The bonding, structure and reactions of CO2 adsorbed on clean and promoted metal surfaces

The last decade has seen remarkable new developments in the field of low energy electron diffraction (LEED) which are reviewed in the present paper. The arrival of sophisticated and fast techniques for the measurement of diffraction intensities in the early 1980s was a challenge to theory. Its answer was the development of tensor LEED (TLEED) in 1985. It allows the fast calculation of intensities for structures not too far from a certain reference. This made quantitative surface structure analysis approach new frontiers both with respect to structural complexity and-with the help of the routine use of reliability factors-to precision. Simultaneously, the new experimental techniques allowed access to two-dimensional intensity maps, i.e. the measurement of diffuse intensity distributions. Theory could be modified to calculate such distributions and so gave birth to the diffuse LEED technique (DLEED) which allows the retrieval of the local structure in case of disordered adsorption. The basics and the development of both TLEED and DLEED is reviewed. TLEED is the basis for direct methods and is used in effective search procedures for surface structures structurally close to a certain reference. It can also be used to simulate the substitution of surface atoms by different chemical species as well as to account for surface vibrations. In addition to carrying the information about the local structure, DLEED patterns very recently could be successfully interpreted in a holographic sense yielding real space images directly.

https://iopscience.iop.org/article/10.1088/0034-4885/58/6/003/pdf

LEED and DLEED as modern tools for quantitative surface structure determination

https://escholarship.org/content/qt6rj7h8dv/qt6rj7h8dv.pdf?t=p0lnso

A diffuse LEED study of the adsorption structure of disordered benzene on Pt(111)

Structural analysis of surfaces by LEED

The universal capabilities of high resolution spot profile analysis low energy electron diffraction for in situ studies of surface morphology and surface defects will be discussed and demonstrated. The position of the diffraction spots is used to determine lateral lattice constants, step heights and the strain state of heterosystems with a precision of 0.02 A. With the knowledge of the spot profile we could determine island and domain size distributions - even during deposition - and correlation functions of arbitrary surface defects. The variation of the spot profile with electron energy allows the evaluation of the 3dim. reciprocal space. With this the power spectrum of surface roughness, facet orientation, or step morphology of flat and vicinal surfaces could be completely characterised.

Growth of semiconductor layers studied by spot profile analysing low energy electron diffraction – Part I1

Diffuse low-energy-electron diffraction measurements at 46 eV for a disordered O/W(100) surface at 120 K have been interpreted by theory to give the local geometry of the oxygen atoms. This first application of the technique shows that phonon scattering does not prevent interpretation of data, and demonstrates sensitivity to surface geometry comparable with that in conventional LEED experiments on ordered surfaces. $R$ factors for the optimum geometry are very low, indicating a highly reliable determination. The prospects for the use of this technique in a whole range of situations previously inaccessible to LEED are thereby opened.

K. Heinz

Papers

Diffuse LEED and surface crystallography.