One-Dimensional Graphene Devices

One-dimensional devices made of graphene are of great interest to study mesoscopic quantum transport phenomena. On one hand, one can define one dimensional channels by electrostatic gating with the advantage that the edges do not play a significant role in the transport characteristics. On the other hand, atomically precise graphene nanoribbons (GNRs) are predicted to exhibit exceptional edge-related properties, such as localized edge states, spin polarization, and half-metallicity. However, creating a good contact between electrodes and GNRs has been a longstanding challenge as it requires the controlled fabrication of sub-20 nm metallic gaps, a clean GNR transfer minimizing damage and organic contamination during the device fabrication, as well as work function matching to minimize the contact resistance. Here, I will discuss examples of both approaches: electron focusing and collimation experiments in bi-layer graphene channels defined by electrostatic gating and our progress in contacting 9-atom-wide armchair-edged GNRs with Pt, MoRe and Pd contacts. The two latter metals are known to provide low-contact resistance to carbon nanotubes. Density functional theory (DFT) calculations combined with the non-equilibrium Green’s function method (NEGF) explain the observed p-type electrical characteristics using Pt electrodes and demonstrate that Pt gives a strong coupling and higher transmission in comparison to other materials such as graphene. Detailed electrical characterizations of the MoRe and Pd nanogaps, at various bias/gate voltages and temperatures allow us to investigate the formation of Schottky barriers at metal-GNR interface and extract the activation energies.