New micro-plasma reactors for the synthesis of heterostructures of 2D films of hexagonal boron nitride and graphene

Graphene is a material of choice for a wide range of promising technological applications in nano- and optoelectronics. To prevent the hindrances of the substrate, graphene can be encapsulated in a material that preserves its properties. The search for new substrates revealed that hexagonal Boron Nitride (h-BN) buffer layers can preserve the properties of graphene [1], thus potentially leading to new disruptive technologies. To try to answer this issue, our work focuses on the development of a new deposition process using a new micro-plasma configuration based on the classical Micro-Hollow Cathode Discharge (MHCD), which has shown promising perspectives [2-4].

A detailed electro-optical characterization of the different micro-plasma devices used has been performed, for several operating conditions, from pure argon to argon-nitrogen mixtures, from few tens to several hundreds of mbars of pressure, from DC to high-frequency (tens of kHz) nano-second pulsed electrical schemes. The complementarity of electric measurements and fast ICCD imaging, from a transverse and longitudinal perspective, along with edge-detection algorithms, allowed to highlight the characteristics of the development of the cathodic expansion as a function of the current deposited in the plasma. The main implications of our experimental results are the fact the plasma is not, as stated in the literature, confined in the hole in the abnormal regime, reaching further out of the hole on the cathode side, depending on the pressure and gas species. In the normal regime, the cathodic expansion spreads at lower currents the further it is from the electrode. When the plasma can no longer extend, limited by the electrode surface, it is forced to undergo through a second abnormal regime, now extending itself in volume.