NUCLEATION OVERPOTENTIAL AND THE ROLE OF NUCLEATION EARLY AND LATE IN
A DEPOSITION CYCLE
Peter A. Adcock, Augustana College, SD, United States
and
Robert J. Fraser, Hatch Associates, Brisbane, QLD, Australia
Interest in monitoring a nucleation overpotential in electrometallurgical processes dates back some 40
years or more. Conversely, remarkable progress has been made in recent years on describing in detail the
processes involved in the formation of thin films by electrodeposition. The newer body of work
underscores a need for greater clarity in speaking about the role of nucleation and in the acquisition and
interpretation of nucleation overpotential measurements – the aim of this paper.
In electrometallurgy, it is generally desirable to form deposits which remain smooth, compact, and
relatively fine-grained while the deposit grows to a thickness on the order of 1 cm, perhaps 100 times
thicker than technological thin films. Hence, we distinguish two kinds of 3-dimensional nucleation that
can result in formation of new grains:- (a) initial nucleation (onto the substrate surface) of islands that
coalesce into growing deposit, and (b) ongoing nucleation of new grains on the deposit surface long after
the substrate has been covered and ceases to have a direct influence. The first should be measured on an
electrode surface truly representative of a real industrial substrate. The second requires judicious choice of
electrode material. In general neither the industrial substrate nor native metal to be deposited is suitable for
measurement of this nucleation overpotential. Both types of nucleation overpotential can be found below
about 1 A/m2 during a galvano-staircase experiment using an appropriate working electrode.
For the future, clear terminology is needed to distinguish these two types of nucleation potential. The latter
is the one for which the type of plot dubbed by Moats and Derrick as an Adcock Plot was first conceived
and correlated with relatively thick zinc electrodeposits. The data of Moats and Derrick showing different
trends for copper electrodeposition on stainless steel and on copper electrodes warrant new types of
interpretation.
KEYWORDS
Electrodeposition, Nucleation, Substrate, Galvano-staircase experiment, Nucleation overpotential