Development of a femtosecond analytical electron microscopy based on a Schottky field emission transmission electron microscope.

Abstract

Ultrafast transmission electron microscopy (UTEM) has gained wide applications in the nanoscale dynamics with femtosecond, even attosecond, resolution. The instrument development is still in progress to satisfy the various applications. At Nankai University, we built an UTEM with a laser-driven Schottky field emitter based on a field emission TEM (Talos200i) of Thermo Fisher Scientific. This study comprehensively examines the performance of the UTEM, including the continuous mode and ultrafast photoemission mode. The investigation focuses on optimizing brightness, temporal resolution, energy dispersion, and stability in ultrafast photoemission mode, achieving a temporal resolution of ∼200 fs and an energy dispersion of 0.7 eV with excellent stability through careful adjustments of laser parameters and equipment settings. In scanning transmission electron microscopy mode, the beam size of the photoemission mode is ∼1.4 nm at specific settings with potential for further improvement. As application examples, we illustrate the results of photoinduced structural dynamics of gold film and MoS2 thin flake by ultrafast electron diffraction. We also report the polarization dependent optical interference pattern characterized by the photoinduced near field microscopy effect in a silicon thin film sample prepared by the focused ion beam method. These findings provide valuable insights for researchers aiming to leverage the UTEM's capabilities for advanced electron microscopy applications and pave the way for future advancements in UTEM technology.