Non-linear annealing effect on correlation between crystallinity and oscillation of carbon nanocoils Kaori Hirahara a,b,n , Kento Nakata b , Yoshikazu Nakayama b a Center for Atomic and Molecular Technologies, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan b Department of Mechanical Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan article info Article history: Received 7 October 2013 Received in revised form 4 December 2013 Accepted 4 December 2013 Available online 10 December 2013 Keywords: Carbon nanocoils Mechanical properties Annealing Electron microscopy Energy dissipation Resonant oscillation abstract The effect of annealing at 1000–2600 1C on the crystallinity of carbon nanocoils (CNCs) has been evaluated to discuss the mechanism of energy dissipation during CNC oscillation and its structural dependence. The crystallinity of the CNCs was evaluated by transmission electron microscopy and electron diffraction. In situ observations of the resonant oscillations of individual cantilevered-CNCs were carried out by inducing a high-frequency electric field in a scanning electron microscope. Experimental results revealed a non-linear correlation between crystallinity and oscillation properties; crystallinity improved with annealing temperature from 1000 to 2600 1C and was comparable to graphite on annealing at 2600 1C, while the quality factor (Q) decreased on annealing above 1400 1C. Q showed a strong correlation with the shear modulus. These results suggest that the oscillation properties of CNCs are dominated by two types of energy dissipation mechanisms, originating in the existence of structural anomalies in less crystalline structures and in interlayer slipping in higher crystallinity structures. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Carbon nanocoils (CNC) are a nanocarbon material with a “coiled” structure and fibers and are only nanometers in diameter [1–3]. CNCs show interesting mechanical and electromagnetic properties related to their unique morphology, which leads to many attractive applications. One potential application is to act as an absorber of electromagnetic waves [4,5]. Composites of CNCs and resin [6] absorb selectively in the MHz to 100 GHz region, with reflectance losses of less than 10 db. CNC-resin composites also show excellent potential for vibration suppression [7,8], and have a loss factor 100% better than those of vapor-grown carbon fiber (VGCF)-resin composites or normal resins [8]. The recent development of CNC mass production by chemical vapor deposi- tion (CVD) using wet catalysts [9,10] means that it is realistic to use these applications on the macroscale. CNCs produced by mass- production CVD are shown in Fig. 1. The diameter of these CNCs range from 200 to 500 nm and their lengths range from 5 to 40 μm. About 2510 wt% carbon by mass of catalyst can be obtained using this fabrication process [10]. Isolated CNCs may also be employed to enable mechanical systems which require spring components that are miniaturized to the sub-micrometer or even nanometer scales. This would allow CNCs to be used as building blocks for the construction of nanoswitches, nanoactuators, and nanosolenoids. These applications, at both the macroscale and single-CNC level, exploit the mechanical-spring characteristics of a single CNC. For further development in these areas, it is therefore crucial to understand the mechanical vibra- tion properties of an individual CNC. In this paper, we aim to understand how crystallinity affects the oscillation of a CNC, because it is expected to strongly affect energy dissipation pro- cesses during oscillations. Although the conventional CVD methods, which use wet catalysts [9], enable us to realize kilogram-order supply of CNCs, the CNCs produced using these methods have poor crystallinity due to a high number of defects. Chen et al. have reported that an electron energy loss (EELS) spectrum measured for CNCs produced by the CVD method was more similar to amorphous carbon than highly oriented pyrolytic graphite (HOPG) or carbon nanotubes (CNTs) [11], even though CNCs have wavy and discontinuous graphitic walls. Sato et al. examined the resonant vibration of CNCs by scanning electron microscopy [12], and reported that the oscillation behavior of CNCs can be explained with a classical continuum model. They also observed that CNCs showed higher quality factors (Q factors) when annealed at 1000 1C in Ar gas. They posited that this may have been due to an improvement in crystallinity caused by the heat treatment, although any significant changes in the structure could not be identified by Raman spectroscopy or direct observation by transmission electron Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A 0921-5093/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msea.2013.12.018 n Corresponding author at: Department of Mechanical Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. Tel./fax: þ81 6 6879 7815. E-mail address: hirahara@mech.eng.osaka-u.ac.jp (K. Hirahara). Materials Science & Engineering A 595 (2014) 205–212