Molecular Beam Epitaxy Growth of Monolayer Hexagonal Boron Nitride on Nickel Substrates Incorporated with Oxygen Atoms

Abstract

Reliable and controllable growth of two dimensional hexagonal boron nitride (h-BN) is essential for its wide range of applications. Here, we carried out molecular beam epitaxy (MBE) growth of monolayer h-BN on nickel (Ni) substrates by using ammonia (NH) and boron oxide (B04) as the sources. It was found that compared with normal growth of h-BN by introducing the NH, and B,0., source at the same time, the pretreatment with B,0, greatly inhibited the following epitaxial growth of h-BN. With the increase of B,0, pretreatment time and then followed by 15 min h-BN growth, the coverage of h-BN exhibited an exponential decay relationship with the treatment time. The samples were analyzed using depth-profiling X-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). The oxygen/Ni peak intensity ratios derived from the XPS showed that the oxygen concentration increased with the increase of B,0, pretreatment time from the surface while decreased gradually with the increase of XPS sputtering depth. Meanwhile, boron incorporation was negligible regardless of treatment time. The epitaxial relationship was studied by using h-BN coverage-dependent RHEED analysis, obtained on samples including Ni substrate after annealing only, Ni substrate with BAO pretreatment, h-BN samples with the B,03 pretreatment and subsequent 50%, and 100% film coverage. Only two sets of patterns were observed and separated by 30, confirming that there is no in-plane rotation between the h-BN and Ni (111) surface. The oxygen incorporated into the Ni substrate not only suppressed h-BN nucleation by passivating the Ni surface active sites, but also decreased the growth rate of single crystal h-BN domains, shifting from larger sizes to smaller shapes. Detailed structural, optical and electrical characterizations of these monolayer h-BN films will also be presented. Our work reveals the influence of oxygen on the catalytic effect of Ni in the MBE growth of monolayer h-BN and provides an efficient way to control the morphology and quality of the 2D h-BN films.