Electrochemical, spectroscopic and SPM evidence for the controlled formation of self-assembled monolayers and organised multilayers of ferrocenyl alkyl thiols on Au(111)
Abstract
Organised multilayers were formed from the controlled self-assembly
of ferrocene alkyl thiols on Au(111) surfaces. The control was accomplished
by increasing the concentration of the thiol solutions used for the assembly.
Cyclic voltammetry, ellipsometry, scanning probe microscopy (STM and AFM)
and in situ FTIR spectroscopy were used to probe the differences
between mono- and multilayers of the same compounds. Electrochemical
desorption studies confirmed that the multilayer structure is attached to
the surface ia one monolayer. The electrochemical behaviour
of the multilayers indicated the presence of more than one controlling factor
during the oxidation step, whereas the reduction was kinetically controlled
which contrasts with the behaviour of monolayers, which exhibit kinetic control
for the oxidation and reduction steps. Conventional and imaging ellipsometry
confirmed that multilayers with well-defined increments in thickness
could be produced. However, STM indicated that at the monolayer stage, the
thiols used promote the mobility of Au atoms on the surface. It is very likely
that the multilayer structure is held together through hydrogen bonding.
To the best of out knowledge, this is the first example of a controlled one-step
growth of multilayers of ferrocenyl alkyl thiols using self-assembly
techniques.