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Electronic structure, vibrational stability, and predicted infrared-Raman spectra of the As 20 , As @ Ni 12 , and As @ Ni 12 @ As 20 clusters Structure and stability of endohedral fullerene Sc 3 N@C 80 were studied by temperature-dependent Raman and infrared spectroscopy as well as by quantum-chemical ͓density-functional-based tight-binding͔ calculations. The material showed a remarkable thermal stability up to 650 K. By both theory and experiment, translational and rotational Sc 3 N modes were found. These modes give a direct evidence for the formation of a Sc 3 N-C 80 bond which induces a significant reduction of the ideal I h -C 80 symmetry. From their splitting pattern a crystal structure with more than one molecule in the unit cell is proposed. According to our results: ͑i͒ a significant charge transfer from the Sc 3 N cluster to the C 80 cage; ͑ii͒ the strength of three Sc-N bonds; ͑iii͒ the chemical bond between triscandium nitride cluster and C 80 cage; and ͑iv͒ a large HOMO-LUMO gap are responsible for the high stability and abundance of Sc 3 N@C 80 .

The electronic and magnetic properties of endohedral fullerenes M k @C 2n for different metals M (such as lanthanides R, Group 3 and Group 2 metals) is a current area of endohedral fullerene research.[1] The influence of the electron transfer from M to the carbon cage, the geometric structure of the M k @C 2n , as well as the location of the metal ion(s) in the cage on the magnetic properties are commonly studied. As shown by ESR spectroscopy, photoemission or Mössbauer spectroscopy, R ions are trivalent in most cases as in Er k @C 82 for k = 1 and 2 [2,3] and Dy@C 2n (2n = 80, 82, 84). [4] Detailed studies of the fullerene magnetization versus applied field and temperature have confirmed these results. [5][6][7][8][9][10][11] On the other hand europium was found to be divalent in fullerenes for 2n = 74 or

We report a study of the electronic structure and charge transfer in the metallofullerene Sc 3 N@C 80 using photoemission and x-ray absorption spectroscopy. Through a comparison of the x-ray absorption spectrum of Sc 3 N@C 80 at the Sc L 2,3 edge with atomic multiplet calculations, the Sc 3d electron count is determined to be 0.6, thus giving an effective Sc valency of 2.4. With the N atom gaining a full electronic shell by means of covalent bonding with the Sc ͑also involving the Sc 3d electron density observed in the x-ray absorption experiments͒, the remaining six valence electrons of the Sc 3 N cluster are then transferred to the carbon cage which stabilizes the C 80 cage structure with I h symmetry, a structure which is not energetically favored in neutral C 80. The presence of the highly symmetric I h cage structure is further supported by the observation of distinct fine structure in the valence band photoemission spectra of the endohedral, which results from the high degree of effective degeneracy of the electronic states in the molecule. Finally, the results of investigations of K-doped Sc 3 N@C 80 using photoemission give insight into the K x Sc 3 N@C 80 phases that are formed upon intercalation.

Four rate-limiting processes for the formation of single-wall carbon nanotubes (SWCNT) could be identified by varying furnace temperature, gas type, and pressure in a pulsed-laser evaporation setup. One rate-limiting process accounts essentially for all relevant gas-pressure dependencies and can be quantitatively described using a single gas-specific constant. One thermally activated process is related to fullerene formation, whereas another process, following a T 2 -law, is discussed in terms of the diffusion of carbon through molten catalyst nanoparticles. The data provide strong support for an "undercooled melt" mechanism of nanotube formation.

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