Electrochemical, spectroscopic and SPM evidence for the controlled formation of self-assembled monolayers and organised multilayers of ferrocenyl alkyl thiols on Au(111)

Organised multilayers were formed from the controlled self-assembly of ferr ocene alkyl thiols on Au(111) surfaces. The control was accomplished by inc reasing the concentration of the thiol solutions used for the assembly. Cyc lic 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 c onfirmed that the multilayer structure is attached to the surface via one m onolayer. The electrochemical behaviour of the multilayers indicated the pr esence of more than one controlling factor during the oxidation step, where as the reduction was kinetically controlled which contrasts with the behavi our of monolayers, which exhibit kinetic control for the oxidation and redu ction steps. Conventional and imaging ellipsometry confirmed that multilaye rs with well-defined increments in thickness could be produced. However, ST M indicated that at the monolayer stage, the thiols used promote the mobili ty of Au atoms on the surface. It is very likely that the multilayer struct ure 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.