• PDF / 569,228 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 8 Downloads / 248 Views

DOWNLOAD

REPORT

---

Structure and properties of C60@SWNT Brian W. Smith, Richard M. Russo, S.B. Chikkannanavar, Ferenc Stercel, David E. Luzzi University of Pennsylvania, Department of Materials Science and Engineering, 3231 Walnut Street, Philadelphia, PA 19104-6272, USA ABSTRACT Our recent achievement of high-yield C60@SWNT synthesis facilitates characterization by various techniques, including selected area electron diffraction (SAD) and Raman spectroscopy. The obtained SAD patterns show that interior C60 molecules sit on a simple 1-D lattice having a parameter of 1.00 nm. Simulated SAD patterns and real-space measurements both support this determination and do not indicate a lattice with a more complex basis, e.g. a dimer basis. Empty and bulk-filled SWNTs (22%, 56%, and 90% yields), each subjected to identical processing steps, were examined by room temperature Raman spectroscopy. Systematic differences are seen between the spectra of filled and unfilled SWNTs, particularly with respect to the G- and RBM-bands of the nanotubes. We present a possible explanation for this behavior. INTRODUCTION The single wall carbon nanotube has garnered fame for its potential to become a seminal engineering material. Intrinsically, a SWNT exhibits remarkable mechanical and electronic properties that make it suitable for use in a broad range of envisaged commercial applications. What is often overlooked, however, is that nanotubes might be selectively modified to improve upon these same properties. For example, the fact that a nanotube encloses an essentially onedimensional lumen opens the possibility for using it as a template to nanostructure atoms, ions, or small molecules into linear arrangements. Certain one-dimensional phenomena have been treated theoretically, but few 1-D systems are known to exist in reality. For this reason, little is known about how materials behave in one-dimension. Indeed, such materials might prove to be extraordinarily important. Presently, the paradigm one-dimensional material is C60@SWNT: a linear array of C60 molecules enclosed by a SWNT via van der Waals interactions. Since its discovery [1] and high-yield synthesis [2], the structure of C60@SWNT has been widely debated. Similarly controversial has been the question of whether the electronic states of the SWNT are perturbed by the presence of interior C60. In this letter, we present a solution to the structure of C60@SWNT using empirical and simulated electron diffraction. We also compare Raman spectra of bulk SWNT material containing filled and empty nanotubes. Our data show systematic differences that are not inconsistent with changes in the measured vibronic states upon filling. EXPERIMENTAL DETAILS C60@SWNT was synthesized in milligram aliquots using methods that are described elsewhere, i.e. in ref. [2]. At the time of synthesis, a separate batch of control samples were Z6.20.1

subjected to the same chemical and thermal processing steps, but no C60 was introduced and so the control SWNTs remained empty. Benchmarking the experimental (filled) samples against