The Schottky electron emitter is a predominant electron-emitting source in today’s electron beam equipment. This book comprehensively covers the Schottky emitter, dealing with its theoretical as well as practical aspects. The main questions that are addressed in this book are: what is the Schottky electron emitter? How does it work? And how do its properties affect the performance of electron beam equipment?
The focus is on the direct link between the operating conditions of the source and the properties of the beam at the target level. This coupling is made clear by discussing the effect of the operating conditions and the geometry of the source and gun on the emission properties of the emitting surface, the effect of Coulomb interactions on the brightness and energy spread in the first few millimeters of the beam path, and the effect of the operating conditions and the shape of the emitter on the consequences of the beam at the target. The final chapter combines all these effects to demonstrate that there is a trade-off to be made between brightness, energy spread, and shape stability.
Table of Contents
Electron emission from a surface
The potential energy barrier at a surface
Emission by heating
The effect of an electric field on the potential energy barrier at a surface
Emission by heating and applying an electric field
Emission from a Schottky emitter
Work function variations across the emitter surface
Applying a bias
Applying a heating current
Total emission current
Emission from the end facet
The facet-extractor lens
The effect of the voltage settings
The effect of the emitter geometry
The effect of the heating current
The final beam for applications
Imaged by the electron-optical system: the virtual source
Current in the source image: practical brightness
Total probe size: source image plus diffraction plus aberration contributions
The effect of electron-electron interactions in the beam
Summarizing: the beam properties relevant to electron optical systems
Observed geometrical changes
Equilibrium crystal shapes
Tip size growth
Changes of the end facet geometry
Collapsing of the end facet
The effect on the beam properties
Maximum performance for different applications
Source monitoring tools
Appendix A. Procedures for monitoring in a few commercial systems
Appendix B. Procedure to characterize system performance
Merijn Bronsgeest obtained her M.Sc. cum laude in 2004 at the Materials Science & Engineering department at Delft University of Technology, the Netherlands, being honored with the award for Best MS&E Graduate of the Year. She earned her Ph.D. in applied physics cum laude from the same university in 2009 for her work on Schottky electron sources, which was a project in collaboration with FEI Company. In 2009 Merijn went to the University of Maryland to work on carbon nanotubes. In a first project, she designed and fabricated a write-one-read-many memory based on carbon nanotube transistors. After that, she focused on the characterization of thermal transport properties of carbon nanotubes with an in situ TEM technique. In 2011 she participated in a session of the Global School of Advanced Studies on graphene in Grenoble, France. This led to her moving to Grenoble in 2012 to work at CEA as a Eurotalents fellow on new two-dimensional materials.
"Really understanding the physics of Schottky electron sources is a must for every sophisticated user of an electron microscope. But also, it is an intellectual pleasure in itself to learn about this ever-changing nanocrystal from which the electrons in the microscope emerge. The author has managed to combine these aspects, usefulness, and theoretical depth, in the elegant and clear style that characterizes her work."
Prof. Pieter Kruit, Delft University of Technology, The Netherlands
"This book describes practical aspects of using Schottky electron sources in electron optical systems on the basis of well-founded physics theory. It makes clear how the electron source performance changes with the operating parameters and why. The book is especially valuable to those who want to make the best use of this high-potential electron source."
Dr. Shin Fujita, Shimadzu Corporation, Japan