Micro-Plasma synthesis of heterostructures of 2D films of Boron Nitride and Graphene – PlasBoNG

The PlasBoNG project aims to develop a new energy-efficient micro-plasma reactor operating at high pressure (100s mbar) and low temperature (< 800 °C) for the synthesis of large surface areas (10s cm2) of films and heterostructures of hexagonal boron nitride (h-BN) and graphene, and to understand the mechanisms involved in that deposition process using reactive plasmas.
Graphene, because of its superior and novel mechanical, electronic, optical, thermal, magnetic and chemical properties, is a material of choice for a wide range of promising technological applications in nano- and opto-electronics, energy generation and storage, and medicine, among others. Being only one atom thick, graphene is vulnerable to perturbations from its supporting substrate, which can significantly alter or destroy its exceptional properties. To counteract the influence of the substrate, one could suspend graphene or encapsulate it in a material that preserves its properties. As h-BN buffer layers preserve the exceptional electronic properties of graphene, encapsulating it in h-BN can, thus, potentially lead to disruptive technology and is emerging as the long-awaited platform for 2D nanophotonics, spintronics and quantum information processing.
Despite being a strategic material for future high-potential applications, the scientific and industrial communities still lack an efficient growth method allowing the deposition of high quality heterostructures of films of graphene encapsulated in h-BN (h-BN/graphene/h-BN) on large surfaces. In particular, one critical issue is the ability to sufficiently and efficiently dissociate a carbon- or nitrogen-containing precursor, so that it can react and contribute to the growth of films of graphene or h-BN, respectively. This usually implies the use of very high growth temperatures, causing lower energy efficiency and higher environmental and financial costs. However, activating the gas phase with a plasma source is a way to improve the chemical dissociation of the precursors while lowering the thermal budget, as the energetic electrons generated by the plasma boost the dissociation at relatively low temperature.
In this project, we propose a new deposition process using novel arrays of Micro-Hollow Cathode Discharges (MHCD), operated sequentially in gas mixtures of N2-Ar and CH4-Ar, for the synthesis of h-BN (using also boron-containing precursors) and graphene, respectively. Since micro-plasmas are not in thermodynamic equilibrium, it is possible to considerably reduce the deposition temperature. Another advantage of micro-plasmas is their high electron densities (up to 1016 cm-3) that can lead to a high dissociation degree of the precursors.
The PlasBoNG project has three main scientific objectives and challenges:
1) To design and manufacture by plasma micro-machining a new MHCD-type reactor for plasma deposition on large surfaces, easily adaptable to established technologies;
2) To study the physico-chemical properties of the micro-plasma reactor running in reactive gases (N2, CH4) as a function of the operating parameters, through complementary experimental and modeling approaches, aiming the production of the highest atomic nitrogen and carbon radicals C2 densities, key parameters for the deposition and growth of h-BN and graphene films, respectively;
3) To deposit on large surfaces (5 cm in diameter) high quality films of h-BN and graphene, separately and in heterostructures of h-BN/graphene/h-BN, and elucidate the deposition mechanisms when using reactive plasmas.
By providing an innovative energy-efficient deposition process of h-BN and graphene films, it is thus expected that this multidisciplinary project will have a high scientific impact, that will ultimately translate into important economic and social impacts, by unleashing the strong potential of h-BN and graphene.