Growth of High-Quality Hexagonal Boron Nitride Single-Layer Films on Carburized Ni Substrates for Metal-Insulator-Metal Tunneling Devices.

Two-dimensional (2D) hexagonal boron nitride (h-BN) plays a significant role in nanoscale electrical and optical devices because of its superior properties. However, the difficulties in the controllable growth of high-quality films hinder its applications. One of the crucial factors that influence the quality of the films obtained via epitaxy is the substrate property. Here, we report a study of 2D h-BN growth on carburized Ni substrates using molecular beam epitaxy. It was found that the carburization of Ni substrates with different surface orientations leads to different kinetics of h-BN growth. While the carburization of Ni(100) enhances the h-BN growth, the speed of the h-BN growth on carburized Ni(111) reduces. As-grown continuous single-layer h-BN films are used to fabricate Ni/h-BN/Ni metal-insulator-metal (MIM) devices, which demonstrate a high breakdown electric field of 12.9 MV/cm.

Role of Carbon Interstitials in Transition Metal Substrates on Controllable Synthesis of High-Quality Large-Area Two-Dimensional Hexagonal Boron Nitride Layers.

Reliable and controllable synthesis of two-dimensional (2D) hexagonal boron nitride (h-BN) layers is highly desirable for their applications as 2D dielectric and wide bandgap semiconductors. In this work, we demonstrate that the dissolution of carbon into cobalt (Co) and nickel (Ni) substrates can facilitate the growth of h-BN and attain large-area 2D homogeneity. The morphology of the h-BN film can be controlled from 2D layer-plus-3D islands to homogeneous 2D few-layers by tuning the carbon interstitial concentration in the Co substrate through a carburization process prior to the h-BN growth step. Comprehensive characterizations were performed to evaluate structural, electrical, optical, and dielectric properties of these samples. Single-crystal h-BN flakes with an edge length of ∼600 µm were demonstrated on carburized Ni. An average breakdown electric field of 9 MV/cm was achieved for an as-grown continuous 3-layer h-BN on carburized Co. Density functional theory calculations reveal that the interstitial carbon atoms can increase the adsorption energy of B and N atoms on the Co(111) surface and decrease the diffusion activation energy and, in turn, promote the nucleation and growth of 2D h-BN.

Effect of high carbon incorporation in Co substrates on the epitaxy of hexagonal boron nitride/graphene heterostructures.

We carried out a systematic study of hexagonal boron nitride/graphene (h-BN/G) heterostructure growth by introducing high incorporation of a carbon (C) source on a heated cobalt (Co) foil substrate followed by boron and nitrogen sources in a molecular beam epitaxy system. With the increase of C incorporation in Co, three distinct regions of h-BN/G heterostructures were observed from region (1) where the C saturation was not attained at the growth temperature (900 °C) and G was grown only by precipitation during the cooling process to form a 'G network' underneath the h-BN film; to region (2) where the Co substrate was just saturated by C atoms at the growth temperature and a part of G growth occurs isothermally to form G islands and another part by precipitation, resulting in a non-uniform h-BN/G film; and to region (3) where a continuous layered G structure was formed at the growth temperature and precipitated C atoms added additional G layers to the system, leading to a uniform h-BN/G film. It is also found that in all three h-BN/G heterostructure growth regions, a 3 h h-BN growth at 900 °C led to h-BN film with a thickness of 1-2 nm, regardless of the underneath G layers' thickness or morphology. Growth time and growth temperature effects have been also studied.