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【原創(chuàng)】2009 Materials Research Society Spring Meeting Scene - Day 1
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2009 MRS Spring Meeting April 13 - 17, 2009 San Francisco, California DAY 1 MONDAY, APRIL 13 The 2009 Materials Research Society (MRS) Spring Meeting commenced in San Francisco on Monday, April 13. The major events of the day included nine tutorials, the Fred Kavli Lecture In Nanoscience by Joanna Aizenberg, a seminar on mastering public presentations and a professional development workshop for women.  Joanna Aizenberg (Harvard University) receiving the Kavli Lectureship Award in Nanoscience from MRS President Shefford Baker CONTENTS Fred Kavli Distinguished Lectureship In Nanoscience: Prof. Joanna Aizenberg Tutorial A: Thin Film Silicon Materials and Devices for Large-Area and Flexible Solar Cells and Electronics Tutorial N: Applications of Thermoelectric Technology Tutorial GG: Introductions to Electron Crystallography and Precession Electron Diffraction Professional Development: Mastering Public Presentations Scenes from the Meeting Spring Meeting Facebook Group MRS Meetings Blog FRED KAVLI DISTINGUISHED LECTURESHIP IN NANOSCIENCE: PROF. JOANNA AIZENBERG Biomineralization Inspires New Nanofabrication Strategies  The recipient of the 2009 Kavli Distinguished Lectureship in Nanoscience is Professor Joanna Aizenberg of Harvard University. She presented her Kavli Lecture in the evening on April 13 during the MRS Spring Meeting. She started by stating that Echinoderms, which are a phylum of marine animals, including the sea star, are amazing in terms of the lessons that they can teach us in nanoscience. She started with crystal growth. The calcitic skeleton in Echinoderms is made up of individual single crystalline elements with pores with controlled sizes. This was used as the inspiration to grow oriented calcite crystals on self-assembled monolayers of organic molecules using stereochemical recognition. The critical issue to be noted here is that this is not epitaxy. She described how ordered arrays of oriented uniform crystals can be formed. In Echinoderms, crystallization of complex structures often occurs through transformation from a transient amorphous phase stabilized by specialized macromolecules, and her group has used this for bottom-up fabrication of micropatterned single crystals.   Next, Aizenberg described the microlens arrays found in brittle stars that change color based on whether it is day or night. This was used as the inspiration to create synthetic tunable microlens arrays with pores by combining polymer synthesis, optics, and microfluidics. She then discussed lessons learned in actuation at the nanoscale. The surfaces of Echinoderms are covered with moving spines and pedicellaria, which are environmentally responsive microactuators that provide a very effective antifouling mechanism. Aizenberg and her co-workers were able to replicate this using arrays of isolated, high-aspect-ratio rigid structures (AIRS) along with hydrogels. In the contracted state of the hydrogel, the nanocolumn structures were bent, but in the swollen state, the nanocolumns stood straight. This was used to create superhydrophobic-hydrophilic transition structures as well as responsive “nanograss.”  Finally, Aizenberg described lessons learnt from dynamic, hierarchical self-assembly. Based on the level of the bending force and capillary force, a critical pillar length can be calculated for nanoscale pillars, and different regimes can be described based on the pillar length, yielding chiral rearrangement, and twisting of pillars. This higher regimes yield higher order helical, chiral assemblies of the nanocolumns. The handedness of the chirality could also be controlled. This was used for particle trapping of polystyrene spheres. Aizenberg concluded by suggesting that Echinoderms and biomineralization have a lot to teach us in the nanofabrication of a space. These bioinspired architectures have enormous potential for a variety of future applications. TUTORIAL A: THIN FILM SILICON MATERIALS AND DEVICES FOR LARGE-AREA AND FLEXIBLE SOLAR CELLS AND ELECTRONICS A two-part tutorial on thin-film Si-based materials for large-area and flexible electronics applications was presented as one of nine tutorials on Monday. Large-area electronics has essentially enabled the flat-panel display industry, which is currently worth over $80 billion annually. Amorphous Si is also extensively used in solar cells, which has seen tremendous growth in recent years. New applications are now emerging in areas such as biosensors and MEMS.  The morning session of the tutorial was presented by Andrew Flewitt of Cambridge University, UK, who described various materials, including amorphous, microcrystalline/nanocrystalline and polycrystalline silicon, as well as silicon carbide, silicon nitride, and silicon oxide. He showed the properties for each of these materials. He then presented various growth and crystallization techniques used such as plasma-enhanced chemical vapor deposition (rf-PECVD) at temperatures under 400°C and low-pressure CVD at 800°C for a-Si:H. Poly-Si is formed by crystallizing a-Si:H using thermal or excimer laser crystallization. He discussed electrical properties of the materials, including doping and metastability. Flewitt summarized various characterization techniques for thin-film Si materials such as ellipsometry, UV-vis spectrometry, FTIR, and Raman spectroscopy. He also discussed contacts, various substrates used, and other technologies including amorphous oxides and organic semiconductors.  In the afternoon session, Arokia Nathan of University College, London, UK, addressed applications of thin-film Si materials. He first discussed thin-film transistors, including a-Si and poly-Si device structures. He then talked about active matrix displays and imagers, including AMLCDs, AMOLEDs. He discussed pixel architectures, driving schemes, imaging detection schemes, device structures and spectral response. All of these are crucial for applications in displays and imagers. He also focused on various fabrication issues. For solar cells, Nathan described p-i-n and n-i-p structures as well as other architectures. He closed with a discussion of other applications including bolometry (for measuring the energy of incident electromagnetic radiation), near-IR imaging, thin-film Si MEMS, thin-film bio-MEMS and a-Si:H photodetectors in biosensors.  TUTORIAL N: APPLICATIONS OF THERMOELECTRIC TECHNOLOGY From deep space exploration to automotive applications and incinerators, Tutorial N, “Applications of Thermoelectric Technology,” examined how to take heat and turn it into electrical power using thermoelectric materials. By coupling the electrical and thermal currents induced by an electric field and a temperature gradient, power can be produced. Thierry Caillat from the Jet Propulsion Laboratory/California Institute of Technology, focused on radioisotope thermoelectric generators, which traditionally use either PbTe or SiGe alloys as the thermoelectric material, and plutonium-238 as a heat source. Because the basis for the energy generation is a temperature gradient, there are not moving parts, and they are reliable over long periods of time. While large temperature gradients cause stress, for space applications, once the hot temperature is reached, it is held steady rather than cycled and poses less of a problem. For SiGe alloys, sublimation is a concern. In addition to loss of material over time, material can deposit on components, affecting conductivity or even shunting some electrical currents. In automotive applications, presented by Francis R. Stabler, Future Tech LLC, thermal cycling is more of an issue, particularly for vehicles with engines that shut off when stopped. Another concern is scaling up the technology, for instance, using elements such as Te, which is relatively rare. Currently, refinery production of Te is 120,000 kg/year, and if all was used for this application, this would be enough for 256,000 cars—a small fraction of 1% of vehicles worldwide. Finally, the cost needs to be considered with respect to all components. Ryoji Funahashi, National Institute of Advanced Industrial Science and Technology, Japan, concluded the tutorial with a focus on oxide thermoelectric generation, noting that two-thirds of energy used is released as waste heat in Japan. The goal is to convert this heat into electrical energy. Thermoelectric conversion can be used for even small amounts of heat and is suitable for recovery from waste heat, and the high-power density is good for small, lightweight, mobile use. Oxides have advantages over previous alternatives to avoid toxic or rare materials and to eliminate concerns of melting and oxidation. Using high-throughput synthesis, oxides of interest include Ca3Co4O9 as a p-type material and LaNiO3 and CaMnO3 as n-type materials. Funahashi described how in Japan, waste is incinerated, and, in general, it is expensive to recover the heat, because the gases can be corrosive to the boiler using more traditional recovery techniques such as steam turbines. However, oxide thermoelectrics can be operated at higher temperatures and thus show great promise.  Theirry Caillat, tutorial N speaker on “Thermoelectric Materials and Components for Radioisotope Thermoelectric Generators.”  Tutorial N speakers Ryoji Funahashi, Francis R. Stabler, and Thierry Caillat TUTORIAL GG: INTRODUCTIONS TO ELECTRON CRYSTALLOGRAPHY AND PRECESSION ELECTRON DIFFRACTION Electron crystallography is an emerging field and technique that has several advantages over the much better known x-ray crystallography (XRD), including the fact that electrons can be focused into an image and due to the much stronger interaction of electrons with matter, which allows for nanoscale samples to be studied. Sven Hovmöller (Stockholm University, Sweden) presented a nice overview of electron crystallography in tutorial GG. Currently, efforts are under way to develop methods for electron crystallography that are as easy to use as the methods available for XRD. While electron crystallography can be used to identify known phases of materials, a more interesting aspect is its ability to determine the 3D structure of new unknown phases. Hovmöller went through the process of identifying a new unknown phase using software developed in his group. He demonstrated the structure determination for a zeolite, a porous silicate, using electron crystallography from 3 axial projections using 3D data (Science, 315 (2007) 1113-1116). This structure could not be solved using conventional x-ray powder diffraction due to its complexity.  A major problem in electron crystallography is multiple scattering, and this is where precession comes into the picture. In precession, the electron beam is rotated in a conical way, such that a crystal aligned along a certain direction becomes misaligned (by up to about 3°). The rotation can be done at any speed, from 1 Hz to 100 Hz. Precession is superb for obtaining high-quality electron diffraction patterns from zone axes. Precession electron diffraction in a transmission electron microscope (TEM) was discovered by Vincent and Midgley (Ultramicroscopy 53 (1994) 271) in Bristol, UK. In the second part of the tutorial, Stavros Nicolopoulos (Consultant, IUCr Electron Crystallography Commission, and Director, NanoMEGAS SPRL, Belgium) detailed precession electron diffraction, including phase and orientation mapping (EBSD-TEM) and structure determination of nanocrystals. He emphasized that precession electron diffraction is the right way to solve nanostructures in a TEM. Precession intensities behave much closer to ideal (kinematical) intensities, and therfore they can be used to solve crystal nanostructures.  Nicolopoulos has developed a novel dedicated device for a TEM for precession electron diffraction called Spinning Star which he described in detail. He presented examples of structure solution using precession including pharmaceutical nanocrystals such as penicillin G-potassium and protein lysozyme nanocrystals. He described a new tool (ASTAR) to perform electron backscattering diffraction (EBSD) analysis that relies on electron diffraction pattterns, for phase mapping and local crystal orientation determination for materials characterization. This allows for ultra-fast TEM orientation mapping. He showed applications in steels, semiconductors, and nanoparticles. The tutorial overall demonstrated that electron crystallography and precession electron diffraction add to the range of techniques available to materials scientists for advanced materials characterization using electron microscopes.  PROFESSIONAL DEVELOPMENT: MASTERING PUBLIC PRESENTATIONS Science education consultant Tim Miller practiced what he preaches during his seminar entitled, “Mastering Public Presentations.” The seminar is one of the latest additions to MRS’s professional development offerings. Over 60 MRS members attended the two-hour-long seminar, which was made possible through funding from the Nanoscale Informal Science Education Network. During the presentation, Miller led attendees through fundamentals of constructing and delivering high-quality presentations. Topics he covered included voice projection, story line construction, appreciation of audience needs, and creation of visually appealing slides and graphs. Refreshments and an opportunity for networking followed the seminar. SCENES FROM THE CONFERENCE  Women's Professional Development Workshop       |
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