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Energetic Ion Bombardment of Carbon Nanotubes Gregory A. Konesky1 1 National NanoTech, Inc., 3 Rolling Hill Rd., Hampton Bays, NY 11946, U.S.A. ABSTRACT Carbon Nanotubes (CNTs) exhibit exceptional properties in terms of high strength-to-weight, high electrical conductivity, and high thermal conductivity, and have been employed as a reinforcement in various composites and other materials. Their tolerance to radiation environments may be suggested by their response to energetic ion bombardment. We discuss the effects of argon ion bombardment of both thin and thick multiwall carbon nanotube films over a range of 4 to 11 keV at fluence levels up to the order of 1021 ions/cm2. While individual carbon atoms are readily displaced from a carbon nanotube by bombardment at these energies, these nanotubes also exhibit a self-healing capability. At moderate energies and fluence, if two or more carbon nanotubes are touching and an ion strikes this point, they heal together where a junction or cross-link between them is created and the nanotubes interpenetrate. Even though some of the properties of the carbon nanotubes may be degraded by ion bombardment at non-junction regions, we have demonstrated a bulk cross-linked thin film of randomly oriented multiwall carbon nanotubes with an isotropic thermal conductivity of 2150 W/m K. At higher energies and fluence, the carbon nanotubes appear to collapse and reform aligned parallel to the incoming ion bombardment trajectory, producing high aspect ratio tapered structures. These structures are, in general, fully dense, unlike the loosely packed random carbon nanotube array from which they originated. There is also a sharp transition at the base of these structures from the dense form to the loose-packed form, suggesting that these structures may inhibit further penetration of the energetic ions. INTRODUCTION This research began as an attempt to develop a commercially viable heat spreader using cross-linked CNTs. Semiconductors and other devices frequently have their performance limited by their ability to reject waste heat. Heat spreaders operate by enlarging the thermal footprint of a given device, effectively reducing the thermal junction resistance between the device and the heat sink. By allowing them to reject more waste heat more efficiently, a laser diode, for example, can operate at higher output power, or a computer CPU at higher clock speeds. CNTs were predicted to have exceptionally high thermal conductivity along their axis, perhaps as much as 6600 W/m K [1] primarily due to ballistic transport of phonons. An individual Multi-Walled CNT (MWCNT) has a measured thermal conductivity of 3000 W/m K [2]. However, bundles or “ropes” of CNTs show lower aggregate thermal conductivity due to quantum interference effects [3, 4] and thin films of MWCNTs demonstrate a thermal conductivity of only 15 W/m K [5]. This low value is due, in part to the open spaces between a random network of CNTs, as seen in figure 1, but the primary contribution is the high thermal junction resistance betwee