Atomic-resolution scanning-tunneling-microscopy investigations of alkali-metal<i>–</i>graphite intercalation compounds

The scanning tunneling microscope has been used to image stage-1 and stage-2 potassium, rubidium, and cesium graphite intercalation complexes with atomic resolution. Images of the stage-1 materials exhibit a 2a modulation for a wide range of tunneling currents (0.5 to 10 nA) and bias voltages (-750 to +750 mV). This new superlattice is also ordered over large (&gt;500\ifmmode\times\else\texttimes\fi{}500 A${\r{}}^{2}$) areas. Images of the stage-2 materials are dominated by a centered hexagonal structure typical of graphite. The vertical corrugation determined for the stage-2 materials is, however, significantly smaller than observed for graphite. These results are discussed with respect to theoretical explanations of the anomalous features observed in images of graphite.