Development and characterization of an electron gun for ultrafast electron microscopy

by Reiner Bormann
Doctoral thesis
Date of Examination:2015-11-27
Date of issue:2015-12-21
Advisor:Prof. Dr. Claus Ropers
Referee:Prof. Dr. Claus Ropers
Referee:Prof. Dr. Markus Münzenberg
Persistent Address: http://dx.doi.org/10.53846/goediss-5440

 

 

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Abstract

English

Ultrafast electron microscopy is an emerging field of research offering the potential to investigate structural processes on a femtosecond time-scale with nanometer resolution. In order to further advance ultrafast electron microscopes, an improvement of the electron gun is necessary with respect to spatial and temporal beam properties as well as the electron yield. In this thesis, photoemission characteristics of laser-driven nanotip cathodes incorporated into a Schottky-type emitter assembly are experimentally and theoretically investigated. Specifically, electron trajectories, emission patterns, transverse beam emittances and electron pulse durations are analyzed with respect to the emission site and settings of the electron gun geometry. Two operation regimes are identified offering high magnification or a large electron count rate. In the last part of this work, measurements of the electron beam quality (emittance, spot size, beam profile, electron yield) are conducted using a laser-driven needle emitter in a transmission electron microscope.
Keywords: Ultrafast Electron Microscopy; Pulsed Electron Gun; Photoemission Characteristics; Nanotip; Emittance; Brightness; Emission Pattern; Nonlinear Photoemission
 
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