Materials Scientist Dan Shechtman Wins 2011 Nobel Prize in Chemistry
 |
On October 5, 2011, the Nobel Prize Committee honored materials scientist Dan Shechtman of Technion in Haifa, Israel, with the 2011 Nobel Prize in Chemistry "for the discovery of quasicrystals." But those five official words describing his discovery in 1982 do not even hint at the years of scientific turmoil from which Shechtman emerged triumphant only after a long battle with prominent dissenters in the scientific community. Shechtman spoke as a plenary lecturer at the XX International Materials Research Congress in Cancun, Mexico, on August 17 this year, and the Materials Research Society filed a version of the following story (with some augmentation here) on his talk.
Quasi-periodic Materials—Crystal Redefined
Plenary Lecture by Dan Shechtman
Plenary Lecture by Dan Shechtman
In a fascinating, funny, and heartfelt exploration of the nature of scientific discovery and the complications that come from being right when most of your colleagues think you are wrong, Dan Shechtman of Technion (Israel) and Iowa State University (United States) told the story surrounding his discovery of quasi-periodic crystals in 1982. Along the way he outlined the history of crystallography and provided a great brush-up tutorial on the subject for those of us who studied it a long time ago.
Shechtman showed the page of his TEM logbook from April 8, 1982, when he performed a selected area diffraction on a pitch black grain of an Al-25%Mg sample and saw a diffraction pattern of 10 spots around a central spot. “Ten spots—that cannot be,” he said to himself, as he carefully counted again. He knew that according to the rules of crystallography, 10-fold symmetry was a forbidden crystallographic symmetry state. He wrote “(10-fold???)” in the logbook and went out into the hall looking for someone to show his discovery, but no one was there. When he started telling colleagues about it, no one believed him, beginning what he called the “the years of rejection,” which lasted from 1982 to 1987. At one point during these years he was called a “disgrace to his research group” and was asked to leave. His attempt to publish his results was rejected by the Journal of Applied Physics in 1984, and finally found a publisher in Metallurgical Transactions in 1985.
“Immediately after publication,” Shechtman said, “all hell broke loose. A lot of people said it was nonsense.” He noted that “at the frontier of science, there is not much difference between science and religion. They [scientists] have their prophets and their beliefs.” Linus Pauling, a two-time Nobel Laureate, was his biggest opponent. Pauling insisted that Shechtman was observing the effects of twinning, not a diffraction pattern from a single crystal. But he persevered in his investigations of this forbidden symmetry, using smaller and smaller electron spot sizes, until it became evident that if there was twinning, the twinned particles would have to be smaller than the 400-angstrom electron spot size he was using. He was eventually vindicated when x-ray diffraction data—the gold standard in deciding crystallographic arguments at the time—showed 5-fold rotational symmetry in 1987.
These crystals were not strictly periodic, so they defied the definition of crystallinity that had been accepted for 70 years. Shechtman had discovered quasi-periodic crystalline materials. Instead of a constant distance between each atom in the lattice, the ratio of distances varied in accordance with the Fibonacci series, hence the term “quasi-periodic.” This paradigm shift led to a formal redefinition of the word crystal by the International Society of Crystallographers: “By crystal we mean any solid having an essentially discrete diffraction diagram, and by aperiodic crystal we mean any crystal in which three-dimensional lattice periodicity can be considered to be absent.” Shechtman noted the “soft” wording of this definition, and said “suddenly the Society of Crystallographers became modest. And a good scientist is a modest scientist.”
In the question and answer session following his plenary lecture, Shechtman was asked what he learned from his scientific struggles. “Tenacity,” he answered. “If you get a result that you believe in, then fight for it.”
Materials in Focus
Special World Materials Summit Coverage
The World Materials Summit, sponsored jointly by the MRS, the European MRS (E-MRS), and the Chinese MRS (C-MRS), took place in Washington, D.C., from October 9-12, 2011. This invitation-only event featured approximately 100 of the world's top experts in materials and energy, along with prominent officials from government energy departments around the world. This summit also included, for the first time, a Student Congress comprising 45 of the most promising graduate students and post-docs from across the globe, who met to learn from the experts, to discuss in detail how materials and energy challenges vary from country to country, and to propose a path forward to a sustainable planet. In the end, the summit issued a formal declaration combining recommendations from both the panels of experts and from the Student Congress regarding the most important steps to be taken to achieve global sustainability. The 2011 World Materials Summit was funded in part by the National Science Foundation, the Department of Energy's Office of Basic Energy Sciences, the Office of Naval Research, Aldrich® Materials Science, American Elements®, Dow®, and the European Science Foundation's Materials Committee.
Here we present the highlights of three talks given by speakers from the three regions sponsoring the World Materials Summit.
Here we present the highlights of three talks given by speakers from the three regions sponsoring the World Materials Summit.
European Union
 |
Bernard Frois of the CEA--the French Alternative Energies and Atomic Energy Commission (Commissariat à l'énergie atomique et aux énergies alternatives)--sees the de-carbonization of transportation technologies through the use of batteries and fuel cells as one key to a sustainable energy future. The CEA proposes to achieve this goal by controlling the whole process chain, including electrode materials, electrochemical cells, battery packs, battery management systems, and intelligent charging technologies. These individual components and combined systems will be tested at every step of the way from laboratory bench tops to vehicle fleets.
Nanomaterials will play a major role in this process, according to Frois, by taking advantage of quantum effects to enable chemical reactions that are not possible with bulk materials. They increase the electrode/electrolyte contact area, thereby increasing the charge/discharge rates. The shorter path lengths available at the nanoscale will lead to increased power generation.
“We have the battery,” Frois said, referring to the iron-phosphate-based LiFePO4/Li4Ti5O12 cell that he called “the best material ever for a battery.” It is safe and stable, he said, and a car powered by it can be can be fully recharged in 10 minutes. Its performance will be enhanced by a battery management system consisting of sensors and actuators in communication with a CPU.
On the fuel cell side, Frois said that “one of these days hydrogen will be everywhere.” He pointed to the very expensive Opel Hydrogen 4 already being sold in Europe by GM as a first step in this direction. This automobile uses compressed hydrogen in a storage tank at 700 bars pressure to reach speeds of 100 mph and distances of 220 mi. The proton exchange membrane systems that fuel cells currently rely on use a Pt catalyst that is too expensive, so much research is taking place to find a substitute for Pt. “Everybody is working on it,” Frois said.
In the future, Frois envisions an electric vehicle as an energy storage device that will become part of the smart grid, downloading energy from it when needed and uploading unused energy to it at favorable times.
China
Nanomaterials will play a major role in this process, according to Frois, by taking advantage of quantum effects to enable chemical reactions that are not possible with bulk materials. They increase the electrode/electrolyte contact area, thereby increasing the charge/discharge rates. The shorter path lengths available at the nanoscale will lead to increased power generation.
“We have the battery,” Frois said, referring to the iron-phosphate-based LiFePO4/Li4Ti5O12 cell that he called “the best material ever for a battery.” It is safe and stable, he said, and a car powered by it can be can be fully recharged in 10 minutes. Its performance will be enhanced by a battery management system consisting of sensors and actuators in communication with a CPU.
On the fuel cell side, Frois said that “one of these days hydrogen will be everywhere.” He pointed to the very expensive Opel Hydrogen 4 already being sold in Europe by GM as a first step in this direction. This automobile uses compressed hydrogen in a storage tank at 700 bars pressure to reach speeds of 100 mph and distances of 220 mi. The proton exchange membrane systems that fuel cells currently rely on use a Pt catalyst that is too expensive, so much research is taking place to find a substitute for Pt. “Everybody is working on it,” Frois said.
In the future, Frois envisions an electric vehicle as an energy storage device that will become part of the smart grid, downloading energy from it when needed and uploading unused energy to it at favorable times.
China
 |
Duan Weng of Tsinghua University in China spoke about “Life Cycle Assessment as a Component of Materials Science and Engineering for a Sustainable World.” He started by trying to distinguish green chemistry from environmentally conscious materials (ecomaterials). “Both have a lot in common,” Weng said, “but they are recognized very differently.” While Weng did not propose a definition of ecomaterials in his talk, the CAP' EM (Cycle Assessment Procedure for Eco-materials) group (http://www.capem.eu/capem/en/6939-capem.html) of five European countries have developed this definition: “An ecological building material/product [ecomaterial] is a material/product with no heavy negative environmental impact and with no negative health impact.”
But Weng’s statements suggested that he would disagree with such a definition. “The perception that ecomaterials are materials for environmental protection is misleading,” Weng said. “In fact, all materials and processes have environmental impacts.” He proceeded to give two examples of controversial ecomaterials: (1) silicon solar cells, which are green during operation, but which require 3-5 years to reclaim the energy consumed during their manufacture, and (2) TiO2, which is used as a photocatalyst for waste water treatment, but which produces 70 kg of wastewater during the production of 1 kg of TiO2.
These examples show that environmental assessment is missing in materials science and engineering, according to Weng, and that a method is needed to quantitatively compare different options and tradeoffs. “Life cycle assessment [LCA] is the best framework for evaluating the environmental impact of materials,” Weng said. He noted that the European Union’s Seventh Framework Program (FP7), which bundles all research-related EU initiatives together to play a crucial role in reaching the goals of growth, competitiveness and employment in the EU, has adopted LCA requirements. The Chinese Energy Conservation and Emission Reduction (ECER) policy also requires LCA for all products and processes, he said. “All materials and processes have environmental impacts along their lifecycles that should be reduced,” Weng concluded.
But Weng’s statements suggested that he would disagree with such a definition. “The perception that ecomaterials are materials for environmental protection is misleading,” Weng said. “In fact, all materials and processes have environmental impacts.” He proceeded to give two examples of controversial ecomaterials: (1) silicon solar cells, which are green during operation, but which require 3-5 years to reclaim the energy consumed during their manufacture, and (2) TiO2, which is used as a photocatalyst for waste water treatment, but which produces 70 kg of wastewater during the production of 1 kg of TiO2.
These examples show that environmental assessment is missing in materials science and engineering, according to Weng, and that a method is needed to quantitatively compare different options and tradeoffs. “Life cycle assessment [LCA] is the best framework for evaluating the environmental impact of materials,” Weng said. He noted that the European Union’s Seventh Framework Program (FP7), which bundles all research-related EU initiatives together to play a crucial role in reaching the goals of growth, competitiveness and employment in the EU, has adopted LCA requirements. The Chinese Energy Conservation and Emission Reduction (ECER) policy also requires LCA for all products and processes, he said. “All materials and processes have environmental impacts along their lifecycles that should be reduced,” Weng concluded.
United States
 |
William Brinkman, Director of the U.S. Department of Energy’s (DOE) Office of Science, stated that the department’s research focus in materials involves efforts to (1) synthesize new materials, (2) characterize them, (3) measure and analyze them, and (4) create theories to further develop new materials. He stressed the importance of theory and simulations in these efforts. Specifically, the recently available petaflop (1015 operations/sec.) supercomputers have allowed simulations of materials to finer resolutions or at larger scales. “We used to talk about electronic band theory,” Brinkman said, “but now we discuss topological insulators with robust surface states.” One aspect of the Materials Genome Project is to find all compounds that can be made out of two metals plus oxygen for use as possible cathode materials, which could not be done in a timely fashion before petascale computers became available.
By 2021, Brinkman expects exascale (1018 operations/sec) computers to be online. But, while increasing the computing power enormously, such computers will also have drawbacks. “An exascale computer needs 100 MW of power," he said. “That’s equivalent to a small power plant.” Also, he noted that as you shrink electronic devices you lose accuracy in calculations, which leads to the challenge of how to handle an increased number of errors.
In terms of characterizing and testing new materials, Brinkman noted the abundance of x-ray, synchrotron, mass spectrometer, and microscopy technologies that have been and are still being developed. He was very excited about a new free-electron laser operating in the x-ray region, which enables femtosecond x-ray protein nanocrystallographic analysis. “A biological liquid droplet is destroyed by the laser,” he said, “but the analysis is fast enough to get its x-ray diffraction pattern before it is destroyed.” Besides this laser technology, he also mentioned the LINAC Coherent Light Source expansion project, which will provide wavelengths less than 2 angstroms; angle-resolved photoemission, which injects one photon into a material to get one electron out; and x-ray speckle imaging that allows scientists to see surface atoms in motion, making it possible to watch phase changes on a surface.
By 2021, Brinkman expects exascale (1018 operations/sec) computers to be online. But, while increasing the computing power enormously, such computers will also have drawbacks. “An exascale computer needs 100 MW of power," he said. “That’s equivalent to a small power plant.” Also, he noted that as you shrink electronic devices you lose accuracy in calculations, which leads to the challenge of how to handle an increased number of errors.
In terms of characterizing and testing new materials, Brinkman noted the abundance of x-ray, synchrotron, mass spectrometer, and microscopy technologies that have been and are still being developed. He was very excited about a new free-electron laser operating in the x-ray region, which enables femtosecond x-ray protein nanocrystallographic analysis. “A biological liquid droplet is destroyed by the laser,” he said, “but the analysis is fast enough to get its x-ray diffraction pattern before it is destroyed.” Besides this laser technology, he also mentioned the LINAC Coherent Light Source expansion project, which will provide wavelengths less than 2 angstroms; angle-resolved photoemission, which injects one photon into a material to get one electron out; and x-ray speckle imaging that allows scientists to see surface atoms in motion, making it possible to watch phase changes on a surface.
by Glennda Chui
Deputy Editor of symmetry at the Stanford Linear Accelerator Center (SLAC)
Deputy Editor of symmetry at the Stanford Linear Accelerator Center (SLAC)
The strength, flexibility, transparency and high electrical conductivity of single-layer graphene make it a potentially unique and valuable material for the next generation of electronic devices. Made of carbon atoms arranged in a honeycomb pattern – think of a chicken-wire fence – it is 97 percent transparent and 1,000 times stronger than steel.
Researchers are working on ways to tune the properties of graphene for specific electronic applications. One way to do that is by doping – introducing small amounts of other elements, such as nitrogen or phosphorus, that either add or subtract electrons from the system. Widely used in silicon technology, doping has been carried out experimentally in single-layer graphene sheets; but until now, the details of how the dopant atoms fit into the sheet and bond with their carbon neighbors remained elusive.
In a study reported Aug. 9 in Science, researchers from Columbia University, Sejong University in Korea, and SLAC and Brookhaven national laboratories used a combination of four techniques to make the first detailed images of nitrogen-doped graphene film [2]. They showed that individual nitrogen atoms had taken the places of carbon atoms in the two-dimensional sheet; that about half of the extra electron contributed by each nitrogen atom was distributed throughout the graphene lattice; and that this changed the electronic structure of the graphene sheet only within a short distance – about the width of two carbon atoms – from the dopant atoms. The ability to control the electronic structure at the atomic level has important implications for tuning the unique electronic properties of graphene for particular device applications.
“We’re not trying to work on existing systems and make them better. We’re looking for new directions that can potentially enable much higher efficiencies,” said paper co-author Theanne Schiros, a surface scientist at the Department of Energy’s Energy Frontier Research Center at Columbia, who is investigating graphene as a possible electrode for novel photovoltaic devices.
“Now we see that doping is a strategy that can be applied to graphene cleanly and robustly,” she said, providing a potential way to create high-quality graphene films for use in electronic applications, including solar cells.
Schiros is no stranger to SLAC, having done her Ph.D. work here under Anders Nilsson. Her current work at Columbia focuses on using X-rays from synchrotron light sources to probe novel materials for use in renewable energy technologies.
For this study, she returned to SLAC to work with Dennis Nordlund, a staff scientist at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), where recent upgrades allowed them to automatically scan many samples of the nitrogen-doped graphene films at once.
The research team grew the films by depositing chemical vapor on a thin sheet of copper foil.
They analyzed some samples of film while it was on the copper foil, and transferred others to silicon dioxide, the standard substrate for device measurements, for testing. Each sample was examined with Raman spectroscopy and scanning tunneling microscopy (STM) at Columbia, and with X-ray beams at SLAC’s SSRL, and Brookhaven’s National Synchrotron Light Source (NSLS).
The Raman spectra showed that the nitrogen dopant had changed the electronic properties of the graphene sheet without disturbing its basic structure. X-ray measurements at SSRL beamlines 10-1 and 13-2 and NSLS beamline U7A indicated that the nitrogen atoms lay within the plane of the graphene sheet and had each bonded with three carbon neighbors; in other words, each nitrogen atom had replaced a carbon in the sheet.
Finally, the STM images showed the nitrogen atoms as bright spots on the graphene surface. By counting those spots, the researchers determined that the concentration of nitrogen dopant per carbon atom varied from .23 to .35 percent. The images also revealed that the nitrogen atoms stuck out from the graphene layer by about .6 Ångstrom, as they would if they had substituted for carbon in the lattice. These results were consistent with STM image simulations based on theory.
The lead author of the paper was Columbia physics graduate student Liuyan Zhao, working in the laboratory of Abhay N. Pasupathy, and the work was carried out in cooperation with the Energy Frontier Research Center at Columbia, which counts SLAC and Stanford among its collaborators.
While most of the research was performed at Columbia, the advanced materials characterization capabilities at SLAC and Brookhaven played an important role, Schiros said. The results demonstrate the value of the synergy between universities, DOE national labs and the DOE’s 46Energy Frontier Research Centers [4], which conduct basic and advanced research needed to establish the scientific foundation for a fundamentally new energy economy in the United States.
Image in Focus
Giraffe's Fur
An atomic force microscope false color image of lanthanum cobalt oxide perovskite film grown on a strontium titanium oxide substrate. By breaking up into grains, this material portrays the surprisingly organic beauty of inorganic thin film growth.
Credit: Virat Mehta, University of California, Berkeley
(Click image to enlarge.)
(Click image to enlarge.)
0 comments:
Post a Comment