AQUEOUS-SOLUTION DEPOSITION KINETICS OF IRON OXYHYDROXIDE ON SULFONIC-ACID TERMINATED SELF-ASSEMBLED MONOLAYERS

The deposition kinetics of iron oxyhydroxide on sulfonic acid terminated self-assembled monolayers were studied. The thin films of FeOOH were formed on the substrates by thermal hydrolysis of millimolar aqueous solutions of Fe(NO3)(3) at a pH of approximately 2.0. The thickness of the films was measured ellipsometrically at various times. Both Fe(NO3)(3) and HNO3 concentrations were independently varied to provide varying degrees of solution supersaturation. Depending on these concentrations, an induction time was observed before film growth commenced. The correlation between supersaturation and induction time was modeled using classical nucleation theory. Very good agreement was observed regardless of whether supersaturation was varied via the concentration of Fe(NO3)(3) or HNO3. From these results an interfacial free energy for nucleation of 148 mJ/m(2) was calculated. The critical nucleus species was identified as a tetrameric iron species by considering the order of nucleation.