Growth Dynamics of Millimeter‐Sized Single‐Crystal Hexagonal Boron Nitride Monolayers on Secondary Recrystallized Ni (100) Substrates

Abstract

DOI: 10.1002/admi.201901198 with a size close to 1 mm are rare.[9,10] Although wafer-scale single crystals have been reported through the coalescence of identically aligned h-BN domains,[11] on twin-free single-crystal Rh (111) thin films,[12] and on low-symmetry Cu (110) vicinal surface,[13] it is noted that discrete h-BN domains or flakes over 1 mm have not been reported, and the understanding of the growth dynamics remains elusive. Controllable synthesis of large-size single-crystal h-BN is highly desirable but challenging. A great deal of h-BN synthesis is carried out on various transition metal substrates, such as Cu,[1,2,14] Co,[15,16] Ni,[17,18] and Fe,[19–21] thanks to their catalytic activities favorable for the nucleation and growth of high-quality h-BN. Nevertheless, rational engineering of catalytic effects of a given transition metal substrate by alloying or incorporating dissimilar species has been rarely studied for the h-BN growth in order to enhance the control of layer number, nucleation density, and domain size; the only available efforts to date are Si-doping or N-doping of Fe substrates,[19,21] oxygen passivation of Cu substrates,[22] and carbon incorporation of Co/Ni substrates.[10] While majority of the h-BN synthesis effort have been performed using chemical vapor deposition (CVD), molecular beam epitaxy (MBE) is versatile in terms of its ability to precisely control solid, gas, and plasma sources and tune the growth parameters. MBE has already been used to grow 2D h-BN and h-BN/graphene heterostructures.[10,23–29] In this work, we report the synthesis of millimeter-size single-crystal h-BN domains through an interstitial carbon assisted approach in an MBE system. While the interstitial carbon assisted growth of h-BN has been proposed in our recent effort,[10] leading to a large single-crystal h-BN flake of 600–700 μm, it is essential to achieve even larger single-crystal h-BN flakes with edge lengths on the order of millimeters or even continuous waferscale single-crystal 2D films. In addition, the growth thermodynamics and kinetics in terms of temperature-dependent growth and substrate surface engineering have not been comprehensively studied; numerical simulations are necessary to further elucidate the effect of the carbon incorporation on the The outstanding physical properties of 2D materials have sparked continuous research interest in exploiting these materials for next-generation highperformance electronic and photonic technology. Scalable synthesis of highquality large-area 2D hexagonal boron nitride (h-BN) is a crucial step toward the ultimate success of many of these applications. In this work, a synthetic approach in which secondary recrystallized Ni (100) substrates underwent a carburization process, followed by the growth of h-BN in a molecular beam epitaxy system is designed. The h-BN growth dynamics is studied by tuning different growth parameters including the substrate temperature, and the boron and nitrogen source flux ratio. With assistance from density functional theory calculations, the role of interstitial C atoms in promoting h-BN growth by enhancing the catalytic effect of the transition metal, which lowers the nucleation activation energy barrier, is rationalized. Through the control of the growth parameters, a single-crystal h-BN monolayer domain as large as 1.4 mm in edge length is achieved. In addition, a high-quality, continuous, large-area h-BN single-layer film with a breakdown electric field of 9.75 MV cm−1 is demonstrated. The high value of the breakdown electric field suggests that single-layer h-BN has extraordinary dielectric strength for high-performance 2D electronics applications.