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[交流] 【原创】IMRC 2009----DAY 5

DAY 5
THURSDAY, August 20
The XVIII International Materials Research Congress 2009 (IMRC 2009) concluded on Thursday after a successful five days of activities. The fifth and final plenary lecture of the conference was presented by Buddy Ratner on Thursday. A number of symposia also held sessions on this final day of the conference in beautiful Cancun.

CasaMagna Marriott (above) and JW Marriott (below) in Cancun, joint venues for the
XIII International Materials Research Congress 2009
CONTENTS
Plenary Lecture - Buddy Ratner
Technical Sessions
PLENARY LECTURE - BUDDY RATNER
Materials, Healing, and Regeneration: The Landscape Shifts

When the profession can no longer evade anomalies that subvert the existing tradition of scientific practice - then begin the extraordinary investigations that lead the profession at last to a new set of commitments, a new basis for the practice of science.
- T.S. Kuhn, The Structure of Scientific Revolutions
Buddy D. Ratner is a Professor of Bioengineering and Chemical Engineering at the University of Washington, and the Director of the University of Washington Engineering Research Center (UWEB). He has held distinguished positions in The Society for Biomaterials, American Institute of Medical and Biological Engineering, Tissue Engineering Society of North America, and Tissue Engineering and Regenerative Medicine International Society. His research into biomaterials, biocompatibility, and tissue engineering is extensive. To date he has published over 400 peer-reviewed works and has been issued 18 patents.
On the final day of the scientific program, Ratner gave an enlightening look into the changing perspective on what it means for a material to be deemed “biocompatible”. Traditionally biomaterials have been defined as materials designed to interface with biological systems. But Ratner noted that perhaps that definition is no longer sufficient. There is now a movement towards thinking of biomaterial properties in terms of precision cell control and tissue engineering. Since the conception of the biomaterial, it has been considered biocompatible if the material only elicits a minimal foreign body response which can include macrophage attack and encapsulation. However, even this nominal foreign body response limits the capabilities of the material and devices associated with it. Ratner suggested biomaterials can be engineered with the ability to integrate with tissues and cells. He illustrated this concept by giving several examples wherein cell phenotype and response were controlled mechanically.
The material 6S, developed by Healionics, contains a precise pore structure that is uniform throughout the material. It is believed that the geometry of these pores incites macrophage cell to behave in a manner that stimulates tissue reconstruction. This process has been observed subcutaneously, intramuscularly and in heart, bone, and scleral tissue among others. The phenomena occurs without respect to polymer type. PHEMA, a hydrophilic polymer, and silicone, a hydrophobic polymer, both show similar results. However pore size does seem to play an important role. Pore sizes close to 35 microns can induce tissue regeneration, but pore sizes outside of that range tend to promote encapsulation. The mechanism for this is not completely understood, but early research indicates the constraint of the pores forces macrophages into the type II phenotype. Ongoing research in scaffold fabrication and skin healing has shown this new approach to work in real world applications. Ratner concluded that perhaps the future of biocompatibility lies with the ability of materials in biological environments to trigger normal wound healing reconstruction and tissue engineering.

TALKS
Symposium 1. Nanostructured Materials and Nanotechnology
Exchange bias phenomenon in nanoparticles
Nanoparticles have large surface area-to-volume ratios, therefire surface and interface properties are especially important in determining nanoparticle properties. "The modulation of interactions at the interfaces represents a powerful route to enegineer the properties of nanoscopic systems," argues Carlos Luna Criado (Universidad Autonoma de Nuevo Leon). A particularly interesting case of interface properties is the coupling between the ferromagnetic (FM) core and antiferromagnetic (AFM) shell of a nanoparticle, producing a phenomenon known as exchange anisotropy or exchange bias. The unidirectional nature of the magnetic field at temperatures below the Neel temperature is unique, in contrast to the uniaxial characteristics of other types of anisotropy, in that it has two equivalent stable states of magnetization, whereas exchange anisotropy has only one. Further, electrical resistance was found to have a well-defined dependence on the applied magnetic field. Luna has fabricated AFM/FM core/shell nanoparticles by first forming noble metal seed particles, then initiating the chemical precipitation of Co and Ni from supersaturated polyol solutions, and finally oxidizing the surface to form an AFM shell to form particles with diameters 10-400 nm. Below the Curie temperature but above the Neel temperature, spins are aligned in the FM core; but when the particle is cooled below the Neel temperature, spins align so that the AFM shell domains closest to the core are aligned with those in the core. ZFC-FC curves were presented, as well as trends in the coersive force as a function of core particle diameter, which show two regimes of dependence, and of temperature, where manifestations of the exchange anisotropy are shown to be inversely proportional to the core diameter at temperatures below the blocking temperature. A shift of the hystersis loop is observed, consistent with prior reports, and the alignment of the AFM spins at the interface is found to be perturbed with cycling by the magnetization reversals of the FM core. Hematite particles were prepared to demonstrate the effects of surfaces and interfaces on spin frustration and disorder to show that the behavior of the core can be very different from that of the shell.
Green Chemistry applied to the synthesis of silver and gold nanostructures

Nanoparticles with tunable optical properties are of particular interest to photonic and biological devices. An environmentally-friendly chemical reduction procedure was used to synthesis Au and Au nanoparticles with controllable diameters, as presented in a poster by A.R. Vilchis-Nestor (Universidad Autonoma del Estado de Mexico). Aqueous Ag+1 and Au+3 were reduced by extracts of Camellia sinensis and Opuntia ficus indica. Bright-field TEM images confirmed the synthesis of nanoparticles, with particle size distributions reported. Diffraction patterns were indexed as the FCC structure for both Au and Ag systems. Absorption efficiency, excitation intensity, and excitation wavelength were all found to vary in both Au and Ag nanoparticle systems with extract concentration by UV-Vis spectroscopy.
Electronic properties of bimetallic clusters

Bimetallic systems exhibit unique and advantageous properties compared to non-doped, pure materials; especially for catalytic, electronic, and magnetic properties. The catalytic activities of these systems are extremely sensitive to cluster size and composition. Marcela Beltran (IIM-UNAM) investigated a variety of bimetallic alloys in small clusters by model potentials, combined with multiple density function theory (DFT) approaches and Guassian- and plane wave-type quantum mechanical calculations, to report electronic properties and ground-state geometries in hope of furthering the current understanding of catalytic activity. Binding energies, electron affinities, ionization potentials of Rh(n)Co(m) clusters, were presented. Au(n)Pd, Cu(n)Pd, and Pt(n)Pd(m) clusters were investigated, and theoretical predictions were compared to photoelectron spectroscopy results collected by collaborators. Beltran found that the geometric structure of Au(n)Pd(m) seemed to be maintained by the substitution of a Au atom by a Pd atom for the smallest clusters and that the structures become more planar with increasing Au incorporation, whereas that of PdPt maintained 3D geometries with increasing Pt content. Next, the geometric configurations of all combinations of PdAu with a total of 13 atoms were presented, with results indicating that Au will always be found at the cluster surface, regardless of the cluster composition, even if the configuration results in distorted geometries. Similarly, Pd was always found at the cluster surface in Cu(n)Pd(m) alloys. Beltran concluded that the electronic properties of CuPd clusters can be tuned by the composition of the alloy.
Ab initio MCSCF theoretical study of Rh(n) (n=2-4) nanoclusters interaction with NO and N2O molecules
Nitric oxide is the most toxic of the pollutants generated in vehicle exhausts. Although nitric oxide should be reduced to harmless molecular nitrogen by a three-way catalytic converter prior to exhaust, this reaction can be inefficient. Enrique Poulain (UAM-A) investigated the molecules produced by the reduction of nitric oxide by Rh catalysts, focusing on nitrogen oxide and nitrous oxide, as these compounds are both formed in the engine and are present in the exhaust pipe. Pure ab initio calculations were performed, without any approximations for the correlation energy, by an approach known as MCSCF-MP2. Geometry optimization was performed for each spin multiplicity of all potential systems. Basis sets for Rh, N, and O were taken from literature. Poulain found that the Rh catalyst atom always captures NO molecules by the nitrogen atom, with no activation of the NO bond, implying that some of the proposed reaction mechanisms in the literature are unlikely. Nitrous oxide was captured and softly activated by Rh. In all cases studied, there was charge transfer from Rh to O through the N atoms, although this process was found to be reversible. Future work is currently being conducted on Au and Pt catalyst atoms, and so far show behaviors different from that of Rh.
Symposium 2. Theory and Computer Simulation of Materials
Rare earths to pnictides: recent theory/computational insights

Significant knowledge gaps remain about the underlying physics of magnetism. B.N. Harmon (Iowa State University, USA) is working to "develop better magnets through property optimization" by computational modeling of Gd5(SixGe(1+-x)4, GdNi, CaFe2As2. Gd5(SixGe(1+-x)4 exhibits giant magnetoresistance, colossal magnetostriction, and the giant magnetocaloric effect, making it a promising candidate for applications in refrigeration. Harmon investigated the martensitic phase transition between the low-temperature orthorhombic phase and the high-temperature monoclinic phase to understand how the bond structure affects ferromagnetism. Characterization was performed by x-ray magnetic circular dichroism (XMCD), allowing for element- and orbital-specific tuning without nuclear absorption. XMCD data at the Ge K and Gd L3 absorption edges were presented, and the Ge K-edge implies that the Ge 4p states are spin-polarized. Agreement between calculated and measured XMCD validates the electronic structure calculation.
GdNi has a CrB-type crystal structure and unusual magneto-structural behavior: at low temperatures, enormous changes in lattice dimensions (with conserved unit cell volume) are observed. "The lattice dimensional change is coupled to the magnetism," explained Harmon. Magnetostriction behavior was presented, indicating strong magnetostriction values around liquid nitrogen temperatures, suggesting applications in actuators, sensors, and sonar. Finally, the unusual volume-collapsing behavior of CaFe2As2 was investigated. Large volume and magnetic moment "collapses" have been observed when CaFe2As2 is subjected to hydrostatic pressure. Harmon found that the minimum total energy phase switched to tetragonal under the collapsed regime when the magnetism was observed to disappear. By comparing inelastic x-ray scattering with first-principles LDA phonon calculations, Harmon showed that his calculations matched experiments best when he included the effects of magnetization, suggesting that the spins are disordered in the collapsed tetrahedral structure.
Symposium 3. LASMAC & Archeological & Arts Issues in Materials Science
XRF Analysis of Photographs at George Eastman House

Alejandra Mendoza is finishing up a 2 year advanced Residency Program in Photograph Conservation as an Andrew W. Mellon Fellow at the George Eastman House (GEH) in Rochester, New York, USA. In a poster presentation, she described the use of a hand-held TRACeR III-V Energy Dispersive X-Ray Fluorescence (XRF) instrument for elemental analysis of photographs from the museum collection. This has allowed her to add to existing knowledge and XRF analysis databases of photographic materials in the field of Conservation. In particular, the influence of the results of elemental XRF examination in two conservation projects at GEH were described. First, analysis of fourteen fine art photographic prints allowed the quick and accurate confirmation of the elements, primary support materials and secondary supports. In a salted paper print (ca. 1843), Ag was found to constitute the image material of the print. Small amounts of Fe and Ca were were present in the paper and board. Co and As were present in the primary support since smalt was used in the production of XIX Century paper as a whitening agent. In a carbon print of the same image from ca. 1920, the pigment and gelatin mixture constituting the image was found to contain Fe, Mn, Cu and Cr. Cr was present from the potassium bichromate solution used to sensitize the gelatin in the carbon print process. Also, an Ansel Adams print (gelatin silver print), from 1962 was also subjected to analysis.

Second, XRF analysis of a whole-plate daguerreotype (Philippines, ca. 1850s) and the components of its housing materials - as part of the documentation process for the Manila Conservation Project (from The Hispanic Society of America collection) - allowed the corroboration of image forming materials of the daguerrean plate, and elemental composition of the decorative elements of the passe-partout housing. These case studies illustrate the practical use of the hand-held TRACeR in the field of Photograph Conservation, demonstrating the capability of conservators to use the instrument in close collaboration with an expert scientist.
Symposium 9. Biomaterials
Study of Paclitaxel Crystallization into Hydrogels for Applications in Paclitaxel-Based Delivery Systems

J. Castro of the Autonomous University, Juarez City, Mexico, presented novel research into the detection of the formation of Paclitaxel crystals within hydrogels. Paclitaxel is a chemotherapeutic used in the treatment of breast cancer. Due to its lipophilic nature, the drug is generally delivered in the toxic solubilizing agent, Cremophor. The use of hydrogels mitigates these toxic effects, however Paclitaxel forms crystal structures within these gels that cannot be dissolved. The goal of this research was to evaluate a method of detecting these crystals. In this study the fluorochrome dye, Rhodamine, was bound to Paclitaxel via tubulin dimers. The polymer hydrogels used in this study were chitosan, agarose, and poly (lactic-co-glycolic) acid. A fluorescent microscope was used to detect the crystals. Castro concluded that Paclitaxel could be fluorescently labeled, and the crystals were able to be detected under visual examination.
Biocompatibility and Anti-Microbial Properties of Silver Modified Amorphous Carbon Films
Argelia Almaguer-Flores, from the Universidad Nacional Autonoma de Mexico, presented work on the use of silver nanoparticles as an anti-microbial agent for dental implant surfaces modified with amorphous carbon. Amorphous carbon improves implant properties by promoting osteoblast cell growth and differentiation. But oral bacteria have a tendency to adhere to the carbon surface, causing the formation of a biofilm. Silver, one of the oldest anti-microbial agents, kills bacteria by binding to bacterial DNA and inhibiting bacterial enzymes. The purpose of this study was to embed silver nanoparticles into amorphous carbon films, and to determine biocompatibility and anti-microbial properties. Biocompatibility tests showed that osteoblast-like cells (MG63) were able to grow and express osteogenic factors on the silver-carbon surface. In a bacterial adherence test, nine different strains of bacteria were exposed to the film over a period of 7 days. The silver-carbon film displayed a time-dependent response, and effects were not seen until the seventh day. At this point the silver-carbon film showed less bacterial growth than the titanium and stainless steel surfaces, and it had a 10% reduction in bacterial growth compared to the amorphous carbon only film.
Symposium 10. Ecomaterials and Climate Change
Structural Analysis and CO2 Chemisorption Study on Non-Stoichiometric Lithium Cuprates (Li2+xCuO2+x/2)

Carbon dioxide (CO2) is the most abundant greenhouse gas and a contributor to global warming.  Lithium cuprate was deemed a good CO2 absorber because of its ability to store additional lithium ions, beyond its correct stoichiometric ratio within its laminar structure.  L. Palacios-Romero of the Universidad Nacional Autonoma de Mexico, presented a poster demonstrating that when lithium oxide (Li2O) is reacted in excess with copper oxide (CuO), the lithium cuprate product will contain extra lithium ions.  The presence of these additional ions was confirmed by NMR and also by changes in morphology visible using SEM and TEM.  The research also showed that the amount of CO2 absorbed correlated directly with the amount of lithium present.  This absorption was verified by thermogravimetric analysis.
Novel Membranes Based on Keratine Extracted from Chicken Feathers and Polyurethane to Remove Cr (VI)
In this poster presentation, V. Saucedo-Rivalcoba, of the Universidad Autonoma del Estado de Mexico, provided a unique solution for the reuse of agricultural waste.  The idea was to take discarded chicken feathers, which are presenting an environmental dilemma in Mexico, and extract the protein keratin for use in a novel membrane.  These membranes are to be used to filter toxins and pollutants from air, water, and soil.  The membranes were synthesized by grafting keratin onto a polyurethane backbone.  The effect of urea salt on the membranes was also studied by adding the protein to a range of saline concentrations.  Analysis was performed by FTIR-spectroscopy, TGA, DSC, and SEM.  The results show a change in thermal properties and phase behavior due to the addition of keratin.  A change in membrane porosity is also observed relative to the change in salt concentration.  The filtration ability of the membrane was tested using a water sample contaminated with hexavalent chromium.  The membrane was able to remove at minimum 24% of the toxin.
Blends of Polycaprolactone and Cassava Thermoplastic Starch with Potential Biodegradable Bag Applicability
Jose Mina, of the Universidad del Valle, presented a study that showed how plastic bags could be made biodegradable by using a natural polymer in conjunction with a synthetic polymer to create a material that degrades over time. His research follows a trend in polymer research to create products that reduce environmental impact.  Thermoplastic starch (TPS), derived from cassava root, on its own does not possess sufficient properties to be suitable for fabricating plastic bags.  It has lower mechanical properties than conventional synthetic polymers, and high water absorption.  The objective of this study is to determine if a blend of polycaprolactone (PCL) and thermoplastic starch possesses suitable mechanical properties.  PCL and TPS were blended with ratios of 50-50, 60-40, and 40-60 (w/w)% and were prepared by extrusion followed by compression molding.  The blends were analyzed for thermal stability, moisture absorption, and tensile strength.  Increase in PCL concentration resulted in an increase in thermal stability; at a PCL concentration of 60%, the blend had a tensile strength seven times greater than TPS alone.  Further analysis using blends of polymers such as low density polyethylene is needed to determine what blend is most suitable to maintain its biodegradability yet increase mechanical strength.

Symposium 11. Composite and Hybrid Materials
Hybrid Coating PMMA-Silica on Stainless Steel 316L
Jenaro Varela-Caselis of the Universidad Autonoma de Puebla described how biocompatibility of stainless steel implants can be improved by coating with a poly(methyl methacrylate) [PMMA] – silica film. Stainless steel 316L is used extensively in medical implant devices. However, in environments where Cl2 is present, the steel corrodes and releases iron ions into local tissue. This can increase the risk of tumors and contribute to mechanical failure. A polymer interface such as PMMA - silica can improve corrosion resistance. A sol-gel technique was used to deposit a coating of PMMA and silica in the form of tetraethoxysilane onto the substrate, and a coating of just PMMA was used as a comparison. The samples were examined for coating thickness, morphology and adhesive properties. Noise resistance as a function of exposure time in 5% NaCL was used to evaluate corrosion protection; values greater than 100 ? were considered good protection. The PMMA - silica film appeared to be smooth, continuous and well-bonded to the substrate and the PMMA-silica coating displayed better corrosion resistance than PMMA alone.
Symposium 13. Advances in Semiconducting Materials
Bandgap engineering of the amorphous wide bandgap semicondunctor (SiCx)(1-x)(AlN)x doped with rare earths and its optical emission properties

Wide band gap semiconductors combine the advantages of insulators and semiconductors for electronic devices; in particular, alloys of SiC and AlN span the range of 3-6 eV, allowing for tuning of the emission wavelength, light emission efficiency, and energy level of dopants. Rare earth elements have unique emission wavelengths that do not depend on the host material and can cover the standard RGB colors and their combinations by sharp intrashell excitonic recombinations across the f electron orbital shells. However, rare earth-doped semiconductors experience strong temperature quenching above room temperature for low-bandgap semiconductors, motivating the use of SiC, AlN, and their alloys.R. Weingartner (Pontificia Universidad Catolica del Peru) investigated amorphous (a) (SiC)x(AlN)(1-x) to reduce temperature quenching effects while maintaining the advantages enumerated above of wide bandgap semiconductor alloys and rare earth dopants. Amorphous films are easily and efficiently fabricated by sputtering, allowing for high incorporation of rare earths. Weingartner employed an RF-magnetron sputtering system, with flexible magnetron targets allowing for access to the full range of alloy compositions, as indicated by energy dispersive spectroscopy. High resolution TEM images show nanocrystals embedded in an amorphous matrix, even after an annealing step to activate the dopants. Optical absorption measurements were performed to determine the alloy bandgap, showing that the entire energy range is accessible, and bowing parameters were calculated. Cathodoluminescence (CL) in an SEM was performed for a variety of dopants within a-SiC and (SiC)x(AlN)(1-x), showing the unique thermal activation profiles of the dopants as a function of annealing temperature.

Symposium 19. Photovoltaics, Solar Energy Materials and Thin-Films
Student Poster Awards
Symposium 19 on Photovoltaics has awarded three poster awards to students. The award includes US$250 and a certificate, which were presented during the conference banquet on Wednesday evening. These awards are sponsored by J.A. Woollam Co., Inc. and Intercovamex. The winners are:
(i) "Structural, morphological, optical and electrical properties of CdTe films deposited by CSS in argon and oxygen atmospheres," M. A. Flores Mendoza, R. Castanedo Perez, G. Torres Delgado, J. Marquez Marin, A. Cruz Orea, O. Zeleya Angel
Presenting author and institution: M. A. Flores Mendoza; CINVESTAV, Queretaro, Mexico
(ii) "Development of PICTS system for the study of trap levels in photovoltaic materials,” Christian Colin Garcia, Jose Campos, Xavier Mathew
Presenting author and institution: Christian Colin Garcia; Centro de Investigacion en Energia-UNAM, Mexico
(iii) “Photoluminescence studies and I-V characterization of CdTe films etched with N/P solution” A.Arce, O. Vigil Galan, C. Mejia Garcia
Presenting author and institution: A.Arce; Escuela Superior de Fisica y Matematica-IPN, Mexico

Symposium 20. Beams and Materials: Ion Beams
Irradiation-Induced Nanostructures by Self-Organization
Nuclear energy is clearly part of our energy future. However, this necessitates materials that can last 50-100 years in a harsh yet ill-defined climate. Radiation resistant materials are crucial and there has been ongoing work. A material subjected to ion beam irradiation receives a continuous energy flux from its environment. This energy is partly converted into heat, but it also shifts atomic locations and creates point defects. In such dissipative systems, a delicate balance is established between the dynamics imposed by the external forcing of atom positions, and the internal dynamics of the system that restores equilibrium, and this balance controls the structural evolution of the material. Bob Averback and co-workers at the University of Illinois, Urbana-Champagne, have found that under certain conditions these competing dynamics can lead to self-organization and compositional patterning on a fixed nanometer length scale. One of the consequences of nanoscale self organization is that the phase boundaries can act as sinks, or traps, for supersaturations of point defects, and thus it can lead to radiation resistance. Thus the major motivation of this work was to develop radiation resistant materials. By judicious choice of the alloying elements, nanoscale patterning can indeed be effected under irradiation and that the nanoscale patterns can persist to very high temperatures. A series of dilute immiscible Cu alloys were used in this study, and computer simulations and irradiation experiments involving x-ray diffraction and atom probe tomography were used.