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DAYS 2, 3: Monday, Tuesday June 28-29

The second and third days of the 2010 American Conference on Neutron Scattering, in Ottawa, Canada, included a number of interesting events and activities. The major event on Tuesday morning was the awards session with various prizes of the Neutron Scattering Society of America (NSSA) awarded by the president of the NSSA Bruce Gaulin and vice-president Simon Billinge. This was followed by two of the prize winners presenting talks.

   Some of the new Fellows of the Neutron Scattering Society of America


 Neutron Scattering Society of America Awards

                Herbert A. Mook (second from right) receiving the 2010 Clifford G.
                 Shull Prize. (l to r) Simon J.L. Billinge, Jaime A. Fernandez-Baca,
                 Herbert A. Mook and Bruce D. Gaulin.

(right) Collin Broholm receives the 2010 Sustained Research Prize, and (right) Craig M.
Brown receives the 2010 Science Prize of the NSSA.

                    Gregory Smith (second from left) and Steven Shapiro (second
                     from right) receiving special NSSA service awards

Student Poster Awards

First Prize: Suanne Mahabir
Mechanism for the growth of "bicelles"
Second Prize: Christopher Metting
Characterization and modeling of off-specular neutron scattering for analysis of two dimensional ordered structures
Third Prize (Honorable Mention): Ping-Yen Hsieh
The gas adsorption behaviors in chiral holmium metal-organic framework materials

 Prize Lectures

The Edge of Magnetism
Collin Broholm,
2010 Sustained Research Prize

“Science is what happens while you are busy making other plans.” Collin Broholm paraphrasing John Lennon

Collin Broholm of Johns Hopkins University is the recipient of the 2010 Sustained Research Prize of the NSSA. He gave a talk on Tuesday morning on "The Edge of Magnetism." He started by stating that in his research career thus far, the dominant theme has been exploring magnetism at its limits. Starting from a system of interacting spins in an insulating solid, how can we supress the development of long range magnetic order and which phases may be found in its place if we succeed, were the questions he posed. Neutron scattering studies have been at the heart of his research at the edge of magnetism.

In his talk, Broholm discussed materials driven to the edge through reduced dimensionality, through competing interactions and through interactions with conduction electrons. He described the potential for novel cooperative phases such as superconductivity emerging at the edge of magnetism. He suggested that instrumentation development formed a parallel narrative in his research and in this talk. Following the thread towards the edge, he also described progress in instrumentation that have opened up new windows on magnetism at the atomic scale. This has yielded higher efficiencies, higher energies, higher resolutions and extreme sample environments.Finally, though he did not speak directly of applications, he said that history has shown that qualitatively new states of matter are necessary input to fuel technologies of the future. This body of work could conceivably yield important applications in the future as has been shown time and again by fundamental scientific research.

Understanding How Hydrogen Interacts With Materials Using Neutrons
Craig Brown, 2010 Science Prize

Hydrogen, the most abundant element in the universe, has great potential as an energy source. Unlike petroleum, it can be easily generated from renewable energy sources. It is also nonpolluting, and forms water as a harmless byproduct during use. Yet it is so difficult to store that its use as a fuel has been limited. Craig Brown (Center for neutron science, NIST) focused his plenary talk on new hydrogen storage materials based on metal-organic frameworks. He emphasized that new materials must achieve higher gravimetric and volumetric densities than those currently available to afford a viable storage systems that can be reversibly refueled.

Despite the fact that capacity of these hydrogen-storage materials has improved over the last decade, there are still many technological challenges that limit optimizing their performance. He highlighted the main obstacles, involving low hydrogen adsorption enthalpy and the lack of understanding of surface packing density. There are a number of mechanisms he discussed to increase the operating temperature, from strong-binding (less than 'Kubas' though), engineered nanospaces, spillover mechanisms, and substitution of hetero-atoms in carbon frameworks. Brown showed several examples of how he has relied in his research on various neutron methods including powder diffraction and quasi-elastic scattering as well as vibrational and rotational spectroscopy to advance understanding and improve system performance.

The Future of Neutron Scattering in Canada - Panel Discussion

The main idea of the panel discussion on Monday was to discuss the perspectives of neutron scattering in Canada to ensure that the Canadian scientific community has access to neutron-based experimental facilities in the coming decades. The session was moderated by Dominic Ryan, president of the Canadian Institute of Neutron Scattering (CINS), and Danial Wayner, vice-president of the National Research Council Canada in Physical Sciences. The six pinalists included Bruce Gaulin (current president of the Neutron Scattering Society of America and Director of the Brockhouse Institute for Materials Research at McMaster University), Thom Mason (Director of Oak Ridge National Laboratory), Denise Carpenter (President of the Canadian Nuclear Association), Basma Shalaby (President of the University Network of Excellence in Nuclear Engineering, and Professor of Engineering Physics at McMaster University), Ben Rouben (Executive Administrator at the Canadian Nuclear Society), and Dean Chapman (representing the proposed Canadian Neutron Source at the University of Saskatchewan).

The session moderators first overviewed the history of neutron scattering in Canada with a focus on the National Research Universal (NRU) reactor at Chalk River which was built 52 years ago to produce isotopes. However, the reactor is showing its age and has been shut down for over a year for repair. The main questions posed were whether Canada needs its own neutron source and what will be the mission of the re-built reactor?

The panel claimed an urgent need for a new type of neutron source in Canada which would significantly contribute to many spheres of society including academia, industry, and healthcare. It was emphasized that Canada’s future depends on the ability to train new scientists and to retain existing expertise and knowledge. The domestic neutron source would support not only basic science experiments but would also provide new resources for medicine and R&D perspectives to the Canadian nuclear industry and the North America neutron community. For example, neutron scattering is essential for materials research and engineering to provide improved understanding of novel systems and high-performance materials. Canada’s leading role in advanced materials is evidenced by Bertram Brockhouse’s Nobel Prize in Physics in 1994. A new multi-purpose research reactor would encourage the entrepreneurial spirit of innovation and would ensure the continued development of highly qualified scientists and engineers. Overall, the reactor would help in securing Canada’s role as a world leader in science and technology and radioisotope production.

The proposed new multi-purpose research reactor in Canada

In summary, according to the panelists, neutron scattering in Canada is at a historic turning point and actions should be taken now to ensure that the next generation gets to use the enormous capabilities of neutron-based multipurpose facilities. The recent failure of the NRU reactor shows the urgent need to develop an orderly succession plan so that Canada’s investment in nuclear research and engineering is not lost and Canada’s leadership in neutron science can continue well into the future.

Technical Talks

Symposium C: Soft Condensed Matter

Dynamic Light Scattering Investigations of NanopartIcle Aggregation Following a Light-Induced pH Jump
There are many important processes where the stability of nanoparticles can change in response to the solution environment. These changes are challenging to study under controlled conditions. In his poster, Vivek Prabhu (NIST) illustrated the use of dynamic light scattering (DLS) to study the initial kinetics of aggregation of carboxylated polystyrene nanoparticles after well-defined pH jumps using aqueous solutions of photoacid generator. He demonstrated that using this approach, the pH of solutions was controlled by exposure to UV light. He found the aggregation kinetics to be very sensitive to solution pH. Particle aggregation was induced by decreasing pH as a result of decreasing the electrostatic repulsion between the particles. Overall, Prabhu demonstrated that the novel pH jump provides access to challenging time-scales (sub 5 sec) in the absence of mixing flows. Importanly, the ability to tailor pH changes via optical exposure affords investigating complex systems like gels and multicomponent mixtures when traditional methods cannot be used.

Early Stages of Oxidative Stress-Induced Lipid Membrane Permeabilization: A Neutron Reflectivity Study

A lipid membrane composed of a bilayer of phopholipids deposited on solid water interfaces is widely used as a attractive model system to mimic cellular membranes. Still, a number of open questions remain in cell membrane behavior. In his invited talk, Jaroslaw Majewski (Los Alamos National Lab.) addressed the topic of membrane stability and described how oxidative stress induced by mild UV irradiation affects properties of lipid membranes such as morphology and structure. He emphasized that oxidative damage of the cell membrane is a very important point to investigate as in the case of apoptosis and Alzheimer’s disease. Majewski described a bilayer of DPPC and POPC phospholipids exposed to UV light wherein the structure was examined by neutron reflectivity. The irradiation of membranes results in a decrease in membrane coverage along with the formation of micropores within the membrane. The unique feature of the membrane to reorganize and form of hydrophilic channels was then confirmed with spectroscopy and microscopy techniques.

Structure Of Lipid Bilayers On Polyethylene Glycol (PEG) Cushions: Fact and Fiction Of PEG Cushioned Membranes
Erik Watkins (University of California, Davis) continued the topic on using lipid bilayers as systems mimicking cellular membranes. In contrast to previous studies which were mostly focused on deposition of bilayers on solid templates, Watkins presented a polymer cushion to support lipid bilayers in a liquid environment. The cushion is made of a highly hydrated and biocompatible PEG grafted to a solid template. The cushion separates the lipid membrane from the solid template thus providing bio-mimicking physiological conditions for the self-supporting membrane. What is more important, in contrast to the conventional surface-tethered films, the cushion-supported system eliminates problems associated with protein denaturing and restricted protein mobility induced by direct binding of lipids to the solid templates. Watkins demonstrated precise structural quantitative characterization of the membranes with the application of neutron and X-ray reflectivity. The hybrid system was shown to be stable with time and allows liquid access to the lipid bilayer on both sides. The highly hydrated nature of the polymer support is very attractive for applications in developing biologically relevant cellular-like membranes. Overall, the system is robust, easily prepared, tunable, and proposed to mimic extracellular matrix, which is crucial for membrane-based biosensors.

Symposium E: Chemistry & Materials

Hydrogen DIffusion in Potassium Intercalated Graphite Studied by Quasielastic Neutron Scattering
Hydrogen is of course being seriously investigated as a future clean and renewable energy source. One option for hydrogen storage is physisorption, and graphite is being investigated as a medium to store hydrogen. Surface adsorption in graphite is low at 4 kJ/mol and hence researchers are considering separating the graphite layers using intercalated guest species to increase interlayer adsorption. Potassium, rubedium and cesium are being investigated as guest species to tailor the the pore width between graphite layers. Justin Purewal (California Institute of Technology) in his invited talk on Monday described an investigation using quasielastic neutron scattering (QENS) to study hydrogen diffusion in MC24 graphite intercalation compounds (M=K, Rb, Cs) with focus on KC24. The QENS spectra were analyzed with a two-dimensional honeycomb lattice jump diffusion model. Molecular dynamics simulation was also used to correlate with experimental data. Hydrogen diffusion in KC24 was found to be similar to that in zeolites with molecular sized pores but an order-of-magnitude slower than diffusion in other carbons. Steric diffusion barriers were the determining factor for the magnitude of the diffusion coefficient. Also, the rate of H2 adsorption slowed at larger H2 compositions likely due to site blocking. The barrier to
H2 rotation in KC24(H2)x was found to be many times larger than in other carbon adsorbents due to confinement between the graphite layers, thus affecting diffusion behavior.

Evidence of Enhanced Hydrogen Storage in Pt-Impregnated Activated Carbon by the Spillover Effect
High hydrogen storage levels are critical for future mobile fuel cell vehicles. While various porous materials are under consideration for hydrogen storage, none of them yet satisfy the targets set, in particular by the U.S. Department of Energy. One potential option is using the "spillover" effect to enhance room temperature hydrogen storage capacity. In the spillover effect, in the case of Pt-doped activated carbon, atomic hydrogen is first generated by dissociation of hydrogen molecules on Pt particles, for instance. The atomic hydrogen then migrates onto the carbon by surface diffusion and is then adsorbed. The spillover effect is still rather poorly understood. Yang Zhang speaking on behalf of Cheng-Si Tao of MIT described the use of small angle neutron scattering (SANS) to study the spillover effect on Pt-impregnated activated carbon. The methodology involved transmission measurement combined with SANS. Inelastic neutron scattering was also used to study the state of the hydrogen and its interaction with the carbon adsorbent and carbon-supported metal particles. The results provided some evidence though not entirely conclusive for the spillover effect. However, the methodology used appears to be very useful for further studies to investigate the spillover effect.


Symposium F: Condensed Matter Physics

Ferromagnetism Induced at the Interface Between Paramagnetic and Antiferromagnetic Perovskite Thin Films
Controlled interfaces between two materials can give rise to novel physical phenomena and functionalities. For instance, when epitaxial LaMnO3 films were grown on SrTiO3 substrates, magnetism was induced at the interface by doping or charge transfer. A method to probe the magnetism of a buried interface is therefore important. Valeria Lauter (Oak Ridge National Laboratory) and her colleagues used polarized neutron reflectometry with off-specular scattering to investigate interfacial structures. Upon cooling from 300K to 5K under H=1T, splitting of lines was observed. This was due to a structural phase transition, wherein reflections on laterally coherent tilt domains were obtained. Thus, there was evidence of a reversible temperature-dependent structural modulation of an LaMnO3 film. In summary, a new type of negative magnetostriction not reported previously was obtained. Reversible temperature-dependent structural changes in LaMnO3 films were observed. PNR experiments revealed the appearance of laterally coherent tilt domains in the LaMnO3 film below T~95 K. Magnetization distribution in an LaMnO3 film was not uniform and was enhanced towards both interfaces.

Study of TiO2 Nanotube Structures Using SANS
TiO2is currently used in a number of fascinating applications, including as photocatalysts. In particular, there is great interest in using
TiO2 nanotubes because of the added surface areas available. Nitrogen doping has been found to reduce the bandgap of TiO2 bringing it within the visible light range for photocatalysis. Also the use of TiO2 nanotube arrays yields new and interesting properties. In a new study, described by Lisa DeBeer-Schmitt of Oak Ridge National Laboratory, SANS was used to characterize TiO2 nanotube arrays to understand their structure and to investigate the effect of nitrogen incorporation into the nanotube structure. While the pure TiO2 was found to have a disordered structure with crystallites formed between the nanotubes, the nitrogen doped specimens were found to be more ordered with no crystallites between the nanotube arrays. This was evident from the additional peaks in the SANS data for the nitrogen doped specimens. The results suggest that the morphology of the nanotube array could be manipulated by varying the growth conditions.

 Scanning the Conference





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