Transport Properties of Bilayer Graphene Nanoribbons
Nov 20, 2012
from 10:00 AM to 12:00 PM
|Where||Engr. IV Bldg., Tesla Room 53-125|
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Advisor: Prof Kang L. Wang
Bilayer graphene and graphene nanoribbon devices have earned great observance for their unique electronic properties and commendable use in electronic applications. In this study, bilayer graphene nanoribbons (BL-GNRs) were fabricated by nanowire mask method, and transport properties were characterized. The measured transport gaps are remarkably larger than the combination of possible confinement gap and field induced gap, revealing the disorder dominant nature. The observed periodic Coulomb oscillations indicate the formation of a single quantum dot within the BL-GNR because of the broad distribution function of the carrier concentration fluctuation at the charge neutrality point. The size of the QD changes as we modulate the relative position between the Fermi level and surface potential. Furthermore, the potential barriers forming the QD remain stable at elevated temperatures and external bias. In combination with the observation of transport gaps, our results suggest that the disordered surface potential creates QDs along the ribbon and governs the electronic transport properties in BL-GNRs.
Furthermore, from the measurement on dual gated BL-GNR devices, the unique evolution pattern of the transport gap with the changing of the perpendicular electrical field at the charge neutral points was clearly observed. Comparing with the theoretically predicted field induced gap, the transport gaps follow the trend of the field induced gap with an energy difference varying from sample to sample at high field, whilst at low field the difference increased to the value of pure transport gap. At the same time, the averaging conductance inside of the transport gap, which is corresponding to the potential fluctuation, also increases with decreasing field. These effects can be explained by the superposition of the potential fluctuation on the field induced gap in bilayer graphene nanoribbons.
Minsheng Wang is currently a PhD candidate in Device Research Laboratory (DRL), Electrical Engineering Department, UCLA. He received both his B.sc. and M.sc. degrees from Electrical engineering department in Tsinghua University, Beijing, China. His research focus is on design, fabrication and characterization carbon based electronic devices.