Molybdenum Di-Sulphide (MoS2): A potential challenger to graphene

Sheets of tin sulphide - The diameter of the roll is about 10 times smaller than a human hair.

A team of researchers from the University of Southampton's Optoelectronics Research Centre (ORC) has developed a new way to fabricate a potential challenger to Manchester's Graphene.

Graphene, a single layer of carbon atoms in a honeycomb lattice, is increasingly being used in new electronic and mechanical applications, such as transistors, switches and light sources, thanks to the unprecedented properties it offers: very low electrical resistance, high thermal conductivity and mechanically stretchable yet harder than diamond.

Molybdenum Di-Sulphide (MoS2)

Now, ORC researchers have developed Molybdenum Di-Sulphide (MoS2), a similar material to graphene that shares many of its properties, including extraordinary electronic conduction and mechanical strength, but made from a metal (in this case molybdenum combined with sulphur).

This new class of thin metal/sulphide materials, known as transition metal di-chalcogenides (TMDCs), has become an exciting complimentary material to graphene.

However, unlike graphene, TMDCs can also emit light allowing applications, such as photodetectors and light emitting devices, to be manufactured.

Until recently, fabrication of TMDCs, such as MoS2, has been difficult, as most techniques produce only flakes, typically just a few hundred square microns in area.

Dr Kevin Huang, from ORC who has led the research, explains: "We have been working on the synthesis of chalcogenide materials using a chemical vapour deposition (CVD) process since 2001 and our technology has now achieved the fabrication of large area (>1000 mm2) ultra- thin films only a few atoms thick."

"Being able to manufacture sheets of MoS2 and related materials, rather than just microscopic flakes, as previously was the case, greatly expands their promise for nanoelectronic and optoelectronic applications."

Dr Huang and his team published their findings in the latest issue of the journal Nanoscale.

They are currently working with several UK companies and universities, as well as leading international centres at MIT and Nanyang Technological University (Singapore).

Dr Huang adds: "Our ability to not only synthesise large uniform thin films but also to transfer these films to virtually any substrate has led to increased demand for our materials."

More Information
"Scalable high-mobility MoS2 thin films fabricated by an atmospheric pressure chemical vapor deposition process at ambient temperature" Author: Chung-Che Huang, Feras Al-Saab, Yudong Wang, Jun-Yu Ou, John C. Walker, Shuncai Wang, Behrad Gholipour, Robert E. Simpsond and    Daniel W. Hewaka - Nanoscale, 2014, Advance Article DOI: 10.1039/C4NR04228J - Received 25 Jul 2014

NASA’s Hubble Finds Supernova Star System Linked to Potential “Zombie Star”

The two inset images show before-and-after images captured by NASA’s Hubble Space Telescope of Supernova 2012Z in the spiral galaxy NGC 1309. 

The white X at the top of the main image marks the location of the supernova in the galaxy.

Image Credit: NASA, ESA

Using NASA’s Hubble Space Telescope, a team of astronomers has spotted a star system that could have left behind a “zombie star” after an unusually weak supernova explosion.

A supernova typically obliterates the exploding white dwarf, or dying star.

On this occasion, scientists believe this faint supernova may have left behind a surviving portion of the dwarf star, a sort of zombie star.

While examining Hubble images taken years before the stellar explosion, astronomers identified a blue companion star feeding energy to a white dwarf, a process that ignited a nuclear reaction and released this weak supernova blast.

This supernova, Type Iax, is less common than its brighter cousin, Type Ia. Astronomers have identified more than 30 of these mini-supernovas that may leave behind a surviving white dwarf.

“Astronomers have been searching for decades for the star systems that produce Type Ia supernova explosions,” said scientist Saurabh Jha of Rutgers University in Piscataway, New Jersey.

“Type Ia’s are important because they’re used to measure vast cosmic distances and the expansion of the universe. But we have very few constraints on how any white dwarf explodes."

"The similarities between Type Iax’s and normal Type Ia’s make understanding Type Iax progenitors important, especially because no Type Ia progenitor has been conclusively identified. This discovery shows us one way that you can get a white dwarf explosion.”

The team’s results will appear in the Thursday, Aug. 7 edition of the journal Nature.

The weak supernova, dubbed SN 2012Z, resides in the host galaxy NGC 1309 which is 110 million light-years away. It was discovered in the Lick Observatory Supernova Search in January 2012.

Luckily, Hubble’s Advanced Camera for Surveys also observed NGC 1309 for several years prior the supernova outburst, which allowed scientists to compare before-and-after images.

Curtis McCully, a graduate student at Rutgers and lead author of the team’s paper, sharpened the Hubble pre-explosion images and noticed a peculiar object near the location of the supernova.

“I was very surprised to see anything at the location of the supernova. We expected the progenitor system would be too faint to see, like in previous searches for normal Type Ia supernova progenitors. It is exciting when nature surprises us,” McCully said.

After studying the object’s colors and comparing with computer simulations of possible Type Iax progenitor systems, the team concluded they were seeing the light of a star that had lost its outer hydrogen envelope, revealing its helium core.

The team plans to use Hubble again in 2015 to observe the area, giving time for the supernova’s light to dim enough to reveal any possible zombie star and helium companion to confirm their hypothesis.

“Back in 2009, when we were just starting to understand this class, we predicted these supernovae were produced by a white dwarf and helium star binary system,” said team member Ryan Foley of the University of Illinois at Urbana-Champaign, who helped identify Type Iax supernovae as a new class.

“There’s still a little uncertainty in this study, but it is essentially validation of our claim.”

Read the full article here

Hubble Begins Search Beyond Pluto For Potential Flyby Targets

This is an artist's rendering of the New Horizons spacecraft encountering a Kuiper Belt object - a city-sized icy relic left over from the birth of our solar system. 

The sun, more than 4.1 billion miles (6.7 billion kilometers) away, shines as a bright star embedded in the glow of the zodiacal dust cloud. 

Jupiter and Neptune are visible as orange and blue "stars" to the right of the sun. 

Image courtesy JHUAPL /SwRI.

After careful consideration and analysis, the Hubble Space Telescope Time Allocation Committee has recommended using Hubble to search for an object the Pluto-bound NASA New Horizons mission could visit after its flyby of Pluto in July 2015.

The planned search will involve targeting a small area of sky in search of a Kuiper Belt object (KBO) for the outbound spacecraft to visit.

The Kuiper Belt is a vast debris field of icy bodies left over from the solar system's formation 4.6 billion years ago.

A KBO has never been seen up close because the belt is so far from the sun, stretching out to a distance of 5 billion miles into a never-before-visited frontier of the solar system.

"I am pleased that our science peer-review process arrived at a consensus as to how to effectively use Hubble's unique capabilities to support the science goals of the New Horizons mission," said Matt Mountain, director of the Space Telescope Science Institute (STScI) in Baltimore, Maryland.

Fully carrying out the KBO search is contingent on the results from a pilot observation using Hubble data.

The space telescope will scan an area of sky in the direction of the constellation Sagittarius to try and identify any objects orbiting within the Kuiper Belt.

To discriminate between a foreground KBO and the clutter of background stars in Sagittarius, the telescope will turn at the predicted rate that KBOs are moving against the background stars.

In the resulting images, the stars will be streaked, but any KBOs should appear as pinpoint objects.

If the test observation identifies at least two KBOs of a specified brightness it will demonstrate statistically that Hubble has a chance of finding an appropriate KBO for New Horizons to visit.

At that point, an additional allotment of observing time will continue the search across a field of view roughly the angular size of the full moon.

Astronomers around the world apply for observing time on the Hubble Space Telescope. Competition for time on the telescope is extremely intense and the requested observing time significantly exceeds the observing time available in a given year.

Proposals must address significant astronomical questions that can only be addressed with Hubble's unique capabilities, and are beyond the capabilities of ground-based telescopes.

The proposals are peer reviewed annually by an expert committee, which looks for the best possible science that can be conducted by Hubble and recommends to the Space Telescope Science Institute director a balanced program of small, medium, and large investigations.

Though Hubble is powerful enough to see galaxies near the horizon of the universe, finding a KBO is a challenging needle-in-haystack search.

A typical KBO along the New Horizons trajectory may be no larger than Manhattan Island and as black as charcoal.

Harsh space weather may doom potential life on red-dwarf planets

This artist's conception shows a hypothetical alien world orbiting a red dwarf star. 

Although it is in the star’s habitable zone, this planet faces an extreme space environment that is stripping its atmosphere and generating powerful aurorae. 

Since they are subjected to such harsh physical conditions, red-dwarf planets may not be habitable after all, so life in the universe might be even rarer than we thought.

Credit: Harvard-Smithsonian Center for Astrophysics (CfA)

Life in the universe might be even rarer than we thought. Recently, astronomers looking for potentially habitable worlds have targeted red dwarf stars because they are the most common type of star, comprising 80 percent of the stars in the universe.

But a new study shows that harsh space weather might strip the atmosphere of any rocky planet orbiting in a red dwarf's habitable zone.

"A red-dwarf planet faces an extreme space environment, in addition to other stresses like tidal locking," says Ofer Cohen of the Harvard-Smithsonian Center for Astrophysics (CfA).

Cohen is presenting their findings today in a press conference at a meeting of the American Astronomical Society.

Earth is protected from solar eruptions and space weather by its magnetic field. Just like the shields of the Starship Enterprise, Earth's magnetic field deflects incoming energy blasts.

We also are protected by distance since Earth orbits 93 million miles from the Sun.

Red dwarf stars are smaller and cooler than the Sun. To be in the star's habitable zone, where the temperature is warm enough for liquid water, a planet would have to be much closer to its star than the Earth is to the Sun. As a result, such a planet would be subjected to severe space weather.

Previous work has looked at the impact of stellar flares from a red dwarf on a nearby planet. In contrast, the new research examines the effect of the red dwarf's constantly blowing stellar wind.

The team used a computer model developed at the University of Michigan to represent three known red-dwarf planets circling a simulated, middle-aged red dwarf.

They found that even an Earth-like magnetic field could not necessarily protect a habitable-zone world from the star's continuous bombardment.

Although there were moments when the planet's magnetic shields held firm, it spent far more time with weak shields than strong shields.

"The space environment of close-in exoplanets is much more extreme than what the Earth faces," explains co-author Jeremy Drake (CfA).

"The ultimate consequence is that any planet potentially would have its atmosphere stripped over time."

The extreme space weather also would trigger spectacular aurorae, or Northern Lights. The aurora on a red-dwarf planet could be 100,000 times stronger than those on Earth, and extend from the poles halfway to the equator.

"If Earth were orbiting a red dwarf, then people in Boston would get to see the Northern Lights every night," adds Cohen.

"Oh the other hand, we'd also be in constant darkness because of tidal locking, and blasted by hurricane-force winds because of the dayside-nightside temperature contrast. I don't think even hardy New Englanders want to face that kind of weather."

Malaysia Airlines flight 370: NOAA Seafloor experts publish new view of potential crash zone

This is the seafloor topography in the Malaysia Airlines flight MH370 search area. 

Dashed lines approximate the search zone for sonar pings emitted by the flight data recorder and cockpit voice recorder popularly called black boxes. 

The first sonar contact (black circle) was reportedly made by a Chinese vessel on the east flank of Batavia Plateau (B), where the shallowest point in the area (S) is at an estimated depth of 1637 meters. 

The next reported sonar contact (red circle) was made by an Australian vessel on the north flank of Zenith Plateau (Z). 

The deepest point in the area (D) lies in the Wallaby-Zenith Fracture Zone at an estimated depth of 7883 meters. 

The Wallaby Plateau (W) lies to the east of the Zenith Plateau. 

The shallowest point in the entire area shown here is on Broken Ridge (BR). Deep Sea Drilling Project (DSDP) site 256 is marked by a gray dot. 

Seafloor depths are from the General Bathymetric Chart of the Oceans [2010] (GEBCO). 

Credit: Walter H.F. Smith and Karen M. Marks

A new illustration of the seafloor, created by two of the world's leading ocean floor mapping experts that details underwater terrain where the missing Malaysia Airlines flight might be located, could shed additional light on what type of underwater vehicles might be used to find the missing airplane and where any debris from the crash might lie.

The seafloor topography map (above) illustrates jagged plateaus, ridges and other underwater features of a large area underneath the Indian Ocean where search efforts have focused since contact with Malaysia Airlines flight MH370 was lost on March 8.

The image was published today in Eos, the weekly newspaper of the Earth and space sciences, published by the American Geophysical Union (AGU).

The new illustration of a 2,000 kilometer by 1,400 kilometer (1,243 miles by 870 miles) area where the plane might be shows locations on the seafloor corresponding to where acoustic signals from the airplane's black boxes were reportedly detected at the surface by two vessels in the area. It also shows the two plateaus near where these "pings" were heard.

It points out the deepest point in the area: 7,883 meters (about five miles) underneath the sea in the Wallaby-Zenith Fracture Zone – about as deep as 20 Empire State buildings stacked top to bottom.

Undersea mountains and plateaus rise nearly 5,000 meters (about three miles) above the deep seafloor, according to the map.

This image, originally appeared on the NOAA map and it shows the possible crash area's location, to the west of Australia.

The illustration, designated as Figure 1 of the Eos article, was created by Walter H.F. Smith and Karen M. Marks, both of the (National Oceanic and Atmospheric Administration) NOAA's Laboratory for Satellite Altimetry in College Park, Maryland, and the former and current chairs, respectively, of the Technical Sub-Committee on Ocean Mapping of the General Bathymetric Chart of the Oceans, (GEBCO).

GEBCO is an international organization that aims to provide the most authoritative publicly available maps of the depths and shapes of the terrain underneath the world's oceans.

Satellite altimetry has made it possible to depict the topography of vast regions of the seafloor that would otherwise have remained unmapped, Smith said.

To illustrate the topography of the search area, Smith and Marks used publicly available data from GEBCO and other bathymetric models and data banks, along with information culled from news reports.

Smith said the terrain and depths shown in the map could help searchers choose the appropriate underwater robotic vehicles they might use to look for the missing plane.

Knowing the roughness and shape of the ocean floor could also help inform models predicting where floating debris from the airplane might turn up.

Smith cautions that the new illustration is not a roadmap to find the missing airplane. Nor does the map define the official search area for the aircraft, he added. "It is not 'x marks the spot'," Smith said of their map.

"We are painting with a very, very broad brush."

Search efforts for the missing airplane have focused on an area of the southern Indian Ocean west of Australia where officials suspect that the plane crashed after it veered off course.

After an initial air and underwater search failed to find any trace of the airplane, authorities announced this month that they will expand the search area and also map the seabed in the area.

Smith pointed out that the search for the missing plane is made more difficult because so little is understood about the seafloor in this part of the Indian Ocean.

In the southeast Indian Ocean, only 5 percent of the ocean bottom has been measured by ships with echo soundings.

Knowledge of the rest of the area comes from satellite altimetry, which provides relatively low-resolution mapping compared to ship-borne methods.

"It is a very complex part of the world that is very poorly known," Smith said.

More information: Paper: onlinelibrary.wiley.com/doi/10.1002/2014EO210001/pdf