Hybrid electrochemical/chemical synthesis of supported, luminescent semiconductor nanocrystallites with size selectivity: Copper(I)iodide

beta-CuI nanocrystallites (NCs) are synthesized on the atomically smooth graphite basal plane surface using a new hybrid electrochemical/chemical (E/C) method. This method involves the following steps: (1) electrochemical deposition of copper NCs onto an electrode surface, (2) electrochemical oxidation of these copper NCs to yield Cu2O, and (3) displacement of oxygen in Cu2O by iodide in an aqueous KI solution. Dispersions of CuI NCs having mean diameters ranging from 10 to 180 Angstrom were prepared using the E/C method. Selected-area electron diffraction analysis reveals that beta-CuI NCs are obtained; these NCs are epitaxially aligned with the hexagonal periodicity of the graphite surface, as are the Cu2O precursor particles. For samples of supported CuI NCs having a mean particle height of <25 Angstrom, individual NCs were well-separated from one another on the graphite surface and were narrowly dispersed in height. Photoluminescence spectroscopic analysis showed a strong, room temperature emission at an energy corresponding to the band gap. As the crystallite diameter was reduced from 180 Angstrom to 13 Angstrom, the energy of this emission shifted from the macroscopic value of 2.92 eV to >3.04 eV, in good agreement with the predictions of the effective mass, strong confinement model.