X-ray photoemission studies of diamond, graphite, and glassy carbon valence bands
The high-resolution x-ray photoemission spectra (XPS) of the total valence bands of atomically clean diamond, graphite, and glassy carbon, obtained with monochromatized Al K ..cap alpha.. radiation, are reported and discussed. By comparing valence-band and carbon-1s photoelectron kinetic energies, the XPS valence-band spectra I'E) of diamond and graphite were rigorously affixed to the same energy scale as earlier K x-ray emission spectra i(E). The two spectra - I'(E) and i(E) - have very different energy dependencies of intensity because selection rules and cross-section ratios render i(E) sensitive only to 2p character and I'(E) far more sensitive to 2s character. Taken together, I'(E) and i(E) show that the fractional p character in the diamond valence band increases from approx. 16% at the bottom of the band to approx. 92% at the top, with an average hybridization of approx. s/sup 1/ /sup 2/p/sup 2/ /sup 8/. The spectra agree well with the density of states of Painter et al, but indicate a valence-band width of 24.2(10) eV rather than their 20.8 eV. The C(1s) binding energy of 284.68(20) eV in graphite agrees well with a recent theoretical estimate of 284.4(3) eV by Davis and Shirley. Analysis of I'(E) i(E) for graphite resolves the valence bands cleanly into sigma and ..pi.. bands, with the spectrum I'(E) of the former resembling that of diamond, but with a stronger 2s admixture (sp/sup 2/ vs sp/sup 3/). The XPS cross section of the (p/sub z/)..pi.. bands was very low, as expected by symmetry. The bandwidth of 24(1) eV somewhat exceeded Painter and Ellis's calculated value of 19.3 eV. Glassy carbon showed an I'(E) between that of diamond and graphite, consistent with an amorphous lattice containing both trigonal and tetrahedral bonds. 8 figures, 3 tables.
- Research Organization:
- Univ. of California, Berkeley, CA (United States)
- OSTI ID:
- 6089150
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Vol. 9:12
- Country of Publication:
- United States
- Language:
- English
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CARBON
STRUCTURAL CHEMICAL ANALYSIS
DIAMONDS
GRAPHITE
BINDING ENERGY
COMPARATIVE EVALUATIONS
CROSS SECTIONS
ELECTRONIC STRUCTURE
ELECTRONS
ENERGY DEPENDENCE
ENERGY RANGE
HYBRIDIZATION
PHOTOEMISSION
SELECTION RULES
VALENCE
X-RAY SPECTRA
ELEMENTARY PARTICLES
ELEMENTS
EMISSION
ENERGY
FERMIONS
LEPTONS
MINERALS
NONMETALS
SECONDARY EMISSION
SPECTRA
360602* - Other Materials- Structure & Phase Studies