The crystallography of clean surfaces and chemisorbed species as determined by low-energy electron diffraction

Abstract

Low-energy electron diffraction (LEED) is a valuable technique for determining not only two-dimensional translational periodicities of surface atoms but also their detailed locations via an analysis of LEED intensities. We outline the experimental diffraction intensity data and various methods of theoretical analysis including dynamical calculations, data averaging, and data inversion methods needed for such structural determinations. The relative merits of the dynamical analysis of either azimuthal intensity distributions at fixed energy, I(φ), or the energy dependence of the intensity, I(E), to determine surface crystallography are examined via model calculations. Dynamical analysis of the I(E) spectra of the oxygen (2 × 1) overlayer and the hydrogen (1 × 2) overlayer structures on Ni(110) are presented. We determine that the oxygen atoms in the (2 × 1) structure reside in the twofold bridge sites on top of 〈110〉 rows of the Ni(110) surface and are located 1.92 ± 0.04 Å from the two adjacent Ni atoms. For the casee of hydrogen on Ni(110) we find that little agreement is found between calculated and experimental I(E) spectra for simple hydrogen adsorption models. A surface distortion model is found to best describe the experimental data where adjacent 〈11〉 rows of Ni atoms are alternately attracted or repelled 0.1 ± 0.05 Å together or apart and compressed into the bulk by 0.1 ± 0.05 Å. The chemical trends of these and other recent LEED determinations as well as the future directions of surface crystallography are briefly discussed. © 1977.