Optical and Electron Microscopy of Au core/CdS Shell Nanoparticles

The combining of metal and semiconductor nanostructures as core/shell
have attracted great interest due to their complementary optical properties; the
localized Plasmon in the core and the exciton in semiconductor. The first,
results in the enhancement of local fields and the second, are the nonradiative
damping due to electron transfer from semiconductor to metal. Composite
nanostructures of metal-core/semiconductor-shell configuration were prepared
using organometalic method. UV-Vis spectra for the colloids show two distinct
bands, one for the gold (Au) metal core surface plasmon at lower energy and
the second for the excitons of semiconductor Cadmium Sulfide (CdS) shell at
higher energy. Second derivative methods were used to determine the precise
absorption peaks in UV-Vis spectra. The shell size was estimated using two
methods, effective mass approximation (EMA), and polynomial fitting function
(PFF), both give shell thickness dimension in the range of few nanometers.
These dimensions were confirmed by imaging the nanostructure using high
resolution transmission electron microscope (HRTEM).