Plasmonic device converts light into electricity

By Lisa Zyga

Surface plasmons on the top electrode in the MIM device can increase the current from the top electrode so that it is greater than the current from the bottom electrode, generating a positive net current. Image credit: Wang and Melosh. ©2011 American Chemical Society

While the most common device for converting light into electricity may be photovoltaic (PV) solar cells, a variety of other devices can perform the same light-to-electricity conversion, such as solar-thermal collectors and rectennas. In a new study, engineers have designed a new device that can convert light of infrared (IR) and visible wavelengths into direct current by using surface plasmon excitations in a simple metal-insulator-metal (MIM) device.

The researchers, Fuming Wang and Nicholas A. Melosh of Stanford University, have published their study on the new device in a recent issue of Nano Letters. “The greatest significance thus far is to show an alternative method to rectennas and PV devices for IR and visible light conversion,” Melosh told PhysOrg.com. “The conversion efficiencies aren't amazingly high compared to a PV in visible, so it’s not going to replace PVs, but it could be used for energy scavenging later on.” The new device’s MIM architecture is similar to that of a rectenna. However, whereas rectennas operate with long-wavelength light such as microwaves and radio waves, the new device operates with a broad spectrum of infrared to visible wavelengths. When the MIM device is illuminated, incoming photons are absorbed by the top and bottom metal electrodes. Upon absorption, each photon excites an electron in the metal into a higher energy state so that it becomes a “hot electron.” About half of the hot electrons travel toward the metal-insulator interface, where they may be collected by the other electrode. However, photon absorption in the upper and lower electrodes generates currents with opposite signs, so a net DC current is achieved only if the absorption is larger at one electrode than the other.

Electron transmission in MIM devices (a) with and (b) without surface plasmon excitations. (c) The measured photocurrent in a device with surface plasmons (black line) is higher than in a device without them (red line). Image credit: Wang and Melosh. ©2011 American Chemical Society

This ability to maximize current from one electrode while minimizing it from the other is one of the biggest challenges for MIM devices. To do this, researchers can change the thicknesses of the electrodes. However, there is a tradeoff, since in a thicker electrode, more photons are absorbed but fewer electrons reach the interface due to increased scattering. Wang and Melosh’s solution is to use a prism to excite surface plamons (SPs) on the metal surface of the electrodes when under illumination. The SPs, which are small electron oscillations, can create a higher concentration of hot electrons in one electrode by efficiently coupling to light. The SP coupling efficiency depends on several factors, such as the thickness of the electrode, the type of metal used, and the wavelength of incoming light.

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Plasmonic device converts light into electricity
More information: Fuming Wang and Nicholas A. Melosh. “Plasmonic Energy Collection through Hot Carrier Extraction.” Nano Letters, DOI: 10.1021/nl203196z

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Sex is best when you lose your head

Review by James Meek

• Promiscuity: An Evolutionary History of Sperm Competition and Sexual Conflict by Tim Birkhead
  
  Faber, 272 pp, £9.99, May 2000, ISBN 0 371 19360 5

In 1853 the Reverend Frederick Morris, an opponent of Charles Darwin’s and a man with a Victorian sense of propriety, urged his parishioners to emulate the fidelity of a small bird called the dunnock. Be thou like the dunnock, he told them – the female and the male impeccably faithful to each other.

Charles Robert Darwin. A copy made by John Collier (1850-1934) in 1883 of his 1881 portrait of Charles Darwin. According to Darwin's son Erasmus, "The picture is a replica of the one in the rooms in the Linnaean Society and was made by Collier after the original. I took some trouble about it and as a likeness it is an improvement on the original." Given to the National Portrait Gallery, London in 1896. See source website for additional information. (Photo credit: Wikipedia)

What would the Rev. Morris have made of the scandalous truth? Far from being monogamous, the dunnocks, from a Victorian point of view, have shockingly lax morals. The female dunnock often takes not one but two males as partners. The best a stern man of religion could say about dunnocks is that there’s no superfluous bump and grind when they mate – it’s strictly fertilisation business, over in 0.1 seconds. Fast enough to do it while your mother’s back is turned.

Tim Birkhead and his fellow evolutionary biologists, exploring the nature of sexuality across species from single-celled organisms to humankind, are the paparazzi of the science world. They travel to remote islands and put up with extreme discomfort in the hope of catching animals having sex with each other, and when they do, splash their names and their pictures over the pages of the science journals. It doesn’t always work out. Fiona Hunter and a colleague, later to expose what the mainstream media dubbed ‘penguin prostitution’ in the Antarctic, once watched a colony of fulmars on Fair Isle for 56 days on the trot, 18 hours a day, only to find the species relatively faithful: a mere 16 per cent of females had sex with a bird who wasn’t their partner, and there were no ‘illegitimate’ chicks. This isn’t a glamorous pursuit. Geoff Parker, one of the human heroes of Birkhead’s story, spent months with his face a few centimetres away from fresh cowpats, watching female dungflies being aggressively mounted by two males in turn. Sometimes the biologists witness scenes more disturbing than they had anticipated: Mats Olsson, observing the rape-like mating of the Lake Eyre dragon in Australia, saw a male lizard bite his female victim so hard while impregnating her that she died.

Often it is not enough to be a mere voyeur with a long lens. Like a manipulative aristocrat in a Jacobean drama, the intrepid investigator arranges things: Birkhead gets live zebra finches to mate with dead ones, Nicholas Davies and Ian Hartley make it possible for female dunnocks to take a third husband.

A Dunnock, Prunella modularis, photographed in Torquay, Devon, England in April 2008. (Photo credit: Wikipedia)

Decades of accumulated work of this kind have changed our understanding of the nature of sex, reproduction and the different roles of male and female. From Darwin’s time up to the late 1960s – not coincidentally, the time when the intellectual assault on male-centred academic thinking got under way in earnest – it was thought that male animals competed for female partners, with the strongest and most attractive impregnating the most females; that females sought only monogamy, and if they did have sex with multiple partners (and biologists couldn’t help noticing that they did) it was against their will, always a form of submission to rape.
In the past thirty years, the conventional wisdom has been destroyed. The truth is that females of most species actively seek multiple partners to have sex with. If the aim of males is to put their sperm into as many females as possible, females are trying, with equal determination, to get the very best sperm to fertilise their eggs – even if that means having sex with many males in turn.

Rivalry between males and discrimination by females extends beyond the sexual act itself. Inside the female, the sperm of different males fight for supremacy – this is sperm competition. At the same time, the female may be able to select the sperm that are best for her – this is sperm choice. This is the true battle of the sexes. The males and females of each species are permanently locked in a struggle to out-evolve each other as their reproductive equipment and behaviour change to achieve their conflicting aims – i.e. maximum fertilisation v. best fertilisation.

Can quantum theory be improved?

by Lisa Zyga

A source emits two spin-half particles traveling to two distant sites where each particle’s spin is measured by a detector. If the particles are initially maximally entangled, then the probability of correctly predicting the result of the measurement on either one of the entangled particles is, according to quantum mechanics, 0.5. Image credit: Stuart, et al. ©2012 American Physical Society

Being correct 50% of the time when calling heads or tails on a coin toss won’t impress anyone. So when quantum theory predicts that an entangled particle will reach one of two detectors with just a 50% probability, many physicists have naturally sought better predictions. The predictive power of quantum theory is, in this case, equal to a random guess. Building on nearly a century of investigative work on this topic, a team of physicists has recently performed an experiment whose results show that, despite its imperfections, quantum theory still seems to be the optimal way to predict measurement outcomes.

The physicists, Terence E. Stuart, et al., from the University of Calgary in Alberta, Canada; ETH Zurich in Switzerland; and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, have published their paper on the predictive power of quantum theory and alternative theories in a recent issue of Physical Review Letters.

“The fact that certain outcomes can only be predicted with probability 50% by quantum theory could in principle be explained in two very different ways,” coauthor Renato Renner of ETH Zurich told Phys.org. “One would be that quantum theory is an incomplete theory whose predictions are only random because we have not yet discovered the parameters that are relevant for determining the outcomes (and that another yet-to-be-discovered theory would therefore allow for better predictions). The other explanation would be that there is ‘inherent’ randomness in Nature. Our work excludes the first possibility. In other words, it is not only quantum theory that predicts randomness, but there is ‘real’ randomness in Nature.”

The physicists began by asking whether it may be possible to improve quantum theory’s predictive power by supplementing it with some additional information (i.e., a local hidden variable). With complete information about a scenario, classical theories can predict an outcome with 100% accuracy. But in the 1960s, physicist John Bell proved that no local hidden variable exists that could enable quantum theory to predict an outcome with complete certainty.

However, Bell’s work didn’t rule out the possibility that quantum theory’s predictive power could be improved a little bit, nor did it refute the existence of any alternative probabilistic theory that has more predictive power than quantum theory.

One recent proposal for improving quantum mechanical prediction was suggested by physicist Tony Leggett in 2003. In this model, a hidden spin vector could increase the predictive probability of quantum theory by 0.25, from 0.5 to 0.75 (with 1.0 being complete certainty). Although Leggett showed that this model is incompatible with quantum theory, there has been no reason to assume that other models don’t exist.
Read more...

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A Skeptic Looks at Alternative Energy

Illustration: Dan Page

In June 2004 the editor of an energy journal called to ask me to comment on a just-announced plan to build the world’s largest photovoltaic electric generating plant. Where would it be, I asked—Arizona? Spain? North Africa? No, it was to be spread among three locations in rural Bavaria, southeast of Nuremberg.

I said there must be some mistake. I grew up not far from that place, just across the border with the Czech Republic, and I will never forget those seemingly endless days of summer spent inside while it rained incessantly. Bavaria is like Seattle in the United States or Sichuan province in China. You don’t want to put a solar plant in Bavaria, but that is exactly where the Germans put it. The plant, with a peak output of 10 megawatts, went into operation in June 2005.

It happened for the best reason there is in politics: money. Welcome to the world of new renewable energies, where the subsidies rule—and consumers pay.

Increasing processor efficiency by 'shutting off the lights'

To promote energy-efficient multitasking, Harvard graduate student Wonyoung Kim has developed and demonstrated a new device with the potential to reduce the power usage of modern processing chips.

Image courtesy of Wonyoung Kim

The multicore voltage regulator responds almost instantaneously to changes in power demand from each core of the processor. As a result, the power supply matches the demand more closely, conserving energy.

There was a time when a laptop could weigh 10 pounds and still sell, a time when a cell phone was larger than a pocket, and a time when an iPod played only music.
Today’s consumers expect mobile devices that are both smaller and more powerful. All the bells and whistles, however, suck up energy — and a phone that lasts only four hours because it’s also a GPS device is only so useful.
To promote energy-efficient multitasking, Harvard graduate student Wonyoung Kim has developed and demonstrated a new device with the potential to reduce the power usage of modern processing chips.
The advance could allow the creation of “smarter” smartphones, slimmer laptops, and more energy-friendly data centers.
Kim’s on-chip, multicore voltage regulator (MCVR) addresses what amounts to a mismatch between power supply and demand.
“If you’re listening to music on your MP3 player, you don’t need to send power to the image and graphics processors at the same time,” Kim says. “If you’re just looking at photos, you don’t need to power the audio processor or the HD video processor.
“It’s like shutting off the lights when you leave the room.”

 Continue reading here...

Also on Physorg here...

NIST Demonstrates First Quantum 'Entanglement' of Ions Using Microwaves

Laura Ost @ NIST.GOV

Physicists at the National Institute of Standards and Technology (NIST) have, for the first time, linked the quantum properties of two separated ions (electrically charged atoms) by manipulating them with microwaves instead of the usual laser beams. The feat raises the possibility of replacing today's complex, room-sized quantum computing "laser parks" with miniaturized, commercial microwave technology similar to that used in smart phones.

Gold ion trap on aluminum nitride backing. In NIST microwave quantum computing experiments, two ions hover above the middle of the square gold trap, which measures 7.4 millimeters on a side. Scientists manipulate and entangle the ions using microwaves fed into wires on the trap from the three thick electrodes at the lower right. Credit: Y. Colombe/NIST View hi-resolution bottom image

Microwaves have been used in past experiments to manipulate single ions, but the NIST group is the first to position microwaves sources close enough to the ions—just 30 micrometers away—and create the conditions enabling entanglement, a quantum phenomenon expected to be crucial for transporting information and correcting errors in quantum computers.

Described in the August 11, 2011, issue of Nature,* the experiments integrate wiring for microwave sources directly on a chip-sized ion trap and use a desktop-scale table of lasers, mirrors and lenses that is only about one-tenth of the size previously required. Low-power ultraviolet lasers still are needed to cool the ions and observe experimental results but might eventually be made as small as those in portable DVD players. Compared to complex, expensive laser sources, microwave components could be expanded and upgraded more easily to build practical systems of thousands of ions for quantum computing and simulations.

"It's conceivable a modest-sized quantum computer could eventually look like a smart phone combined with a laser pointer-like device, while sophisticated machines might have an overall footprint comparable to a regular desktop PC," says NIST physicist Dietrich Leibfried, a co-author of the new paper.

Quantum computers would harness the unusual rules of quantum physics to solve certain problems—such as breaking today's most widely used data encryption codes—that are currently intractable even with supercomputers. A nearer-term goal is to design quantum simulations of important scientific problems, to explore quantum mysteries such as high-temperature superconductivity, the disappearance of electrical resistance in certain materials when sufficiently chilled.

Ions are a leading candidate for use as quantum bits (qubits) to hold information in a quantum computer. Although other promising candidates for qubits—notably superconducting circuits, or "artificial atoms"—are manipulated on chips with microwaves, ion qubits are at a more advanced stage experimentally in that more ions can be controlled with better accuracy and less loss of information.

The use of microwaves reduces errors introduced by instabilities in laser beam pointing and power as well as laser-induced spontaneous emissions by the ions. However, microwave operations need to be improved to enable practical quantum computations or simulations. The NIST researchers achieved entanglement 76 percent of the time, well above the minimum threshold of 50 percent defining the onset of quantum properties but not yet competitive with the best laser-controlled operations at 99.3 percent.

The research was supported by the Intelligence Advanced Research Projects Activity, Office of Naval Research, Defense Advanced Research Projects Agency, National Security Agency and Sandia National Laboratories.

For more details, see the NIST  news announcement "NIST Physicists 'Entangle' Two Atoms Using Microwaves for the First Time" at www.nist.gov/pml/div688/microwave-quantum-081011.cfm.

 

Interstellar Travel Not Possible Before 2200AD, Suggests Study

A new estimate of the amount of energy needed to visit the stars suggests we won't have enough for at least another two centuries

By KFC  @ [Source]

How soon could humanity launch a mission to the stars? That's the question considered today by Marc Millis, former head of NASA's Breakthrough Propulsion Physics Project and founder of the Tau Zero Foundation which supports the science of interstellar travel.

This is a question of increasing importance given the rate at which astronomers are finding new planets around other stars. Many believe that it's only a matter of time before we find an Earth analogue. And when we do find a place with the potential to host life like ours, there is likely to be significant debate about the possibility of a visit.

The big problem, of course, is distance. In the past, scientists have studied various factors that limit our ability to traverse the required lightyears. One is the speed necessary to travel that far, another is the cost of such a trip.

By looking at the rate at which our top speed and financial clout are increasing, and then extrapolating into the future, it's possible to predict when such missions might be possible. The depressing answer in every study so far is that interstellar travel is centuries away.

Today, Millis takes a different approach. He looks at the energy budget of interstellar missions. By looking at the rate at which humanity is increasing the energy it has available and extrapolating into the future, Millis is able to estimate when we will have enough to get to the stars.

To make his extrapolation, Millis looked at the amount of energy the US has used to launch the shuttle over the last thirty years or so, as a fraction of the total energy available to the country. He assumes that a similar fraction will be available for interstellar flight in future. He then calculates how much energy two different types of mission will consume.

The first mission is a human colony of 500 people on a one-way journey into the void. He assumes that such a mission requires 50 tones per human occupant and that each person will use about 1000W, equal to the average amount used by people in the US in 2007.

From this, he estimates that the ship would need some 10^18 Joules for rocket propulsion. That compares to a shuttle launch energy of about 10^13 Joules

The second mission is an unmanned probe designed to reach Alpha Centauri, just over 4 light years away, in 71 years. Such a ship would be some three orders of magnitude less massive than a colony ship so it's easy to imagine that it would require less energy.

But Millis places another constraint on this mission. Not only must it accelerate towards its destination, it must decelerate when it gets there (although why this isn't a requirement for a colony ship isn't clear).

That changes the the numbers significantly. Millis estimates that the probe would require some 10^19 Joules.

The final step in is to determine when humanity will have this kind of energy available for these kinds of missions. By extrapolation, Millis calculates that the required energy will not be available until at least the year 2196. "This study found that the first interstellar mission does not appear possible for another 2 centuries centuries," he says.

That's necessarily a crude calculation but a sobering one nonetheless. It implies that while we will soon be able to gaze with wonder upon other Earths, it will not be possible to visit them within the lifetime of anybody alive today.

In other words, for the foreseeable future, we're trapped.

Ref: arxiv.org/abs/1101.1066: Energy, Incessant Obsolescence And The First Interstellar Missions

 

 

New combination of nanoparticles and graphene results in a more durable catalytic material for fuel cells

Mary Beckman, PNNL [Source]

Bracing catalyst in material makes fuel cell component work better and last longer

A nanoparticle of indium tin oxide (green and red) braces platinum nanoparticles (blue) on the surface of graphene (black honeycomb) to make a hardier, more chemically active fuel cell material. A new combination of nanoparticles and graphene results in a more durable catalytic material for fuel cells, according to work published today online at the Journal of the American Chemical Society. The catalytic material is not only hardier but more chemically active as well. The researchers are confident the results will help improve fuel cell design.

"Fuel cells are an important area of energy technology, but cost and durability are big challenges," said chemist Jun Liu. "The unique structure of this material provides much needed stability, good electrical conductivity and other desired properties."

Liu and his colleagues at the Department of Energy's Pacific Northwest National Laboratory, Princeton University in Princeton, N.J., and Washington State University in Pullman, Wash., combined graphene, a one-atom-thick honeycomb of carbon with handy electrical and structural properties, with metal oxide nanoparticles to stabilize a fuel cell catalyst and make it better available to do its job.

"This material has great potential to make fuel cells cheaper and last longer," said catalytic chemist Yong Wang, who has a joint appointment with PNNL and WSU. "The work may also provide lessons for improving the performance of other carbon-based catalysts for a broad range of industrial applications."

Muscle Metal Oxide

Fuel cells work by chemically breaking down oxygen and hydrogen gases to create an electrical current, producing water and heat in the process. The centerpiece of the fuel cell is the chemical catalyst — usually a metal such as platinum — sitting on a support that is often made of carbon. A good supporting material spreads the platinum evenly over its surface to maximize the surface area with which it can attack gas molecules. It is also electrically conductive.

Fuel cell developers most commonly use black carbon — think pencil lead — but platinum atoms tend to clump on such carbon. In addition, water can degrade the carbon away. Another support option is metal oxides — think rust — but what metal oxides make up for in stability and catalyst dispersion, they lose in conductivity and ease of synthesis. Other researchers have begun to explore metal oxides in conjunction with carbon materials to get the best of both worlds.

As a carbon support, Liu and his colleagues thought graphene intriguing. The honeycomb lattice of graphene is porous, electrically conductive and affords a lot of room for platinum atoms to work. First, the team crystallized nanoparticles of the metal oxide known as indium tin oxide — or ITO — directly onto specially treated graphene. Then they added platinum nanoparticles to the graphene-ITO and tested the materials.

Platinumweight

The team viewed the materials under high-resolution microscopes at EMSL, DOE's Environmental Molecular Sciences Laboratory on the PNNL campus. The images showed that without ITO, platinum atoms clumped up on the graphene surface. But with ITO, the platinum spread out nicely. Those images also showed catalytic platinum wedged between the nanoparticles and the graphene surface, with the nanoparticles partially sitting on the platinum like a paperweight.

To see how stable this arrangement was, the team performed theoretical calculations of molecular interactions between the graphene, platinum and ITO. This number-crunching on EMSL's Chinook supercomputer showed that the threesome was more stable than the metal oxide alone on graphene or the catalyst alone on graphene.

But stability makes no difference if the catalyst doesn't work. In tests for how well the materials break down oxygen as they would in a fuel cell, the triple-threat packed about 40% more of a wallop than the catalyst alone on graphene or the catalyst alone on other carbon-based supports such as activated carbon.

Last, the team tested how well the new material stands up to repeated usage by artificially aging it. After aging, the tripartite material proved to be three times as durable as the lone catalyst on graphene and twice as durable as on commonly used activated carbon. Corrosion tests revealed that the triple threat was more resistant than the other materials tested as well.

The team is now incorporating the platinum-ITO-graphene material into experimental fuel cells to determine how well it works under real world conditions and how long it lasts.

---

Reference: Rong Kou, Yuyan Shao, Donghai Mei, Zimin Nie, Donghai Wang, Chongmin Wang, Vilayanur V Viswanathan, Sehkyu Park, Ilhan A. Aksay, Yuehe Lin, Yong Wang, Jun Liu, Stabilization of Electrocatalytic Metal Nanoparticles at Metal-Metal Oxide-Graphene Triple Junction Points, February 8, 2011, J. Am. Chem. Soc., DOI 10.1021/ja107719 (http://pubs.acs.org/doi/full/10.1021/ja107719u.

This work was supported by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy.

High-performance capacitor could lead to better rechargeable batteries

By Lisa Zyga @ physorg.com 

Abstract

Zeolite-templated carbon is a promising candidate as an electrode material for constructing an electric double layer capacitor with both high-power and high-energy densities, due to its three-dimensionally arrayed and mutually connected 1.2-nm nanopores. This carbon exhibits both very high gravimetric (140−190 F g⁻¹) and volumetric (75−83 F cm⁻³) capacitances in an organic electrolyte solution. Moreover, such a high capacitance can be well retained even at a very high current up to 20 A g⁻¹. This extraordinary high performance is attributed to the unique pore structure.

The unique 3D array of nanopores in zeolite-templated carbon enables it to be used as an electrode for high-performance supercapacitors that have a high capacitance and quick charge time. Image credit: Hiroyuki Itoi, et al. ©2011 American Chemical Society.

In order to develop next-generation electric vehicles, solar energy systems, and other clean energy technologies, researchers need an efficient way to store the energy. One of the key energy storage devices for these applications and others is a supercapacitor, also called an electric double-layer capacitor. In a recent study, scientists have investigated the possibility of using a material called zeolite-templated carbon for the electrode in this type of capacitor, and found that the material’s unique pore structure greatly improves the capacitor's overall performance.

To store energy, the electric double-layer capacitor is charged by ions that migrate from a bulk solution to an electrode, where they are adsorbed. Before reaching the electrode’s surface, the ions have to travel through narrow nanopores as quickly and efficiently as possible. Basically, the quicker the ions can travel down these paths, the quicker the capacitor can be charged, resulting in a high rate performance. Also, the greater the adsorbed ion density in the electrode, the greater the charge that the capacitor can store, resulting in a high volumetric capacitance.

Recently, scientists have been testing materials with pores of various sizes and structures to try to achieve both quick ion transport and high adsorption ion density. But the two requirements are somewhat contradictory, since ions can travel more quickly through larger nanopores, but large nanopores make the electrode density low and thus decrease the adsorbed ion density.

The zeolite-templated carbon consists of nanopores that are 1.2 nm in diameter (smaller than most electrode materials) and that have a very ordered structure (whereas other pores can be disordered and random). The nanopores’ small size makes the adsorbed ion density high, while the ordered structure – described as a diamond-like framework – allows the ions to quickly pass through the nanopores. In a previous study, the researchers showed that zeolite-templated carbon with nanopores smaller than 1.2 nm cannot enable fast ion transport, suggesting that this size may provide the optimal balance between high rate performance and high volumetric capacitance.

In tests, the zeolite-templated carbon’s properties exceeded those of other materials, demonstrating its potential to be used as an electrode for high-performance electric double-layer capacitors.

More information: Hiroyuki Itoi, et al. “Three-Dimensionally Arrayed and Mutually Connected 1.2-nm Nanopores for High-Performance Electric Double Layer Capacitor.” Journal of the American Chemical Society. DOI:10.1021/ja108315p