MORPHOLOGICAL INSTABILITIES INDUCED BY ULTRATHIN FILMS ON W(111)

Using ultrahigh vacuum surface science methods, we find that the atomically rough W(111) surface coated with approximately 1 monolayer of certain metals (Pt,PdAu,...) undergoes extensive restructuring to form a highly faceted surface with pyramidal microfacets after annealing to T > 750 K. The dominant facet orientation is W{211}, and facet dimensions range from approximately 1-100 nm. Not all metal monolayer films cause faceting of W(111): metals having Pauling electronegativities > 2.0 (Pt,Pd,Ir,Rh,Au) induce faceting of W(111) upon annealing, whereas those with electronegativities less than 2.0 (Ti,Co,Ni,Cu,Ag) do not. Electronic effects appear to be the driving factors in the observed morphological instability of W(111).