Electronic Structure of Doped Buckminsterfullerene
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ELECTRONIC STRUCTURE OF DOPED BUCKMINSTERFULLERENE ARNE ROSfN AND DANIEL OSTLING Department of Physics,Chalmers University of Technology and University of GOteborg, S-412 96 GOTEBORG, Sweden ABSTRACT Molecular cluster calculations within the local density approximation have been performed in a study of the electronic structure of the C60 molecule - "Buckminsterfullerene" doped with K, B and N. Calculations for the KC6 0 molecule, with the K atom located at the centre of the cage as well as at different show how the valence 4s positions inside or outside the cage, of the bare C60 transferred to the LUMO state electron is molecule. Doping with a B or N atom located at the centre of the cage creates a molecule with a partly occupied level of 2p similar to donor and character in the HOMO and LUMO gap, doped the band gap of traditionally levels in acceptor Doping by substitution of one or two of the semiconductors. carbon atoms in the cage with X = B or N, as modelled with the C 5 9 Xi or C 5 8 X2 clusters, gives a different structure with a the HOMO and LUMO levels in the pure C60 molecule splitting of with the and with the creation of acceptor and donor levels substitution of B and N, respectively. INTRODUCTION laser The methods for production of free clusters using vaporization of materials followed by supersonic expansion, have for the production and during the last decade, opened a new area studies of new materials with unique properties (1-3]. The most spectacular discovery is probably that of C60 [4] which was even This discovery own name "Buckminsterfullerene". given its initiated a lot of experimental and theoretical activity to characterize the electronic and geometrical properties, although The discovery of most of the research was of basic nature [5,6]. the electric arc evaporation method by Kratschmer and Huffman [ 7-9] for production of macroscopic amounts of fullerene compounds a "boom" of initiated has, however, within a very short time experimental and theoretical research which has shifted the field from basic science to different applications in Solid State Physics, Materials Science and Chemistry [10-12]. The interest in doped compounds of C 6 0 has been particularly stimulated by the discovery of Haddon et al [13] that films of C60 doped with alkali atoms are conductive at room temperature. Still more exciting was the discovery that the films became superconducting at a temperature of 18 K when doping with K [14]. More recent works have also shown superconductivty with onset Tc = 33 K using Rb temperatures of Tc = 28 K with Rb [15] and and Cs as doping elements [16]. However, the existence of metal When Rohlfing, Cox and containing fullerenes is not new (17]. time observed big free carbon clusters for the first Kaldor [18] using the laser vaporization technique, a number of potassium
Mat. Res. Soc. Symp. Proc. Vol. 270. 01992 Materials Research Society
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using potassium doped observed containing clusters were Kroto et al [4] studied carbon graphite samples. Later when clusters and interpreted
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