Two dimensional materials have been put forward as a promising component for future electronic, photonic, energy, sensing and even other applications. Since the discovery of graphene, new 2D materials (e.g. transition metal dichalcogenides - TMDs) have emerged and are actively investigated. The 2D nature of these TMDs offer ultimate thickness scaling and have the potential to be used as an active material in future low-power electronic applications. Hexagonal boron nitride (h-BN) is another 2D material that receives considerable attention as a dielectric material for 2D electronics. Due to its sp2 hybridized bonding and inter-planar van der Waals bonds, h-BN is often called ‘white graphene’. The idealized h-BN material has no dangling bonds and is atomically flat. A h-BN layer combines these properties with a low dielectric screening and a large optical bandgap. As a result, the material has shown to be an ideal substrate for graphene or TMDs and can serve as a 2D gate dielectric. A lot of the pioneering work has been done with exfoliated h-BN flakes, which showed that h-BN is a superior substrate for graphene and TMDs. Furthermore, a h-BN layer could also serve as an ideal template for subsequent graphene or TMD growth, which will also minimize the number of transfer steps.
The growth and transfer of high quality h-BN with a controlled number of layers remains a very challenging task. Chemical vapor deposition synthesis of single layer h-BN with grains of several tens of micrometer has recently been demonstrated at high temperatures, but pathways to further reduce the h-BN defectivity and increase control over the number of layers need to be explored. Compared to graphene, the growth of h-BN is inherently more complex since two elements need to be incorporated in the 2D structure. Incorporation of B and N from the surface, subsurface and bulk of the catalyst layer needs to be taken into account. In order to grow high quality material with a minimum of grain boundaries, an orientation distribution of h-BN domains and twin domains on the catalyst layer are preferably avoided. An in-depth characterization procedure of the as-grown material will have to be developed, and several analysis techniques (e.g. scanning electron microscopy, Raman, atomic force microscopy, transmission electron microscopy, X-ray photoemission spectroscopy... ) will have to be combined to understand thoroughly the h-BN properties. Electrical characterization of h-BN using hybrid 2D devices or metal/hBN/metal capacitors will be another possibility to assess the h-BN material. The h-BN layers will be combined with other 2D materials. The stacking of synthetic 2D materials will need to be optimized, which could be the way forward to achieve clean interfaces and reproducible 2D device characteristics.
Type of work: 10% Literature study, 60% Experimental work (CVD growth, development of wafer catalyst) and 30% Data analysis
Supervisor: Stefan De Gendt
Daily advisor: Steven Brems
The reference code for this PhD position is STS1712-38. Mention this reference code on your application form.