cluster ions. Furthermore, strongly bound clusters are field evaporated as multiply charged ions. An interesting finding is the detection of many large carbon cluster ions. The number of carbon atoms is not random but quite characteristic such as 11, 17, 19 and so on. The mass peaks of doubly and triply charged ions are very sharp without a tail indicating strong C-H bonds. On the other hand the mass peaks of singly charged cluster ions have a tail. This implies that the C-H bonds are weak and the C-H cluster are dissociated before entering the ion detector. Detection of the large cluster may imply that the CNT is field evaporated as a nano-size graphene sheet and not as a carbon chain. The electronic state of the specimens and the correlation between the size of cluster and the ratio of the number of carbon atoms to that of hydrogen atoms will be discussed.