Step-doubling at Vicinal Ni(111) Surfaces Investigated with a Curved Crystal

Abstract

Vicinal surfaces may undergo structural transformations as a function of temperature or in the presence of adsorbates. Step-doubling in which monatomic steps pair up forming double-atom high staircases is the simplest example. Here we investigate the case of Ni(111) using a curved crystal surface, which allows us to explore the occurrence of step-doubling as a function of temperature and vicinal plane (miscut α and step type). We find a striking A-type ({100}-like microfacets) versus B-type ({111}-like) asymmetry toward step-doubling. The terrace-width distribution analysis performed from scanning tunneling microscopy data points to elastic step interactions overcoming entropic effects at very small miscut α in A-type vicinals, as compared to B-type steps. For A-type vicinals, we elaborate the temperature/miscut phase diagram, on which we establish a critical miscut α c = 9.3° for step-doubling to take place.