Graphite nanofibers (GNF) and multi-wall carbon nano tubes (MWCNT) are mass analyzed utilizing the unique capability of the scanning atom probe (SAP). A minute lump of densely intertwined CNT was mounted at the apex of a dull tungsten tip with silver paste. GNF were grown on a SUS304 needle by the thermal CVD method. Source gases were CO (50%) and H2 (50%) at 100 kPa, and growth temperature was 600°C for 20 minutes. The mass analysis of the CNT and GNF by the SAP was conducted by applying DC and pulsed voltages to a specimen at room temperature. The mass resolution m/Δm of the SAP is better than 1000.
Various clusters of carbon and hydrogen are detected from MWCNT for the mass range m=0-100. No major mass peaks are seen in the mass range from 100 to 300. The largest mass peak is C28H4+ with two satellite mass peaks which are expected from the abundance of 13C. The hypothetical structure of this cluster is the three by three rows of nine hexagonal cells. Each cluster has four carbon atoms with a hydrogen-terminated bond at its edge.
Few H+ ions were found but the significant number of COH+, C2OH3+ and C3OH5+ were detected at the beginning of the mass analysis of GNF. After the removal of the surface layer, the detection rate of the largest cluster, C23H2, increased. The proposed structure of C23H2+ is the triangularly arranged six hexagonal cells with one extra C atom at one corner and a H terminated C atom at other two corners. Normally, the ratio of the voltage for field emission and that for field evaporation is 1 to 10. However, the evaporation voltage of GNF is found to be significantly low, smaller than 1 to 5. This implies that GNF is the piled small graphene sheets in the direction of the GNF axis.
Clarification of cluster structures may provide a guide line for the production of high quality CNT and GNF.
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