Ultra-thin films of solution-exfoliated hexagonal boron nitride by Langmuir deposition

Hexagonal boron nitride (hBN) is being increasingly used in optoelectronic devices to electronically and/or chemically isolate materials like graphene and carbon nanotubes from the environment or other device components. Solution exfoliation is a scalable method to produce large quantities of nanometer-thick hBN but it remains challenging to integrate these discrete flakes into uniform thin films by conventional solution processing approaches. In this work, we demonstrate how a modified Langmuir–Blodgett coating approach can be used to assemble densely tiled layers of the exfoliated hBN flakes arranged edge-to-edge at the air–water interface. These floating films can be transferred to effectively any solid substrate yielding pure hBN films without utilizing any surfactant or polymer additive. Building films layer-by-layer yields pinhole-free films over large areas (>cm²) with high optical transparency per deposition. The use of room temperature processing makes the approach particularly well-suited for use in transparent and flexible devices.