Nanoporous graphene arrays show promise for advanced electronics and sensing.

The potential of graphene, a single-atom-thick sheet of carbon, continues to drive materials science, with ongoing research focused on tailoring its properties for advanced electronic devices. Recent advances in on-surface synthesis have yielded nanoporous graphenes (NPGs), two-dimensional arrays of covalently bonded nanoribbons, offering a pathway to control electron flow at the nanoscale. Gaetano Calogero, Isaac Alcón, Alan E. Anaya Morales, and colleagues report detailed investigations into the quantum transport characteristics of hybrid NPGs, materials incorporating alternating doped and undoped nanoribbons. Their work, entitled ‘Quantum transport in nitrogen-doped nanoporous graphenes’, utilises computational modelling to demonstrate lateral carrier propagation and proposes design strategies to achieve directional charge transport with sub-nanometer precision over distances exceeding one micrometer, a significant result for this class of material.

Nanoporous Graphene Enables Precise Control of Quantum Electronic Properties

Nanoporous graphenes (NPGs) represent a developing class of two-dimensional carbon nanomaterials attracting attention for potential applications in nanoelectronics and biosensing. These materials are synthesised using a bottom-up approach, constructing structures directly on surfaces to achieve precise control over their architecture, a significant advantage over top-down methods which often introduce defects and limit precision. NPGs are built from arrays of laterally bonded graphene nanoribbons (GNRs), offering a pathway to control electronic properties at the nanoscale and enabling the creation of novel devices with tailored functionalities. Graphene nanoribbons, the fundamental building blocks of NPGs, exhibit semiconducting behaviour dependent on their width and edge structure, allowing for electrostatic control of current flow crucial for nanoelectronic devices.

Recent advancements have led to the synthesis of hybrid-NPGs (hNPGs), incorporating both nitrogen-doped GNRs (nGNRs) and undoped GNRs (cGNRs) to create materials with unique electronic characteristics. This alternating arrangement within hNPGs induces a type II band-staggering effect, where the valence and conduction bands originate from different materials, creating a lateral heterojunction with atomically sharp band offsets. These offsets open possibilities for applications in optoelectronics, photovoltaics, and selective ion sieving, expanding the potential of NPGs beyond traditional electronic applications.

Researchers actively investigate NPG as a promising material for constructing carbon nanocircuitry, focusing on understanding and controlling electron transport within these structures. They employ computational methods, specifically utilising Green’s function simulations, a technique rooted in quantum mechanics that predicts how electrons move through the material, moving beyond simple approximations. These simulations, implemented with codes like Transiesta, calculate the electronic structure and transport properties of NPG, offering a detailed understanding of current flow at the atomic scale and enabling the design of optimised structures.

Simulations reveal that injected electrons within hNPG do not simply travel along a single nanoribbon, but instead spread laterally across multiple ribbons, a behaviour dictated by the arrangement of doped and non-doped segments. Crucially, this spreading can be selectively confined to ribbons of a single type, either doped or non-doped, offering a degree of control over the direction of current flow and enabling the creation of directional pathways for electrons. Researchers developed a simplified model identifying key parameters governing electronic propagation, allowing them to predict and optimise the material’s performance. Furthermore, the team explored alternative hNPG designs, manipulating the arrangement of nanoribbons to enhance or restrict the spreading of charge carriers and introduce anisotropy, meaning direction-dependent conductivity. One particularly successful design demonstrated the ability to transmit directed electrical signals with sub-nanometer precision over distances exceeding one micrometer, a result unprecedented in NPG research.

Investigations detail the quantum transport properties of hybrid NPGs (hNPGs), materials constructed from alternating doped and undoped graphene nanoribbons (GNRs), exhibiting a band staggering effect advantageous for applications ranging from photocatalysis to carbon-based circuitry. Researchers employ Green’s function simulations to model how charge carriers propagate through hNPGs, revealing that injected carriers spread laterally across multiple GNRs, often selectively through either doped or undoped ribbons. Researchers propose a model to identify the critical parameters governing electronic propagation and explore alternative hNPG designs to manipulate charge transport, controlling both its direction and confinement. Notably, one specific hNPG design facilitates the transmission of directed electric signals with sub-nanometre precision over distances reaching one micrometre. This precision stems from the engineered electronic structure and the controlled lateral propagation of charge carriers, suggesting potential for creating highly integrated nanoscale circuits.

This research establishes NPG as a promising material for nanoscale electronics, demonstrating precise control over electron transport through manipulation of quantum interference and electrochemical gating. Calculations utilising Density Functional Theory and the Non-Equilibrium Green’s Function method confirm the Talbot effect within NPG structures, revealing periodic interference patterns that significantly influence current flow. The ability to engineer these quantum interference effects allows for directional control and modulation of current magnitude, paving the way for advanced device architectures. The study highlights the effectiveness of electrochemical gating as a means to dynamically tune the charge carrier density within NPG, effectively creating a switchable or modulatory element for electronic circuits. This control extends to hybrid NPG (hNPG) structures, where alternating doped and non-doped graphene nanoribbons exhibit band staggering, influencing carrier propagation. Simulations reveal that injected carriers spread laterally through the nanoribbon network, preferentially through ribbons of a single doping type, offering a pathway to control anisotropy in charge transport.

Notably, the research demonstrates directed electrical signal propagation with sub-nanometre precision over distances reaching one micrometre within a specifically designed hNPG structure, exceeding previously reported distances and establishing a potential for complex nanoscale circuitry. The multiradical character of the biphenylene network within NPG also contributes to its unique electronic properties and transport behaviour, further enhancing its versatility. Furthermore, the investigation explores the impact of twisting NPG on graphene substrates, revealing the decoupling of electronic properties and the generation of chiral currents. Acetylene molecules mediate electron transport within both NPG and hexagonal boron nitride structures, offering an additional mechanism for controlling conductivity. These findings collectively demonstrate the potential for creating robust quantum transport in NPG, even at room temperature, a crucial factor for practical applications.

Future work should focus on the fabrication and characterisation of these advanced hNPG designs, validating the simulation results and exploring their performance in functional devices. Investigating the long-term stability and scalability of these structures is also essential, alongside expanding the range of dopants and exploring alternative molecular mediators to further enhance control over charge transport and unlock new functionalities. Finally, integrating these NPG-based components into larger, more complex circuits represents a key step towards realising the full potential of this material for next-generation nanoelectronics and quantum computing.