Measuring the dielectric constant of materials from valence EELS

• Published in: Micron (Oxford, England : 1993) Vol. 40; no. 2; pp. 262 - 268
• Main Authors: Potapov, P.L., Engelmann, H.-J., Zschech, E., Stöger-Pollach, M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.02.2009
• Subjects: Cherenkov effect; Dielectric constant; Dielectric properties; High-resolution EELS; Kramers–Kronig transformation; Optical properties; Relativistic losses; Valence EELS; VEELS; Kramers–Kronig transformation; VEELS; Cherenkov effect; Dielectric constant; Relativistic losses; Dielectric properties; Optical properties; Valence EELS; High-resolution EELS
• ISSN: 0968-4328; 1878-4291
• DOI: 10.1016/j.micron.2008.07.006

Valence EELS combined with STEM provides an approach to determine the dielectric constant of materials in the optical range of frequencies. The paper describes the experimental procedure and discusses the critical aspects of valence electron energy-loss spectroscopy (VEELS) treatment. In particular, the relativistic losses might affect strongly the results, and therefore they have to be subtracted from the spectra prior the analysis. The normalization of the energy-loss function is performed assuming an uniform thickness of the investigated area, which is reasonably fulfilled for carefully prepared FIB samples. This procedure requires the presence of at least one reference material with known dielectric properties to determine the absolute thickness. Examples of measuring the dielectric constant for several materials and structures are presented.