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Bandgap measurement of high refractive index materials by off-axis EELS

Abstract

In the present work Cs aberration corrected and monochromated scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) has been used to explore experimental set-ups that allow bandgaps of high refractive index materials to be determined. Semi-convergence and –collection angles in the µrad range were combined with off-axis or dark field EELS to avoid relativistic losses and guided light modes in the low loss range to contribute to the acquired EEL spectra. Off-axis EELS further supressed the zero loss peak and the tail of the zero loss peak. The bandgap of several GaAs-based materials were successfully determined by simple regression analyses of the background subtracted EEL spectra. The presented set-up does not require that the acceleration voltage is set to below the Čerenkov limit and can be applied over the entire acceleration voltage range of modern TEMs and for a wide range of specimen thicknesses.
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Category

Academic article

Language

English

Author(s)

  • Maryam Vatanparast
  • Ricardo Egoavil
  • Turid Worren Reenaas
  • Johan Verbeeck
  • Randi Holmestad
  • Per Erik Vullum

Affiliation

  • SINTEF Industry / Materials and Nanotechnology
  • University of Antwerp
  • Norwegian University of Science and Technology

Date

19.06.2017

Year

2017

Published in

Ultramicroscopy

ISSN

0304-3991

Volume

182

Page(s)

92 - 98

View this publication at Norwegian Research Information Repository