Corey Nelson (Zhu Group)
1:00pm - 2:00pm
Interfacial charge transfer is ubiquitous to many chemical and physical processes and can occur on sub picosecond timescales. Probing dynamics associated with interfacial charge transfer requires the use of ultrafast laser spectroscopies, but obtaining information from real interfaces is notoriously difficult because of an overwhelming contribution from the bulk of either constituent to the measured signal.
To minimize bulk contributions, even-order nonlinear spectoscopies have been used to selectivly probe charge transfer events. Previous research has demonstrated that time-resolved electric field induced second harmonic generation (TR-EFISH) is a valuable tool in elucidating charge transfer dynamics at buried interfaces [Science 328, 1543 (2010); Nat. Mater. 12, 66 (2013); J. Phys. Chem. C 117, 10974 (2013)]. The second harmonic signal, however, has many contributions arising from the surface, electric fields at the interface, resonances due to surface states, and other contributions from the bulk. All of these make unambigous determination of charge transfer an extremely difficult task.
In order to overcome the above difficulties and improve our understanding of the TR-EFISH signal, we have developed a spectral interferometry technique for second harmonic generation with time, energy, and phase resolution. We have applied it to two model systems: the GaAs(100) surface and the CuPc/GaAs(100) interface. This new method has allowed us to observe the interference between static and time-resolved SH signals and obtain insight into interfacial states and their dynamics. We have discovered excited interfacial states in the spectral domain on these model systems and observed their electronic coupling to the bulk semiconductor. These initial results demonstrate the power of time-resolved second harmonic spectral interferometry in providing a wealth of information on electronic states and their dynamics at buried interfaces.