Speaker
Description
Interfaces between different phases or materials are where all the action is. Solid and liquid interfaces are central to chemical and biological as well as technological and industrial processes, yet their molecular level structure and functioning are difficult to directly study for a variety of reasons. In this talk I will discuss the use of nonlinear X-ray spectroscopy as a direct probe of liquid and solid interfaces. X-ray second harmonic generation and sum frequency generation are interface selective probes that are just now becoming possible with the availability of Terawatt pulses from X-ray free-electron lasers. Combining these with the recent development of sub-micron liquid sheets and heterostructures, has enabled us to report the first observation of soft X-ray second harmonic generation from the surface of liquid water, revealing a surface Hydrogen bonding structure that is distinct from that of the bulk liquid. The technique is now also being applied to buried functional interfaces in Perovskite solar-cell devices.