Tuesday, June 21, 2011

Two-state dynamics recorded in glassy silicon

Using high-resolution imaging technology, University of Illinois researchers have answered a question that had confounded semiconductor researchers: Is amorphous silicon a glass? The answer? Yes -- until hydrogen is added.

Led by chemistry professor Martin Gruebele, the group published its results in the journal Physical Review Letters.

Amorphous silicon (a-Si) is a semiconductor popular for many device applications because it is inexpensive and can be created in a flexible thin film, unlike the rigid, brittle crystalline form of silicon. But the material has its own unusual qualities: It seems to have some characteristics of glass, but cannot be made the way other glasses are.

Most glasses are made by rapidly cooling a melted material so that it hardens in a random structure. But cooling liquid silicon simply results in an orderly crystal structure. Several methods exist for producing a-Si from crystalline silicon, including bombarding a crystal surface so that atoms fly off and deposit on another surface in a random position.

To settle the debate on the nature of a-Si, Gruebele's group, collaborating with electrical and computer engineering professor Joseph Lyding's group at the Beckman Institute for Advanced Science and Technology, used a scanning tunneling microscope to take sub nanometer-resolution images of a-Si surfaces, stringing them together to make a time-lapse video.

The video shows a lumpy, irregular surface; each lump is a cluster about five silicon atoms in diameter. Suddenly, between frames, one bump seems to jump to an adjoining space. Soon, another lump nearby shifts neatly to the right. Although few of the clusters move, the action is obvious.

Such cluster "hopping" between two positions is known as two-state dynamics, a signature property of glass. In a glass, the atoms or molecules are randomly positioned or oriented, much the way they are in a liquid or gas. But while atoms have much more freedom of motion to diffuse through a liquid or gas, in a glass the molecules or atom clusters are stuck most of the time in the solid. Instead, a cluster usually has only two adjoining places that it can ferry between.

"This is the first time that this type of two-state hopping has been imaged in a-Si," Gruebele said. "It's been predicted by theory and people have inferred it indirectly from other measurements, but this is the first time we're been able to visualize it."

The group's observations of two-state dynamics show that pure a-Si is indeed a glass, in spite of its unorthodox manufacturing method. However, a-Si is rarely used in its pure form; hydrogen is added to make it more stable and improve performance.

Researchers have long assumed that hydrogenation has little to no effect on the random structure of a-Si, but the group's observations show that this assumption is not quite correct. In fact, adding hydrogen robs a-Si of its two-state dynamics and its categorization as a glass. Furthermore, the surface is riddled with signs of crystallization: larger clusters, cracks and highly structured patches.

Such micro-crystalline structure has great implications for the properties of a-Si and how they are studied and applied. Since most research has been conducted on hydrogenated a-Si, Gruebele sees a great opportunity to delve into the largely unknown characteristics of the glassy state.

"In some ways, I think we actually know less about the properties of glassy silicon than we think we do, because a lot of what's been investigated of what people call amorphous or glassy silicon isn't really completely amorphous," Gruebele said. "We really need to revisit what the properties of a-Si are. There could yet be surprises in the way it functions and the kind of things that we might be able to do with it."

Next, the group hopes to conduct temperature-depended studies to further establish the activation barriers, or the energy "humps" that the clusters must overcome to move between positions.

The National Science Foundation supported this work.


Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Illinois at Urbana-Champaign.

Journal Reference:

S. Ashtekar, G. Scott, J. Lyding, M. Gruebele. Direct Imaging of Two-State Dynamics on the Amorphous Silicon Surface. Physical Review Letters, 2011; 106 (23) DOI: 10.1103/PhysRevLett.106.235501

New catalyst will allow commercialization of revolutionary fuel cells

Cheap, much lighter than before and allowing for continuous operation -- what traditional batteries can not offer -- direct formic acid fuel cells can revolutionize the portable electronics market. A new catalyst developed at the Institute of Physical Chemistry of the Polish Academy of Sciences will enable a widespread use of fuel cells, researchers say.

You can hardly find a consumer electronics user who would not be irritated by problems with power supply. The batteries run out quickly and require continuous replacements or take a long time charging. Fuel cells could significantly improve the comfort of using electronic devices. Their commercialization, however, is hampered by many technological problems. A new catalyst developed at the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw represents a substantial milestone on the way to dissemination of cheap, durable, light and environment friendly fuel cells powered by formic acid.

Fuel cell is a device converting chemical energy into electric power. The current is generated directly due to fuel combustion in the presence of catalysts used on the anode and the cathode of the fuel cell. "Theoretical efficiency of conversion of chemical energy into electric power in the cells can reach even one hundred percent. The best present fuel cells, powered by hydrogen, reach up to 60% in real life. For comparison, the efficiency of low-compression engines is as low as 20%," says Dr Andrzej Borodziński from the IPC PAS.

The biggest obstacle to dissemination of hydrogen fuels is the storage of hydrogen. The issue turned out to be extremely technologically challenging and still is waiting for satisfactory solutions. An alternative to fuel cells powered by pure hydrogen is the methanol fuel cell technology. Methanol, however, is toxic and the methanol powered fuel cells must be produced with expensive platinum based catalysts. Moreover, methanol fuel cells have low power and are operated at a relatively high and so potentially hazardous temperature (approximately 90°C).

An alternative solution is formic acid fuel cells. In this case, the reactions occur at room temperature, and the efficiency and power of these fuel cells are clearly higher than those for methanol ones. In addition, formic acid is easy to store and transport. To have, however, formic acid fuel cell stable in operation you need an efficient and durable catalyst.

"The catalyst developed by us has initially lower activity then the existing catalysts made of pure palladium. The difference disappears, however, already after two hours of operation. And further it is only better. Our catalyst is stable in operation, whereas the activity of a pure palladium-based catalyst decreases in time," says Dr Borodziński.

An advantage of the catalyst developed in the IPC PAS, particularly important from the economic point of view, is that it preserves its properties while operated in formic acid of low purity. Such formic acid can be easily produced in large quantities, also from biomass, so the fuel for new fuel cells would be very cheap.

Formic acid produced from biomass would be a fully environment friendly fuel. The reactions involving formic acid in fuel cells generate as products water and carbon dioxide. The latter is, as a matter of fact, a greenhouse gas, but the biomass is obtained from plants which use carbon dioxide for their growth. As a result, formic acid produced from biomass and consumed in fuel cells would not change the content of carbon dioxide in atmospheric air. The risk of natural environment contamination by formic acid is also low.

Formic acid fuel cells would find numerous applications. They would be particularly suitable in portable electronic devices -- mobile phones, laptops or GPS-based devices. They could also be installed as power supply sources in vehicles, from wheelchairs through electric bicycles up to yachts.

At the IPC PAS the research is being undertaken on the first batteries based on formic acid fuel cells. The researchers expect that a prototype of a commercial device should be ready within a couple of years.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Institute of Physical Chemistry of the Polish Academy of Sciences, via AlphaGalileo.

Clariant installs additional capacity at its emulsion plant in Argentina

 Clariant has scaled-up production capacity for its Mowilith® emulsions by 35%. The additional capacity is especially intended for its wide-ranging line of copolymers and terpolymers.

The investment will also enable the unit to enhance its portfolio with new products offering commercial and technical benefits for customers. Clariant will incorporate into its production, among others, a line of elastomeric terpolymers and new alternatives for emulsions to solvent varnishes and enamels.

“The introduction of our new products, with their commercial and technical benefits, will support our customers in both expanding their current business activities and in exploring new areas", highlights the director and global head of Business Unit Emulsions, Sven Schultheis. “Clariant is one of the companies with the greatest versatility on the market to produce emulsions obtained from a variety of monomer systems. We have a strong tradition in this business: under the Mowilith® brand, we have been creating innovative emulsions for almost one hundred years”, said the executive.

"Market demand has been growing constantly and Clariant is committed to keeping up with this growth, providing its customers with customized solutions supported by our global Research & Development network", said Guillermo Bruno, Business Unit Emulsions Manager for Clariant Argentina. He also says that the expansion, besides meeting the domestic demand, will also benefit Uruguay and Paraguay markets, which are served by this industrial plant.


Rhodia and SIBUR sign letter of intent for joint venture in surfactants in Russia and CIS

 Rhodia and SIBUR have signed a letter of intent to create a joint venture in specialty surfactants. This strategic alliance would be focused on creating a leader in the CIS market where specialty surfactants are used particularly in home & personal care, and oil & gas industries, with the surfactants sector growing at more than 6% per year.

Rhodia will provide its expertise in surfactant technologies, its knowledge of formulations and market applications and its customer network, including global key accounts with a strong presence in this region.

SIBUR will contribute its raw materials, production and logistics capabilities.  With its longstanding experience of the Russian petrochemicals market, SIBUR will also support the development of the surfactants business in oil and gas markets in Russia and the CIS.

It is expected that the new 50:50 joint venture will site a local production in Russia at Dzerzhinsk, near SIBUR’s petrochemicals operations, 400km east of Moscow, and is expected to be operational in 2013.

“This strategic partnership is a key step in our development in the dynamic surfactants market in the CIS and Eastern Europe,” commented Christophe Clemente, Rhodia Novecare’s Vice President Europe.  “This alliance will reinforce our leading position worldwide in specialty surfactants and is fully aligned with our growth strategy. It demonstrates our commitment to become the preferred partner of our customers as they expand in fast growing countries,” added Emmanuel Butstraen, President of Rhodia Novecare.

“SIBUR and Rhodia have strong complementary activities and expertise. The association with a worldwide leader in specialty surfactants will allow us to provide value added products to meet the fast growing demand for more sophisticated and complex solutions”, commented Sergey Merzlyakov, Vice-President - Head of the Plastics and Organic Synthesis business unit of SIBUR. “Collaboration with Rhodia is in line with our strategy of expanding into carefully chosen specialty chemicals business segments”, concluded Dmitry Konov, CEO of SIBUR.

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