Day 3: Tuesday, November 27

DAY 3
Tuesday, November 27, 2007

DAVID TURNBULL LECTURE

The David Turnbull Lectureship is one of the Society's premier awards and is named in honor of Prof. David Turnbull. This year is especially significant because Turnbull passed away on April 28. At the Turnbull lecture on Tuesday, Prof. Mike Aziz of Harvard University, one of Turnbull's former graduate students, paid him a very moving tribute. Turnbull rarely missed the MRS Fall Meetings, and his absence at this Fall Meeting was felt by those who had seen him here in the past.
[View the David Turnbull website on the MRS website]

This year's Turnbull Lectureship recipient is Prof. Ramamoorthy Ramesh of the University of California, Berkeley, and his lecture was titled "Whither Oxide Electronics"? He started by acknowledging all his past and present collaborators at various institutions. He said that this whole field of oxide electronics truly stands on the shoulders of giants, including von Hippel, Ted Geballe, Goodenough and Cross. Complex oxides are the subject of tremendous research by numerous groups. Ramesh's talk covered the advances in this field chronologically and based around his work from the eighties until the present. The focus was on perovskite related structures though there are other classes of oxides. The birth of oxide electronics is directly related to the discovery of high temperature superconductors in the 1980s. Ramesh described his early efforts at Bellcore aimed at eliminating polarization fatigue which was eventually solved.

This subsequently led to the discovery of colossal magnetoresistance (CMR) for which he is best known. In the magnetoresistive La-Ca-Mn-O system for instance, a thousand fold change in resistivity was observed. This essentially led to a new field of research which is very active today. Ramesh indicated that MRS has been the home for this field since CMR was reported. Ramesh next detailed multiferroics, another major area of current research for oxides. By combining the ferroelectric and magnetic properties of perovskites, yields multiferroics such as BiFeO₃. He described work on heterostructures and nanostructures of multiferroics. There is tremendous current work to achieve deterministic control of magnetism using an electric field, and there are opportunities for new materials physics as well as a new generation of electrically controlled magnetic devices for storage, logic and sensing. He described growth of complex oxides to form heteroepitaxial structures of BiFeO₃/SrRuO₃/SrTiO₃. These can be grown with precise control. He also mentioned recent efforts at understanding order in BiFeO₃, electric control of antiferromagnetism and creating exchange heterostructures. There are tremendous challenges and opportunities for research in the field. He concluded by indicating that in the 20 years since high Tc superconductivity was discovered, oxide electronics have made significant scientific and technological progress. Chemical doping plays a critical role in inducing electronic/ionic instabilities converting a boring system into something very interesting and useful. So in answer to his original question, "Whither oxide electronics?", Ramesh's response was "The future of oxide electronics is bright".

Ramesh ended his talk by indicating that he read David Turnbulls autobiography and was moved by Turnbull's humanity. He concluded by quoting Turnbull's words "In my view, commitment to humanity arises naturally from a wide ranging and deeply sensitive human consciousness which leads one human to feel sharply within one's self the aspirations or pains of another. I believe it is such consciousness which has led people to imagine or feel that there exists a just and humane basis for ultimate reality."

SYMPOSIUM X (AUTHORITATIVE REVIEWS FOR NONSPECIALISTS)

Material Challenges in Nano-electronics
The descent of electronics down to the nanoscale presents numerous materials challenges and opportunities. Symposium X speaker, Paul Heremans (IMEC), examined both this ultimate scaling and the growth of nanotechnology, literally built on the base of nanoelectronics. Deep scaling, with transistors so small that 50 of them could fit on a virus and with oxide thicknesses of only 1.5 nm, continues to lead to performance improvements, but new materials and architectures are needed to compensate for the slowing performance improvements with further size reductions. Silicon, which has endured decades of scaling, still forms the backbone of electronics, but with thin slivers of it replaced by other materials to boost performance. Germanium and III-V semiconductors, nanowires, and graphene are finding homes as high mobility channel materials, although integrated into just the top few monolayers. Also high dielectric constant materials and metal gates are being introduced. For back-end interconnects, low dielectric constant materials are needed. Zeolites have attractive properties in this regime, as pore sizes are extremely uniform (less than a nm) and with good mechanical properties. However, the hydrophilic nature of zeolites is a challenge. With air as an ideal dielectric, architectures are being developed with air gaps built into the structures. Now 30% porosity is achievable without significant loss of Young's modulus. Moving into a broader regime, nanoelectronics represents a mature platform for nanotechnology, such as nanophotonics, nonomagnetics, and nanofluidics, Heremans said. He described integrating with silicon chips high data rate transceivers, optical interconnects, and sensors. Cell isolation from blood can be achieved by on-chip magnetic particle manipulation, and even interfaces of neurons with integrated circuits.

POSTER AWARD WINNERS

 
D6.6 Analytical Study on Initial Growth Stage of Metal Atomic Layer Deposition By Synchrotron Radiation X-Ray Reflectivity Analysis. Han-Bo-Ram Lee , Woo-Hee Kim, Yong Jun Park, Sunggi Baik and Hyungjun Kim; Material Science and Engineering, POSTECH (Pohang University of Science and Technology), Pohang, South Korea.

 
G6.8 Nanofabricated Negative Index Optical Elements from InP/InGaAsP and SOI Heterostructures. Ravinder K Banyal 1 , B. D. F. Casse 1 , Wentao Lu 1 , Y. Huang 1 , S. Selvarasah 2 , M. Dokmeci 2 and S. Sridhar 1 ; 1 Department of Physics and Electronic Materials Research Institute, Northeastern University, Boston, Massachusetts; 2 Department of Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts.

 
FF5.22 Electrochemical Preparation of Bamboo-like Nanowires and Nanotubes. Maoshi Guan1 and Elizabeth J Podlaha-Murphy2; 1Chemical Engineering, Louisiana State University, Malden, Massachusetts; 2Chemical Engineering, Northeastern University, Boston, Massachusetts.

TECHNICAL TALKS

Symposium A: Combinatorial Methods for High-Throughput Materials Science
Combinatorial Searching for Noble Metal-Based Amorphous Alloy Thin Films
Functional optical lenses are used in various applications such as aspherical glass lenses for high storage density optical discs. Such lenses have specific precise structures such as a diffraction grating on them. The mold used to form such glass lenses need to have these structures incorporated. It is difficult to create such molds using conventional hard mold materials. A possible replacement material could be amorphous alloys. Junpei Sakurai (Tokyo Institute of Technology) described the use of a combinatorial technique to identify amorphous compositions of alloys for such an application. The technique is termed combinatorial arc plasma deposition or CAPD wherein three different elements can be deposited using three arc guns and deposited as a compositionally graded layer. In this study, Pt, Ni and Zr or Hf were deposited yielding 1089 samples and the compositions were examined for amorphous characteristics. To evaluate the mechanical properties, larger samples for identified amorphous compositions were obtained separately. Two compositions Pt₅₁Zr₃₉Ni₁₀ and Pt₅₂Hf₃₆Ni₁₂ were identified to be amorphous but the former did not achieve the target glass transition temperature Tx while the latter achieved the target Tx but was very brittle. The researchers then replaced some of the Zr with Hf and identified the composition of Pt₅₁Hf₂₀Zr₁₇Ni₁₂ to yield the best properties.

Symposium T: Materials Innovations for Next-Generation Nuclear Energy
On the second day, symposium T attendees joined with those from symposium E to together focus on how modelling and simulation can be used to predict the properties of nuclear materials under a combination of high radiation, stress and temperature. A particular focus was the development of joined-up modeling across length and time scales under these extremes of the environment.

Symposium V: Materials Science of Water Purification
Creating Advanced Water Treatment Membranes using Nanocomposite Materials
Access to adequate supplies of clean water is a growing concern throughout the world, and efficient and cost-effective desalination is sought. In Symposium V, Eric M. Hoek (UCLA) considered creating advanced water treatment membranes using nanocomposite materials technology. Reverse osmosis is the process of applying a hydraulic pressure to an aqueous solution to force water through a semipermeable membrane, thus separating salt from water. Yet, membrane filtration and desalination processes remain relatively nonselective, energy intensive, and fouling-prone. Fouling can be reduced by reducing the sticking efficiency. However, even when pure water passes through some membranes, the pressures can cause mechanical changes, compacting the membranes, and squeezing the pores. This further increases the pressure, and further compacts the film. Advanced membrane materials are combing organic and inorganic materials at the nanoscale to attempt to capture the best of both materials classes, such as stability, selectivity, flexibility, and processibility. The challenges include integration of the materials and how much of the nanoparticles can be loaded into the composite. Nanoparticles of 50-200 nm integrated with zeolite molecular sieve thin films of similar thickness are being used to create superhydrophilic surfaces that are highly negatively charged. This helps pull the water through the membrane. Hoek described a polyimide membrane with nanoparticles, showing that increasing the nanoparticle component led to more negative, hydrophilic, and even smoother membranes. Some films were even shown to not only resist fouling by bacteria, but to inactivate bacteria.

Symposium CC: Materials for New Security and Defense Applications
Materials for Applications in Space Environments
The space environment is critical for security and defense purposes because of the large number of satellites that are used. Phillip J. Cole (Sandia National Laboratories and Office of Nonproliferation Research & Development, National Nuclear Security Administration, Washington D.C) described the materials challenges faced by satellites. Materials have a major impact in this arena and there are several materials-related challenges that need to be considered. A primary driver in this community is the reduction of size, weight, power consumption, and cost for satellite payloads. Novel materials approaches and processes are required to enable these reductions. In addition, satellites must function in a variety of harsh environments that can include extreme temperature fluctuations, radiation exposure, particulate collisions, and long lifetime requirements. Cole described some of the materials that might enable large-scale transformations in the satellite community include novel and light weight composites and nano-composites for shielding, thermal management, and three dimensional electronics packaging, as well as coatings and sensor materials to dramatically enhance detection efficiency in current systems. He discussed the various orbits of interest such as LEO, MEO, GEO, Molniya and Tundra orbits. Each has its own peculiar set of issues and requirements. He elaborated on particulate filled high Z/polymer matrix composites as an example of the types of materials research being conducted and necessary in the future.

Symposium JJ: Nanowires--Novel Assembly Concepts and Device Integration
Precision Transport and Positioning of Nanowires by Electric Fields
Nanowires are an important class of nanoscale materials. However, it is very difficult to control and manipulate them in suspension. In her talk in symposium JJ, Donglei Fan (Johns Hopkins University) described the use of an electric field to precisely move and manipulate charged nanowires. A combination of dielectrophoretic (DEP) force and electrophoretic (EP) force generated by electric fields from patterned electrodes was used. This represents a combination of a DC field and an AC field. Thus transport and orientation of the charged nanowires could be independently controlled by the DC and AC fields. Fan demonstrated parallel, perpendicular and random movements of the nanowires, as well as programmed movement patterns such as a zigzag motion. She also demonstrated selective connection of two specific nanowires that were separated by 185 µm. A high precision of at least 150 nm was achieved. Finally, to reiterate how well they can control the nanowires using electric fields, Fan demonstrated nanowires "dancing" to music.

Ultra-thin Nanosheet Fabrication from Ultra-narrow PbS Nanowires
Currently, nanosheets, such as graphenes, are of significant interest both from the viewpoint of fundamental interest as well as potential applications. In his talk, Somobrata Acharya (National Institute for Materials Science, Tsukuba, Japan) described the use of the Langmuir Blodgett (LB) technique to form nanosheets of PbS nanowires as a bottom-up approach. The PbS nanowires coated with a surfactant (TOA) are floated on a liquid surface, similar to logs on a river, and are then pushed together. The LB technique is used to lift up the sheets and transferred en masse. Multiple layers are also possible. Acharya indicated that the highest ever pitch was achieved for these nanowires. The advantages of this method include scalability and the ability to heirarchically pattern these beyond the lithographic limit. A high yield of interconnected devices is possible. These nanosheets offer the opportunity for fabricating 2D devices for testing quantum confinement for example.

Symposium LL: Bioinspired Polymer Gels and Networks
DNA-Crosslinked Gels
Bernard Yurke of Bell Laboratories described the use of DNA as a means to cross-link polyacrylamide hydrogels resulting in novel functionality. It is known that two DNA strands can bind with each other very strongly if their base sequences are complementary, such as A-T and C-G. This can be used to form DNA-based nanostructures. It is also possible to form motors such as DNA tweezers wherein one part is double stranded forming a hinge while the others parts are single stranded and sloppy. By appropriately using hybridized single strand DNA, it is possible to close or open the tweezers, since duplex DNA is is stiffer than single-stranded DNA. Also, one member of duplex DNA can be displaced from the second member by a DNA strand that can form more base pairs with the second member. This process is called strand displacement. These properties of DNA can be used to cross-link gels. Yurke described the construction of gels that can be induced to undergo sol-gel transformations or viscosity changes through the application of particular DNA strands. Reversible gels can be formed which allow for swelling and shrinkage depending on the density of the cross-linkers. Such DNA cross-linked gels exhibit properties not easily realized using other materials. They can be isothermally assembled or disassembled. The mechanical properties can be modulated through the application of DNA. Yurke indicated that several potential applications are envisaged including drug delivery, scaffolding and as a substrate for tissue engineering and therapeutics or prosthetics.

IPOD WINNERS

The winners of Sunday's MyMRS iPod drawing are:

The winners are instructed to go to the MyMRS booth at the Hynes Convention Center to claim the iPods.

© Materials Research Society, 2007