Scientists have developed a unique way to build electronic components so small they are made from chains of individual molecules - creating a toolbox to help build materials that could power the next generation of technology.
Publishing their findings today (23 April) in Nature Communications, an international research team led by the Universities of Birmingham and Warwick, have created 'nanoribbons' with tailored electronic properties.
This advance could help future development of:
Flexible organic electronics that can be printed or 'painted' – for example in smart clothing
Ultra‑small electronic circuits for 'Internet of Things' devices
Bioelectronics that could be used in animal/human implants
More efficient solar cells
New types of sensors
Quantum or molecular electronics
Professor Giovanni Costantini, from the School of Chemistry and the School of Physics and Astronomy at the University of Birmingham and corresponding author of the study, said: "While atomically precise nanoribbons have been explored before, this is the first time they have been built by directly combining electron donor and acceptor units. Because we can choose exactly where these units appear, we can design their electronic properties in advance and realise them with atomic precision.
"By controlling the sequence and length of the molecular units, we can precisely programme and realise the material's electronic properties in practice – paving the way for an unprecedented level of control, essential for next-generation technologies."
Researchers used donor–acceptor (D–A) chemistry, a method widely employed in high‑performance plastics for electronics – creating some molecules that 'give up' electrons and others that 'take in' electrons in controlled sequences.
Using advanced microscopes that can image individual molecules and even resolve atoms and chemical bonds within them, they could see the exact shape of each nanoribbon whilst detecting tiny irregularities and measuring how electrons behave within the ribbons.
Traditionally, nanoribbons have been made from graphene, which does not naturally behave as a semiconductor unless reshaped into nanoribbons or chemically modified with other elements. Even then, controlling the material's electrical behaviour has been difficult.
Researchers led by Davide Bonifazi at the University of Vienna designed and synthesised two special molecules - an electron donor and an electron acceptor. The Warwick-Birmingham team then placed these molecules onto a gold surface in a vacuum and heated them so they would naturally join into nanoribbons, producing donor-only ribbons, acceptor-only ribbons, and mixed D–A.
Davide Bonifazi said: "By embedding donor–acceptor concepts into these on-surface fabrication strategies it became possible to prepare extended nanoribbon structures that are otherwise difficult to make in solution."
James Lawrence, who co-led much of this work as a PhD student at the University of Warwick and is now at the National University of Singapore, said: "This research creates a new toolbox for building electronic materials with atomic precision. Building nanoribbons directly on a metal surface can produce perfectly defined structures, which is difficult to achieve using traditional chemistry."
Researchers discovered that as they heated the D and A molecules, these lost bromine atoms and bonded into chains. The shape of the chains depended on how the molecules met, and impurities sometimes caused bends or defects.
Longer all-D ribbons became better electron donors, while longer all-A ribbons became stronger electron acceptors. In mixed ribbons, the electronic properties depended on the precise sequence of D and A units. By establishing a simple theoretical model to describe this relationship, the researchers provide a foundation for designing materials with application-specific electronic behaviour through controlled subunit composition.
Gabriele Sosso, who oversaw the computational aspects of the work at the University of Warwick, said: "From a modelling perspective, these nanoribbons show how atomic-scale design can be used to fine-tune real world electronic properties. Capturing the effects of the supporting surface and local environment will be key to guiding this approach further."
The next step is to apply this approach to design materials with targeted properties for organic electronics, bioelectronics, and photovoltaics.
