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NANOARTOGRAPHY COMPETITION

Revolutionary molecular graphene nanoribbons pave the way for ultra-clean electronics


Atomic force microscopy height images of 1a (left) and 2 (right), deposited on highly oriented pyrolytic graphite. @ University of Oxford
Atomic force microscopy height images of 1a (left) and 2 (right), deposited on highly oriented pyrolytic graphite. @ University of Oxford

In a groundbreaking study, scientists have successfully enhanced the solubility of graphene nanoribbons, creating exceptionally clean electronic devices directly from solution. This breakthrough could potentially revolutionize the field of nanoelectronics, and pave the way for advanced quantum experiments.


Graphene, a one-atom-thick layer of carbon atoms arranged in a hexagonal lattice, has been the subject of extensive research for its remarkable electronic, mechanical, and thermal properties. Molecular graphene nanoribbons (MGNRs), chemically synthesized strips of graphene with precise control over their edges and topology, have emerged as a very promising candidate for electronic nanodevices. For example, they could lead to transistors with low power consumption. However, the poor solubility of MGNRs has limited their potential for use in quantum electron transport experiments.



a, Normalized UV–visible absorption spectra of 1 (blue) and 2 (green) in chloroform. The insets show the molecular structure. b, Photographs of the chloroform solutions of MGNR2 at different concentrations, showing dispersibility. @ University of Oxford
a, Normalized UV–visible absorption spectra of 1 (blue) and 2 (green) in chloroform. The insets show the molecular structure. b, Photographs of the chloroform solutions of MGNR2 at different concentrations, showing dispersibility. @ University of Oxford


In a recent study, published in the journal Nature Materials, researchers demonstrated a significant improvement in the solubility of MGNRs by edge functionalisation. By introducing bulky side groups on the edges of the nanoribbons, scientists were able to achieve excellent solubility in common solvents like dichloromethane, chloroform, and toluene. The resulting solutions were stable for months without any observable precipitates, and the solubility surpassed that of previously reported MGNRs.


The increased solubility and suppression of π-stacking among the nanoribbons led to the development of ultra-clean transport devices with sharp single-electron features. These devices displayed exceptional cleanliness and a level of detail that was, up to now, only achievable using suspended carbon nanotubes, a type of devices that is very hard to fabricate. The sharpness of the electronic features observed in these devices opens new possibilities for exploiting spin and vibrational properties in atomically precise graphene nanostructures.


Enhancement of the quantum transport. b, Scanning electron microscopy images of two typical devices for the two geometries, in false colours. d, Stability diagrams for two devices obtained with 2 (shown at the top left), showing the source–drain differential conductance GSD, in units of the conductance quantum G0. All measurements are taken below T = 500 mK, and, where possible, diamonds are labelled with respect to an arbitrary number of electrons, N. @ University of Oxford
Enhancement of the quantum transport. b, Scanning electron microscopy images of two typical devices for the two geometries, in false colours. d, Stability diagrams for two devices obtained with 2 (shown at the top left), showing the source–drain differential conductance GSD, in units of the conductance quantum G0. All measurements are taken below T = 500 mK, and, where possible, diamonds are labelled with respect to an arbitrary number of electrons, N. @ University of Oxford

One notable finding from this research is the strong coupling between the electrons and the vibrations, so strong that the scientists could see the vibrational modes appear as peaks in the current. This offers inviting possibilities for new sensors. The novel devices are extremely promising to observe coupling to other phenomena, such as exotic forms of magnetism and optical emission.


Electron–vibron coupling in nanoribbons with enhanced solubility. a, Detail of vibrational state suppression in the differential conductance G versus VSD and VG for 2 (left) and corresponding simulation using a quantum rate equation model (right). Arrows indicate the excited states, and measurements are at T = 20 mK. @ University of Oxford
Electron–vibron coupling in nanoribbons with enhanced solubility. a, Detail of vibrational state suppression in the differential conductance G versus VSD and VG for 2 (left) and corresponding simulation using a quantum rate equation model (right). Arrows indicate the excited states, and measurements are at T = 20 mK. @ University of Oxford

Who knows what the future holds? Now that scientists can now create these ultra-clean electronic devices, quantum experiments are at hand, and future technologies based on electronic topology and quantum coherence might be within reach.


Reference

Exceptionally clean single-electron transistors from solutions of molecular graphene nanoribbons

Wenhui Niu, Simen Sopp, Alessandro Lodi, Alex Gee, Fanmiao Kong, Tian Pei, Pascal Gehring, Jonathan Nägele, Chit Siong Lau, Ji Ma, Junzhi Liu, Akimitsu Narita, Jan Mol, Marko Burghard, Klaus Müllen, Yiyong Mai, Xinliang Feng, and Lapo Bogani.

Nature Materials, 22(2), 180-185.


University of Oxford

NWA Magazine - Nov2023 - Cover - Final.PNG

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