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Backscattering correction for quantitative auger analysis
A109 Surface Science I 15 (1982) 237-246 North-Holland publishing Company
237
THE
ADSORPTION OF CARBON MONOXIDE O N Cu(ll0)-Ni SURFACES PREPARED BY DISSOCIATION OF NICKEL CARBONYL
C.M.A.M. MESTERS, A.F.H. WIELERS, J.W. GEUS and G.A. BOOTSMA *
O.L.J. GIJZEMAN,
Van 't Hoff Laboratory, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands Received 18 June 1981; accepted for publication 10 December 1981 Cu(110)-Ni surface alloys were prepared by dissociation of nickel carbonyl on clean Cu(110). The adsorption of CO is reversible in the temperature region of 22-200°C and the pressure range of 5 × 10-8-0.7 Torr, as monitored with ellipsometry and AES. The amount of adsorbed CO depends on the amount of preadsorbed oxygen but not on the amount of carbon present at the surface. The isosteric heat of adsorption decreases from 31 -+ 3 kcal/mole to 18 ± 2 kcal/mole with increasing CO coverage (up to 0 = 0.14 0ma,,) but is constant for higher coverages (up to 0 = 0.4 0m~,~l-
Surface Science 115 (1982) 247-258 North-Holland Publishing Company GAS-SURFACE
SCATI~RING
247 DISTRIBUTIONS
ACCORDING
TO
THE HARD-SPItEROID MODEL Christoph STEINBROCHEL
Laboratories RCA, Ltd., Badenerstrasse 569, CH-8048 Ziirich, Swttzerland Received 28 September 1981 ; accepted for publication 27 November 1981 Gas-surface scattering distributions are calculated on the basis of the hard-spheroid model. This new model is related to the hard-cube model but incorporates surface structure by letting the surface atoms have hard spherical caps. Surface structure is found to reduce the maximum scattered intensity and to broaden the scattering distribution. The decrease in the maximum scattered intensity is most pronounced for a light gas. Broadening is asymmetric relative to the direction of maximum scattered intensity in that backscattering towards the surface is favored. Adding surface structure to the hard-cube model improves significantly the agreement between model predictions and experimental results.
259
Surface Science 115 (1982) 259-269 North-Holland Publishing Company BACKSCATYERING ANALYSIS II.
CORRECTION
FOR QUANTITATIVE
Verifications of the backscattering factors through quantification
by
AES S. I C H I M U R A
a n d R. S H I M I Z U
Department of Applied Physics, Osaka University. Suita, Osaka 565, Japan and
AUGER
AllO T. I K U T A
Department of Applied Electronics, Osaka Electro-Communication Universi(v, Nevagawa, Osaka 572, Japan Received 3 June 1981; accepted for publication 17 November 1981 The validity and utility of the backscattering correction factors obtained from Monte Carlo calculations for quantitative analysis by Auger electron spectroscopy (AES) were examined through practical quantification of surface concentrations of binary alloys. Quantifications were attempted, first, to access the surface composition of a sputter-deposited Ni-Pt layer, which is probably the most appropriate test-sample with known surface composition for surface analysis. The quantification by AES has led to the result that the surface composition of the layer agrees well with the bulk composition of the sputtered Ni-Pt alloy, as expected. The composition of a sputtered Au-Cu alloy surface was, then, examined according to the same correction procedure as for the N i - P t layer, leading to the confirmation that no preferential sputtering is observed for Au-Cu alloys by AES as F~rber et al. reported.
270 ATOMIC
Surface Science 115 (1982) 270-278 North-Holland Publishing Company STRUCTURE
S. T O U G A A R D
OF THE SCANDIUM
(0001) SURFACE
* a n d A. I G N A T I E V
Department of Physics, University of Houston, Houston, Texas 77004, USA Received 2 November 1981 The atomic structure of the scandium (0001) surface has been determined through a lowenergy-electron-diffraction analysis. Intensity profiles calculated on the basis of different structural models corresponding to different terminations of the bulk structure were compared to the experimental data. The comparison showed that the surface of scandium terminated in hcp stacking and that the outermost layer soPacing is 2.59-+0.02 A corresponding to a - 2 % contraction with respect to the bulk spacing (2.64 A).
Surface Science 115 (1982) 279-289 North-Holland Publishing Company THE COADSORPTION J.B. B E N Z I G E R *
279
OF CO AND H 2 ON Fe(100)
a n d R.J. M A D I X
Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA Received 8 December 1980; accepted for publication 4 November 1981 The coadsorption of CO and hydrogen on an Fe(100) surface was studied by temperature programmed desorption and X-ray photoelectron spectroscopy. It was found that CO adsorption blocked the subsequent dissociative adsorption of H2, although it did not seem to affect the hydrogen binding energy. Preadsorption of hydrogen was observed to reduce the binding energy of CO subsequently adsorbed and to inhibit the dissociation of CO. A new surface species was identified in a coadsorbed layer of CO and hydrogen. This species was evidenced by the formation of a desorption peak for H 2 at 475 K when CO was adsorbed subsequent to H 2 adsorption.
237
THE
ADSORPTION OF CARBON MONOXIDE O N Cu(ll0)-Ni SURFACES PREPARED BY DISSOCIATION OF NICKEL CARBONYL
C.M.A.M. MESTERS, A.F.H. WIELERS, J.W. GEUS and G.A. BOOTSMA *
O.L.J. GIJZEMAN,
Van 't Hoff Laboratory, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands Received 18 June 1981; accepted for publication 10 December 1981 Cu(110)-Ni surface alloys were prepared by dissociation of nickel carbonyl on clean Cu(110). The adsorption of CO is reversible in the temperature region of 22-200°C and the pressure range of 5 × 10-8-0.7 Torr, as monitored with ellipsometry and AES. The amount of adsorbed CO depends on the amount of preadsorbed oxygen but not on the amount of carbon present at the surface. The isosteric heat of adsorption decreases from 31 -+ 3 kcal/mole to 18 ± 2 kcal/mole with increasing CO coverage (up to 0 = 0.14 0ma,,) but is constant for higher coverages (up to 0 = 0.4 0m~,~l-
Surface Science 115 (1982) 247-258 North-Holland Publishing Company GAS-SURFACE
SCATI~RING
247 DISTRIBUTIONS
ACCORDING
TO
THE HARD-SPItEROID MODEL Christoph STEINBROCHEL
Laboratories RCA, Ltd., Badenerstrasse 569, CH-8048 Ziirich, Swttzerland Received 28 September 1981 ; accepted for publication 27 November 1981 Gas-surface scattering distributions are calculated on the basis of the hard-spheroid model. This new model is related to the hard-cube model but incorporates surface structure by letting the surface atoms have hard spherical caps. Surface structure is found to reduce the maximum scattered intensity and to broaden the scattering distribution. The decrease in the maximum scattered intensity is most pronounced for a light gas. Broadening is asymmetric relative to the direction of maximum scattered intensity in that backscattering towards the surface is favored. Adding surface structure to the hard-cube model improves significantly the agreement between model predictions and experimental results.
259
Surface Science 115 (1982) 259-269 North-Holland Publishing Company BACKSCATYERING ANALYSIS II.
CORRECTION
FOR QUANTITATIVE
Verifications of the backscattering factors through quantification
by
AES S. I C H I M U R A
a n d R. S H I M I Z U
Department of Applied Physics, Osaka University. Suita, Osaka 565, Japan and
AUGER
AllO T. I K U T A
Department of Applied Electronics, Osaka Electro-Communication Universi(v, Nevagawa, Osaka 572, Japan Received 3 June 1981; accepted for publication 17 November 1981 The validity and utility of the backscattering correction factors obtained from Monte Carlo calculations for quantitative analysis by Auger electron spectroscopy (AES) were examined through practical quantification of surface concentrations of binary alloys. Quantifications were attempted, first, to access the surface composition of a sputter-deposited Ni-Pt layer, which is probably the most appropriate test-sample with known surface composition for surface analysis. The quantification by AES has led to the result that the surface composition of the layer agrees well with the bulk composition of the sputtered Ni-Pt alloy, as expected. The composition of a sputtered Au-Cu alloy surface was, then, examined according to the same correction procedure as for the N i - P t layer, leading to the confirmation that no preferential sputtering is observed for Au-Cu alloys by AES as F~rber et al. reported.
270 ATOMIC
Surface Science 115 (1982) 270-278 North-Holland Publishing Company STRUCTURE
S. T O U G A A R D
OF THE SCANDIUM
(0001) SURFACE
* a n d A. I G N A T I E V
Department of Physics, University of Houston, Houston, Texas 77004, USA Received 2 November 1981 The atomic structure of the scandium (0001) surface has been determined through a lowenergy-electron-diffraction analysis. Intensity profiles calculated on the basis of different structural models corresponding to different terminations of the bulk structure were compared to the experimental data. The comparison showed that the surface of scandium terminated in hcp stacking and that the outermost layer soPacing is 2.59-+0.02 A corresponding to a - 2 % contraction with respect to the bulk spacing (2.64 A).
Surface Science 115 (1982) 279-289 North-Holland Publishing Company THE COADSORPTION J.B. B E N Z I G E R *
279
OF CO AND H 2 ON Fe(100)
a n d R.J. M A D I X
Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA Received 8 December 1980; accepted for publication 4 November 1981 The coadsorption of CO and hydrogen on an Fe(100) surface was studied by temperature programmed desorption and X-ray photoelectron spectroscopy. It was found that CO adsorption blocked the subsequent dissociative adsorption of H2, although it did not seem to affect the hydrogen binding energy. Preadsorption of hydrogen was observed to reduce the binding energy of CO subsequently adsorbed and to inhibit the dissociation of CO. A new surface species was identified in a coadsorbed layer of CO and hydrogen. This species was evidenced by the formation of a desorption peak for H 2 at 475 K when CO was adsorbed subsequent to H 2 adsorption.