Probing Structure and Dynamics at Complex Interfaces

<strong>Seminar of the School of Physical Sciences -------------------------------------------------</strong> <strong>Title: Probing Structure and Dynamics at Complex Interfaces</strong> <strong>Speaker: Ravindra Pandey</strong> (University of Texas, Austin) Date: <strong>May 18, 2016 </strong>(Wednesday) <strong>Abstract: </strong>Interfaces play an important role in a number of intriguing charge transfer processes relevant in biology, catalysis, environmental chemistry, and molecular electronics. Fundamental information about molecules at an interface is limited as many experimental methods are incapable of selectively probing these regions. However, owing to its inherent interfacial sensitivity, sum frequency generation (SFG) spectroscopy is an ideally suited technique to provide information on the structure and dynamics of molecules at interfaces. I will highlight two examples where SFG spectroscopy is used to determine how molecules arrange themselves at protein-water interfaces and at junctions within organic semiconductor (OSC) devices. I will describe how specific bacteria trigger ice formation by controlling the molecular structure of interfacial water. The freezing transition is further facilitated by the highly effective removal of latent heat from the nucleation site, as apparent from time-resolved vibrational SFG spectroscopy. SFG can also be applied in the visible spectral range to nondestructively investigate the interfacial electronic structure of OSC thin films, coper phthalocyanine (CuPc) deposited on SiO2. By modelling SFG spectra measured as a function of film thickness we can identify changes in CuPc's electronic density of states at both its buried interface with SiO2 and air-exposed surface. Such information will significantly help to improve strategies for designing OSC-based optoelectronics.