Abstract
To study the mechanism and the kinetics of electrocrystallization, electrochemical measurements were supplemented with in situ microscopic observations of growing copper electrodeposits. The growth was followed on main crystal planes of copper single crystals up to an average thickness of the deposit corresponding to 10 coulomb/cm2. Highly purified solutions of 
in 
were used.
Triangular and hexagonal pyramids form on the (111) plane at low 
current densities. Edges in the bases of these pyramids are either parallel to the 
or to the 
direction. At higher current densities 
, the pyramids truncate and gradually transform into blocks. On the (110) plane, ridge types of deposit develop. At 2 and 5 ma/cm2, the ridges are parallel to the [100] direction. At 10 ma/cm2 and higher current densities, they are parallel to the [110] direction. Details of the types of deposit which are formed are given. Rates of growth of individual growth forms are determined and analyzed.
On all crystal planes, at any given current density the electrode potential changes with the time of deposition. On the (100) plane, the trend is for the potential to increase with deposition time until the average thickness of the deposit corresponds to about 3 coulomb/cm2. On the (111) plane, however, there is a large decrease in the potential, which reaches a steady value once the average thickness of the deposit corresponds to about 6 coulomb/cm2. On the (110) plane, the magnitude of the change in the potential with time of deposition is the lowest of the three planes considered.
Current‐potential plots, both from the data at the initial stages of deposition, and from those obtained at an average thickness of deposit corresponding to 10 coulomb/cm2 and the same type of growth, show Tafel slopes close to 
. This slope is consistent with a mechanism where the first charge transfer is rate‐controlling.
From the current‐potential plots for the initial stages of deposition, exchange current densities on different crystal planes are found to be in the order
The decrease in the potential with time on the (111) plane is accounted for in terms of the formation and growth of new and more active crystal faces over the growing substrate. With this hypothesis, the observed change in the potential on the (100) plane is also explained. The observed exchange current densities at any instant of deposition is an average over all crystal faces of different activities. The dependence of the exchange current density on the crystal plane is discussed.