Study of the influence of different dopings on the electronic structure of deposed single fullerenes by means of scanning tunnel spectroscopy

In this PhD thesis the scanning tunneling microscope is used to perform topographic and spectroscopic investigations on various fullerenes (C60, Ce rate at C60, Ce rate at C50, Ce rate at C44, Ce rate at C36, La rate at C44, La rate at C60, Y rate at C60, and C59N). C60 and the endohedral doped fullerenes have been produced in a laser vaporization source and have been mass-selected prior to soft-landing onto a highly oriented pyrolytic graphite. (C59N)2-powder has been evaporated in situ. After localising the deposited fullerenes onto the substrate surface using topographic measurements, spectroscopic investigations has been performed locally on the individual fullerenes. The results of these investigations demonstrated a dramatic change of the electronic structure depending on the doping and geometric structure of the fullerenes. Specifically the gap of all the endohedral doped fullerenes is smaller than the gap of pure C60. In detail, all cerium-doped fullerenes possess semiconducting properties with an increasing gap for decreasing cage size. No gap has been detected for La rate at C60 und Y rate at C60. Thus, these fullerenes exhibit metallic behaviour. For endohedral doped fullerenes there is only a weak interaction with the substrate. The interaction effect on the electronic structure is negligible in comparison with the effect of endohedral doping. The gap of the heterofullerene C59N is large in comparison with the gap of the endohedral doped fullerenes but less than the gap of pure C60. Furthermore, there is a strong interaction between the heterofullerene and the graphit substrate. (orig.)