Surface Crystallography by LEED

Surface science has experienced an impressive growth in the last two decades. The attention has focussed mainly on single-crystal surfaces with, on the atomic scale, relatively simple and well-defined structures (for example, clean surfaces and such surfaces with limited amounts of additional foreign atoms and molecules). One of the most fundamental types of information needed about solid surfaces concerns the relative atomic positions. The geometrical arrangement of surface atoms influences most physical and chemical properties of surfaces, the list of which is long and includes a number of important technological applications: electronic surface states, contact potentials, work functions, oxidation, heterogeneous catalysis, friction, adhesion, crys­ tal growth etc. Surface crystallography - the determination of relative atomic positions at surfaces - has found a successful tool in Low-Energy Electron Diffraction (LEED): this technique has now determined the atomic positions for nearly a hundred surfaces, whether in the clean state or with additional foreign atoms or molecules. The main aim of this book is to publish a set of computer pro­ grams that has been specifically designed for and extensively used in surface crystallography by LEED. These programs are based on the dynamical (i.e.

Inhalt

1. Introduction.- 1.1 LEED as a Tool for Surface Studies.- 1.2 Purpose of the Computational Programs.- 1.3 Physical Processes Included in the Programs.- 1.4 Capabilities of the Programs.- 1.5 Size, Speed and Limitations of the Programs.- 1.6 Relation to Other LEED Programs.- 1.7 Some Computational Considerations.- 2. The Physics of LEED.- 2.1 A Simple Description of the LEED Process: Clean Crystals and Bragg Reflections in One Dimension.- 2.2 Peak Width and Electron Penetration Depth.- 2.3 Three-Dimensional Effects.- 2.4 Overlayer Effects.- 2.5 Elements of a LEED Theory.- 3. Basic Aspects of the Programs.- 3.1 Units and Geometrical Conventions.- 3.2 Layers, Subplanes and Plane Waves.- 3.3 Superlattices.- 3.4 Atomic Scattering and the Calculation of Phase Shifts.- 3.5 Thermal Vibrations.- 3.6 Ordering of (?,m) Pairs.- 4. Symmetry and Its Use.- 4.1 Symmetry and Registries.- 4.2 Symmetry Among Beams.- 4.3 Some Formulas.- 4.4 Summary.- 5. Calculation of Diffraction Matrices for Single Bravais-Lattice Layers.- 5.1 Layer Diffraction Matrices.- 5.2 Subroutine MSMF.- 5.3 The Intralayer Multiple-Scattering Matrix X.- 5.4 Scattering Amplitudes and Temperature Effects.- 6. The Combined Space Method for Composite Layers: by Matrix Inversion.- 6.1 The Formalism.- 6.2 Subroutine MTINV.- 7. The Combined Space Method for Composite Layers: by Reverse Scattering Perturbation.- 7.1 The Formalism of Reverse Scattering Perturbation (RSP) Theory.- 7.2 Combining RSP and Matrix Inversion.- 7.3 Subroutine MPERTI.- 8. Stacking Layers by Layer Doubling.- 8.1 The Formalism.- 8.2 Bulk Treatment: Subroutine SUBREF.- 8.3 Surface Treatment: Subroutines ADREF1, DBLG, DBG.- 9. Stacking Layers by Renormalized Forward Scattering (RFS) Perturbation.- 9.1 The Formalism.- 9.2 Subroutines RFS03, RFS02 and Others.- 10. Assembling a Program: the Main Program and the Input.- 10.1 Preparing a Calculation.- 10.2 The Main Program.- 10.3 Explanation of Output.- 10.3.1 Print Output.- 10.3.2 Punch Output.- 10.4 Main Program for Clean fcc (111) and hcp (0001) Faces, Including Possible Top-Layer Registry Shifts, Using RFS.- 10.5 Main Program for a Small-Atom p(2 Overlayer on a fcc (111) Substrate, Using RSP and RFS.- 10.6 Main Program for a Clean fcc or bcc (100) Surface, Using RFS.- 10.7 Main Program for a p(2 Overlayer on an fcc or bcc (100) Substrate, Using Layer Doubling.- 10.8 Main Program for a c(2 Overlayer on an fcc or bcc (100) Substrate, with Rumpling of the Topmost Substrate Layer, Using Matrix Inversion and RFS.- 10.9 Main Program for an Upright Diatomic Molecule on an fcc or bcc (100) Substrate, Using Layer Doubling.- 11. Subroutine Listings.- 12. Structural Results of LEED Crystallography.- 12.1 Non-Metals.- 12.2 Clean Metals.- 12.3 Adsorption on Metals.- 12.4 Bibliography.- Appendix A. Symmetry Among Plane Waves.- Appendix B. Lattice Sums Over Sublattices.- Appendix C. A Line-Printer Plotting Program.- References.