Signatures of phonon and defect-assisted tunneling in planar metal-hexagonal boron nitride-graphene junctions
Abstract
Electron tunneling spectroscopy measurements on van der Waals heterostructures consisting of metal and graphene (or graphite) electrodes separated by atomically thin hexagonal boron nitride tunnel barriers are reported. The tunneling conductance, dI/dV, at low voltages is relatively weak, with a strong enhancement reproducibly observed to occur at around |V| ≈ 50 mV. While the weak tunneling at low energies is attributed to the absence of substantial overlap, in momentum space, of the metal and graphene Fermi surfaces, the enhancement at higher energies signals the onset of inelastic processes in which phonons in the heterostructure provide the momentum necessary to link the Fermi surfaces. Pronounced peaks in the second derivative of the tunnel current, d2I/dV2, are observed at voltages where known phonon modes in the tunnel junction have a high density of states. In addition, features in the tunneling conductance attributed to single electron charging of nanometer-scale defects in the boron nitride are also observed in these devices. The small electronic density of states of graphene allows the charging spectra of these defect states to be electrostatically tuned, leading to "Coulomb diamonds" in the tunneling conductance.
Additional Information
© 2016 American Chemical Society. Received: October 18, 2016; Revised: November 17, 2016; Published: November 28, 2016. We thank S. Das Sarma, T. Klapwijk, R. Sensarma and L. Zhao for useful discussions, and G. Rossman for the use of his Raman spectroscopy facility. Atomic force microscopy was done at the Molecular Materials Research Center of the Beckman Institute at the California Institute of Technology. This work was supported by the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation through Grant No. GBMF1250. The authors declare no competing financial interest.Attached Files
Accepted Version - acs_2Enanolett_2E6b04369.pdf
Submitted - 1610.03189.pdf
Supplemental Material - nl6b04369_si_001.pdf
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Additional details
- Eprint ID
- 72365
- DOI
- 10.1021/acs.nanolett.6b04369
- Resolver ID
- CaltechAUTHORS:20161129-090026289
- Institute for Quantum Information and Matter (IQIM)
- NSF
- Gordon and Betty Moore Foundation
- GBMF1250
- Created
-
2016-11-29Created from EPrint's datestamp field
- Updated
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2021-11-11Created from EPrint's last_modified field
- Caltech groups
- Institute for Quantum Information and Matter