Research / Advanced Nanofabrication
To date, the 2D materials family has thousands of crystals with diverse optoelectronic properties, including wide and narrow-band semiconductors, metals and semimetals, superconductors, ferromagnets and antiferromagnets. The most famous representatives include the semi-metallic graphene, the wide band-gap insulator hBN, and the semiconducting transition metal dichalcogenides (TMDs), which gained scientific momentum due to their exciting properties and exceptional environmental stability in monolayer form.
However, 2D crystals are not only interesting in isolated form. Much of the excitement of 2D materials stems from our ability to combine them in any desired sequence layer-by-layer and with controlled twisting angles to produce 2D material heterostructures (2DMH) with atomically sharp and clean interfaces. Unlike conventional crystal growth, their fabrication is not restrained by lattice matching or interfacial chemistry and therefore offers a versatile platform for creating unique quantum and optoelectronic metamaterials with properties tailored for particular applications.
2DMHs are fabricated stacking atomically thin layers of materials on top of each other, in a fashion similar to LEGO blocks.
Trapped hydrocarbon bubbles at the graphene-hBN interface.
Despite the great academic interest and high application potential, the field has been held back by the extreme cleanliness necessary to reach the limit where 2DMH display quantum properties. All existing techniques rely on polymeric matrices to produce the stacks, and cannot avoid the presence of airborne hydrocarbon molecules on the surface of the exfoliated crystals. When trapped between layers, these molecules coalesce into bubbles and distort the properties of the 2DMH.
Furthermore, many 2D materials are very sensitive to air, degrading fast when exposed to the atmosphere. Thus, they require special fabrication procedures performed in controlled environments such as argon or vacuum, in order to preserve the intrinsic properties of the crystals.
One of our main directions is development of a unique ultrahigh vacuum (UHV) multi-chamber cluster tool, that allows stacking 2D crystals at pressures down to UHV, comparable with the state-of-the-art of other fabrication techniques such as molecular beam epitaxy (MBE).
Together with this, a ground-breaking heterostructure fabrication procedure has been developed by the team substituting the ubiquitous polymeric matrices by completely inorganic, UHV-compatible technology. The combination of these two technologies ensures the complete removal of hydrocarbon contamination, and eliminates the oxygen- and water-induced degradation of sensitive 2D materials. Removing this obstacles bring us much closer to achieving electronic-grade 2D heterostructure technology, the key for the development of novel nanoscale applications based on 2D materials in quantum technologies, low-power (opto)electronics.