Instrumental effects on in situ electrochemical STM studies: an investigation of a current surge induced Pd deposit on HOPG.

Knowledge of instrumental complications is vital both in interpreting experimental observations and in achieving true results. In a study of palladium electrodeposition on highly ordered pyrolytic graphite by in situ electrochemical scanning tunnelling microscopy, some unexpected experimental artefacts caused by instrumental design and tip-surface interactions have been recognised. The electrodeposition system employed in our in situ studies has been found to be very sensitive to an initial cathodic current surge when the potentiostat control was applied to the electrodes at the measured open circuit potential. As a result, palladium and/or hydrogen were immediately deposited on the graphite surface within a small radius under the imaging tip. The cause of this current surge was investigated and found to be related to the performance of the potentiostat. The deposit was removed either by anodic potential sweeps or under positive local electric fields of the imaging tip. Further cathodic deposition was possible on the surge-induced deposit. Characterisation, by ex situ x-ray diffraction, atomic force microscopy, scanning transmission electron microscopy and high resolution electron microscopy, showed that the deposits were Pd. Use of the various techniques demonstrated their complementarity in studies of the structure and dimensions of surface deposits.