In situ characterization of vertically oriented carbon nanofibers for three-dimensionalnano-electro-mechanical device applications

Abstract

We have performed mechanical and electrical characterization of individual as-grown,vertically oriented carbon nanofibers (CNFs) using in situ techniques, where suchhigh-aspect-ratio, nanoscale structures are of interest for three-dimensional (3D)electronics, in particular 3D nano-electro-mechanical-systems (NEMS). Nanoindentationand uniaxial compression tests conducted in an in situ nanomechanical instrument,SEMentor, suggest that the CNFs undergo severe bending prior to fracture, which alwaysoccurs close to the bottom rather than at the substrate–tube interface, suggestingthat the CNFs are well adhered to the substrate. This is also consistent withbending tests on individual tubes which indicated that bending angles as large as ∼ 70° could be accommodated elastically. In situ electrical transport measurements revealed thatthe CNFs grown on refractory metallic nitride buffer layers were conducting via thesidewalls, whereas those synthesized directly on Si were electrically unsuitable forlow-voltage dc NEMS applications. Electrostatic actuation was also demonstratedwith a nanoprobe in close proximity to a single CNF and suggests that suchstructures are attractive for nonvolatile memory applications. Since the magnitude ofthe actuation voltage is intimately dictated by the physical characteristics ofthe CNFs, such as diameter and length, we also addressed the ability to tunethese parameters, to some extent, by adjusting the plasma-enhanced chemicalvapor deposition growth parameters with this bottom-up synthesis approach.