Van der Waals epitaxy with C 60 molecules and change of the growth mechanism by Ba-doping

Abstract

Hot-Wall Epitaxy (HWE) allows to grow epitaxial layers very close to thermodynamic equilibrium, which is very essential in the case of Van der Waals epitaxy of fullerenes. The semiclosed nature of the HWE reactor provides a growth regime at high vapour pressures without loss of source material, and offers the possibility to dope the epilayers with Ba or to form Ba-compounds during growth. As soon as Ba was used in the growth reactor, the growth rate of the C 60 layers was mainly controlled by the Ba source temperature. This behaviour can be interpreted by the assumption that the incorporated Ba causes a charge transfer to C 60 and controls, in that way, the sticking coefficient for the C 60 molecules that are always present in a surplus in the vapour. In that way the growth mechanism changes from Van der Waals epitaxy, which is typical of pure fullerenes, to a different mechanism resulting from a stronger bonding type evoked by the charge transfer. A clear decrease of the resistivity with increasing Ba content in the C 60 layers was observed with a saturation value of 4 × 10 −4 Ω cm.