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First Single-Molecule LED

Illustration: APS
Artist illustration of a single-molecule organic light-emitting diode

By coaxing light out of a single polymer molecule, researchers have made the world’s tiniest light-emitting diode. This work is part of an interdisciplinary effort to make molecular scale electronic devices, which hold the potential for creating smaller but more powerful and energy-efficient computers.

Guillaume Schull and his colleagues at the University of Strasbourg in France made the device with the conducting polymer polythiophene. They used a scanning tunneling microscope tip to locate and grab a single polythiophene molecule lying on a gold substrate. Then they pulled up the tip to suspend the molecule like a wire between the tip and the substrate.

The researchers report in the journal Physical Review Letters that when they applied a voltage across the molecule, they were able to measure a nanoampere-scale current passing through it and to record light emitted from it.

Conventional organic light-emitting diodes are semiconductors sandwiched between two electrodes. A voltage applied between the electrodes creates electrons and holes. When these two oppositely charged particles meet, photons are emitted.

The same thing happens here, except on a much tinier, single-molecule level. When the microscope tip had a large negative voltage, the researchers calculate that one photon was emitted for every 100 000 electrons that surged from the tip and into the molecule. The photon had a red wavelength. When the researchers flipped the voltage bias, the light emission was negligible.

IEEE Spectrum on Your Phone: New and Improved!

If you routinely visit IEEE Spectrum on your phone, you've probably noticed some big changes recently. If you've never tried looking at this site on your phone, now's the perfect time to start! We've made major overhauls to the the mobile view—here's a brief sample of what's new.

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Google Highlights Value of Patents in Motorola Sale to Lenovo

Google has exited the smartphone manufacturing business and shored up Android's legal defenses in the smartphone patent wars in a single week. The technology giant sold off Motorola Mobility to Lenovo in a US $12.5-billion deal on Wednesday that allowed it to hold onto most of Motorola's patent portfolio.

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Bitcoin Investors Urge Restraint at Regulatory Hearing

The New York State Department of Financial Services held its first of two public hearings yesterday to discuss the regulation of Bitcoin. The discussion comes at a turbulent time for the cryptocurrency, and the stakes are high for both investors betting on Bitcoin-based ventures and authorities seeking to prevent criminal operators from exploiting the privacy afforded by virtual currencies.

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Tech Giants' NSA Deal Leaves Start-Ups in the Shadows

A group of U.S. technology giants has struck a deal with the Obama administration that allows the companies to disclose more details on customer data turned over to government agencies such as the National Security Agency (NSA) and the Federal Bureau of Investigation (FBI). But the fine print in the agreement leaves smaller companies such as start-ups with greater restrictions on when they can publicly reveal national security data requests for their users' data.

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Modular Concepts at CES Hint at the Future of Mobile Computing

One of the highlights for us at CES is checking out concept products that will probably never see the light of day because they're just too crazy to give to consumers. You can think of them like pieces of designer clothing at a runway show: nobody actually wears that stuff, but it has the potential to influence the direction in which designs might be heading.

A trend that we noticed with concept products at CES this year was modularity: the idea that you shouldn't have to settle for a mobile device (like a cellphone or a tablet or a laptop) that only exists in a single form factor. We use these gadgets in all kinds of ways that they weren't really intended for (like, watching a movie on a cellphone or editing an Excel spreadsheet using a tablet's touchscreen)—wouldn't it be fantastic if we could dynamically reconfigure them to best fit our immediate needs? This is a significant hardware problem, and nobody has quite found the right way to solve it yet, but we saw some CES concepts that suggest a few different approaches that could eventually work.

Here, then are the modular highlights:

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How to Make Electricity With Bacteria-Coated Rubber

A new electric generator has a modest and unexpected energy source: A small strip of latex rubber coated with bacterial spores. 

The contraption makes use of the harmless soil bacterium Bacillus subtilis, which has a neat survival trick. When nutrients are scarce, it turns itself into a tough little spore that can withstand heat, desiccation, chemical assaults, radiation, and anything else the world can throw at it. These spores respond to changes in humidity. When the air dries they shrivel up like grapes turning into raisins; when the air is moist they plump up again. Researchers from Harvard's Wyss Institute and several other universities realized they could harness that physical movement, and could make an actuator to generate electricity.  

In the experiment, published this week in Nature Nanotechnology, the researchers slathered one side of a sheet of rubber with the bacterial spores. When the sheet dried it curled up, much like a leaf does after it falls from a tree. Increasing the humidity caused the sheet to straighten out again. Researcher Ozgur Sahin then built a humidity driven generator out of Legos, in which the spore-coated rubber acts as a cantilever that flips back and forth, driving a rotating magnet to produce electricity. 

Such a device, properly scaled up, could use the natural evaporation of water to generate useful amounts of clean electricity, the researchers say. 

Images and video: Xi Chen/Columbia University

China's "Jade Rabbit" Moon Rover Faces Premature End

UPDATE: China's Jade Rabbit lunar rover has been officially pronounced "dead" by an official Chinese news service on Feb. 12. The rover's earlier mechanical failure may have allowed certain critical systems to become fatally exposed to the cold during the long lunar night, according to New Scientist.

China's first lunar rover faces a "mechanical control abnormality" that could bring its mission on the moon to an early end. Official Chinese news sources have already begun warning of the possibility that the rover, named Jade Rabbit, may never wake up from a scheduled dormant period during the long lunar night.

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New "Look And Link" Wireless Technology Enables Device-to-Device Links By Pointing

Researchers from South Korea’s Electronics and Telecommunications Research Institute demoed a new wireless technology this week that could enable better device-to-device (D2D) communications, allowing smart gadgets such as phones to link to one another without going through a base station. Many researchers believe that D2D capability will be a key feature in the next generation of wireless networks after 4G LTE and LTE-Advanced. It could help decongest overloaded base stations and usher in new applications, such as screening a video clip on a big screen while it's actually stored on your phone, or downloading the service manual directly from your smart car.

Now, I know what you’re thinking: Don’t D2D technologies already exist? Sure they do. You may be scrolling through this story using a Bluetooth-connected mouse. Perhaps you bought a cup of coffee this morning by tapping your smartphone to a near field communication (NFC)-enabled cash register. Other D2D standards already available or in the works include Wi-Fi Direct, LTE Direct, and Peer Awareness Communications.

But these technologies have yet to catch on in a big way. And maybe for good reason. Surveys show that users don’t particularly like touching their phones to things or scanning a list of available devices to connect with the one they want, which Wi-Fi Direct and most other D2D technologies require. Most people find all that tapping, scrolling, and clicking to be physically demanding, annoying, or just plain awkward. Given the choice, we would much rather engage with smart objects simply by pointing our smartphones or tablets at them—or better yet, by looking at them, such as with smart glasses.

But here’s the problem: In order to connect with, say, a smart poster or with your friend’s television, your phone must know its ID, such as an IP address or a given nickname. Without knowing this information or making you select it from a list, how would your phone identify the device you’re pointing it at?

The South Korean team, led by Young-Hoon Kim, devised a solution using a novel beamforming technique. Dubbed “Look And Link,” it uses an array of antennas to direct a phone’s transmissions toward the correct receiving device. The demo took place on Wednesday at an IEEE wireless standards meeting in Los Angeles.

So how does Look And Link work? Imagine, for instance, that you are strolling down the street, and you see a restaurant that you think you might want to try. But this is the future, so rather than walk in and ask for a menu, you simply stare through your smart glasses at the smart sign in the window. Using a built-in antenna array, your smart glasses form a directional beam to transmit a query toward the smart sign, thus avoiding querying other nearby devices.

But not just any beam pattern will do the trick. Conventional techniques, for instance, would create a beamform that, while concentrating most of its gain toward the smart sign, would also radiate in unintended directions. So devices that you’re not looking at, but that are close to you, might receive a signal that’s just as strong—or stronger—than the signal received by the smart sign. In the below figure, for example, both the device you’re pointing at (Device A) and a nearby device (Device B) will receive your query quite strongly.

Kim and his team solved this problem by randomly varying the shape of the beam over short time intervals—a technique they call jittering. Only the gain in the direction of the target device stays the same. The effect is that while the smart sign receives a signal of consistently high strength, other nearby devices see huge gain changes. The researchers illustrate the concept nicely in the figures below:


So now, when your smart glasses send out a query to the smart sign, nearby devices know not to answer. Meanwhile, the smart sign transmits back its ID, allowing your glasses to connect with it using some other wireless standard, such as LTE Direct. Then you can download information from the sign, such as menus and operating hours. Maybe you even decide to make a reservation for later that evening.

Kim points out that another advantage of Look And Link, besides enabling device identification through pointing, is that it allows devices to link with one another quickly. Using Look And Link, he says, two devices can connect in a just a few seconds, compared to almost a minute using Bluetooth.

At Wednesday’s demo, the researchers used a prototype transmitter with four antennas, according to Byung-Jae Kwak, one of the team members. He concedes that four or more antennas may not fit into today’s smartphones, which currently have no more than two. But, he says, cellular carriers as well as unlicensed device makers are beginning to look toward higher frequencies, which require smaller antennas. The South Korean team demoed Look And Link, for instance, using 5 GHz spectrum. “We are also interested in using 60 GHz,” Kwak said in an e-mail. “In that case, we can easily put eight antennas in the space of a finger nail.”

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