Fabrication and electrical transport properties of twisted bilayer graphene devices

Twisted bilayer graphene devices have been in the spotlight since 2018 and the discovery of superconducting states at the magic angle. It is probably the simplest member of the broader family of 2D Van der Waals heterostructures. The many degrees of freedom in these structures, ranging from the chemical nature of the layers to the relative orientations of their crystalline lattices, yield the access to a wide variety of properties, many of which are yet to be discovered. In twisted bilayer graphene, it is the ability to continuously tune the band structure and especially the band velocity that has sparked the interest of researchers. In particular, at the so-called magic angle, the band velocity of twisted bilayer graphene almost vanishes giving rise to strongly correlated electronic systems, home to many exotic properties, such as the superconducting state. In this master thesis, a fabrication process for the creation of twisted bilayer graphene devices is developed and presented. Twisted bilayer graphene encapsulated in hexagonal boron nitride samples were created from scratch and characterized optically and with Raman spectroscopy. The process is based on dry transfer of exfoliated graphene and h-BN flakes. The presented method is especially easy and efficient for the creation of a wide variety of Van der Waals heterostructures. The characterization of the samples indicated that the method was successful at stacking the different layers in the desired configurations. For example, the Raman signatures of the twist angle between the graphene layers has been observed. However, this works also presents some minor issues that still need to be addressed before the process can serve for the creation of usable samples.