Jp. Wilcoxon et al., SYNTHESIS AND OPTICAL-PROPERTIES OF MOS2 AND ISOMORPHOUS NANOCLUSTERSIN THE QUANTUM CONFINEMENT REGIME, Journal of applied physics, 81(12), 1997, pp. 7934-7944
Highly crystalline nanoclusters of hexagonal (2H polytype) MoS2 and se
veral of its isomorphous Mo and W chalcogenides have been synthesized
with excellent control over cluster size down to similar to 2 nm. Thes
e clusters exhibit highly structured, bandlike optical absorption and
photoluminescence spectra which can be understood in terms of the band
-structures for the bulk crystals. Key results of this work include: (
1) strong quantum confinement effects with blue shifts in some of the
absorption features relative to bulk crystals as large as 4 eV for clu
sters similar to 2.5 nm in size, thereby allowing great tailorability
of the optical properties; (2) the quasiparticle (or excitonic) nature
of the optical response is preserved down to clusters less than or si
milar to 2.5 nm in size which are only two unit cells thick; (3) the d
emonstration of the strong influence of dimensionality on the magnitud
e of the quantum confinement. Specifically, three-dimensional confinem
ent of the carriers produces energy shifts which are over an order of
magnitude larger than those due to one-dimensional (perpendicular to t
he layer planes) confinement emphasizing the two-dimensional nature of
the structure and bonding; (4) the observation of large increases in
the spin-orbit splittings at the top of the valence band at the K and
M points of the Brillouin zone with decreasing cluster size, a feature
that reflects quantum confinement as well as possible changes in the
degree of hybridization of the electronic orbitals which make up the s
tates at these points; and (5) the observation of photoluminescence du
e to both direct and surface recombination. Several of these features
bode well for the potential of these materials for solar photocatalysi
s. (C) 1997 American Institute of Physics.