Adsorption of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{84}$ on the Si(100)2×1 surface studied by using the scanning tunneling microscope

The adsorption of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{84}$ on the Si(100)2×1 surface is investigated by using the scanning tunneling microscope (STM) and the scanning tunneling spectroscope (STS). Both of the molecules occupy the trough surrounded by four neighboring dimers. The results show that both ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{84}$ form strong bonds with the Si substrate. Multiple-layer adsorption of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{84}$ results in formation of ordered crystalline islands with the fcc(111) configuration. The internal structures have also been observed for the ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{84}$ molecules of the first layer adsorbed on the Si(100) surface. In the case of the ${\mathrm{C}}_{84}$ molecules, those of the ordered multiple-layer surface also show similar internal structures. We take these STM images as evidence that the rotation of the individual fullerenes is suppressed significantly on the Si surface. Comparing with the theoretical results, these STM images are attributed to the reflection of the partial charge density of the states of the molecule near the Fermi level. The electronic structures characterized by STS are in good agreement with the recent theoretical calculation and show significant charge transfer from the Si substrate to the adsorbates.