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

The deposition kinetics of iron oxyhydroxide on sulfonic acid terminat ed self-assembled monolayers were studied. The thin films of FeOOH wer e formed on the substrates by thermal hydrolysis of millimolar aqueous solutions of Fe(NO3)(3) at a pH of approximately 2.0. The thickness o f the films was measured ellipsometrically at various times. Both Fe(N O3)(3) and HNO3 concentrations were independently varied to provide va rying degrees of solution supersaturation. Depending on these concentr ations, an induction time was observed before film growth commenced. T he correlation between supersaturation and induction time was modeled using classical nucleation theory. Very good agreement was observed re gardless of whether supersaturation was varied via the concentration o f Fe(NO3)(3) or HNO3. From these results an interfacial free energy fo r nucleation of 148 mJ/m(2) was calculated. The critical nucleus speci es was identified as a tetrameric iron species by considering the orde r of nucleation.