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Spectroscopy with the Low Energy Electron Microscope

  • Rudolf TrompEmail author
Chapter
Part of the Springer Handbooks book series (SHB)

Abstract

Photo electron emission microscopy (PEEM), going back to the earliest days of electron microscopy, and low-energy electron microscopy (LEEM), successfully deployed since the late 1980s, are examples of cathode lens microscopy in which the sample itself is an integral part of the image forming system. While applications have naturally gravitated towards the acquisition of images to elucidate structure and structural evolution, recent years have also seen a rapidly expanding range of spectroscopic capabilities. These address, for example, the occupied and unoccupied electronic band structures of materials, electrical transport in 2-D systems, crystal growth and 2-D strain, inelastic electron energy loss mechanisms, as well as radiation damage in organic materials during low-energy electron irradiation. In this chapter, we discuss applications of these new spectroscopic methods, as well as recent instrumental developments that further expand the potential uses of cathode lens microscopy.

Keywords

Spectroscopy low energy electron microscopy Cathode LENS electron mirror LEEM-IV angle resolved reflected electron spectroscopy potentiometry spot-profile analysis electron energy loss spectroscopy radiation effects electron-volt TEM 

Notes

Acknowledgements

The author is grateful to Jim Hannon, Michael Altman, Sense Jan van der Molen, Jan Aarts, Alexander van der Torren, Johannes Jobst, Daniel Geelen, and Eugene Krasovskii for their generous support and assistance in putting this chapter together. Thanks are also due to Ernst Bauer for numerous discussions and inspiration.

References

  1. O. Hayes Griffith, W. Engel: Historical perspective and current trends in emission microscopy, mirror electron microscopy and low-energy electron microscopy, Ultramicroscopy 36, 1–28 (1991)Google Scholar
  2. E. Bauer: Surface Microscopy with Low Energy Electrons (Springer, Berlin 2014)Google Scholar
  3. E. Brüche: Elektronenmikroskopische Abbildung mit lichtelektrischen Elektronen, Z. Phys. 86, 448 (1933)Google Scholar
  4. M. Knoll, E. Ruska: Das Elektronenmikroskop, Z. Phys. 78, 318–339 (1932)Google Scholar
  5. D. Gabor: The Electron Microscope—Its Development, Present Performance and Future Possibilities (Chemical Publishing, Brooklyn, New York 1948)Google Scholar
  6. P.W. Hawkes: The long road to spherical aberration correction, Biol. Cell 93, 432–439 (2001)Google Scholar
  7. W. Engel: Emission microscopy with different kinds of electron emission. In: Proc. 6th Intern. Congr. Electron Microsc., Kyoto, ed. by R. Ueda (Maruzen, Tokyo 1966) pp. 217–218Google Scholar
  8. E. Bauer: A brief history of PEEM, J. Electron Spectrosc. Relat. Phenom. 185, 314–322 (2012)Google Scholar
  9. L. Mayer: Electron mirror microscopy of magnetic domains, J. Appl. Phys. 28, 975–983 (1957)Google Scholar
  10. A.E. Luk'yanov, G.V. Spivak, R.S. Gvozdover: Mirror electron microscopy, Sov. Phys. Usp. 16, 529–552 (1973)Google Scholar
  11. W. Telieps, E. Bauer: An analytical reflection and emission UHV surface electron microscope, Ultramicroscopy 17, 57–66 (1985)Google Scholar
  12. R.M. Tromp, M.C. Reuter: Design of a new photo-emission/low-energy electron microscope for surface studies, Ultramicroscopy 36, 99–106 (1991)Google Scholar
  13. L.H. Veneklasen: Design of a spectroscopic low-energy electron microscope, Ultramicroscopy 36, 76–90 (1991)Google Scholar
  14. M.S. Altman, H. Pinkvos, J. Hurst, H. Poppa, G. Marx, E. Bauer: Polarized low energy electron microscopy of surface magnetic structure, Mater. Res. Soc. Symp. Proc. 232, 125 (1991)Google Scholar
  15. G.F. Rempfer, D.M. Desloge, W.P. Skoczylas, O.H. Griffith: Simultaneous correction of spherical and chromatic aberrations with an electron mirror: an electron optical achromat, Microsc. Microanal. 3, 14–27 (1997)Google Scholar
  16. R. Fink, M.R. Weiss, E. Umbach, D. Preikszas, R. Spehr, P. Hartel, W. Engel, R. Degenhardt, R. Wichtendahl, H. Kuhlenbeck, K. Ihmann, R. Schlögl, H.-J. Freund, A.M. Bradshaw, T. Schmidt, E. Bauer, G. Benner: SMART: a planned ultrahigh-resolution spectromicroscope for BESSY II, J. Electron Spectrosc. Relat. Phenom. 84, 231–250 (1997)Google Scholar
  17. R.M. Tromp, J.B. Hannon, A.W. Ellis, W. Wan, A. Berghaus, O. Schaff: A new aberration-corrected, energy-filtered LEEM/PEEM instrument. I. Principles and design, Ultramicroscopy 110, 852–861 (2010)Google Scholar
  18. R.M. Tromp, J.B. Hannon, W. Wan, A. Berghaus, O. Schaff: A new aberration-corrected, energy-filtered LEEM/PEEM instrument. II. Operation and results, Ultramicroscopy 127, 25–39 (2013)Google Scholar
  19. T. Schmidt, H. Marchetto, P.L. Lévesque, U. Groh, F. Maier, D. Preikszas, P. Hartel, R. Spehr, G. Lilienkamo, W. Engel, R. Fink, E. Bauer, H. Rose, E. Umbach, H.-J. Freund: Double aberration correction in a low-energy electron microscope, Ultramicroscopy 110, 1358–1361 (2010)Google Scholar
  20. R. Comin, A. Damascelli: ARPES: a probe of electronic correlations. In: Strongly Correlated Systems, Springer Series in Solid-State Sciences, Vol. 180, ed. by A. Avella, F. Mancini (Springer, Berlin 2014) pp. 31–71Google Scholar
  21. Y. Fujikawa, T. Sakurai, R.M. Tromp: Micrometer-scale band mapping of single silver islands in real and reciprocal space, Phys. Rev. B 79, 121401 (2009)Google Scholar
  22. C. Tusche, M. Ellguth, A. Krasyuk, A. Winkelmann, D. Kutnyakhov, P. Luschyk, K. Medjanik, G. Schönhense, J. Kirchner: Quantitative spin polarization analysis in photoelectron emission microscopy with an imaging spin filter, Ultramicroscopy 130, 70–76 (2013)Google Scholar
  23. G. Schönhense, K. Medjanik, H.-J. Elmers: Space-, time- and spin-resolved photoemission, J. Electron Spectrosc. Relat. Phenom. 200, 94–118 (2015)Google Scholar
  24. E. Bauer: The resolution of the low energy electron reflection microscope, Ultramicroscopy 17, 51 (1985)Google Scholar
  25. G.F. Rempfer, O.H. Griffith: The resolution of photoelectron microscopes with UV, X-ray, and synchrotron excitation sources, Ultramicroscopy 27, 273–300 (1989)Google Scholar
  26. A.B. Pang, T. Müller, M.S. Altman, E. Bauer: Fourier optics of image formation in LEEM, J. Phys. Condens. Matter 21, 314006 (2009)Google Scholar
  27. S.M. Kennedy, N.E. Schofield, D.M. Paganin, D.E. Jesson: Wave optical treatment of surface step contrast in low-energy electron microscopy, Surf. Rev. Lett. 16, 855–867 (2009)Google Scholar
  28. S.M. Schramm, A.B. Pang, M.S. Altman, R.M. Tromp: A contrast transfer function approach for image calculations in standard and aberration-corrected LEEM and PEEM, Ultramicroscopy 115, 88–108 (2012)Google Scholar
  29. R.M. Tromp, W. Wan, S.M. Schramm: Aberrations of the cathode objective lens up to fifth order, Ultramicroscopy 119, 33–39 (2012)Google Scholar
  30. J.B. Hannon, J. Sun, K. Pohl, G.L. Kellogg: Origins of nanoscale heterogeneity in ultrathin films, Phys. Rev. Lett. 96, 246103 (2006)Google Scholar
  31. J.I. Flege, E.E. Krasovskii: Intensity-voltage low-energy electron microscopy for functional materials characterization, Phys. Status Solidi Rapid Res. Lett. 8, 463–477 (2014)Google Scholar
  32. J. Jobst, J. Kautz, D. Geelen, R.M. Tromp, S.J. van der Molen: Nanoscale measurements of unoccupied band dispersion in few-layer graphene, Nature Commun. 6, 8926 (2015)Google Scholar
  33. J. Jobst, A.J.H. van der Torren, E.E. Krasovskii, J. Balgley, C.R. Dean, R.M. Tromp, S.J. van der Molen: Quantifying electron band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy, Nature Commun. 7, 13621 (2016)Google Scholar
  34. M. Henzler: LEED studies of surface imperfections, Appl. Surf. Sci. 11/12, 450–469 (1982)Google Scholar
  35. T.-M. Lu, M.G. Lagally: Diffraction from surfaces with randomly distributed steps, Surf. Sci. 120, 47–66 (1982)Google Scholar
  36. A.J.H. van der Torren: Growing Oxide Thin Films in a Low-Energy Electron Microscope, Ph.D. Thesis (Leiden Univ., Leiden 2016)Google Scholar
  37. K.L. Man, M.S. Altman: Small-angle lattice rotations in graphene on Ru(0001), Phys. Rev. B 84, 235415 (2011)Google Scholar
  38. J. Kautz, J. Jobst, C. Sorger, R.M. Tromp, H.B. Weber, S.J. van der Molen: Low-energy electron potentiometry: Contactless imaging of charge transport on the nanoscale, Sci. Rep. 5, 13604 (2015)Google Scholar
  39. L. Reimer (Ed.): Energy-Filtering Transmission Electron Microscopy (Springer, Berlin 1994)Google Scholar
  40. Y. Fujikawa, T. Sakurai, R.M. Tromp: Surface plasmon microscopy using an energy-filtered low energy electron microscope, Phys. Rev. Lett. 100, 126803 (2008)Google Scholar
  41. J. Sun, J.B. Hannon, R.M. Tromp, P. Johari, A.A. Bol, V.B. Shenoy, K. Pohl: Spatially-resolved structure and electronic properties of graphene on polycrystalline Ni, ACS Nano 4, 7073–7077 (2010)Google Scholar
  42. A. Thete, D. Geelen, S. Wuister, S.J. van der Molen, R.M. Tromp: Low-energy electron (0-100 eV) interaction with resists using LEEM, Proc. SPIE 9422, 94220A (2015)Google Scholar
  43. S. Bhattarai, A.R. Neureuther, P.A. Naulleau: Study of energy delivery and mean free path of low energy electrons in EUV resists, Proc. SPIE 9779, 97790B (2016)Google Scholar
  44. A. Thete, D. Geelen, S.J. van der Molen, R.M. Tromp: Charge catastrophe and dielectric breakdown during exposure of organic thin films to low-energy electron radiation, Phys. Rev. Lett. 119, 266803 (2017)Google Scholar
  45. R.M. Tromp: Low-voltage transmission electron microscopy, US Patent 85869191 (2013)Google Scholar
  46. D. Geelen, A. Thete, O. Schaff, A. Kaiser, S.J. van der Molen, R.M. Tromp: eV-TEM: Transmission electron microscopy in a low energy cathode lens instrument, Ultramicroscopy 159, 482–487 (2015)Google Scholar
  47. S. Tanuma, C.J. Powell, D.R. Penn: Calculations of electron inelastic mean free paths. IX. Data for 41 elemental solids over the 50 eV to 30 keV range, Surf. Interface Anal. 43, 689–713 (2011)Google Scholar
  48. D. Gabor: A new microscopic principle, Nature 161, 777 (1948)Google Scholar
  49. C.J. Davisson, C.J. Calbick: Electron lenses, Phys. Rev. 42, 580 (1932)Google Scholar
  50. R.M. Tromp: Measuring and correcting aberrations of a cathode objective lens, Ultramicroscopy 111, 273–281 (2011)Google Scholar
  51. O. Scherzer: Über einige Fehler von Elektronenlinsen, Z. Phys. 101, 593–600 (1936)Google Scholar
  52. E. Abbe: Beiträge zur Theorie des Mikroskops und der mikroskopischen Wahrnehmung, Arch. Mikrosk. Anat. 9, 413–468 (1873)Google Scholar
  53. M. Herzberger, N.R. McClure: The design of superachromatic lenses, Appl. Opt. 2, 553–560 (1963)Google Scholar
  54. R.M. Tromp: Catadioptric aberration correction in cathode lens microscopy, Ultramicroscopy 151, 191–198 (2015)Google Scholar
  55. O. Scherzer: Sphärische and chromatische Korrektur von Elektronenlinsen, Optik 2, 114–132 (1947)Google Scholar
  56. A. Recknagel: Zur Theorie des Elektronenspiegels, Z. Phys. 104, 381–394 (1937)Google Scholar
  57. R. Rüdenberg: Electron lenses of hyperbolic field structure, J. Frankl. Inst. 246, 311–339–377–407 (1948)Google Scholar
  58. G.F. Rempfer: A theoretical study of the hyperbolic electron mirror as a correcting element for spherical and chromatic aberration in electron optics, J. Appl. Phys. 67, 6027–6040 (1990)Google Scholar
  59. W. Wan, J. Feng, H.A. Padmore, D.S. Robin: Simulation of a mirror corrector for PEEM3, Nucl. Instrum. Methods Phys. Res. A 519, 222–229 (2004)Google Scholar
  60. L. Wang, E. Munro, J. Rouse, H. Liu: Simulation of electron mirrors by the differential algebraic method, Phys. Procedia 1, 297–304 (2008)Google Scholar
  61. R.M. Tromp: Characterization of the cathode objective lens by real-space microspot low energy electron diffraction, Ultramicroscopy 130, 2–6 (2013)Google Scholar
  62. R.M. Tromp: An adjustable electron achromat for cathode lens microscopy, Ultramicroscopy 159, 497–502 (2015)Google Scholar
  63. R.M. Tromp, M.S. Altman: Defocus in cathode lens instruments, Ultramicroscopy 183, 2–7 (2017)Google Scholar
  64. S.M. Schramm, S.J. van der Molen, R.M. Tromp: Intrinsic instability of aberration-corrected electron microscopes, Phys. Rev. Lett. 109, 163901 (2012)Google Scholar
  65. J. Barthel, A. Thust: On the optical stability of high-resolution transmission electron microscopes, Ultramicroscopy 134, 6–17 (2013)Google Scholar
  66. R.M. Tromp, M. Mankos, M.C. Reuter, A.W. Ellis, M. Copel: A new low energy electron microscope, Surf. Rev. Lett. 5, 1189–1197 (1998)Google Scholar
  67. R. Könenkamp, R. Word, G.F. Rempfer, T. Dixon, L. Almaraz, T. Jones: 5.4 nm spatial resolution in biological photoemission electron microscopy, Ultramicroscopy 110, 899–902 (2010)Google Scholar
  68. R. Sissingh: Metingen over de Elliptische Polarisatie van het Licht (S.C. van Doesburgh, Leiden 1885)Google Scholar
  69. C.J. Davisson, L.H. Germer: Diffraction of electrons by a crystal of nickel, Phys. Rev. 30, 705–740 (1927)Google Scholar
  70. E.J. Scheibner, L.H. Germer, C.D. Hartman: Apparatus for direct observation of low-energy electron diffraction patterns, Rev. Sci. Instrum. 31, 112 (1960)Google Scholar
  71. W. Ehrenberg: A new method of investigating the diffraction of slow electrons by crystals, Lond. Edinb. Dublin Philos. Mag. J. Sci. 18(122), 878 (1934)Google Scholar
  72. G.P. Thomson, A. Reid: Diffraction of cathode rays by a thin film, Nature 119, 890 (1927)Google Scholar
  73. E. Ruska: The development of the electron microscope and of electron microscopy, Nobel Prize Lecture (1986)Google Scholar
  74. J.M. McLaren, J.B. Pendry, P.J. Rous, D.K. Saldin, G.A. Somorjai, M.A. van Hove, D.D. Vvedensky: Surface Crystallographic Information Service—A Handbook of Surface Structures (Springer, Dordrecht 1987)Google Scholar
  75. A.K. Schmid, W. Święch, C.S. Rastomjee, B. Rausenberger, W. Engel, E. Zeitler, A.M. Bradshaw: The chemistry of reaction-diffusion fronts investigated by microscopic LEED I–V fingerprinting, Surf. Sci. 331–333, 225–230 (1995)Google Scholar
  76. M. Li, J.B. Hannon, R.M. Tromp, J. Sun, J. Li, V. Shenoy, E. Chason: Equilibrium shapes of graphene domains on Ni(111), Phys. Rev. B 88, 041402(R) (2013)Google Scholar
  77. D. Jariwala, T.J. Marks, M.C. Hersam: Mixed-dimensional van der Waals heterostructures, Nature Mater. 16, 170–181 (2017)Google Scholar
  78. H. Hibino, H. Kageshima, F. Maeda, M. Nagase, K. Kobayashi, Y. Kobayashi, H. Yamaguchi: Microscopic thickness determination of thin graphite films formed on SiC from quantized oscillation in reflectivity of low-energy electrons, E-J. Surf. Sci. Nanotech. 6, 107–110 (2008)Google Scholar
  79. R.M. Feenstra, M. Widom: Low-energy electron reflectivity from graphene: first-principles computations and approximate models, Ultramicroscopy 130, 101–108 (2013)Google Scholar
  80. P.C. Mende, Q. Gao, A. Ismach, H. Chou, M. Widom, R. Ruoff, L. Colombo, R.M. Feenstra: Characterization of hexagonal boron nitride layers on nickel surfaces by low-energy electron microscopy, Surf. Sci. 659, 31–42 (2017)Google Scholar
  81. S.C. de la Barrera, Y.-C. Lin, S.M. Eicheld, J.A. Robinson, Q. Gao, M. Widom, R.M. Feenstra: Thickness characterization of atomically thin WSe2 on epitaxial graphene by low-energy electron reflectivity oscillations, J. Vac. Sci. Technol. B 34, 04J106 (2016)Google Scholar
  82. M.S. Altman, W.F. Chung, Z.Q. He, H.C. Poon, S.Y. Tong: Quantum size effect in low energy electron diffraction of thin films, Appl. Surf. Sci. 169–170, 82–87 (2001)Google Scholar
  83. W. Jin, P.-C. Yeh, N. Zaki, D. Zhang, J.T. Sadowski, A. Al-Mahboob, A.M. van der Zande, D.A. Chenet, J.I. Dadap, I.P. Herman, P. Sutter, J. Hone, R.M. Osgood Jr.: Direct measurement of the thickness-dependent electronic band structure of MoS2 using angle-resolved photoemission spectroscopy, Phys. Rev. Lett. 111, 106801 (2013)Google Scholar
  84. M. Escher, N. Weber, M. Merkel, C. Ziethen, P. Bernhard, G. Schönhense, S. Schmidt, F. Forster, F. Reinert, B. Krömker: Nanoelectron spectroscopy for chemical analysis, a novel energy filter for imaging x-ray photoemission microscopy, J. Phys. Condens. Matter 17, S1329–S1338 (2005)Google Scholar
  85. R.M. Tromp, Y. Fujikawa, J.B. Hannon, A.W. Ellis, A. Berghaus, O. Schaff: A simple energy filter for low energy electron microscopy/photoelectron emission microscopy, J. Phys. Condens. Matter 21, 314007 (2009)Google Scholar
  86. F.J. Himpsel, T. Fauster: Probing valence states with photoemission and inverse photoemission, J. Vac. Sci. Technol. A 2, 815–821 (1984)Google Scholar
  87. G. Denninger, V. Dose, H.P. Bonzel: Evidence for direct optical interband transitions in isochromat spectra from Pt single-crystal surfaces, Phys. Rev. Lett. 48, 279–282 (1982)Google Scholar
  88. D.W. Jepsen, P.M. Marcus, F. Jona: Low-energy-electron-diffraction spectra from [001] surfaces of face-centered cubic metals: theory and experiment, Phys. Rev. B 5, 3933–3952 (1972)Google Scholar
  89. P.J. Møller, M.H. Mohamed: Total current spectroscopy, Vacuum 35, 29–37 (1985)Google Scholar
  90. E.E. Krasovskii, W. Schattke, V.N. Strocov, R. Claessen: Unoccupied band structure of NbSe2 by very low-energy electron diffraction: Experiment and theory, Phys. Rev. B 66, 235403 (2002)Google Scholar
  91. T.O. Mentes, A. Locatelli: Angle-resolved X-ray photoemission electron microscopy, J. Electron Spectrosc. Relat. Phenom. 185, 323–329 (2012)Google Scholar
  92. O. Klemperer, W.D. Right: The investigation of electron lenses, Proc. Phys. Soc. 51, 296–317 (1939)Google Scholar
  93. P. Muralt, D.W. Pohl: Scanning tunneling potentiometry, Appl. Phys. Lett. 48, 514–516 (1986)Google Scholar
  94. A. Bannani, C. Bobisch, R. Möller: Local potentiometry using a multiprobe scanning tunneling microscope, Rev. Sci. Instrum. 79, 083704 (2008)Google Scholar
  95. S.-H. Ji, J.B. Hannon, R.M. Tromp, V. Perebeinos, J. Tersoff, F.M. Ross: Atomic-scale transport in epitaxial graphene, Nature Mater. 11, 114–119 (2012)Google Scholar
  96. A.L.F. Cauduro, R. dos Reis, G. Chen, A.K. Schmid, H.-G. Rubahn, M. Madsen: Work function mapping of MoOx thin-films for application in electronic devices, Ultramicroscopy 183, 99–103 (2017)Google Scholar
  97. J. Jobst, L.M. Boers, C. Yin, J. Aarts, R.M. Tromp, S.J. van der Molen: Quantifying work function differences using low-energy electron microscopy: The case of mixed-terminated strontium titanate, Ultramicroscopy 200, 43–49 (2019)Google Scholar
  98. C. Klein, T. Nabbefeld, H. Hattab, D. Meyer, M. Kammler, F.-J. Meyer zu Heringdorf, A. Golla-Franz, B.H. Müller, T. Schmidt, M. Henzler, M. Horn-von Hoegen: Lost in reciprocal space? Determination of the scattering condition in spot profile analysis low-energy electron diffraction, Rev. Sci. Instrum. 82, 035111 (2011)Google Scholar
  99. H. Ibach, D.L. Mills: Electron Energy Loss Spectroscopy and Surface Vibrations (Academic Press, London 1982)Google Scholar
  100. K.P. Weidkamp, R.M. Tromp, R.J. Hamers: Epitaxial growth of large pentacene crystals on Si(001) surfaces functionalized with molecular monolayers, J. Phys. Chem. C 111, 16489–16497 (2007)Google Scholar
  101. R.M. Tromp, M.C. Reuter: Wavy steps on Si(001), Phys. Rev. Lett. 68, 820–822 (1992)Google Scholar
  102. R.S. Becker, G.S. Higashi, Y.J. Chabal, A.J. Becker: Atomic-scale conversion of clean Si(111):H-1×1 to Si(111)-2×1 by electron-stimulated desorption, Phys. Rev. Lett. 65, 1917–1920 (1990)Google Scholar
  103. R.D. Ramsier, J.T. Yates Jr.: Electron-stimulated desorption: Principles and applications, Surf. Sci. Rep. 12, 243–378 (1991)Google Scholar
  104. V. Bakshi (Ed.): EUV Lithography (SPIE, Bellingham 2009)Google Scholar
  105. M. Pope, C.E. Swemberg: Electronic Processes in Organic Crystal and Polymers (Oxford Univ. Press, Oxford 1998)Google Scholar
  106. Y. Lin, D.C. Joy: A new examination of secondary electron yield data, Surf. Interface Anal. 37, 895–900 (2005)Google Scholar
  107. M.P. Seah, W.A. Dench: Quantitative electron spectroscopy of surfaces: A standard data base for electron inelastic mean free paths in solids, Surf. Interface Anal. 1, 2–11 (1979)Google Scholar
  108. H.W. Fink, H. Schmid, H.J. Kreuzer, A. Wierzbicki: Atomic resolution in lensless low-energy electron holography, Phys. Rev. Lett. 67, 1543 (1991)Google Scholar
  109. J.C.H. Spence, W. Qian, A.J. Melmed: Experimental low-voltage point-projection microscopy and its possibilities, Ultramicroscopy 52, 473–477 (1993)Google Scholar
  110. H. Hibino, H. Kageshima, F.-Z. Guo, F. Maeda, M. Kotsugi, Y. Watanabe: Two-dimensional emission patterns of secondary electrons from graphene layers formed on SiC(0001), Appl. Surf. Sci. 254, 7596 (2008)Google Scholar

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Authors and Affiliations

  1. 1.IBM T.J. Watson Research CenterYorktown Heights, NYUSA

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