Sprinkled Nanocubes Could Hold Light Tight for Efficient Solar Panels

A device based on scattered silver cubes could scale up light absorption for solar power

Just sprinkle on and harvest light — that is the procedure with nanoscale cubes of silver that could be used to make efficient solar panels, heat detectors and specialist cameras.

The cubes are scattered randomly on a piece of polymer-coated metal to form a device that absorbs nearly all the light that hits it. Unlike other light absorbers, it is relatively simple and cheap to make, and could be produced on a large scale for industrial and even domestic applications.

The material, which can be tuned to ensnare the desired wavelength of light, is described today in Nature. It was developed by David Smith, a materials scientist at Duke University in Durham, North Carolina, and his colleagues.

Trapped in a gap

Absorbers that can capture all, or almost all, of the light that hits them are typically made with metamaterials — materials engineered to have particular properties not found in nature. They usually have precisely placed components smaller than the wavelength of light, which gives them the ability to manipulate light in weird ways (see ‘Ideal focus’).

These minuscule components are painstakingly fabricated in a laborious, expensive etching process using lithography, so the light absorbers are difficult to make in large quantities.

Smith and his team took a different approach. They mounted a thin piece of gold on a piece of glass, and dipped it into two organic chemicals to build a uniform polymer layer just a few nanometers thick on top of the gold. They then made silver cubes about 74 nanometers wide, and scattered them on top of the polymer.

When light with a certain wavelength hits a nanocube in the device, it excites the cube’s electrons, which start to oscillate together with the electrons in the gold film. This ‘plasmon resonance’ between film and nanocube seems to pull light into the insulating polymer gap between them, and traps it there, explains Smith.

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via Scientific American – Katharine Sanderson and Nature magazine
 

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Metallic material can switch back and forth between hard and soft states

We may not yet have the liquid metal depicted in the Terminator movies, but scientists have now developed something that’s vaguely along the same lines.

German materials scientist Dr. Jörg Weißmüller and Chinese research scientist Hai-Jun Jin have created a metallic material that can change back and forth between being strong but brittle and soft but malleable, via electrical signals.

The metals used in the material are typically precious ones, such as gold or platinum. They are placed in an acidic solution, which causes minute pores to form within them – in other words, they start corroding. Those pores are then impregnated with a conductive liquid, such as saline solution or diluted acid.

By varying an electrical current that is applied to the liquid, electrons are added to or withdrawn from the surface atoms of the metal. This can increase the strength of the material as a whole by up to 200 percent, or it can cause it to become softer, but also better able to absorb energy without shattering.

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New material combines the strength of steel and the moldability of plastic

Rotary wheel blow molding machine operation

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Could have the same impact on society as the development of synthetic plastics

Scientists at Yale University have done what materials scientists have been trying to do for decades – create a material that boasts the look, strength and durability of metal that can be molded into complex shapes as simply and cheaply as plastic.

The scientists say the development could have the same impact on society as the development of synthetic plastics last century and they have already used the novel metals to create complex shapes, such as metallic bottles, watch cases, miniature resonators and biomedical implants, that are twice as strong as typical steel and can be molded in less than a minute.

Unlike the crystalline structure found in ordinary metals that makes them strong but also results in them requiring three separate steps for processing (shaping, joining and finishing), the metal alloys recently developed by the Yale team are amorphous metals known as bulk metallic glasses (BMGs), whose randomly arranged atoms and low critical cooling rate allows them to be blow-molded into complex shapes like plastics. This allows the researchers to combine the three traditional time- and energy-intensive metal processing steps into one blow molding process that takes less than a minute.

Although the different metals used to make the alloys, such as zirconium, nickel, titanium and copper, cost about the same as high-end steel, they can be processed as cheaply as plastic, according to Jan Schroers, a materials scientist at Yale that led the team.

The BMGs ability to soften and flow as easily as plastic at low temperatures and low pressures, without crystallizing like regular metal is what allows the material to be shaped with unprecedented ease, versatility and precision, Schroers said. To ensure the ideal temperature for blow molding was maintained, the team shaped the BMGs in a vacuum or in fluid.

“The trick is to avoid friction typically present in other forming techniques,” Schroers said. “Blow molding completely eliminates friction, allowing us to create any number of complicated shapes, down to the nanoscale.”

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Glassy Metal Set to Rival Steel

Super-resilient material is the first to combine strength and toughness

A metal alloy masquerading as a glass is the first material to be fabricated that is as strong and as tough as the toughest steel. The feat could eventually see such materials replace steel in buildings, cars or bridges.

The terms ‘strength’ and ‘toughness’ may be used almost interchangeably in everyday life, but until now, no materials have been found that display both these characteristics. Some materials, such as glass, are strong — that is, they are scratch-resistant and it is difficult to permanently bend them out of shape when you place a heavy load on them — but they also tend to be brittle. Others, such as metal, are tough — that is, they are more difficult to shatter — but they are generally more malleable.

“The challenge has always been to achieve both high strength and toughness,” says Marios Demetriou, a materials scientist at the California Institute of Technology in Pasadena. “But until now we have always had to compromise between the two.”

Demetriou and his colleagues have developed an alloy that combines the best features of both by turning to ‘amorphous metals’. Their work is published in Nature Materials today.

Strength in weakness

Normal metals are weak and malleable because their atoms are lined up in a crystalline structure and easily slip past each other when placed under a heavy load. Amorphous metals are stronger. They are made by rapidly cooling molten metal, so that its atoms are stuck in a disordered arrangement — resembling the structure of glass. It takes much more energy to permanently shift these atoms around.

Unfortunately, for a long time these ‘glassy metals’ also seemed to be inherently brittle. This is because they contain small defects that can clump together into bands, as the material begins to fail, says Demetriou. These bands can rapidly turn into cracks, and the material shatters.

However, materials scientists now know that, ironically, generating an extremely large number of these bands could have the opposite effect — making the material tougher. “If you dramatically amplify the number of bands, they start to interlace and form networks,” says Demetriou. “When new cracks evolve in the glassy metal, these networks cluster around the crack tips, blocking them from growing.”

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