Step edge-mediated assembly of periodic arrays of long graphene nanoribbons on Au(111)

Abstract

The influence of substrate steps on the bottom-up synthesis of atomically precise graphene nanoribbons (GNRs) on an Au(111) surface is investigated. A straight surfacestep is found to promote the assembly of long and compact arrays of polymers with enhanced interchain π−π stacking interaction, which creates a steric hindrance effect on cyclodehydrogenation to suppress the H passivation of polymer ends. The modified two-stage growth process results in periodic arrays of GNRs with doubled average length near step edges.

On-surface cyclodehydrogenation reaction pathway determined by selective molecular deuterations

“…Below we differentiate these cyclodehydrogenation pathways using Raman and in-situ mass spectrometry measurements along with theoretical calculations. structures to those of the pristine 7-aGNRs, 16,32,33,36,41 and thus the analysis of our STM data here 8 modes of BLM3 in the pristine and deuterated 7-aGNRs (grey for C, red for D, and white for H).…”

“…The dihedral angle between the neighboring anthrylene units is less than 90° even for the initial polymer state. 33 Consequently, the two local atomic orbitals at the two bridge-head C atoms are not completely orthogonal to each other. 49 As the neighboring anthrylene units rotate about the polymer axis to approach each other, the dihedral angle between them is reduced from that in the initial state i.…”

“…[20][21][22][23][24][26][27][28] A prominent case is the seven-carbon-wide armchair GNR (7-aGNR) made from 10,10'-dibromo-9,9'-bianthracene (DBBA) molecular precursors on Au(111) surface through dehalogenation/polymerization 29 followed by cyclodehydrogenation. 16,[30][31][32][33] The cyclodehydrogenation step presents extremely high regioselectivity resulting from the steric hindrance effect between neighboring anthrylene units, making it a prototypical reaction for unraveling the mechanisms by experimental studies along with density functional theory (DFT) calculations. In 2011, Björk et al proposed theoretically a reaction pathway where new C aryl -C aryl bond formation is followed by simultaneous elimination of two H atoms from the two bonding C atoms to the Au(111) substrate.…”

Band Structure and Energy Level Alignment of Chiral Graphene Nanoribbons on Silver Surfaces

“…In fact, in addition to the uniaxially aligned ribbons on top of the flat terraces, the ribbons display a particular affinity to the steps, adsorbing in a tilted configuration with either side of the GNR on each of the two neighboring terraces (Figure 2a). Both of these findings were expected, since stepped surfaces have been used often for alignment purposes [7,[20][21][22][23][24], and many molecules, including GNRs [22,25], are known to display a particular affinity for adsorption on the undercoordinated and thus more reactive step atoms. Around the central (111) substrate orientation, displaying ample flat terraces, the ribbons adsorb with multiple azimuthal orientations, as expected from the six-fold symmetry of the surface (Figure 2b).…”

“…2a). Both of these findings were expected, since stepped surfaces have been used often for alignment purposes 7,14-18 and many molecules, including GNRs, 16,19 are known to display particular affinity for adsorption on the undercoordinated and thus more reactive step atoms. In the central part of the crystal, displaying ample flat terraces, the ribbons adsorb with multiple azimuthal orientations, as expected from the six-fold symmetry of the surface (Fig.…”