Reproducible Synthesis of C 60 @SWNT in 90% Yields
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Reproducible synthesis of C60@SWNT in 90% yields 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 In previous works, we have shown our discovery of C60@SWNT and first described the general mechanism of filling, which involves the vapor phase transport of C60 molecules to openings in the SWNTs’ walls. Here, we discuss the high-yield synthesis of C60@SWNT by refinements to our method. Yields are measured by a calibrated weight uptake technique, a methodology that is not subject to many of the potential pitfalls inherent to other techniques that have been applied. At certain processing conditions, yields exceeding 90% were obtained and corroborated by transmission electron microscopy. From our data, we determine the parameters most important for creating endohedral SWNT supramolecular assemblies by the vapor phase method. Our results pave the way for successful single-tube measurements and for high-yield filling with non-fullerenes. INTRODUCTION In previous studies, we have shown that C60@SWNT is synthesized by a vapor phase route, whereby the sublimation of solid C60 in the presence of open SWNTs caused the fullerenes to enter the SWNTs and self-assemble into 1-D chains [1]. Subsequently, these experiments were independently reproduced [2-5], although no one has yet rigorously quantified the high-yield filling of SWNTs with molecules. Not only does this prevent the study of C60@SWNT with bulk characterization techniques, but also it increases the risk associated with attempts to measure directly the properties of an individual fullerene peapod. For example, such an experiment might require the spin-coating of SWNTs onto a substrate, and the TEM is of little use in assuring that the SWNTs are not empty. In the present work, we show by way of a parametric study how the filling fraction can be reliably measured and maximized. EXPERIMENTAL DETAILS We have devised a series of simple experiments to measure the yield of C60@SWNT by calibrated weight uptake, a proven technique for determining the stoichiometry of a doped system. Although it was not feasible to comprehensively examine all permutations of the synthesis parameters, a number of representative examples are discussed. In each experiment, samples of SWNTs were prepared for filling by prescribed processing steps, with the final step in each case being filtration to form a buckypaper that was dried in air at 110° C. The distal edges were trimmed from the buckypaper, which was then cut into samples weighing a few milligrams and uniquely identifiable by shape. Each sample was immediately weighed on a two-pan balance to ± 0.006 mg. The weighed samples were processed as quickly as possible, but whenever necessary they were stored in a desiccator evacuated to roughing vacuum to minimize atmospheric exposure. Z3.13.1
Multiple samples from each processing condition were split into control and experim
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