Mechanism of film growth of tellurium by electrochemical deposition in the presence and absence of cadmium ions.

The growth morphology and the kinetics of a thin film of Te on Au during electrochemical deposition at -62 mV (vs Ag/AgCl/3 M NaCl) have been studied. The deposition conditions are similar to those used previously by us to grow nanowires inside Au nanotubes by electrochemical deposition in the presence of Cd ions (Cd(2+)). By using electrochemical deposition on a planar Au electrode, we explored the growth of the Te film for two conditions: in the presence of Cd(2+) (0.1 mM TeO(2) + 1 mM CdSO(4) + 50 mM H(2)SO(4) solution) and in the absence of Cd(2+) (0.1 mM TeO(2) + 50 mM H(2)SO(4) solution). We used several surface investigation techniques to study the growth such as: in situ electrochemical atomic force microscopy (EC-AFM), in situ electrochemical surface plasmon resonance (EC-SPR), electrochemical methods, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). In the presence of Cd(2+), in situ electrochemical atomic microscopy showed that Cd(2+) acted as a mediator at the early deposition stage and caused smoothing of the Te deposit obtained. In the absence of Cd(2+), Te had an island growth. The electrochemical surface plasmon resonance showed that the deposit was characterized by a slower deposition rate in the presence of Cd(2+) than in the absence of Cd(2+). Additionally, the thickness of the film was evaluated using EC-AFM measurements, electrochemical stripping analysis, and EC-SPR. The results obtained from all three measurements agree well with the Te film obtained in the presence of Cd(2+), where a continuous and uniform film was formed. In the presence of Cd(2+), a Te film with a thickness of 1.04 nm and atomically flat surface was deposited on an ultraflat Au surface. The XPS spectrum showed no significant amount of Cd in the deposit, indicating that the Cd ion acted as a mediator and not as a co-deposition element.