Recent research highlights

To date NOWNANO/Graphene NOWNANO students published 176 papers in international refereed journals, with a third of all publications appearing in high-impact journals, including Nature, Science, Nano Letters, Chemical Communications and Applied Physics Letters. Below are several examples of high-profile publications where Graphene NOWNANO CDT students (names in bold) have made crucial contributions.

Tunable sieving of ions using graphene oxide membranes

Jijo Abraham, Kalangi S. Vasu, Christopher D. Williams, Kalon Gopinadhan, Yang Su, Christie T. Cherian, James Dix, Eric Prestat, Sarah J. Haigh, Irina V. Grigorieva, Paola Carbone, Andre K. Geim & Rahul R. Nair
Nature Nanotechnology 12, 546–550 (2017)

A team of researchers at the University of Manchester, including CDT student James Dix, unveiled a graphene-oxide membrane that sieves salt out of seawater, producing a drinkable liquid. Prior research done by the team demonstrated that, if submerged deep in water, graphene-oxide membranes become swollen, allowing smaller salts to flow through while blocking larger molecules. The group further advanced these membranes and discovered a method to avoid the swelling that occurs when they’re exposed to water. They found that the pore size can be controlled and sieve out common salts in seawater, producing safe drinking water.

“Realization of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology,” said Professor Rahul Nair. By 2025, the UN predicts that 14% of the world’s population will suffer from water scarcity. This technology has the ability to revolutionize water filtration across the world, especially in countries that cannot afford large-scale desalination plants.

Portraying entanglement between molecular qubits with four-dimensional inelastic neutron scattering

E. Garlatti, T. Guidi, S. Ansbro, P. Santini, G. Amoretti, J. Ollivier, H. Mutka, G. Timco, I. J. Vitorica-Yrezabal, G. F. S. Whitehead, R. E. P. Winpenny & S. Carretta
Nature Communications 8, 14543 (2017)

Entanglement is a crucial resource for quantum information processing and its detection and quantification is of paramount importance in many areas of current research. An international collaboration between the Institut Laue-Langevin, the University of Parma, ISIS and CDT student George Whitehead at the University of Manchester have used the (Cr7Ni)2 dimer as a benchmark system to demonstrate the capability of ‘four-dimensional’ inelastic neutron scattering to investigate entanglement between molecular qubits.

Such a measurement enables one to portray and quantify entanglement between weakly coupled molecular nanomagnets, which provide ideal test beds for investigating entanglement in spin systems. This technique can be an important tool in the understanding and engineering of molecules with the right characteristics for efficiently encoding and processing quantum information, supporting the development of quantum computers.

Water-based and biocompatible 2D crystal inks for all-inkjet-printed heterostructures

Daryl McManus, Sandra Vranic, Freddie Withers, Veronica Sanchez-Romaguera, Massimo Macucci, Huafeng Yang, Roberto Sorrentino, Khaled Parvez, Seok-Kyun Son, Giuseppe Iannaccone, Kostas Kostarelos, Gianluca Fiori & Cinzia Casiraghi
Nature Nanotechnology 12, 343–350 (2017)

A team of researchers led by CDT student Daryl McManus and his supervisor Cinzia Casiraghi have come up with a new way to inkjet print several 2D materials, including graphene, MoS2, WS2 and hexagonal boron nitride, to make functional electronic devices. By carefully selecting the sequence of the 2D materials in the stack, the researchers succeeded in producing fully-printed arrays of photodetectors on silicon, paper and plastic. They used the same approach to print logic memories made solely from 2D materials.

The structures produced have many good properties, Cinzia explains, “First, they are water-based, and water is a friendly, low-cost, low boiling point solvent. They are also highly concentrated, which reduces printing time, since more material is printed per unit area. They are optimized for inkjet printing too and no pre-treatment or heating of the substrate is required. This means that we can also print them on temperature-sensitive materials like paper and plastic.”

Graphene ballistic nano-rectifier with very high responsivity

Gregory Auton, Jiawei Zhang, Roshan Krishna Kumar, Hanbin Wang, Xijian Zhang, Qingpu Wang, Ernie Hill & Aimin Song
Nature Communications 7, 11670 (2016)

A graphene-based electrical nano-device has been created which could substantially increase the energy efficiency of fossil fuel-powered cars. The nano-device, known as a 'ballistic rectifier', is able to convert heat which would otherwise be wasted from the car exhaust and engine body into a useable electrical current. The resulting device is the most sensitive room-temperature rectifier ever made. Conventional devices with similar conversion efficiencies require cryogenically low temperatures.

CDT alumnus Greg Auton, who, together with CDT student Roshan Kumar, performed most of the experiment said, “Graphene has exceptional properties; it possesses the longest carrier mean free path of any electronic material at room temperature. Despite this, even the most promising applications to commercialize graphene in the electronics industry do not take advantage of this property." The Manchester-based group is now looking to scale up the research by using large wafer-sized graphene and perform high-frequency experiments. The resulting technology can also be applied to harvesting wasted heat energy in power plants.

Negative local resistance caused by viscous electron backflow in graphene

D. A. Bandurin, I. Torre, R. Krishna Kumar, M. Ben Shalom, A. Tomadin, A. Principi, G. H. Auton, E. Khestanova, K. S. Novoselov, I. V. Grigorieva, L. A. Ponomarenko, A. K. Geim, M. Polini
Science 351, 1055-1058 (2016).

This paper reported that electrons in graphene act like slow-pouring honey, prompting a new approach to fundamental physics. Electrons are known to move through metals like bullets being reflected only by imperfections, but in graphene they move like in a very viscous liquid.

The possibility of a highly viscous flow of electrons in metals was predicted several decades ago but, despite numerous efforts, never observed, until now, as reported by a team of University of Manchester researchers that included two NOWNANO CDT students, both of whom made crucial contributions to the research.

Gain modulation by graphene plasmons in aperiodic lattice lasers

S. Chakraborty, O. P. Marshall, T. G. Folland, Y.-J. Kim, A. N. Grigorenko, K. S. Novoselov
Science 351, 246-248 (2016).

Despite the myriad uses we have for lasers, once the wavelengths of light have been set for a laser, it's usually fixed for that device. In the above Science paper, a Graphene NOWNANO CDT student, Tom Folland, working in a team of University of Manchester researchers, demonstrated that it is possible to tune a terahertz laser so that there is reversible control over its emission. The scientists have achieved this by combining a graphene sheet with a terahertz quantum cascade laser.

The key to the control over the laser’s emission is manipulating the doping of the graphene layer that changes the concentration of charge carriers and generates tunable plasmons (waves of electrons that are formed when photons hit a metal). When the ability of graphene plasmons to be tuned is combined with terahertz quantum cascade lasers, it becomes possible to reversibly alter laser’s emission which is of great importance for practical applications.

Attoliter Chemistry for Nanoscale Functionalization of Graphene

Michael Hirtz, Sarah Varey, Harald Fuchsand, Aravind Vijayaraghavan
ACS Applied Materials & Interfaces 8, 33371–33376 (2016)

A new method to chemically modify small regions of graphene with high precision is the result of an international collaboration between NOWNANO DTC student Sarah Varey, her supervisor Aravind Vijayaraghavan and researchers at the Karlsruhe Institute of Technology, Germany. The team showed that it is possible to combine graphene with chemical and biological molecules and form patterns that are just 100 nanometres wide, leading to extreme miniaturisation of chemical and biological sensors.

Using technology that resembles writing with a quill or a fountain pen, the scientists were able to deliver chemical droplets to the surface of graphene in volumes less than 100 attolitres (10-16 L). This technique is key to enabling graphene sensors which can be used in real-world applications, for example, in blood tests, minimising the amount of blood a patient is required to give.

Nanomechanical electro-optical modulator based on atomic heterostructures

Philip A. Thomas, Owen P. Marshall, Francisco J. Rodriguez, Gregory H. Auton, Vasyl G. Kravets, Dmytro Kundys, Yang Su and Alexander N. Grigorenko
Nature Communications 7, 13590 (2016).

A team of Manchester researchers led by NOWNANO DTC student Philip Thomas and his supervisor Alexander Grigorenko have shown that it is possible to combine graphene, boron nitride and a nanoscale gold grating to create a new class of optical modulators. The new device can process information using light in much the same way as computers process information using electrons.

“This could pave the way for faster circuits, which is the main selling point of using light instead of electrical signals,” Philip said. “But probably the bigger result from this work is that it could allow for a dramatic reduction in the size of these circuits. It is rare to have a modulator which both creates a strong modulation effect and is so tiny.”

Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures

J. R. Wallbank1, D. Ghazaryan, A. Misra, Y. Cao, J. S. Tu, B. A. Piot, M. Potemski, S. Pezzini, S. Wiedmann, U. Zeitler, T. L. M. Lane, S. V. Morozov, M. T. Greenaway, L. Eaves, A. K. Geim, V. I. Fal'ko, K. S. Novoselov, A. Mishchenko
Science 353, 575-579 (2016)

Among the unusual properties of graphene, one of the most exciting and least understood is the additional degree of freedom experienced by its electrons. It is called the pseudospin and it determines the probability to find electrons on neighbouring carbon atoms. The possibility to control this degree of freedom would allow for new types of experiments, but potentially also enable to use it for electronic applications.

In this paper, Manchester physicists demonstrate how electrons with well-controlled pseudospin can be injected into graphene. The pseudospin state of the tunnelling electrons can be chosen by applying a strong magnetic field parallel to the graphene layers. Professor Vladimir Fal’ko added, “We hope that the opportunity to control the pseudospin and chirality of electrons in graphene will expand the range of quantum phenomena studied in this remarkable material”.

Light-emitting diodes by band-structure engineering in van der Waals heterostructures

F. Withers, O. Del Pozo-Zamudio, A. Mishchenko, A. P. Rooney, A. Gholinia, K. Watanabe, T. Taniguchi, S. J. Haigh, A. K. Geim, A. I. Tartakovskii & K. S. Novoselov
Nature Materials 14, 301–306 (2015)

Researchers at the University of Manchester, including CDT student Aiden Rooney, and the University of Sheffield have shown that new 2D 'designer materials' can be produced to create flexible, see-through and more efficient electronic devices. The LED device was constructed by combining different 2D crystals and emits light from across its whole surface. Being so thin, at only 10-40 atoms thick, these new components can form the basis for the first generation of semi-transparent smart devices.

By building heterostructures - stacked layers of various 2D materials - to create bespoke functionality and introducing quantum wells to control the movement of electrons, new possibilities for graphene based optoelectronics have now been realised. Freddie Withers said, "As our new type of LED's only consist of a few atomic layers of 2D materials they are flexible and transparent. We envisage a new generation of optoelectronic devices to stem from this work, from simple transparent lighting and lasers and to more complex applications."

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