OBSERVATION OF A SUPERLATTICE IN SILVER-INTERCALATED NBSE2 BY SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscope measurements were performed on UHV cleav ed samples of pure and silver intercalated 2H-NbSe2 at room temperatur e. Samples intercalated to stage 2 showed a root 13a(0)x root 13a(0) h exagonal superlattice. We suggest that the superlattice arises from a surface charge density wave (CDW). Pure 2H-NbSe2 does not display a CD W at room temperature but develops a 3a(0)x3a(0) CDW superlattice belo w 30 K. The superlattice in the intercalated samples is similar to the CDW lattices observed in many 1-T polymorphs of the dichalcogenide ma terials. We suggest that the observed superlattice may result from a c hange in the stacking order of NbSe2 layers near the surface from 2H t ype to 1-T type in silver intercalated samples.