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Signatures of phonon and defect-assisted tunneling in planar metal-hexagonal boron nitride-graphene junctions

Chandni, U. and Watanabe, K. and Taniguchi, T. and Eisenstein, J. P. (2016) Signatures of phonon and defect-assisted tunneling in planar metal-hexagonal boron nitride-graphene junctions. Nano Letters, 16 (12). pp. 7982-7987. ISSN 1530-6984. doi:10.1021/acs.nanolett.6b04369.

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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.

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Watanabe, K.0000-0003-3701-8119
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.
Group:Institute for Quantum Information and Matter
Funding AgencyGrant Number
Institute for Quantum Information and Matter (IQIM)UNSPECIFIED
Gordon and Betty Moore FoundationGBMF1250
Subject Keywords:Coulomb blockade; graphene; hBN; hBN defects; hexagonal boron nitride; IETS; phonon-assisted tunneling; Tunneling
Issue or Number:12
Record Number:CaltechAUTHORS:20161129-090026289
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Official Citation:Signatures of Phonon and Defect-Assisted Tunneling in Planar Metal–Hexagonal Boron Nitride–Graphene Junctions U. Chandni, K. Watanabe, T. Taniguchi, and J. P. Eisenstein Nano Letters 2016 16 (12), 7982-7987 DOI: 10.1021/acs.nanolett.6b04369
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:72365
Deposited By: Tony Diaz
Deposited On:29 Nov 2016 18:08
Last Modified:11 Nov 2021 05:00

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