VAN-DER-WAALS EPITAXY WITH C-60 MOLECULES AND CHANGE OF THE GROWTH-MECHANISM BY BA-DOPING

Hot-Wall Epitaxy (HWE) allows to grow epitaxial layers very close to t hermodynamic equilibrium, which is very essential in the case of Van d er Waals epitaxy of fullerenes. The semiclosed nature of the HWE react or provides a growth regime at high vapour pressures without loss of s ource 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 th e growth reactor, the growth rate of the C-60 layers was mainly contro lled by the Ba source temperature. This behaviour can be interpreted b y 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 o bserved with a saturation value of 4 X 10(-4) Omega cm. (C) 1997 Elsev ier Science S.A.