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2019-05-22
S3 SEMINAR Tony Cafolla
15:00 - 16:00
Date and Time: Wednesday May 22, 2019 - 15.00
Venue: S3 Seminar Room, Third Floor, Physics Building, FIM Department
Speaker: Tony Cafolla
Dublin City University
Title: Synchrotron and STM studies of bottom-up synthesised graphene nanoribbons
Abstract:In recent years graphene nanoribbons (GNRs) have received much attention due to their remarkable structural and electronic properties. These properties vary dramatically with
changes in the atomic structure of the GNR in terms of width, edge termination, dopant
heteroatoms, and crystallographic symmetry. Moreover, the electronic properties can be
modulated even further by the appropriate design of GNR heterostructures or by additional
functionalisation. This enormous tunability of the electronic properties is thus extremely
promising for next-generation nanoelectronic and optoelectronic devices. The high
susceptibility of these properties to small changes in the GNR structure also indicates the
need for atomic precision in GNR synthesis. To date, the bottom up synthesis, first
demonstrated by Cai et al. [1], is the only technique offering the required level of precision.
While a large range or precursor molecules have been synthesised for the bottom up
synthesis of GNRs with different edge orientations, widths, or heteroatoms, only a few GNRs
have been successfully synthesised with the required precision. To date, the most widely
studied nanoribbon is the armchair oriented GNR with seven dimer lines across its width (7-
AGNR) grown from 10,10?-dibromo-9,9?-bianthracene precursor in a multistep reaction,
including dehalogenation, polymerization and cyclodehydrogenation. In this talk I discuss the
effect of the structure and chemistry of the underlying metal substrate on the GNR growth
process. The growth of GNRs has been followed in detail by combining core level and x-ray
absorption spectroscopies, scanning tunnelling microscopy, and density functional theory
calculations, thus providing a clear correlation between the spectroscopic fingerprints and
the different reaction processes [2,3]. For the fabrication of functional multicomponent
nano-systems the covalent bonding of organic molecules within the GNR is desirable. In this
talk we also discuss an on-surface synthesis method for functionalization of GNRs with
porphyrin molecules. These novel porphyrin-functionalised graphene-nanoribbons (PyfGNRs),
are expected to exhibit significantly different electronic, chemical, transport and
optical properties than the GNR or Py. The versatile chemical functionality of the different
transition metals within the integrated-porphyrin macrocycle (TM-Py), determines much of
these electronic, optical, and chemical properties, as well as defining the transport and spintransport
properties. With STM we determine the possible distinct configurations that occur
when the porphyrin couples to the GNR. These configurations are explored by DFT
calculations which reveal a large reduction in the HOMO-LUMO band-gap on the porphyrin
molecule.
[1] J. Cai et al., Atomically precise bottom-up fabrication of graphene nanoribbons. Nature 466,
pages 470–473 (2010). doi:10.1038/nature09211
[2] K.A. Simonov et al., Synthesis of armchair graphene nanoribbons from the 10,10 '-dibromo-9,9'-
bianthracene molecules on Ag(111): the role of organometallic intermediates. Scientific
Reports, 8 Article 3506 (2018)
[3] K.A. Simonov et al., From Graphene Nanoribbons on Cu(111) to Nanographene on Cu(110):
Critical Role of Substrate Structure in the Bottom-Up Fabrication Strategy. ACS Nano, 9, 9 8997
(2015)
Host: Valentina De Renzi valentina.derenzi@unimore .it.