A Hybrid Chemical/Electrochemical Synthesis
of Copper(I)Iodide Nanocrystallites on Graphite
Principle Scientist: Gregor Hsiao
G. Hsiao, M.G. Anderson, S. Gorer, D. Harris, and R.M. Penner,
A Hybrid Electrochemical/Chemical Synthesis of Supported, Luminescent Semiconductor Nanostructures With Size Selectivity: Copper(I) Iodide.,
J. Am. Chem. Soc., 119 (1997) 1439.[PDF]
A fundamentally new approach for synthesizing semiconductor nanocrystals - size-selectively - has been developed. 
-CuI nanocrystallites (NCs) have been synthesized on the atomically smooth graphite basal plane surface using a hybrid electrochemical/chemical (henceforth E/C) method. This method involves the following steps (shown schematically in the diagram below): 1) Electrochemical deposition of metal (e.g. Cu) NCs onto an electrode surface, 2) Electrochemical oxidation of these metal NCs to yield either an oxide or a hydroxide intermediate (e.g. Cu2O in this case) and, 3) Displacement of oxygen (or hydroxide) by iodide (or sulfide) in an aqueous KI (Na2S) solution.
Here's what a few of these nanocrystals looks like in the atomic force microscope (AFM):
The dispersions of nanocrystals generated by the E/C method possess the following characteristics: Single crystallinity, good-to-excellent size monodispersity, epitaxial alignment (with the hexagonal periodicity of the graphite(0001) surface). In addition, as shown below, E/C deposited particles on graphite exhibit strong room-temperature luminescence.
The AFM broadens particles making them appear up to 100 time wider than they really are. These CuI nanocrystals, for example, are approximately spherical and about 20 in diameter. However the height of each particle is accurately rendered by the AFM. For this reason, AFM data can conveniently be used to obtain size histograms for many particle on a particular surface.
A characteristic feature of the E/C synthetic method is that the size and size monodispersity of the semiconductor nanocrystals which are obtained is decided by the corresponding characteristics of the metal nanocrystallites which are deposited electrochemically in step (1) above. In addition, because both steps (1) and (2) are, in principle, applicable to a variety of different metals, a variety of I-VII and II-VI compound semiconductors and semiconducting metal oxides are accessible using variants of this approach. Cadmium Sulfide is another material which we have recently synthesized using the E/C approach. Amazingly, the E/C method is also easily implemented with standard electrochemical instrumentation, and is FAST: The "total synthesis" of CuI nanocrystals, for example, requires less than one minute.
