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INTRODUCTION

CARBON nanotubes (CNTs) posess several properties that make them attractive for use as resonating members in many nanoscale devices. The use of CNT resonators has already been demonstrated as a radio tuner,[1] an entire radio receiver,[2] and a radio transmitter.[3] In addition, CNT resonators have been used to measure minuscule masses,[4] even down to the mass of a single Au atom,[5] and to approach the quantum limits of vibration.[6] In addition to these demonstrated applications, the potential uses for CNT resonators are much broader, being applicable to any nanoscale device that requires controlled vibration, such as gyroscopes, mechanical processing of signals, and simple mechanical time keeping. The reasons why CNTs are so suitable are multifold: The extraordinarily high stiffness of CNTs combined with their low density enables them to attain high natural frequencies and frequency sensitivity. That CNTs are quasi one-dimensional or string like provides well-defined strategies for tuning their frequency—for example, one may alter their length or put them under tension. Finally, CNTs can be both driven, and sensed, electronically by several different methods, which makes it possible to integrate CNTs into more complex nanoelectromechanical systems (NEMS) in which the resonator is only one part of the device. To date, the biggest impediment to the use of CNTs as resonators is their poor quality factor Q, which P. ALEX GREANEY, Postdoctoral Researcher, and JEFFREY C. GROSSMAN, Professor, are with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Contact e-mail: [email protected] GIOVANNA LANI, PhD Student, is with the Laboratoire des Solides Irradis, Ecole Polytechnique, 91128 Palaiseau Cedex, France. GIANCARLO CICERO, Professor, is with INFM and Physics Department, Polytechnic of Torino, I-10129 Torino, Italy. Manuscript submitted March 21, 2010. Article published online August 16, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A

when measured at ambient temperatures (and under conditions of constant driving) falls in the range of 8– 300. (Q is defined to be 2p times the inverse fraction of oscillator energy lost per cycle, and it may be thought of as roughly the number of oscillations it takes for the energy to reduced by 99.8 pct.) This result has been resistant to improvement, having been observed both under vacuum and at ambient pressure; in both cantilevered and doubly clamped geometries with many different clamping methods; and through many different measurement techniques.[4,7–10] Only recently by cooling to milikelvin temperatures have Qs in excess of 105 been attained.[11] The universally poor ambient temperature results suggest that an intrinsic damping mechanism may be dominant. Roukes and colleagues,[12,13] and others[14] suggested that the intrinsic thermoelastic damping mechanism can produce low Q factors in CNTs because of their small surfaceto-volume ratio. Previous computational work by Jiang et al.,[15] of an open-ended, cantilevere