Unidirectional alignment and orientation pinning mechanism of h-BN nucleation on Ir(111) via reactive probe atomic force microscopy

Abstract

Abstract The epitaxial growth of wafer-scale single-crystalline two-dimensional materials requires precise control over the crystallographic orientation and morphology of clusters formed during the initial stages of nucleation. However, there is limited knowledge about the critical nucleus and its growth mechanism for h-BN on high-symmetry surfaces of transition metals. In this study, we provide atomic insights into h-BN nucleation on Ir(111) using scanning tunneling microscopy and noncontact atomic force microscopy, corraborated by density functional theory (DFT) calculations. The atomic-resolved structural characterization reveals that the smallest h-BN cluster, exhibiting a non-1:1 stoichiometric ratio of boron and nitrogen atoms, maintains a triangular shape with zigzag-type edges. Through force spectroscopy, individual B and N atoms within the cluster, as well as the N-termination edge, are clearly identified, indicating the atomic-scale elemental sensitivity of the chemical-reactive metallic tip. While DFT calculations suggest that the NtopBfcc configuration is thermodynamically favored for larger clusters, a predominant crystalline orientation is observed for nuclei of various sizes, unequivocally attributed to the NtopBhcp registry. This orientation pinning behavior presents opportunities for large-scale growth of binary and ternary materials by impeding rotational alignment of nuclei in the early stages of nucleation.