Master's thesis presentation Johanna Huhtasaari

Examiner: Samuel Lara-Avila
Opponent: Karn Rongrueangkul

Abstract: In this presentation, I will show the initial steps towards flat-band physics in graphene-based devices. Flat bands – constant electron energy dispersion in a solid – can give rise to many intriguing quantum states such as superconductivity observed in twisted magic angle graphene.
I will present an approach intended to relax the experimental conditions to achieve flat bands in twisted layers of graphene, using AB-stacked bilayer graphene. The starting point is epitaxial monolayer graphene on silicon carbide (epigraphene) which is subsequently hydrogen intercalated. Intercalation transforms epigraphene into AB-stacked bilayer graphene, and weakens the adhesion to the substrate, facilitating delamination and transfer of the entire crystal onto arbitrary substrates.
Material is characterized using surface science techniques and electron transport measurements.  Angle-Resolved Photoemission Spectroscopy (ARPES) and Low-Energy Electron Diffraction (LEED) indicate that hydrogen intercalation of epigraphene results in AB-stacked bilayer on SiC. Electronic transport measurements on graphene transferred to SiO2 display mobilities in the 1000 cm2/(V s) range. At low temperatures (T = 2 K) and low magnetic fields (B ≲ 200 mT), weak localization reveals different scattering mechanisms of the transferred graphene.
Altogether, the uniformity and reproducibility of transfer of millimeter-scale graphene single-crystals, together with the observed electronic quality, make this a promising material platform to build twisted stacks of graphene.