Casimir Force Reduced to Lowest Recorded Level through metallic surface nanostructuring

A research team that includes a physics professor at Indiana University-Purdue University Indianapolis (IUPUI) has recorded a drastically reduced measurement of the Casimir effect, a fundamental quantum phenomenon experienced between two neutral bodies that exist in a vacuum.

The experiment revealed the Casimir pressure was reduced at more than twice the expected levels when the sphere and the grating surface were separated from one another by up to 500 nanometers.

Nature Communication - Strong Casimir force reduction through metallic surface nanostructuring

The Casimir force between bodies in vacuum can be understood as arising from their interaction with an infinite number of fluctuating electromagnetic quantum vacuum modes, resulting in a complex dependence on the shape and material of the interacting objects. Becoming dominant at small separations, the force has a significant role in nanomechanics and object manipulation at the nanoscale, leading to a considerable interest in identifying structures where the Casimir interaction behaves significantly different from the well-known attractive force between parallel plates. Here we experimentally demonstrate that by nanostructuring one of the interacting metal surfaces at scales below the plasma wavelength, an unexpected regime in the Casimir force can be observed. Replacing a flat surface with a deep metallic lamellar grating with sub-100 nm features strongly suppresses the Casimir force and for large inter-surfaces separations reduces it beyond what would be expected by any existing theoretical prediction.

POSTED BY BRIAN WANG AT 10/01/2013

http://nextbigfuture.com/2013/10/casimir-force-reduced-to-lowest.html

Plasmonic nanostructures could prove a boon to solar cell technology

Do 'plasmonic nanostructures' hold the key to next-generation solar power? (Photo: Shutterstock/Pavelk)Image Gallery (2 images)

Researchers at the University of Pennsylvania have found a way to harvest energy from sunlight more efficiently, with the help of so-called plasmonic nanostructures. The new findings suggest that plasmonic components can enhance and direct optical scattering, creating a mechanism that is more efficient than the photoexcitation that drives solar cells. The development could therefore provide a real boost to solar cell efficiency and lead to faster optical communication.

When photons hit the surface of a solar cell, the energy they carry is absorbed by the atoms of a doped semiconductor. If the energy absorbed is higher than a set threshold, known as the energy gap, then electrons are set free and can be used to generate electricity.

Theoretically, the energy gap can be manipulated to maximize the number of electrons that will be set free by a photon; but setting this threshold isn't straightforward, because some photons carry more energy than others.

Photons in the infrared typically don't carry enough energy to knock electrons off a silicon atom. Red photons carry just enough energy to knock down a single electron, and photons in the blue spectrum and beyond carry enough to knock off one electron, but the rest of the energy is wasted as heat. This large amount of wasted energy compromises solar cell efficiency.

Plasmonic nanostructures could significantly
enhance the efficiency of solar cells (Image: University of Pennsylvania)

Building on their previous work, Prof. Dawn Bonnell and colleagues have now demonstrated that there is another way to harvest energy from light – a method that has tested up to 10 times more efficient than conventional photoexcitation and that could greatly improve the efficiency of solar cells and optoelectronic devices that convert light signals into electricity.

The University of Pennsylvania researchers focused on plasmonic nanostructures, materials made from arrays of gold nanoparticles and light-sensitive molecules of porphyin arranged in specific patterns.

When a photon hits these structures, it generates an electrical current that moves in a direction controlled by the size and the layout of the gold particles. By controlling and enhancing the way light scatters across them, these nanostructures can transduce light into electricity more efficiently than was previously possible. The freed up electrons can then be extracted from the plasmons and used to power molecular electronic optoelectronic devices.

Since their first results in 2010, the researchers led by Prof. Bonnell had suspected that their method could lead to significant increases in performance, but they couldn't prove it. Now, in this new study, they managed to do just that.

"In our measurements, compared to conventional photoexcitation, we saw increases of three to 10 times in the efficiency of our process," Bonnell says. "And we didn’t even optimize the system. In principle you can envision huge increases in efficiency."

"Light impinges on an array of metal nanoparticles connected with optically active molecules, and the resulting current is detected across the array," Prof. Bonnell tells Gizmag. "This process can produce more electrons in principle. You can imagine building energy harvesting devices made of the nanoparticles and organic molecules, or you could envision putting the nanoparticles into a silicon solar cell."

The nanostructures can be optimized for specific applications by changing the size and spacing of the nanoparticles, which would alter the wavelength of light to which the plasmon responds, in the same way that multi-junction solar cells are built to absorb photons of different wavelengths more effectively.

Applications could include the more efficient transduction of optical signals (e.g. from fiber optics) into electrical signals and, of course, more efficient solar cell technology. "You could imagine having a paint on your laptop that acted like a solar cell to power it using only sunlight," Bonnell says.

Promising as they may sound, we must remember that these results are largely theoretical; through this study the researchers have shown that generating electricity using plasmonic nanostructures can be more efficient than by using standard photoexcitation, but there's no telling how soon devices exploiting this principle could reach mass-production, or even what kind of actual efficiency gains they could bring.

The results were recently published on the journal ACS Nano.

Source: University of Pennsylvania

By Dario Borghino

September 15, 2013

http://www.gizmag.com/plasmonic-nanostructures-solar/29067/

Des nanostructures pour produire de l'hydrogène solaire

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Dans la perspective de la montée en puissance des véhicules à hydrogène et du fort développement des énergies renouvelables, tant sur le plan thermique que pour la production d'électricité, la production massive et propre d'hydrogène va devenir absolument nécessaire dans les années qui viennent.

Des chercheurs de l'Ecole polytechnique fédérale de Lausanne, associés à des scientifiques du centre israélien Technion ont réussi, grâce à l'utilisation du microscope électronique en transmission (TEM), à concevoir des nanostructures d'oxyde de fer qui devraient permettre de produire de l'hydrogène propre à un faible coût. « L'originalité de notre approche consiste à utiliser la rouille, un matériau particulièrement abondant, stable et bon marché », précise Michael Grätzel qui dirige ces recherches.

Ce chercheur mondialement connu, directeur du Laboratoire de photonique et interfaces de l'EPFL, a notamment découvert et perfectionné les cellules photoélectrochimiques à colorant, qui pourraient permettre d'ici quelques années d'apposer partout des revêtements solaires photovoltaïques à très faible coût.

Actuellement, une cellule photovoltaïque classique, couplée à un électrolyseur, produit de l'hydrogène à un coût d'au moins 15 euros par kilo. Avec ces nanostructures en oxyde de fer, les scientifiques espèrent diviser ce coût par trois et descendre à cinq euros le kilo.

Article rédigé par Georges Simmonds pour RT Flash

Nature

Jeudi, 18/07/2013 - 07:51

http://www.rtflash.fr/nanostructures-pour-produire-l-hydrogene-solaire/article