(a) Theoretical multiple scattering (MS) calculations
at the Zn K-edge as a function of the cluster size for ZnO for clusters
with increasing atomic shells: 3, 5, 7, 11, 16, 20, and 24. The 24-shell
cluster corresponds to a sphere of radius 10 Å. The experimental
ZnO curve is shown above as a reference. Feature D develops when 5
shells (short-range order) are considered and C appears when 11 shells
(midrange order) are considered, predominantly pertaining to multiple
scattering. (b) Calculations of the partial density of states (pDOS)
of ZnO plotted together with the experimental XAS spectrum. The earlier
part of conduction band is composed of hybridized O 2p–Zn 4sp
states. (c) Theoretical MS calculations at the Zn K-edge as a function
of the cluster size for ZnS for clusters with increasing atomic shells:
2, 3, 5, 6, 8, 11, and 13. The 13-shell cluster corresponds to a sphere
of radius 10 Å. The experimental ZnS curve is shown above as
a reference. Feature G and H develop when 5 shells (midrange order)
are considered, predominantly pertaining to multiple scattering. (d)
Calculations of the partial density of states (pDOS) of ZnS plotted
together with the experimental XAS spectrum. The earlier part of conduction
band is composed of hybridized S 3p–Zn 4sp states. Calculations
of the partial density of states (pDOS) relative to the Fermi level
(total density of states shifted so onset of band gap is at 0 eV)
plotted together with the experimental XAS spectra [XAS spectrum aligned
by matching max intensity to max pDOS intensity of absorbing atom]
for b and d.