Scanning tunneling microscopy (STM) has been used in situ to study
the epitaxial growth of CdTe bilayers
electrodeposited onto Au single-crystal surfaces. The films were
produced by the alternate reductive
underpotential deposition of Te and Cd by the electrochemical atomic
layer epitaxy (ECALE) technique.
The kinetics of electrocrystallization were found to be consistent
with an instantaneous 2-D nucleation and
growth model. Atomic resolution images of the corresponding first
UPD structures of tellurium prior to Cd
deposition in a CdSO4 solution have been obtained.
Cd/Te bilayer structures formed by Cd UPD on Au(111)-(12×12)Te, Au(110)-c(2×8)Te, and
Au(100)-(2×2)Te were Au(111)-(3×3)CdTe,
Au(110)-(2×3)CdTe,
and Au(100)-c(2×2)CdTe bilayers, respectively. To
maintain stoichiometry, bilayer formation was accompanied where necessary (increasing in the order
Au(111)-(3×3)CdTe < Au(110)-(2×3)CdTe <
Au(100)-c(2×2)CdTe) by a significant rearrangement of the Te
structure during bilayer growth. This process
was found to take place without three-dimensional nucleation and
resulted in the exposure of large Au(100)
patches randomly distributed on the terraces, on which Cd was
deposited. In striving for structural epitaxy
on the gold substrates, structures exhibiting a compression of the bulk
lattice planes were observed for cases
where both excess and insufficient Te in the UPD layer was present to
form the bilayer of ideal density.
This observed inhomogeneity in the growth of
Au(100)-c(2×2)CdTe was consistent with a Cd-induced
structure
in the Te stripping peak on Au(100) and a Coulometric excess of
adsorbed Cd in the overall layer.