Synthesis of Graphene Nanoribbons on a Kinked Au Surface: Revealing the Frontier Valence Band at the Brillouin Zone Center (original) (raw)
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Electronic Structure Evolution during the Growth of Graphene Nanoribbons on Au(110)
2017
Surface-assisted polymerization of molecular monomers into extended chains can be used as the seed of graphene nanoribbon (GNR) formation, resulting from a subsequent cyclo-dehydrogenation process. By means of valence-band photoemission and ab-initio density-functional theory (DFT) calculations, we investigate the evolution of molecular states from monomer 10,10'-dibromo-9,9'bianthracene (DBBA) precursors to polyanthryl polymers, and eventually to GNRs, as driven by the Au(110) surface. The molecular orbitals and the energy level alignment at the metal-organic interface are studied in depth for the DBBA precursors deposited at room temperature. On this basis, we can identify a spectral fingerprint of C-Au interaction in both DBBA single-layer and polymerized chains obtained upon heating. Furthermore, DFT calculations help us evidencing that GNRs interact more strongly than DBBA and polyanthryl with the Au(110) substrate, as a result of their flatter conformation.
Electronic Structure of Spatially Aligned Graphene Nanoribbons on Au(788)
Physical Review Letters, 2012
We report on a bottom-up approach of the selective and precise growth of subnanometer wide straight and chevron-type armchair nanoribbons (GNRs) on a stepped Au(788) surface using different specific molecular precursors. This process creates spatially well-aligned GNRs, as characterized by STM. High-resolution direct and inverse photoemission spectroscopy of occupied and unoccupied states allows the determination of the energetic position and momentum dispersion of electronic states revealing the existence of band gaps of several electron volts for straight 7-armchair, 13-armchair, and chevron-type GNRs in the electronic structure.
Graphene nanoribbons synthesized from molecular precursor polymerization on Au(110)
2015
A spectroscopic study of 10,10-dibromo-9,9 bianthracene (DBBA) molecules deposited on the Au(110) surface is presented, by means of ultraviolet and X-ray photoemission, and X-ray absorption spectroscopy. Through a thermally activated procedure, these molecular precursors polymerize and eventually form graphene nanoribbons (GNRs) with atomically controlled shape and width, very important building blocks for several technological applications. The GNRs observed by scanning tunneling microscopy (STM) appear as short segments on top of the gold surface reconstruction, pointing out the delicate balance among surface diffusion and surface corrugation in their synthesis on the Au(110) surface.
Precursor Geometry Determines the Growth Mechanism in Graphene Nanoribbons
The Journal of Physical Chemistry C, 2017
On-surface synthesis with molecular precursors has emerged as the de-facto route to atomically well-defined graphene nanoribbons (GNRs) with controlled zigzag and armchair edges. On Au(111) and Ag(111) surfaces, the prototypical precursor 10-10dibromo-9-9-bianthryl (DBBA) polymerizes via an Ullmann route to form straight GNRs with armchair edges. However, on Cu(111), irrespective of the bianthryl precursor (dibromo-, dichloro-or halogen-free bianthryl), the Ullmann route is inactive and instead, identical chiral GNRs are formed. Using atomically resolved non-contact atomic force microscopy (nc-AFM), we study the growth mechanism in detail. In contrast to the non-planar BA-derived precursors, planar dibromo-perylene (DBP) molecules do form armchair GNRs via Ullmann coupling on Cu(111), similar to Au(111). This highlights the role of the substrate, precursor shape and molecule-molecule interactions as decisive factors in determining the reaction pathway. Our findings establish a new design paradigm for the molecular precursors and opens a route to realization of previously unattainable covalently bonded nanostructures.
Electronic structure changes during the surface-assisted formation of a graphene nanoribbon
The Journal of Chemical Physics, 2014
High conductivity and a tunability of the band gap make quasi-one-dimensional graphene nanoribbons (GNRs) highly interesting materials for the use in field effect transistors. Especially bottom-up fabricated GNRs possess well-defined edges which is important for the electronic structure and accordingly the band gap. In this study we investigate the formation of a sub-nanometer wide armchair GNR generated on a Au(111) surface. The on-surface synthesis is thermally activated and involves an intermediate non-aromatic polymer in which the molecular precursor forms polyanthrylene chains. Employing angle-resolved two-photon photoemission in combination with density functional theory calculations we find that the polymer exhibits two dispersing states which we attribute to the valence and the conduction band, respectively. While the band gap of the non-aromatic polymer obtained in this way is relatively large, namely 5.25 ± 0.06 eV, the gap of the corresponding aromatic GNR is strongly reduced which we attribute to the different degree of electron delocalization in the two systems.
On-Surface Synthesis and Characterization of 9-Atom Wide Armchair Graphene Nanoribbons
ACS nano, 2017
The bottom-up approach to synthesize graphene nanoribbons strives not only to introduce a band gap into the electronic structure of graphene but also to accurately tune its value by designing both the width and edge structure of the ribbons with atomic precision. We report the synthesis of an armchair graphene nanoribbon with a width of nine carbon atoms on Au(111) through surface-assisted aryl-aryl coupling and subsequent cyclodehydrogenation of a properly chosen molecular precursor. By combining high-resolution atomic force microscopy, scanning tunneling microscopy, and Raman spectroscopy, we demonstrate that the atomic structure of the fabricated ribbons is exactly as designed. Angle-resolved photoemission spectroscopy and Fourier-transformed scanning tunneling spectroscopy reveal an electronic band gap of 1.4 eV and effective masses of ≈0.1 me for both electrons and holes, constituting a substantial improvement over previous efforts toward the development of transistor applicati...
The Journal of Physical Chemistry C
On-surface synthesis has emerged in the last decade as a method to create graphene nanoribbons (GNRs) with atomic precision. The underlying premise of this bottomup strategy is that precursor molecules undergo a well-defined sequence of inter-and intramolecular reactions, leading to the formation of a single product. As such, the structure of the GNR is encoded in the precursors. However, recent examples have shown that not only the molecule, but also the coinage metal surface on which the reaction takes place, plays a decisive role in dictating the nanoribbon structure. In this work, we use scanning probe microscopy and X-ray photoelectron spectroscopy to investigate the behavior of 10,10′-dichloro-9,9′-bianthryl (DCBA) on Ag(111). Our study shows that Ag(111) can induce the formation of both seven-atom wide armchair GNRs (7-acGNRs) and 3,1-chiral GNRs (3,1-cGNRs), demonstrating that a single molecule on a single surface can react to different nanoribbon products. We additionally show that coadsorbed dibromoperylene can promote surface-assisted dehydrogenative coupling in DCBA, leading to the exclusive formation of 3,1-cGNRs.
Atomically precise bottom-up fabrication of graphene nanoribbons
Nature, 2010
Graphene nanoribbons-narrow and straight-edged stripes of graphene, or single-layer graphite-are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices 1-3 . In particular, although the twodimensional parent material graphene 4,5 exhibits semimetallic behaviour, quantum confinement and edge effects 2,6 should render all graphene nanoribbons with widths smaller than 10 nm semiconducting. But exploring the potential of graphene nanoribbons is hampered by their limited availability: although they have been made using chemical 7-9 , sonochemical 10 and lithographic 11,12 methods as well as through the unzipping of carbon nanotubes 13-16 , the reliable production of graphene nanoribbons smaller than 10 nm with chemical precision remains a significant challenge. Here we report a simple method for the production of atomically precise graphene nanoribbons of different topologies and widths, which uses surface-assisted coupling 17,18 of molecular precursors into linear polyphenylenes and their subsequent cyclodehydrogenation 19,20 . The topology, width and edge periphery of the graphene nanoribbon products are defined by the structure of the precursor monomers, which can be designed to give access to a wide range of different graphene nanoribbons. We expect that our bottom-up approach to the atomically precise fabrication of graphene nanoribbons will finally enable detailed experimental investigations of the properties of this exciting class of materials. It should even provide a route to graphene nanoribbon structures with engineered chemical and electronic properties, including the theoretically predicted intraribbon quantum dots 21 , superlattice structures 22 and magnetic devices based on specific graphene nanoribbon edge states 3 . sketches the basic graphene nanoribbon (GNR) fabrication steps for the prototypical armchair ribbon 6 of width N 5 7 obtained from 10,109-dibromo-9,99-bianthryl precursor monomers. Thermal sublimation of the monomers onto a solid surface removes their halogen substituents, yielding the molecular building blocks of the targeted graphene ribbon in the form of surface-stabilized biradical species. During a first thermal activation step, the biradical species diffuse across the surface and undergo radical addition reactions 17 to form linear polymer chains as imprinted by the specific chemical functionality pattern of the monomers. In a second thermal activation step a surface-assisted cyclodehydrogenation establishes an extended fully aromatic system. shows GNRs obtained according to the scheme in , using precursor monomers 1 and a Au(111) surface. The first step to GNR fabrication-intermolecular colligation through radical addition-is thermally activated by annealing at 200 uC, at which temperature the dehalogenated intermediates have enough thermal energy to diffuse along the surface and form single covalent C-C bonds between each monomer to give polymer chains. Scanning tunnelling microscopy (STM) images of the colligated monomers show protrusions that appear alternately on both sides of the chain axis and with a periodicity of 0.86 nm , in excellent agreement with the periodicity of the bianthryl core of 0.85 nm. Steric hindrance between the hydrogen atoms of adjacent anthracene units rotates the latter around the s-bonds connecting them, resulting in opposite tilts of successive anthracene units with respect to the metal surface. This deviation from planarity explains the large apparent height of the polyanthrylenes of about 0.4 nm , with the finite size of the scanning probe tip moreover imaging the polymer with a width much larger (1.5 nm) than expected from the structural 1 Br Br Precursor monomer 'Biradical' intermediate Graphene nanoribbon Linear polymer Figure 1 | Bottom-up fabrication of atomically precise GNRs. Basic steps for
On-Surface Synthesis of Rylene-Type Graphene Nanoribbons
Journal of the American Chemical Society, 2015
The narrowest armchair graphene nanoribbon (AGNR) with five carbons across the width of the GNR (5-AGNR) was synthesized on Au(111) surfaces via sequential dehalogenation processes in a mild condition by using 1,4,5,8-tetrabromonaphthalene as the molecular precursor. Gold-organic hybrids were observed by using high-resolution scanning tunneling microscopy and considered as intermediate states upon AGNR formation. Scanning tunneling spectroscopy reveals an unexpectedly large band gap of Δ = 2.8 ± 0.1 eV on Au(111) surface which can be interpreted by the hybridization of the surface states and the molecular states of the 5-AGNR.