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TY  - THES
AU  - Schmitz, Hans Michael
TI  - CVD-grown graphene in high magnetic fields
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2024-00704
SP  - 1 Online-Ressource : Illustrationen
PY  - 2024
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
N1  - Dissertation, RWTH Aachen University, 2024
AB  - The chemical vapor deposition (CVD) on metal catalyst surfaces is the most promising candidate to enable scalable growth of the two-dimensional (2D) carbon allotrope graphene (Gr), thereby opening the door to applications on industrial scales not realizable by the tape exfoliation techniques commonly applied to cleave micrometer sized Gr flakes from bulk graphite crystals. However, the widely employed wet methods to transfer CVD-grown Gr (CVD-Gr) onto arbitrary substrates were demonstrated to degrade its structural and electronic quality precluding industrial harvesting of its various fascinating properties and even casting doubts over the intrinsic quality of CVD-Gr and its suitability for high-quality (HQ) applications. This thesis aims to prove the equality of the intrinsic capabilities of CVD-Gr and the exfoliated reference material by employing and improving the recently introduced dry-transfer method for CVD-Gr, which allows a direct pick-up from the metal growth substrate and subsequent encapsulation in other 2D-materials, thus avoiding the quality degradation associated with wet transfers. Electronic transport devices patterned from such heterostructures were characterized in temperature-dependent magneto-transport measurements in a high magnetic field laboratory. Quantum Hall effect (QHE) measurements reveal a clear formation of Landau levels (LLs) that is overlayed upon increasing magnetic field and decreasing temperature by symmetry-broken LLs and, finally, by a series of clearly pronounced fractional quantum Hall states with composite fermion filling factors up to ν<sup>*</sup> = 4 and activation gaps well comparable with those observed in similar devices based on exfoliated graphene (Ex-Gr). These data prove for the first time that the quantum mobilities of CVD-Gr match those of Ex-Gr if a suitable transfer method is applied. Discarding fears of intrinsic differences to Ex-Gr, the CVD-Gr devices could be used as a HQ references within a set of other graphene devices hosting varying level of disorder. In a series of further high magnetic fields measurements, the crucial role of long range disorder for the manifestation of the QHE at room temperature (RT) could be clarified, as an increasingly pronounced effect was observed with increasing disorder level and the QHE vanishing in the HQ CVD-Gr devices well below 150 K at 30 T. In a similar study on the device set, a transition of the predominant scattering mechanism in the RTQHE regime from an extrinsic, disorder-mediated to an intrinsic, electron-phonon mediated scattering mechanism with decreasing disorder level could be revealed.
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2024-00704
UR  - https://publications.rwth-aachen.de/record/977415
ER  -