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Effect of Electron Injection in Copper-Contacted Graphene Nanoribbons
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. MAX IV, Lund University, Box 118, 22100 Lund, Sweden.; St Petersburg State Univ, VA Fock Inst Phys, St Petersburg 198504, Russia.
MAX IV, Lund University, Box 118, 22100 Lund, Sweden.; St Petersburg State Univ, VA Fock Inst Phys, St Petersburg 198504, Russia.
V.A. Fock Institute of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia.
MAX IV, Lund University, Box 118, 22100 Lund, Sweden.; St Petersburg State Univ, VA Fock Inst Phys, St Petersburg 198504, Russia.
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2016 (English)In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 9, no 9, 2735-2746 p.Article in journal (Refereed) Published
Abstract [en]

For practical electronic device applications of graphene nanoribbons (GNRs), it is essential to have abrupt and well-defined contacts between the ribbon and the adjacent metal lead. By analogy with graphene, these contacts can induce electron or hole doping, which may significantly affect the I/V characteristics of the device. Cu is among the most popular metals of choice for contact materials. In this study, we investigate the effect of in situ intercalation of Cu on the electronic structure of atomically precise, spatially aligned armchair GNRs of width N = 7 (7-AGNRs) fabricated via a bottom-up method on the Au(788) surface. Scanning tunneling microscopy data reveal that the complete intercalation of about one monolayer of Cu under 7-AGNRs can be facilitated by gentle annealing of the sample at 80 A degrees C. Angle-resolved photoemission spectroscopy (ARPES) data clearly reflect the one-dimensional character of the 7-AGNR band dispersion before and after intercalation. Moreover, ARPES and core-level photoemission results show that intercalation of Cu leads to significant electron injection into the nanoribbons, which causes a pronounced downshift of the valence and conduction bands of the GNR with respect to the Fermi energy (Delta E similar to 0.5 eV). As demonstrated by ARPES and X-ray absorption spectroscopy measurements, the effect of Cu intercalation is restricted to n-doping only, without considerable modification of the band structure of the GNRs. Post-annealing of the 7-AGNRs/Cu/Au(788) system at 200 A degrees C activates the diffusion of Cu into Au and the formation of a Cu-rich surface Au layer. Alloying of intercalated Cu leads to the recovery of the initial position of GNR-related bands with respect to the Fermi energy (E (F)), thus, proving the tunability of the induced n-doping.

Place, publisher, year, edition, pages
2016. Vol. 9, no 9, 2735-2746 p.
Keyword [en]
graphene nanoribbons, bottom-up method, copper intercalation, charge injection, ARPES, Scanning tunneling microscopy
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-295867DOI: 10.1007/s12274-016-1162-2ISI: 000382882200023OAI: oai:DiVA.org:uu-295867DiVA: diva2:935266
Funder
Swedish Energy AgencySwedish Research CouncilEU, European Research Council, 321319Knut and Alice Wallenberg Foundation
Available from: 2016-06-10 Created: 2016-06-10 Last updated: 2016-10-26Bibliographically approved
In thesis
1. Effect of Substrate on Bottom-Up Fabrication and Electronic Properties of Graphene Nanoribbons
Open this publication in new window or tab >>Effect of Substrate on Bottom-Up Fabrication and Electronic Properties of Graphene Nanoribbons
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Taking into account the technological demand for the controlled preparation of atomically precise graphene nanoribbons (GNRs) with well-defined properties, the present thesis is focused on the investigation of the role of the underlying metal substrate in the process of building GNRs using bottom-up strategy and on the changes in the electronic structure of GNRs induced by the GNR-metal interaction. The combination of surface sensitive synchrotron-radiation-based spectroscopic techniques and scanning tunneling microscopy with in situ sample preparation allowed to trace evolution of the structural and electronic properties of the investigated systems.

Significant impact of the substrate activity on the growth dynamics of armchair GNRs of width N = 7 (7-AGNRs) prepared on inert Au(111) and active Cu(111) was demonstrated. It was shown that unlike inert Au(111) substrate, the mechanism of GNRs formation on Ag(111) and Cu(111) includes the formation of organometallic intermediates based on the carbon-metal-carbon bonds. Experiments performed on Cu(111) and Cu(110), showed that a change of the balance between molecular diffusion and intermolecular interaction significantly affects the on-surface reaction mechanism making it impossible to grow GNRs on Cu(110).

It was demonstrated that deposition of metals on spatially aligned GNRs prepared on stepped Au(788) substrate allows to investigate GNR-metal interaction using angle-resolved photoelectron spectroscopy. In particular intercalation of one monolayer of copper beneath 7-AGNRs leads to significant electron injection into the nanoribbons, indicating that charge doping by metal contacts must be taken into account when designing GNR/electrode systems. Alloying of intercalated copper with gold substrate upon post-annealing at 200°C leads to a recovery of the initial position of GNR-related bands with respect to the Fermi level, thus proving tunability of the induced n-doping. Contrary, changes in the electronic structure of 7-AGNRs induced by the deposition of Li are not reversible.  It is demonstrated that via lithium doping 7-AGNRs can be transformed from a semiconductor into a metal state due to the partial filling of the conduction band. The band gap of Li-doped GNRs is reduced and the effective mass of the conduction band carriers is increased.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 101 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1385
Keyword
graphene nanoribbons, bottom-up, substrate, metal contact, electronic structure, electron doping, PES, ARPES, NEXAFS, STM
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics Other Physics Topics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-295884 (URN)978-91-554-9610-4 (ISBN)
External cooperation:
Public defence
2016-09-23, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2016-08-16 Created: 2016-06-10 Last updated: 2016-08-25

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