AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Thursday Sessions
       Session NS-ThM

Paper NS-ThM4
Carbon Nanotubes as Ballistic Phonon Waveguides and Electro-Mechanical Switches

Thursday, November 3, 2005, 9:20 am, Room 210

Session: Nanotube-based Devices
Presenter: V. Deshpande, California Institute of Technology
Authors: V. Deshpande, California Institute of Technology
H.-Y. Chiu, California Institute of Technology
H. Postma, California Institute of Technology
M. Bockrath, California Institute of Technology
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PART I: Carbon nanotubes' exceptional thermal conductivity suggests that they may serve as efficient heat conduits to aid in the cooling of nanoscale circuits. Here, we report ballistic phonon transport, which provides the ultimate limit for heat dissipation. Upon heating freestanding nanotube devices with an electrical current, we find that the power required for the nanotube to reach a particular temperature is independent of nanotube length for devices shorter than ~500 nm, and follows a universal scaling law in the tube radius. This provides evidence for ballistic phonon propagation and suggests that, over such length scales, the heat carrying capacity of nanotubes has only fundamental limits imposed by their 1D nature. From our data, we obtain an estimate for the quantum of thermal conductance that is in good agreement with the Landauer picture of phonon transport. We then present a coherent picture of nanotube breakdown based on the thermal activation of bond-weakening electronic transitions. Finally, we find that the efficient propagation of heat to the electrical contacts enables the contacts to be annealed and improved in-situ. PART II: NEMS devices are competitive in switching speed with electronic devices, because of their low mass and small size. We are developing relay devices using multi-walled nanotubes (MWNTs) that exploit the ability of concentric nanotube shells to act as low-friction linear bearings. Analysis of our data yields a measurement of the retraction force on the inner nanotube shells from the outer shells, which agrees with theoretically expected value. We are able to electrostatically telescope shells of a MWNT to establish electrical contact and turn the device to a conducting "on" state. The device can be turned "off" again by applying a sufficiently large gate voltage to bend the nanotube segments until the connection is broken. Possible applications include memories, logic gates, and high-gain nanomechanical amplifiers.