MORPHOLOGICAL INSTABILITIES INDUCED BY ULTRATHIN FILMS ON W(111)

Using ultrahigh vacuum surface science methods, we find that the atomi cally rough W(111) surface coated with approximately 1 monolayer of ce rtain 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 dimensi ons range from approximately 1-100 nm. Not all metal monolayer films c ause 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 mo rphological instability of W(111).