12-Mar-2018: Gallium joins graphene in the second dimension
Researchers at Rice University and the Indian Institute of Science have now isolated a 2D form of the soft metal gallium, dubbed "Gallenene," which could make for efficient, thin metal contacts in electronic devices.
Reducing a regular 3D material into two dimensions can fundamentally change its electric, magnetic, physical or chemical properties. Scientists have created 2D versions of materials like black phosphorus, molybdenum disulfide, and chromium triiodide, which is so far the only material capable of retaining magnetism in two dimensions.
In its familiar 3D state, gallium has a low melting point of just below 30° C (86° F). That makes it a great candidate for applications that need liquid metals at roughly room temperature, and we've seen gold-gallium and indium-gallium alloys put to work in "metal glue," flexible electronic circuits, fluidic transistors and cancer-hunting "Nano-Terminators."
The problem is, atomically-thin layers of the material are hard to isolate using conventional methods. In the early days, samples of graphene could be peeled off of chunks of graphite using plain old adhesive tape, but gallium's atomic bonds are too strong for that to work. The metal's low melting point also makes it unsuitable for vapor phase deposition techniques.
The team managed to make the Gallenene by first heating gallium to 29.7° C (85.5° F), just below its melting point, then letting it drip onto a glass slide. While it was still relatively warm, the researchers then pressed a sheet of silicon dioxide onto it, separating a few thin layers of the material. The teams says the thin, conductive film that resulted is to gallium what graphene is to carbon.
Gallenene was found to bind easily to other substrates too, including sheets of gallium nitride, gallium arsenide, silicone and nickel. These all had different electronic properties, which opens up plenty of avenues for future work with the stuff.
The current work utilizes the weak interfaces of solids and liquids to separate thin 2D sheets of gallium. The same method can be explored for other metals and compounds with low melting points.
Since Gallenene binds well to semiconductors and can now be created using a relatively simple technique, it could be used as an efficient metal contact in nanoscale electronics, a field which currently doesn't have many 2D metal options for these kinds of applications.
Near 2D metals are difficult to extract, since these are mostly high-strength, nonlayered structures, so Gallenene is an exception that could bridge the need for metals in the 2D world.
12-Mar-2018: Scientists find ultra-rare Ice-VII on Earth for the first time
Researchers at the University of Nevada who were looking for a specific form of carbon dioxide in diamonds serendipitously detected the first ever samples of naturally occurring ice-VII on Earth. While it’s almost nonexistent on Earth, ice-VII might play an important role elsewhere in the solar system. Now, we’ve got a way to study this material up close.
All the ice you’ve ever put in a drink or scraped off your car windshield is what’s known as ice-I. When water freezes, the oxygen atoms move into a hexagonal arrangement. That’s why ice expands and has lower density than water. Compressing ice can change the shape of the crystals, turning ice-I into ice-II (rhombus-shaped crystals), ice-III (tetragonal crystals), and so on.
Ice-VII, with its cubic crystals, is unique in that it remains stable even as pressure increases dramatically. It’s 1.5 times more dense than ice-I as well. There’s (almost) nowhere on Earth for ice-VII to form, because it requires both low temperatures and high pressure exceeding 30,000 atmospheres (3 gigapascals). The only place you can reach that pressure is deep in the Earth’s mantle, but it’s too hot for ice to form there. That’s where diamonds come into play.
Diamonds often pick up molecules during their formation deep in the Earth. These so-called inclusions can affect the quality or color of the diamond, but sometimes the inclusion is just water. One interesting property of diamonds is the internal structures don’t relax when they leave the high-pressure mantle. So, the water inside a diamond remains compressed, even though it’s technically in a liquid state.
The formation of ice-VII doesn’t require freezing temperatures — as long as the pressure is high enough, ice-VII can form at room temperature. When researchers exposed diamonds to x-ray scans, they detected the distinctive crystal structure of ice-VII. This discovery indicates that some diamonds form under such high pressure that water trapped inside can become super-rare ice-VII. It might have started as water, but in a cooler environment it spontaneously formed ice-VII.
Scientists believe that ice-VII might be present deep in the ice sheets on moons like Enceladus and Europa, or as part of the ocean floor under Titan’s hydrocarbon seas. Having naturally occurring samples of ice-VII on Earth for study could help us understand the environments on those moons.
5-Mar-2018: Rare mineral discovered in plants for first time
Scientists have found that the mineral vaterite, a form (polymorph) of calcium carbonate, is a dominant component of the protective silvery-white crust that forms on the leaves of a number of alpine plants.
Naturally occurring vaterite is rarely found on Earth. Small amounts of vaterite crystals have been found in some sea and freshwater crustaceans, bird eggs, the inner ears of salmon, meteorites and rocks. This is the first time that the rare and unstable mineral has been found in such a large quantity and the first time it has been found to be associated with plants.
Biochemists are working to synthetically manufacture vaterite as it has potential for use in drug delivery, but it is not easy to make. Vaterite has special properties that make it a potentially superior carrier for medications due to its high loading capacity, high uptake by cells and its solubility properties that enable it to deliver a sustained and targeted release of therapeutic medicines to patients. For instance, vaterite nanoparticles loaded with anti-cancer drugs appear to offload the drug slowly only at sites of cancers and therefore limit the negative side-effects of the drug.
Other potential uses of vaterite include improving the cements used in orthopaedic surgery and as an industrial application improving the quality of papers for inkjet printing by reducing the lateral spread of ink.
Vaterite was often associated with outer space and had been detected in planetary objects in the Solar System and meteorites. Vaterite is not very stable in the Earth's humid atmosphere as it often reverts to more common forms of calcium carbonate, such as calcite. This makes it even more remarkable that we have found vaterite in such large quantities on the surface of plant leaves.
Although many species in this section produced vaterite along with calcite, there was at least one species, Saxifraga sempervivum, that was producing pure vaterite.