Soft interfaces with multiple species are common in biology, the environment, and technological applications. Probing these, particularly when the interface is buried between two condensed phases presents many challenges. The only current method available to probe such interfaces with molecular specificity is the vibrational spectroscopy, sum frequency generation (SFG). SFG attains surface sensitivity due to its nonlinear nature, but that nonlinearity carries a price: separating overlapping signals is difficult, usually leading to nonunique separation. This problem has long been recognized by SFG practitioners and several methods for determining the complex components of the signal have been devised. None produce an absolute measurement of the complex signal. This contribution reports a nonlinear interferometer, that not only addresses this complex measurement issue, but also detects even low concentration interfacial species. The nonlinear interferometer has been demonstrated in both scanning and broadband SFG systems. Thin films and other interfaces will be discussed. Specifically, we show that the conformation of molecules in a hydrophobic interface are significantly altered by water in the film.
Speaker: Mary Jane Shultz, Tufts University
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