Jingya Sun
Jingya Sun, Beijing Institute of Technology, China
Title: Real-space Imaging of Carrier Dynamics of Materials Surfaces by Second Generation of Four-dimensional Scanning Ultrafast Electron Microscopy
Biography
Biography: Jingya Sun
Abstract
In the field of photo-catalysis and photovoltaics, ultrafast dynamical processes including carrier trapping and recombination on material surfaces are among the key factors in determining the overall conversion efficiency. A precise knowledge of these dynamical events on the nanometer and femtosecond scales was until very recently not accessible but is urgently needed for further optimization of the device performance. The only possible way to fully access such fundamental processes is to map the surface dynamics in real space and time. Here, we established and developed the second generation of four-dimensional scanning ultrafast electron microscopy (4D S-UEM) to take time-resolved images (snapshots) of material surfaces with 650 femtoseconds and 5 nanometers (nm) temporal and spatial resolutions, respectively. In this method, the surface of specimen is excited by a clocking optical pulse and a pulsed primary electron beam as a probe pulse, generating secondary electrons which are emitted from the very top of surface of the specimen in a manner that is sensitive to the local electron/hole density, providing direct and controllable dynamical information about surface dynamics. We demonstrate clearly how the surface morphology, grains, defects and nano-structured features can significantly impact the overall dynamical processes on the photoactive-material surfaces. In addition, two regimes of dynamical probing and the energy loss of secondary electrons will be also discussed.