  The optical and vibrational properties of nanocrystalline thin films of MoS2,
comprised of a mixture of edge terminated vertically aligned (ETVA) and
(001)-oriented regions, on large insulating substrates are reported. From high
resolution transmission electron microscopy (HRTEM), the average size of ETVA
nanocrystals were ~5 nm and each nanocrystal consisted of only 3 to 5
monolayers of MoS2. The films were highly transparent (~80%) but the percent of
transmittance decreased as the energy of the incident light approached to the
band gap. Additionally, weak excitonic peaks were observed both in the
absorption and transmission spectra. The room temperature Raman study showed
that both the E12g and A1g modes were significantly broader, and a few
additional Raman modes were observed when compared to bulk MoS2. The broadening
of the A1g mode was analyzed using the phonon-confinement model and the
calculated particle size was in good agreement with TEM observations. Moreover,
the temperature coefficient of the A1g mode was estimated from the temperature
dependent Raman studies.
