Controlling the electronic properties of graphene

News from Physikalisch-Technische Bundesanstalt on plasmonics in graphene.

The release:

Graphene: What projections and humps can be good for

Investigators from Hanover and Braunschweig measure how the electronic properties of graphene can be controlled with purposefully used roughnesses

This release is available in German.

		IMAGE: A residual interaction with the SiC substrate causes the formation of the six-fold satellite reflex structure. Click here for more information.

At present, graphene probably is the most investigated new material system worldwide. Due to its astonishing mechanical, chemical and electronic properties, it promises manifold future applications – for example in microelectronics. The electrons in graphene are particularly movable and could, therefore, replace silicon which is used today as the basic material of fast computer chips. In a research cooperation, scientists of Leibniz University Hanover and of the Physikalisch-Technische Bundesanstalt (PTB) have now investigated in which way a rough base affects the electronic properties of the graphene layer. Their results suggest that it will soon be possible to control plasmons, i.e. collective oscillations of electrons, purposefully in the graphene, by virtually establishing a lane composed of projections and humps for them. The results were published in the current edition of the New Journal of Physics.

The structure of graphene itself is fascinating: It consists of exactly one single, regular layer of carbon atoms. To manufacture this incredibly thin layer absolutely neatly is a great challenge. A possible method to recipitate graphene extensively on an insulating substrate is epitaxy, i.e. the controlled growth of graphene on insulating silicon carbide. For this purpose, a silicon carbide crystal is heated in vacuum. Starting from a specific temperature, carbon atoms migrate to the surface and form a monoatomic layer on the – still solid – silicon carbide. An important question for later applications is, how defects and steps of the silicon carbide surface affect the electronic properties of the graphene grown on it.

Within the scope of a research cooperation between PTB and Leibniz University Hanover, the influence of defects in the graphene on the electronic properties has been investigated. During the investigations, special attention was paid to the influence of the defects on a special electronic excitation, the so-called plasmons.

By different sample preparation, first of all silicon carbide crystals with different surface roughness and, thus, with a different concentration of surface defects were investigated, on which, subsequently, graphene formed. The influence of the defects on the plasmon excitations was then investigated by means of low-energy electron diffraction (SPA-LEED) and electron loss spectroscopy (EELS).

The process revealed a strong dependence of the lifetime of plasmon on the surface quality. Defects, as they are caused on step edges and grain boundaries, strongly impede the propagation of the plasmons and drastically shorten their lifetime. Here it is remarkable that the other electronic properties of the plasmons, in particular their dispersion, remain largely unaffected.

This opens up interesting possibilities for the future technical application and use of plasmons (the so-called “plasmonics”) in graphene. By selective adjustment of the surface roughness, different graphene ranges could be generated in which the plasmons are either strongly dampened or can propagate almost unobstructedly. In this way, the plasmons could be conducted along “plasmon conductors” with low surface roughness specifically from one point of a graphene chip to another.

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Original publication:
T. Langer, J. Baringhaus, H. Pfnür, H. W. Schumacher and C. Tegenkamp:
“Plasmon damping below the Landau regime: the role of defects in epitaxial graphene”.
New Journal of Physics 12, 033017 (2010).
http://iopscience.iop.org/1367-2630/12/3/033017/

Plasma kills superbugs dead

Via KurzweilAI.net — This is good news for a serious medical concern.

Device spells doom for superbugs

BBC News, Nov. 26, 2009 A prototype device that uses “cold atmospheric plasma” to rid hands, feet, or even underarms of bacteria, including the hospital superbug MRSA, has been developed by Max Planck Institute for Extraterrestrial Physics researchers. The team says that an exposure to the plasma of only about 12 seconds reduces the incidence of bacteria, viruses, and fungi on hands by a factor of a million, a number that stands in sharp contrast to the several minutes hospital staff can take to wash using traditional soap and water. (New Journal of Physics)   Read Original Article>>

Moving toward quantum-encrypted communication networks

Very exciting news in milestone setting quantum-encrypted communications networking.

The release:

Researchers unite to distribute quantum keys

Researchers from across Europe have united to build the largest quantum key distribution network ever built. The efforts of 41 research and industrial organisations were realised as secure, quantum encrypted information was sent over an eight node, mesh network.

With an average link length of 20 to 30 kilometres, and the longest link being 83 kilometres, the researchers from organisations such as the AIT Austrian Institute of Technology (formerly Austrian Research Centers), id Quantique, Toshiba Research in the UK, Université de Genève, the University of Vienna, CNRS, Thales, LMU Munich, Siemens, and many more have broken all previous records and taken another huge stride towards practical implementation of secure, quantum-encrypted communication networks.

A journal paper, ‘The SECOQC Key Distribution Network in Vienna’, published as part of IOP Publishing’s New Journal of Physics‘ Focus Issue on ‘Quantum Cryptography: Theory and Practice’, illustrates the operation of the network and gives an initial estimate for transmission capacity (the maximum amount of keys that can be exchanged on a quantum key distribution, QKD, network).

Undertaken in late 2008, using the company internal glass fibre ring of Siemens and 4 of its dependencies across Vienna plus a repeater station, near St. Pölten in Lower Austria, the QKD demonstration involved secure telephone communication and video-conference as well as a rerouting experiment which demonstrated the functionality of the SEcure COmmunication network based on Quantum Cryptography (SECOQC).

One of the first practical applications to emerge from advances in the sometimes baffling study of quantum mechanics, quantum cryptography has become a soon-to-be reached benchmark in secure communications.

Quantum mechanics describes the fundamental nature of matter at the atomic level and offers very intriguing, often counter-intuitive, explanations to help us understand the building blocks that construct the world around us. Quantum cryptography uses the quantum mechanical behaviour of photons, the fundamental particles of light, to enable highly secure transmission of data beyond that achievable by classical methods.

The photons themselves are used to distribute cryptographic key to access encrypted information, such as a highly sensitive transaction file that, say, a bank wishes to keep completely confidential, which can be sent along practical communication lines, made of fibre optics. Quantum indeterminacy, the quantum mechanics dictum which states that measuring an unknown quantum state will change it, means that the information cannot be accessed by a third party without corrupting it beyond recovery and therefore making the act of hacking futile.

The researchers write, “In our paper we have put forward, for the first time, a systematic design that allows unrestricted scalability and interoperability of QKD technologies.”

 

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Quantum cryptography becoming practical

Looks like things are moving that direction. Very cool.

The release:

Computer hackers R.I.P. — making quantum cryptography practical

Quantum cryptography, a completely secure means of communication, is much closer to being used practically as researchers from  and Cambridge University’s Cavendish Laboratory have now developed high speed detectors capable of receiving information with much higher key rates, thereby able to receive more information faster.

Published as part of IOP Publishing’s New Journal of Physics‘ Focus Issue on ‘Quantum Cryptography: Theory and Practice’, the journal paper, ‘Practical gigahertz quantum key distribution based on avalanche photodiodes’, details how quantum communication can be made possible without having to use cryogenic cooling and/or complicated optical setups, making it much more likely to become commercially viable soon.

One of the first practical applications to emerge from advances in the often baffling study of quantum mechanics, quantum cryptography has become the soon-to-be-reached gold standard in secure communications.

Quantum mechanics describes the fundamental nature of matter at the atomic level and offers very intriguing, often counter-intuitive, explanations to help us understand the building blocks that construct the world around us. Quantum cryptography uses the quantum mechanical behaviour of photons, the fundamental particles of light, to enable highly secure transmission of data beyond that achievable by classical encryption.

The photons themselves are used to distribute keys that enable access to encrypted information, such as a confidential video file that, say, a bank wishes to keep completely confidential, which can be sent along practical communication lines, made of fibre optics. Quantum indeterminacy, the quantum mechanics dictum which states that measuring an unknown quantum state will change it, means that the key information cannot be accessed by a third party without corrupting it beyond recovery and therefore making the act of hacking futile.

While other detectors can offer a key rate close to that reported in this journal paper, the present advance only relies on practical components for high speed photon detection, which has previously required either cryogenic cooling or highly technical optical setups, to make quantum key distribution much more user-friendly.

Using an attenuated (weakened) laser as a light source and a compact detector (semiconductor avalanche photodiodes), the researchers have introduced a decoy protocol for guarding against intruder attacks that would confuse with erroneous information all but the sophisticated, compact detector developed by the researchers.

As the researchers write, “With the present advances, we believe quantum key distribution is now practical for realising high band-width information-theoretically secure communication.”

Governments, banks and large businesses who fear the leaking of sensitive information will, no doubt, be watching closely.

 

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Quantum paradox observed

Big, big news in physics.

The release:

Quantum paradox directly observed — a milestone in quantum mechanics

In quantum mechanics, a vanguard of physics where science often merges into philosophy, much of our understanding is based on conjecture and probabilities, but a group of researchers in Japan has moved one of the fundamental paradoxes in quantum mechanics into the lab for experimentation and observed some of the ‘spooky action of quantum mechanics’ directly.

Hardy’s Paradox, the axiom that we cannot make inferences about past events that haven’t been directly observed while also acknowledging that the very act of observation affects the reality we seek to unearth, poses a conundrum that quantum physicists have sought to overcome for decades. How do you observe quantum mechanics, atomic and sub-atomic systems that are so small-scale they cannot be described in classical terms, when the act of looking at them changes them permanently?

In a journal paper published in the New Journal of Physics, ‘Direct observation of Hardy’s paradox by joint weak measurement with an entangled photon pair’, today, Wednesday, 4 March, authored by Kazuhiro Yokota, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto from the Graduate School of Engineering Science at Osaka University and the CREST Photonic Quantum Information Project in Kawaguchi City, the research group explains how they used a measurement technique that has an almost imperceptible impact on the experiment which allows the researchers to compile objectively provable results at sub-atomic scales.

The experiment, based on Lucien Hardy’s thought experiment, which follows the paths of two photons using interferometers, instruments that can be used to interfere photons together, is believed to throw up contradictory results that do not conform to our classical understanding of reality. Although Hardy’s Paradox is rarely refuted, it was only a thought experiment until recently.

Using an entangled pair of photons and an original but complicated method of weak measurement that does not interfere with the path of the photons, a significant step towards harnessing the reality of quantum mechanics has been taken by these researchers in Japan.

As the researchers write, “Unlike Hardy’s original argument, our demonstration reveals the paradox by observation, rather than inference. We believe the demonstrated joint weak measurement is useful not only for exploiting fundamental quantum physics, but also for various applications such as quantum metrology and quantum information technology.”

 

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The time has come for flexi display tech

I’ve blogged on flexible display technology before (such as here in the middle of three news bits) and this is some exciting news from researchers at Sony and the Max Planck Institute.

The release:

Flexi display technology is now

Rigid television screens, bulky laptops and still image posters are to be a thing of the past as new research, published today, Thursday, 2 October, in the New Journal of Physics, heralds the beginning of a technological revolution for screen displays.

Screen display technology is taking a significant step forward as researchers from Sony and the Max Planck Institute demonstrate the possibility of bendable optically assessed organic light emitting displays for the first time, based on red or IR-A light upconversion.

The paper, ‘Annihilation Assisted Upconversion: All-Organic, Flexible and Transparent Multicolour Display’, makes feasible the design of computers that can be folded up and put in your pocket, the mass-production of moving image posters for display advertising, televisions which can be bended to view or, even, newspaper display technology which allows readers to upload daily news to an easy-to-carry display contraption.

All organic, upconversion multicolour displays have significant advantages when compared to the traditional technology used for projection displays and televisions. Namely UC displays are:

 

• All-organic − transparent and flexible
• Ultra low excitation intensity (red or IR)– less than 15 mWcm-2
• Emissive display – no speckles
• Coherent or non-coherent excitation allowed
• High efficiency – at the moment ca. 6 %
• Fast response times – ca. 1 µs up to 500 µs on request (LCDs have ms)
• Almost unlimited viewing angle – up to the total internal reflection angle
• Tailoring of emitted colours realised even when using the same excitation source
• Multilayer Displays
• Size limited only by the size of the substrates

 

With LCD-based projection displays, the liquid crystal acts as a filter for the light being shone through so when coherent excitation is used (e.g. laser diodes) the problems with speckles are serious. For this organic emissive UC displays, the organic molecules themselves emit non-coherent light in 4 (all directions) to produce an image.

Sony announced the development of flexible OLED display screens in 2006 but glitches such as size and resolution limitations, and the difficulty of structuring the organic compounds so as not to be distorted when bent, have stopped designs coming to market. This new technology for optically excited organic emissive displays hasn’t got this problem and gives further opportunities for new applications.

The research published today concludes through the use of a new structure and unique combinations for the organic compounds within viscous polymeric matrix, that there need be no size or resolution limitations for the new screens.

The researchers conclude, “To the best of our knowledge we demonstrate for the first time a versatile colour all-organic and transparent UC-display. The reported displays are also flexible and have excellent brightness.”

 

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There is a small film of a prototype screen in action available.

Update — Technology Review covers this story here.