2004 MRS Fall Meeting

"Science is People"
Alan MacDiarmid, 2004 Chemistry Nobel Laureate, speaking at the Fall Meeting

The 2004 MRS Turnbull Lecturer is Frank S. Bates (Univ. Minnesota). Bates presented his Turnbull Lecture in the afternoon on "Network Phases in Block Copolymer Melts". Linear polymers, such as polystyrene (S) and poly(isoprene) (I), contain long sequences of repeating chemical moieties (“mers”) that result in familiar products including clear plastics (e.g., S) and rubbery elastomers (e.g., I). Individually, these versatile materials find many commercial applications, for example, as clear packaging materials (S), or key constituents in automobile and aircraft tires (I). Linking two or more chemically distinct polymers end-to-end leads to an entirely different class of macromolecules, known as block copolymers (BC’s), which combine the desirable attributes of individual polymer blocks in a single hybrid compound. Diblock (e.g., SI) and triblock (e.g., SIS) copolymers have been studied experimentally, and produced commercially, for about four decades, and these “two-mer” compounds are well understood theoretically.

In general, thermodynamic differences drive segregation of polymer blocks into regions (usually referred to as domains) rich in each chemically distinct block type. However, chemical connectivity (i.e., covalent bonds) restricts such chain clustering to a molecular scale, resulting in an array of nanoscale morphologies that are governed by the overall polymer molecular weight, and composition (fraction of each block). Typical block copolymer domain dimensions lie between 5 and 50 nm. Whereas only four basic domain morphologies are encountered with two-mer BC’s (spheres, cylinders, lamellae, and a cubic network), at least twenty five different ordered structures have been documented with linear three-mer, or ABC, block copolymers. Bates described an experimental strategy that was employed to identify molecular parameters (molecular weight and block compositions) that lead to the formation of triply periodic and triply continuous morphologies referred to as network phases. These intricate structures offer unprecedented opportunities to combine three different polymers, endowed with various physical properties, in single component self-assembling multicontimuous nanocomposites.

Model poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock copolymers were prepared by anionic polymerization, and characterized using a variety of techniques. 1,2 Small-angle x-ray scattering (SAXS) was employed to establish the ordered state symmetry of these materials. Three different network phases were identified, one with orthorhombic symmetry, flanked as a function of composition by two different cubic phases. Transmission electron microscopy (TEM) images obtained from each network structure, interpreted with the aid of mathematical modeling of the spatial distribution of polymer nanostructures, resulted in a definitive phase portrait. These phase assignments were further tested using dynamic mechanical spectroscopy and birefringence (rotation of polarized light) measurements. Recent (unpublished) self-consistent mean-field calculations performed by Chris Tyler and Dave Morse, also from the University of Minnesota, provide a fundamental theoretical basis for understanding these results.

This presentation summarized the achievements of five of Bates' students: Travis Bailey, Cordell Hardy , Thomas Epps, Eric Cochran, and Ryan Waletzco. Their research accomplishments provided fresh insights into the molecular factors that govern complex self-assembly in block copolymers. All three equilibrium network morphologies, and a fourth metastable one 3, are topologically related, each being constructed from a skeleton structure characterized by three-fold connector symmetry. Along with advancing our understanding of soft material phase behavior (a field that encompasses various other forms of amphiphilic compounds such as lipids, soaps, and surfactants, along with liquid crystals and colloids), these discoveries offer exciting prospects for developing new nanocomposites with a variety of practical applications.

The second day on symposium X featured two talks on biomaterials and metallic glasses. Rebecca Bergman (Medtronic Inc.) gave the first talk on innovations in biomaterials. She started by defining biomaterials as materials in medical devices that are intended to interact with biological systems. Currently, medical devices form a $50 billion industry with over 11,000 companies in the US alone. Bergman gave a quick historical overview of biomaterials with the most progress made over the past three decades or so going from materials to biactive devices to biointeractive devices. She stressed the fact that it is a regulated industry, with the FDA (U.S. Food and Drug Administration) approving devices and not materials per se. Bringing a biomaterial to market is still a long, expensive process which may explain why Medtronic uses only 25 polymers and 11 metals in all its approved devices. She admitted that innovation may be stifled because of the long path for testing and approval. She then discussed four representative innovations in the field: Surface modification (examples of plasma treatment of silicones and chemical grafting for blood compatibility), drug/device combination (example, drug eluting stents with a coating), new materials such as Nitinol, and tissue engineering. Looking forward, Bergman suggested that four major areas of advances, computers (bits), networks (neurons), biotech (genes) and nanotech (atoms) are all coming together leading to very exciting possibities iin terms of new technologies and applications. She concluded by expressing her strong belief that the future will see a tremendous transformation in healthcare going from treatment to cure and prevention.

The second symposium X talk was given by Prof. William Johnson (California Inst. Tech/LiquidMetal) on bulk metallic glasses (amorphous alloys). Johnson started with a description of bulk metallic glasses (BMG) and their mechanical properties. He described the evolution of BMG engineering materials over the last few decades. However, the most significant advances have come in recent years including development of Cu-based and Fe-based amorphous alloys in large-enough sizes that they can be considered for structural applications. Johnson described various processing conditions and parameters for these materials. He also described applications including in medical arenas and sports (golf clubs). Johnson concluded by suggesting that bulk metallic alloys have tremendous potential. They have very high strengths and outstanding mechanical properties. Processes such as high pressure injection casting of complex parts and thermoplastic injection molding can be performed with relative ease yielded high quality parts. The technology is now being extended to low-cost alloys. He concluded by suggesting that bulk metallic alloys represent a pervasive and high-impact technology.

A5.13
Preparation of TiO₂ Micro Wire Sensor Prepared by Phase Separation-Selective Leaching Method. Atsuo Yasumori, Jun Yoshida, Hayato Matsumoto and Keishi Nishio; Department of Materials Science and Technology, Tokyo University of Science, Noda-shi, Chiba, Japan.

C5.5
Metal Nanotube Membranes with Sub-100 nm Apertures and their Lithographic Applications. Woo Lee¹, Hongjin Fan¹, Sung-Kyun Lee¹, Stefan Richter¹, Sven Matthias¹, Wulf Wulfhekel¹, Margit Zacharias¹, Dietrich Hesse¹, Juergen Kirschner¹, Eric Moyen², Margit Hanbuecken², Kornelius Nielsch¹ and Ulrich Goesele¹; ¹Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany; ²CRMCN-CNRS, Campus de Luminy, case 913, 13288 Marseille Cedex, France.

M5.14
Analytical TEM Study of the Degradation Phenomena in Proton Exchange Membrane Fuel Cell. Tomoki Akita, Junko Maekawa, Akira Taniguchi, Koji Tanaka, Masanori Kohyama and Kazuaki Yasuda; Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan.

Y6.14
Time-dependent Mechanical Behavior of Human Stratum Corneum Kenneth S. Wu¹, Eilidh Bedford², David J. Moore³ and Reinhold H. Dauskardt⁴; ¹Mechanical Engineering, Stanford University, Stanford, California; ²Unilever Research and Development, Port Sunlight, United Kingdom; ³Unilever Research and Development, Edgewater, New Jersey; ⁴Materials Science and Engineering, Stanford University, Stanford, California.

Symposium B
Kent Choquette (Univ. Illinois, Urbana-Champaign) presented a paper on photonic crystal vertical cavity surface emitting lasers. Vertical Cavity Surface Emitting Lasers (VCSELs) are promising sources for telecommunications wavelengths, but generally display undesirable multiple transverse modes. Choquette’s group has demonstrated a single-transverse mode quantum-well VCSEL with more than 3mW of power whose transverse confinement is due to a periodic array of holes etched into the VCSEL surface. The holes form a 2D photonic crystal that supports only one transverse mode when a single hole position is left un-etched (a “defect”). The group has also demonstrated multi-lobed far-field laser patterns when several defects are present. The physics of the confinement is the same as that of photonic crystal (PC) fibers, although the scaled depth of the holes is much shorter than in PC fibers and therefore does not provide as strong transverse confinement.

Symposium J
The first session in symposium J was on Magnetic-Photonic Crystals with three invited speakers. Mitsuteru Inoue (Toyohashi Univ. of Tech.) presented results on the fabrication and testing of SiO2/Bi:YIG (yttrium iron garnet) magnetophotonic crystals (MPCs). By applying a bias magnetic field along the axis of optical propagation, Inoue demonstrated simultaneous high optical transmission and large Faraday rotation in a thin-film, one-dimensional MPC. His system includes an extra-long central Bi:YIG layer which forms an effective Fabry-Perot cavity, leading to concentration of optical intensity in this layer and thus enhanced magneto-optical effects. Dr. Inoue is also investigating 2D MPCs based on Al2O3 templates and Bi:YIG rods and 3D MPCs using a self-organizing technique. This technology is likely to have important applications for magneto-optical devices including optical isolators and spatial light modulators for holographic memories.

In the next talk, Alex Figotin (Univ. California, Irvine) discussed the use of magnetic photonic crystals as artificial magnetoelectric media. Unlike their dielectric counterparts, magnetophotonic crystals (MPCs) can display non-reciprocal spectral properties, including asymmetric dispersion relations and unidirectional propagation of light. Dr. Figotin argued that both time reversal and space inversion symmetry must be lacking in an MPC for it to display non-reciprocal properties. He predicted the existence of a “frozen mode” in which the group velocity of an optical pulse in a 1D MPC with three-layer unit cells is large in one direction and nearly zero in the opposite direction. The frozen mode regime can display very little pulse reshaping, and could be useful for optical isolation or optical pulse storage.

Soren Kahl (Swedish Royal Inst. of Tech.) next gave a presentation on the magneto-optical response of a one-dimensional all-garnet photonic crystal in transmission and reflection. Kahl’s group has fabricated and tested a magnetophotonic crystal (MPC) made of alternating bismuth and iron ytrrium garnet (BIG andYIG) layers, with a total thickness of 1.5 mm and transmission peak around 750nm. The structure contains an extended central BIG layer that acts as a Fabry-Perot cavity, and displays high transmission and Faraday rotation. Kahl also reported studying the system in reflection by coating one side with a Ag reflection layer, which led to strongly enhanced Faraday rotation at the transmission peak. He concluded by proposing using reflection-coated MPCs in magneto-optical imaging, calculating good contrast and sensitivity for such a technique.

Symposium M
Koji Sugioka reported on progress in the area of lab-on-chip device manufacturing. These devices combine microfluidic, micromechanical, and microoptical components that can be used for field-deployable chemical analysis with high efficiency, high accuracy, and high performance. Such devices can be used for human gene and protein analysis, medical inspection, and new drug development. Sugioka showed how 3-D hollow microstructures in photosensitive glass can be made by direct writing of latent images in the glass using a femtosecond laser, baking the samples, and then etching in diluted HF for selective removal of modified regions. Structures were demonstrated that combine streams of fluids and control their flow with microvalves, which then can be analyzed with light controlled by micromirrors, all on a chip.

Symposium Y
In symposium Y, Dinesh Katti from North Dakota State University presented studies on nacre that were carried out over the last several years. In particular, his group is interested in the very advanced mechanical properties of nacre that are comparable to modern “high technology” ceramic materials. The eventual goal of this research is simulation-based design of biomimetic nanocomposites. In his research group, simulations of nacre based on the finite element method using nanoscale material properties obtained from nanoindentation tests were started several years ago. Back then, they conducted simulations on a simple “brick-mortar” model of nacre. Among other simulations, the group carried out tensile test simulations including elastic and inelastic response to address yield conditions. They discovered that organic material in nacre feature extremely high Young’s moduli of the order of 20 GPa, and they find that the yield stress of organic would need to be as high as 400 MPa based on calculations with the simple brick-mortar architecture model. When mineral contacts are incorporated, results suggest that the mineral contacts break long before yielding of nacre occurs. More recently, the group addressed the role of nano-asperities on the properties of nacre. Additional research focused on experimental investigations based on dog bone shaped samples of nacre, in which their group studied fracture mechanisms and fracture surfaces of nacre. An additional interesting observation was that the Katti group discovered platelet-platelet interlocks from observation of fracture surfaces which they believe is one of the key reasons for the strength and high toughness exhibited by nacre. The scientists using FE simulations of nacre with interlocks undergoing loading observed that these interlocks show progressive failure, which along with deformation of the organic and aragonite leads to toughening. This suggests that the interlocks play an important role in the relatively large-strain behavior of nacre before it fails.

Symposium Z
In symposium Z in the afternoon, in the session on bio-optics and biophotonics, the first talk was given by Joanna Aizenberg (Bell Labs/Lucent) on biologically formed microlens arrays. The focus of her talk was on brittlestars which are light-sensitive. The skeleton of the brittlestar consists of five components which are made of calcite, and the underlying substrate was shown to be a complete single crystal. The dorsal arm plate has unusual and very regular spherical structures which were determined to be lenses. This was shown by using these as imaging lenses and using a photoresist and shining light through the lenses. Quantitative characterization of the microlenses was carried out and spot size at the focal plane was ~3 microns with a light enhancement of ~50 at the focal point. Detailed studies indicated that the organism is able to correct for spherical aberrations and birefringence. At the focal point for each lens element, a bundle of nerves was observed whose size is about the same as the focal spot size. Similar to adjustable sunglasses, the organism uses these lenses to detect the light intensity and inject pigment to the surface leading to a color change. Aizenberg mentioned that it has compound eye capability and is the only know inorganic compound eye. She also described the calcite crystal as being mechanically reinforced by intercalated proteins leading to unusual mechanical properties. She concluded by saying that this is a great example of a multifunctional material, and an inspirational system for technology. The system is a nearly perfect combination of microlenses for "crystal-clear vision".

Symposium HH
The long wait for commercial carbon nanotube-based electronic devices is almost over according to Jean-Christophe Gabriel from Nanomix Inc., a California based start up that expects to be marketing single-walled carbon nanotube (SWNT)-based hydrogen sensors by early 2005. Delivering an invited talk in Symposium HH, Gabriel discussed the tremendous versatility of sensors based on carbon nanotube field effect transistors, which he compared to nerve cells capable of sensing different stimuli. While single nanotube transistors are too fragile to be useful over long periods of time, networks and arrays of nanotubes make robust sensors, while also giving high signal-to-noise ratios with low power consumption, therefore enabling wireless applications. The tremendous sensitivity of the transport properties of SWNT devices to small environmental changes is ideal for sensing applications but also requires that nanotubes be functionalized to be selective and specific for certain analytes. Metal functionalized nanotubes make for excellent hydrogen sensors capable of detecting levels of hydrogen with great sensitivity. Further applications being explored at Nanomix include a polymer functionalized SWNT sensor for CO2 and biofunctionalized nanotube sensors for biomolecule detection in liquid environments.

Symposium II
David Srolovitz ( Princeton Univ.) presented an invited talk in symposium II on continuum mechanics-based modeling of carbon nanotubes. Particular focus was on carbon nanotubes with “inclusions” or so-called intercalations of specific atomic species or molecules into carbon nanotubes. He focused on C60 molecules (buckyballs) intercalated inside carbon nanotubes, also referred to as a “pea in a pod” system. Srolowitz’s group succeeded in modeling the interaction of the “peas” with the “pod” and deriving associated analytical expressions. The scientists discovered that the displacement due to the pea decays exponentially with the distance from the pea, and the solution features an oscillatory character. A virtual work argument was used to calculate the interaction energy of two peas. Srolovitz also covered composite nanotubes which are new materials based on using different type of CNTs made out of different atomic species, such as C, BN, or WS2. Tubular structures of different types are incorporated into a single tube to form complex composite nanotubes. Such structures have been synthesized recently for example as multi-wall tubes with different layers. Srolovitz reported analytical models for such multilayer tubes in which the interactions between different concentric tubes are dominated by van der Waals interactions.

Prof. William Goddard, III (California Inst. Tech.) reported recent progress in first principles-based multiscale modeling of novel nanoscale devices. A particular focus of the first part of his talk was on Heath-Stoddard switches based on catenane and rotaxane molecules that can be used as “solid-state” switches. Important questions that were addressed include how the molecules interact and pack on surfaces, and to determine some of the details of the behavior of these switches by computer simulations, such as current-voltage relationships. Goddard and his group used the Green function approach to obtain the current-voltage relationships of molecular switches from first principle simulations. Interestingly, the quantum mechanical modeling clearly supports some of the key experimental results of current-voltage behavior. Another question that was addressed was how the molecules pack on surfaces. This was done by performing simulations of langmuir monolayers of amphilic rotaxane molecules. Computations were used to find the optimum coverage of the molecules at the surface. As an outlook, Goddard proposed development of switches that feature three states instead of two.He mentioned several ongoing projects of ab initio based modeling of small-scale devices. For example, he presented recent progress in studying electronic transport through organic molecules. Other projects include development of an organic nanoscale transistor, modeling of carbon nanotube formation based on reactive force field modeling, as well as development of new “smart” actuator materials that operate at frequencies of up to 8-10 GHz. Design of new actuators based on theory helps to examine their properties before actually building the system in the lab, and is a relevant example of de novo materials design.

Symposium OO
To measure diffusion in metals at low temperatures you “need a grad student to be around for a few hundred years,” Alex King said in Symposium OO. Since that is not always possible, the usual alternative is to extrapolate from high temperature behavior. However, such extrapolation is vulnerable to error if the diffusion mechanism changes within the range of the extrapolation. As an alternative, can examining an artifact shed light on low-temperature diffusion? King, from Purdue University, described the examination of a Sheffield plate—a silver-clad copper manufacturing technique used between 1740 and 1840—to understand low-temperature diffusion in the Cu-Ag eutectic system. The bond is formed in 1 minute at 780 degrees C, but then the samples have sat for about 200 years at 25 degrees C. Bulk diffusion profiles can be observed due to this initial processing and modeled as the starting point of the long-term, low-temperature diffusion experiment. The samples show the result of grain-boundary diffusion over the next few hundred years. Comparing the results of this diffusion profile showed that the diffusion is either the same or lower than that extrapolated by several models, which is good for trying to ensure stability over long time-scales at low temperatures.

Venetian painters of the 1500s such as Titian and Giovanni are noted for the brilliance of their colors, which distinguishes their work from other painters of the day. The discovery of a 1543 materials inventory of a Venetian pigment store has led Barbara Berrie (National Gallery of Art) to re-examine the materials that make up the Renaissance Venetian palette. Using scanning electron microscopy and energy dispersive spectrometry techniques, Berrie has found evidence of the use of fine glass particles as paint extenders and colorizers in paintings by several Italian painters of the period, including Lorenzo Lotto, Raphael, and Tintoretto. An audience member noted that the optical properties of silicon particles depend strongly on their size and asked whether these painters may have experimented with creating some form of glass-particle light traps in their paints to achieve their brilliant colors, to which Berrie replied that Renaissance painters may have done so, and were likely “better technologists” than is commonly thought.

Also in symposium OO, Sharon Miller (NASA Glenn Research Center) discussed atomic oxygen treatment and its effects on a variety of artist’s media. While atomic oxygen treatment was initially developed to study the durability of materials for low-Earth orbit, it has become a useful tool in cleaning works of art. Using a plasma of atomic oxygen, Dr. Miller has been able to remove soot damage from a variety of artist media including oil and acrylic paint and watercolors, with minimal spectral or brightness change to the materials. She has also demonstrated that the technique can eliminate a large variety of ink-based graffiti marks. Among various works of art to which it has been applied, Miller’s atomic oxygen technique successfully removed a lipstick stain from the valuable Andy Warhol sketch “Bathtub”, kissed by an admirer during a 1997 party thrown by a cosmetics company.

Symposium PP
Martin Bakker's group (Univ. Alabama) has nearly completed its materials-education computer game designed to educate middle-school students about the periodic table. The game, sponsored by the NSF, MRS, and the University of Alabama, is broken into seven modules of increasing difficulty as reported by him in symposium PP. Successful players earn “Carbon Cash” and can improve their “Dream Room” as rewards for correctly mastering concepts and facts related to the periodic table. Shipment of the beta version has been delayed until Spring 2005 because Dr. Bakker ran afoul of bureaucratic requirements at the university. As he declared in his Lessons Learned slide, “Never underestimate paperwork!” Any educator interested in obtaining a copy of the game should contact Dr. Bakker at bakker@bama.ua.edu.

NIST SEMINAR

On Tuesday evening, as part of the government seminars, Clare Allocca and Douglas Smith of the National Institute of Standards and Technology gave a presentation on NIST's role in the U.S. National Nanotechnology Initiative. Earlier this year, an interagency Workshop was held to address the Grand Challenges of this initiative. NIST led the session on instrumentation and metrology for nanotechnology. They assessed the needs and priorities for nanomechanics. The issues of standardization and calibration and of modeling of nanomechanical experiments came out on top. A Roadmap is being drafted and is scheduled for release next year.

NSF MRSECs - 10th ANNIVERSARY CELEBRATION

The NSF MRSEC program is celebrating its 10th anniversary and a special function was organized in the evening. Dr. W. Lance Haworth, Executive Officer of the National Science Foundation Division of Materials Research, gave an overview presentation of the MRSEC program using the Paul Gauguin painting (displayed in the Museum of Fine Arts, Boston) "Where Do We Come From? What Are We? Where Are We Going?" as a metaphor for the talk. He said the title was very appropriate for the celebration.

Haworth presented a historical overview of the program starting with the original MRLs, which were the precursors to the MRSECs. He suggested that peopl could visit the MRSEC website to get all the information they needed on the program and the centers. Haworth presented a current snapshop of the program and gave examples of interdisciplinary research stemming from the various MRSECs. He mentioned that it was still a challenge broadening participation of women and minorities in the program. He suggested that it may be useful to list some big questions for future materials research, or perhaps that in itself be the wrong question to ask. He concluded by indicating that by all accounts the program has been a complete success.

Next, Alan MacDiarmid (Univ. Penn.) who is one of the 2000 Nobel Laureates in Chemistry, talked about interdisciplinarity and its importance for scientific research, particularly for materials research. He described the work done by himself (synthetic organometallic chemist), Alan Heeger (experimental physicist) and Hideki Shirakawa (synthetic organic chemist) that led to the discovery of conducting polymers that won the 2000 Nobel prize in chemistry. MacDiarmid suggested that the breakthoughs came because of the interdisciplinary nature of their collaboration. He said that interdisciplinarity is at the heart of the MRSCE program. He concluded by suggesting that cheap alternate energy is the solution for a number of problems facing humankind and we need an international crash research program similar to the Apollo moon program last century.

Following the talks, there was a poster session displaying the work and accomplishments of the various MRSECs and a reception.

Compiled and edited by Gopal Rao, MRS Web Science Editor, with additional contributions by Betsy Fleischer, Judy Meiksin, Sarbajit Banerjee, Markus Buehler, Colin McCormick