Darius Constantin Merk
This thesis reports on a novel method for graphene transfer that is fully UHV compatible, which has remained a challenge for a long time due to the necessity of supporting graphene for transfer and most often requiring supporting layer removal post-transfer. Our graphene transfer method is based on the wafer-bonding approach, where graphene is stamped onto a target surface, from a support to which it is weakly bound. We use a bilayer of graphene supported by a teflon tape for the low adhesion between graphene layers and the flexibility of teflon tape to allow adaptability to the target surface.We demonstrate successful transfer onto Cu(100) and Ir(111) single crystal surfaces as well as on gr/Ir(111), thus forming a (partial) graphene bilayer on Ir(111). For in-situ characterization, we use Auger electron spectroscopy and STM. Auger measurements confirm that we are able to transfer an average 0.8-0.9 ML of carbon, by comparison to CVD grown samples. After transfer onto Ir(111), we show that by annealing to 1000 °C, we are able to observe by STM the characteristic moiré pattern formed by CVD grown graphene on Ir(111). Auger spectra show that the graphene-Iridium interaction undergoes a change from physisorption to chemisorption upon annealing. XAS and Raman spectroscopy demonstrate that the annealing step taken post transfer to observe the moiré by STM is only necessary to induce a change in interaction strength but not to heal graphene defects, to increase its domain size, or to make it flat. After transfer onto Cu(100), Raman spectra show that the transferred graphene is of the same quality as the CVD grown graphene before transfer, without further annealing. Comparison of synchrotron based high resolution XAS spectra of transferred gr/Ir(111) to CVD grown samples confirms that the transferred graphene is flat on top of the Ir(111) crystal surface.This enables sample and device fabrication, usually hampered by impurities, to be carried out in UHV leading to fully reproducible results. Clean twisted bilayer graphene samples can be made and studied in UHV. Further, surface science can be extended to the third dimension, by capping layers and continuing growth, etc., all under clean conditions.
EPFL2022
