Intelligent Machines

From the Labs: Materials

New publications, experiments and breakthroughs in materials–and what they mean.

Metamaterial Prism
A new material for ultrahigh-­resolution ­microscopes

Light bending: An image produced by a ¬scanning electron microscope shows a wedge-shaped prism. The device was carved from layers of metal and insulating material (inset) punched with rectilinear holes.

Source: “Three-dimensional optical metamaterial with a negative refractive index”
Xiang Zhang et al.
Nature 455: 376-379

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Results: Researchers have fabricated a material that interacts with near-infrared light in a way that no naturally occurring material does. A prism made from the material has a negative refractive index: that is, it bends light in the direction opposite the one in which ordinary materials bend it.

Why it matters: The prism is the first practical device for redirecting near-infrared light in this way. Devices made from the material could be used in microscopes to produce much sharper images. They could also be used to route light on a microchip or even to render objects invisible to near-infrared wavelengths by directing light around them. Some previous negative-­index materials worked only with microwaves; others, which did work with visible or infrared wavelengths, transmitted little light and were so thin that they were difficult to use. The new material is thicker and transmits more light, making it potentially more useful.

Methods: The material is made up of alternating layers of a metal, which conducts electricity, and an insulating material; both are punched with a grid of square holes. This structure gives the material its unusual properties: it creates electrical circuits that respond to the magnetic field of light and change the way light moves through the material.

Next steps: The first applications are likely to be in high-resolution microscopy. The researchers are currently developing methods for making the material in larger quantities

Cool Fuel Cells
A new electrolyte works at room temperature.

Source: “Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures”
Jacobo Santamaria et al.
Science 321: 676-680

Results: A new electrolyte developed for use in solid-oxide fuel cells has 100 million times the ionic conductivity of conventional electrolytes at room temperature.

Why it matters: Solid-oxide fuel cells show promise for power generation because they convert a wide variety of fuels–including gasoline, hydrogen, and natural gas–into electricity more efficiently than conventional generators do. But they have been very expensive, and limited in their applications, because they require electrolytes that function only at temperatures above 600 °C. The new electrolyte works at temperatures hundreds of degrees cooler.

Methods: A solid-oxide fuel cell consists of two electrodes separated by an electrolyte. Fuel is fed to one electrode and oxygen to the other. The electrolyte transfers oxygen ions from one electrode to the other, where they combine with the fuel in a chemical reaction that releases electrons, producing an electric current. Conventional electrolytes require high temperatures because they don’t conduct ions well at room temperature.

To make the new material, the researchers combined nanometer-thick layers of the electrolyte, an yttria-stabilized zirconia, with 10-­nanometer-thick layers of strontium titanate. The difference between the crystal structures of these two materials leads to gaps in the electrolyte that allow oxygen ions to move freely at relatively low temperatures.

Next steps: Ionic ­conductivity is difficult to measure in extremely thin films like the one tested, so the improvement requires verification. What’s more, creating low-temperature fuel cells will also require new electrodes that operate at low temperatures.

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