Photoemission sources and beam blankers for ultrafast electron microscopy.

Lixin Zhang,Jacob P. Hoogenboom,Ben Cook,Pieter Kruit

doi:10.1063/1.5117058

Abstract

Observing atomic motions as they occur is the dream goal of ultrafast electron microscopy (UEM). Great progress has been made so far thanks to the efforts of many scientists in developing the photoemission sources and beam blankers needed to create short pulses of electrons for the UEM experiments. While details on these setups have typically been reported, a systematic overview of methods used to obtain a pulsed beam and a comparison of relevant source parameters have not yet been conducted. In this report, we outline the basic requirements and parameters that are important for UEM. Different types of imaging modes in UEM are analyzed and summarized. After reviewing and analyzing the different kinds of photoemission sources and beam blankers that have been reported in the literature, we estimate the reduced brightness for all the photoemission sources reviewed and compare this to the brightness in the continuous and blanked beams. As for the problem of pulse broadening caused by the repulsive forces between electrons, four main methods available to mitigate the dispersion are summarized. We anticipate that the analysis and conclusions provided in this manuscript will be instructive for designing an UEM setup and could thus push the further development of UEM.

Highlights

Many processes such as phase transitions, chemical reactions, electron transport, and molecular vibrations occur at ultrafast time scales
To make a “molecular movie” in which we see atoms move while a molecule changes shape, as proposed by Dwyer et al.[1], is an inspiring goal for ultrafast electron microscopy (UEM)
We have evaluated, to our knowledge, all photoemission sources and beam blankers used to obtain pulsed electron beams for UEM reported to date

Summary

Introduction

Many processes such as phase transitions, chemical reactions, electron transport, and molecular vibrations occur at ultrafast time scales. These time scales can typically be as short as a few picoseconds or even femtoseconds.[1] The development of ultrafast electron microscopy (UEM) has led to the prospect that dynamic information can be obtained at higher spatial resolution (

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