Establishing Ohmic contacts for in situ current–voltage characteristic measurements on a carbon nanotube inside the scanning electron microscope

Multi-walled carbon nanotubes (CNTs), either on an SiO(2) substrate or suspended above the substrate, were contacted to W, Au and Pt tips using a nanoprobe system, and current-voltage (I-V) characteristics were measured inside a scanning electron microscope. Linear I-V curves were obtained when Ohmic contacts were established to metallic CNTs. Methods for establishing Ohmic contacts on a CNT have been developed using the Joule heating effect when the tips are clean and e-beam exposing the contacting area of the tip when the tips are covered by a very thin contamination layer. When the contact is not good, non-linear I-V curves are obtained even though the CNTs that have been contacted are metallic. The resistance measured from the metal tip-CNT-metal tip system ranges from 14 to 200 k Ω. When the CNT was contacted via with Ohmic contacts the total resistance of the CNT was found to change roughly linearly with the length of the CNTs between the two tips. Field effect measurements were also carried out using a third probe as the gate, and field effects were found on certain CNTs with non-linear I-V characteristics.

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