Electrical and mechanical investigations of carbon nanotubes

Carbon nanotubes are fascinating materials both for fundamental research and practical application. Their diameters range from ∼1 nanometer for single-walled nanotubes (SWNTs) to tens of nanometers for multi-walled nanotubes (MWNT). The discovery of this new allotrope of carbon about ten years ago has attracted considerable interest ever since.; There are three methods of synthesis: Chemical vapor deposition (CVD), arc discharge and laser vaporization. Our work focuses on CVD growth of nanotubes and takes advantage of control over location, orientation and yield. Substrates and integration into devices incorporate well-known silicon micro-processing materials and techniques.; Carbon nanotubes have unique electrical and mechanical properties, which derive from their graphene sheet precursors. Nanotubes are metallic or semiconducting, depending on their chiralities, and can be ballistic quantum wires, quantum dots, field effect transistors or sensors. We use a local-gating approach with scanning probes to modulate individual and crossing nanotubes. The intrinsic properties of SWNTs and the metal contacts are investigated. The technique allows for identification of the nature of the individual or crossing nanotubes, as well as depletion or enhancement of small sections of the devices. Nanotubes are also extremely strong materials, with high stiffness and resiliency. They are ideal field emitters and provide high current densities at low applied electric fields. Amplification of the local electric field on the tips of MWNTs enhances electron emission.; Manipulation of suspended SWNTs with AFM tips directly examines the coupling between the electrical and mechanical properties. Deflection of the nanotube results in a completely reversible conductance change of two orders of magnitude at relatively low bending angles. When the external force is removed, the SWNT returns to its original physical and electronic structure. Theoretical support attributes the results to local deformation and a transition from sp2 to sp3 hybridization at the tip/tube contact point. Suspended SWNTs can also be used as templates for various metal nanostructures. The dimensions and large aspect ratios of nanotubes are translated to metals. The temperature and magnetic field dependences of these nanowires are tested.