Atomically seamless, thinnest-possible semiconductor junctions created

Kurzweil AI - Mon, 08/09/2014 - 2:53pm

As seen under an optical microscope, the heterostructures have a triangular shape. The two different monolayer semiconductors can be recognized through their different colors (green and yellow). (Credit: University of Washington)

University of Washington researchers have have developed what they believe is the thinnest-possible semiconductor, a new class of nanoscale materials made in sheets only three atoms thick.

They joined two different single-layer semiconductor materials in a heterojunction.

The new finding  could be the basis for next-generation flexible and transparent computing, better light-emitting diodes (LEDs), and solar technologies.

“Heterojunctions are fundamental elements of electronic and photonic devices,” said senior author Xiaodong Xu, a UW assistant professor of materials science and engineering and of physics. “Our experimental demonstration of such junctions between two-dimensional materials should enable new kinds of transistors, LEDs, nanolasers, and solar cells to be developed for highly integrated electronic and optical circuits within a single atomic plane.”

The research was published in Nature Materials.

How to create a seamless heterojunction

The researchers discovered that two flat semiconductor materials can be connected edge-to-edge with crystalline perfection. They worked with two single-layer (monolayer) materials — molybdenum diselenide and tungsten diselenide — that have very similar structures, which was key to creating the composite two-dimensional semiconductor.

The researchers created the junctions in a small furnace at the UW. First, they inserted a powder mixture of the two materials into a chamber heated to 900 degrees Celsius (1,652 F). Hydrogen gas was then passed through the chamber and the evaporated atoms from one of the materials were carried toward a cooler region of the tube and deposited as single-layer crystals in the shape of triangles.

After a while, evaporated atoms from the second material then attached to the edges of the triangle to create a seamless semiconducting heterojunction.

A high-resolution scanning transmission electron microscopy (STEM) image shows the lattice structure of the heterojunctions at atomic precision (credit: University of Washington)

Collaborators from the electron microscopy center at the University of Warwick in England found that all the atoms in both materials formed a single honeycomb lattice structure, without any distortions or discontinuities.

This heterostructure provides the strongest possible link between two single-layer materials, which is necessary for flexible devices. Within the same family of materials, it is feasible that researchers could bond other pairs together in the same way, the researchers suggest.

Scalable

“This is a scalable technique,” said Sanfeng Wu, a UW doctoral student in physics and one of the lead authors. “Because the materials have different properties, they evaporate and separate at different times automatically. The second material forms around the first triangle that just previously formed. That’s why these lattices are so beautifully connected.”

With a larger furnace, it would be possible to mass-produce sheets of these semiconductor heterostructures, the researchers said. On a small scale, it takes about five minutes to grow the crystals, with up to two hours of heating and cooling time.

This photoluminescence intensity map shows a typical piece of the lateral heterostructures. The junction region produces an enhanced light emission, indicating its application potential in optoelectronics. (Credit: University of Washington)

“In the future, combinations of two-dimensional materials may be integrated together in this way to form all kinds of interesting electronic structures such as in-plane quantum wells and quantum wires, superlattices, fully functioning transistors, and even complete electronic circuits,” said senior author David Cobden, a UW professor of physics.

The researchers have already demonstrated that the junction interacts with light much more strongly than the rest of the monolayer, which is encouraging for optoelectric and photonic applications like solar cells.

University of Warwick and University of Hong Kong researchers were also involved in the study.

The research was funded by the U.S. Department of Energy, the UW’s Clean Energy Institute, the Research Grant Council of Hong Kong, the University Grants Committee of Hong Kong, the Croucher Foundation, the Science City Research Alliance, and the Higher Education Funding Council for England’s Strategic Development Fund.

Abstract of Nature Materials paper

Categories: Science

Feds Say NSA "Bogeyman" Did Not Find Silk Road's Servers

Slashdot - Mon, 08/09/2014 - 2:14pm
An anonymous reader writes The secret of how the FBI pinpointed the servers allegedly used by the notorious Silk Road black market website has been revealed: repeated login attempts. In a legal rebuttal, the FBI claims that repeatedly attempting to login to the marketplace revealed its host location. From the article: "As they typed 'miscellaneous' strings of characters into the login page's entry fields, Tarbell writes that they noticed an IP address associated with some data returned by the site didn't match any known Tor 'nodes,' the computers that bounce information through Tor's anonymity network to obscure its true source. And when they entered that IP address directly into a browser, the Silk Road's CAPTCHA prompt appeared, the garbled-letter image designed to prevent spam bots from entering the site. 'This indicated that the Subject IP Address was the IP address of the SR Server,' writes Tarbell in his letter, 'and that it was "leaking" from the SR Server because the computer code underlying the login interface was not properly configured at the time to work on Tor.'"

Read more of this story at Slashdot.








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Spacecraft's 'Fireball' Re-Entry Snapped By Space Station | Video

Space.com - Mon, 08/09/2014 - 1:56pm
Orbital Sciences' Cygnus spacecraft burned up in the atmosphere on August 17th, 2014. ISS crew member Alexander Gerst captured imagery to create a time-lapse of the fireworks. Full Story: http://goo.gl/nPJv5R
Categories: Science

Sun-powered desalination for villages in India

Science Daily - Mon, 08/09/2014 - 1:37pm
Around the world, there is more salty groundwater than fresh, drinkable groundwater. For example, 60 percent of India is underlain by salty water -- and much of that area is not served by an electric grid that could run conventional reverse-osmosis desalination plants. Sun-powered desalination could deliver clean water for off-grid villages.
Categories: Science

Bacteria from bees possible alternative to antibiotics

Science Daily - Mon, 08/09/2014 - 1:37pm
Thirteen lactic acid bacteria found in the honey stomach of bees have shown promising results in a series of studies. The group of bacteria counteracted antibiotic-resistant MRSA in lab experiments. The bacteria, mixed into honey, has healed horses with persistent wounds. The formula has previously been shown to protect against bee colony collapse.
Categories: Science

Food craving is stronger, but controllable, for kids

Science Daily - Mon, 08/09/2014 - 1:37pm
Children show stronger food craving than adolescents and adults, but they are also able to use a cognitive strategy that reduces craving, according to new research. "These findings are important because they suggest that we may have another tool in our toolbox to combat childhood obesity," says psychological scientist and the study's lead researcher.
Categories: Science

New knowledge of cannabis paves way for drug development

Science Daily - Mon, 08/09/2014 - 1:37pm
Revolutionary nanotechnology method could help improve the development of new medicine and reduce costs. Researchers have developed a new screening method that makes it possible to study cell membrane proteins that bind drugs, such as cannabis and adrenaline, while reducing the consumption of precious samples by a billion times.
Categories: Science

Layered graphene sandwich for next generation electronics

Science Daily - Mon, 08/09/2014 - 1:36pm
Sandwiching layers of graphene with white graphene could produce designer materials capable of creating high-frequency electronic devices, scientists have found.
Categories: Science

Climate change to increase forest fire danger in Europe

Science Daily - Mon, 08/09/2014 - 1:36pm
Climate change is expected to contribute to a dramatic increase in forest fire damage in Europe, but better forest management could mitigate the problem, according to new research.
Categories: Science

Light detector to revolutionize night vision technology

Science Daily - Mon, 08/09/2014 - 1:36pm
A light detector that could revolutionize chemical sensing and night vision technology has been developed by researchers. Based on graphene, the detector is capable of detecting light over an unusually broad range of wavelengths, included in this are terahertz waves -- between infrared and microwave radiation, where sensitive light detection is most difficult.
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How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science

How Astrophysicists Hope To Turn the Entire Moon Into a Cosmic Ray Detector

Slashdot - Mon, 08/09/2014 - 1:30pm
KentuckyFC writes One of the great mysteries in astrophysics surrounds the origin of ultra-high energy cosmic rays, which can have energies of 10^20 electron volts and beyond. To put that in context, that's a single proton with the same energy as a baseball flying at 100 kilometers per hour. Nobody knows where ultra-high energy cosmic rays come from or how they get their enormous energies. That's largely because they are so rare--physicists detect them on Earth at a rate of less than one particle per square kilometer per century. So astronomers have come up with a plan to see vastly more ultra high energy cosmic rays by using the Moon as a giant cosmic ray detector. When these particles hit the lunar surface, they generate brief bursts of radio waves that a highly sensitive radio telescope can pick up. No radio telescope on Earth is currently capable of this but astronomers are about to start work on a new one that will be able to pick up these signals for the first time. That should help them finally tease apart the origins of these most energetic particles in the Universe .

Read more of this story at Slashdot.








Categories: Science