a b s t r a c t 5 a r t i c l e i n f o 6 7Available online xxxx The influence of N and C chemisorption on the morphology and local structure of nominal Ni (810) and Ni(911) 18 surfaces, both vicinal to (100) but with [001] and 011 h i step directions, respectively, has been investigated using 19 scanning tunnelling microscopy (STM) and low energy electron diffraction. Ni(911) undergoes substantial step 20 bunching in the presence of both adsorbates, with the (911)/N surface showing (411) facets, whereas for 21 Ni (810), multiple steps 2-4 layers high are more typical. STM atomic-scale images show the (2 × 2)pg 'clock' re-22 construction on the (100) terraces of the (810) surfaces with both C and N, although a second c(2 × 2) structure, 23 most readily reconciled with a 'rumpling' reconstruction, is also seen on Ni(810)/N. On Ni(911), the clock recon-24 struction is not seen on the (100) terraces with either adsorbate, and these images are typified by protrusions on 25 a (1 × 1) mesh. This absence of clock reconstruction is attributed to the different constraints imposed on the 26 lateral movements of the surface Ni atoms adjacent to the up-step edge of the terraces with a 011 h i step direction.
27