IN-SITU SCANNING TUNNELING MICROSCOPIC STUDY OF NICKEL ELECTRODEPOSITION ON HOPG

The early stages of the electrodeposition of nickel on highly oriented pyrolytic graphite (HOPG) were investigated by in situ scanning tunnelling microscopy, scanning electron microscopy and electrochemical measurements. Experimental results showed that the electrodeposition of nickel on HOPG followed an island growth mechanism. An individual island was composed of some larger grains which could be observed by both STM and SEM. However, a number of small grains, so-called subgrains, could be observed only by STM. In situ and real-time observation of the island growth revealed that the formation of the subgrains resulted from the progressive nucleation and 3D growth around the kinks of nickel crystallites. It was found that the nuclei were formed in a specific crystallographic direction, which led to the propagation of the long-range order crystallites. During the continuous tracing of the progress of nickel deposition, the formation of new islands was not observed. This reproducible phenomenon meant that the nuclei acting as the ''growth centres'' of the islands were formed instantaneously in the initial period of electrodeposition.