EFFECT OF CURRENT DISTRIBUTION ON QUARTZ-CRYSTAL MICROBALANCE MEASUREMENTS

Spatially nonuniform electrodeposition can cause discrepancies between predicted and experimentally measured mass loadings on an electrochem ical quartz crystal microbalance (EQCM) because the sensitivity of the quartz crystal varies significantly from point to point. These discre pancies can be significant even if the current distribution is nearly uniform. These effects were examined experimentally by varying the con ductivity of the electrolyte and the current. density during the elect rodeposition of copper on an EQCM, effecting changes in the spatial, d eposited-mass distribution in a controlled manner. The resulting frequ ency shifts agree with results predicted by current distribution simul ations, validated a posteriori with profilometry measurements. Our res ults permit determination of the spatial variation of the quartz cryst al sensitivity factor, or of the current distribution on the EQCM.