Speaker
Description
The unique physical and chemical properties of interfaces are governed by a finite depth that describes the transition from the topmost atomic layer to the properties of the bulk material. Understanding the physical nature of interfaces thus requires detailed insight into the different structures, chemical compositions, and physical processes that form this interfacial region. Such insight has traditionally been difficult to obtain from experiments, as it requires combination of structural and chemical sensitivity with spatial depth resolution on the nanometer scale. Here we present a vibrational spectroscopic approach that can overcome these limitations. By combining phase resolved Sum- and Difference-Frequency Generation spectroscopy and selectively determine different nonlinear interaction pathways, we can extract precise depth information on the nanometer scale and correlate these to specific vibrationally resonant modes of interfacial species. We demonstrate the applicability of this technique in two sets of experiments on selected model samples. The analysis of the results shows an almost perfect match between experiment and theory, revealing the high precision of the method. In the second part first results from depth resolved measurements on liquid-air interfaces are presented and their implications are discussed.
