[Paper Review] 2D abrupt nano-junctions blending sp-sp2 bonds on atomically precise heterostructures

Alice Cartoceti, Simona Achilli+9 more|arXiv (Cornell University)|Jan 27, 2026

Graphene research and applications0 citations

TL;DR

Demonstrates on-surface synthesis of covalently bonded lateral heterostructures between armchair graphene nanoribbons and metalated hydrogenated graphdiyne networks on Au(111); analyzes formation mechanism, Br/H control, and electronic transport implications.

ABSTRACT

Two-dimensional heterostructures combining sp-sp2 hybridization,blending graphene with graphyne-based allotropes, offer substantial potential for enhancing the tunability of electronic and transport properties while providing significant structural flexibility. These attributes are desirable for next generation nanoscale electronic applications. Despite such potential, their experimental realization remains elusive, as synthesized carbon heterostructures are limited to doped, graphene-based systems exhibiting exclusively sp2 hybridization. Here, we demonstrate the on-surface synthesis of covalently bonded sp-sp2 lateral heterostructures between graphene nanoribbons and graphdiyne networks on Au(111). Atomic-resolution scanning tunnelling microscopy, combined with density functional theory, reveals the formation mechanism of the covalent interfacial bonds between nanoribbons and graphdiynes, also highlighting the key role of surface chemistry. Bromine atoms deriving from the molecules dehalogenation and chemisorbed along the nanoribbon inhibit the junction formation, but bonding efficiency can be boosted up to 71% by controlled removal of these by-products. Electronic structure and transport calculations show that the 2D heterostructure by itself is characterized by disentangled properties for the two subsystems, forming an atomically narrow junction enabling voltage-tunable spatial current separation in two dimensions. There results define a viable strategy for engineering graphene-based sp-sp2 heterostructures, paving the way for the design and synthesis of all-carbon nanoscale electronic architectures.

Motivation & Objective

• Demonstrate covalently bonded hGDY–aGNR lateral heterostructures on Au(111) using on-surface synthesis.
• Elucidate the bonding mechanism and role of Br atoms in junction formation via LT-STM and DFT.
• Quantify how atomic hydrogen dosing affects bonding efficiency.
• Characterize electronic structure and transport properties of the freestanding and Au-supported heterostructures.

Proposed method

• On-surface synthesis on Au(111) from DBTP and tBEB precursors to form metalated hGDY in between aGNRs.
• Low-temperature STM with CO-functionalized tips to resolve covalent interfaces and bond lengths.
• Density functional theory to model bonding configurations (Top, Bridge, 1H, 2H) and compute PDOS.
• Non-equilibrium Green’s function (NEGF) transport calculations to obtain T(E) and eigenchannels.
• Hydrogen dosing to modulate Br surface density and assess bonding efficiency.

Experimental results

Research questions

• RQ1 Can covalent sp–sp2 bonding be established at the graphene nanoribbon–graphdiyne interface on Au(111)?
• RQ2 What is the bonding mechanism and preferred configuration at the hGDY–aGNR interface?
• RQ3 How do Br adatoms and atomic hydrogen dosing affect the formation efficiency of the heterojunction?
• RQ4 How does the metal substrate influence the electronic structure and transport across the heterojunction?
• RQ5 What are the potential device implications of an electronically abrupt all-carbon heterojunction?

Key findings

• Covalent hGDY–aGNR bonds form after annealing at 530 K, with 83% at 90° and 17% at 60°-120° relative to the GNR axis.
• Bond length at the interface is about 1.151 Å (approximately 151 pm) for the C–C bond.
• Formation likely proceeds from a ‘Top’ configuration, transitioning to ‘1H’ or ‘2H’ with hybridization changes (sp to sp2 or sp3) at the interface.
• Freestanding hGDY–aGNR shows preserved DOS features with an abrupt interface, while Au(111)-supported junctions show substrate-induced DOS shifts and ~0.5 e transfer from hGDY to aGNR.
• Br atom density strongly modulates bonding efficiency: standard Br density ~0.53 nm^-2 yields ~47% bonding; increasing Br to ~0.84 nm^-2 reduces to ~31%; reducing Br via atomic H dosing to ~0.19 nm^-2 increases bonding efficiency to ~71%.
• Electronic transport calculations indicate multiple transmission channels at certain energies, with potential for current spatial separation in aGNR vs hGDY regions in the freestanding case.