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Evaluating Angular Ion Current Density for Atomically Defined Nanotips

Published online by Cambridge University Press:  10 July 2014

Radovan Urban*
Affiliation:
Department of Physics, University of Alberta, Edmonton, AB, Canada T6G 2G9 National Institute for Nanotechnology, Edmonton, AB, Canada T6G 2M9
Robert A. Wolkow
Affiliation:
Department of Physics, University of Alberta, Edmonton, AB, Canada T6G 2G9 National Institute for Nanotechnology, Edmonton, AB, Canada T6G 2M9
Jason L. Pitters
Affiliation:
National Institute for Nanotechnology, Edmonton, AB, Canada T6G 2M9
*
*Corresponding author. radovan@ualberta.ca
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Abstract

In this paper we investigate methods to characterize angular current density from atomically defined gas field ion sources. We show that the ion beam emitted from a single apex atom is described by a two-dimensional Gaussian profile. Owing to the Gaussian shape of the beam and the requirement to collect the majority of the ion current, fixed apertures have inhomogeneous illumination. Therefore, angular current density measurements through a fixed aperture record averaged angular current density. This makes comparison of data difficult as averaged angular current density depends on aperture size. For the same reasons, voltage normalization cannot be performed for fixed aperture measurements except for aperture sizes that are infinitely small. Consistent determination of angular current density and voltage normalization, however, can be achieved if the beam diameter as well as total ion current are known. In cases where beam profile cannot be directly imaged with a field ion microscope, the beam profile could be extracted from measurements taken at multiple acceleration voltages and/or with multiple aperture sizes.

Type
Materials Applications
Copyright
© Microscopy Society of America 2014 

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