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Thickness Measurements Using Photonic Modes in Monochromated Electron Energy-Loss Spectroscopy

Published online by Cambridge University Press:  10 March 2014

Aycan Yurtsever ,
Martin Couillard ,
Jerome K. Hyun  and
David A. Muller
Aycan Yurtsever
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14850, USA
Martin Couillard
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14850, USA
Jerome K. Hyun
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14850, USA
David A. Muller*
Affiliation:
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14850, USA Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY 14850, USA
*
*Corresponding author.david.a.muller@cornell.edu
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Abstract

Characteristic energies of photonic modes are a sensitive function of a nanostructures’ geometrical parameters. In the case of translationally invariant planar waveguides, the eigen-energies reside in the infrared to ultraviolet parts of the optical spectrum and they sensitively depend on the thickness of the waveguide. Using swift electrons and the inherent Cherenkov radiation in dielectrics, the energies of such photonic states can be effectively probed via monochromated electron energy-loss spectroscopy (EELS). Here, by exploiting the strong photonic signals in EELS with 200 keV electrons, we correlate the energies of waveguide peaks in the 0.5–3.5 eV range with planar thicknesses of the samples. This procedure enables us to measure the thicknesses of cross-sectional transmission electron microscopy samples over a 1–500 nm range and with best-case accuracies below ±2%. The measurements are absolute with the only requirement being the optical dielectric function of the material. Furthermore, we provide empirical formulation for rapid and direct thickness estimations for a 50–500 nm range. We demonstrate the methodology for two semiconducting materials, silicon and gallium arsenide, and discuss how it can be applied to other dielectrics that produce strong optical fingerprints in EELS. The asymptotic form of the loss function for two-dimensional materials is also discussed.

Keywords

electron microscopyCherenkov radiationoptical modesplanar waveguidesdielectric materials
Type
EDGE Special Issue
Information
Microscopy and Microanalysis , Volume 20 , Issue 3 , June 2014 , pp. 723 - 730
Copyright
© Microscopy Society of America 2014 

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Footnotes

†

Current address: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA

‡

Current address: National Research Council Canada, 1200 Montreal Road, Ottawa, Ontario, Canada K1A 0R6.

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