Abstract
We have studied electronic excitations at the surfaces of NiO (100), Cr2O3(111), and Al2O3(111) thin films with Electron Energy Loss Spectroscopy (EELS). On NiO (100) we observe surface electronic excitations in the energy range of the band gap which shift upon adsorption of NO. Ab initio cluster calculations show that these excitations occur within the Ni ions at the oxide surface. The (111) surface of Cr2O3 is characterized by distinct excitations which are also strongly influenced by the interaction with adsorbates. Temperature-dependent measurements show that two different states of the surface exist which are separated by an activation energy of about 10 meV. For Al2O3(111) we present data for a CO adsorbate. The oxide is quite inert with respect to CO adsorption as indicated by desorption temperatures between 38 K and 67 K. Due to the weak interaction with the substrate the a3II valence excitation of CO shows a clearly detectable vibrational splitting which has not been observed previously for a CO adsorbate in the (sub)monolayer coverage range. For several different adsorption state the lifetimes of the a3II state could be estimated from the halfwidths of the loss peaks, yielding values between ≈10−15 s for the most strongly bound species and ≈10−14 s for the CO multilayer.
Similar content being viewed by others
References
H. Ibach, D.L. Mills: Electron Energy Loss Spectroscopy and Surface Vibrations (Academic, New York 1982)
R.E. Palmer, P.J. Rous: Rev. Mod. Phys. 64, 383 (1992)
L. Sanche: J. Phys. B 23, 1597 (1990)
H.-J. Freund, R.P. Messmer, W. Spiess, H. Behner, G. Wedler, C.M. Kao: Phys. Rev. B 33, 5228 (1986)
F.P. Netzer, J.U. Mack, E. Bertel, J.A.D. Matthew: Surf. Sci. Lett. 160, 509 (1985)
F.P. Netzer, J.U. Mack: J. Chem. Phys. 79, 1017 (1983)
B.E. Koel, D.E. Peebles, J.M. White: Surf. Sci. 125, 739 (1983)
C. Xu, B. Dillmann, H. Kuhlenbeck, H.J. Freund: Phys. Rev. Lett. 67, 3551 (1991)
H. Kuhlenbeck, G. Odörfer, R. Jaeger, C. Xu, T. Mull, B. Baumeister, G. Illing, M. Menges, H.-J. Freund, D. Weide, P. Andresen, G. Watson, E.W. Plummer: Vacuum 41, 34 (1990)
R.M. Jaeger, H. Kuhlenbeck, H.-J. Freund, M. Wuttig, W. Hoffmann, R. Franchy, H. Ibach: Surf. Sci. 259, 235 (1991)
M. Wuttig, W. Hoffmann, R. Jaeger, H. Kuhlenbeck, H.-J. Freund: Mater. Res. Soc. Symp. Proc. (MRSPD4) 221, 143 (1991)
H. Kuhlenbeck, G. Odörfer, R. Jaeger, G. Illing, M. Menges, Th. Mull, H.-J. Freund, M. Pöhlchen, V. Staemmler, S. Witzel, C. Scharfschwerdt, K. Wennemann, T. Liedtke, M. Neumann: Phys. Rev. B 43, 1969 (1991)
M. Bäumer, D. Cappus, H. Kuhlenbeck, H.-J. Freund, G. Wilhelmi, A. Brodde, H. Neddermeyer: Surf. Sci. 253, 116 (1991)
M. Bäumer, D. Cappus, G. Illing, H. Kuhlenbeck, H.-J. Freund: J. Vac. Sci. Technol. A 10, 2407 (1992)
C.G. Kinniburgh, J.A. Walker: Surf. Sci. 63, 274 (1977)
M. Prutton, J.A. Walker, M.R. Welton-Cook, R.C. Felfon, J.A. Ramsey: Surf. Sci. 89, 95 (1979)
P.A. Redhead: Vacuum 12, 203 (1962)
A. Freitag, V. Staemmler, D. Cappus, C.A. Ventrice, Jr, K. Al-Shamery, H. Kuhlenbeck, H.-J. Freund: Chem. Phys. Lett. 210, 10 (1993)
D. Cappus, C. Xu, D. Ehrlich, B. Dillmann, C.A. Ventrice, Jr, K. Al-Shamery, H. Kuhlenbeck, H.-J. Freund: Chem. Phys. 177, 533 (1993)
D. Adler, J. Feinleib: Phys. Rev. B 2, 3112 (1970)
R. Newman, R.M. Chrenko: Phys. Rev. 114, 1507 (1959)
P.A. Cox, A.A. Williams: Surf. Sci. 152, 791 (1985)
J.P. Kemp, S.T.P. Davies, P.A. Cox: J. Phys. Condens. Matter 1, 5313 (1989)
J. Wasilewski: Int. J. Quantum Chem. 36, 503 (1989)
U. Meier, V. Staemmler: Theoret. Chim. Acta 76, 95 (1989)
V. Staemmler, R. Jaquet: Theoret. Chim. Acta 59, 487 (1981)
R. Fink, V. Staemmler: Theoret. Chim. Acta 87, 129 (1993)
A. Gorschlüter, H. Merz: Int. J. Mod. Phys. B 7, 341 (1993)
C. Xu, M. Haßel, H. Kuhlenbeck, H.-J. Freund: Surf. Sci. 258, 23 (1991)
H. Kuhlenbeck, C. Xu, B. Dillmann, M. Haßel, B. Adam, D. Ehrlich, S. Wohlrab, H.-J. Freund, U.A. Ditzinger, H. Neddermeyer, M. Neuber, M. Neumann: Ber. Bunsenges. Phys. Chem. 96, 15 (1992)
D. Ehrlich: Unpublished
D.S. McClure: In Electronic States of Inorganic Compounds: Experimental Techniques, ed. by P. Day (Reidel, Dordrecht 1975) pp. 113–139
Y. Sakisaka, H. Kato, M. Onchi: Surf. Sci. 120, 150 (1982)
G. Smith: Phys. Chem. Miner. 3, 375 (1978)
G. Amthauer, G.R. Rossmann: Phys. Chem. Miner. 11, 37 (1984)
S.M. Mattson, G.R. Rossmann: Phys. Chem. Miner. 14, 163 (1987)
D.S. McClure: Solid State Phys. 9, 399 (1959)
D.S. McClure: J. Chem. Phys. 38, 2289 (1963)
S. Sugano, Y. Tanabe, H. Kamimura: Multiplets of Transition Metal Ions in Crystals (Academic, New York 1970)
C. Xu: Adsorption und Reaktion kleiner Moleküle auf Cr2O3(111)/Cr(110). Dissertation, Ruhr-Universität Bochum, Bochum (1991)
Gmelins Handbuch der anorganischen Chemie, Vol. 52 B (Verlag Chemie, Weinheim 1962) p. 38
H. Isern, G.R. Castro: Surf. Sci. 211/212, 865 (1989)
R.M. Jaeger, H. Kuhlenbeck, H.-J. Freund: Chem. Phys. Lett. 203, 41 (1993)
R.M. Jaeger: Adsorptionsuntersuchungen an epitaktisch gewachsenen Al2O3/NiAl-Schichten. Dissertation, Ruhr-Universität Bochum, Bochum (1992)
R.M. Jaeger, J. Libuda, M. Bäumer, K. Homann, H. Kuhlenbeck, H.-J. Freund: J. Electron. Spectrosc. Relat. Phenom. 64/65, 217 (1993)
K. Homann, H. Kuhlenbeck: J. Electron. Spectrosc. Relat. Phenom. 62, 273 (1993)
N. Swanson, C.E. Kuyatt, J.W. Cooper, M. Krauss: Phys. Rev. Lett. 28, 948 (1972)
Gmelins Handbuch der anorganischen Chemie, Vol. C(1) (Verlag Chemie, Weinheim 1970) p. 183
J. Bahrdt, P. Gürtler, N. Schwentner: J. Chem. Phys. 86, 6108 (1987)
J. Bahrdt, N. Schwentner: J. Chem. Phys. 88, 2869 (1988)