To enable nanolaser operation at room temperature using single molecular layer and thin silicon beam

 

For the first time in human history, researchers have built a nanolaser that uses only a single molecular layer. This is placed on a thin silicon beam, which operates at room temperature. The new device, developed by a team of researchers from Arizona State University and Tsinghua University, Beijing, China, could potentially be used to send information between different points on a single computer chip. The lasers also may be useful for other sensing applications in a compact, integrated format.

"This is the first demonstration of room-temperature operation of a nanolaser made of the single-layer material," said Cun-Zheng Ning, an ASU electrical engineering professor who led the research team. Details of the new laser are published in the July online edition of Nature Nanotechnology.

In addition to Ning, key authors of the article, "Room-temperature Continuous-wave Lasing from Monolayer Molybdenum Ditelluride Integrated with a Silicon Nanobeam Cavity," include Yongzhuo Li, Jianxing Zhang, Dandan Huang from Tsinghua University.

Ning said pivotal to the new development is use of materials that can be laid down in single layers and efficiently amplify light (lasing action). Single layer nanolasers have been developed before, but they all had to be cooled to low temperatures using a cryogen like liquid nitrogen or liquid helium. Being able to operate at room temperatures (~77 F) opens up many possibilities for uses of these new lasers," Ning said.

The joint ASU-Tsinghua research team used a monolayer of molybdenum ditelluride integrated with a silicon nanobeam cavity for their device. By combining molybdenum ditelluride with silicon, which is the bedrock in semiconductor manufacturing and one of the best waveguide materials, the researchers were able to achieve lasing action without cooling, Ning said.

A laser needs two key pieces – a gain medium that produces and amplifies photons, and a cavity that confines or traps photons. While such materials choices are easy for large lasers, they become more difficult at nanometer scales for nanolasers. Nanolasers are smaller than 100th of the thickness of the human hair and are expected to play important roles in future computer chips and a variety of light detection and sensing devices.

The choice of two-dimensional materials and the silicon waveguide enabled the researchers to achieve room temperature operation. Excitons in molybdenum telluride emit in a wavelength that is transparent to silicon, making silicon possible as a waveguide or cavity material. Precise fabrication of the nanobeam cavity with an array of holes etched and the integration of two-dimensional monolayer materials was also key to the project. Excitons in such monolayer materials are 100 times stronger than those in conventional semiconductors, allowing efficient light emission at room temperature.

Because silicon is already used in electronics, especially in computer chips, its use in this application is significant in future applications.

"A laser technology that can also be made on Silicon has been a dream for researchers for decades," said Ning. "This technology will eventually allow people to put both electronics and photonics on the same silicon platform, greatly simplifying manufacture."

Silicon does not emit light efficiently and therefore must be combined with other light emitting materials. Currently, other semiconductors are used, such as Indium phosphide or Indium Garlium Arsenide which are hundreds of times thicker, to bond with silicon for such applications.

The new monolayer materials combined with Silicon eliminate challenges encountered when combining with thicker, dissimilar materials. And, because this non-silicon material is only a single layer thick, it is flexible and less likely to crack under stress, according to Ning.

Looking forward, the team is working on powering their laser with electrical voltage to make the system more compact and easy to use, especially for its intended use on computer chips.

SpaceX at it again. reusing Dragon to ISS

SpaceX's Dragon. Nasa.gov

Remember the last post about SpaceX?  Well they are at it again!

This time, SpaceX has propelled supplies to International space station on saturday.More so is that they used a verssel that has flown before.

The refurbished Dragon cargo capsule propeled into space annexed to a Falcon 9 rocket at 5:07 pm (2107 GMT) from Cape Canaveral, Florida.

With a countdown made by NASA spokesman Mike Curie, the rocket blazed a steady vertical path into the clouds.

 

The last time this particular spaceship(Dragon) flew to space was in 2014.

The Dragon on present mission is packed with almost 6,000 pounds (2,700 kilograms) of science research, crew supplies and hardware and should arrive at the Monday(ISS time).

The supplies for special experiments include live mice to study the effects of osteoporosis and fruit flies for research on microgravity's impact on the heart.

The spacecraft is also loaded with solar panels and equipment to study neutron stars.

After about 10 minutes after launch, SpaceX successfully returned the first stage of the Falcon 9 rocket back to a controlled landing at Cape Canaveral.

The rocket powered its engines and guided itself down to Landing Zone One, not far from the launch site.

"The first stage is back," Curie said in a NASA live webcast, as video images showed the tall, narrow portion of the rocket touch down steadily in a cloud of smoke.

SpaceX said it marked the company's fifth successful landing on solid ground. Several of its Falcon 9 rockets have returned upright to platforms floating in the ocean.

The effort is part of SpaceX's push to make spaceflight cheaper by re-using costly rocket and spaceship components after each launch, rather than ditching them in the ocean.

The launch was the 100th from NASA's historic launch pad 39A, the starting point for the Apollo missions to the Moon in the 1960s and 1970s, as well as a total of 82 shuttle flights.

A Self ventilating suit to keep you dry and cool while you perform exercise

 

                                                                                    

Images of garment prototype before exercise with flat ventilation flaps (F) and after exercise with curved ventilation flaps (G). Credit: Science Advances (2017). advances.sciencemag.org/content/3/5/e1601984

           

A team of MIT researchers has designed a breathable workout suit with ventilating flaps that open and close in response to an athlete's body heat and sweat. These flaps, which range from thumbnail- to finger-sized, are lined with live microbial cells that shrink and expand in response to changes in humidity. The cells act as tiny sensors and actuators, driving the flaps to open when an athlete works up a sweat, and pulling them closed when the body has cooled off.

The researchers have also fashioned a running shoe with an inner layer of similar cell-lined flaps to air out and wick away moisture. Details of both designs are published today in Science Advances.
Why use live cells in responsive fabrics? The researchers say that moisture-sensitive cells require no additional elements to sense and respond to humidity. The microbial cells they have used are also proven to be safe to touch and even consume. What's more, with new genetic engineering tools available today, cells can be prepared quickly and in vast quantities, to express multiple functionalities in addition to moisture response.
To demonstrate this last point, the researchers engineered moisture-sensitive cells to not only pull flaps open but also light up in response to humid conditions.
"We can combine our cells with genetic tools to introduce other functionalities into these living cells," says Wen Wang, the paper's lead author and a former research scientist in MIT's Media Lab and Department of Chemical Engineering. "We use fluorescence as an example, and this can let people know you are running in the dark. In the future we can combine odor-releasing functionalities through genetic engineering. So maybe after going to the gym, the shirt can release a nice-smelling odor."
Wang's co-authors include 14 researchers from MIT, specializing in fields including mechanical engineering, chemical engineering, architecture, biological engineering, and fashion design, as well as researchers from New Balance Athletics. Wang co-led the project, dubbed bioLogic, with former graduate student Lining Yao as part of MIT's Tangible Media group, led by Hiroshi Ishii, the Jerome B. Wiesner Professor of Media Arts and Sciences.
Shape-shifting cells
In nature, biologists have observed that living things and their components, from pine cone scales to microbial cells and even specific proteins, can change their structures or volumes when there is a change in humidity. The MIT team hypothesized that natural shape-shifters such as yeast, bacteria, and other microbial cells might be used as building blocks to construct moisture-responsive fabrics.

"These cells are so strong that they can induce bending of the substrate they are coated on," Wang says.
The researchers first worked with the most common nonpathogenic strain of E. coli, which was found to swell and shrink in response to changing humidity. They further engineered the cells to express green fluorescent protein, enabling the cell to glow when it senses humid conditions.
They then used a cell-printing method they had previously developed to print E. coli onto sheets of rough, natural latex.
The team printed parallel lines of E. coli cells onto sheets of latex, creating two-layer structures, and exposed the fabric to changing moisture conditions. When the fabric was placed on a hot plate to dry, the cells began to shrink, causing the overlying latex layer to curl up. When the fabric was then exposed to steam, the cells began to glow and expand, causing the latex flatten out. After undergoing 100 such dry/wet cycles, Wang says the fabric experienced "no dramatic degradation" in either its cell layer or its overall performance.
No sweat
The researchers worked the biofabric into a wearable garment, designing a running suit with cell-lined latex flaps patterned across the suit's back. They tailored the size of each flap, as well as the degree to which they open, based on previously published maps of where the body produces heat and sweat.
"People may think heat and sweat are the same, but in fact, some areas like the lower spine produce lots of sweat but not much heat," Yao says. "We redesigned the garment using a fusion of heat and sweat maps to, for example, make flaps bigger where the body generates more heat."
Support frames underneath each flap keep the fabric's inner cell layer from directly touching the skin, while at the same time, the cells are able to sense and react to humidity changes in the air lying just over the skin. In trials to test the running suit, study participants donned the garment and worked out on exercise treadmills and bicycles while researchers monitored their temperature and humidity using small sensors positioned across their backs.
After five minutes of exercise, the suit's flaps started opening up, right around the time when participants reported feeling warm and sweaty. According to sensor readings, the flaps effectively removed sweat from the body and lowered skin temperature, more so than when participants wore a similar running suit with nonfunctional flaps.
When Wang tried on the suit herself, she found that the flaps created a welcome sensation. After pedaling hard for a few minutes, Wang recalls that "it felt like I was wearing an air conditioner on my back."
Ventilated running shoes
The team also integrated the moisture-responsive fabric into a rough prototype of a running shoe. Where the bottom of the foot touches the sole of the shoe, the researchers sewed multiple flaps, curved downward, with the cell-lined layer facing toward—though not touching—a runner's foot. They again designed the size and position of the flaps based on heat and sweat maps of the foot.
"In the beginning, we thought of making the flaps on top of the shoe, but we found people don't normally sweat on top of their feet," Wang says. "But they sweat a lot on the bottom of their feet, which can lead to diseases like warts. So we thought, is it possible to keep your feet dry and avoid those diseases?"
As with the workout suit, the flaps on the running shoe opened and lit up when researchers increased the surrounding humidity; in dry conditions the flaps faded and closed.
Going forward, the team is looking to collaborate with sportswear companies to commercialize their designs, and is also exploring other uses, including moisture-responsive curtains, lampshades, and bedsheets.
"We are also interested in rethinking packaging," Wang says. "The concept of a second skin would suggest a new genre for responsive packaging."
"This work is an example of harnessing the power of biology to design new materials and devices and achieve new functions," says Xuanhe Zhao, the Robert N. Noyce Career Development Associate Professor in the Department of Mechanical Engineering and a co-author on the paper. "We believe this new field of 'living' materials and devices will find important applications at the interface between engineering and biological systems."

New theory on how Earth's crust was created

A composite image of the Western hemisphere of the Earth. Credit: NASA

More than 90% of Earth's continental crust is made up of silica-rich minerals, such as feldspar and quartz. But where did this silica-enriched material come from? And could it provide a clue in the search for life on other planets?

Conventional theory holds that all of the early Earth's crustal ingredients were formed by volcanic activity. Now, however, McGill University earth scientists Don Baker and Kassandra Sofonio have published a theory with a novel twist: some of the chemical components of this material settled onto Earth's early surface from the steamy atmosphere that prevailed at the time.
First, a bit of ancient geochemical history: Scientists believe that a Mars-sized planetoid plowed into the proto-Earth around 4.5 billion years ago, melting the Earth and turning it into an ocean of magma. In the wake of that impact—which also created enough debris to form the moon—the Earth's surface gradually cooled until it was more or less solid. Baker's new theory, like the conventional one, is based on that premise.
The atmosphere following that collision, however, consisted of high-temperature steam that dissolved rocks on the Earth's immediate surface—"much like how sugar is dissolved in coffee," Baker explains. This is where the new wrinkle comes in. "These dissolved minerals rose to the upper atmosphere and cooled off, and then these silicate materials that were dissolved at the surface would start to separate out and fall back to Earth in what we call a silicate rain."
To test this theory, Baker and co-author Kassandra Sofonio, a McGill undergraduate research assistant, spent months developing a series of laboratory experiments designed to mimic the steamy conditions on early Earth. A mixture of bulk silicate earth materials and water was melted in air at 1,550 degrees Celsius, then ground to a powder. Small amounts of the powder, along with water, were then enclosed in gold palladium capsules, placed in a pressure vessel and heated to about 727 degrees Celsius and 100 times Earth's surface pressure to simulate conditions in the Earth's atmosphere about 1 million years after the moon-forming impact. After each experiment, samples were rapidly quenched and the material that had been dissolved in the high temperature steam analyzed.
The experiments were guided by other scientists' previous experiments on rock-water interactions at high pressures, and by the McGill team's own preliminary calculations, Baker notes. Even so, "we were surprised by the similarity of the dissolved silicate material produced by the experiments" to that found in the Earth's crust.
Their resulting paper, published in the journal Earth and Planetary Science Letters, posits a new theory of "aerial metasomatism"—a term coined by Sofonio to describe the process by which silica minerals condensed and fell back to earth over about a million years, producing some of the earliest rock specimens known today.
"Our experiment shows the chemistry of this process," and could provide scientists with important clues as to which exoplanets might have the capacity to harbor life Baker says.
"This time in early Earth's history is still really exciting," he adds. "A lot of people think that life started very soon after these events that we're talking about. This is setting up the stages for the Earth being ready to support life."