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The boundary conditions between spatially dispersive media
A427 Surface Science 112 (1981) 133-152 North-Holland Publishing C o m p a n y
133
R E C O N S T R U C T I O N OF TIlE O X Y G E N - C O V E R E D Cu( 110} S U R F A C E IDENTIFIED W I T H LOW ENERGY Ne + A N D I-I20 + I O N SCA'I'TERING R.P.N. B R O N C K E R S a n d A.G.J. D E WIT Fysisch Laboratorium der Rijksuniversiteit Utrecht, Princetonplein 5, 3538 CC Utrecht, The Netherlands Received 18 December 1980; accepted for publication 17 June 1981 The structure of the oxygen-covered Cu{ 110} surface was investigated using low energy (keV region) Ne ÷ and H 2 0 + bombardment. This involved measuring photograms and ~-ff diagrams of scattered Ne ÷ and O - ions and of positively and negatively charged oxygen recoil ions. The adsorbate-induced structure was studied by the methods described in our earlier papers. The oxygen covered surface was found to be reconstructed. The reconstruction can be described by the "missing row" model, in which all {100) atom rows adjacent to the oxygen-containing (100) rows have disappeared from the surface. The lateral position of chemisorbed oxygen atoms is found in the bridge position in the ~ 100) surface row. The Cu atoms in the oxygen-containing surface rows are in the same positions as they were on the clean surface. This reconstruction can explain the (2 × I) LEED pattern observed for oxygen-covered surfaces, since the unit cell in the reconstructed surface is twice as large as the unit cell of the clean surface. The m a x i m u m coverage degree for exposures up to 100 L is found to be one oxygen atom per unit cell of the reconstructed surface. From the differences between the photograms of O - and of O + recoil ions it is deduced that there may be a second kind of adsorption site in the first two surface layers where oxygen can become chemisorbed. It is suggested that this site is near the second layer, below the position of the missing row in the surface.
Surface Science 112 (1981) 153-167 North-Holland Publishing C o m p a n y
153
T H E B O U N D A R Y C O N D I T I O N S B E T W E E N SPATIALLY DISPERSIVE MEDIA A.D. B O A R D M A N * Department of Pure and Applied Physics, University of Salford, Salford M5 4 WT, UK and
R. R U P P I N ** Department of Physics, University of California, lrvine, California 92717, USA Received 16 February 1981; accepted for publication 7 July 1981 The additional boundary conditions that apply at the interface between two spatially dispersive media are derived from macroscopic models. For a metal-metal interface the hydrodynamic model is used, and for the general dielectric-dielectric interface an isotropic dielectric solid model is employed. It is found that if certain physically acceptable boundary conditions are used, the continuity of the normal component of the energy current density is automatically ensured. Thus, some previously derived additional boundary conditions, based on energy current arguments, are unnecessary. As an example the dispersion curves of the interface plasmon-polaritons at a p o t a s s i u m - a l u m i n i u m boundary are calculated.
133
R E C O N S T R U C T I O N OF TIlE O X Y G E N - C O V E R E D Cu( 110} S U R F A C E IDENTIFIED W I T H LOW ENERGY Ne + A N D I-I20 + I O N SCA'I'TERING R.P.N. B R O N C K E R S a n d A.G.J. D E WIT Fysisch Laboratorium der Rijksuniversiteit Utrecht, Princetonplein 5, 3538 CC Utrecht, The Netherlands Received 18 December 1980; accepted for publication 17 June 1981 The structure of the oxygen-covered Cu{ 110} surface was investigated using low energy (keV region) Ne ÷ and H 2 0 + bombardment. This involved measuring photograms and ~-ff diagrams of scattered Ne ÷ and O - ions and of positively and negatively charged oxygen recoil ions. The adsorbate-induced structure was studied by the methods described in our earlier papers. The oxygen covered surface was found to be reconstructed. The reconstruction can be described by the "missing row" model, in which all {100) atom rows adjacent to the oxygen-containing (100) rows have disappeared from the surface. The lateral position of chemisorbed oxygen atoms is found in the bridge position in the ~ 100) surface row. The Cu atoms in the oxygen-containing surface rows are in the same positions as they were on the clean surface. This reconstruction can explain the (2 × I) LEED pattern observed for oxygen-covered surfaces, since the unit cell in the reconstructed surface is twice as large as the unit cell of the clean surface. The m a x i m u m coverage degree for exposures up to 100 L is found to be one oxygen atom per unit cell of the reconstructed surface. From the differences between the photograms of O - and of O + recoil ions it is deduced that there may be a second kind of adsorption site in the first two surface layers where oxygen can become chemisorbed. It is suggested that this site is near the second layer, below the position of the missing row in the surface.
Surface Science 112 (1981) 153-167 North-Holland Publishing C o m p a n y
153
T H E B O U N D A R Y C O N D I T I O N S B E T W E E N SPATIALLY DISPERSIVE MEDIA A.D. B O A R D M A N * Department of Pure and Applied Physics, University of Salford, Salford M5 4 WT, UK and
R. R U P P I N ** Department of Physics, University of California, lrvine, California 92717, USA Received 16 February 1981; accepted for publication 7 July 1981 The additional boundary conditions that apply at the interface between two spatially dispersive media are derived from macroscopic models. For a metal-metal interface the hydrodynamic model is used, and for the general dielectric-dielectric interface an isotropic dielectric solid model is employed. It is found that if certain physically acceptable boundary conditions are used, the continuity of the normal component of the energy current density is automatically ensured. Thus, some previously derived additional boundary conditions, based on energy current arguments, are unnecessary. As an example the dispersion curves of the interface plasmon-polaritons at a p o t a s s i u m - a l u m i n i u m boundary are calculated.