Ultrafast Spatially Resolved Carrier Dynamics in Individual ZnO Rods

Tuesday, December 6, 2011

4:30pm | 203 Teer Building

Presenter

John Papanikolas , Associate Professor

We have used femtosecond transient absorption microscopy to investigate the charge carrier dynamics in needle-shaped ZnO rods that are 10-30 mm in length and 200-1800 nm in diameter. Localized photoexcitation of the structure (e.g. end versus middle) is accomplished through a two-photon excitation of the ZnO by a 730 nm near-infrared laser pulse focused to a diffraction limited spot by the microscope objective. The photoinduced charge-carrier dynamics are then probed by the change in transmission of a weak 810 nm probe pulse that is spatially overlapped with the excitation pulse. The pump-probe microscope has a lateral resolution of 350 nm and a time resolution better than 500 fs. Experiments performed at different locations within the structure reveal dramatically different dynamical signatures, with the ends of the rod exhibiting faster electron-hole recombination than the interior.

Bio: John Papanikolas received his BA in Chemistry from Bowdoin College in Brunswick Maine in 1987. He earned his Ph.D in Chemical Physics from the University of Colorado at Boulder 1994 and was a postdoctoral associate at JILA in Boulder Colorado from 1994-1997. From Colorado he moved to Chapel Hill where he joined the faculty of the Chemistry Department at UNC.  His interests are in application of ultrafast spectroscopic methods to the study of molecular materials and nanomaterials, and in recent years has pursued the development of optical imaging methods that can follow the carrier dynamics in individual semiconductor structures on the femtosecond time scale.