LONG-RANGE INHIBITION OF THE W[001] CLEAN SURFACE DISPLACIVE PHASE BY NITROGEN

Half-order LEED beam intensities and half-widths produced by the low-temperature ( square root 2* square root 2)R45 degrees displacive phase on W(001) have been determined as a function of nitrogen adatom coverage. The clean surface structure is found to be strongly inhibited by very low coverages (1-2*1013 atoms/cm2, or 1-2% of a monolayer), and the radius of influence of a N adatom pair is estimated as 20 AA. The results provide evidence for the influence of long-range effects, such as charge-density waves or surface-state coupling, on the formation of the ordered displacive phase.