Platinum nanocrystals were deposited on basal plane oriented graphite surfaces from dilute (1.0 mM) PtCl 6 2-containing electrolytes using a pulsed potentiostatic method. The deposition of platinum nanocrystals occurred via an instantaneous nucleation and diffusion-limited growth mechanism which resulted in narrow particle size distributions (relative standard deviation <35%) for mean crystallite diameters smaller than 40 Å. The number of particles per unit area on these surfaces was 10 9 -10 10 cm -2 . Noncontact atomic force microscopy images reveal that platinum nanocrystals nucleated both at defect sitesssuch as step edgessand on apparently defect-free regions of the atomically smooth graphite basal plane. Using electron transparent graphite surfaces, selected area electron diffraction analyses revealed that the structure of deposited platinum nanocrystals was fcc with a lattice constant that was indistinguishable from bulk fcc platinum. Platinum nanocrystals were not epitaxially oriented on the graphite basal plane surface.

Grain growth in nanocrystalline (nc) Al with a grain size of 26 nm produced by cryogenic mechanical milling was studied through x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Grain growth kinetics resembled those of ball-milled nc Fe. For homologous temperatures (T/TM) of 0.51–0.83, the time exponent n from D1/n − D01/n = kt was 0.04–0.28, tending toward 0.5 as T/TM increased. Two grain-growth regimes were distinguished: below T/TM = 0.78 growth ceased at an approximate grain size of 50 nm while at higher temperatures, grain growth proceeded steadily to the submicrometer range. Grain growth over the range of temperatures studied cannot be explained in terms of a single thermally activated rate process. The observed high grain size stability was attributed primarily to impurity pinning drag associated with the grain growth process.

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