Growth, domain structure, and atomic adsorption sites of hBN on the Ni(111) surface

Abstract

One of the most important functionalities of the atomically thin insulator hexagonal boron nitride (hBN) is its ability to chemically and electronically decouple functional materials from highly reactive surfaces. It is therefore of utmost importance to uncover its structural properties on surfaces on an atomic and mesoscopic length scale. In this paper, we quantify the relative coverages of structurally different domains of a hBN layer on the Ni(111) surface using low-energy electron microscopy and the normal incidence x-ray standing wave technique. We find that hBN nucleates on defect sites of the Ni(111) surface and predominantly grows in two epitaxial domains that are rotated by ${60}^{\ensuremath{\circ}}$ with respect to each other. The two domains reveal identical adsorption heights, indicating a similar chemical interaction strength with the Ni(111) surface. The different azimuthal orientations of these domains originate from different adsorption sites of N and B. We demonstrate that the majority ($\ensuremath{\approx}70%$) of hBN domains exhibit a $(\mathrm{N},\mathrm{B})=(\mathrm{top},\mathrm{fcc})$ adsorption site configuration while the minority ($\ensuremath{\approx}30%$) show a $(\mathrm{N},\mathrm{B})=(\mathrm{top},\mathrm{hcp})$ configuration. Our study hence underlines the crucial role of the atomic adsorption configuration in the mesoscopic domain structures of in situ fabricated two-dimensional materials on highly reactive surfaces.