of the surface free energy from øb initÃo r'rret}rods as a function of pressure and. 1,. 2 .... positive bias; bottom, negative bias) images of the surface of a NiO('100) ...
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t5 Properties of Oxide Surfaces Martin Sterrer and Hans-Joachim Freund
15.r
lntroduction Oxides comprise
a
very diverse class of compounds with properties covering aimost
all aspects of material science and physics. Oxides can be both superconductors and insulators. The bonding characteristics may be classified as covalent for one system and highly ionic for the other. Oxides find applications in many fields of technical interest, from paint pigments via nonlinear optics to sensors and cataþsis. In some cases, the bulk properties are important, as, for example, very often in nonlinear optics; in other cases, the surface properties play a major role, as in catalysis.. The bulk properties of simple binary oxides are pretty well understood and there are excellent reviews and books available treating the thermodynamics, the structure - and its nonstoichiometric aspects, which are parricularþ important for oxides - the spectroscopy, and the transport and mechanical properties [1-6]. Bulk properties of even more complicated oxides such as ternary and quaternary oxides are being intensively investigated, partly due to their importance in high-T. superconductivity [7]. While the bulk properties of simple binary oxides are weli underslood, rather iittle is known aþout the surfaces of oxides, even the most simple ones. Only recently, if compared \Mith the 3Oyears of surface science that have passed by [8], researchers have started to study the surface science of oxides. There is a very usefirl book by V. E. Henrich and P. A. Cox that marks the first milestone in this effort entitled "The Surface Science of Oxides" [9]. Since the publication of this book, several reviews have appeared that have covered the field up to the present date ¡tO-t6]. It is understood that there are classes of technologicaþ very important oxides e>o)
0
o
= o
c
o LL
Lrl
5
Mso(001) 0
0
Wave vector Figure 15.34 Phonon dispersion relations of the MgO(001) model for a thick (208 atoms) slab consisting of 30 and 78 curves. Solid lines correspond to surface modes; from Parlinski, 2006 [54].
