Abstract
We present the design and fabrication of a micrometer-scale electron gun for the implementation of ultrafast low-energy electron diffraction from surfaces. A multi-step process involving photolithography and focused-ion-beam nanostructuring is used to assemble and electrically contact the photoelectron gun, which consists of a nanotip photocathode in a Schottky geometry and an einzel lens for beam collimation. We characterize the low-energy electron pulses by a transient electric field effect and achieve pulse durations of 1.3 ps at an electron energy of 80 eV. First diffraction images in a backscattering geometry (at 50 eV electron energy) are shown.
Highlights
Ultrafast electron diffraction1 and microscopy2 are rapidly evolving tools for the study of structural dynamics
A multi-step process involving photolithography and focused-ion-beam nanostructuring is used to assemble and electrically contact the photoelectron gun, which consists of a nanotip photocathode in a Schottky geometry and an einzel lens for beam collimation
Employing nanoscale photocathodes22–28 and minimized propagation distances, this limitation was overcome in a compact transmission Ultrafast low-energy electron diffraction (ULEED) setup for the study of structural dynamics in monolayers and ultrathin films
Summary
Ultrafast electron diffraction and microscopy are rapidly evolving tools for the study of structural dynamics. Photoemitter embedded in a shielded micrometer-scale electrostatic lens assembly (total outer diameter of 80 lm; Fig. 1(d)) Utilizing this photoelectron source, we achieve a temporal resolution in electron projection imaging of 1.3 ps at an electron energy of only 80 eV and a source-sample distance of 400 lm. High-quality electron diffraction patterns are recorded in a backscattering geometry, demonstrating the high spatial coherence of the generated electron beam. This photoelectron gun combines ultrafast temporal resolution with high momentum resolution and ultimate surface sensitivity, promoting access to numerous ultrafast phenomena in the structural dynamics at surfaces
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