Energy-filtered dark-field imaging of nanoparticles by PINEM in 4D electron microscopy

Abstract

Time-resolved dark-field imaging of alpha Fe2O3 nanoparticle and Ag nanowires using scattered electrons by selected crystal planes are realized by photon-induced near-field electron microscopy (PINEM) selecting probing electrons which absorb energy from a transient laser field during their passage through the target particles in a four-dimensional transmission electron microscope (4D-TEM). The high laser fluence illuminated on the particles causes significant part of probing swift electrons exchange energy with the laser light, creating enough PINEM electrons required for the dark-field imaging of particles with high spatiotemporal resolution at nanometer and femtosecond scale. Different from the bright-field PINEM imaging of particles where the outerspace with a close distance to the particle are illuminated by transmitted PINEM electrons, illumination is confined on the particles by selected scattered PINEM electrons, leading to a much more defined and sharp imaging of particles compared with a bright-field PINEM image. In combination with PINEM temporal gating and dark-field selective imaging, the PINEM dark-field imaging technique in the 4D-TEM enables the studies of structural dynamics of selective crystal planes or elements with high spatiotemporal resolution.