The background of the recent developments in studies of surfaces is critically described. Next, the adsorption site and adsorption species for hydrogen adsorption on W (100) are discussed on the basis of experimental data, which have been obtained extensively by using various methods such as low energy electron diffraction, flash desorption, electron spectroscopy, work function measurements, and electron stimulated desorption.
Main features of RHEED patterns from a cleavage face of a single crystal are outlined especially relating to elastic diffraction spots, the thermal diffuse scattering and the Kikuchi pattern. Peculiar character of the diffration effect due to the excitation of surface electron waves as well as its role as expecteel in the surface studies in future are discussed
A new approach to surface structure studies has been tried by using a new type apparatus of reflection high energy electron diffraction (RHEED) . On the basis of experimental results obtained in studies of Si (111) surfaces, it is concluded that the RHEED method including the new techniques is, in principle, superior to LEED for the surface structure research almost in all respects.
Surface wave resonance is a peculiar phenomenon in reflection electron diffraction from LEED to RHEED. Its characteristics are 1) the excitation of surface waves, 2) the enhancement of the diffraction pattern, 3) the localized wave field of the incident electron, 4) the many beam effect, 5) its sensitivity to the surface structure and 6) to the surface potential barrier. This phenomenon and its application to the surface structure analysis and other surface studies are discussed on the basis of the characteristics mentioned above. It is pointed out that this phenomenon gives rise to a useful tool for observing a single crystal surface with or without reconstruction and chemisorbed surface.
It has been considered that the surface atoms (ions) of the (100) face of a NaCl-type alkali halide are rumpled. In this review, it is described that the surface structure of solids can be estimated by the Kikuchi patterns of LEED in surface state resonance and of RHEED. The surface ions in MgO (001) lie in a plane in the as-cleaved face and are rumpled in the annealed face, in which the angle between the Mg-O bond direction and the (001) face is 3°
Recent studies in surface structure analysis by means of ion beams are reviewed. At first, it is introduced to get informations on the surface structures in real space, surface relaxation effect and the thermal amplitude of surface atoms by measuring the“surface peak”which is observed in axial channeling spectra of the Rutherford backscattered ions. The low energy ion beam (<10 keV) which is not neutralized by scattering only at crystal surface is also useful for structure analysis of surface layer of foreign atoms. At last studies on the surface channeling, where the incident ions enter a crystal with small glancing angle, are summerized.
The Debye-Waller factors and resonances in the diffraction of the atomic and molecular beams from solid surfaces are described. The Debye temperatures determined by means of molecular beams are always larger than those obtained from LEED. These results are discussed qualitatively on the basis of the facts that the properties of the interactions of atoms and molecules with solid surfaces are considerably different from those of the interactions with solid surfaces. The anomalous behavior of the diffraction intensities, which is called a resonance, has been found for many systems of molecules-solid surfaces. The intensity profiles in resonance are explained from the viewpoint of the standard scattering theory. Also it is emphasized that the interaction potentials of molecules with solid surfaces are determined by analysing only the resonance positions in the observed intensity curves.
Present status of researches on clean and adsorbed surfaces of solids by means of photoemission spectroscopy is briefly reviewed. Theoretical background developed in last decade is summarized very simply, in which the classical three-step-process is derived naturally from a view-point of recent one-step process as a special case. Some experimental results are shown as the examples for practical analyses of the data in order to get inf ormations about the electronic structures and also the atomic geometries on the surfaces. A shorthand bibliography for the experiments performed within last few years on this concern is given in the Appendix, where the papers are classified into the sample, surface net plane and adatoms.
The recent advances of the surface structure determination by means of Auger electron and uv-photoelectron angle-resolved spectroscopies are reviewed. The experimental results on the Auger electron angular distributions from Al, Fe, Ni and Cu single crystal clean surfaces and from the c (2x2) -O, -S, -Se adsorbed structures on Ni (100) surfaces are shown. For anisotropic Auger emissions from both single crystal surfaces and ordered adsorbed atoms, the angular momenta of valence Auger electrons play an important role as well as the multiple diffraction effect. The very recent theoretical investigations indicate that the Auger electron angular distribution from adsorbed atoms is very sensitive to the structural parameters such as the adsorbed site and the adsorbate-substrate distance. The dependence of the uv-photoelectron emission intensity on photon incident angle, photon energy, polarization and polar emission angle are presented and discussed for the p (2x2) -O, c (2x2) -O, c (2x2) -S and c (2x2) -CO on Ni (100) surfaces to estimate the atomic geometry of adsorbed species. It has been clear, from the comparison between experimental and theoretical results, that the calculations including anisotropies of the initial states as well as of the final states are useful to determine the bonding configuration of adsorbed species.