Molecular electronic nanodevices get closer with graphene electrodes

via Nature

An international team of researchers led by the University of Bern and the National Physical Laboratory (NPL) has revealed a new way to tune the functionality of next-generation molecular electronic devices using graphene. The results could be exploited to develop smaller, higher-performance devices for use in a range of applications including molecular sensing, flexible electronics, and energy conversion and storage, as well as robust measurement setups for resistance standards.

The field of nanoscale molecular electronics aims to exploit individual molecules as the building blocks for electronic devices, to improve functionality and enable developers to achieve an unprecedented level of device miniaturization and control. The main obstacle hindering progress in this field is the absence of stable contacts between the molecules and metals used that can both operate at room temperature and provide reproducible results. Graphene possesses not only excellent mechanical stability, but also exceptionally high electronic and thermal conductive properties, making the emerging 2D material very attractive for a range of possible applications in molecular electronics.

A team of experimentalists from the University of Bern and theoreticians from NPL (UK) and the University of the Basque Country (UPV/EHU, Spain), with the help of collaborators from Chuo University (Japan), have demonstrated the stability of multi-layer graphene-based molecular electronic devices down to the single molecule limit. The findings, reported in the journal Science Advances, represent a major step change in the development of graphene-based molecular electronics, with the reproducible properties of covalent contacts between molecules and graphene (even at room temperature) overcoming the limitations of current state-of-the-art technologies based on coinage metals.

Connecting single molecules

Adsorption of specific molecules on graphene-based electronic devices allows device functionality to be tuned, mainly by modifying its electrical resistance. However, it is difficult to relate overall device properties to the properties of the individual molecules adsorbed, since averaged quantities cannot identify possibly large variations across the graphene’s surface.

Dr Alexander Rudnev and Dr Veerabhadrarao Kaliginedi, from the Department of Chemistry and Biochemistry at the University of Bern, performed measurements of the electric current flowing though single molecules attached to graphite or multi-layered graphene electrodes using a unique low-noise experimental technique, which allowed them to resolve these molecule-to-molecule variations. Guided by the theoretical calculations of Dr Ivan Rungger (NPL) and Dr Andrea Droghetti (UPV/EHU), they demonstrated that variations on the graphite surface are very small and that the nature of the chemical contact of a molecule to the top graphene layer dictates the functionality of single-molecule electronic devices.

“We find that by carefully designing the chemical contact of molecules to graphene-based materials, we can tune their functionality,” said Dr Rungger. “Our single-molecule diodes showed that the rectification direction of electric current can be indeed switched by changing the nature of chemical contact of each molecule,” added Dr Rudnev.

“We are confident that our findings represent a significant step towards the practical exploitation of molecular electronic devices, and we expect a significant change in the research field direction following our path of room-temperature stable chemical bonding,” summarized Dr Kaliginedi. The findings will also help researchers working in electro-catalysis and energy conversion research design graphene/molecule interfaces in their experimental systems to improve the efficiency of the catalyst or device.

Learn more:Graphene electrodes offer new functionalities in molecular electronic nanodevices



The Latest on: Molecular electronic nanodevices
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“GPS in space”: NPL and University of Leicester bring autonomous interplanetary travel closer to reality



An accurate method for spacecraft navigation takes a leap forward today as the National Physical Laboratory (NPL) and the University of Leicester publish a paper that reveals a spacecraft’s position in space in the direction of a particular pulsar can be calculated autonomously, using a small X-ray telescope on board the craft, to an accuracy of 2km.

The method uses X-rays emitted from pulsars, which can be used to work out the position of a craft in space in 3D to an accuracy of 30 km at the distance of Neptune. Pulsars are dead stars that emit radiation in the form of X-rays and other electromagnetic waves. For a certain type of pulsar, called ‘millisecond pulsars’, the pulses of radiation occur with the regularity and precision of an atomic clock and could be used much like GPS in space.

The paper, published in Experimental Astronomy, details simulations undertaken using data, such as the pulsar positions and a craft’s distance from the Sun, for a European Space Agency feasibility study of the concept. The simulations took these data and tested the concept of triangulation by pulsars with current technology (an X-ray telescope designed and developed by the University of Leicester) and position, velocity and timing analysis undertaken by NPL. This generated a list of usable pulsars and measurements of how accurately a small telescope can lock onto these pulsars and calculate a location. Although most X-ray telescopes are large and would allow higher accuracies, the team focused on technology that could be small and light enough to be developed in future as part of a practical spacecraft subsystem. The key findings are:

–          At a distance of 30 astronomical units – the approximate distance of Neptune from the Earth – an accuracy of 2km or 5km can be calculated in the direction of a particular pulsar, called PSR B1937+21, by locking onto the pulsar for ten or one hours respectively

–          By locking onto three pulsars, a 3D location with an accuracy of 30km can be calculated

This technique is an improvement on the current navigation methods of the ground-based Deep Space Network (DSN) and European Space Tracking (ESTRACK) network as it:

–          Can be autonomous with no need for Earth contact for months or years, if an advanced atomic clock is also on the craft. ESTRACK and DSN can only track a small number of spacecraft at a time, putting a limit on the number of deep space manoeuvres they can support for different spacecraft at any one time.

–          In some scenarios, can take less time to estimate a location. ESTRACK and DSN are limited by the time delay between the craft and Earth which can be up to several hours for a mission at the outer planets and even longer outside the solar system.

Dr Setnam Shemar, Senior Research Scientist, NPL, said: “Our capability to explore the solar system has increased hugely over the past few decades; missions like Rosetta and New Horizons are testament to this. Yet how these craft navigate will in future become a limiting factor to our ambitions. The cost of maintaining current large ground-based communications systems based on radio waves is high and they can only communicate with a small number of craft at a time. Using pulsars as location beacons in space, together with a space atomic clock, allows for autonomy and greater capability in the outer solar system. The use of these dead stars in one form or another has the potential to become a new method for navigating in deep space and, in time, beyond the solar system.”

Dr John Pye, Space Research Centre Manager, University of Leicester, concludes:

“Up until now, the concept of pulsar-based navigation has been seen just as that – a concept. This simulation uses technology in the real world and proves its capabilities for this task. Our X-ray telescope can be feasibly launched into space due to its low weight and small size; indeed, it will be part of a mission to Mercury in 2018. NPL’s timing analysis capability has been developed over many years due to its long heritage in atomic clocks. We are entering a new era of space exploration as we delve deeper into our solar system, and this paper lays the foundations for a potential new technology that will get us there.” 

Learn more: “GPS in space”: NPL and University of Leicester bring autonomous interplanetary travel closer to reality



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British scientists develop solar panels which work better on a cloudy day

English: Cloudy morning Sun shining through cloud (Photo credit: Wikipedia)

In a departure from ‘blue sky thinking’ scientists in Britain have developed solar panels that work better on a cloudy day.

Their material is as thin and flexible as cloth, and can be made in any colour and printed in sheets on a 3D printer.

Although the technology is still at development stage, researchers hope that in future it could be used to make coats or bags which could charge phones or laptops or keep the wearer warm.

It is so lightweight that it could also be fitted to homes cheaply without the need to reinforce roofs and would be virtually invisible so homeowners would not be forced to put up with the eyesore of solar panels.

Car manufactures Fiat and Ford are also testing it to see if it could be added to car roofs to charge electrical circuits and avoid flat batteries.

Traditional solar cells are made of semi-conductors such as crystalline silicon. When light strikes the cell some of the energy is absorbed and knocks electrons loose in the silicon which can be forced into a current and drawn off for external use.

The new technology use small organic molecules as semi conductors which can be dissolved in a solution and printed in any shape using a 3D printer.

Most photovoltaics work best in strong, direct, sunlight of an intensity that is rarely seen in northern European countries.

But intriguingly the new material – known as organic photovoltaic – works more efficiently when out of direct sunlight, so is well suited for Britain’s inclement weather.

Scientists discovered that when testing it in direct sunlight desert conditions it could only manage 10 per cent efficiency, but in cloudy conditions that jumped to 13 per cent.

Dr Fernando Castro, principal research scientists at the National Physical Laboratory in Teddington, said: “Organic photovoltaics work much better in low and diffused light conditions. Even if it’s cloudy they still work.

“It’s not that they are going to produce more power but they are more efficient at generating power from the light that is available. So they would work better than normal soar cells do in cloud.”

The material would be cheaper and more environmentally friendly than traditional solar cells, slashing the cost of installing them on homes.

Read more . . .


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Printing silver onto fibers could pave the way for flexible, wearable electronics


A new technique for depositing silver onto clothing fibres could open up huge opportunities in wearable electronics.

Scientists at the National Physical Laboratory (NPL), the UK’s National Measurement Institute, have developed a way to print silver directly onto fibres. This new technique could make integrating electronics into all types of clothing simple and practical. This has many potential applications in sports, health, medicine, consumer electronics and fashion.

Most current plans for wearable electronics require weaving conductive materials into fabrics, which offer limited flexibility and can only be achieved when integrated into the design of the clothing from the start. NPL’s technique could allow lightweight circuits to be printed directly onto complete garments.

Silver coated fibres created using this technique are flexible and stretchable, meaning circuits can be easily printed onto many different types of fabric, including wool which is knitted in tight loops.

The technique involves chemically bonding a nano?silver layer onto individual fibres to a thickness of 20 nm. The conductive silver layer fully encapsulates fibres and has good adhesion and excellent conductivity.

Chris Hunt, Project Lead, says: “The technique has many potential applications. One particularly exciting area is wearable sensors and antennas which could be used for monitoring, for example checking on patients and vulnerable people; data capture and feedback for soldiers in the field; and performance monitoring in sports. It offers particular benefits over the ‘weaving in’ approach, as the conductive pattern and flexibility ensures that sensors are always positioned in the same location on the body.”

The technique could also create opportunities in fashion and consumer technology, such as incorporating LED lighting into clothing or having touch-screens on shirt sleeves.

Read more . . .


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‘Maser’ source of microwave beams comes out of the cold

“A new type of electronic device”

Researchers have shown off a microwave-emitting version of the laser, called a maser, that works at room temperature.

Masers were invented before the laser, but have languished in obscurity because they required high magnetic fields and difficult cooling schemes.

A report in Nature outlines a far simpler version using a crystalline material and no cooling or magnets.

The resulting intense microwave beams could be used in applications ranging from medical diagnostics to astronomy.

Masers were borne of an idea first postulated by Albert Einstein: that in some materials, energy could be pumped in and concentrated into a beam of electromagnetic waves oscillating in synchrony.

The first maser – an acronym of microwave amplification by stimulated emission of radiation – was built in 1953, and later masers were used, for example, in the first transatlantic television broadcast.

But researchers carried the work on, coaxing materials to amplify visible light instead of microwaves, earning three of them the 1964 Nobel prize in physics.

These “lasers” reached complete ubiquity as simple designs for them were perfected and applications for them proliferated.

However, the relative complexity of masers has relegated them to niche applications.

Masers remain in use – in a form much like those of the early prototypes – in applications such as atomic clocks and as the amplifiers for the minuscule communication signals coming from space probes.

Now researchers at the National Physical Laboratory (NPL) and Imperial College London in the UK have completely revamped the way “masing” is done, by carrying it out in a crystal of material called p-terphenyl that is infiltrated by chains of five-sided molecules called pentacene.

Their radically new design uses yellow light from a commercially available medical laser to “pump” energy in, producing synchronised microwaves at room temperature and in air, with no need for strong magnets or complex cooling and vacuum schemes.

Mark Oxborrow of NPL, lead author of the paper, called the design “a new type of electronic device” whose applications may, like the laser itself, stretch far beyond those imaginable in these early days.

The key value of masers lies not in their ability to produce a useful beam as lasers do, but to carry out the amplification process in a particularly clean way, without adding much noise.

That is why they are used to detect the tiny signals coming from space missions as distant as the Voyager probes, billions of kilometres away.

Read more . . .

via BBC – Jason Palmer

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