Surface defects and thermodynamics of chemisorbed layers

Chemisorbed overlayers on single crystal surfaces can in many cases be considered as lattice gases. The general features of temperature–coverage phase diagrams resulting from attractive or repulsive adatom interactions in such systems are discussed in analogy with binary solid solutions. The effect of surface and overlayer defects on the determination of phase boundaries is considered. The use of low-energy electron diffraction (LEED) to study surface defects and overlayer phase diagrams is briefly summarized.