Nucleation, Cluster Growth, and Structure of Crystalline C 60 and C 70
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NUCLEATION, CLUSTER GROWTH, AND STRUCTURE OF CRYSTALLINE C60 AND C70 Nan Yao, S. K. Behal, C. F. Klein, M. M. Disko, S. C. Fung, R. D. Sherwood, K. M. Creegan, D. M. Cox Exxon Research and Engineering Company, Annandale, New Jersey 08801-0998, USA
ABSTRACT The nucleation and cluster growth of C60 and C70 crystallites on various substrates at ambient temperature have been investigated using electron microscopy. It was found that the initial nucleation is closely associated with surface defects, and the fullerenes are much more strongly bonded to each other than to the substrate. Sublimed C60 or C70 crystallites nucleate at the step edge in the liquid state and are aligned with the step walls and terraces through the process of coalescence. Reflection Electron Microscopy (REM) studies have shown an abnormal profile of C60 grown crystals as a result of the interaction of C60 molecules with the surface strain field during crystal growth. Transmission electron diffraction patterns reveal a twin structure with (110) habit plane for the low temperature ordered phase.
INTRODUCTION Since the production of C60 in sufficient quantities became available, C60 and its functionalized derivatives have attracted wide interest due to the great potential for various applications[1-4]. C60 is the only molecule known up to date which has icosahedral symmetry and a pseudospherical shape, and crystalline C60 is a van der Waals bonded molecular crystal with the structure characteristic of cubic close-packed pseudospheres. Its crystal lattice is face-centered-cubic with Fm(-3)m symmetry at ambient temperature, and it becomes a simple-cubic structure below -18°C with a symmetry of Pa(-3) via a first order transition[4, 5]. C70 is the next-larger fullerene with an elongated "rugby-ball" shape. Its crystal lattice is an fcc structure at ambient temperature with many properties similar to those of C60 [5, 6]. Electron diffraction and microscopy techniques are sensitive to small variations in periodic structure or lattice imperfection at individual crystals, and thus have made it possible to relate the structure with physical properties for individual C60 molecules, crystals of fullerite, and C6. assemblies supported on surfaces[7-10]. The properties of thin fullerite deposits are of
Mat. Res. Soc. Symp. Proc. Vol. 270. @1992 Materials Research Society
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considerable experimental and theoretical interest. Several experimental investigations have been carried out to understand the early stages of C60 growth. Studies using scanning tunneling microscopy (STM) have shown the formation of hexagonally-symmetric twodimensional islands of C60 on Au(111) surface. Similar studies of the single or multilayer growth regime of C60 on GaAs(1 10) and mica (001) substrates have also been conducted by STM and transmission electron microscopy (TEM), which demonstrated the epitaxial growth of single and multilayer C60 at ambient temperature condition with defected structure[11-13]. In this paper we present preliminary studies of nucleation, cluster growth
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