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(PNAS, Early Edition) We have demonstrated an ultrafast relocation of charge that is induced by electronic excitation and steered by coherent low-frequency motions of the ionic crystal lattice. Our results reveal the nonequilibrium charge dynamics in ionic materials on their intrinsic length and time scales. Such insight is relevant for a large range of polar materials and their ultrafast dynamic response. In principle, low-frequency lattice motions can be controlled by interaction with tailored optical pulses. Our results suggest that such schemes allow for an ultrafast all-optical control of electric polarization in potassium dihydrgen phosphate and related ionic materials.
(Gizmag) In Twin Creeks Technologies’ proprietary Hyperion process, three-millimeter-thick disks of crystalline silicon are placed in a vacuum chamber, where they’re bombarded with a beam of hydrogen ions. The ion accelerator that’s used is reportedly ten times more powerful than anything else commercially available. Through control of the voltage of its beam, a layer of ions is precisely deposited on each disk. Those ions proceed to penetrate the silicon, so they’re located just below its surface. The disks are then robotically transferred to a furnace and heated. This causes the ions to expand into microscopic bubbles of hydrogen gas, which in turn causes a 20-micrometer-thick layer of silicon to peel off the surface of each disk. A supportive metal backing is then applied to that layer, and it’s ready for use.
Researchers in Harvard’s School of Engineering and Applied Sciences have cleared an important hurdle in the development of advanced materials, called metamaterials, that bend light in unusual ways. Working at a scale applicable to infrared light, the Harvard team has used extremely short and powerful laser pulses to create three-dimensional patterns of tiny silver dots within a material. Those suspended metal dots are essential for building futuristic devices like invisibility cloaks. The new fabrication process, described in the journal Applied Physics Letters, advances nanoscale metal lithography into three dimensions-and does it at a resolution high enough to be practical for metamaterials.
Inspired by the paper-folding art of origami, chemists at the University of Texas at Austin have developed a 3D paper sensor that may be able to test for diseases such as malaria and HIV for less than 10 cents a pop. Such low-cost, “point-of-care” sensors could be incredibly useful in the developing world, where the resources often don’t exist to pay for lab-based tests, and where, even if the money is available, the infrastructure often doesn’t exist to transport biological samples to the lab. A hydrophobic material, such as wax or photoresist, is laid down into tiny canyons on chromatography paper. It channels the sample that’s being tested — urine, blood, or saliva, for instance — to spots on the paper where test reagents have been embedded.
(Nature) Pressure has an essential role in the production1 and control of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature Tc to a record high of 55 K in these materials. In the same way as Tc exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned Tc typically drops monotonically after passing the optimal pressure. Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly reemerges above 11.5 GPa, after the Tc drops from the first maximum of 32 K at 1 GPa. The Tc of the reemerging superconducting phase is considerably higher than the first maximum, reaching 48.0-48.7 K for Tl0.6Rb0.4Fe1.67Se2, K0.8Fe1.7Se2 and K0.8Fe1.78Se2.