Nonlinear Optical Surface Studies of Iron and its Oxides

The surfaces of iron and its oxides are important in a variety of industrial, environmental, catalytic, and biological processes but their study by optical methods is curtailed due to the ‘strong absorber problem’ (Fig. 1) posed by these fascinating materials. This proposal focuses on the synthesis, characterization, and study of nm-thin films of iron and some of its most important redox active oxides, namely magnetite (Fe3O4) and hematite (-Fe2O3), using physical vapor deposition and atomic layer deposition (ALD) to overcome the strong absorber problem posed by macroscopically thick iron samples. Studying the interaction of aqueous solutions containing redox inactive and active metal cations with nm-thin films will  Provide quantitative data regarding the interfacial potential, surface charge density, and redox activity;  Serve as important benchmarks for experiments and computer simulations of metal ions at iron/water interfaces; and  Quantitatively advance our current state of knowledge regarding free energy relationships within common electrical double layer models. In the experiments, redox active and inactive metal cations will be used, including Fe(II)/(III) and Cr(III)/(VI). E-beam deposited nm-thick Fe(0) films will be used as a model to study interfacial chemistry relevant to permeable reactive barriers that are based on zero-valent iron for Cr(VI) remediation. Special attention will be paid to the role of surface passivation by iron oxidation and the formation of sparingly soluble Fe/Cr complexes at the interface. The proposed experimental design is surface selective and employs environmentally relevant pH, temperature, electrolyte, and metal ion concentrations.