Very Interesting – How to Make a Better Invisibility Cloak—With Lasers

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Images: Clockwise from top left: Karlsruhe Institute of Technology; Karlsruhe Institute of Technology/ Nature Materials; Karlsruhe Institute of Technology; Karlsruhe Institute of Technology/Applied Physics Letters
Made From Scratch: Lasers were used to draw the micrometer-scale structures in these metamaterials. Pictured clockwise from top left are a bichiral photonic crystal [top view], a photonic quasicrystal, a bichiral photonic crystal [oblique view], and a pentamode metamaterial.

For a century or more, nearly all technological advances have depended on our ability to produce and manipulate the vast variety of materials that nature has given us. Nowhere is that dependence more evident than in the field of electronics. From a smorgasbord of semiconductors, polymers, and metals, we’ve been able to create a dazzling array of circuitry that now underpins pretty much every aspect of modern life.

So now imagine what we could do if we weren’t limited to the materials found in nature. Researchers have long believed that it would someday be possible to produce artificial materials, or “metamaterials,” and that they would bring about some stunning, otherworldly technologies—the sort that have figured in science fiction tales for years. These innovations include invisibility cloaks that could mask the presence of objects or their electromagnetic signatures, “unfeelability cloaks” that could mechanically mask the tactile feel of an object, superlenses that could resolve features too small to be seen with ordinary microscope lenses, and power absorbers that could capture essentially all of the sunlight hitting a solar cell.

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Graphene Circuit Competes Head-to-Head With Silicon Technology

IBM has built on their previous graphene research and developed what is being reported as the best graphene-based integrated circuit (IC) built to date, with 10 000 times better performance than previously reported efforts.

This graphene-based IC serves as a radio frequency receiver that performs signal amplification, filtering and mixing. In tests, the IBM team was able to use the circuit to send text messages (in this case, “IBM”) without any distortion.

“This is the first time that someone has shown graphene devices and circuits to perform modern wireless communication functions comparable to silicon technology,” IBM Research director of physical sciences Supratik Guha said in a release.

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Spray-On Technique Could Bring Carbon Nanotubes to Retailers’ Shelves

Carbon nanotubes appear to be getting back some of their glory—after seemingly being eclipsed by graphene—with the news yesterday that an entire computer could be made from the material.  Now researchers at Technische Universität München (TUM) in Germany are continuing the carbon nanotube comeback with a new, inexpensive process that promises to enable their use in a wide range of applications including electronic skin and sensors integrated into food packaging.

The process, which involves simply spraying the carbon nanotubes onto a flexible, plastic substrate, is described in the journal Carbon (“Fabrication of carbon nanotube thin films on flexible substrates by spray deposition and transfer printing”)

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Nanostructured Ceramic Coatings Enable the Potential of Thermophotovoltaics

The concept of the thermophotovoltaic (TPV) device has been around for more than 50 years.  In that time, its promise of a theoretical conversion efficiency of over 80 percent has been a tantalizing improvement over the still meek conversion efficiencies found in the average commercially available single-junction, silicon-based solar cells that reach just 15 percent.

Despite their theoretical promise, TPV devices haven’t been able to achieve much higher than 8 percent conversion efficiency. The problem has been that the thermal emitter (one of the two main components that make up a TPV device, the other being the photovoltaic diode) has yet to be made of a material that can withstand the temperatures required to make it effective.

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Band-Gap Engineering of Nanowires Could Boost Batteries

The reason for replacing graphite in the electrodes of the ubiquitous lithium-ion (Li-ion) battery is clear to anyone who uses a smartphone: The batteries run out of charge in just a few hours under regular use.

One answer has been to replace the graphite with silicon. Unfortunately, the expanding and contracting that occurred as the lithium ions transported in and out of silicon electrodes quickly cracks it.

The next solution was to create “nanostructured silicon” electrodes, sometimes with the help of graphene or good old carbon nanotubes.

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Silicon and Graphene: Two Great Materials That Stay Great Together

The use of graphene as a transparent conducting film has been hotly pursued of late, in large part because it offers a potentially cheaper alternative to indium tin oxide (ITO) where a bottleneck of supply seems to be looming.

It has not been clear whether photovoltaic manufacturers have taken any interest in graphene as an alternative for transparent conducting films. This lack of interest may in part be the result of there being little research into whether graphene maintains its attractive characteristic of high carrier mobility when used in conjunction with silicon.

Now researchers at the Helmholtz Zentrum Berlin (HZB) Institute in Germany have shown that graphene does not lose its impressive conductivity characteristics even when mated with silicon.

“We examined how graphene’s conductive properties change if it is incorporated into a stack of layers similar to a silicon based thin film solar cell and were surprised to find that these properties actually change very little,” said Marc Gluba of the HZB Institute for Silicon Photovoltaics in a press release.

The research, which was published in the journal Applied Physics Letters (“Embedded graphene for large-area silicon-based devices”), used the method of growing the graphene by chemical vapor deposition on a copper sheet and then transferring it to a glass substrate. This was then covered with a thin film of silicon.

The researchers experimented with two different forms of silicon commonly used in thin-film technologies: amorphous silicon and polycrystalline silicon. In both cases, despite completely different morphology of the silicon, the graphene was still detectable.

“That’s something we didn’t expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon,” said Norbert Nickel, another researcher on the project, in a press release.

In their measurements, the researchers determined that the carrier mobility of the graphene layer was roughly 30 times greater than that of conventional zinc oxide-based contact layers.

Although the researchers concede that connecting the graphene-based contact layer to external contacts is difficult, it has garnered the interest of their thin-film technology colleagues. “Our thin film technology colleagues are already pricking up their ears and wanting to incorporate it,” Nickel adds.

Ref: http://spectrum.ieee.org/nanoclast/semiconductors/nanotechnology/silicon-and-graphene-two-great-materials-that-stay-great-together

Spray-On Technique Could Bring Carbon Nanotubes to Retailers’ Shelves

Carbon nanotubes appear to be getting back some of their glory—after seemingly being eclipsed by graphene—with the news yesterday that an entire computer could be made from the material.  Now researchers at Technische Universität München (TUM) in Germany are continuing the carbon nanotube comeback with a new, inexpensive process that promises to enable their use in a wide range of applications including electronic skin and sensors integrated into food packaging.

The process, which involves simply spraying the carbon nanotubes onto a flexible, plastic substrate, is described in the journal Carbon (“Fabrication of carbon nanotube thin films on flexible substrates by spray deposition and transfer printing”)

“To us it was important to develop an easily scalable technology platform for manufacturing large-area printed and flexible electronics based on organic semiconductors and nanomaterials,” said postdoctoral researcher Alaa Abdellah in a press release. “To that end, spray deposition forms the core of our processing technology.”

In the food packaging application, the carbon nanotubes would serve as gas sensors. Nanotubes have long proven themselves to be good sensors. They can be made to bind to certain substances, which changes the electrical properties of the nanotubes in a way that can be measured with a high degree of sensitivity.

In practical applications, the carbon-nanotube-enabled plastic would cover a grocery store product like chicken. If the product contained the chemical indicators of, say, salmonella, the packaging would detect them and alert the consumer.

While this sounds great, the obstacle preventing this from becoming a reality has always been cost. Thin-film sensory packaging may make sense for a high-cost item, but for an inexpensive grocery store product, it’s hard to justify an additional cost that may be as much as the product itself. I made this point nearly a decade ago in report I authored titled, “The Future of Nanotechnology in Printing and Packaging”.

This doesn’t even take into account the often biased opinion people have about nanotechnology in relation to food.

For these reasons, I recommend that the researchers focus their attention on high-ticket applications such as electronic skin for robotics and bionics. In those applications, they will likely find greater resistance to the fear mongering practiced by the NGOs. And it just might make more economic sense to adopt their technology for those applications.

Image: Uli Benz/TUM

Ref: http://spectrum.ieee.org/nanoclast/semiconductors/nanotechnology/spray-on-technique-could-bring-carbon-nanotubes-to-retailers-shelves