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AFM scans of dispersed MWNTs. Note the scans show a typical MWNT has a number of shells which terminate at different overall lengths. (a) AFM topography image of dispersed MWNTs on HOPG. The tubes show a tendency to align with threefold symmetry. This is understood as representing locking to the commensurate crystal structure of the underlying HOPG lattice. (b) Distribution of MWNTs diameters as measured by AFM topography sections. The solid line is a fit to a normal distribution with mean of .
Experimental setup. Inset is a scanning electron microscopy picture showing individual MWNTs protruding from the bundle’s tip (scale bar is ).
Simultaneous thermal and electrical conductance measurements in vacuum on a HOPG substrate at room temperature for different bundles. (a) Tip 1: . The electrical conductance step is and thermal conductance step is . Inset shows an example of successive approach and withdrawal curves for electrical and thermal measurements. (b) Tip 2: . The electrical conductance step is and thermal conductance step is .
Correlation between thermal and electrical conductance steps for MWNTs on HOPG for a number of different CNTs with a range of temperature differences (see legend). The trend lines show calculated ratios of to for both armchair (long-short dash line) and zig-zag tubes (dash line) at the extremes of the diameter range observed for our tubes (0.9 and 3.3 nm, respectively). Solid line is linear fit to all the measured data with slope of 250.
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