10th February 2008
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4 articles from Manchester University news. Good read.
Graphene’s high-speed seesaw
30 Apr 2013
A new transistor capable of revolutionising technologies for medical imaging and security screening has been developed by graphene researchers from the Universities of Manchester and Nottingham.
Writing in Nature Communications, the researchers report the first graphene-based transistor with bistable characteristics, which means that the device can spontaneously switch between two electronic states. Such devices are in great demand as emitters of electromagnetic waves in the high-frequency range between radar and infra-red, relevant for applications such as security systems and medical imaging.
Bistability is a common phenomenon – a seesaw-like system has two equivalent states and small perturbations can trigger spontaneous switching between them. The way in which charge-carrying electrons in graphene transistors move makes this switching incredibly fast – trillions of switches per second.
Wonder material graphene is the world’s thinnest, strongest and most conductive material, and has the potential to revolutionise a huge number of diverse applications; from smartphones and ultrafast broadband to drug delivery and computer chips. It was first isolated at The University of Manchester in 2004.
The device consists of two layers of graphene separated by an insulating layer of boron nitride just a few atomic layers thick. The electron clouds in each graphene layer can be tuned by applying a small voltage. This can induce the electrons into a state where they move spontaneously at high speed between the layers.
Because the insulating layer separating the two graphene sheets is ultra-thin, electrons are able to move through this barrier by ‘quantum tunnelling’. This process induces a rapid motion of electrical charge which can lead to the emission of high-frequency electromagnetic waves.
These new transistors exhibit the essential signature of a quantum seesaw, called negative differential conductance, whereby the same electrical current flows at two different applied voltages. The next step for researchers is to learn how to optimise the transistor as a detector and emitter.
One of the researchers, Professor Laurence Eaves, said: “In addition to its potential in medical imaging and security screening, the graphene devices could also be integrated on a chip with conventional, or other graphene-based, electronic components to provide new architectures and functionality.
“For more than 40 years, technology has led to ever-smaller transistors; a tour de force of engineering that has provided us with today’s state-of-the-art silicon chips which contain billions of transistors. Scientists are searching for an alternative to silicon-based technology, which is likely to hit the buffers in a few years’ time, and graphene may be an answer.”
“Graphene research is relatively mature but multi-layered devices made of different atomically-thin materials such as graphene were first reported only a year ago. This architecture can bring many more surprises”, adds Dr Liam Britnell, University of Manchester, the first author of the paper.
Notes for editors
The paper, Resonant tunnelling and negative differential conductance in graphene transistors, by L. Britnell, R. V. Gorbachev, A. K. Geim, L. A. Ponomarenko, A. Mishchenko, M. T. Greenaway, T. M. Fromhold, K. S. Novoselov and L. Eaves, is available on request from the Press Office.
Professor Eaves and Dr Britnell are available for interview on request.
More information about graphene is available from www.graphene.manchester.ac.uk and high-resolution images are available from http://www.condmat.physics.mancheste.../imagelibrary/
How graphene and friends could harness the Sun’s energy
03 May 2013
Combining wonder material graphene with other stunning one-atom thick materials could create the next generation of solar cells and optoelectronic devices, scientists have revealed.
University of Manchester and National University of Singapore researchers have shown how building multi-layered heterostructures in a three-dimensional stack can produce an exciting physical phenomenon exploring new electronic devices.
The breakthrough, published in Science, could lead to electric energy that runs entire buildings generated by sunlight absorbed by its exposed walls; the energy can be used at will to change the transparency and reflectivity of fixtures and windows depending on environmental conditions, such as temperature and brightness.
The isolation of graphene, by University of Manchester Nobel Laureates Professor Andre Geim and Professor Kostya Novoselov in 2004, led to the discovery of the whole new family of one-atom-thick materials.
Graphene is the world’s thinnest, strongest and most conductive material, and has the potential to revolutionise a huge number of diverse applications; from smartphones and ultrafast broadband to drug delivery and computer chips.
Collectively, such 2D crystals demonstrate a vast range of superlative properties: from conductive to insulating, from opaque to transparent. Every new layer in these stacks adds exciting new functions, so the heterostructures are ideal for creating novel, multifunctional devices.
One plus one is greater than two – the combinations of 2D crystals allow researchers to achieve functionality not available from any of the individual materials.
The Manchester and Singapore researchers expanded the functionality of these heterostructures to optoelectronics and photonics. By combining graphene with monolayers of transition metal dichalcogenides (TMDC), the researchers were able to created extremely sensitive and efficient photovoltaic devices. Such devices could potentially be used as ultrasensitive photodetectors or very efficient solar cells.
In these devices, layers of TMDC were sandwiched between two layers of graphene, combining the exciting properties of both 2D crystals. TMDC layers act as very efficient light absorbers and graphene as a transparent conductive layer. This allows for further integration of such photovoltaic devices into more complex, more multifunctional heterostructures.
Professor Novoselov said: “We are excited about the new physics and new opportunities which are brought to us by heterostructures based on 2D atomic crystals. The library of available 2D crystals is already quite rich, covering a large parameter space.
“Such photoactive heterostructures add yet new possibilities, and pave the road for new types of experiments. As we create more and more complex heterostructures, so the functionalities of the devices will become richer, entering the realm of multifunctional devices.”
University of Manchester researcher and lead author Dr Liam Britnell added: “It was impressive how quickly we passed from the idea of such photosensitive heterostructures to the working device. It worked practically from the very beginning and even the most unoptimised structures showed very respectable characteristics”
Professor Antonio Castro Neto, Director of the Graphene Research Centre at the National University of Singapore added: “We were able to identify the ideal combination of materials: very photosensitive TMDC and optically transparent and conductive graphene, which collectively create a very efficient photovoltaic device.
“We are sure that as we research more into the area of 2D atomic crystals we will be able to identify more of such complimentary materials and create more complex heterostructures with multiple functionalities. This is really an open field and we will explore it.”
Dr Cinzia Casiraghi, from The University of Manchester, added: “Photosensitive heterostructures would open a way for other heterostructures with new functionalities. Also, in future we plan for cheaper and more efficient heterostructure for photovoltaic applications.”
Catching graphene butterflies
16 May 2013
Wonder material graphene, when combined with other graphene-like materials, paves the way for vast new areas of scientific discovery and previously unheard-of applications, University of Manchester researchers have revealed.
Writing in Nature, a large international team led Dr Roman Gorbachev from The University of Manchester shows that, when graphene placed on top of insulating boron nitride, or ‘white graphene’, the electronic properties of graphene change dramatically revealing a pattern resembling a butterfly.
The pattern is referred to as the elusive Hofstadter butterfly that has been known in theory for many decades but never before observed in experiments.
Combining graphene with other materials in multiple-layered structures could lead to novel applications not yet explored by science or industry.
Graphene is the world’s thinnest, strongest and most conductive material, and promises a vast range of diverse applications; from smartphones and ultrafast broadband to drug delivery and computer chips. It was first demonstrated at The University of Manchester in 2004.
Initial trials of consumer products involving graphene-based touch screens and batteries for mobile phones and composite materials for sports goods are being carried out by major multinational companies.
One of the most remarkable properties of graphene is its high conductivity – thousands of times higher than copper. This is due to a very special pattern created by electrons that carry electricity in graphene. The carriers are called Dirac fermions and mimic massless relativistic particles called neutrinos, studies of which usually require huge facilities such as at CERN. The possibility to address similar physics in a desk-top experiment is one of the most renowned features of graphene.
Now the Manchester scientists have found a way to create multiple clones of Dirac fermions. Graphene is placed on top of boron nitride so that graphene’s electrons can ‘feel’ individual boron and nitrogen atoms. Moving along this atomic ‘washboard’, electrons rearrange themselves once again producing multiple copies of the original Dirac fermions.
The researchers can create even more clones by applying a magnetic field. The clones produce an intricate pattern; the Hofstadter butterfly. It was first predicted by mathematician Douglas Hofstadter in 1976 and, despite many dedicated experimental efforts, no more than a blurred glimpse was reported before.
In addition to the described fundamental interest, the Manchester study proves that it is possible to modify properties of atomically-thin materials by placing them on top of each other. This can be useful, for example, for graphene applications such as ultra-fast photodetectors and transistors, providing a way to tweak its incredible properties.
Professor Andre Geim, Nobel Laureate and co-author of the paper, said: “Of course, it is nice to catch the beautiful ‘butterfly’ which elusiveness tormented physicists for generations.
”More importantly, this work shows that we are now able to build up a principally new kind of materials by stacking individual atomic planes in a desired sequence.”
Dr Gorbachev added: “We prepared a set of different atomically-thin materials similar to graphene then stacked them on top of each other, one atomic plane at a time. Such artificial crystals would have been science fiction a few years ago. Now they are reality in our lab. One day you might find these structures in your gadgets.”
Professor Geim added: “This is an important step beyond ‘simple graphene’. We now build foundations for a new research area that seems richer and even more important than graphene itself.”
The Manchester paper is collaboration that involved researchers from the University of Lancaster in the UK, Instituto de Ciencia de Materiales de Madrid in Spain and National High-Field Laboratory in Grenoble, France.
It will appear in Nature back to back with another paper reporting similar butterflies in two layers of graphene, which comes from a group of Dr Philip Kim, Columbia University.
These are the kind of people and jobs that Graphene will attract to Manchester.
Manchester appoints world-leading academic to bring graphene closer to medicine
07 May 2013
The University of Manchester has today announced the appointment of a world-leading academic, who is playing a pivotal role in nanomedicine - a growing field with potential to benefit patients suffering from neurodegenerative disease and cancer.
Professor Kostas Kostarelos also brings to Manchester his Nanomedicine Laboratory which generates tiny materials to assist clinicians and is ranked among the top in the world.
His appointment, along with his 15-strong team of scientists, will help bring graphene closer to medicine with collaborations across the University and with its partner hospitals.
It follows a three-year collaboration with the University’s Nobel Laureates Professor Andre Geim and Professor Kostya Novoselov, who first isolated graphene, the world’s thinnest, strongest and most conductive material, in 2004. This led to the discovery of a whole new family of one-atom-thick materials.
Professor Kostarelos’s expertise includes developing minuscule needles to inject drugs into brain and other cells which in the future could help the treatment of neurodegenerative diseases and cancer. He sees great potential to use graphene in medicine.
He said: “Our Nanomedicine Lab has been collaborating with Manchester since 2010 in order to develop and use graphene material safely and effectively in medicine. Along with the activities around the creation of the National Graphene Institute in Manchester and the EU-funded Graphene
Flagship research programme, we will surely expand and reinforce this collaboration. Our broader aim is to bring graphene closer to medicine across The University of Manchester campus and its great hospitals.”
Professor Novoselov said: “There is great potential for using graphene for medical applications and procedures and I am greatly looking forward to working with Professor Kostarelos on this fascinating and important area. He brings a wealth of world-class experience in the field of nanomedicine.”
The move north was also prompted by the opportunity to work more closely with academics and clinicians in The University of Manchester, the Manchester Academic Health Sciences Network (MAHSC) and the Manchester Cancer Research Centre (MCRC).
MAHSC, a partnership between the University and six NHS organisations, brings clinicians and academics together to work on rapid dissemination and translation of health research and education in to practice to benefit patients. MCRC is a partnership between The University, The Christie Hospital and Cancer Research UK.
Professor Kostarelos, who joins the University in June, added: “At Manchester clinicians and biomedical scientists are very conscious about their conviction and drive to bridge the gap between nanotechnology and medicine. This is not common around the world and strongly influenced my decision to move, along of course with the opportunity to collaborate with great scientists in Manchester from a wide range of disciplines.’’
“I’m hoping our relocation will reinforce our existing efforts in using nanotechnologies to deliver genetic information to specific regions of the brain for patients suffering from neurodegenerative disorders.
“It should also help in my second major research area in cancer. Manchester has an excellent reputation in cancer research and my team wants to build strong links here. We believe we can be a very strong asset trying to get nano-technology treatments for cancer and developing applications to work on tumours.”
Professor Kostarelos trained as a chemical engineer and graduated from Imperial College London. He has held posts at the University of California in San Francisco, Memorial Sloan-Kettering Cancer Centre and Weill Medical College of Cornell University both in New York, Imperial College and University College London. His research has raised more than £7million of direct grant funding for his Nanomedicine Lab during the last few years. The Nanomedicine Lab he founded is investigating novel gene therapies, clinical use of stem cells, advanced delivery systems for radio- and chemo-therapeutic agents against cancer and engineering smart vector systems for imaging and therapeutics.
Professor Dame Nancy Rothwell, the President and Vice-Chancellor of The University of Manchester, said: “I am delighted that Professor Kostarelos will be joining us. He brings unique expertise which spans from nanomaterials to biomedicine.”
Professor Ian Jacobs, Dean of the University’s Faculty of Medical and Human Science and MAHSC Director, added: “Professor Kostarelos is an outstanding academic who will add to our efforts to translate cutting-edge science into novel approaches to health care. He will work with other outstanding scientists and clinicians in Manchester to make a difference to the care of patients locally and on an international scale.”