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Classical surface rainbow scattering from a reconstructed W(001) surface
A384 Surface Science 157 (1985) 233-243 North-Holland, Amsterdam
233
AN ISS-XPS STUDY ON THE OXIDATION OF hl(lll); IDENTIFICATION OF STOICHIOMETRIC AND REDUCED
OXIDE
SURFACES C. O C A L , B. B A S U R C O
a n d S. F E R R E R
Departamento de F~tsica Fundamental e lnstituto de lqlsicadel Estado Sblido, Universidad A u t b n o m a de Madrid, Cantoblanco, 28049- Madrid, Spain
Received 31 August 1984; accepted for publication 27 December 1984
We have studied by ISS and XPS the initial stages of the 3D oxidation of AI(lll). We found that the incorporation of oxygen into the crystal bulk is well described by a second order process with an activation energy of 0.50+0.05 eV. XPS indicates that the chemical shift of the 2p emission upon oxidation varies from 2.6 to 3.7 eV depending on growth procedure and oxide thickness. The growth procedure also affects noticeably the surface composition. We have been able to prepare oxide surfaces with an important concentration of oxygen vacancies. The rate of growth, at low temperature of these defective oxides is several times larger than the rate exhibited by more perfect oxides. These results are discussed in the light of the Cabrera-Mott theory of oxidation of metals.
Surface Science 157 (1985) 245-260 North-Holland, Amsterdam CLASSICAL SURFACE RAINBOW SCATI'ERING RECONSTRUCTED W(001) SURFACE E. H U L P K E
245 FROM
A
a n d K. M A N N
M a x - Planck - lnstitut fft?" Str~mungsforschung, B~ttingerstrasse 4 - 8, D - 3400 G~ttingen, F e d Rep. of Germany
Received 4 December 1984; accepted for publication 12 March 1985 Hydrogen induced reconstruction forming the H(¢2 x v~)R45 ° phase has been found to have a strong influence on the angular distributions of K ÷ ions scattered from W(001) at energies between 10 and 30 eV. These changes in the measured surface rainbow structure result from the altered corrugation profile and because of the small concentration of adsorbed hydrogen can be attributed solely to the rearrangement of the W atoms. The K + scattering from the reconstructed surface has been applied to test the validity of different structure models. In order to improve these tests the scattering of K ÷ from W(ll0) has been used to serve as an experimental "calibration": parameters of the K + + W(ll0) interaction potential have been extracted from the scattering data and provide, together with the sti'ucture model, the basis for a molecular dynamics computer simulation of the scattering from the reconstructed surface. The experiments strongly favour the "dimer"-model for H(vr2- x ¢r2)R45° W(001), the displacements of the W atoms being slightly smaller than 0.2 A.
233
AN ISS-XPS STUDY ON THE OXIDATION OF hl(lll); IDENTIFICATION OF STOICHIOMETRIC AND REDUCED
OXIDE
SURFACES C. O C A L , B. B A S U R C O
a n d S. F E R R E R
Departamento de F~tsica Fundamental e lnstituto de lqlsicadel Estado Sblido, Universidad A u t b n o m a de Madrid, Cantoblanco, 28049- Madrid, Spain
Received 31 August 1984; accepted for publication 27 December 1984
We have studied by ISS and XPS the initial stages of the 3D oxidation of AI(lll). We found that the incorporation of oxygen into the crystal bulk is well described by a second order process with an activation energy of 0.50+0.05 eV. XPS indicates that the chemical shift of the 2p emission upon oxidation varies from 2.6 to 3.7 eV depending on growth procedure and oxide thickness. The growth procedure also affects noticeably the surface composition. We have been able to prepare oxide surfaces with an important concentration of oxygen vacancies. The rate of growth, at low temperature of these defective oxides is several times larger than the rate exhibited by more perfect oxides. These results are discussed in the light of the Cabrera-Mott theory of oxidation of metals.
Surface Science 157 (1985) 245-260 North-Holland, Amsterdam CLASSICAL SURFACE RAINBOW SCATI'ERING RECONSTRUCTED W(001) SURFACE E. H U L P K E
245 FROM
A
a n d K. M A N N
M a x - Planck - lnstitut fft?" Str~mungsforschung, B~ttingerstrasse 4 - 8, D - 3400 G~ttingen, F e d Rep. of Germany
Received 4 December 1984; accepted for publication 12 March 1985 Hydrogen induced reconstruction forming the H(¢2 x v~)R45 ° phase has been found to have a strong influence on the angular distributions of K ÷ ions scattered from W(001) at energies between 10 and 30 eV. These changes in the measured surface rainbow structure result from the altered corrugation profile and because of the small concentration of adsorbed hydrogen can be attributed solely to the rearrangement of the W atoms. The K + scattering from the reconstructed surface has been applied to test the validity of different structure models. In order to improve these tests the scattering of K ÷ from W(ll0) has been used to serve as an experimental "calibration": parameters of the K + + W(ll0) interaction potential have been extracted from the scattering data and provide, together with the sti'ucture model, the basis for a molecular dynamics computer simulation of the scattering from the reconstructed surface. The experiments strongly favour the "dimer"-model for H(vr2- x ¢r2)R45° W(001), the displacements of the W atoms being slightly smaller than 0.2 A.