Effect of Organic Adsorbates on the Initial Stage of Electrolytic Metal Deposition: Development and Use of a Spectroscopic Ellipsometer.

摘要

A study was performed to define the functional role of surface active agents during the initial stage of electrocrystallization. The system selected for investigation involved Cu as the electrode substrate, Pb as the deposited metal, and rhodamine-B chloride as the model inhibitor. The strong absorption band of rhodamine-B in the visible spectrum made it detectable by optical techniques in submonolayer amounts on the electrode. Deposit thicknesses ranged from a single monolayer (the underpotential deposit, UPD) to thicknesses of about 1000 Angstroms. It has been found that (1) the free energy of Pb electrosorption is about 7 kcal/mol; (2) the Pb adatom in the underpotential layer is completely discharged; and (3) in the absence of rhodamine-B, a Pb monolayer completely covers the Cu surface before three-dimensional nucleation of the bulk Pb phase; (4) the bulk phase which forms on the monolayer consists of a granular, porous layer covered by large dendritic islands; (5) addition of rhodamine-B prevents complete formation of the Pb monolayer and results in more compact bulk deposits than are possible in its absence; (6) rhodamine-B inhibits dendrite growth; (7) rhodamine-B is simultaneously reduced with the Pb exp ++ ion and is depleted from the electrode surface, which results in a mass transfer controlled inhibitory effect; and (8) the dye species responsible for inhibition has a preferential normal orientation on the electrode surface. A self-compensating, magneto-optic spectroscopic ellipsometer was developed for this in situ study. To support interpretations of ellipsometry data, light scattering measurements from electrode surfaces during deposit formation were also done. (ERA citation 08:033963)