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Cerenkov losses in Valence EELS, pesented at the int. EELS-workshop EDGE 2005 in Grundlsee, Austria

VEELS is short for Valence Electron Energy Loss Spectrometry and deals with th low loss part of the energy loss spectrum in the range of 0-50 eV.

VEELS is used for detecting bandgaps or for characterizing optical properties of materials. Because of the high operation voltage of a TEM which accelerates the electrons to 0.7 times the speed of light, relativistic effects can be observed in the loss spectrum hampering the determination of bandgaps and optical properties.

The theory of VEELS based on  Maxwell's theory was described by Erhard Kröger (Zeitschrift für Physik, 216 (1968), S. 115-135), but was forgotten throughout the years. The reason might ly in the bad spatial and energy resolution available experimentally in the late 60s of the 20th century. Todays instruments achieve both, excellent spatial and fantastic energy resolutions. The team of USTEM re-described in 2004 these relativistic effects and presented first results at the international EELS workshop EDGE 2005 in Grundlsee, Austria,   (Cerenkov losses in valence EELS, M. Stöger-Pollach et. al). Since then retardation losses are a hot topic in EELS research.

A main research field of USTEM is therefore  - beside the detection of magnetic circular dichroism in the TEM  and low voltage EELS - ther experimental and mathematical removal of retardation losses in the EELS spectrum to keep on top in future times in VEELS.

On behalf of completeness a list of foreign literature can be found at the end of this page.

For detailled information please contact Dr. Michael Stöger-Pollach.


Publications in peer-reviewed journals:

  1. Cerenkov losses: A limit for bandgap determination and Kramers-Kronig analysis
    M. Stöger-Pollach, H. Franco, P. Schattschneider, S. Lazar, B. Schaffer, W. Grogger, H.W. Zandbergen
    Micron, 37 (2006), 5; pp. 396 - 402

  2. Comment on "Investigation on optical properties of ZnO nanowires by electron energy-loss spectrocopy"
    M. Stöger-Pollach, T. Galek
    Micron, 37 (2006), 8; pp. 748 - 750

  3. Retardation Effects in Valence - EELS Spectra
    M. Stöger-Pollach, C. Hébert, P. Schattschneider, A. Laister
    Microscopy and Microanalysis, 12 (2006); pp. 1136  - 1137

  4. Numerical Aspects of Valence Electron Energy Loss Spectrometry
    T. Galek, C. Hébert, M. Stöger-Pollach, P. Schattschneider
    Microscopy and Microanalysis, 12 (2006); pp. 1180  - 1181

  5. The influence of relativistic energy losses on bandgap determination using valence EELS
    M. Stöger-Pollach, P. Schattschneider
    Ultramicroscopy, 107 (2007), 12; pp. 1178 - 1185

  6. Removing relativistic effects in EELS for the determination of optical properties
    M. Stöger-Pollach, A. Laister, P. Schattschneider, P. Potapov, H.J. Engelmann
    Springer Proc. in Phys. 120 (2007); 345-348

  7. Determination of dielectric permittivity from EELSpectra in semiconductors
    P.L. Potapov, H.J. Engelmann, E. Zschech, M. Stöger-Pollach
    Microscopy and Microanalysis 13 (2007); pp. 1252-1253

  8. Treating retardation effects in valence EELS spectra for Kramers–Kronig analysis
    M. Stöger-Pollach, A. Laister and P. Schattschneider
    Ultramicroscopy, 108 (2008), 5; pp. 439 - 444

  9. Optical properties and bandgaps from low loss EELS: pitfalls and solutions (review)
    M. Stöger-Pollach
    Micron, 39 (2008); pp. 1092-1110

  10. Measuring the dielectric constant from valence EELS
    P. Potapov, H.J. Engelmann, E. Zschech, M. Stöger-Pollach
    Micron, 40 (2009); pp.262-268

Invited talks:

  1. Determination of optical properties and bandgaps by means of EELS
    M. Stöger-Pollach
    Seminar: AMD Environmental, Health & Safety, Dresden, BRD; 13.03.2006

  2. Optical properties from low loss spectra - pitfalls and soltions
    M. Stöger-Pollach
    int. workshop on "New trends in electron microscopy", Max-Planck-Institute for Metals Research-Stuttgart,  Ringberg Castle, Germany; 07.03.2007 - 09.03.2007

  3. Theory of valence electron losses
    P. Schattschneider
    Internat. workshop on "New trends in electron microscopy", Max-Planck-Institute for Metals Research-Stuttgart,  Ringberg Castle, Germany; 07.03.2007 - 09.03.2007

  4. Kramers-Kronig Analysis of VEELS spectra from semiconducting materials
    M. Stöger-Pollach
    Seminar: Imperial College London / London Centre for Nanotechnology, London, UK, 22nd Febuary 2008

  5. Optical properties measured with fast electrons and high spatial resolution
    M. Stöger-Pollach
    Seminar: Institut für Festkörperphysik, TU Wien, Austria; 9th April 2008

  6. The dielectric function obtained with high spatial resolution
    M. Stöger-Pollach and P. Schattschneider
    60th IUVSTA workshop: "Low Energy Spectroscopy and Simulation", Vienna, Austria, 11th-13th Nov. 2009

  7. Erweiterungen der analytischen Methoden des TEM: Untersuchungen der optischen und magnetischen Eigenschaften mit hoher Ortsauflösung
    M. Stöger-Pollach
    Seminar: Forschungsplattform Material- und Nanowissenschaften, Innsbruck, Austria, 3rd December 2009

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Recent literature from other research groups:

As can be seen, other EELS-research groups started working on this topic later than USTEM.  This demonstrates once the actuality of this topic and second it shows that USTEM has a lead over other groups in VEELS.

(Papers with * cite our work.)

  1. Band-gap measurements of direct and indirect semiconductors using monochromated electrons*
    L. Gu,V. Srot, W. Sigle, C. Koch, P. van Aken, F. Scholz, S.B. Thapa, C. Kirchner, M. Jetter, M. Rühle
    Phys. Rev. B, 75 (2007), pp. 195214

  2. Competition between Interface and Bulk Modes in Valence EELS of Thin Films*
    Martin Couillard, Aycan Yurtsever and David A. Muller
    Microscopy and Microanalysis 13 Supp.2 (2007), pp. 1246-1247

  3. Retardation, Surface and Interface Effects in VEELS
    R. Erni, N. D. Browning, P. Specht, and C. Kisielowski
    Microscopy and Microanalysis 13 Supp.2 (2007), pp. 1250-1251

  4. Bandgap measurement of dielectric thin films by using monochromated STEM-EELS*
    J. Park, S. Heo, J.G. Chung, H. Kim, G.-S. Park
    Microscopy and Microanalysis 13 Supp.2 (2007), pp. 1306-1307

  5. Analytical Performance of the SESAM Microscope*
    E Essers, M Matijevic, G Benner, R Höschen, W Sigle, C Koch
    Microscopy and Microanalysis
    13 Supp.3 (2007), pp. 18-19

  6. Low-loss EELS measurements with monochromated electrons*
    G. Kothleitner, W. Grogger, F. Hofer, B. Schaffer
    Microscopy and Microanalysis 13 Suppl. 3 (2007), pp. 46-47

  7. Low-k material characterization with high spatial resolution: K value and e modulus*
    Zschech, E., Potapov, P., Chumakov, D., Engelmann, H.-J., Geisler, H., Sukharev, V.
    AIP Conference Proceedings 945 (2007), pp. 142-151

  8. Multiple-interface coupling effects in local electron-energy-loss measurements of band gap energies *
    Couillard, M., Kociak, M., Stéphan, O., Botton, G.A., Colliex, C.
    Physical Review B  76 (2007), pp. 165131

  9. Nano-characterisation of dielectric breakdown in the various advanced gate stack MOSFETs*
    K.L. Pey, C.H. Tung, R. Ranjan, V.L. Lo, M. MacKenzie, A.J. Craven
    Int. Journal of Nanotechnology 4 (2007), pp. 347-376

  10. The impact of surface and retardation losses on valence electron energy-loss spectroscopy*
    R. Erni and N.D. Browning
    Ultramicroscopy, 108 (2008), pp. 84-99

  11. Prospects for analyzing the electronic properties in nanoscale systems by VEELS
    Rolf Erni, Sorin Lazar and Nigel D. Browning
    Ultramicroscopy, 108 (2008), pp. 270-276

  12. Competition between bulk and interface plasmonic modes in valence electron energy-loss spectroscopy of ultrathin SiO2 gate stacks*
    M. Couillard, A. Yurtsever, and D. A. Muller
    Phys. Rev. B 77 (2008), pp. 085318 1-8

  13. Advanced Monochromatic STEM for Nano-Electronics Industry Applications*
    C.H. Tung, M. Bosman and C.K. Cheng
    Microscopy and Analysis 22 EU (2008), pp. 5-8

  14. Nanomaterial electronic structure investigation by valence electron energy loss spectroscopy - An example of doped ZnO nanowires*
    J. Wang, Q. Li, C. Ronning, D. Stichtenoth, S. Müller, D. Tang
    Micron 39 (2008), pp. 703-708

  15. Optimizing EELS acquisition*
    M. Bosman and V.J. Keast
    Ultramicroscopy 108 (2008), pp. 837-846

  16. Formation of guided Cherenkov radiation in silicon-based nanocomposites*
    A. Yurtsever, M. Couillard, D.A. Muller
    Physical Review Letters 100 (2008), art. no. 217402

  17. Dielectric properties of Ti2AlC and Ti2AlN MAX phases: The conductivity anisotropy*
    N. Haddad, E. Garcia-Caurel, L. Hultman, M.W. Barsoum, G. Hug
    Journal of Applied Physics 104 (2008), art. no. 023531

  18. Retrieving the dielectric function of diamond from valence electron energy-loss spectroscopy*
    L. Zhang, R. Erni, J. Verbeeck, G. Van Tendeloo
    Physical Review B
    77 (2008), art. no. 195119

  19. The Theory and Interpretation of Electron Energy Loss Near-Edge Fine Structure*
    Peter Rez, David A. Muller
    Annual Review of Materials Research 38 (2008); 535-558

  20. Electron low energy-loss functions of Pb (Mg1/3 Nb2/3) O3: Theory and experiment*
    Ning Lu and Jing Zhu
    Journal of Applied Physics 104 (2008); 034109

  21. Analysis of VEEL spectra of diamond using a dedicated STEM: isolation of Cerenkov loss contributions*
    Eccles JWL, Bangert U
    Journal of Physics Conf. Ser. 126 (2008);  12004

  22. Towards measuring bandgap inhomogeneities in InAs/GaAs quantum dots*
    Kadkhodazadeh S, Ashwin MJ, Jones TS, McComb D
    Journal of Physics Conf. Ser. 126 (2008);  12049

  23. Electron energy-loss spectroscopy in the TEM*
    Raymond F Egerton
    Rep. Prog. Phys. 72 (2009); art. no. 016502

  24. The dielectric response of the H2TiO7 nanotube invstigated by valence electron energy loss spectrometry*
    Junag Wang, Quan Li, L.M. Peng and Marek Malak
    Applied Phys. Lett. 94 (2009) 011915

  25. Structure and bonding at the atomic scale by scanning transmission electron microscopy*
    David A. Muller
    Nature Materials 8 (2009); 263-270

  26. Optical excitations in electron microscopy*
    F.J. García de Abajo
    Review of Modern Physics, 82 (2010); pp. 209-275

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