New Transparent Insulating Film Could Enable Energy-Efficient Displays
In his Johns Hopkins materials science lab, Howard E. Katz adjusts probes used for testing electronic devices. (Photo by Will Kirk, Homewoodphoto.jhu.edu)
Johns Hopkins materials scientists have found a new use for a chemical compound that has traditionally been viewed as an electrical conductor, a substance that allows electricity to flow through it. By orienting the compound in a different way, the researchers have turned it into a thin film insulator, which instead blocks the flow of electricity, but can induce large electric currents elsewhere. The material, called solution-deposited beta-alumina, could have important applications in transistor technology and in devices such as electronic books.
The discovery is described in the November issue of the journal Nature Materials and appears in an early online edition.
“This form of sodium beta-alumina has some very useful characteristics,” said Howard E. Katz, a professor of materials science and engineering who supervised the research team. “The material is produced in a liquid state, which means it can easily be deposited onto a surface in a precise pattern for the formation of printed circuits. But when it’s heated, it forms a solid, thin transparent film. In addition, it allows us to operate at low voltages, meaning it requires less power to induce useful current. That means its applications could operate with smaller batteries or be connected to a battery instead of a wall outlet.” (more…)
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Cement’s Basic Molecular Structure Finally Decoded - Environmental Ramifications
By Denise Brehm
The Blue Circle Cement Works, Shoreham, Sussex
In the 2,000 or so years since the Roman Empire employed a naturally occurring form of cement to build a vast system of concrete aqueducts and other large edifices, researchers have analyzed the molecular structure of natural materials and created entirely new building materials such as steel, which has a well-documented crystalline structure at the atomic scale.
Oddly enough, the three-dimensional crystalline structure of cement hydrate - the paste that forms and quickly hardens when cement powder is mixed with water - has eluded scientific attempts at decoding, despite the fact that concrete is the most prevalent man-made material on earth and the focus of a multibillion-dollar industry that is under pressure to clean up its act. The manufacture of cement is responsible for about 5 percent of all carbon dioxide emissions worldwide, and new emission standards proposed by the U.S. Environmental Protection Agency could push the cement industry to the developing world. (more…)
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A New Approach to Engineering for Extreme Environments
by Anne Trafton
Scientist creates model to design radiation-resistant materials.
Michael Demkowicz (Photo / Donna Coveney)
Composite materials such as fiberglass, which take on a mix of properties of their constituent compounds, have been around for decades. Now, an MIT materials scientist is taking composites to the nanoscale, where entirely new properties, not found in any of the original compounds, can emerge.
Michael Demkowicz, an assistant professor in MIT’s Department of Materials Science and Engineering, is part of a team based at Los Alamos National Laboratory that recently received a federal Energy Frontier Research Centers grant to develop nanocomposite materials that can endure high temperatures, radiation and extreme mechanical loading. The ultimate goal is to use these materials in energy applications including nuclear power, fuel cells, solar energy and carbon sequestration.
“All sectors of energy production need materials that can withstand extreme conditions,” says Demkowicz, whose model offers a new approach to designing nanocomposites with desirable traits. (more…)
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See the Force: Mechanical Stress Leads to Self-sensing in Solid Polymers
Progressive images of a mechanophore linked elastomer during tensile loading. After the polymer reaches a critical strain, a force-induced red color results from selective covalent bond cleavage in the mechanophore just prior to failure.(Photo Beckman Institute ITG, Darren Stevenson and Alex Jerez)
Parachute cords, climbing ropes, and smart coatings for bridges that change color when overstressed are several possible uses for force-sensitive polymers being developed by researchers at the University of Illinois.
The polymers contain mechanically active molecules called mechanophores. When pushed or pulled with a certain force, specific chemical reactions are triggered in the mechanophores. (more…)
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Mapping Atoms in Nanowire Offers Electronic Nano-Engineering Possibilities
By Emily Ayshford
3D reconstruction of an individual Ge nanowire with each green sphere representing an individual Ge atom. The dimensions are 50x50x100 nm3. The region enclosed by the red box is displayed at upper right, with single atomic planes visible in the center of the image. The grey spheres are phosphorous dopant atoms used to control the conductivity. (The dimensions are 5x25x15 nm3). The region enclosed by the blue box is displayed in the lower right, revealing an inhomogeneous distribution of phosphorous atoms. (The dimensions are 50x50x10 nm3). The 'shell' of enhanced doping results from surface reactions during growth of the nanowire.
Semiconductor nanowires — tiny wires with a diameter as small as a few billionths of a meter — hold promise for devices of the future, both in technology like light-emitting diodes and in new versions of transistors and circuits for next generation of electronics. But in order to utilize the novel properties of nanowires, their composition must be precisely controlled, and researchers must better understand just exactly how the composition is determined by the synthesis conditions.
Nanowires are synthesized from elements that form bulk semiconductors, whose electrical properties are in turn controlled by adding minute amounts of impurities called dopants. The amount of dopant determines the conductivity of the nanowire.
But because nanowires are so small — with diameters ranging from 3 to 100 nanometers — researchers have never been able to see just exactly how much of the dopant gets into the nanowire during synthesis. (more…)
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Ocean Becoming More Acidic, Potentially Threatening Marine Life
Acidification from absorbing atmospheric CO2 is changing the ocean's chemistry.
A dramatic increase in carbon dioxide levels is making the world’s ocean more acidic, which may adversely affect the survival of marine life and organisms that depend on them, such as humans. An article on this topic is scheduled for the Feb. 23 issue of Chemical & Engineering News, ACS’ weekly newsmagazine.
In the article, C&EN Associate Editor Rachel Petkewich notes that the increased use of fossil fuels has caused levels of carbon dioxide in the atmosphere to nearly double since the Industrial Revolution. The ocean absorbs large amounts of carbon dioxide — about 22 million tons a day — causing the water’s pH to decrease or acidify. The pH scale measures how acidic or alkaline substances are. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is alkaline. The ocean’s pH is currently about 8.1, down from 8.2 in the 18th century, the article notes. Scientists project that the ocean’s pH will fall by about 0.3 more units in the next 50 to 100 years. (more…)
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