PREPARATION OF PRISTINE AND BA-DOPED C-60 FILMS BY HOT-WALL EPITAXY

The hot-wall epitaxy (HWE) allows to grow epitaxial layers very close to thermodynamic equilibrium, which is very essential in the case of V an der Waals epitaxy of fullerenes. The semiclosed nature of the HWE r eactor provides a growth regime at high vapour pressures without loss of source material and offers the possibility to dope the epilayers or to form compounds during growth. The successful growth of C-60 epilay ers was further improved by a post-growth in situ annealing process. A n additional Ba source was used in the HWE reactor to dope the C-60 la yers and to grow BaxC60 films. The Ba source could be heated separatel y so that the vapour pressure of C-60 and Ba could be controlled indep endently. To measure the electrical properties of the BaxC60 layers, w hich are not stable in air, it was necessary to install electrical con tacts at the sample holder for resistance measurements during growth. After the growth, the thickness of the BaxC60 layers was measured and the resistivity evaluated. A clear decrease of the resistivity with in crease in Ba incorporated in the C-60 layers was observed with a satur ation value of 4 x 10(-4) Ohm cm.