The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Photoemission spectroscopy demonstrates the formation of a surface gold nitride upon irradiation of a Au͑110͒ surface with 500 eV nitrogen ions at room temperature. After irradiation two N1s peaks are observed at binding energies of 396.7± 0.2 eV and 397.7± 0.2 eV along with a broadening of the Au4d 5/2 line. Changes in valence-band spectra are also observed, including an additional density of states at 1.6 eV binding energy and new states at ϳ3.1 eV. Annealing experiments indicate that the two N1s lines are associated with nitrogen compounds of differing thermal stability, possibly due to the formation of more than one nitride phase. To further investigate the properties of gold nitride we have undertaken ab initio pseudopotential calculations on the most likely nitride stoichiometry, Au 3 N, and identified a novel triclinic crystal structure of a significantly lower energy than the anti-ReO 3 expected from a simple consideration of the periodic table, although the latter structure is also found to be stable. The triclinic structure is determined to be metallic, of importance to possible applications.
Hollow onionlike carbon ͑OLC͒, generated by annealing nanodiamond at 2140 K, has been studied by core-level and valence-band photoemission spectroscopy. Upon intercalation with potassium, core and valence states of the OLC show an almost rigid shift to higher binding energies, and the density of states at the Fermi level (E F ) is observed to increase. An asymmetric broadening of the C1s line from the OLC as intercalation proceeds indicates an increase in electron-hole pair excitations. Both core and valence-band spectra are consistent with charge transfer from the intercalated potassium to the OLC, and support the conclusion that the electronic structure of the carbon onions bears strong similarity to that of graphite, although differences do exist. In consequence the conclusion can be drawn that these species behave as graphite ''nanocrystals'' rather than as large fullerene molecules.
The thermally driven reaction of carbon nanotubes with a silicon substrate is studied by photoemission spectroscopy and atomic force microscopy. Carbon nanotubes with a relatively high defect density are observed to decompose under reaction with silicon to form silicon carbide at temperatures ͑650Ϯ10°C͒ substantially lower than the analogous reaction for adsorbed C 60 . The morphology of the resultant silicon carbide islands appears to reflect the morphology of the original nanotubes, suggesting a means by which SiC nanostrutures may be produced. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1530747͔Understanding the interaction of carbon nanotubes with silicon and the resultant formation of silicon carbide at elevated temperatures is of importance due to the need to create well-defined nanotube/semiconductor heterojunctions 1 and the growing interest in fabricating silicon carbide nanorods from carbon nanotube precursors.2-4 Moreover, knowledge of the temperature at which carbide formation occurs is necessary to determine the stability of silicon/carbon nanotube interfaces which would result from integration of carbon nanotubes with silicon-based electronics. Although much effort has been directed toward understanding the interaction and thermal decomposition of C 60 on Si͑111͒ surfaces, 5-11 a closely related system, the inability to evaporate carbon nanotubes makes exploring the interaction of these species with elemental surfaces difficult.In this letter, we report an approach in which nanotubes are deposited on hydrogen passivated Si͑111͒ surfaces in an ambient atmosphere. Hydrogen is subsequently desorbed from beneath the nanotubes in an ultrahigh vacuum ͑UHV͒ environment allowing the study of the nanotube/silicon interface as a function of temperature by photoemission spectroscopy. Desorption of hydrogen from Si͑100͒-2ϫ1-H has previously been observed to occur beneath a C 60 monolayer enabling molecules to bond directly to the silicon surface. 12 We find that defective carbon nanotubes decompose on Si͑111͒ after a short anneal at 650Ϯ10°C, about 150°C ͑Refs. 6 -10͒ lower than the decomposition temperature of C 60 on Si͑111͒-7ϫ7. Ex situ atomic force microscopy ͑AFM͒ indicates that the morphology of silicon carbide islands resulting from nanotube decomposition is governed by initial nanotube geometry, suggesting a route for fabrication of nanometer scale silicon carbide structures.Photoemission experiments were undertaken at Beamline 4.1 of the Synchrotron Radiation Source, Daresbury, UK. Hydrogen passivated Si͑111͒ substrates were produced by conventional techniques and AFM images show large flat terraces, while x-ray photoelectron spectroscopy ͑XPS͒ demonstrated very low levels of residual oxide contamination. Purified single-wall carbon nanotubes ͑SWNTs͒ were supplied by the Sussex Fullerene Group and were placed in suspension by agitating small quantities in acetone in a conventional ultrasonic bath. Several droplets of the sol were cast upon a hydrogen passivated Si͑111͒ sample, and the sample...
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