A scanning tunnelling microscopy study of C and N adsorption phases on the vicinal Ni(100) surfaces Ni(810) and Ni(911)

- STM shows C- and N-induced step bunching and reconstruction of Ni(100) vicinals.
- Ni(810)/C and Ni(100)/N terraces both show (2 × 2) 'clock' reconstruction.
- Clock reconstruction of (100) terraces suppressed by < 110 > (but not < 100 >) steps.
- Evidence of 'rumpling' reconstructions on terraces with < 110 > steps.
- Different terrace reconstructions rationalised by lateral constraints at steps.

The influence of N and C chemisorption on the morphology and local structure of nominal Ni(810) and Ni(911) surfaces, both vicinal to (100) but with [001] and 011¯ step directions, respectively, has been investigated using scanning tunnelling microscopy (STM) and low energy electron diffraction. Ni(911) undergoes substantial step bunching in the presence of both adsorbates, with the (911)/N surface showing (411) facets, whereas for Ni(810), multiple steps 2-4 layers high are more typical. STM atomic-scale images show the (2 × 2)pg 'clock' reconstruction on the (100) terraces of the (810) surfaces with both C and N, although a second c(2 × 2) structure, most readily reconciled with a 'rumpling' reconstruction, is also seen on Ni(810)/N. On Ni(911), the clock reconstruction is not seen on the (100) terraces with either adsorbate, and these images are typified by protrusions on a (1 × 1) mesh. This absence of clock reconstruction is attributed to the different constraints imposed on the lateral movements of the surface Ni atoms adjacent to the up-step edge of the terraces with a 011¯ step direction.

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