The photophysics and electron transfer (ET) dynamics of quantum confined MoS2 nanoclusters have been studied using static and time resolved emission spectroscopy. The MoS2 nanoclusters consist of a single S–Mo–S trilayer, having diameters of ∼2.5 or 4.5 nm. Two types of electron acceptors are adsorbed on these nanoclusters: 2,2′-bipyridine (bpy) and 4,4′,5,5′-tetramethyl-2,2′-bipyridine (TMB). The ET reaction exothermicities may be varied by changing the electron acceptor or by varying the size of the MoS2 nanocluster. TMB is harder to reduce, and thus has a smaller ET driving force than bpy. The smaller nanoclusters have a higher energy conduction band, and thus have a larger ET driving force. In all cases, the ET driving force may be calculated from bulk MoS2 properties and quantum confinement theory. Both ‘‘normal’’ and ‘‘inverted’’ behaviors are observed. A reorganization energy of 0.40 eV is calculated from energy dependent ET rates.
We describe the construction and performance of a small-angle x-ray scattering ͑SAXS͒ instrument which we have used on several beam lines at the National Synchrotron Light Source. The analyzer crystal was a channel cut Si͑1,1,1͒ designed for use at ϭ1.54 Å with a measured efficiency of 60% and an angular resolution full width at half maximum of 0.001°. In the case of strongly scattering samples ͑i.e., powders͒, momentum transfer q between 1ϫ10 Ϫ4 ÅϽqϽ0.1 Å Ϫ1 could be studied with over eight decades of dynamic intensity range. We demonstrate the versatility of this instrument by performing scattering experiments on a variety of spherical latex samples spanning the size range from 50 to 800 nm, liquid crystal samples with sharp, asymmetrical Bragg peaks, and metal clusters with sizes less than 10 nm. Small-angle x-ray scattering data for the larger polystyrene samples is compared with light scattering data and theoretical structure factors, and the relative roles of instrument smearing, sample polydispersity, and interparticle interference are elucidated. In the case of the liquid crystal samples, the high resolution of the instrument allows structural features to be observed that were previously obscured by the instrumental resolution in other small-angle neutron and synchroton-based Kratky camera data taken on the same samples.
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