The Preparation of C 60 /C 70 and the Characterization by Different Techniques
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THE PREPARATION OF C6 o/C 7o AND THE CHARACTERIZATION BY DIFFERENT TECHNIQUES P. Hiiussler H. Best en, and H.-U. ter Meer Hoechst Ad, CentrajResearch, 6230 Frankfurt 80, Germany ABSTRACT We report on the preparation of C 60 /C 7 o by the arc method. Evidence of monofunctional C 60 0, and C 60 -CH 2 has been observed by mass spectrometry. Dependent on their preparation conditions, high resolution transmission electron microscopy of crystals consisting of mixtures of C6 0 /C 70 show different structure. Needle-like crystals grown from toluene show superlattice formation while single crystals obtained by sublimation have fcc structure. UV-VIS-absorption spectra in toluene are compared to those of films of various thickness and crystallinity. INTRODUCTION Immediately after the discovery of highly stable carbon clusters of C6 0 and C7 0 by laser evaporation, experimental evidence was reported for endohedral clusters of La@C 6o [1]. After the invention of the arc method [2] and the preparation of macroscopic quantities of C60 and C70 , research on this field became more intense. Hetero fullerenes as C 59 B with one carbon atom of the geodesic network substituted by a boron atom have been reported [3]. Research on the functionalization and the chemistry of fullerenes became even more intense after the discovery of relatively high superconductivity of alkaline doped solids of C60 [4]. These materials are highly reactive and superconductivity disappears after hours if brought to air. An endohedral trapping of the dopants is thought to reduce this high reactivity. The crystal structure was determined at the very beginning to be hexagonal closely packed with large disorder [5]. C6 0 sublimed on different substrates, on the other hand, revealed fcc crystal structure with planar defects [6]. Orthorhombic crystal structure [7] and unidentified ones [8] were also reported. The crystal habit shows large variations from thin platelets, rods and stars [5] to needles up to a length of millimeters [7, 9]. The crystal habit as well as the structure seem to depend very much on preparation conditions, arid in particular, on the content of included solvent [7, 10]. An important question is how the conditions of deposition and therefore the type of crystal symmetry and content of solvent influence electronic structure. Optical absorption provides important information on electronic states. Theoretical predictions are manyfold [11]. A review of the physics and chemistry of fullerenes is given elsewhere [12]. In the present contribution we briefly report on preparation conditions of fullerenes and spurious amounts of some functionalized fullerenes which get formed during arc preparation. Structural characterization of different forms of solid mixtures of C6 0/C 70 is performed by scanning electron microscopy (SEM), electron diffraction (ED), as well as high resolution transmission-electron microscopy (HRTEM). The electronic characterization is performed by UV-VIS absorption spectroscopy. RESULTS AND DISCUSSION Preparation The preparation was
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