|M.Sc Student||Gassman Aaron|
|Subject||Investigation of the Electrical Properties of Carbon|
Nanofibers with Embedded Carbon Nanotubes
|Department||Department of Nanoscience and Nanotechnology||Supervisors||Professor Eyal Zussman|
|Dr. Yuval Yaish|
|Full Thesis text|
Harnessing the potential advantages of nanotechnology for fabricating innovative composite materials, such as ultra-lightweight, high-aspect ratio, conductive nanowires, requires the development of techniques for fabricating, ordering, manipulating, and characterizing at the sub-micron scale. In the research presented in this thesis, an interdisciplinary approach was employed to fabricate and characterize individual electrically active composite nanofibers. First, the electrospinning method was utilized to fabricate polymer-based [poly(acrylonitrile) (PAN)] carbon fibers having diameters of ~100-300 [nm] and to embed such fibers with multi-walled carbon nanotubes (MWCNT) at various concentrations (0-10% (w/w)). Then, micro-electronic processing techniques, e.g., e-beam lithography, mask writing, and metal electrode evaporation, were used to fabricate semiconductor circuit devices for the electrical characterization of individual nanofibers. For the first time, electrical conductivity measurements and contact resistance measurements are reported for single composite nanofibers of this type.
Carbonized PAN nanofibers (0% MWCNT (w/w)) are known to exhibit moderate electrical conductivity (σ~500 [S/m]) due to the short-range ordered graphitic structure of the carbonized matrix (Y. Wang et al., 2002). MWCNTs (filler) were embedded in the carbonized nanofibers (matrix) with the aim of increasing the electrical conductivity of the composite nanofibers by creating percolation paths between conducting regions. Morphological characterization of the composite nanofibers was carried out through optical microscopy, SEM, TEM, and AFM.
The nanofibers' responses to Vds and Vgate ranges was measured, while four-probe measurements yielded the contact resistances encountered at the metal-carbon interfaces. The room temperature dc conductivity was substantially enhanced by the presence of MWCNTs, with an increase of nearly an order of magnitude, to ~3000 [S/m], in the 7% MWCNT (w/w) composite nanofibers. Also, the contact resistance values for all concentrations of nanofibers tested were found to very low (<10 [kΩ]). The results suggest that MWCNTs can bridge the matrices' short-range ordered graphitic structures and therefore increase the electrical conductivity of individual composite nanofibers. The enhanced conductivity and low contact resistance of the composites nanofibers make them potential building blocks for CNT-based devices such as "smart chaff", circuitry components, and sensory devices.