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Effect of Substrate Chemistry on the Bottom-Up Fabrication of Graphene Nanoribbons: Combined Core-Level Spectroscopy and STM Study
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.
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.
V.A. Fock Institute of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia.
MAX IV, Lund University, Box 118, 22100 Lund, Sweden.
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2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 23, 12532-12540 p.Article in journal (Refereed) Published
Abstract [en]

Atomically precise graphene nanoribbons (GNRs) can be fabricated via thermally induced polymerization of halogen containing molecular precursors on metal surfaces. In this paper the effect of substrate reactivity on the growth and structure of armchair GNRs (AGNRs) grown on inert Au(111) and active Cu(111) surfaces has been systematically studied by a combination of core-level X-ray spectroscopies and scanning tunneling microscopy. It is demonstrated that the activation threshold for the dehalogenation process decreases with increasing catalytic activity of the substrate. At room temperature the 10,10'-dibromo-9,9'-bianthracene (DBBA) precursor molecules on Au(111) remain intact, while on Cu(111) a complete surface-assisted dehalogenation takes place. Dehalogenation of precursor molecules on Au(111) only starts at around 80 degrees C and completes at 200 degrees C, leading to the formation of linear polymer chains. On Cu(111) tilted polymer chains appear readily at room temperature or slightly elevated temperatures. Annealing of the DBBA/Cu(111) above 100 degrees C leads to intramolecular cyclodehydrogenation and formation of flat AGNRs at 200 degrees C, while on the Au(111) surface the formation of GNRs takes place only at around 400 degrees C. In STM, nanoribbons have significantly reduced apparent height on Cu(111) as compared to Au(111), 70 +/- 11 pm versus 172 +/- 14 pm, independently of the bias voltage. Moreover, an alignment of GNRs along low-index crystallographic directions of the substrate is evident for Cu(111), while on Au(111) it is more random. Elevating the Cu(111) substrate temperature above 400 degrees C results in a dehydrogenation and subsequent decomposition of GNRs; at 750 degrees C the dehydrogenated carbon species self-organize in graphene islands. In general, our data provide evidence for a significant influence of substrate reactivity on the growth dynamics of GNRs.

Place, publisher, year, edition, pages
2014. Vol. 118, no 23, 12532-12540 p.
National Category
Physical Chemistry Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:uu:diva-228705DOI: 10.1021/jp502215mISI: 000337497400051OAI: oai:DiVA.org:uu-228705DiVA: diva2:734873
Funder
Swedish Research CouncilSwedish Energy AgencyEU, European Research Council, 321319
Available from: 2014-07-21 Created: 2014-07-21 Last updated: 2017-12-05
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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Simonov, Konstantin A.Mårtensson, Nils

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