專題演講 Seminar

2017/01/20(Fri)     14:00 -15:00    五樓第一會議室 5F, 1st Meeting Room

Title

4D electron microscopy of photoinduced anomalous Brownian motion of nanoparticles in liquid and ballistic charged carrier dynamics in p-n junctions

Speaker

湯朝暉 博士 (加利福尼亞理工學院)

Dr. Jau Tang (Noyes Laboratory, California Institute of Technology)

Abstract

In the first Science work, we demonstrated novel applications of ultrafast electron microscopy (UEM) in liquid solution. We have discovered very fast anomalous Brownian motion of gold nanoparticles upon femtosecond laser excitation. Unlike the well-known linear time dependence for the mean square displacement of Einstein's theory for Brownian motion, the observed dynamics exhibits various time dependence, covering ballistic, superdiffusion and normal diffusion regimes. Moreover, the corresponding diffusion constant is 3 to 4 orders of magnitude greater than same nanoparticles without laser excitation. We elucidated the impulsive driving forces due to water steam nanobubbles from laser heating.
In another Science work, we presented ultrafast scanning electron microscopy (USEM) of photoinduced carrier dynamics. We observed fast charge separation of electrons and holes at the p-n junction and extremely high speed ballistic carrier dynamics, novel to the conventional solid state textbook description. We attributed such phenomena to slower electron-phonon collision time on the surface at high carrier temperatures and also polarity-dependent gating mechanism at the junction. (CV請查附件)
「作者相關資訊:https://www.facebook.com/tecolasd/posts/484937351698658」

CV

Language

演講語言 (Language): in English