Ultrafast Electron Crystallography of Surface Structural Dynamics with Atomic-Scale Resolution

摘要

Progress over the past two decades has made it possible to study atomic-scale femtosecond molecular dynamics in all phases of matter.The atomic-scale spatial resolution has been achieved with both X-ray and electron diffraction,and only recently has the combination of spatial and temporal reso-lution been advanced successfully for studies of isolated chemical reactions by ultrafast electron diffraction and bulk crystal phonons and melting by X-ray diffraction.For surface structures and molecules on surfaces,ultrafast electron crystallography (UEC) is unique,and herein we demonstrate its potential for the direct determination of surface structural dynamics of crystalline solids (GaAs),following impulsive fs laser excitation.From the change of Bragg diffraction (shift,width,and intensity),we show,by direct inversion of the diffraction data,that compression and expansion of the atoms occur on the - 0.01 A to +0.02 A scale,respectively,and that the transient temperature reaches its maximum value (1565 K) in 7 ps.