| Abstract
| - The synthesis and characterization of 3.5, 4.5, and 8 nm diameter MoS2 nanoclusters are described. Each sizeis characterized by TEM images, electron diffraction, and optical spectroscopy. These nanoclusters can besynthesized directly or may be synthesized from samples of polydisperse nanoclusters. Obtaining larger orsmaller discrete sizes from polydisperse samples indicates that these nanocluster sizes are thermodynamicallyfavored, that is, these sizes correspond to free-energy minima. Electron diffraction and static spectroscopicresults indicate that the particles are three atoms thick, specifically, single S−Mo−S trilayer disks. Static andtime-resolved absorption and emission spectroscopy were used to determine the polarizations of the lowestenergy allowed transitions in each case. We find that the 8 nm particles have a lowest energy absorptionmaximum at 473 nm that has mixed x − y and z polarizations, 4.5 nm particles have absorption maxima at400 and 440 nm that are x − y and z polarized, respectively, and 3.5 nm particles have an absorption maximumat 362 nm that is z polarized. These results indicate that the polarization of the lowest observed transition issize-dependent and that the ordering of the lowest excited states changes as the particle size decreases.
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