Stoichiometric edges during the intrinsic growth of hexagonal boron nitride on Ir(111)

The growth of hexagonal boron nitride, hBN, on Ir(111) at 1150-1200 K by thermal decomposition of borazine has been monitored in situ by means of low energy electron microscopy, LEEM. A major and unexpected hBN growth induced transformation of the step morphology on Ir(111) is observed. The dominant orientation of the steps evolves persistently from < 1-10 > during the initial experiment(s), towards < 11-2 > after numerous experiments. The latter orientation was established directly from an involved analysis of the profile of the specular beam in a selected area diffraction pattern. Images of the hBN islands grown on surface regions with dominant < 1-10 > steps reveal that the hBN edges are oriented along < 1-10 > and < 11-2 > directions in about equal abundance. Using the direct ascertainment of the step orientations we are able to identify unequivocally the nature of the edges of individual hBN islands on areas with predominant < 11-2 > steps as solely of the armchair type. This assessment consolidates both the major evolution of the step morphology from < 1-10 > into dominant < 11-2 > steps during hBN growth on Ir(111) and the earlier reported alignment of the moire pattern with the substrate.