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Design of Graphene-Nanoribbon Heterojunctions from First Principles
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0003-0007-0394
2011 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 25, 12616-12624 p.Article in journal (Refereed) Published
Abstract [en]

Graphene nanoribbons with armchair and zigzag edges are known to have very different electronic structure and properties. We show here that the fusion of an armchair and a zigzag graphene-nanoribbon (aGNR vertical bar zGNR) can form heterojunctions with remarkable electron transport properties. First-principles calculations reveal that the heterojunction can be either metallic or semiconducting depending on the width of the nanoribbon. A well-defined oscillation of the zero-bias conductance as a function of the ribbon width is observed, which is originated from the resonance and nonresonance of frontier orbitals between aGNR and zGNR We find that the current/voltage characteristics of the aGNR vertical bar zGNR heterojunction possess pronounced rectification effect, and a high rectification ratio can be achieved by tuning the width of the zGNR to minimize the backward current. The unique properties of the proposed heterojunction could be very useful for manufacturing graphene-based electronic devices.

Place, publisher, year, edition, pages
2011. Vol. 115, no 25, 12616-12624 p.
Keyword [en]
MOLECULAR RECTIFICATION, ELECTRONIC TRANSPORT, QUANTUM INTERFERENCE, ROOM-TEMPERATURE, RECTIFIERS
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-36238DOI: 10.1021/jp202188tISI: 000291896000049Scopus ID: 2-s2.0-79959505713OAI: oai:DiVA.org:kth-36238DiVA: diva2:430608
Note
QC 20110711Available from: 2011-07-11 Created: 2011-07-11 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Electron and Spin Transport in Graphene-Based Nanodevices
Open this publication in new window or tab >>Electron and Spin Transport in Graphene-Based Nanodevices
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is devoted to the multi-scale modeling of electron and spin transport in graphene-based nanodevices. Several devices with fascinating structures and attractive properties have been designed by means of state-of-the-art computational methods, which include ab-initio molecular dynamics (MD) simulations for the geometry, density functional theory (DFT) for the electronic structure, and non-equilibrium Green’s functions (NEGF) for carriers transport properties.

Poly-crystalline graphenes offer ample opportunities to make devices with desirable properties. We have systematically studied a type of poly-crystalline graphene constructed by zigzag and armchair graphene nanoribbons (ZGNR and AGNR). It is found that the choice of the supercells in modeling with periodic boundary conditions (PBC) has strong implications on the electronic and magnetic properties of such hybrid systems. A model with minimal lattice mismatch is obtained, which could be regarded as the most appropriate model for hybrid GNRs. With this model, it is revealed that the hybrid GNR is of ferromagnetism with a high Curie temperature. We have then designed armchair/zigzag graphene nanoribbon heterojunctions (AGNR|ZGNR) with a well-defined conductance oscillation and rectification behavior. It is shown that the resonance or nonresonance of the frontier orbitals between AGNR and ZGNR is the source of the oscillation and the asymmetric structure is the root of the rectification. A high rectification ratio can be achieved by tuning the width of ZGNR to enhance the asymmetric character of transmission function and to minimize the backward current.

The electron transport properties of graphene can be modified by hydrogenation strips (HSs) formed from the absorbed hydrogen atoms. We have designed a new graphene nanoribbon that has zigzag-edged HSs placed at its middle region. It is found that the HS can electrically separate the GNR into sub-GNRs and each HS introduces two spin-polarized conducting edge-like states around the Fermi level. This leads to a significant enhancement of the conductance and the spinpolarization. We have also found that by introducing embedding a short sp3-edged section into the sp2-edged ZGNRs or a short sp2-edged section into the sp3-edged ZGNRs, the orbital symmetry mismatch between these two sections can induce the opening of the conductance energy gap in ZGNRs over a wide energy region. This simple strategy explains many unexplained experimental results and offers a simple strategy to design GNRs with a proper energy gap.

We have also carefully examined the spin-polarization of chiral GNRs with reconstructed (2,1)-edges. It is found that the unsaturated (2,1)-edged chiral GNRs can possess strong current polarizations (nearly 100%) and a striking negative differential resistance (NDR) behavior.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xii, 85 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2013:3
National Category
Theoretical Chemistry
Research subject
SRA - Transport
Identifiers
urn:nbn:se:kth:diva-116568 (URN)978-91-7501-622-1 (ISBN)
Public defence
2013-02-18, FA32, AlbaNova Universitetscentrum, Roslagstullsbacken, Stockholm, 15:02 (English)
Opponent
Supervisors
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20130123

Available from: 2013-01-23 Created: 2013-01-21 Last updated: 2013-01-23Bibliographically approved

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