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Seminars
Dan Gamota Since the late 1990’s, scientists have suggested the use of non-photolithographic technologies to fabricate integrated circuits (IC). The recent discovery of several advanced electrically active inorganic and organic inks formulated with nanoscale particles has led to wide spread interest to design and launch a new family of printed electronic products e.g. signage/displays, sensors, and low RF devices. The total available market opportunities for these applications depend on cost. To achieve these cost targets, the materials and processes developed in the laboratory must be transferable to high-volume manufacturing environments. One low cost manufacturing approach that has been proposed is based on traditional graphic arts printing platforms. The use of these platforms is being enabled by the continual development of novel classes of electrically functional inks (conductive, dielectric, and semiconductive inks). In addition to the development of core printed electronics technologies, the need for a family of IEEE Standards and technology roadmaps such as the iNEMI Printed and Organic Electronics Roadmap is discussed. James D. Hoefelmeyer Technological implementation of an energy efficient water oxidation process has proven to be a significant challenge. Preliminary data using colloidal RuO2 to catalyze water oxidation are encouraging. Since particle size and shape can significantly influence the electronic structure and surface site profile of a substance, we hypothesize that there is an optimum dimensional combination for which RuO2 affords a maximum of activity toward catalytic water oxidation. In order to obtain structurally well defined samples, we propose to synthesize RuO2 nanocrystals using a non-hydrolytic method. The nanocrystals will be characterized using XRD and TEM facilities. The RuO2 will be supported on high surface area carbon. Thermal treatment of the material to remove the organic passivating layer will result in a pristine metal oxide surface. This RuO2/C will be used as a heterogeneous catalyst in a N2 purged aqueous solution containing a sacrificial oxidant in order to study water oxidation. As the reaction proceeds, the oxidant concentration and oxygen evolution will be measured using UV-visible spectroscopy and gas chromatography, respectively. The surface sites on the RuO2 will be quantified using gas adsorption experiments. Kinetics of water oxidation versus RuO2 particle size and shape will be compared. Jeff Shield Nanocomposite permanent magnets are the most promising class of permanent magnets to come along in recent years. These materials combine hard and soft magnetic phases at the nanoscale, and through exchange interactions achieve extraordinarily high remanence values. While great advancements in the energy density of permanent magnets have been predicted for these materials, the great expectations have not been realized. In our work, we have developed a better understanding of the magnetic reversal processes that occur in exchange-spring permanent magnets. This allows us to design specific microstructures that better resist demagnetization. Here, we utilize cluster assembly using inert gas condensation to construct “perfect” nanocomposite permanent magnets. Two structures have been investigated. The first imbeds soft magnetic a-Fe clusters in a hard magnetic FePt matrix. While improved energy products of 20.7 MGOe have been realized, the soft magnetic phase fraction remains relatively low. The second structure imbeds clusters in a non-magnetic matrix, minimizing interactions between clusters. The clusters in this case have compositions in a two-phase region, and after phase separation combine hard and soft magnetic phases at a scale of 2-3 nm. Here, the soft magnetic phase fraction is significantly increased, with a concomitant improvement in energy density to 25.5 MGOe. The greater understanding of magnetic reversal and the design of new structures provide renewed hope that ultra-high energy densities can be someday achieved in nanocomposite permanent magnets. Douglas B. Chrisey Pulsed lasers have unique qualities that can be applied to process living biomaterial/ceramic composites and they have proven to be an invaluable tool in research and development. We have developed advanced laser-based processing technologies for the deposition of patterns of biomaterials including ceramics, polymers, proteins, and even living biomaterials. In conventional tissue engineering, a three-dimensional porous scaffold is homogeneously seeded with cells. Ideally, through the controlled release of various growth stimulation and differentiation biomolecules from the scaffold, the cells will proliferate in a bioreactor and differentiate into a tissue that demonstrates characteristic biological function. Our approach allows the near cell-by-cell re-construction of biological tissue by a CAD design. This approach is superior to conventional tissue engineering because it can create a construct that is orders of magnitude more heterogeneous and thus representative of the desired tissue or organ to be created. The instantaneous heterogeneity only achievable by this technique is akin to the desired long-term differentiation obtained through conventional tissue engineering approaches. The more precise replication of natural tissue by direct writing will result in advanced tissue development and function and; it better utilizes nature’s genetic machinery for directed self-assembly. While directed self-assembly construction does not occur in typical synthetic molecules, it does occur in nature, partly because of the stereospecificity, homodispersity, periodicity and complementarity of the molecules built by the machinery of the cell. There are many applications for precise biomaterial patterns and robust tissue constructs including: basic studies of intercellular communication, biocompatibility studies for new materials and scaffolds, hybrid microfluidic and bioMEMs devices, tissue and organ regeneration, tissue-based biosensors, computer-aided surgery, and living microdissection and culturing. Dr. Juana Moreno Spin-based electronic (spintronic) devices utilize both carrier spin and charge to transmit or store information. Ferromagnetic semiconductors are ideal candidates for spintronic applications. We focus on developing a reliable theory of the magnetic, transport and optical properties of dilute magnetic semiconductors, such as GaMnAs. We employ the dynamical mean-field theory and its cluster generalizations to identify the materials properties that optimize the transition temperature for a generalized model of magnetic semiconductors. Since the successful design of spintronic nanostructures based on ferromagnetic semiconductors must include an understanding and careful analysis of disorder and spatial correlations, I also will discuss how we include these effects in our approach by using a new algorithm specific to dilute systems. I will discuss how we plan to extend our approach to heterostructures and thin films of magnetic, organic semiconductors. Professor John Ralston The interaction between a liquid and a solid surface is the key to understanding wetting phenomena, irrespective of whether they are static or dynamic. A very large number of natural and industrial processes rely on the delicate manipulation of this interaction. Controlled wetting is of central importance in microfluidics, mineral flotation, high speed coating, electronic display technologies, oil recovery, lubrication and plant protection. Scott A. Chambers Continued progress in spintronics requires the advent of ferromagnetic semiconductors in which magnetically aligned dopant spins couple to the band structure of the host lattice, resulting in spin polarization of free carriers. The Dietl prediction of Curie points (Tc) above room temperature (RT) in Mn-doped ZnO(1), and the subsequent observation of RT ferromagnetism in Co-doped TiO2 by Matsumoto et al.(2) have resulted in significant efforts aimed at discovering and understanding new candidate diluted magnetic semiconductors (DMS). The associated "high-Tc fever" has produced many false reports of new oxide DMS materials based on substandard materials science. Despite indefensible claims and invalid papers, the field is slowly progressing toward an understanding of the nature of the magnetism in these materials. Our approach is to combine careful epitaxial growth, detailed materials characterization, transport and magnetic measurements, and theory to allow structure-function relationships to be determined. In this talk, I will present our recent efforts on two classes of candidate oxide DMSs: (i) Co- and Cr-doped TiO2 anatase, and (ii) Ti-doped Fe2O3. We have explored the phase space of MBE growth conditions for doped anatase and have found parameters which lead to a significant improvement in crystalline quality relative to earlier work. We can now grow Cr- and Co-doped TiO2 with very high degrees of crystalline quality and uniform dopant distributions. Much to our surprise, the structurally near-perfect films are intrinsically paramagnetic.(3) RT ferromagnetism is associated with the formation of small-angle grain boundaries, as revealed by mosaic spread. The paramagnetic ground state for structurally perfect Cr-doped TiO2 with substitutional Cr(III) is predicted by FLAPW-DFT calculations.(4) Ti-doped Fe2O3 marks a different approach to DMS synthesis. Rather than dope a nonmagnetic semiconductor with a transition metal containing unpaired spins, as is typically done, we dope an antiferromagnetic semiconductor with a d0 transition metal. This approach amounts to removing rather than adding spins. α-Fe2O3 is an antiferromagnetic wide bandgap semiconductor (Eg = 2.2 eV) which exhibits strong ferromagnetic coupling within cation layers perpendicular to the c axis, and antiferromagnetic coupling between adjacent cation layers. LSDA + U calculations predict that substituting Ti for Fe should lead to a ferrimagnetic state with a large moment per Ti because Ti is predicted to substitute for Fe preferentially in alternating cation layers perpendicular to the c axis.(5,6) To test this prediction, we have used oxygen plasma assisted molecular beam epitaxy to grow α-TixFe2-xO3, for which x varied between 0.01 and 0.04, on α-Al2O3(0001). Excellent heteroepitaxy was achieved by first growing a α-Cr2O3 buffer layer to grade the lattice mismatch between α-Fe2O3 and α-Al2O3. All Fe was found to be in the +3 charge state by Fe K-shell XAS and Fe 2p XPS. Ti was found to be in the +4 charge state and to uniformly substitute for Fe(III) in the lattice by Ti K-shell XAS and EXAFS, along with ion channeling. The conductivity increased monotonically with x, achieving a value of ~100 Ohm-cm at x = 0.04. All doped films were found to be weakly ferromagnetic at room temperature, as expected if Fe ions were replaced with Ti(IV) ions in a statistical fashion in all cation layers. The coercive field was found to be ~800 Oe, independent of x. The moment was found to be ~0.5 μB per Ti dopant, considerably lower than the 4 μB per Ti dopant predicted by LSDA + U theory.(5,6)
Dr. Dean C. Webster
A series of UV cured polymer-clay nanocomposite films were
prepared from organomodified clays and a series of donor-acceptor matrix
resins. These films are being designed for use as high performance
laminates in flexibile electronic devices. Materials were processed by
mixing the clay with the matrix resin, followed by sonication to
disperse the clay. Studies of the photopolymerization of these systems
using real-time infrared spectroscopy indicated that the rate is
enhanced in the presence of the clay. X-Ray diffraction and
transmission electron microscopy showed that an intercalated morphology
was obtained. Cured films of the material showed improvements in the
glass transition temperature and modulus compared to the unmodified
polymer. The thermal stability of the systems was not affected by the
incorporation of clay.
Dr. David Galipeau There is a strong need for improved toxic gas sensors for many applications in homeland security, industry and agriculture. The objective of this work was to determine the feasibility of using electric field enhanced oxidation (EFEO) by scanning probe microscope (SPM) to fabricate semiconducting metal-oxide nanowires that could be used for sensing toxic gases. The effects of fabrication parameters such as metal film thickness, ambient relative humidity, SPM tip bias voltage, tip force, scan speed and number of scans, on the growth of nanowires was determined. Metal-oxide nanowires were also released from the metal films on which they were grown and the chemical composition of the nanowires was verified using Auger electron spectroscopy. These results indicate that certain metal-oxide nanowires can be grown and released from thin metal films.
Stephen Ducharme
Unique opportunities are emerging from the discovery of a method for
fabricating ferroelectric nanomesas approximately 10 nm high by 100
nm in diameter from Langmuir-Blodgett films of vinylidene fluoride
copolymers. The nanomesas, which are the smallest isolated
ferroelectric crystals, retain all the properties of the bulk
ferroelectric polymer: crystal structure, polarization hysteresis, a
ferroelectric-paraelectric phase transition, pyroelectric response,
piezoelectric response. They are promising materials for use in
high-density nonvolatile random-access memories, or infrared imaging
arrays. Further, they are can be combined with other active materials
to form nanoscale composites with potentially superior dielectric and
electroactive materials. Both nanomesa and nanowell patterns
fabricated by the same method may also provide useful templates for
forming or contact-printing nanostructured arrays of other materials.
Dr. Jan Puszynski
Dr. Randy Lewis Spiders produce both the strongest biological fibers as well as the most elastic. These fibers are composed almost exclusively of protein. The proteins involved in these fibers have been elucidated and their sequences determined from over 30 different spider species. Key features of these sequences will be presented and structures described. Based on these data the specific sequences responsible for elasticity and for strength have been hypothesized. To test these hypotheses synthetic protein genes have been generated and the proteins produced. These proteins contain either larger amounts of sequences for elasticity or strength. Examples will be shown. Additionally, computer modeling of the stretching of single protein molecules, assemblies of molecules mimicking those in a fiber and combinations for different molecules in the assemblies have been done. Examples of the stretching will be shown as well as the comparisons of strength and elongation for the different combinations.
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