Surface segregation study of Ib-VIII single-crystal alloys

Reniers, François; Delplancke, Marie Paule; Asskali, Abderrahman; Jardinier‐Offergeld, M.; Bouillon, Florent

doi:10.1016/0169-4332(94)00159-6

Cited by 12 publications

(2 citation statements)

References 31 publications

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“…Comparing the Ag/Pd ratio (from XPS) with the bulk ratio (from AAS) Naganson et al [41] suggested surface enrichment with Ag for Pd-Ag/Al 2 O 3 catalyst after reduction. Relevant results have already been reported for unsupported [42], silica supported [43], pumice supported [26] and alumina supported Pd-Ag catalysts [25].…”

Section: Discussionsupporting

confidence: 58%

Interaction between Pd and Ag on the surface of silica

Karski

Witońska

Rogowski

et al. 2005

Journal of Molecular Catalysis A: Chemical

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Section: Discussionsupporting

confidence: 58%

Interaction between Pd and Ag on the surface of silica

Karski

Witońska

Rogowski

et al. 2005

Journal of Molecular Catalysis A: Chemical

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“…33. Comparison with experiments on bulk samples is not straightforward because contradictory results are found in the literature for what concerns surface compositions, from Pd surface enrichment, 34 to bulk composition, 35 to weak Ag enrichment [36][37][38] and to strong Ag segregation. 39,40 Comparing the results in bulk and nanoparticles, we can see that the subsurface enrichment is stronger at the nanoscale.…”

Section: Discussionmentioning

confidence: 97%

Chemical ordering in magic-size Ag–Pd nanoparticles

Bochicchio

Ferrando

Novaković

et al. 2014

Phys. Chem. Chem. Phys.

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Chemical ordering in magic-size Ag-Pd nanoalloys is studied by means of global optimization searches within an atomistic potential developed on the basis of density functional theory calculations. Ag-rich, intermediate and Pd-rich compositions are considered for fcc truncated octahedral, icosahedral and decahedral geometric structures. Besides a surface enrichment in Ag, we find a significant subsurface enrichment in Pd, which persists to quite high temperatures as verified by Monte Carlo simulations. This subsurface Pd enrichment is stronger in nanoparticles than in bulk systems and is rationalized in terms of the energetics of the inclusion of a single Pd impurity in an Ag host nanoparticle. Our results can be relevant to the understanding of the catalytic activity of Ag-Pd nanoparticles in those reactions in which subsurface sites play a role.

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Use of matrix corrections in the calculation of surface composition of AgPd alloys in auger electron spectroscopy

Reniers

1995

Surface & Interface Analysis

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The surface segregation in binary alloys is often studied by Auger electron spectroscopy. However, the information obtained in the Auger spectra is representative of a region thicker than one monolayer. The Auger signal must be decomposed into the contributions of the different atomic layers. On the other hand, it is now well known that matrix correction factors must he used to relate the intensity of the Auger signal to the composition of the sample.As these two parameters are seldom put together in the treatment of Auger data, we tried to combine them for the study of the surface segregation in silver-palladium alloys. We calculated the matrix correction factors for AgPd alloys in the whole range of concentrations. The attenuation length corrections and the backscattering corrections were calculated on the basis of different models (Seah and Dench, Penn, Tanuma-Powell-Peno, IchimuraShimizu-Langeron, Reuter-Ichimura, etc.). The matrix corrections were compared to the Hall and Morabito approach and with previously published results. The matrix corrections were then introduced into a layer-by-layer model of interpretation of the Auger signal. While the surface composition calculated without matrix correction reveals silver enrichment relative to the bulk of the samples, the use of matrix corrections lead to an enrichment in silver that is strongly attenuated. INTRODUCTIONAuger electron spectroscopy is a widely used surface analysis technique. Part of the success of this method is that the Auger current for a given transition can be easily related to the atomic concentration of the emitting element. Auger electron spectroscopy is considered as a surface analysis technique because the attenuation length of the Auger electrons is small (typically a few monolayers, depending on the kinetic energy of the electrons). A lot of papers in the field of surface science were published 20 years ago, where the atomic concentration was linearly connected to the intensity of the Auger current detected by assuming that the composition calculated using the well-known formula (1) was the surface compositionwhere li is the Auger current of element i, X i is the atomic fraction of element i and Si is the sensitivity coefficient of the element i. However, two main restrictions to this simple formalism quickly appear :(1) The intensity of the Auger signal does not vary linearly with the atomic concentration of the emitting element and so some correction factors due to matrix effects must be intr~duced.'-~ (2) The Auger signal does not come only from the first atomic layer (the 'surface' of the sample) but also from the second, third, etc. layer, depending on the attenuation length of the electrons,4g5 and eqn. (1) assumes that the composition is uniform within the sampling depth of the electrons. Many studies have been published on each of these two restrictions, separately. In this paper, we examine the influence of the matrix effects combined with a layer-by-layer model in the calculation for the surface composition of a silver-pallad...

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Surface segregation study of Ib-VIII single-crystal alloys

Cited by 12 publications

References 31 publications

Interaction between Pd and Ag on the surface of silica

Interaction between Pd and Ag on the surface of silica

Chemical ordering in magic-size Ag–Pd nanoparticles

Use of matrix corrections in the calculation of surface composition of AgPd alloys in auger electron spectroscopy

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