Spirit In Action

Change IS coming. WE can make it GOOD.


Leave a comment

Crystals ripple in response to light: First propagating surface phonon polaritons in a van der Waals crystal — ScienceDaily

Crystals ripple in response to light: First propagating surface phonon polaritons in a van der Waals crystal

Date:
March 6, 2014
image

Source:
University of California – San Diego

Summary:
Minuscule waves that propagate across atom — thin layers of crystal could carry information, light, and heat in nanoscale devices. For the first time, the frequency and amplitude of these waves, called surface phonon polaritons, can be tuned by altering the number of layers of crystals, and they travel far making practical applications for these signals feasible.

(See full article at the link below)

Crystals ripple in response to light: First propagating surface phonon polaritons in a van der Waals crystal

Date:

March 6, 2014

Source:

University of California – San Diego

Summary:

Minuscule waves that propagate across atom — thin layers of crystal could carry information, light, and heat in nanoscale devices. For the first time, the frequency and amplitude of these waves, called surface phonon polaritons, can be tuned by altering the number of layers of crystals, and they travel far making practical applications for these signals feasible.

image

This image shows surface phonon polaritons launched by infrared light propagate across layers of hexagonal boron nitride, a van der Waals crystal.

Credit: Siyuan Dai

[Click to enlarge image]

Light can trigger coordinated, wavelike motions of atoms in atom-thin layers of crystal, scientists have shown. The waves, called phonon polaritons, are far shorter than light waves and can be “tuned” to particular frequencies and amplitudes by varying the number of layers of crystal, they report in the early online edition of Science March 7.

These properties — observed in this class of material for the first time — open the possibility of using polaritons to convey information in tight spaces, create images at far finer resolution than is possible with light, and manage the flow of heat in nanoscale devices.

“A wave on the surface of water is the closest analogy,” said Dimitri Basov, professor of physics at the University of California, San Diego, who led the project. “You throw a stone and you launch concentric waves that move outward. This is similar. Atoms are moving. The triggering event is illumination with light.”

The team used infrared light to launch phonon polaritons across a material called hexagonal boron nitride — crystals that form sheet-like layers held together by the weakest of chemical bonds.

Siyuan Dai, a graduate student in Basov’s research group who was responsible for much of the experimental work and is the first author of the report, focused an infrared laser on the tip of an atomic-force microscope as it scanned across this material, registering motions in the crystalline lattice.

The measurements revealed interference patterns created as the traveling waves reached edges of the material and reflected back. The amplitude and frequency of the waves depended on the number of layers in the crystal. Both properties will prove useful in the design of nanodevices.

“You can bounce these waves off edges. You can bounce them off defects. You can play all sorts of cool tricks with them. And of course, you can design the wavelength and amplitude of these oscillations in a way that suits your purpose,” Basov said.

The finding was something of a surprise. Boron nitride is an insulator used as a support structure for other materials, like graphene, which this group recently showed could support waves of electron densities called plasmon polaritons. Although similarly compact, plasmon polaritons rapidly dissipate.

“Because these materials are insulators, there is no electronic dissipation. So these waves travel further,” Basov said. “We didn’t expect them to be long-lived, but we are pleased that they are. It’s becoming kind of practical.”

Story Source:

The above story is based on materials provided by University of California – San Diego. The original article was written by Susan Brown. Note: Materials may be edited for content and length.

Journal Reference:

S. Dai, Z. Fei, Q. Ma, A. S. Rodin, M. Wagner, A. S. Mcleod, M. K. Liu, W. Gannett, W. Regan, K. Watanabe, T. Taniguchi, M. Thiemens, G. Dominguez, A. H. Castro Neto, A. Zettl, F. Keilmann, P. Jarillo-Herrero, M. M. Fogler, D. N. Basov. Tunable Phonon Polaritons in Atomically Thin van der Waals Crystals of Boron Nitride. Science, 2014 DOI: 10.1126/science.1246833

Cite This Page:

MLAAPA

University of California – San Diego. “Crystals ripple in response to light: First propagating surface phonon polaritons in a van der Waals crystal.” ScienceDaily. ScienceDaily, 6 March 2014. .


Leave a comment

Arctic seafloor methane releases double previous estimates

Arctic seafloor methane releases double previous estimates

Natalia Shakhova,


Methane burns as it escapes through a hole in the ice in a lagoon above the East Siberian Arctic Shelf. (Credit: Photo courtesy Natalia Shakhova)

Nov. 25, 2013 — The seafloor off the coast of Northern Siberia is releasing more than twice the amount of methane as previously estimated, according to new research results published in the Nov. 24 edition of the journal Nature Geoscience.

The East Siberian Arctic Shelf is venting at least 17 teragrams of the methane into the atmosphere each year. A teragram is equal to 1 million tons.

“It is now on par with the methane being released from the arctic tundra, which is considered to be one of the major sources of methane in the Northern Hemisphere,” said Natalia Shakhova, one of the paper’s lead authors and a scientist at the University of Alaska Fairbanks. “Increased methane releases in this area are a possible new climate-change-driven factor that will strengthen over time.”

Methane is a greenhouse gas more than 30 times more potent than carbon dioxide. On land, methane is released when previously frozen organic material decomposes. In the seabed, methane can be stored as a pre-formed gas or asmethane hydrates. As long as the subsea permafrost remains frozen, it forms a cap, effectively trapping the methane beneath. However, as the permafrost thaws, it develops holes, which allow the methane to escape. These releases can be larger and more abrupt than those that result from decomposition.

The findings are the latest in an ongoing international research project led by Shakhova and Igor Semiletov, both researchers at the UAF International Arctic Research Center. Their twice-yearly arctic expeditions have revealed that the subsea permafrost in the area has thawed much more extensively than previously thought, in part due to warming water near the bottom of the ocean. The warming has created conditions that allow the subsea methane to escape in much greater amounts than their earlier models estimated. Frequent storms in the area hasten its release into the atmosphere, much in the same way stirring a soda releases the carbonation more quickly.

“Results of this study represent a big step forward toward improving our understanding of methane emissions from the East Siberian Arctic Shelf,” said Shakhova. She noted that while the ESAS is unusual in its expansive and shallow nature, the team’s findings there speak to the need for further exploration of the subsea Arctic. “I believe that all other arctic shelf areas are significantly underestimated and should be paid very careful attention to.”

The East Siberian Arctic Shelf is a methane-rich area that encompasses more than 2 million square kilometers of seafloor in the Arctic Ocean. It is more than three times as large as the nearby Siberian wetlands, which have been considered the primary Northern Hemisphere source of atmospheric methane. Previous estimates performed for the ESAS suggested that the area was releasing 8 teragrams of methane into the atmosphere yearly.

During field expeditions, the research team used a variety of techniques — including sonar and visual images of methane bubbles in the water, air and water sampling, seafloor drilling and temperature readings — to determine the conditions of the water and permafrost, as well as the amount of methane being released.

Methane is an important factor in global climate change, because it so effectively traps heat. As conditions warm, global research has indicated that more methane is released, which then stands to further warm the planet. Scientists call this phenomenon a positive feedback loop.

“We believe that the release of methane from the Arctic, and in particular this part of the Arctic, could impact the entire globe,” Shakhova said. “We are trying to understand the actual contribution of the ESAS to the global methane budget and how that will change over time.”

Story Source:

The above story is based on materialsprovided by University of Alaska Fairbanks.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

tory Source:The above story is based on materialsprovided by University of Alaska Fairbanks.Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:Natalia Shakhova, Igor Semiletov, Ira Leifer, Valentin Sergienko, Anatoly Salyuk, Denis Kosmach, Denis Chernykh, Chris Stubbs, Dmitry Nicolsky, Vladimir Tumskoy, Örjan Gustafsson. Ebullition and storm-induced methane release from the East Siberian Arctic Shelf. Nature Geoscience, 2013; DOI: 10.1038/ngeo2007