AVS 51st International Symposium
    Semiconductors Thursday Sessions
       Session SC+EM-ThM

Paper SC+EM-ThM9
X-ray Absorption and Emission Studies of Diamond Nanoparticles

Thursday, November 18, 2004, 11:00 am, Room 304B

Session: Wide Bandgap Semiconductors
Presenter: T.M. Willey, Lawrence Livermore National Laboratory
Authors: T. van Buuren, Lawrence Livermore National Laboratory
C. Bostedt, HASYLAB at DESY, Hamburg, Germany
T.M. Willey, Lawrence Livermore National Laboratory
R.W. Meulenberg, Lawrence Livermore National Laboratory
J.Y. Raty, University of Liege, Belgium
G. Galli, Lawrence Livermore National Laboratory
L.J. Terminello, Lawrence Livermore National Laboratory
Correspondent: Click to Email
Carbon nanoparticles, produced in detonations, are found to have a core of diamond with a coating fullerene-like carbon. X-ray diffraction and TEM show that the nanodiamonds are crystalline and approximately 4 nm in diameter. These nano-sized diamonds do not display the charateristic property of other group IV nanoparticles: a strong widening of the energy gap between the conduction and valence bands owing to quantum-confinement effects. For nano-sized diamond with a size distribution of 4 nm, there is no shift of the band energies relative to bulk diamond@footnote 1@. The C 1s core exciton feature clearly observed in the K-edge absorption of bulk diamond is attenuated and broadened in the nanodiamond case due to increased overlap of the excited electron with the core hole in the small particle. Also the depth of the second gap in the nanodiamond spectra is shallower than that of bulk diamond. A feature at lower energy in the X-ray absorption spectra that is not present in the bulk samples is consistent with a fullerene like surface reconstruction. By exposing the diamond nanoparticles to an Argon / Oxygen plasma then annealing in a UHV environment, we have obtained a hydrogen free surface. The nanodiamonds processed in this manner show an increase fullerene type contribution in the carbon x-ray absorption pre-edge. High spatial resolution EELS measurements of the empty states of a single nanodiamond particle acquired with a filed emission TEM also show the core of the particle is bulk diamond like whereas the surface has a fullerene like structure. Density-functional theory calculations on clusters show an increase in bandgap only for clusters smaller than 1 nm, and confirm the fullerene-like surface reconstruction. @FootnoteText@ This work is supported by the U.S. DOE, BES Materials Sciences under contract W-7405-ENG-48, LLNL.@footnote 1@ J. Y. Raty, G. Galli, C. Bostedt, T. van Buuren, L. J. Terminello, Phys. Rev. Lett. 90, p.401 (2003) .