Development of in-situ RF-enabled high-brightness femtosecond electron microscopy for complex material research*

Correlated structural and electronic degrees of freedom in electronic materials help engineer macroscopic functional responses to external control parameters. Increasingly, new functionalities have been explored through integrating different electronic materials to form hybrid interfaces. Spatially and temporally resolved imaging and spectroscopy probe could provide a new perspective to study functionalities in ever increasing complexity in these new material platforms. However, significant challenges exist in reaching adequate sensitivities at the ultrafast timescale and nanometer spatial scale. Here we report a new development of ultrafast in-situ electron microscopy to address this limitation through active control of high-intensity femtosecond electron pulses, targeting the respective probe space using adaptive optics. An integrated system with compact DC gun, RF compression optics, and commercial TEM electron optics is established with the aim of nanometer-scale selected area imaging and core-level spectroscopy with combined ~100 femtosecond and ~1 eV resolution. We demonstrate our first application in studying the inhomogeneous phase transitions in VO₂ microelectronic devices.