From a carpet of nanorods to a thin film solar cell absorber within a few seconds

Research teams at the HZB and at the University of Limerick, Ireland, have discovered a novel solid state reaction which lets kesterite grains grow within a few seconds and at relatively low temperatures. For this reaction they exploit a transition from a metastable wurtzite compound in the form of nanorods to the more stable kesterite compound. At the EDDI Beamline at BESSY II, the scientists could observe this process in real-time when heating the sample: in a few seconds Kesterite grains formed. The size of the grains was found to depend on the heating rate. With fast heating they succeeded in producing a Kesterite thin film with near micrometer-sized crystal grains, which could be used in thin film solar cells. These findings have now been published in the journal “Nature Communications”.

Grain formation during growth of kesterite solar cells observed in real-time
As starting material for the formation of the kesterite film serves a “carpet of nanorods”: With the help of solution-based chemical processing, the chemists around Ajay Singh and Kevin Ryan at the University of Limerick have fabricated films of highly ordered wurtzite nanorods, which have exactly the same composition as kesterite Cu₂ZnSnS₄. With the help of real-time X-ray diffraction at the EDDI beamline of BESSY II, HZB physicists around Roland Mainz and Thomas Unold could now observe how a phase transition from the metastable wurtzite phase to the stable kesterite phase leads to a rapid formation of a thin film with large kesterite grains. “It is interesting to see that the complete formation of the kesterite film is so fast”, says Mainz. And the faster the samples are heated up, the larger the grains grow. Mainz explains that at low heating rate, the transition from wurtzite to kesterite starts at lower temperature at which many small grains form – instead of a few larger grains. Additionally, more defects are formed at lower temperatures. During fast heating, the transition takes place at higher temperature at which grains with less defects form.

Moreover, the comparison of the time-resolved evolution of the phase transition during slow and during fast heating shows that not only the grain growth is triggered by the phase transition, but also the phase transition is additionally accelerated by the grain growth. The HZB physicists have developed a model which can explain these findings. By means of numerical model calculations, they demonstrated the accordance of the model with the measured data.

Novel synthesis pathway for thin film semiconductors with controlled morphology
The work points towards a new pathway for the fabrication of thin microcrystalline semiconductor films without the need of expensive vacuum technology. Cu₂ZnSnS₄-based kesterite semiconductors have gained increasing attention in the past, since they are a promising alternative for the Cu(In,Ga)Se₂ chalcopyrite solar cells which already achieved efficiencies above 20%. Kesterite has similar physical properties as the chalcopyrite semiconductors, but consist only of elements which are abundantly present in the earth crust. The new procedure could also be interesting for the fabrication of micro- and nanostructured photoelectric devices as well as for semiconductor layers consisting of other materials, says Mainz. “But we continue to focus on kesterites, because this is a really exciting topic at the moment.”

The results have been published in Nature communications doi: 10.1038/ncomms4133

Source: http://www.helmholtz-berlin.de/pubbin/news_seite?nid=13909;sprache=en;typoid=3228

Researchers split water into hydrogen, oxygen using light, nanoparticles

Researchers split water into hydrogen, oxygen using light, nanoparticles

Researchers from the University of Houston have found a catalyst that can quickly generate hydrogen from water using sunlight, potentially creating a clean and renewable source of energy.

Their research, published online Sunday in Nature Nanotechnology, involved the use of cobalt oxide nanoparticles to split water into hydrogen and oxygen.

Jiming Bao, lead author of the paper and an assistant professor in the Department of Electrical and Computer Engineering at UH, said the research discovered a new photocatalyst and demonstrated the potential of nanotechnology in engineering a material's property, although more work remains to be done.

Bao said photocatalytic water-splitting experiments have been tried since the 1970s, but this was the first to use cobalt oxide and the first to use neutral water under visible light at a high energy conversion efficiency without co-catalysts or sacrificial chemicals. The project involved researchers from UH, along with those from Sam Houston State University, the Chinese Academy of Sciences, Texas State University, Carl Zeiss Microscopy LLC, and Sichuan University.

Researchers prepared the nanoparticles in two ways, using femtosecond laser ablation and through mechanical ball milling. Despite some differences, Bao said both worked equally well.

Different sources of light were used, ranging from a laser to white light simulating the solar spectrum. He said he would expect the reaction to work equally well using natural sunlight.

Once the nanoparticles are added and light applied, the water separates into hydrogen and oxygen almost immediately, producing twice as much hydrogen as oxygen, as expected from the 2:1 hydrogen to oxygen ratio in H2O water molecules, Bao said.

The experiment has potential as a source of renewable fuel, but at a solar-to-hydrogen efficiency rate of around 5 percent, the conversion rate is still too low to be commercially viable. Bao suggested a more feasible efficiency rate would be about 10 percent, meaning that 10 percent of the incident solar energy will be converted to hydrogen chemical energy by the process.

Other issues remain to be resolved, as well, including reducing costs and extending the lifespan of cobalt oxide nanoparticles, which the researchers found became deactivated after about an hour of reaction.

"It degrades too quickly," said Bao, who also has appointments in materials engineering and the Department of Chemistry.

The work, supported by the Welch Foundation, will lead to future research, he said, including the question of why cobalt oxide nanoparticles have such a short lifespan, and questions involving chemical and electronic properties of the material.

University of Houston (2013, December 15). Researchers split water into hydrogen, oxygen using light, nanoparticles. ScienceDaily. Retrieved December 16, 2013, from http://www.sciencedaily.com­/releases/2013/12/131215160904.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily%2Ftop_news%2Ftop_science+%28ScienceDaily%3A+Top+News+--+Top+Science%29

Graphene could yield cheaper optical chips

Optoelectronic devices built from graphene could be much simpler in design than those made from other materials. If a method for efficiently depositing layers of graphene—a major area of research in materials science—can be found, it could ultimately lead to optoelectronic chips that are simpler and cheaper to manufacture.

"Another advantage, besides the possibility of making device fabrication simpler, is that the high mobility and ultrahigh carrier-saturation velocity of electrons in graphene makes for very fast detectors and modulators," says Dirk Englund, the Jamieson Career Development Assistant Professor of Electrical Engineering and Computer Science at MIT, who led the new research.

Graphene is also responsive to a wider range of light frequencies than the materials typically used in photodetectors, so graphene-based optoelectronic chips could conceivably use a broader-band optical signal, enabling them to move data more efficiently. "A two-micron photon just flies straight through a germanium photodetector," Englund says, "but it is absorbed and leads to measurable current—as we actually show in the paper—in graphene."

Read more at: http://phys.org/news/2013-09-graphene-yield-cheaper-optical-chips.html

More information: http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2013.253.html

Have you ever seen an atom ?

A 3D microscopic slicing show the atomic arrangement in a platinum nanoparticle.

Shining a little light changes metal into semiconductor

Shining a little light changes metal into semiconductor 

          

By blending their expertise, two materials science engineers at Washington University in St. Louis changed the electronic properties of a new class of materials — just by exposing it to light.

With funding from the Washington University International Center for Advanced Renewable Energy and Sustainability (I-CARES), Parag Banerjee, PhD, and Srikanth Singamaneni, PhD, both assistant professors of materials science, brought together their respective areas of research.

Singamaneni’s area of expertise is in making tiny, pebble-like nanoparticles, particularly gold nanorods. Banerjee’s area of expertise is making thin films. They wanted to see how the properties of both materials would change when combined.

The research was published online in August in ACS Applied Materials & Interfaces.

The research team took the gold nanorods and put a very thin blanket of zinc oxide, a common ingredient in sunscreen, on top to create a composite. When they turned on light, they noticed that the composite had changed from one with metallic properties into a semiconductor, a material that partly conducts current. Semiconductors are commonly made of silicon and are used in computers and nearly all electronic devices.

“We call it metal-to-semiconductor switching,” Banerjee said. “This is a very exciting result because it can lead to opportunities in different kinds of sensors and devices.”

Banjeree said when the metallic gold nanorods are exposed to light, the electrons inside the gold get excited and enter the zinc oxide film, which is a semiconductor. When the zinc oxide gets these new electrons, it starts to conduct electricity.

“We found out that the thinner the film, the better the response,” he said. “The thicker the film, the response goes away. How thin? About 10 nanometers, or a 10 billionth of a meter.”

Other researchers working with solar cells or photovoltaic devices have noticed an improvement in performance when these two materials are combined; however, until now, none have broken it down to discover how it happens, Banerjee said.

“If we start understanding the mechanism for charge conduction, we can start thinking about applications,” he said. “We think there are opportunities to make very sensitive sensors, such as an electronic eye. We are now looking to see if there is a different response when we shine a red, blue or green light on this material.”

Banerjee also said this same technology can be used in solar cells.

---

Source:  Wu F, Tian L, Kanjolia R, Singamaneni S, Banerjee P. Plasmonic Metal-to-Semiconductor Switching in Au Nanorod-ZnO nanocomposite films. ACS Applied Materials & Interfaces. Dx.doi.org/10.1021/am402309x.

Progress in Molecular Nanotechnology

Stanford scientists use DNA to assemble a transistor from graphene

Stanford scientists use DNA to assemble a transistor from graphene

DNA meets electronics

DNA is the blueprint for life. Could it also become the template for making a new generation of computer chips based not on silicon, but on an experimental material known as graphene?

That's the theory behind a process that Stanford chemical engineering professor Zhenan Bao reveals in Nature Communications.

Bao and her co-authors, former post-doctoral fellows Anatoliy Sokolov and Fung Ling Yap, hope to solve a problem clouding the future of electronics: consumers expect silicon chips to continue getting smaller, faster and cheaper, but engineers fear that this virtuous cycle could grind to a halt.

Why has to do with how silicon chips work.

Everything starts with the notion of the semiconductor, a type of material that can be induced to either conduct or stop the flow of electricity. Silicon has long been the most popular semiconductor material used to make chips.

The basic working unit on a chip is the transistor. Transistors are tiny gates that switch electricity on or off, creating the zeroes and ones that run software.

To build more powerful chips, designers have done two things at the same time: they've shrunk transistors in size and also swung those gates open and shut faster and faster.

The net result of these actions has been to concentrate more electricity in a diminishing space. So far that has produced small, faster, cheaper chips. But at a certain point, heat and other forms of interference could disrupt the inner workings of silicon chips.

"We need a material that will let us build smaller transistors that operate faster using less power," Bao said.

Graphene has the physical and electrical properties to become a next-generation semiconductor material – if researchers can figure out how to mass-produce it.

Graphene is a single layer of carbon atoms arranged in a honeycomb pattern. Visually it resembles chicken wire. Electrically this lattice of carbon atoms is an extremely efficient conductor.

Bao and other researchers believe that ribbons of graphene, laid side-by-side, could create semiconductor circuits. Given the material's tiny dimensions and favorable electrical properties, graphene nano ribbons could create very fast chips that run on very low power, she said.

"However, as one might imagine, making something that is only one atom thick and 20 to 50 atoms wide is a significant challenge," said co-author Sokolov.

To handle this challenge, the Stanford team came up with the idea of using DNA as an assembly mechanism.

Physically, DNA strands are long and thin, and exist in roughly the same dimensions as the graphene ribbons that researchers wanted to assemble.

Chemically, DNA molecules contain carbon atoms, the material that forms graphene.

The real trick is how Bao and her team put DNA's physical and chemical properties to work.

The researchers started with a tiny platter of silicon to provide a support (substrate) for their experimental transistor. They dipped the silicon platter into a solution of DNA derived from bacteria and used a known technique to comb the DNA strands into relatively straight lines.

Next, the DNA on the platter was exposed to a copper salt solution. The chemical properties of the solution allowed the copper ions to be absorbed into the DNA.

Next the platter was heated and bathed in methane gas, which contains carbon atoms. Once again chemical forces came into play to aid in the assembly process. The heat sparked a chemical reaction that freed some of the carbon atoms in the DNA and methane. These free carbon atoms quickly joined together to form stable honeycombs of graphene.

"The loose carbon atoms stayed close to where they broke free from the DNA strands, and so they formed ribbons that followed the structure of the DNA," Yap said.

So part one of the invention involved using DNA to assemble ribbons of carbon. But the researchers also wanted to show that these carbon ribbons could perform electronic tasks. So they made transistors on the ribbons.

"We demonstrated for the first time that you can use DNA to grow narrow ribbons and then make working transistors," Sokolov said.

The paper drew praise from UC Berkeley associate professor Ali Javey, an expert in the use of advanced materials and next-generation electronics.

"This technique is very unique and takes advantage of the use of DNA as an effective template for controlled growth of electronic materials," Javey said. "In this regard the project addresses an important research need for the field."

Bao said the assembly process needs a lot of refinement. For instance, not all of the carbon atoms formed honeycombed ribbons a single atom thick. In some places they bunched up in irregular patterns, leading the researchers to label the material graphitic instead of graphene.

Even so, the process, about two years in the making, points toward a strategy for turning this carbon-based material from a curiosity into a serious contender to succeed silicon.

"Our DNA-based fabrication method is highly scalable, offers high resolution and low manufacturing cost," said co-author Yap. "All these advantages make the method very attractive for industrial adoption."

Source : http://www.eurekalert.org/pub_releases/2013-09/ssoe-ssu090613.php

Dr. Hildy -- Nanoethics: The Ethical and Social Implications of Nanotechnology

September 28, 2011 -- One Cell One Light Radio with Dr. Hildegarde Staninger, RIET-1 Guest: Dr. Daniel F. Moore http://danielfmoore.com

Source: http://www.nanopaprika.eu

Glass that cleans itself

Eyeglasses need never again to be cleaned, and dirty windscreens are a thing of the past! Researchers at the Max Planck Institute for Polymer Research in Mainz and the Technical University Darmstadt are now much closer to achieving this goal. They have used candle soot to produce a transparent superamphiphobic coating made of glass. Oil and water both roll off this coating, leaving absolutely nothing behind. Something that even held true when the researchers damaged the layer with sandblasting. The material owes this property to its nanostructure. Surfaces sealed in this way could find use anywhere where contamination or even a film of water is either harmful or just simply a nuisance.

Doris Vollmer hates it that her eyeglasses always get dirty so quickly. However, the scientist, who heads a research group at the Max Planck Institute for Polymer Research, is looking for a solution to the problem - and she and her team are now a good deal closer to finding one. A transparent coating that is very good at repelling water and oil, as is now being presented by the Mainz-based researchers, could not only keep water and dirt away from the lenses in glasses and car windscreens, but also, for example, from the glass facades of skyscrapers. It could also prevent residues of blood or contaminated liquids on medical equipment.

The coating essentially consists of an extremely simple material: silica, the main constituent of all glass. The researchers coated this with a fluorinated silicon compound, which already makes the surface water and oil repellent, like a non-stick frying pan. The really clever part is the structure of the coating, however. This is what makes the glass super water repellent and super oil repellent. In a frying pan with this type of coating, water and oil would simply roll around in the form of drops. The structure of the layer resembles a sponge-like labyrinth of completely unordered pores, which is made up of tiny spheres.

More info: http://www.physorg.com/news/2011-12-glass.html

Nanotechnology may speed up drug testing

Nanotechnology may speed up drug testing

ScienceDaily (Dec. 19, 2011) — Testing the effectiveness of new pharmaceuticals may get faster thanks to a new technique incorporating quantum dots developed at the University of Central Florida.

Some drug testing can take a decade or more, but UCF associate professor Swadeshmukul Santra and his team have created an electronic quantum dots (Qdots) probe that "lights up" when a drug it is delivering attaches to cancer cells.

The research appears online in this month's Biomaterials.

A researcher can use a microscope to see where and how much of the drug has been delivered because the probe emits a reddish color under special lighting or via MRI because of its optical and magnetic components.

As the drug testing continues, images can be taken over and over without any loss of optical or MRI signal. Researchers can then measure the size of the tumor and number of cancer cells that "light up" compared with the original untreated tumor.

Source: University of Central Florida (2011, December 19). Nanotechnology may speed up drug testing. ScienceDaily. Retrieved January 9, 2012, from http://www.sciencedaily.com­/releases/2011/12/111219152721.htm

What is Nanoscience?

What is nano?

"What is Nano?" is the first part of the NANOYOU film, an introduction to the strange new world of Nanoscience, narrated by Stephen Fry.