2D Carbon Heterostructures: Atomically Precise sp–sp² Junctions Achieved
An international study coordinated by NanoLab at the Department of Energy of Politecnico di Milano has been published in Advanced Materials. The research demonstrates the synthesis of lateral junctions between graphene nanoribbons and graphdiyne, opening up new possibilities for controlling the electronic properties of two-dimensional materials.
The article “2D Abrupt Nano-Junctions Blending sp–sp² Bonds on Atomically Precise Heterostructures” was published online on 23 August 2026 in Advanced Materials, one of the leading international scientific journals in materials science.
The study’s authors from the Department of Energy of Politecnico di Milano are Alice Cartoceti, Paolo D’Agosta, Andrea Li Bassi and Carlo S. Casari. The research was conducted in collaboration with the University of Milan, the University of Pavia, the University of Padua and the University of Zaragoza in Spain.
Different materials made entirely of carbon
The research focuses on two-dimensional heterostructures: systems in which materials with different properties are placed side by side within a layer just a few atoms thick. The region where the two materials meet—the junction—is particularly important because it can determine how electric charges are distributed and move through the system.
The research team created an all-carbon lateral junction by connecting graphene nanoribbons and hydrogenated graphdiyne on a crystalline gold surface. Although composed of the same element, these are two distinct materials with different structures and properties.
In graphene, carbon atoms exhibit sp² hybridisation, which gives rise to its characteristic planar hexagonal lattice and excellent electron transport properties. Graphdiyne, on the other hand, combines sp and sp² bonding in a more open network, in which carbon rings are connected by linear chains containing single and triple bonds. This different atomic architecture gives the material electronic properties that complement those of graphene.
A junction built with atomic precision
The study’s innovation lies in the experimental synthesis of an atomically sharp, controlled covalent interface between these two two-dimensional forms of carbon. Until now, experimentally produced carbon heterostructures have mainly been based on graphene variants featuring only sp² hybridisation.
The structure was produced through on-surface synthesis, a bottom-up process in which carefully designed molecular precursors react on a metal substrate, gradually forming the desired nanostructure. Covalent bonds at the interface were observed using low-temperature scanning tunnelling microscopy capable of achieving atomic resolution. The experimental data were complemented by density functional theory calculations, used to reconstruct the junction formation mechanism and analyse its electronic properties.
The study also highlights the crucial role of surface chemistry. Bromine atoms released during the transformation of the molecular precursors can remain adsorbed along the nanoribbons and hinder bond formation between graphene and graphdiyne. Their controlled removal using atomic hydrogen increases junction formation efficiency to as much as 66%.
Tunable electronic properties
The calculations show that, even after covalent bonding, the two materials retain distinct electronic characteristics. The atomically sharp interface can therefore spatially separate current pathways within the structure.
Specifically, changing the applied voltage makes it possible to adjust the contribution of each component to electron transport and preferentially direct the current through either the graphene nanoribbon or the graphdiyne. This ability to control charge pathways is the most significant functional aspect of the findings and suggests a potential role for sp–sp² junctions in the design of future nanoscale electronic components.
The study represents an advance in fundamental research: it does not yet present a device ready for application, but demonstrates that all-carbon lateral heterostructures can be synthesised and controlled by combining different forms of the same element with atomic precision. The work thus establishes a strategy for designing new 2D architectures in which chemical structure and electron transport can be tailored during synthesis.
Further reading
A. Cartoceti et al., “2D Abrupt Nano-Junctions Blending sp–sp² Bonds on Atomically Precise Heterostructures”, Advanced Materials, published online on 23 August 2026. DOI: 10.1002/adma.74740.
The Department of Energy’s Micro- and Nanostructured Materials (NanoLab) research group brings together faculty members and researchers with expertise in condensed matter physics and focuses on the development and characterization of materials for energy applications. Drawing on expertise in solid-state, surface and plasma physics, the group investigates how the nanoscale structure of materials influences their electronic, optical and chemical properties. Its activities combine theoretical and experimental approaches, synthesis techniques and advanced microscopy and spectroscopy tools, with a particular focus on thin films and surfaces for photovoltaics, photocatalysis and nuclear technologies.
.
