Graphene Nanoribbon-Graphdiyne Lateral Heterojunctions with Atomically Abrupt Interfaces

TL;DR

The paper addresses the challenge of creating all-carbon lateral 2D heterostructures with atomically abrupt interfaces. It employs on-surface synthesis on Au(111) to forge covalently bonded hGDY–aGNR heterostructures, supported by LT-STM imaging and DFT/NEGF transport modeling. Key findings include a bonding mechanism via thermally induced rupture of C–Au and Au–Br leading to C–C interfacial links, Br chemisorption suppressing junction formation, and atomic hydrogen dosing increasing bonding efficiency up to 71%; freestanding junctions show electronically abrupt interfaces while substrate coupling modulates the electronic structure and transport channels. This work provides a viable route to all-carbon nanoscale circuitry with potential for voltage-tunable current separation and atomically scaled circuitry.

Abstract

Carbon-based 2D heterostructures represent an attractive platform for nanoelectronics owing to their tunable electronic and transport properties, yet achieving precise control over their fabrication remains elusive. Here, we demonstrate the on--surface synthesis of covalently bonded lateral heterostructures between armchair graphene nanoribbons and metalated hydrogenated graphdiyne networks on Au(111). Atomic--resolution scanning tunnelling microscopy combined with density functional theory reveals the formation mechanism of covalent interfacial bonds and highlights the critical influence of surface chemistry. In particular, chemisorbed bromine atoms suppress junction formation, while controlled atomic hydrogen dosing increases the bonding efficiency to 71\%. Electronic structure and transport calculations demonstrate how the metallic substrate influences the supported heterostructure, whereas in the freestanding limit, the two carbon subsystems retain their intrinsic properties, forming an atomically narrow junction that enables voltage-tunable spatial current separation. These results define a viable strategy for engineering graphene--graphdiyne heterostructures and advance the design of all-carbon nanoscale electronic architectures.

Figures (4)

• Figure 1: (a) Schematic representation of the OSS of the hGDY–aGNR heterostructure on Au(111). On the left, the ball-and-stick atomic model of 4,4"-dibromo-p-terphenyl (DBTP) and 1,3,5-tri(bromoethynyl)benzene (tBEB) molecular precursors. Large-scale (b) and atomically-resolved CO-functionalized tip (c-e) LT-STM images of the as-deposited system on Au(111) before the hGDY–aGNR bonding. (d) Bond-resolved close-up of the squared blue region in (c). White circles in (c) and (d) mark Au-Br complex facing and not facing the nanoribbon. (e) Close-up of the squared green region in (c), showing an atomically-resolved LT-STM image of the Au-Br complex facing a 3-aGNR nanoribbon. The corresponding ball-and-stick atomic model is superimposed on the image. STM setpoint: (b) -50mV/10pA, (c) -5mV/20pA, (d) -5mV/10pA, (e) -2mV/50pA.
• Figure 2: (a)-(b) High resolution LT-STM images of two regions of the hGDY–aGNR heterostructure on Au(111) upon annealing at 530 K. The black circles in (a) exemplify the generated bonds between the hGDY and a 3- and a 6-aGNR. The line profiles taken along the blue, green and red lines on (b) are shown on the right, together with the ball-and-stick atomic model of the benzene ring and the gold adatoms. (c) Close-up, with CO-functionalized tip, of (b), rotated by 65º. The cyan circle encloses the hGDY–aGNR covalent bond. The inset shows the same LT-STM image as (c) processed with convolution filtering, with the cyan circle enclosing the hGDY–aGNR covalent bond. (d)-(e) Constant-height and constant-current LT-STM images of two junction points between hGDY and a 6- and 3-aGNR, respectively. The white circle in (d) exemplifies an Au-Br complex not facing the nanoribbon. White arrows in (d)-(e) indicate the position of the covalent hGDY–aGNR bonds. STM setpoint: (a) -10mV/80pA, (b) -10mV/80pA, (c) -3mV/80pA, (d) constant height at 0V, (e) 1mV/200pA.
• Figure 3: a, b) hGDY-aGNR bonding mechanism: rupture of C-AuBr at 530 K in AuBr-terminated free edges of hGDY and consequent desorption of AuBr complexes; formation of a covalent bond with the nanoribbon and release of molecular hydrogen. Bond dissociation energies are reported in (a), together with the most probable breaking point (dashed). (c-f) Simulated model structures (close-up of the interface, as in red square of panel b) for the freestanding lateral heterostructure. Nomenclature of the carbon atoms at the interface adopted for the evaluation of the bond lengths reported in Table 1. g) Vertical distortion of the heterojunction in the most stable freestanding configuration ("2H"). h) Structural model for the gold-supported heterostructure in the "1H" configuration, together with the constant height (2 Å) STM simulation for filled states (integration range [E$_F-0.5$ eV, E$_F$]. i) Enlargement of the bonding site: STM simulation at constant current and structural model (top and lateral view) for "1H" configuration on Au.
• Figure 4: PDOS on carbon atoms of 6-GNR (red) and hGDY (blue) in the freestanding "2H" (a) and gold-supported "1H" (b) heterojunction. c) Average total LDOS projected on all the atoms with the same y coordinates as a function of the lateral position along the freestanding "2H" heterojunction. The band alignment at the junction is evidenced by white lines that mark the edges of the gap in the two subsystems. d) Zero-bias transmission function of the freestanding "2H" heterostructure. PDOS and transmission of the freestanding "1H" heterojunction are reported in Figure S13. e) First conductive transmission eigenchannels at E=-0.2 eV and f) at E=1 eV.