Spatially resolved valence band study of nanostructured carbon films containing transition metal nanocrystals

We studied the electronic structure of nanostructured C films produced by ultrasonic cluster beam deposition with the intention to find out the bonding configuration of the C network and to determine the modification induced by transition metal cluster inclusion in the film. Exploiting the energy and spatial resolution of the Spectromicroscopy beamline at Elettra Synchrotron, we were able to follow the valence band features depicted in 95.0 eV-excited photoemission spectra with a 0.5 μm lateral resolution. The spectroscopic results allowed to conclude that nanostructured C films have a mixed sp2/sp3 bond configuration and an amorphous-like structure and that those features are uniformly distributed in the film. The inclusion of metal cluster (Ni, Ti and Mo) in the film strongly modifies the valence band spectra. The surface stoichiometry of the embedded metal clusters and the keeping of their metallic nature are determined by a detailed analysis of the spatial dependence of the ultraviolet photoemission spectroscopy (UPS) spectra and by a comparison with previous studies on metal-carbide and -oxide surfaces.

[1]  J. Robertson.  Diamond-like amorphous carbon , 2002 .

[2]  L. Johansson,et al.  Valence-band structure of TiC and TiN , 1980 .

[3]  P. Milani,et al.  Thermal annealing and hydrogen exposure effects on cluster-assembled nanostructured carbon films embedded with transition metal nanoparticles , 2003 .

[4]  Martin,et al.  Structural and electronic properties of amorphous carbon. , 1989, Physical review letters.

[5]  Galli,et al.  Microscopic structure of hydrogenated amorphous carbon. , 1994, Physical review. B, Condensed matter.

[6]  Robertson,et al.  Electronic and atomic structure of amorphous carbon. , 1987, Physical review. B, Condensed matter.

[7]  Ley,et al.  Photoemission study of amorphous carbon modifications and comparison with calculated densities of states. , 1996, Physical review. B, Condensed matter.

[8]  A. Bianco,et al.  Spectromicroscopy beamline at ELETTRA: Performances achieved at the end of commissioning , 2000 .

[9]  I. Lindau,et al.  Atomic subshell photoionization cross sections and asymmetry parameters: 1 ⩽ Z ⩽ 103 , 1985 .

[10]  J. Rodríguez,et al.  Chemistry of thiophene on Mo(110), MoCx and MoSx surfaces: photoemission studies , 2000 .

[11]  Mckenzie,et al.  Microscopic structure of tetrahedral amorphous carbon. , 1996, Physical review letters.

[12]  P. Milani,et al.  Synthesis and characterization of cluster-assembled carbon thin films , 1997 .

[13]  Gerhard Ertl,et al.  Low Energy Electrons and Surface Chemistry , 1974 .

[14]  R. Zimmermann,et al.  ELECTRONIC STRUCTURE SYSTEMATICS OF 3D TRANSITION METAL OXIDES , 1998 .

[15]  Jinghua Guo,et al.  In situ and ex situ characterization of thin films by soft X-ray emission spectroscopy , 2000 .

[16]  Peter Oelhafen,et al.  The molybdenum–carbon interface: formation and electronic structure of the carbide layer , 2000 .

[17]  Liming Wu,et al.  A density functional study on the electronic structures of TiX (X=C, N, O). Part II. Investigations on the electronic structures of TiC bulk and surfaces , 2000 .

[18]  Shik Shin,et al.  Resonant soft X-ray fluorescence study of rutile (TiO2) , 1996 .

[19]  P. Oelhafen,et al.  Electronic properties of diamond/nondiamond carbon heterostructures , 1999 .

[20]  F. Himpsel,et al.  Experimental bulk energy bands for diamond using hν-dependent photoemission , 1980 .

[21]  A. Bianconi,et al.  Photoemission studies of graphite high-energy conduction-band and valence-band states using soft-x-ray synchrotron radiation excitation , 1977 .