Integration of an electrochemical quartz crystal microbalance into a scanning electrochemical microscope for mechanistic studies of surface patterning reactions

The scanning electrochemical microscope (SECM) is used in combination with an electrochemical quartz crystal microbalance (EQCM) to investigate princi ple modes of tip-induced interactions. The focus is on the influence of aco ustic waves and surface modifying processes on the resonant frequency. Cons iderable importance is attached to high frequency resolution and its enduri ng accuracy, especially with regard to mechanistic studies of microstructur ing processes. A two-dimensional pattern of standing acoustic waves over th e entire quartz crystal was monitored for the first time, revealing the ani sotropic thickness-shear motion. In the vertical direction, we detected sta nding pressure waves caused by reflection at the plane apex of the very sma ll tip, which caused frequency changes below 1 Hz. The mass sensitivity dis tribution of the 10 MHz quartz crystal was mapped two-dimensionally, and an anisotropy due to the orientation of the electrode tabs was found, corrobo rating published results. The measured mass sensitivity at the center provi des a maximum mass resolution of 50 pg, which is sufficient to elucidate me chanistic sequences involved in microstructuring processes. (C) 2000 Elsevi er Science Ltd. All rights reserved.