Wednesday, February 23, 2011

Scientists elevate warfighter readiness against invisible threats

 In asymmetric warfare, early detection and identification of trace level chemical and biological agents and explosive compounds is critical to rapid reaction, response, and survivability. While there are many methods currently being used that can detect these threats, none allow for the unique fingerprinting of threat agents at trace levels.

A research team, led by Drs. Joshua Caldwell and Orest Glembocki, scientists at the U.S. Naval Research Laboratory, Electronic Science and Technology Division, has overcome this limitation with surface enhanced Raman scattering (SERS) using optically stimulated plasmon oscillations in nanostructured substrates.

Shown to provide enhancements of the Raman signal, large-area gold (Au) coated silicon (Si) nanopillar arrays are over 100 million times (108) more sensitive than Raman scattering sensing alone, while maintaining a very uniform response with less than 30 percent variability across the sensor area.

"These arrays are over an order-of-magnitude more sensitive than the best reported SERS sensors in the literature and the current state-of-the-art large-area commercial SERS sensors," said Caldwell. "These arrays can be a key component of fully integrated, autonomously operating chemical sensors that detect, identify and report the presence of a threat at trace levels of exposure."

Raman devices use laser light to excite molecular vibrations, which in turn causes a shift in the energy of the scattered laser photons, up or down, creating a unique visual pattern. In the case of trace amounts of molecules in gases or liquids, detection through ordinary Raman scattering is virtually impossible. However, the Raman signal can be enhanced via the SERS effect using metal nanoparticles.

Despite surface-enhanced Raman scattering being first observed in the late 1970s, efforts to provide reproducible SERS-based chemical sensors has been hindered by the inability to make large-area devices with a uniform SERS response. The ability to reproducibly pattern nanometer-sized particles in periodic arrays has finally allowed this requirement to be met.

"While many tools are currently available to detect trace amounts of chemical warfare and biological agents and explosive compounds, a device using SERS can be used to identify these minute quantities of the chemicals of interest by providing a 'fingerprint' of the material, which all but eliminates the prevalence of false alarms," says Glembocki.

SERS offers several potential advantages over other spectroscopic techniques because of its measurement speed, high sensitivity, portability, and simple maneuverability. SERS can additionally be used to enhance existing Raman technologies, such as the hand held and standoff units that are already in use in field applications.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Naval Research Laboratory.

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New method takes snapshots of proteins as they fold

Scientists have invented a way to 'watch' proteins fold -- in less than thousandths of a second -- into the elaborate twisted shapes that determine their function.

People have only 20,000 to 30,000 genes (the number is hotly contested), but they use those genes to make more than 2 million proteins. It's the protein molecules that do most of the work in the human cell. After all, the word protein comes from the Greek prota, meaning "of primary importance."

Proteins are created as chains of amino acids, and these chains of usually fold spontaneously into what is called their "native form" in milliseconds or a few seconds.

A protein's function depends sensitively on its shape. For example, enzymes and the molecules they alter are often described as fitting together like a lock and key. By the same token, misfolded proteins are behind some of the most dreaded neurodegenerative diseases, such as Alzheimer's, Parkinson's and mad cow disease.

Scientists can't match the speed with which proteins fold. Predicting how chains of amino acids will fold from scratch requires either powerful supercomputers or cloud sourcing (harnessing the pattern recognition power of thousands of people by means of games such as Folding@home).

Either way, prediction is time-consuming and often inaccurate, so much so that the protein-structure bottleneck is slowing the exploitation of DNA sequence data in medicine and biotechnology.

A clever way of watching proteins fold and unfold may finally provide the kind of detail needed to improve protein structure predictions.

In a recent issue of the online version of the Journal of the American Chemical Society three scientists, led by Michael L. Gross, PhD, professor of chemistry in Arts & Sciences and of medicine and immunology in the School of Medicine at Washington University in St. Louis, describe a proof-of-principle study in which they use the new approach to watch the folding of a small protein called barstar.

What they do is roughly analogous to filming flying bullets or bursting balloons with a stroboscope and a fast camera. The "stills" taken by the camera slow motion to the point that normally imperceptible events are laid open to scrutiny.

The scientists are using a version of this old trick to "watch" proteins fold. The "strobe light" is a temperature jump and the "camera" is a fast chemical reaction whose outcome is measured by a sensitive mass spectrometer.

Why folding is a complex problem

One of the dogmas of modern biology is that the sequence of amino acids determines how a protein will fold. If the amino acid sequence is known, it should be possible to calculate the protein's final structure from scratch.

But like many things in life, it's harder than it looks.

"Think of a protein as thousands of atoms connected together by springs," says Gross, who is also director of the National Institutes of Health/ National Center for Research Resources (NIH/NCRR) Mass Spectrometry Resource "If you were to suspend this object with a string from the ceiling and let it flop around, imagine how many shapes it could take."

"An enormous number, because it is free to move in so many different ways."

In practice, scientists often predict protein structure not from scratch but by analogy. They sift through large databases for proteins with similar sequences of amino acids and assume similar amino-acid chains will fold in similar ways.

"But," says Gross, "at some point any method for predicting protein structure has to be checked against experimental evidence that shows how proteins actually do fold."

That's what his research is all about.

A model protein for the experiment

Barstar is a small protein synthesized by a soil bacterium that is often used in folding studies.

Importantly, barstar's "native state" is known, as is its primary structure, the sequence of the protein subunits called amino acids of which it is made. What isn't known is how the amino-acid chain twists and coils to form the final structure.

Fortunately for the scientists, barstar, unlike most proteins, is unfolded at zero degrees Celsius and begins to fold as it warms.

The folding takes place in microseconds (thousandths of a second).

How the method works

The scientists begin by injecting a cold solution of barstar and a tiny amount of hydrogen peroxide into an optical fiber so thin it is difficult to believe it is actually hollow.

"Plugs" of sample in the fiber are then hit with two laser pulses in quick succession.

The first pulse, called a T jump, heats the solution just enough to make a different protein conformation energetically favorable.

The second pulse then breaks some of the hydrogen peroxide (H2O2) molecules into two haves, each of which is a very reactive hydroxyl (-OH) radical.

The radicals react with those parts of the protein that are exposed to the solution, "painting" them with oxygen atoms.

"Imagine," says Gross, "that you suspended a styrofoam model of a partially folded protein and spray-painted it blue. The outside parts would be painted blue; those buried within would remain white."

The radical reactions must be terminated rapidly; otherwise some "painting" may occur within the structure. Within a microsecond, a scavenger amino acid clears away any remaining hydroxyl radicals to prevent them from breaking bonds and altering the protein's configuration.

The same process is repeated 500 times, taking rapid-fire "snapshots" of the protein's quickly changing confirmation.

"The hydroxyl radicals don't mark everything," says Gross. "But they mark about half the amino acids, which is really pretty good. Most other chemical reagents are too specific and too slow for this experiment. Compared to hydroxyl radicals they're just plain ponderous."

Weighing the painted proteins

"We collect each drop of marked protein as it emerges from the fiber," says Gross. "Then we digest the protein very slowly and carefully with an enzyme that cleaves the amino acid chains at specific locations, creating a known set of protein fragments, called peptides

These protein fragments are separated according to type by liquid chromatography, and a mass spectrometer then "weighs" each fragment type to see whether it has picked up oxygen atoms.

"Detecting an extra oxygen is child's play for a modern mass spectrometer," says Gross. "Most instruments can even detect an extra proton, with is one-sixteenth the mass of an oxygen atom."

"In the same instrument, on the fly, we break apart the protein fragments and again 'weigh' the bits to see which one still carries the oxygen atom. This lets us deduce the oxygen's location on the original fragment."

By following barstar to its first intermediate state, or way station enroute to its native state, the scientists demonstrated that the new technique can follow folding and unfolding on a submillisecond time scale.

'Massive amounts of detail'

Gross is the first to say that this proof-of-principle experiment stands at the end of a long line of elegant experiments of a similar type, called pump-probe experiments.

Other techniques probe the change in protein structure by monitoring the absorption or emission of light--or a similar physical effect. They can provide only global information, such as the rate constant of a folding reaction.

"Because we use a chemical rather than a physical probe, we can see what's going on in much greater detail," says Gross. "We can say which part of the structure closes first, which second, and so on."

The new technique caught the attention of protein scientist Martin Gruebele of the University of Illinois, who spotlighted it in the Dec. 2, 2010, issue of the journal Nature.

It "could provide truly massive amounts of detail about fast protein folding," wrote Gruebele, which might finally allow scientists "to correctly predict the biologically active structure of a protein starting from the unfolded state."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Washington University in St. Louis. The original article was written by Diana Lutz.

Journal Reference:

Jiawei Chen, Don L. Rempel, Michael L. Gross. Temperature Jump and Fast Photochemical Oxidation Probe Submillisecond Protein Folding. Journal of the American Chemical Society, 2010; 132 (44): 15502 DOI: 10.1021/ja106518d

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Mimicking photosynthesis path to solar-derived hydrogen fuel

Inexpensive hydrogen for automotive or jet fuel may be possible by mimicking photosynthesis, according to a Penn State materials chemist, but a number of problems need to be solved first.

"We are focused on the hardest way to make fuel," said Thomas Mallouk, Evan Pugh Professor of Materials Chemistry and Physics. "We are creating an artificial system that mimics photosynthesis, but it will be practical only when it is as cheap as gasoline or jet fuel."

Splitting water into hydrogen and oxygen can be done in a variety of ways, but most are heavily energy intensive. The resultant hydrogen, which can be used to fuel vehicles or converted into a variety of hydrocarbons, inevitably costs more than existing fossil-based fuels.

While some researchers have used solar cells to make electricity or use concentrated solar heat to split water, Mallouk's process uses the energy in blue light directly. So far, it is much less efficient than other solar energy conversion technologies.

The key to direct conversion is electrons. Like the dyes that naturally occur in plants, inorganic dyes absorb sunlight and the energy kicks out an electron. Left on its own, the electron would recombine creating heat, but if the electrons can be channeled -- molecule to molecule -- far enough away from where they originate, the electrons can reach the catalyst and split the hydrogen from the oxygen in water.

"Currently, we are getting only 2 to 3 percent yield of hydrogen," Mallouk told attendees on Feb. 19 at the annual meeting of the American Association for the Advancement of Science. "For systems like this to be useful, we will need to get closer to 100 percent," he added.

But recombination of electrons is not the only problem with the process. The oxygen-evolving end of the system is a chemical wrecking ball and this means the lifetime of the system is currently limited to a few hours.

"The oxygen side of the cell is making a strong oxidizing agent and the molecules near can be oxidized," said Mallouk. "Natural photosynthesis has the same problem, but it has a self-repair mechanism that periodically replaces the oxygen-evolving complex and the protein molecules around it."

So far, the researchers do not have a fix for the oxidation, so their catalysts and other molecules used in the cell structure eventually degrade, limiting the life of the solar fuel cell.

Currently, the researchers are using only blue light, but would like to use the entire visible spectrum from the sun. They are also using expensive components -- a titanium oxide electrode, a platinum dark electrode and iridium oxide catalyst. Substitutions for these are necessary, and other researchers are working on solutions. A Massachusetts Institute of Technology group is investigating cobalt and nickel catalysts, and at Yale University and Princeton University they are investigating manganese.

"Cobalt and nickel don't work as well as iridium, but they aren't bad," said Mallouk. "The cobalt work is spreading to other institutions as well."

While the designed structure of the fuel cell directs many of the electrons to the catalyst, most of them still recombine, giving over their energy to heat rather than chemical bond breaking. The manganese catalysts in photosystem II -- the photosynthesis system by which plants, algae and photosynthetic bacteria evolve oxygen -- are just as slow as ours, said Mallouk. Photosystem II works efficiently by using an electron mediator molecule to make sure there is always an electron available for the dye molecule once it passes its current electron to the next molecule in the chain.

"We could slow down major recombination in the artificial system in the same way," said Mallouk. "Electron transfer from the mediator to the dye would effectively outrun the recombination reaction."

Currently the system uses only one photon at a time, but a two-photon system, while more complicated, would be more effective in using the full spectrum of sunlight.

Mallouk's main goal now is to track all the energy pathways in his cell to understand the kinetics. Once he knows this, he can model the cells and adjust portions to decrease energy loss and increase efficiency.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Penn State.

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World's smallest magnetic field sensor: Researchers explore using organic molecules as electronic components

Further development of modern information technology requires computer capacities of increased efficiency at reasonable costs. In the past, integration density of the relevant electronic components was increased constantly. In continuation of this strategy, future components will have to reach the size of individual molecules. Researchers from the KIT Center for Functional Nanostructures (CFN) and IPCMS have now come closer to reaching this target.

For the first time, a team of scientists from KIT and the Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS) have now succeeded in combining the concepts of spin electronics and molecular electronics in a single component consisting of a single molecule. Components based on this principle have a special potential, as they allow for the production of very small and highly efficient magnetic field sensors for read heads in hard disks or for non-volatile memories in order to further increase reading speed and data density.

Use of organic molecules as electronic components is being investigated extensively at the moment. Miniaturization is associated with the problem of the information being encoded with the help of the charge of the electron (current on or off). However, this requires a relatively high amount of energy. In spin electronics, the information is encoded in the intrinsic rotation of the electron, the spin. The advantage is that the spin is maintained even when switching off current supply, which means that the component can store information without any energy consumption.

The German-French research team has now combined these concepts. The organic molecule H2-phthalocyanin that is also used as blue dye in ball pens exhibits a strong dependence of its resistance, if it is trapped between spin-polarized, i.e. magnetic electrodes. This effect was first observed in purely metal contacts by Albert Fert and Peter Grünberg. It is referred to as giant magnetoresistance and was acknowledged by the Nobel Prize for Physics in 2007.

The giant magnetoresistance effect on single molecules was demonstrated at KIT within the framework of a combined experimental and theoretical project of CFN and a German-French graduate school in cooperation with the IPCMS, Strasbourg. The results of the scientists are now presented in the journal Nature Nanotechnology.

Karlsruhe Institute of Technology (KIT) is a public corporation and state institution of Baden-Wuerttemberg, Germany. It fulfills the mission of a university and the mission of a national research center of the Helmholtz Association. KIT focuses on a knowledge triangle that links the tasks of research, teaching, and innovation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Karlsruhe Institute of Technology.

Journal Reference:

Stefan Schmaus, Alexei Bagrets, Yasmine Nahas, Toyo K. Yamada, Annika Bork, Martin Bowen, Eric Beaurepaire, Ferdinand Evers, Wulf Wulfhekel. Giant magnetoresistance through a single molecule. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.11

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Nanonets give rust a boost as agent in water splitting's hydrogen harvest

Coating a lattice of tiny wires called Nanonets with iron oxide (rust) creates an economical and efficient platform for the process of water splitting -- an emerging clean fuel method that harvests hydrogen from water, Boston College researchers report in the online edition of the Journal of the American Chemical Society.

Assistant Professor of Chemistry Dunwei Wang and his clean energy lab pioneered the development of Nanonets in 2008 and have since shown them to be a viable new platform for a number of energy applications by virtue of the increased surface area and improved conductivity of the nano-scale netting made from titanium disilicide, a readily available semiconductor.

Wang and his team report that coating the Nanonets with hematite, the plentiful mineral form of iron oxide, showed the mineral could absorb light efficiently and without the added expense of enhancing the material with an oxygen evolving catalyst.

The results flow directly from the introduction of the Nanonet platform, Wang said. While constructed of wires 1/400th the size of a human hair, Nanonets are highly conductive and offer significant surface area. They serve dual roles as a structural support and an efficient charge collector, allowing for maximum photon-to-charge conversion, Wang said.

"Recent research has shown that the use of a catalyst can boost the performance of hematite," said Wang. "What we have shown is the potential performance of hematite at its fundamental level, without a catalyst. By using this unique Nanonet structure, we have shed new light on the fundamental performance capabilities of hematite in water splitting."

On its own, hematite faces natural limits in its ability to transport a charge. A photon can be absorbed, but has no place to go. By giving it structure and added conductivity, the charge transport abilities of hematite increase, said Wang. Water splitting, a chemical reaction that separates water into oxygen and hydrogen gas, can be initiated by passing an electric current through water. But that process is expensive, so gains in efficiency and conductivity are required to make large-scale water splitting an economically viable source for clean energy, Wang said.

"The result highlights the importance of charge transport in semiconductor-based water splitting, particularly for materials whose performance is limited by poor charge diffusion," the researchers report in the journal. "Our design introduces material components to provide a dedicated charge transport pathway, alleviates the reliance on the materials' intrinsic properties, and therefore has the potential to greatly broaden where and how various existing materials can be used in energy-related applications."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Boston College, via EurekAlert!, a service of AAAS.

Journal Reference:

Yongjing Lin, Sa Zhou, Stafford W. Sheehan, Dunwei Wang. Nanonet-Based Hematite Heteronanostructures for Efficient Solar Water Splitting. Journal of the American Chemical Society, 2011; 110209093040054 DOI: 10.1021/ja110741z

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Paperweight for platinum: Bracing catalyst in material makes fuel cell component work better and last longer

A new combination of nanoparticles and graphene results in a more durable catalytic material for fuel cells, according to work published 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.


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.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Pacific Northwest National Laboratory.

Journal 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. Journal of the American Chemical Society, 2011; 110208101227051 DOI: 10.1021/ja107719u

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New technology for cheaper, more efficient solar cells

The sun provides more than enough energy for all our needs, if only we could harness it cheaply and efficiently. Solar energy could provide a clean alternative to fossil fuels, but the high cost of solar cells has been a major barrier to their widespread use.

Stanford researchers have found that adding a single layer of organic molecules to a solar cell can increase its efficiency three-fold and could lead to cheaper, more efficient solar panels. Their results were published online in ACS Nano on Feb. 7.

Professor of chemical engineering Stacey Bent first became interested in a new kind of solar technology two years ago. These solar cells used tiny particles of semiconductors called "quantum dots." Quantum dot solar cells are cheaper to produce than traditional ones, as they can be made using simple chemical reactions. But despite their promise, they lagged well behind existing solar cells in efficiency.

"I wondered if we could use our knowledge of chemistry to improve their efficiency," Bent said. If she could do that, the reduced cost of these solar cells could lead to mass adoption of the technology.

Bent discussed her research on Feb. 20, at the annual meeting of the American Association for the Advancement of Science in Washington, D.C.

In principle, quantum dot cells can reach much higher efficiency, Bent said, because of a fundamental limitation of traditional solar cells.

Solar cells work by using energy from the sun to excite electrons. The excited electrons jump from a lower energy level to a higher one, leaving behind a "hole" where the electron used to be. Solar cells use a semiconductor to pull an electron in one direction, and another material to pull the hole in the other direction. This flow of electron and hole in different directions leads to an electric current.

But it takes a certain minimum energy to fully separate the electron and the hole. The amount of energy required is specific to different materials and affects what color, or wavelength, of light the material best absorbs. Silicon is commonly used to make solar cells because the energy required to excite its electrons corresponds closely to the wavelength of visible light.

But solar cells made of a single material have a maximum efficiency of about 31 percent, a limitation of the fixed energy level they can absorb.

Quantum dot solar cells do not share this limitation and can in theory be far more efficient. The energy levels of electrons in quantum dot semiconductors depends on their size -- the smaller the quantum dot, the larger the energy needed to excite electrons to the next level.

So quantum dots can be tuned to absorb a certain wavelength of light just by changing their size. And they can be used to build more complex solar cells that have more than one size of quantum dot, allowing them to absorb multiple wavelengths of light.

Because of these advantages, Bent and her students have been investigating ways to improve the efficiency of quantum dot solar cells, along with associate Professor Michael McGehee of the department of Materials Science and Engineering.

The researchers coated a titanium dioxide semiconductor in their quantum dot solar cell with a very thin single layer of organic molecules. These molecules were self-assembling, meaning that their interactions caused them to pack together in an ordered way. The quantum dots were present at the interface of this organic layer and the semiconductor. Bent's students tried several different organic molecules in an attempt to learn which ones would most increase the efficiency of the solar cells.

But she found that the exact molecule didn't matter -- just having a single organic layer less than a nanometer thick was enough to triple the efficiency of the solar cells. "We were surprised, we thought it would be very sensitive to what we put down," said Bent.

But she said the result made sense in hindsight, and the researchers came up with a new model -- it's the length of the molecule, and not its exact nature, that matters. Molecules that are too long don't allow the quantum dots to interact well with the semiconductor.

Bent's theory is that once the sun's energy creates an electron and a hole, the thin organic layer helps keep them apart, preventing them from recombining and being wasted. The group has yet to optimize the solar cells, and they have currently achieved an efficiency of, at most, 0.4 percent. But the group can tune several aspects of the cell, and once they do, the three-fold increase caused by the organic layer would be even more significant.

Bent said the cadmium sulfide quantum dots she is currently using are not ideal for solar cells, and the group will try different materials. She said she would also try other molecules for the organic layer, and could change the design of the solar cell to try to absorb more light and produce more electrical charge. Once Bent has found a way to increase the efficiency of quantum dot solar cells, she said she hopes their lower cost will lead to wider acceptance of solar energy.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Stanford University, via EurekAlert!, a service of AAAS.

Journal Reference:

Pendar Ardalan, Thomas P. Brennan, Han-Bo-Ram Lee, Jonathan R. Bakke, I-Kang Ding, Michael D. McGehee, Stacey F. Bent. Effects of Self-Assembled Monolayers on Solid-State CdS Quantum Dot Sensitized Solar Cells. ACS Nano, 2011; : 110207102503043 DOI: 10.1021/nn103371v

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.