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Oxygen uptake by thin lead deposits on polycrystalline gold
A288 Surface Science 186 (1987) 339-356 North-Holland, Amsterdam
339
SCANNING AUGER ELECTRON MICROSCOPE RESOLUTION DETERMINED BY A QUANTITATIVE AES METHOD H. T O K U T A K A ,
K. N I S H I M O R I ,
J. M A T S U U R A
Department of Electronica, FaculO, of Engineering. Tottori Unwersity, Kr~vama, Tottori, Japan and Vdronique PINET
Centre d'Etudes de Chimie M~tallurgique, CNRS, 15 rue Georges Urhain. 94400 Vito,-sur,Seine, France Received 30 September 1985; accepted for publication 26 February 1987 In quantitative Auger electron spectroscopy (AES) analysis, the emphasis is generally laid on the vertical variation in signal from an element versus the variation in composition from the surface to the bulk. In such a framework, a quantitative method has been previously developed by the authors, which provides such information as the thickness of a segregated layer or the initial growth process of a thin film. Here, this method is applied to study a horizontal variation of composition, i.e. the signal variation of a scanning Auger electron microscope (SAM) when the incident electron beam is scanned across the boundary of grains of different composition. In order to evaluate the SAM resolution, for the case of an ideal step boundary, calculations are carried out by taking into account the influence of angular distributions, of attenuation length of primary, secondary and Auger electrons, of secondary electron yield and of the beam shape (point, Gaussian or columnar). The results for the cases of Ag-Au, Si-Ag and Be-Cu, lead to a SAM spatial resolution of - 30 ,~ for a primary beam of 2-3 keV with an infinitesimal diameter and a resolution of the order of the beam size for Gaussian and columnar beams. Extrapolation of this method to a primary beam energy of 20 keV is discussed and leads to results similar to those obtained by Monte Carlo simulation.
Surface Science 186 (1987) 357-375 North-Holland, Amsterdam
357
O X Y G E N U P T A K E BY T H I N L E A D D E P O S I T S ON POLYCRYSTALLINE GOLD J.G. MACMILLAN-JONES,
F.A. LONDRY
a n d A.J. S L A V I N
Department of Physics. Trent University, Peterborough, Ontario, Canada KgJ 7B8 Received 19 December 1986: accepted for publication 11 March 1987 The oxidation of thin lead overlayers on a predominantly (111) polycrystalline gold surface at room temperature and oxygen pressure of 8 x 10 -6 Tort was investigated using Auger electron spectroscopy (AES). Oxidation was monitored using the oxide lead peak obtained by spectral decomposition. This peak experiences a shift from pure lead of 2.3_+0.1 eV for deposits up to 3 monolayer-equivalents (ME) and 2.7_+0.1 eV for deposits greater than about 4 ME. The oxygen signal for a 1 ME deposit at saturation exposure is about 20% of the value expected for a complete oxygen monolayer. This is explained in terms of clusters of about 5 Pb atoms for each oxygen
A289
atom. This differs from the PbO stoichiometry which has been observed under similar conditions on bulk lead and also claimed for the oxidation of thin lead deposits on Ag and Cu. Also contrary to results on Ag and Cu is the rate of oxygen uptake on Au which increases with lead coverage in the submonolayer region; this is explained by the absence of adsorption and surface diffusion of oxygen on gold, and the need for clusters of about 5 lead atoms for oxidation to occur. Deposition of more than 1 ME of lead results in lead-gold compound formation as observed by previous authors. Exposure of this compound to oxygen causes oxidation of the surface lead with inward migration of gold from the surface. The oxide layer is about 2 monolayers thick and greatly reduces the rate of further oxidation. The large decrease in the gold substrate signal on oxidation is a sensitive method for differentiating between compound formation and alternative growth modes for the bimetallic surface.
376
Surface Science 186 (1987) 376-382 North-Holland, Amsterdam
AES
AND
ON
Cu(II0)
EELS
A. SANTONI
INVESTIGATION
AND
OF CARBONACEOUS
LAYERS
Cu(100)
a n d J. U R B A N
Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradavweg 4-6. D-1000 Berlin 33, Germany Received 1 September 1986: accepted for publication 30 March 1987 Carbonaceous layers on C u ( l l 0 ) and Cu(100) were investigated by means of AES and EELS. The carbidic carbon overlayer, obtained on the Cu(110) surface by exposing the sample to a CO atmosphere was found to transform into graphitic carbon by heating the sample to a temperature of 573 K. During this process new carbon Auger lineshapes were observed, which were assumed to he related to "'intermediate" carbon species. This new kind of lineshapes was found also on Cu(100), although no graphitic carbon Auger lines were detected in this case. This finding could be explained by supposing that the Cu(100) surface does not have suitable sites for carbon atoms arranged in the graphitic structure.
Surface Science 186 (1987) 383-392 North-Holland, Amsterdam THIN
Cu FILMS
ON
A PHOTOEMISSION V. D I C A S T R O
383
ALUMINIUM: INVESTIGATION
and G. POLZONETTI
Department of ChemisttT, University "La Sapienza", P. le A. Moro, 5, 00185 Rome, ltalv Received 11 March 1986: accepted for publication 13 March 1987 The initial growth of a Cu film (up to 100 A) on polycrystalline aluminium at room temperature has been studied by photoemission spectroscopy using synchrotron radiation. For low coverages (1-8 ,~) copper diffusion in the aluminium substrate is observed, whilst at higher coverages copper clusters seem to be formed and increase in size on the surface. A further indication on copper clusters formation comes from the oxidation of a 12 ,~ C u / A I system which shows formation of an AIzO 3 layer on top of the unchanged C u / A I interface.
339
SCANNING AUGER ELECTRON MICROSCOPE RESOLUTION DETERMINED BY A QUANTITATIVE AES METHOD H. T O K U T A K A ,
K. N I S H I M O R I ,
J. M A T S U U R A
Department of Electronica, FaculO, of Engineering. Tottori Unwersity, Kr~vama, Tottori, Japan and Vdronique PINET
Centre d'Etudes de Chimie M~tallurgique, CNRS, 15 rue Georges Urhain. 94400 Vito,-sur,Seine, France Received 30 September 1985; accepted for publication 26 February 1987 In quantitative Auger electron spectroscopy (AES) analysis, the emphasis is generally laid on the vertical variation in signal from an element versus the variation in composition from the surface to the bulk. In such a framework, a quantitative method has been previously developed by the authors, which provides such information as the thickness of a segregated layer or the initial growth process of a thin film. Here, this method is applied to study a horizontal variation of composition, i.e. the signal variation of a scanning Auger electron microscope (SAM) when the incident electron beam is scanned across the boundary of grains of different composition. In order to evaluate the SAM resolution, for the case of an ideal step boundary, calculations are carried out by taking into account the influence of angular distributions, of attenuation length of primary, secondary and Auger electrons, of secondary electron yield and of the beam shape (point, Gaussian or columnar). The results for the cases of Ag-Au, Si-Ag and Be-Cu, lead to a SAM spatial resolution of - 30 ,~ for a primary beam of 2-3 keV with an infinitesimal diameter and a resolution of the order of the beam size for Gaussian and columnar beams. Extrapolation of this method to a primary beam energy of 20 keV is discussed and leads to results similar to those obtained by Monte Carlo simulation.
Surface Science 186 (1987) 357-375 North-Holland, Amsterdam
357
O X Y G E N U P T A K E BY T H I N L E A D D E P O S I T S ON POLYCRYSTALLINE GOLD J.G. MACMILLAN-JONES,
F.A. LONDRY
a n d A.J. S L A V I N
Department of Physics. Trent University, Peterborough, Ontario, Canada KgJ 7B8 Received 19 December 1986: accepted for publication 11 March 1987 The oxidation of thin lead overlayers on a predominantly (111) polycrystalline gold surface at room temperature and oxygen pressure of 8 x 10 -6 Tort was investigated using Auger electron spectroscopy (AES). Oxidation was monitored using the oxide lead peak obtained by spectral decomposition. This peak experiences a shift from pure lead of 2.3_+0.1 eV for deposits up to 3 monolayer-equivalents (ME) and 2.7_+0.1 eV for deposits greater than about 4 ME. The oxygen signal for a 1 ME deposit at saturation exposure is about 20% of the value expected for a complete oxygen monolayer. This is explained in terms of clusters of about 5 Pb atoms for each oxygen
A289
atom. This differs from the PbO stoichiometry which has been observed under similar conditions on bulk lead and also claimed for the oxidation of thin lead deposits on Ag and Cu. Also contrary to results on Ag and Cu is the rate of oxygen uptake on Au which increases with lead coverage in the submonolayer region; this is explained by the absence of adsorption and surface diffusion of oxygen on gold, and the need for clusters of about 5 lead atoms for oxidation to occur. Deposition of more than 1 ME of lead results in lead-gold compound formation as observed by previous authors. Exposure of this compound to oxygen causes oxidation of the surface lead with inward migration of gold from the surface. The oxide layer is about 2 monolayers thick and greatly reduces the rate of further oxidation. The large decrease in the gold substrate signal on oxidation is a sensitive method for differentiating between compound formation and alternative growth modes for the bimetallic surface.
376
Surface Science 186 (1987) 376-382 North-Holland, Amsterdam
AES
AND
ON
Cu(II0)
EELS
A. SANTONI
INVESTIGATION
AND
OF CARBONACEOUS
LAYERS
Cu(100)
a n d J. U R B A N
Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradavweg 4-6. D-1000 Berlin 33, Germany Received 1 September 1986: accepted for publication 30 March 1987 Carbonaceous layers on C u ( l l 0 ) and Cu(100) were investigated by means of AES and EELS. The carbidic carbon overlayer, obtained on the Cu(110) surface by exposing the sample to a CO atmosphere was found to transform into graphitic carbon by heating the sample to a temperature of 573 K. During this process new carbon Auger lineshapes were observed, which were assumed to he related to "'intermediate" carbon species. This new kind of lineshapes was found also on Cu(100), although no graphitic carbon Auger lines were detected in this case. This finding could be explained by supposing that the Cu(100) surface does not have suitable sites for carbon atoms arranged in the graphitic structure.
Surface Science 186 (1987) 383-392 North-Holland, Amsterdam THIN
Cu FILMS
ON
A PHOTOEMISSION V. D I C A S T R O
383
ALUMINIUM: INVESTIGATION
and G. POLZONETTI
Department of ChemisttT, University "La Sapienza", P. le A. Moro, 5, 00185 Rome, ltalv Received 11 March 1986: accepted for publication 13 March 1987 The initial growth of a Cu film (up to 100 A) on polycrystalline aluminium at room temperature has been studied by photoemission spectroscopy using synchrotron radiation. For low coverages (1-8 ,~) copper diffusion in the aluminium substrate is observed, whilst at higher coverages copper clusters seem to be formed and increase in size on the surface. A further indication on copper clusters formation comes from the oxidation of a 12 ,~ C u / A I system which shows formation of an AIzO 3 layer on top of the unchanged C u / A I interface.