Single atom transistor gets precise position on chip

The basic unit of matter could become the basic unit of computing. A lone atom of phosphorus embedded in a sheet of silicon has been made to act as a transistor.

It is not the first single-atom transistor, but it can be much more precisely positioned than its predecessors, potentially making it a lot more useful.

“It’s an absolutely fantastic piece of engineering,” says physicist Bruce Kane at the University of Maryland, who was not involved in the work.

Elaborate production methods would initially prevent single-atom phosphorus transistors from being a worthwhile addition to traditional computers, but they may be necessary one day. The devices could also find an application in futuristic, super-speedy quantum computers.

A transistor is essentially a lump of conducting material sitting between two electrodes that acts as a switch. A pulse of voltage is supplied by a further electrode,”opening” the switch and allowing current to flow through the transistor.

Wiggling atom

Combining transistors on a chip produces logic circuits that can carry out computations. A goal shared by computer chip makers is to keep shrinking the transistor: squeeze ever more onto a single chip and you increase its computational power.

To dictate the exact position of their single atom, Michelle Simmons at the University of New South Wales, Australia, and colleagues started by covering a silicon sheet with a layer of hydrogen. Then they used the tip of a scanning tunnelling microscope to remove hydrogen atoms according to a precise pattern. They exposed two perpendicular pairs of exposed silicon strips plus a tiny rectangle made of just six silicon atoms that sat at the junction between these strips (see diagram, right).

Adding phosphine gas (PH₃) and heating caused phosphorus atoms, which are conducting, to bind to these exposed areas of silicon. In the case of the rectangle only one atom inserted itself into the silicon network.

The result was four phosphorus electrodes and a single phosphorus atom.

Boutique operation

One pair of electrodes was separated by a 108-nanometre gap. Creating a voltage between them allowed current to flow between the two perpendicular electrodes – separated from each other by just 20 nanometres, through the single phosphorus atom, which acted as a transistor.

Kane points out that the atomic transistor works at temperatures below 1 kelvin and that fabrication is difficult. “It’s a very slow, boutique operation to make one of these,” he says.

Simmons agrees, but counters that the traditional computer makers may be forced to adopt this technology if they want to make ever smaller chips. “This is one of the only techniques that allows you to make single atom devices,” she says.

Physicist Jeremy Levy of the University of Pittsburgh in Pennsylvania reckons the future of single atom transistors lies in quantum computers. The spin of the electrons in isolated phosphorus atoms could serve as qubits, the quantum equivalent of the bits in today’s computers. Controlling the interaction between qubits requires knowing the exact location of each one. Now that the location of individual atoms can be controlled, the next challenge is to link two of these transistors, Levy says.

Journal reference: Nature Nanotechnology, DOI: 10.1038/nnano.2012.21

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How fresco-wrecking salty towers build themselves

CORAL-like formations of salt sometimes sprout up on walls, damaging frescoes and other artwork, and now researchers know why.
Experiments and simulations by Marc Prat at the University of Toulouse in France and colleagues show how salty water evaporating from the pores in these materials leaves behind patches of salt crystals that grow into towers rather than a uniform film.
The towers are themselves porous and suck in more salty water. As they grow, water evaporating from their sides inhibits evaporation from surrounding areas, preventing crystal growth around the towers (Physical Review Letters, DOI: 10.1103/physrevlett.108.054502).
The work suggests that maintaining the right distribution of humidity over delicate frescoes may prevent such structures from forming.

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App's glowing arrows guide you around a new building

 

WHETHER it's a cavernous department store or a rabbit warren of offices, finding your way around an unfamiliar building can be a struggle. But now an augmented reality app can point you in the right direction.

Developed by Jaewoo Chung at MIT's Media Lab, Guiding Light consists of a wearable badge with magnetic sensors and a software app that makes use of a projector built into many Samsung smartphones to cast arrows onto the ground in front of you as you walk.

The system relies on a map of the building based on fluctuations in its magnetic field, created by the presence of steel in the walls, floor and ceiling. In tests, Guiding Light was able to determine a user's position to within a metre.

Look for the arrow (Image: Jack Wild/Getty)

To create the map, someone walks through a building wearing a badge that contains four magnetic sensors, which record changes in the magnetic field at each point in the building. The map is then loaded onto a phone. To navigate around the building, the user must wear a similar badge that "talks" to the map on the phone, confirming the user's position.

If the user wants to reach a specific location, they can key it into the app and Guiding Light will project an arrow onto the floor ahead. Like a compass, the arrow changes direction as the sensors in the badge shift in orientation. The projection can also give extra information: if you point your phone at an office door, say, the phone's accelerometer detects the change and the projection tells you the name, photo and job title of the occupant (see video: newscientist.com/article/dn21419).

Several technology companies have recently unveiled indoor positioning systems (IPS) that work with mobile phones - but these rely on nearby Wi-Fi nodes or Bluetooth sensors embedded in walls throughout a building to locate the user. Chung says his system is cheaper and easier to use, because all that is needed is a badge. What's more, he says, other systems require the user to stare at maps on their phones to see where they are headed, whereas Guiding Light does not. "We wanted people's eyes to be on their environment."

Professor Babak Parviz at the University of Washington in Seattle, who has worked on an augmented reality contact lens, says the system is a "creative" app. "If someday the [sensors] can be integrated into the phone for indoor navigation it becomes even more compelling," he says.

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Should police and coastguards use laser dazzlers?

 

Is the future bright? (Image: Olivier Laban-Mattei/AFP/Getty Images)

Devices that temporarily blind people can now be used by US police, but are they worth the risks?

THE US police and coastguard may soon start using laser "dazzlers" like those the American and British militaries have employed for years at checkpoints in Iraq and Afghanistan.

At the SHOT Show last month in Las Vegas, Nevada, B.E. Meyers Electro-Optics of Redmond, Washington, unveiled the first laser dazzler that has been approved for non-military law enforcement by the US Food and Drug Administration. Though they are purportedly less harmful than other non-lethal weapons, such as tasers and rubber bullets, the International Committee of the Red Cross is concerned that not enough has been done to lessen the risk of people suffering permanent blindness.

Dazzlers are designed to warn people away by temporarily blinding them with pulses of green laser light. Unlike tasers or rubber bullets, there is no possibility that the lasers could kill a person, they just create a beam that is too intense to look at.

Most models that have been built for military use are designed to work at distances of 300 to 500 metres during the day and a kilometre or so at night. This makes them attractive for long-range use at sea to stop vessels suspected of drug trafficking, for example. At 40 metres, however, the intense beam of a 200-milliwatt laser can permanently damage eyes. Despite this, they have seen regular use in Iraq since 2006.

"We have had some injuries," says a former researcher at the US army's Brooke Army Medical Center in San Antonio, Texas, who asked not to be named, "but for the most part they have been minor." That is partly because, when faced with a bright light, people instinctively look away. Also, the pupil of the eye contracts in a tenth of a second, quickly reducing the amount of light reaching the retina.

Not all injuries are minor, however. The researcher recounted the story of a soldier he interviewed after an incident in Iraq a few years ago. While on duty, the soldier fumbled a dazzler he was trying to point at an oncoming vehicle a safe distance away. "He was in an awkward position and illuminated a rearview mirror in such a way that he got a beam directly back into the eye." The beam had gone less than 6 metres when it hit the soldier in the centre of vision of his right eye, burning the retina and leaving his vision in that eye permanently damaged.

In order to win FDA approval, the 200-milliwatt GLARE Enforcer built by Meyers comes equipped with a harmless low-power laser that probes the line of fire and automatically reduces the dazzler's power to safe levels if it detects a person or reflective object inside the 40-metre hazard zone. Most military-issue dazzlers do not have this feature.

The Red Cross - which pushed under Protocol IV of the Geneva Convention for the existing ban on lasers intentionally designed to blind people - remains sceptical, and in November it called for a discussion on how to minimise the risk of permanent blinding by laser dazzlers.

In the end, though, the biggest hazard may not come from soldiers or police, but from ordinary people. Dazzlers several times more powerful than most military devices are readily available online for less than $1000 and do not come with safety features. They have already been used against the police: last June, Greek protesters zapped police believed to have been beating demonstrators.

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Charging up an all-electric 320 km/h racing car

Keeping the Lola-Drayson concept car going is more impressive than its flat-out speed

HOW do you get more power out of an electric car than its main battery pack can deliver? Simple, turn the car's very bodywork into a battery, extract power from every bounce of its suspension system and, while you're at it, suck energy from the road surface too.

Such are the measures being built into an electric racing car capable of reaching 320 kilometres (200 miles) per hour by a UK-based consortium. Their aim is to perfect a multitude of novel electric-vehicle (EV) technologies and ultimately to transfer them to road cars. Led by Drayson Racing Technologies of Oxford and Lola Cars of Huntingdon, the 10-firm consortium also includes aerospace heavyweight BAE Systems in Warton, UK, and 3G-cellphone pioneer Qualcomm of San Diego, California. They want to improve on the range of today's EVs, says consortium leader Paul Drayson, which are normally limited to around 160 kilometres (100 miles).

"Don't judge electric cars by what you are seeing on the street right now," he says.

The first way they plan to improve range is to free the car's main battery from ancillary tasks like headlights. Enter BAE Systems' closely guarded "structural battery" technology - which allows sections of carbon-fibre bodywork to supply power. "They are made out of honeycombs of carbon fibre filled with a solution that gives them the energy storage capacity of a battery," says Julian Sole, chief designer at Lola Cars. "Their advantage is they can form any shape."

The structural battery is built into the rear of the car but there is no limit to how many of the car's surfaces could become batteries.

The next energy-scavenging trick comes from Multimatic of Rockingham, UK, which has harnessed the up-and-down motion of the car's suspension to generate electricity on the move. This charges a capacitor, whose discharge can be used to propel the car or power movable aerodynamic surfaces, which provide the super-slippery concept vehicle with road-holding downforce. The system mirrors the way regenerative braking in EVs and hybrids harvests deceleration energy rather than losing it as heat.

Meanwhile, Qualcomm's London-based Halo Inductive Power Transfer division is addressing another major EV hurdle: charging the main battery.

HaloIPT has developed doormat-sized pads packed with copper coils - one in the car, one in the road - that transfer power wirelessly to the car through electromagnetic induction. A HaloIPT spokesman claims that the system is 92 per cent efficient.

Drayson wants to populate the racing line on racetracks with the pads, so cars charge from the track during races. This kind of innovative charging technology, designed to keep the concept car flying around the track, will inevitably have wider applications. "The new generation of technology we are showcasing in electric racing will amaze people when it gets to road cars," he promises.

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Your heartbeat could keep your data safe

HAVING trouble remembering your password? Perhaps you need to use your heart instead of your head. An encryption system that uses the unique pattern of your heartbeat as a secret key could potentially be used to make a hard drive that will only decrypt in response to your touch.

Our heartbeats follow an irregular pattern that never quite repeats and that is unique to everyone. Chun-Liang Lin at the National Chung Hsing University in Taichung, Taiwan, and colleagues used an electrocardiograph (ECG) to extract the unique mathematical features underlying this pattern. They then used the information to generate a secret key that forms part of an encryption scheme based on the mathematics of chaos theory, by which small changes in initial conditions lead to very different outcomes.

As a proof of concept, Lin's system currently takes the user's ECG reading from each palm once, and a key based on that reading is stored and used for all later decryptions. He says the goal is to build the system into external hard drives and other devices that can be decrypted and encrypted simply by touching them.

The work will appear in the

journal Information Sciences (DOI: 10.1016/j.ins.2012.01.016).

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Paper robots could have a strong, gentle touch

Surprisingly what you can do with paper (Image: R. Martinez, C. R. Fish, X. Chen, G. M. Whitesides/Wiley)

Paper structures built using the principles of origami could lead to cheap, easy-to-make robots that are very different than their more traditional metal brethren.

George Whitesides and colleagues at Harvard University have previously built squid-inspired robots with artificial muscles made from soft plastic and powered by pneumatic air pumps. Now they have combined this technique with paper to create a series of lightweight structures capable of bending, twisting and even lifting heavy weights.

Paper is flexible, but unlike plastic it does not stretch, making it useful for forming rigid structures when a paper balloon is filled with air. For example, paper folded into a bellows-like shape embedded in flexible plastic extends straight upwards when inflated, creating a 1-centimetre-wide tube weighing just over 8 grams that is able to lift a 1 kilogram weight.

Gluing different parts of the bellows together lets it inflate into a U shape or twist as it extends.

These simple designs could be improved upon to create "soft" robots able to work closely with humans, unlike some robots currently used on factory assembly lines. The team says they could be used to provide extra hands for surgeons or handle delicate objects such as eggs or fruit.

Journal reference: Advanced Functional Materials, DOI: 10.1002/adfm.201102978

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Stock trading 'fractures' may warn of next crash

 

Automated traders do the job at lightning speed (Image: KeystoneUSA-ZUMA/Rex Features)

Might a fleeting and little understood aspect of stock market dynamics hold the key to warding off financial crashes? That is the tantalising suggestion to emerge from a group of physicists who have been studying stock movements.

The study is the first to focus on an ultra-fast feature of market dynamics that the team, led by Neil Johnson at the University of Miami in Coral Gables, calls a "fracture". Fractures happen when the price of a stock briefly shoots up or down, often before returning to its original level. They take place so quickly, sometimes lasting less than half a second, that they can be invisible to any human following the price. "If you blink you miss it," says Johnson. His research shows that there seems to be a link between these fractures and sudden stock market crashes, known as "black swans".

If fractures are a source of instability, computerised trading algorithms may be to blame. Use of these algorithms, which make automated trades in milliseconds, has mushroomed in recent years. Competition between rival algorithms is so great that one company is spending $300 million to build a transatlantic cable that will shave 6 milliseconds off the time it takes to exchange signals between the financial hubs of London and New York. But finance experts fear that one or more out-of-control algorithms could cause a crash, as may have happened in the so-called Flash Crash of May 2010.

Johnson's research, which was posted online on 8 February, is based on price logs from over 60 different markets collected by Eric Hunsader of Nanex, a Chicago-based company that sells streaming market data. Johnson and Hunsader trawled through the data and found that fractures are remarkably common – 18,520 took place between 2006 and 2010.

Intriguingly, the number of daily fractures increased about a week before the stock market crash of September 2008, and also before a sudden but smaller crash in May 2010, which is still not fully understood. Johnson thinks that the build-up of fractures can in some cases destablise the entire market, much as the accumulation of tiny cracks can lead to catastrophic failures in structures such as aircraft wings. "You're seeing something starting to break open," says Johnson.

Fracture forecasts

The link between fractures and stock market crashes requires further investigation, but suggests it might be possible to build an early-warning system based on the rate at which fractures occur. "Johnson makes a compelling case," says Dave Cliff, an expert in complex systems at the University of Bristol, UK. "Developing [his] analysis techniques into methods or tools for reliably predicting crashes is a very appealing prospect." Forecasting every crash is probably impossible, adds Cliff, but the research could lead to a system that at least alerts regulators to incipient instability. "This work could turn out to be a major first step in that direction."

"There is a huge amount of interconnected algorithms that cannot be controlled by regulators," says Tobias Preis, a researcher at Boston University in Massachusetts and founder of Artemis Capital Asset Management in Holzheim, Germany.

When Johnson analysed the frequency at which fractures of different size and duration occur, he found that fractures lasting one second or less follow a different statistical pattern to longer ones. The one-second cut-off is significant, says Johnson, since it is about the time it takes a human trader to weigh up a piece of evidence and make a decision. On shorter timescales computers control market dynamics since they can make decisions in mere milliseconds.

This ultra-fast computing-controlled trading regime is barely recognised, let alone controlled by any government regulator with an interest in preventing crashes. "Nobody really knows what's going on down there," says Johnson. "It's like the wild west."

Journal reference: arxiv.org/abs/1202.1448

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