Surface Alloys and Alloys Surfaces

553 Pages·2002·29.26 MB·English

by  D.P. Woodruff (Eds.)

THE CHEMICAL PHYSICS OF SOLID SURFACES
THE CHEMICAL PHYSICS OF SOLID SURFACES
Volume 1
CLEAN SOLID SURFACES
Volume 2
ADSORPTION AT SOLID SURFACES
Volume 3
CHEMISORPTION SYSTEMS
Volume 4
FUNDAMENTAL STUDIES OF HETEROGENEOUS CATALYSIS
Volume 5
SURFACE PROPERTIES OF ELECTRONIC MATERIALS
Volume 6
COADSORPTION, PROMOTERS AND POISONS
Volume 7
PHASE TRANSITIONS AND ADSORBATE
RESTRUCTURING AT METAL SURFACES
Volume 8
GROWTH AND PROPERTIES OF ULTRATHIN EPITAXIAL LAYERS
Volume 9
OXIDE SURFACES
Volume 10
SURFACE ALLOYS AND ALLOY SURFACES
TH E CH EMICAL PHYSICS
OF SOL! D SU RFACES
EDITED BY
D.P. W O O D R U F F
B.Sc. (Bristol), Ph.D., D.Sc. (Warwick)
Professor of Physics,
University of Warwick
VOLUME I0
SU RFACE ALLOYS AN D ALLOY SU RFACES
2002
ELSEVIER
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First edition 2002
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ISBN 0-444-51152-0 (Vol. 10)
ISBN 0-444-41971-3 (Series)
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Contributors to Volume I0
D.A. ADAMS Institute of Physics and Astronomy,
University of Aarhus,
DK-8000 Aarhus C, Denmark
J.N. ANDERSEN Department of Synchrotron Radiation Research,
Institute of Physics,
Lund University,
S-223 62 Lund, Sweden
C.J. BADDELEY School of Chemistry,
University of St Andrews,
St Andrews, Fife KY 16 9ST, UK
U. BARDI Dipartimento di Chimica,
Universith di Firenze,
Via G. Caponi 9,
50014 Firenze, Italy
C.J. BARNES School of Chemical Sciences,
Dublin City University,
Dublin 9, Republic of Ireland
J.C. BERTOLINI Insitut de Recherches sur la Catalyse- CNRS,
2, avenue Albert Einstein,
F-69626 Villeurbanne Cedex, France
G. BOZZOLO Ohio Aerospace Institute,
22800 Cedar Point Rd.,
Cleveland, OH 44142, USA
and
NASA Glenn Research Center,
Cleveland, OH 44135, USA
J.E. GARCES Ohio Aerospace Institute,
22800 Cedar Point Rd.,
Cleveland, OH 44142, USA
and
Centro Atomica Bariloche,
8400 Bariloche, Argentina
J. HRBEK Department of Chemistry,
Brookhaven National Laboratory,
Upton, New York 11973, USA
Y. JUGNET Insitut de Recherches sur la Catalyse- CNRS,
2, avenue Albert Einstein,
F-69626 Villeurbanne Cedex, France
G.L. KELLOGG Sandia National Laboratories,
Albuquerque, NM 87185-1415, USA
M. POLAK Department of Chemistry,
Ben-Gurion University of the Negev,
Beer-Sheva 84105, Israel
H. NIEHUS Humboldt-Universit~t zu Berlin,
Institut fur Physik,
Oberfl~chenphysik und Atomsto6prozesse,
InvalidenstralSe 110,
D- 10115 Berlin, Germany
J.K. NORSKOV Centre for Atomic-scale Materials Physics and
Department of Physics,
Technical University of Denmark,
DK-2800 Lyngby, Denmark
J.A. RODRIGUEZ Department of Chemistry,
Brookhaven National Laboratory,
Upton, New York 11973, USA
vii
A.V. RUBAN Centre for Atomic-scale Materials Physics and
Department of Physics,
Technical University of Denmark,
DK-2800 Lyngby, Denmark
L. RUBINOVICH Department of Chemistry,
Ben-Gurion University of the Negev,
Beer-Sheva 84105, Israel
M. SCHMID Institut fur Allgemeine Physik,
Technische Universit~it Wien,
A- 1040 Wien, Austria
H.L. SKRIVER Centre for Atomic-scale Materials Physics and
Department of Physics,
Technical University of Denmark,
DK-2800 Lyngby, Denmark
S. SPELLER Research Institute for Materials,
University of Nijmegen,
Toernooiveld 1,
6525 ED Nijmegen, The Netherlands
P. VARGA Institut fur Allgemeine Physik,
Technische Universit~it Wien,
A- 1040 Wien, Austria
E. VLIEG NSRIM Department of Solid State Chemistry,
University of Nijmegen,
Toernooiveld 1,
6525 ED Nijmegen, The Netherlands
D.P. WOODRUFF Physics Department,
University of Warwick,
Coventry CV4 7AL, UK
...
Vlll
Preface
During the late 1960s and 1970s the commercial availability of ultra-high
vacuum (UHV) systems allowed the development of a plethora of new
techniques which were devised to probe materials in a surface-specific fashion,
and this in turn led to the creation of modem surface science; the study of the
structural, electronic and chemical properties of extremely well-characterised
surfaces on an atomic scale. When David King and I first conceived this series
of volumes in the later 1970s our objective was to recognise the growing
maturity of this new scientific discipline which was already starting to apply
these techniques in a combined fashion to understand surface processes. In the
20 years since the first volume was published, this perception has certainly
proved to be well-founded, and while new techniques have continued to
appear, they have rapidly been assimilated into the general armoury of
methods (the increasing pervasiveness of scanning probe microscopies is
evident again in the current volume), and it is the combination of methods
which has proved most effective.
The topic of the present volume, Sufluce Alloys and Alloy Sufluces, provides
new insights into a mixture of old and new problems. The surfaces of bulk
alloys have long been known to be of practical interest for their chemical
properties, be it novel activity or selectivity to certain reactions in a way which
differs from the constituent elements in isolation or novel passiveness to
corrosion. It has also long been known that the surface composition of such
alloys commonly differs from that of the underlying bulk, and some of the
basic thermodynamics of this segregation is far from new. Nevertheless, our
understanding of these chemical and physical phenomena is far from complete,
and the application of surface science methods to investigate these phenomena
is a manifestation of a general trend to the study of surfaces of increasing
complexity. A phenomenon which has been fully recognised far more recently
is that of surface alloy formation the intermixing of substrate atoms and
-
adatoms in the outermost atomic layer, or few atomic layers of a solid, to form
a stable ultra-thin alloy phase which may be in equilibrium with an essentially
elementally pure substrate and may even involve the intermixing of elements
which are immiscible in the bulk. There are now many examples of these
surface alloys, and quite complex alloying and de-alloying behaviour may be
observed a function of surface stoichiometry. It is this combination of
as
surface alloys and alloy surfaces which is addressed in the chapters of this
volume.
The first three chapters, by Ruban, Skriver and N~rskov,b y Bozzolo and
Garces, and by Polak and Rubinovich, are concerned with different theoretical
descriptions of some of these phenomena from which one gains physical
1X
insight and predictive powers into the mixing, segregation and ordering
phenomena.
There follows a series of chapters based on experimental studies of surface
composition, ordering and structure based on a variety of different materials
and techniques. Schmid and Varga show, in particular, the remarkable power
of scanning tunnelling microscopy, when chemical discrimination of the
elemental components of an alloy surface is possible, to gain an atomic-scale
understanding of some of the effects of segregation and ordering. Kellogg
describes phenomena particularly in the Cu/Pb system based on information
from many techniques but including the application of low energy electron
microscopy to follow the processes of alloying and de-alloying. Speller and
Bardi and Adams and Andersen describe the results of extensive structural
studies of Pt-Sn alloys and Al-alkali surface alloy phases respectively. The
latter systems, involving mixtures of superficially 'simple' metals, show a
remarkably rich range of ordering and intermixing phenomena. Woodruff and
Vlieg describe some detailed quantitative structural aspects of some metallic
surface alloys including the systematics of surface alloy layer atomic rumpling
and associated effective atomic radii, while Barnes surveys the structural
aspects of surface alloys on Cu(100). Finally, in this group of chapters, Niehus
discusses some results on the surface order of bulk alloys, especially Cu3Au
and related systems, and ordered overlayers on these surfaces.
The final group of chapters by Bertolini and Jugnet, Rogriguez, Hrbek and
Baddeley address issues more directly related to the chemical properties of
these surfaces, the first three of these chapters being concerned directly with
the relationship of the nature of the surface alloys (and alloy surfaces) and their
reactivity, while Baddeley turns the problem round in addressing the issue of
adsorbate-induced modification of surface segregation; not only does the alloy
surface modify the reactivity, but also the reaction modifies the surface alloy.
March 2002 D.P.Woodruff