From deep-ultraviolet light sources to protective coatings and solid-state lubricants, hexagonal boron nitride (hBN) is a contender for a range of applications and could be the lynchpin for heterogeneous 2D devices. So what’s the snag? As with many 2D materials, there is currently no adequate means of synthesizing hBN in sufficiently high quantities without compromising the material quality, a situation partly attributable to the ambiguity that surrounds how these films grow at all. Now research by Luigi Colombo at Texas Instruments Incorporated and colleagues at the University of Texas at Austin has demonstrated a method for controlled growth of hBN on arbitrary substrates, while shedding light on the growth mechanism itself.

Some of the attributes researchers hope to conserve while scaling up production of hBN include high thermal conductivity, its atomically flat crystal surface, excellent insulating properties, superior oxidation resistance, excellent chemical inertness and low friction coefficient. Although mechanical exfoliation is known to yield high-quality samples, Colombo and colleagues investigated the characteristics of hBN grown by chemical vapour deposition, which is a more promising approach for scaling up the quantity produced.

The researchers exposed metal films to diborane and ammonia at high temperatures before allowing it to cool. They used Raman spectroscopy, high-resolution transmission electron microscopy, energy dispersive spectroscopy and time-of-flight secondary ion mass spectroscopy to verify the presence and quality of the films, and confirmed that hBN grew by diffusing into the metal film before segregating out. By controlling the thickness of the metal film substrate, Colombo and colleagues were able to control the thickness of hBN that grew on it.

They then characterized the optical and electrical properties of the film through its breakdown behaviour and its performance integrated into a graphene-based field effect transistor and concluded that the resulting h-BN films had “a near theoretical optical bandgap” and “excellent breakdown strength”. The team suggest that the segregation-precipitation method may be a useful approach that can be applied on any arbitrary substrate for producing h-BN films that can be extended to the wafer scale.

Full details are reported in 2D Materials.