Nano-LEDs emit full visible spectrum of light

Nano-LEDs emit full visible spectrum of light

  2:04:00 AM    Science Lover

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Physicists through Taiwan possess designed along with fabricated nano-sized light-emitting diodes (LEDs) that emit light source spanning your whole visible spectrum. Although all the tiny full-color LEDs aren't meant for commercial lighting fixtures applications, they must be useful within high-resolution microscopy and additionally subwavelength photolithography.

A single nanodisk-nanorod LED viewed with a field-emission
scanning electron microscope. (Right) Some colors of light
emissions from nanodisk-nanorod LEDs - violet, blue, cyan,
green, and yellow - viewed with an optical microscope.
Image credit: Lu, et al. ©2011 American Institute of Physics

A researchers, Yu-Jung Lu, et ing., from National Tsing-Hua University or college in Hsinchu, Taiwan, have published their study to the nano-LEDs in a the latest issue of Applied Physics Letters.

The new nano-LEDs have a very good unique structure that is made of 40-nm-thick nanodisks sandwiched involving two layers of nanorods, creating a nanodisk-in-nanorod geometry. The nanodisks are made from indium gallium nitride (InGaN), a semiconducting material that is definitely widely used in LEDs and solar cells, while the nanorods are made from gallium nitride (GaN). Having said that, InGaN LEDs capable of emitting light belonging to the entire visible spectrum haven’t been achieved until now.



“The InGaN/GaN nanodisk/nanorod structure is just like a well-known quantum well structure, but in a lower dimensionality (reduction during lateral sizes), ” coauthor Shangjr Gwo, your physics professor at National Tsing-Hua University, told PhysOrg. com. “The InGaN nanodisks sandwiched regarding the p- and n-GaN regions be working as the full-color visible-light emitters anytime electrons and holes are injected through the p-n junction at a forward bias voltage. The electroluminescent light hails from the electron-hole recombination during the InGaN nanodisks. ”

As being the researchers explained, the essential to achieving full-color LEDs was first overcoming large lattice traces, which degrade long-wavelength emissions. The InGaN/GaN nanorod method resolves this issue as a consequence of strain relaxation in all the nanostructured geometry.

The researchers hope the full-color nano-LEDs work extremely well in high-resolution imaging techniques which could resolve ultrasmall subwavelength features of objects. To do this approach, these techniques must overcome the diffraction limit, the fundamental limit on imaging resolution as a result of the spreading out – and / or “diffraction” – of surf. Imaging techniques can find their way this limit by employing evanescent waves, which reveal home elevators objects’ subwavelength features, and decay exponentially away through the object. Due to the short range of the evanescent waves, imaging techniques that detect them depend on near-field optics.

One of such techniques is scanning near-field optical microscopy (SNOM), which operates on the all tiny probe to acquire and retrieve evanescent ocean. One of the biggest challenges in SNOM gets a light source that could be small and versatile enough to function on this probe, and that’s where new nano-LEDs come for. While previous research has demonstrated learn about using nano-LEDs on your probes, this is to start with that a nano-LED using a full-color range has already been available.

“For microscopy, we will use the nano-LED as being a localized excitation light source with a chosen wavelength to selectively inspire specific fluorescent molecules, ” Lu reported.

In their study, the researchers experimentally demonstrated making use of the nanodisk-in-nanorod LEDs for subwavelength photolithography, in which light is used to generate a pattern on a light-sensitive materials. They predict that, by way of fabricating the nano-LEDs upon the SNOM probe suggestions, they could achieve far better spatial control for near future subwavelength photolithography.

“For a applications of photolithography, the freedom of utilizing nano-LEDs at any wavelength broadens the options of photoresist and consists of the control of most of the photo-response, ” Lu reported.

More information: Yu-Jung Lu, et ing. “Single InGaN nanodisk lumination emitting diodes as full-color subwavelength lighting sources. ” Applied Physics Albhabets. DOI: 10. 1063/1. 3597211.

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Early Light Refines Brain's Circuitry for Vision: Studies Show Importance of Visual Stimulation in Wiring Up Species' Brains to See

Early Light Refines Brain's Circuitry for Vision: Studies Show Importance of Visual Stimulation in Wiring Up Species' Brains to See

  10:08:00 AM    Science Lover

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Any parent knows that newborns still have a lot of neurological work to do to attain fully acute vision. In a wide variety of nascent animals, genes provide them with only a rough wiring plan and then leave it to the developing nervous system to do its own finish work. Two studies by Brown University researchers provide new evidence of a role for exposure to light in the environment as mouse pups and tadpoles organize and refine the circuitry of their vision systems.

Light and sight: connected at the beginning Because 
the retinal layer of rods and cones is not connected 
early in mice, neuroscientists had no reason to suspect 
that light helps develop neural connections for vision. 
David Berson, right, with Jordan Renna, has shown 
that photosensitive cells he discovered a decade ago are 
connected and do help with neural development. 
(Credit: Mike Cohea/Brown University)

"Through a combination of light-independent and light-dependent processes, the visual system is getting tuned up over time," said David Berson, professor of neuroscience.

His new work, published in advance online June 5 in Nature Neuroscience, offers the surprising result that light exposure can enhance how well mice can organize the nerve endings from their left eye and their right eye in an area of the brain where they start out somewhat jumbled. Neuroscientists had thought that mammals were unable to see at this stage, but a new type of light-sensitive cell that Berson discovered a decade ago turns out to let in the light.

Meanwhile, Berson's colleague Carlos Aizenman, assistant professor of neuroscience, co-authored a paper online May 31 in the Journal of Neuroscience showing that newborn tadpoles depend on light to coordinate and improve the response speed, strength and reliability of a network of neurons in a vision-processing region of their brains.

"This is how activity is allowing visual circuits to refine and sort themselves out," said Aizenman. "Activity is fine-tuning all these connections. It's making the circuit function in a much more efficient, synchronous way."

Not completely blind mice
Berson, postdoctoral scholar Jordan Renna, and former postdoctoral researcher Shijun Weng conducted several experiments in newborn mice to see whether light influences the process by which the mice rewire to distinguish between their eyes.

"For certain functions, the brain wants to keep track of which eye is which," Berson said. Among those functions are the perception of depth and distance.

At a circuit level, the brain keeps signals from the two eyes distinct by segregating their nerve endings into separate regions in the dorsal lateral geniculate nucleus (dLGN), a key waystation on the path to the visual cortex and conscious visual perception. Scientists have long known this sorting-out process depends on waves of activity that spontaneously excite cells in the inner retina. They did not know until now that the waves are influenced by a light-sensitive type of cell called intrinsically photosensitive retinal ganglion cells (ipRGCs).

About a decade ago, a team Berson led at Brown discovered the ipRGCs, which are the first light-sensitive cells to develop in the eye. They reside in the inner retina, the home of retinal cells that send visual information directly to the brain. The outer retina is where the more familiar rods and cones sense light. Early in life, when the brain is segregating nerve endings into distinct regions in the dLGN, the two retinal layers are not connected, so until ipRGCs were discovered there was no reason to believe that light would affect the sorting process.

The new research doesn't say anything definitive about the consequences of light exposure at this stage for eyesight in adults, especially given that some mammals (such as monkeys) experience this developmental stage in utero.

"Whether different animals in nature are exposed to enough light to induce a change in segregation patterns is unclear," Renna said.

But the research shows that light exposure does improve how well the sorting goes, Berson said, and the work advances neuroscientists' understanding of the eye-distinction process, which is widely studied as a model of "activity-driven" neural development.

To assess the effect of light on retinal waves, Renna used electrodes to record the activity of cells in the inner retinas of newborn mice, first recording in the dark, then in the light, and then again in the dark. In every case retinas experienced waves, but when the retinas were exposed to light, the waves lasted about 50 percent longer.

Renna then tested whether the light-sensitive cells were really creating this wave-lengthening effect by repeating the study in "knock-out" mice in which the ability of the ipRGCs to sense light had been genetically abolished. With the cells disabled, exposure to light no longer made any difference in the duration of the waves.

Finally, to assess the effect of light on the left-right sorting process in the dLGN, Renna examined the tissues from normal mice and the mice whose ipRGCs couldn't sense light. In each case he fluorescently labeled the nerve endings from one eye red and the other green. A computer comparison of the tissues showed that the normal mice developed a higher degree of segregation between red and green than the knockout mice. In other words, the ability of ipRGCs to sense light improved sorting out one eye from another in the dLGN.

Twinkling tadpoles

In his study, Aizenman collaborated with Arto Nurmikko, professor of engineering and physics, to investigate the function of in the optic tectum of tadpole brains. They flooded the tectal neurons in live tadpoles with a molecule that makes calcium ions fluoresce. As whole networks of neurons became active, they'd take in the ions and glow. The researchers recorded the tadpoles with a high-resolution, high-speed camera that could capture the millisecond-to-millisecond activity of the neurons.

Led in the lab by engineering graduate student Heng Xu, the lead author, and postdoctoral researcher Arseny Khakhalin, the team reared some young tadpoles under normal conditions of 12 hours of light and 12 hours of darkness during the crucial days of development when the tectum is developing. They reared others in the dark, and still others with a chemical that blocks the activity of NMDA receptors, a subtype of receptor to the neurotransmitter glutamate, that is known to promote neural rewiring.

Then they exposed all the tadpoles, however they were reared, to blue LED light flashes delivered via a fiber optic cable mounted next to the eye.

What they found over the course of several experiments was that the neural networks in the tectums of tadpoles reared under normal conditions developed a faster, more cohesive, and stronger response (in terms of the number of neurons) to light.

The tectal neural networks of tadpoles kept in the dark during development failed to progress at all. Those whose NMDA receptors were blocked occupied a middle ground, showing more progress than dark-reared tadpoles but less than normal tadpoles. Tadpoles, they found, train their brains with the light they see.

Aizenman said he hopes the calcium ion imaging technique will prove useful in a wide variety of other neuroscience experiments, including studying how tadpoles neurally encode behaviors such as fleeing when they see certain stimuli.

In the meantime, his team and Berson's have added to the understanding scientists have been building of how creatures turn the somewhat mushy approximations of their brains at birth into high-functioning animal minds.

"That's what everybody is after," Aizenman said. "How do you get this fine-tuned, finely wired brain in the first place?"

Berson and Renna's work was funded by the National Institutes of Health. Aizemnan and Nurmikko's research received support from the National Science Foundation, the NIH's National Eye Institute, and the Whitehall Foundation.

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Will LED Light Bulbs Best Your CFLs and Incandescents?

Will LED Light Bulbs Best Your CFLs and Incandescents?

  9:44:00 AM    Science Lover

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The first LED bulb designed to replace the 60-watt incandescent has arrived, but compact fluorescents remain the most affordable option for efficient home lighting—for now.

Philips EnduraLED

  

Solid-state lighting has long been touted as the next generation of efficient bulbs, but technical challenges have so far limited product offerings to 40-watt equivalents—and consumers haven't exactly rushed shelves to purchase bulbs to read by. Developing light-emitting diodes (LEDs) that generate full-spectrum color—white light—is particularly difficult. Another hurdle has been finding a way to efficiently manage LED temperature: If the bulb gets too hot, it fails. Now, the first LED bulbs to rival the 60-watt, screw-in incandescent are finally poised to hit the market. If they win over consumers, the efficiency gains could yield impressive reductions not only in individual electricity bills but also in global carbon emissions. The Department of Energy estimates that replacing regular light bulbs with LEDs could potentially save 190 terawatt-hours annually (pdf)—the equivalent of lighting over 95 million homes.

The 12-watt EnduraLED, recently announced by Philips Lighting, has a rated life of 25,000 hours (nearly 3 years). The 9-watt Definity LED made by Lighting Science Group may last twice as long. But longevity in a super-efficient package doesn't come cheap. Each Definity LED will cost about 30 dollars and the EnduraLED may top 50 dollars—as much as the lighting fixture it's destined for. The price tag will almost certainly cause consumers to stop short and weigh the real benefits. But even with the current high price, LEDs are one of the most promising light sources available for consumers, beating out everything on the current market for reliability, efficiency and longevity.

Where CFLs Fall Short ... Studies from the Program for the Evaluation and Analysis of Residential Lighting (PEARL) show that compact fluorescent bulbs often don't live up to manufacturer's claims. Glenn Reed of Energy Futures Group in Burlington, Vt., and his colleague Chris Granda at Grasteu Associates recently analyzed five years' worth of PEARL testing data on 1500 Energy Star–qualified CFLs. They found that some CFLs began to lose brightness quickly. For example, almost half of reflector CFLs—the kind used in recessed lighting—were more than a quarter dimmer before they had reached half of their rated lifetime. Although CFLs typically perform worse in recessed lighting, Reed found that these CFLs weren't even living up to their Energy Star ratings. One possible explanation is that the recessed cans that house reflectors trap heat that wears out the bulb.

The PEARL studies also revealed that the average lifespan of CFLs often fell short, echoing a common complaint among CFL users. Among eight frequently tested brands, including Philips Lighting and General Electric, early failure rates ranged from 2 to 13 percent. The National Lighting Product Information Program has found similar differences in quality among Energy Star–labeled brands. Reed notes that PEARL only tested 10 bulbs per brand and that the same brand wasn't necessarily tested all five years. These data limitations make it difficult to rank best and worst brands, but, says Reed, "it's definitely a yellow flag." 

Lighting Science Group's DefinityLED
bulb will be available this Fall.

 

... LEDs Step In
Solid-state lighting can potentially overcome many problems with CFLs, including those highlighted by the PEARL studies. LEDs perform well in all lighting applications, including recessed lighting, and unlike all but specialized compact fluorescent bulbs LEDs are dimmable. Because of recent advances in optics, LEDs have a quality of light superior to all other types of lighting—and they deliver it more efficiently. For example, Lighting Science Group's Definity LED delivers 112 lumens per watt compared to a CFL's 50 to 70 lumens per watt.

Improvements in managing the LED chip's temperature have contributed to their marathon life span: LEDs can last up to 50,000 hours, more than eight times as long as CFLs. The bulbs are also likely to deliver on their lifetime claims because they won't face the same quality-assurance issues that have plagued CFLs. Energy Star only recently began performing "random, off-the-shelf testing" of Energy Star–qualified CFLs. In contrast, random testing has been a part of Energy Star's eligibility criteria for solid-state lighting since the beginning. Even if CFL quality becomes more consistent now, they still can't compete with LED efficiency or, because of their mercury content, be recycled as easily.

Zach Gibler, the CEO of Lighting Science Group, says LED prices will begin to drop over the next 12 to 36 months. A lower retail price for the 60-watt replacement combined with rebates, which companies already offer on many CFL and LED purchases, will provide strong incentives for consumers to replace CFLs with LEDs. "Right now for day-to-day use, CFLs are still an inexpensive energy-efficient alternative to incandescents," Reed says, "but they are really just a transitional technology."

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Hi-tech walking stick brings wind-up torch and alarm for elderly

Hi-tech walking stick brings wind-up torch and alarm for elderly

  12:23:00 AM    Science Lover

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The new Slik-Stik walking stick is fitted with a torch, one-button alarm, and a magnet, and is powered by simply winding up a crank in the handle (inset)

A walking stick that uses wind-up technology to power a built-in torch and safety lights has been unveiled by a 70-year-old British inventor.

Developed by Trevor Baylis – who invented the wind-up radio almost two decades ago – the lightweight ‘Slik-Stik’ carries a personal alarm, can collapse to become tiny, and has a magnet to solve the tricky issue of picking up dropped keys.

His firm, Trevor Baylis Brands, recently launched the walking stick at an exhibition in London.

The Slik-Stik is the brainchild of Baylis’ 44-year-old protégé Denise Anstey, a disabled lady who was dissatisfied with the poor ergonomics and basic function of conventional walking sticks.

“When I was walking, I felt very vulnerable – a walking target. I thought it would be good for the elderly to have something they could immediately press to alert people to help,” she said.

The hi-tech walking stick is fitted with an induction generator system, with which a minute’s winding of the retractable handle is sufficient to provide several minutes of emergency illumination.

The front of the ergonomic hand-grip incorporates an LED torch light which shines a forward beam, and a foot-fall floodlight to ensure safe footing at night. The rear of the handle is fitted with a built-in panic alarm that can be activated to alert for help.

Finally, one further frustration for Denise has been addressed by the handy inclusion of a strong pick-up magnet in the handle. So in case she drops a set of keys, all she needs to do is flip the stick around.

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