Electrochemical Deposition of Silver Nanocrystallites on the Atomically Smooth Graphite Basal Plane

Abstract

A potentiostatic pulse method has been employed to electrochemically deposit silver nanocrystallites on the atomically smooth graphite basal plane surface. Voltage pulses having amplitudes of 100, 250, and 500 mV vs Ag0 and durations of 10 or 50 ms were applied to graphite surfaces immersed in dilute (≈1.0 mM) aqueous silver nitrate. During the deposition pulse, the current increased in approximate proportion to (time)1/2 as expected for an instantaneous nucleation and three-dimensional growth mode of deposition. Consistent with this growth mode, noncontact atomic force microscopy (NC-AFM) examination of graphite surfaces following silver deposition revealed the existence of silver particles at a coverage of near 1010 cm-2 which were well-separated from one another on atomically smooth regions of the graphite basal plane surface. These particles were disk-shaped having a height of 15−50 Å and an apparent diameter which varied from 200 to 600 Å; particle dimensions increased smoothly with the coulometric loading, QAg, over the interval from 0.31 to 36 μC cm-2 and in approximate proportion to QAg1/3. Significantly, silver nanocrystallites present on the atomically smooth regions of a graphite surface could not be observed by using either the scanning tunneling microscope (STM) or a conventional repulsive mode atomic force microscope (AFM). In addition to NC-AFM, the characterization of these silver nanocrystallites by transmission electron microscopy lattice imaging and Auger electron spectroscopy is reported.