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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Bilinguals See the World in a Different Way, Study Suggests

Bilinguals See the World in a Different Way, Study Suggests

  10:22:00 AM    Science Lover

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Learning a foreign language literally changes the way we see the world, according to new research. Panos Athanasopoulos, of Newcastle University, has found that bilingual speakers think differently to those who only use one language.

Colour perception is an ideal way of testing bilingual 
concepts because there is a huge variation between 
where different languages place boundaries on the 
colour spectrum. (Credit: iStockphoto)

 

And you don't need to be fluent in the language to feel the effects -- his research showed that it is language use, not proficiency, which makes the difference.

Working with both Japanese and English speakers, he looked at their language use and proficiency, along with the length of time they had been in the country, and matched this against how they perceived the colour blue.

Colour perception is an ideal way of testing bilingual concepts because there is a huge variation between where different languages place boundaries on the colour spectrum.

In Japanese, for example, there are additional basic terms for light blue (mizuiro) and dark blue (ao) which are not found in English.

Previous research has shown that people are more likely to rate two colours to be more similar if they belong to the same linguistic category.

"We found that people who only speak Japanese distinguished more between light and dark blue than English speakers," said Dr Athanasopoulos, whose research is published in the current edition of Bilingualism: Language and Cognition. "The degree to which Japanese-English bilinguals resembled either norm depended on which of their two languages they used more frequently."

Most people tend to focus on how to do things such as order food or use public transport when they learn another language to help them get by, but this research has shown that there is a much deeper connection going on.

"As well as learning vocabulary and grammar you're also unconsciously learning a whole new way of seeing the world," said Dr Athanasopoulos. "There's an inextricable link between language, culture and cognition.

"If you're learning language in a classroom you are trying to achieve something specific, but when you're immersed in the culture and speaking it, you're thinking in a completely different way."

He added that learning a second language gives businesses a unique insight into the people they are trading with, suggesting that EU relations could be dramatically improved if we all took the time to learn a little of each other's language rather than relying on English as the lingua-franca.

"If anyone needs to be motivated to learn a new language they should consider the international factor," he said. "The benefits you gain are not just being able to converse in their language -- it also gives you a valuable insight into their culture and how they think, which gives you a distinct business advantage.

"It can also enable you to understand your own language better and gives you the opportunity to reflect on your own culture, added Dr Athanasopoulos, who speaks both Greek and English.

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Novel Negative-Index Metamaterial Bends Light 'Wrong' Direction

Novel Negative-Index Metamaterial Bends Light 'Wrong' Direction

  7:48:00 PM    Science Lover

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A group of scientists led by researchers from the California Institute of Technology (Caltech) has engineered a type of artificial optical material -- a metamaterial -- with a particular three-dimensional structure such that light exhibits a negative index of refraction upon entering the material. In other words, this material bends light in the "wrong" direction from what normally would be expected, irrespective of the angle of the approaching light.

Arrays of coupled plasmonic coaxial waveguides offer 
a new approach by which to realize negative-index 
metamaterials that are remarkably insensitive to angle 
of incidence and polarization in the visible range. 
(Credit: Caltech/Stanley Burgos)

This new type of negative-index metamaterial (NIM), described in an advance online publication in the journal Nature Materials, is simpler than previous NIMs -- requiring only a single functional layer -- and yet more versatile, in that it can handle light with any polarization over a broad range of incident angles. And it can do all of this in the blue part of the visible spectrum, making it "the first negative index metamaterial to operate at visible frequencies," says graduate student Stanley Burgos, a researcher at the Light-Material Interactions in Energy Conversion Energy Frontier Research Center at Caltech and the paper's first author.

"By engineering a metamaterial with such properties, we are opening the door to such unusual -- but potentially useful -- phenomena as superlensing (high-resolution imaging past the diffraction limit), invisibility cloaking, and the synthesis of materials index-matched to air, for potential enhancement of light collection in solar cells," says Harry Atwater, Howard Hughes Professor and professor of applied physics and materials science, director of Caltech's Resnick Institute, founding member of the Kavli Nanoscience Institute, and leader of the research team

What makes this NIM unique, says Burgos, is its engineering. "The source of the negative-index response is fundamentally different from that of previous NIM designs," he explains. Those previous efforts used multiple layers of "resonant elements" to refract the light in this unusual way, while this version is composed of a single layer of silver permeated with "coupled plasmonic waveguide elements."

Surface plasmons are light waves coupled to waves of electrons at the interface between a metal and a dielectric (a non-conducting material like air). Plasmonic waveguide elements route these coupled waves through the material. Not only is this material more feasible to fabricate than those previously used, Burgos says, it also allows for simple "tuning" of the negative-index response; by changing the materials used, or the geometry of the waveguide, the NIM can be tuned to respond to a different wavelength of light coming from nearly any angle with any polarization. "By carefully engineering the coupling between such waveguide elements, it was possible to develop a material with a nearly isotopic refractive index tuned to operate at visible frequencies."

This sort of functional flexibility is critical if the material is to be used in a wide variety of ways, says Atwater. "For practical applications, it is very important for a material's response to be insensitive to both incidence angle and polarization," he says. "Take eyeglasses, for example. In order for them to properly focus light reflected off an object on the back of your eye, they must be able to accept and focus light coming from a broad range of angles, independent of polarization. Said another way, their response must be nearly isotropic. Our metamaterial has the same capabilities in terms of its response to incident light."

This means the new metamaterial is particularly well suited to use in solar cells, Atwater adds. "The fact that our NIM design is tunable means we could potentially tune its index response to better match the solar spectrum, allowing for the development of broadband wide-angle metamaterials that could enhance light collection in solar cells," he explains. "And the fact that the metamaterial has a wide-angle response is important because it means that it can 'accept' light from a broad range of angles. In the case of solar cells, this means more light collection and less reflected or 'wasted' light."

"This work stands out because, through careful engineering, greater simplicity has been achieved," says Ares Rosakis, chair of the Division of Engineering and Applied Science at Caltech and Theodore von Kármán Professor of Aeronautics and Mechanical Engineering.

Their work was supported by the Energy Frontier Research Centers program of the Office of Science of the Department of Energy, the National Science Foundation, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek, and "NanoNed," a nanotechnology program funded by the Dutch Ministry of Economic Affairs.

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