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 i n situ electrochemical scanning tunnelling microscopy, some unexpected experimental artefacts caused by instrumental design and tip-surface interactions have been recognised. The electrodeposition system employ ed in our in situ studies has been found to be very sensitive to an in itial 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 thi s current surge was investigated and found to be related to the perfor mance of the potentiostat. The deposit was removed either by anodic po tential sweeps or under positive local electric fields of the imaging tip. Further cathodic deposition was possible on the surge-induced dep osit. Characterisation, by ex situ x-ray diffraction, atomic force mic roscopy, scanning transmission electron microscopy and high resolution electron microscopy, showed that the deposits were Pd. Use of the var ious techniques demonstrated their complementarity in studies of the s tructure and dimensions of surface deposits. (C) 1996 Wiley-Liss, Inc.