Local symmetry breaking in stage-1 alkali-metal–graphite intercalation compounds studied by scanning tunneling microscopy

Abstract

Scanning tunneling microscopy has been used to study surfaces of stage-1 Cs and Rb graphite intercalation compounds on the atomic scale. We have found a (2\ifmmode\times\else\texttimes\fi{}2) superlattice as well as a one-dimensional ordering of the alkali-metal atoms corresponding to nonhexagonal (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{}4) and (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}13 ) superlattice structures. Three rotational domains of the one-dimensional phase have been observed, inclined at 120\ifmmode^\circ\else\textdegree\fi{} to each other, with sizes ranging from 10 nm to typically 60 nm. The origin of the superlattices and a transition process, based on a surface depletion of the alkali metal, are discussed.