LEED Holography applied to a complex superstructure: a direct view of the adatom cluster on SiC(111)-(3x3)

TL;DR

This paper demonstrates that LEED holography can directly reveal the local atomic structure of adatom clusters on complex superstructures like SiC(111)-(3x3), with implications for surface analysis and reconstruction understanding.

Contribution

It introduces a holographic interpretation of LEED spot intensities for large superstructures, showing how to determine local adatom geometries and stacking information.

Findings

Holography can visualize adcluster geometry up to the fourth layer.

Vacancies like cornerholes can hinder accurate atomic position detection.

Substrate reconstructions have minimal impact on holographic images.

Abstract

For the example of the SiC(111)-(3x3) reconstruction we show that a holographic interpretation of discrete Low Energy Electron Diffraction (LEED) spot intensities arising from ordered, large unit cell superstructures can give direct access to the local geometry of a cluster around an elevated atom, provided there is only one such prominent atom per surface unit cell. By comparing the holographic images obtained from experimental and calculated data we illuminate validity, current limits and possible shortcomings of the method. In particular, we show that periodic vacancies such as cornerholes may inhibit the correct detection of the atomic positions. By contrast, the extra diffraction intensity due to slight substrate reconstructions, as for example buckling, seems to have negligible influence on the images. Due to the spatial information depth of the method the stacking of the cluster can be imaged down to the fourth layer. Finally, it is demonstrated how this structural knowledge of the adcluster geometry can be used to guide the dynamical intensity analysis subsequent to the holographic reconstruction and necessary to retrieve the full unit cell structure.