London at night

 

 

Mastering extraordinary properties of an emerging semiconductor

 

Wed, 06/03/2015 - 10:58am École Polytechnique de Montréal   Chemical analysis by hyperspectral TEM-EELS spectroscopy of a multilayer 2D-phosphane exfoliated under ambient light in air.A team of researchers from Université de Montréal, Polytechnique Montréal and the Centre national de la recherche scientifique (CNRS) in France is the first to succeed in preventing two-dimensional layers of black phosphorus from oxidating. In so doing, they have opened the doors to exploiting their striking properties in a number of electronic and optoelectronic devices. The study's results were published in the journal Nature Materials.  Black phosphorus: future key player in new technologies Black phosphorus, a stable allotrope of phosphorus that presents a lamellar structure similar to that of graphite, has recently begun to capture the attention of physicists and materials researchers. It is possible to obtain single atomic layers from it, which researchers call 2D phosphane. A cousin of the widely publicized graphene, 2D phosphane brings together two very sought-after properties for device design.  First, 2D phosphane is a semiconductor material that provides the necessary characteristics for making transistors and processors. With its high-mobility, it is estimated that 2D phosphane could form the basis for electronics that is both high-performance and low-cost.  Furthermore, this new material features a second, even more distinctive, characteristic: its interaction with light depends on the number of atomic layers used. One monolayer will emit red light, whereas a thicker sample will emit into the infrared. This variation makes it possible to manufacture a wide range of optoelectronic devices, such as lasers or detectors, in a strategic fraction of the electromagnetic spectrum.  A scientific first: preserving single-atom layers of 2D phosphane from degrading Until now, the study of 2D phosphane's properties was slowed by a major problem: in ambient  conditions, very thin layers of the material would degrade, to the point of compromising its future in the industry despite its promising potential.  As such, the research team has made a major step forward by succeeding in determining the physical mechanisms at play in this degradation, and in identifying the key elements that lead to the layers' oxidation.  “We have demonstrated that 2D phosphane undergoes oxidation under ambient conditions, caused jointly by the presence of oxygen, water and light. We have also characterized the phenomenon's evolution over time by using electron beam spectroscopy and Raman spectroscopy,” reports Professor Richard Martel of Université de Montréal's Department of Chemistry. Next, the researchers developed an efficient procedure for producing these very fragile single-atom layers and keeping them intact. “We were able to study the vibration modes of the atoms in this new material. Since earlier studies had been carried out on heavily degraded materials, we revealed the as-yet-unsuspected effects of quantum confinement on atoms' vibration modes,” notes Professor Sébastien Francoeur of Polytechnique's Department of Engineering Physics. The study's results will help the world scientific community develop 2D phosphane's very special properties with the aim of developing new nanotechnologies that could give rise to high-performance microprocessors, lasers, solar cells and more. This work is financially supported by the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and Fonds de Recherche du Québec-Nature et technologie. SOURCE: École Polytechnique de Montréal

New drug shows potential for blood cancer

 

Multiple myeloma patients saw survival gains when elotuzumab was added to treatment. A two-pronged immune-boosting drug could provide new hope for people stricken with multiple myeloma, a cancer of the blood and bone marrow, according to clinical trial findings. The experimental drug, elotuzumab, reduced the risk of cancer progression and death by 30 percent when doctors combined it with the standard two-drug therapy for multiple myeloma, researchers found. Elotuzumab works against this relatively rare cancer through a dual mechanism, said senior study author Dr. Sagar Lonial. It makes cancer cells vulnerable to immune attack, and also enhances the immune system's ability to kill cancer. "It's a bit of a double-whammy," said Lonial, executive vice chair of hematology and oncology at Emory University School of Medicine in Atlanta. Patients receiving the three-drug elotuzumab cocktail did not seem to suffer an increase in side effects, compared with those who took the two-drug standard regimen. Elotuzumab is being developed by Bristol-Meyers Squibb and AbbVie Pharmaceuticals, which helped fund the study. The findings were presented Tuesday at the American Society of Clinical Oncology annual meeting in Chicago and published in the New England Journal of Medicine. Multiple myeloma is caused by malignant plasma cells in the bloodstream and bone marrow, according to the U.S. National Institutes of Health. Myeloma patients tend to suffer bone pain and easily broken bones, weakness or fatigue, weight loss, and frequent infections. About 26,850 new cases of myeloma are expected to occur this year, according to the American Cancer Society. More than 11,000 are expected to die from myeloma in 2015. The standard therapy for myeloma involves the chemotherapy drug lenalidomide and the steroid medication dexamethasone, Lonial said. But researchers wondered if they'd get better results by adding the experimental drug elotuzumab. In 2014, the drug was granted a breakthrough therapy designation by the U.S. Food and Drug Administration for treatment of relapsed multiple myeloma alongside lenalidomide and dexamethasone. This designation is intended to speed up the development and review of drugs for serious or life-threatening conditions. Elotuzumab, administered by intravenous infusion, targets a protein called SLAMF7, which is found on the surface of myeloma cells and also on a type of immune cell called natural killer cells. In the study, 646 patients with recurring, already treated myeloma received the standard two-drug treatment. About half also received elotuzumab. At an average follow-up period of 24 months, elotuzumab reduced risk of cancer progression and death by 30 percent, researchers found. Patients in the elotuzumab group experienced a longer period of remission, about 19.4 months on average compared with 14.9 months for those who had standard treatment. The three-drug cocktail also produced a response rate of 79 percent, compared with 66 percent for the standard treatment, the study found. "Patients who received elotuzumab had a longer duration of remission, had a higher overall response rate, and this improvement in clinical parameters occurred without a significant increase in adverse events or toxicity," Lonial said. The most common side effects experienced by both groups of patients were anemia, low levels of white blood cells and platelets, fatigue and diarrhea. Mild infusion reactions occurred after the first few doses in 10 percent of patients in the elotuzumab group. Elotuzumab represents the first potentially effective immunotherapy drug for myeloma, said Dr. Julie Vose, president-elect of the American Society of Clinical Oncology. Benefits without additional side effects are being seen even in patients who have received multiple prior treatments for their cancer, said Vose, professor of hematology and oncology at the University of Nebraska Medical Center. "The results are very encouraging, giving renewed hope to patients who have relapsed," Vose said.

Understanding a new kind of magnetism

 

A sample of the mineral herbertsmithite. Credit: ROB LAVINSKY/IROCKS.COM Using low-frequency laser pulses, a team of researchers has carried out the first measurements that reveal the detailed characteristics of a unique kind of magnetism found in a mineral called herbertsmithite. In this material, the magnetic elements constantly fluctuate, leading to an exotic state of fluid magnetism called a "quantum spin liquid." This is in contrast to conventional magnetism, found in materials called ferromagnets—where all of the magnetic forces align in the same direction, reinforcing each other—or antiferromagnets, where adjacent magnetic elements align in opposite directions, leading to complete cancellation of the material's overall magnetic field. Although a spin-liquid state has previously been observed in herbertsmithite, there has never been a detailed analysis of how the material's electrons respond to light—a key to determining which of several competing theories about the material is correct. Now a team at MIT, Boston College and Harvard University has successfully carried out these measurements. The new analysis is reported in a paper in Physical Review Letters, co-authored by Nuh Gedik, the Biedenharn Career Development Associate Professor of Physics at MIT, graduate student Daniel Pilon, postdoc Chun Hung Lui and four others. Their measurements, using laser pulses lasting just a trillionth of a second, reveal a signature in the optical conductivity of the spin-liquid state that reflects the influence of magnetism on the motion of electrons. This observation supports a set of theoretical predictions that have not previously been demonstrated experimentally. "We think this is good evidence," Gedik says, "and it can help to settle what has been a pretty big debate in spin-liquid research." "Theorists have provided a number of theories on how a spin-liquid state could be formed in herbertsmithite," Pilon explains. "But to date there has been no experiment that directly distinguishes among them. We believe that our experiment has provided the first direct evidence for the realization of one of these theoretical models in herbertsmithite." The concept of quantum spin liquids was first proposed in 1973, but the first direct evidence for such a material was only found within the last few years. The new measurements help to clarify the fundamental characteristics of this exotic system, which is thought to be closely related to the origins of high-temperature superconductivity. Gedik says, "Although it is hard to predict any potential applications at this stage, basic research on this unusual phase of matter could help us to solve some very complicated problems in physics, particularly high-temperature superconductivity, which might eventually lead to important applications." In addition, Pilon says, "This work might also be useful for the development of quantum computing." Leon Balents, a professor of physics at the University of California at Santa Barbara who was not involved in this work, says, "If the observed optical conductivity in these measurements is truly intrinsic, it is an important and exciting result, which will be very important in understanding the nature of the spin-liquid state." Balents adds that further work is needed to confirm this result, but says "this is clearly an exciting and important measurement, which I hope will be pursued further by extending the frequency and magnetic field range in the future." The paper is titled "Spin-Induced Optical Conductivity in the Spin-Liquid Candidate Herbertsmithite." Explore further: Physicists make first observation of the pushing pressure of light More information: prl.aps.org/abstract/PRL/v111/i12/e127401 This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Newly identified 'universal' property of metamagnets may lead to everyday uses

 

Physics professor Bellave Shivaram has discovered a universal law governing the properties of metamagnets. Credit: Dan Addison (Phys.org) —A new physics discovery made by a University of Virginia-led team may lead to more efficient refrigerators, heat pumps and airport scanners, among many possible uses –perhaps within a decade. The team of physicists and materials scientists have discovered a universal law governing the magnetic properties of metamagnets – metal alloys that can undergo dramatic increases in magnetization when a small external magnetic field is applied, such as from a permanent magnet or an electromagnet. The scientists have discovered that the magnetic effect of apparently all metamagnets is that it is non-linear. When these metamagnets are placed in an initial magnetic field and the field is doubled, they more than double in magnetic strength. This is significant because eventually scientists and engineers likely will harness this unique property for a variety of applications, including refrigeration. "We found that this nonlinear property has the same quantitative behavior in all different types of metamagnets, which is the universal law," said Bellave Shivaram, a University of Virginia professor of physics who led the studies, which were conducted in his lab and using materials synthesized at Argonne National Laboratory in Illinois. The findings are published in separate papers currently online in the journals Physical Review B: Rapid Communications, and Review of Scientific Instruments. According to Shivaram, the newly unveiled non-linear property can be exploited in many ways. "A very useful property of this type of magnetism is in magnetic refrigeration," he said. "Magnetic refrigerators are not commonplace; they still are in the experimental stage. But they could eventually become part of everyday home appliances, from heat pumps to the refrigerators we store food in." Currently, metamagnets produce efficient cooling only at very low temperatures, using superconducting magnets, making them impractical for general refrigeration. "With the new discoveries of the properties of metamagnets, they could become part of everyday home appliances within a decade or so," Shivaram said. Current refrigerators are among the biggest consumers of energy in the home. They include several moving parts, which make them costly to repair, and they can leak fluorocarbons into the atmosphere, which can deplete ozone. Refrigerators of the future, using metamagnets, would have fewer moving parts, would not require refrigerants, and, likely would use less electricity, Shivaram said. "In these new materials, the magnetism can be cycled on and off, enabling heat to be pumped away in a manner similar to what happens in a heat pump today," Shivaram said. "In today's heat pump, we use pressure to cycle the cooling medium from liquid to vapor phase. In the new magnetic refrigerators we will use a magnetic material and cycle the magnetic field instead." Another possible application for metamagnets would be, as an example, more effective airport screening devices. Such screeners use harmless terahertz waves to scan through materials. A screener using metamagnets would generate more efficient generation of terahertz waves, Shivaram said, by converting high-powered, low-frequency radio waves into terahertz waves by using the non-linear properties of metamagnets. "By discovering the properties of these materials we've shown their promise," Shivaram said. "We will figure out future directions and what new materials we should go after for possible uses." His co-authors on the Physical Review B paper are former U.Va. graduate student Brian Dorsey, materials scientist David Hinks of Argonne National Laboratory and physicist Pradeep Kumar of the University of Florida. This collaborative work is continuing and recently has been augmented with the participation of Vittorio Celli, U.Va. professor emeritus of physics. www.phys.org

The Air Force Wants to Go Hypersonic in the Next Decade

 

Wikimedia Commons Using technologies first tested with the X-51, the Air Force wants to build a hypersonic jet by 2023. The service already has outlined a few parameters for the new jet: It must be able to go Mach 5, or 3,806 miles per hour. It should use a scramjet engine, which largely relies on swift airflow for oxidation to propel the plane forward. And it needs to be able to operate at the scalding-hot temperatures created by the friction at speeds far exceeding the speed of sound. Thanks to X-51 tests, the military knows that scramjet technology is feasible (though some hypersonic tests over the past few years didn't go quite so well). Mach 5 is also just the beginning. The eventual goal is to reach speeds up to Mach 10, which is ... very, very fast. It's about 7,612 mph, or almost fast enough to travel the entire diameter of the world in the space of an hour. Because of the speeds reached, these vehicles are likely to be unmanned, and some of the technology may be incorporated into new weapons developed by the military. Source: Military.com via The Verge

Strong Magnets With Printed Poles Have Endless Engineering Applications

 

The Brilliant Idea: Magnets printed with multiple poles, opening the door to myriad applications.   Snowboard Bindings Two magnets tightly attract when aligned but repel when twisted more than 45 degrees, easily clicking on and off. Other apps: cycling cleats, pick-proof locks, standard prosthetic-limb fittings. Spinal Implants Magnetic discs attract and repel simultaneously, offering friction-free cushioning for bones of the spine. Other apps: bearings for energy-storing flywheels, assembly-line arms. Idiot-Proof Assembly Magnets on the joints of furniture or toys click together only when correctly aligned, making Christmas Eve easier for dads everywhere. Other apps: car parts, aircraft machinery. (Icons by Dogo) Innovator: Larry Fullerton, Correlated Magnetics Research Larry Fullerton set out to invent a self-assembling magnetic toy that would fuel his grandchildren's passion for science. Instead, he invented a way to manipulate magnetic fields that redefines one of the fundamental forces of nature. Fullerton's breakthrough tramples the long-held assumption that magnets have two opposing poles, one on each side. He found that if he used heat to erase a magnetic field, he could then reprogram material to have multiple north and south poles of differing strengths. "People look at magnets as having a north pole and a south pole. That limits your thinking," he says. "I came along from the field of radar and said, 'Hey, that's not a magnet—it's a vector field!'" To program the magnets, Fullerton invented a device—picture a printer whose head emits 200,000-amp bursts of electricity rather than ink—that creates magnetic pixels he calls "maxels." Using the printer and some vector math, Fullerton is now learning how to produce magnets that exhibit different behaviors. The practical applications appear limitless: from precision switches and a new generation of fasteners to robots that can scale walls without touching them. www.popularmechanics.com