C u60 fullerene tubes as removable templates
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Crystalline microtubes (inner diameter 240–2100 nm) consisting of C60 fullerene molecules were prepared in the mixture of C60-saturated pyridine and isopropyl alcohol kept at 0 °C. Characterization by transmission electron microscopy showed a linear relationship between the outer diameter and the inner diameter for the C60 fullerene tubes. Optical observations suggested that the specimens already had tubular structure when they were grown in the solution. Deposition of guest crystals inside the C60 fullerene tubes was performed by the following procedure: (i) ultrasonic pulverization to obtain the C60 fullerene tubes with open ends, (ii) absorption of methyl alcohol solution of KBr into the tubes by the capillary attraction, and (iii) evaporation of methyl alcohol to precipitate KBr inside the tubes. Columnar KBr crystals were then obtained by dissolving the fullerene tube walls in toluene.
I. INTRODUCTION
The discovery of the method to manufacture bulk fullerenes in macroscopic quantities enabled us to see macroscopic-scale assemblies of solid fullerenes. 1 Precipitation from solutions can yield various morphologies and structures of solid fullerene including twodimensional and one-dimensional forms. 1–5 Recent research has shown the formation of tubular assemblies of fullerenes.6–10 Those fullerene tubes with outer diameters smaller than 1000 nm should be called fullerene nanotubes.9 The first example of the fullerene nanotubes was fabricated by dip-and-dry process of porous alumina templates into a toluene solution of C60; the obtained materials were arrays of tubes with polycrystalline walls of C60.6,7 On the other hand, a simple combination of a good solvent and a poor solvent of fullerenes (liquid– liquid interfacial precipitation method)5 also precipitates fullerene nanotubes without any template; the materials grow spontaneously into the form of tubes with single crystalline walls. By the liquid–liquid interfacial precipitation method, fullerene nanotubes have been successfully obtained in toluene saturated with C60 containing (2–C60)Pt(PPh3)2 and isopropyl alcohol (IPA) system,8 C70-saturated pyridine and IPA system,9 pyridine saturated with C60–24 mol% C70 and IPA system,9 and C60saturated pyridine and IPA system.10 Compared with so-called carbon nanotubes consisting of cylindrical graphene sheets,11 the tube walls of
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2006.0066 J. Mater. Res., Vol. 21, No. 2, Feb 2006
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fullerene nanotubes can be dissolved again in a proper solvent, which implies the potential use of fullerene nanotubes as templates for nanofabrication. In the present study, C60 fullerene nanotubes with a wide distribution of inner diameter were prepared in the C60-saturated pyridine and IPA system at 0 °C and characterized by Fourier-transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) observation. Insertion of liquid
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