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Category: materials

Can black phosphorous rival #graphene?

A new experimental revelation about black phosphorus nanoribbons should facilitate the future application of this highly promising material to electronic, optoelectronic and thermoelectric devices. A team of researchers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has experimentally confirmed strong in-plane anisotropy in thermal conductivity, up to a factor of two, along the zigzag and armchair directions of single-crystal black phosphorous nanoribbons.

“Imagine the lattice of black phosphorous as a two-dimensional network of balls connected with springs, in which the network is softer along one direction of the plane than another,” says Junqiao Wu, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the University of California (UC) Berkeley’s Department of Materials Science and Engineering. “Our study shows that in a similar manner heat flow in the black phosphorous nanoribbons can be very different along different directions in the plane. This thermal conductivity has been predicted recently for 2D black phosphorous crystals by theorists but never before observed.”

Wu is the corresponding author of a paper describing this research in Nature Communications titled “Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100K.” The lead authors are Sangwook Lee and Fan Yang. (See below for a complete list of authors)

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A new approach developed by researchers at the University of Waterloo could hold the key to greatly improving the performance of commercial lithium-ion batteries. The scientists have developed a new type of silicon anode that would be used in place of a conventional graphite anode, which they claim will lead to smaller, lighter and longer-lasting batteries for everything from personal devices to electric vehicles.

Graphite has served the lithium-ion battery world as material for negative electrodes well so far, but also presents something of a roadblock for improved capacity. This is due to the relatively small amount of energy it can store, which comes in at around 370 mAh/g (milliamp hours per gram). Silicon has become an increasingly popular substitute for battery researchers looking to up the ante, with a specific capacity of 4,200 mAh/g. However, it isn’t without its limitations either.

As silicon interacts with lithium inside the cell during each charge cycle, it expands and contracts by as much as as 300 percent. This immense swelling brings about cracks that diminish the battery’s performance over time, leading to short circuits and ultimately cell failure. Other recent attempts to overcome this problem have turned up battery designs that use sponge-like silicon anodes developed at the nanoscale, silicon nanowires measuring only a few microns long and ones that bring graphene and carbon nanotubes into the mix.

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A team of physicists led by Caltech’s David Hsieh has discovered an unusual form of matter—not a conventional metal, insulator, or magnet, for example, but something entirely different. This phase, characterized by an unusual ordering of electrons, offers possibilities for new electronic device functionalities and could hold the solution to a long-standing mystery in condensed matter physics having to do with high-temperature superconductivity—the ability for some materials to conduct electricity without resistance, even at “high” temperatures approaching −100 degrees Celsius.

“The discovery of this was completely unexpected and not based on any prior theoretical prediction,” says Hsieh, an assistant professor of physics, who previously was on a team that discovered another form of matter called a topological insulator. “The whole field of electronic materials is driven by the discovery of new phases, which provide the playgrounds in which to search for new macroscopic physical properties.”

Hsieh and his colleagues describe their findings in the November issue of Nature Physics, and the paper is now available online. Liuyan Zhao, a postdoctoral scholar in Hsieh’s group, is lead author on the paper.

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One of the oddest predictions of quantum theory – that a system can’t change while you’re watching it – has been confirmed in an experiment by Cornell physicists. Their work opens the door to a fundamentally new method to control and manipulate the quantum states of atoms and could lead to new kinds of sensors.

The experiments were performed in the Utracold Lab of Mukund Vengalattore, assistant professor of physics, who has established Cornell’s first program to study the physics of materials cooled to temperatures as low as .000000001 degree above absolute zero. The work is described in the Oct. 2 issue of the journal Physical Review Letters

Graduate students Yogesh Patil and Srivatsan K. Chakram created and cooled a gas of about a billion Rubidium atoms inside a vacuum chamber and suspended the mass between laser beams. In that state the atoms arrange in an orderly lattice just as they would in a crystalline solid.,But at such low temperatures, the atoms can “tunnel” from place to place in the lattice. The famous Heisenberg uncertainty principle says that the position and velocity of a particle interact. Temperature is a measure of a particle’s motion. Under extreme cold velocity is almost zero, so there is a lot of flexibility in position; when you observe them, atoms are as likely to be in one place in the lattice as another.

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Coronary artery structure being 3-D bioprinted (credit: Carnegie Mellon University College of Engineering)

Carnegie Mellon scientists are creating cutting-edge technology that could one day solve the shortage of heart transplants, which are currently needed to repair damaged organs.

“We’ve been able to take MRI images of coronary arteries and 3-D images of embryonic hearts and 3-D bioprint them with unprecedented resolution and quality out of very soft materials like collagens, alginates and fibrins,” said Adam Feinberg, an associate professor of Materials Science and Engineering and Biomedical Engineering at Carnegie Mellon University.

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In the television series Star Trek, virtual reality-chambers called “holodecks” take humans into computer-generated worlds where they interact with avatars — and with each other. Imagine being able to visit a distant planet or Tahiti during your lunch break. In Star Trek, holodecks come into existence in the 24th century and reproduce all sensory perceptions, including touch and smell.

Chambers that replicate the touch and feel of solid materials are still a decade or two away. But virtual reality worlds that are amazingly similar to what we saw in Star Trek are already here. Hundreds of companies are working on virtual reality hardware, software, applications and content. I expect that 2016 will be the year when we start visiting exotic lands from the comfort of our offices and living rooms.

There are several technology developments which are bringing the future to us ahead of the Star Trek schedule. For starters, there is what is called “full-immersion virtual reality.” These are systems that take us out of the real world, into an entirely different digital realm. We hear stereo sounds and see panoramic displays that are so convincing that users lose track of time and space (they also, until very recently, suffered from serious nausea and motion sickness). Facebook’s Oculus Rift is the leading immersive virtual reality (VR) system but numerous others are either on the market or in the works.

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As of this month, over 4,000 Americans are on the waiting list to receive a heart transplant. With failing hearts, these patients have no other options; heart tissue, unlike other parts of the body, is unable to heal itself once it is damaged. Fortunately, recent work by a group at Carnegie Mellon could one day lead to a world in which transplants are no longer necessary to repair damaged organs.

“We’ve been able to take MRI images of coronary arteries and 3-D images of embryonic hearts and 3-D bioprint them with unprecedented resolution and quality out of very like collagens, alginates and fibrins,” said Adam Feinberg, an associate professor of Materials Science and Engineering and Biomedical Engineering at Carnegie Mellon University. Feinberg leads the Regenerative Biomaterials and Therapeutics Group, and the group’s study was published in the October 23 issue of the journal Science Advances. A demonstration of the technology can be seen below.

“As excellently demonstrated by Professor Feinberg’s work in bioprinting, our CMU researchers continue to develop novel solutions like this for problems that can have a transformational effect on society,” said Jim Garrett, Dean of Carnegie Mellon’s College of Engineering. “We should expect to see 3-D bioprinting continue to grow as an important tool for a large number of medical applications.”

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A low-cost, high-speed method for printing graphene inks using a conventional roll-to-roll printing process, like that used to print newspapers and crisp packets, could open up a wide range of practical applications, including inexpensive printed electronics, intelligent packaging and disposable sensors.

Developed by researchers at the University of Cambridge in collaboration with Cambridge-based technology company Novalia, the method allows graphene and other electrically conducting materials to be added to conventional water-based inks and printed using typical commercial equipment, the first time that graphene has been used for printing on a large-scale commercial printing press at high speed.

Graphene is a two-dimensional sheet of carbon atoms, just one atom thick. Its flexibility, optical transparency and electrical conductivity make it suitable for a wide range of applications, including printed electronics. Although numerous laboratory prototypes have been demonstrated around the world, widespread commercial use of graphene is yet to be realised.

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Electrons are so 20th century. In the 21st century, photonic devices, which use light to transport large amounts of information quickly, will enhance or even replace the electronic devices that are ubiquitous in our lives today. But there’s a step needed before optical connections can be integrated into telecommunications systems and computers: researchers need to make it easier to manipulate light at the nanoscale.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have done just that, designing the first on-chip metamaterial with a refractive index of zero, meaning that the phase of can travel infinitely fast.

This new metamaterial was developed in the lab of Eric Mazur, the Balkanski Professor of Physics and Applied Physics and Area Dean for Applied Physics at SEAS, and is described in the journal Nature Photonics.

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