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Masked Photocathode for Photoinjector

Description: In this research note, we propose a scheme to insert a photocathode inside a photoinjector for generating high brightness electron beam. Instead of mounting the photocathode onto the electrode, a masked electrode with small hole is used to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material very simple by rotating the photocathode behind the mask into the hole. This will significantly increase the usage lifetime of a photocathode. Furthermore, this also helps reduce the dark current or secondary electron emission from the photocathode. The hole on the mask also provides a transverse cut-off to the Gaussian laser profile which can be beneficial from the beam dynamics point of view.
Date: January 21, 2010
Creator: Qiang, Ji
Partner: UNT Libraries Government Documents Department

IMPACT-T User Document Version 1.6

Description: IMPACT-T is a fully three-dimensional program to track relativistic particles taking into account space charge forces and short-range longitudinal and transverse wakenelds. IMPACT-T is one of the few codes used in the photoinjector community that has a parallel implementation, making it very useful for high statistics simulations of beam halos and beam diagnostics. It has a comprehensive set of beamline elements, and furthermore allows arbitrary overlap of their fields, which gives the IMPACT-T a capability to model both the standing wave structure and traveling wave structure. It is also unique in its use of space-charge solvers based on an integrated Green function to efficiently and accurately treat beams with large aspect ratio, and a shifted Green function to efficiently treat image charge effects of a cathode. It is also unique in its inclusion of energy binning in the space-charge calculation to model beams with large energy spread. IMPACT-T has a flexible data structure that allows particles to be stored in containers with common characteristics; for photoinjector simulations the containers represent multiple slices, but in other applications they could correspond, e.g., to particles of different species. Together, all these features make IMPACT-T a powerful and versatile tool for modeling beams in photoinjectors and other systems.
Date: May 17, 2010
Creator: Qiang, Ji
Partner: UNT Libraries Government Documents Department

The compressibility of cubic white and orthorhombic, rhombohedral, and simple cubic black phosphorus

Description: The effect of pressure on the crystal structure of white phosphorus has been studied up to 22.4 GPa. The ?alpha phase was found to transform into the alpha' phase at 0.87 +- 0.04 GPa with a volume change of 0.1 +- 0.3 cc/mol. A fit of a second order Birch- Murnaghan equation to the data gave Vo = 16.94 ? 0.08 cc/mol and Ko = 6.7 +- 0.5 GPa for the alpha phase and Vo = 16.4 +- 0.1 cc/mol and Ko = 9.1 +- 0.3 GPa for the alpha' phase. The alpha' phase was found to transform to the A17 phase of black phosphorus at 2.68 +- 0.34 GPa and then with increasing pressure to the A7 and then simple cubic phase of black phosphorus. A fit of a second order Birch-Murnaghan equation to our data combined with previous measurements gave Vo = 11.43 +- 0.05 cc/mol and Ko = 34.7 +- 0.5 GPa for the A17 phase, Vo = 9.62 +- 0.01 cc/mol and Ko = 65.0 +- 0.6 GPa for the A7 phase and , Vo = 9.23 +- 0.01 cc/mol and Ko = 72.5 +- 0.3 GPa for the simple cubic phase.
Date: March 10, 2010
Creator: Clark, Simon M & Zaug, Joseph
Partner: UNT Libraries Government Documents Department

Synchrotron X-Ray Microdiffraction Studies of Electromigration in Interconnect lines at the Advanced Light Source

Description: Synchrotron polychromatic X-ray microdiffraction is a particularly suitable technique to study in situ the effect of electromigration in metal interconnects as add spatial resolution to grain orientation and strain sensitivity. This technique has been extensively used at the Advanced Light Source to monitor changes in aluminum and copper interconnect test structures while high-density current is passed into them during accelerated tests at elevated temperature. One of the principal findings is the observation of electromigration-induced plasticity in the metal lines that appear during the very early stages of electromigration. In some of the lines, high density of geometrically necessary dislocation are formed leading to additional diffusion paths causing an enhancement of electromigration effect at test temperature.
Date: December 1, 2009
Creator: Tamura, Nobumichi; Chen, Kai & Kunz, Martin
Partner: UNT Libraries Government Documents Department

Dual Selectivity Expressed in [2+2+1] Dynamic Clipping of Unsymmetrical [2]Catenanes

Description: A {pi}-templated dynamic [2+2+1] clipping protocol is established for the synthesis of [2]catenanes from two parts dialdehyde, two parts diamine and one part tetracationic cyclophane. It is further diversified for the selective formation of an unsymmetrical [2]catenane showing great translational selectivity by employing two different dialdehydes in a one-pot reaction. The dual selectivity and the dynamic nature are verified by {sup 1}H NMR spectroscopy, X-ray single crystal structural studies and exchange experiments.
Date: June 11, 2010
Creator: Liu, Yi
Partner: UNT Libraries Government Documents Department

Photon Science for Renewable Energy

Description: Our current fossil-fuel-based system is causing potentially catastrophic changes to our planet. The quest for renewable, nonpolluting sources of energy requires us to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels. Light-source facilities - the synchrotrons of today and the next-generation light sources of tomorrow - are the scientific tools of choice for exploring the electronic and atomic structure of matter. As such, these photon-science facilities are uniquely positioned to jump-start a global revolution in renewable and carbonneutral energy technologies. In these pages, we outline and illustrate through examples from our nation's light sources possible scientific directions for addressing these profound yet urgent challenges.
Date: March 31, 2010
Creator: Hussain, Zahid; Tamura, Lori; Padmore, Howard; Schoenlein, Bob & Bailey, Sue
Partner: UNT Libraries Government Documents Department

Improved Spatial Resolution for Reflection Mode Infrared Microscopy

Description: Standard commercial infrared microscopes operating in reflection mode use a mirror to direct the reflected light from the sample to the detector. This mirror blocks about half of the incident light, however, and thus degrades the spatial resolution by reducing the umerical aperture of the objective. Here, we replace the mirror with a 50% beamsplitter to allow full illumination of the objective and retain a way to direct the reflected light to the detector. The improved spatial resolution is demonstrated using two different microscopes apable of diffraction-limited resolution: the first microscope is coupled to a synchrotron source and utilizes a single point detector, whereas the second microscope has a standard blackbody source and uses a focal planetarray (FPA) detector.
Date: October 9, 2009
Creator: Bechtel, Hans A.; Martin, Michael C.; May, T.E. & Lerch, Philippe
Partner: UNT Libraries Government Documents Department

Improved Spatial Resolution For Reflection Mode Infrared Spectromicroscopy

Description: Standard commercial infrared microscopes operating in reflection mode use a mirror to direct the reflected light from the sample to the detector. This mirror blocks about half of the incident light, however, and thus degrades the spatial resolution by reducing the numerical aperture of the objective. Here, we replace the mirror with a 50% beamsplitter to allow full illumination of the objective and retain a way to direct the reflected light to the detector. The improved spatial resolution is demonstrated using a microscope coupled to a synchrotron source.
Date: August 13, 2009
Creator: Bechtel, Hans A; Martin, Michael C.; May, T. E. & Lerch, Philippe
Partner: UNT Libraries Government Documents Department

Probing Compositional Variation within Hybrid Nanostructures

Description: We present a detailed analysis of the structural and magnetic properties of solution-grown PtCo-CdS hybrid structures in comparison to similar free-standing PtCo alloy nanoparticles. X-ray absorption spectroscopy is utilized as a sensitive probe for identifying subtle differences in the structure of the hybrid materials. We found that the growth of bimetallic tips on a CdS nanorod substrate leads to a more complex nanoparticle structure composed of a PtCo alloy core and thin CoO shell. The core-shell architecture is an unexpected consequence of the different nanoparticle growth mechanism on the nanorod tip, as compared to free growth in solution. Magnetic measurements indicate that the PtCo-CdS hybrid structures are superparamagnetic despite the presence of a CoO shell. The use of X-ray spectroscopic techniques to detect minute differences in atomic structure and bonding in complex nanosystems makes it possible to better understand and predict catalytic or magnetic properties for nanoscale bimetallic hybrid materials.
Date: June 22, 2010
Creator: Yuhas, Benjamin D.; Habas, Susan E.; Fakra, Sirine C. & Mokari, Taleb
Partner: UNT Libraries Government Documents Department

Evolution of ferroelectric domain structures embedded inside polychrystalline BaTiO3 during heating

Description: The evolution of ferroelectric domains inside a single grain of a polycrystalline BaTiO{sub 3} ceramic was investigated under quasistatic heating by using polychromatic scanning x-ray microdiffraction. Four domain orientations were observed, three of which exhibited a classic of {approx}90{sup o} ferroelastic relationship. The fourth domain orientation was found to be crystallographically related with one of the other orientations by a rotation of either 180.47{sup o} or 0.47{sup o}. While heating the polycrystalline BaTiO{sub 3} from room temperature to above the Curie temperature (125 C), all four ferroelectric domain orientations rotated toward a paraelectric cubic orientation which was found to be at an intermediate orientation relative to the four domain orientations. The crystallographic relationships of the domains with respect to paraelectric phase were explained using a domain structure model by Nepochatenko.
Date: January 1, 2010
Creator: Varlioglu, Mesut; Ustundag, Ersan; Tamura, Nobumichi & Jones, Jacob L.
Partner: UNT Libraries Government Documents Department

Ferrimagnetic ordering of single crystal Fe1-xGax thin films

Description: Molecular beam epitaxy was used to deposit body centered cubic single crystal Fe{sub 1-x}Ga{sub x} thin films on MgO(001) and ZnSe/GaAs(001) substrates well beyond the bulk stability concentration of about 28%. The crystal quality of the substrate surface and each deposited layer was monitored in situ by reflection high energy electron diffraction. The magnetization of the samples as a function of Ga is found to decrease more rapidly than a simple dilution effect, and element-specific x-ray magnetic circular dichroism ascribes this trend to a decrease in the Fe moment and an induced moment in the Ga that is antialigned to the Fe moment.
Date: October 19, 2009
Creator: McClure, A.; Arenholz, E. & Idzerda, Y. U.
Partner: UNT Libraries Government Documents Department

Reconciling FTIR Spectroscopy with Top-off Operations at the Advanced Light Source

Description: Top-off operations is a quasi-continuous injection mode that increases the flux and brightness of a synchrotron source and improves thermal stability of optical components by maintaining a constant current in the storage ring. Although the increased and constant flux is advantageous for FTIR measurements, the frequent injections (about one every 30 seconds in the ALS case) introduce artifacts into the spectrum by creating spikes in the interferogram data. These spikes are caused by brief beam motion during the injection event. Here, we describe our efforts to minimize the effects of top-off generated interferogram spikes on several FTIR spectrometers. They include using a fast feedback mirror system to correct for beam motion and a gating signal to inhibit interferogram collection during a top-off injection.
Date: August 13, 2009
Creator: Vernoud, Laetitia; Bechtel, Hans A.; Borondics, Ferenc & Martin, Michael C.
Partner: UNT Libraries Government Documents Department

A Soft X-ray Spectrometer using a Highly Dispersive Multilayer Grating

Description: There is a need for higher resolution spectrometers as a tool for inelastic x-ray scattering. Currently, resolving power around R = 10,000 is advertised. Measured RIXS spectra are often limited by this instrumental resolution and higher resolution spectrometers using conventional gratings would be prohibitively large. We are engaged in a development program to build blazed multilayer grating structures for diffracting soft x-rays in high order. This leads to spectrometers with dispersion much higher than is possible using metal coated-gratings. The higher dispersion then provides higher resolution and the multilayer gratings are capable of operating away from grazing incidence as required. A spectrometer design is presented with a total length 3.8m and capable of 10{sup 5} resolving power.
Date: January 31, 2010
Creator: Warwick, Tony; Padmore, Howard; Voronov, Dmitriy & Yashchuk, Valeriy
Partner: UNT Libraries Government Documents Department

X-ray Spectromicroscopy Study of Protein Adsorption to a Polystyrene-Polylactide Blend

Description: Synchrotron-based X-ray photoemission electron microscopy (X-PEEM) was used to study the adsorption of human serum albumin (HSA) to polystyrene-polylactide (40:60 PS-PLA, 0.7 wt percent) thin films, annealed under various conditions. The rugosity of the substrate varied from 35 to 90 nm, depending on the annealing conditions. However, the characteristics of the protein adsorption (amounts and phase preference) were not affected by the changes in topography. The adsorption was also not changed by the phase inversion which occured when the PS-PLA substrate was annealed above Tg of the PLA. The amount of protein adsorbed depended on whether adsorption took place from distilled water or phosphate buffered saline solution. These differences are interpreted as a result of ionic strength induced changes in the protein conformation in solution.
Date: June 9, 2010
Creator: Leung, Bonnie; Hitchcock, Adam; Cornelius, Rena; Brash, John; Scholl, Andreas & Doran, Andrew
Partner: UNT Libraries Government Documents Department

Development of a new generation of optical slope measuring profiler

Description: We overview the results of a broad US collaboration, including all DOE synchrotron labs (ALS, APS, BNL, NSLS-II, LLNL, LCLS), major industrial vendors of x-ray optics (InSync, Inc., SSG Precision Optronics-Tinsley, Inc., Optimax Systems, Inc.), and with active participation of HBZ-BESSY-II optics group, on development of a new generation slope measuring profiler -- the optical slope measuring system (OSMS). The desired surface slope measurement accuracy of the instrument is<50 nrad (absolute) that is adequate to the current and foreseeable future needs for metrology of x-ray optics for the next generation of light sources.
Date: July 9, 2010
Creator: Yashchuk, Valeriy V.; Takacs, Peter Z.; McKinney, Wayne R. & Assoufid, Lahsen
Partner: UNT Libraries Government Documents Department

Compressive auto-indexing in femtosecond nanocrystallography

Description: Ultrafast nanocrystallography has the potential to revolutionize biology by enabling structural elucidation of proteins for which it is possible to grow crystals with 10 or fewer unit cells. The success of nanocrystallography depends on robust orientation-determination procedures that allow us to average diffraction data from multiple nanocrystals to produce a 3D diffraction data volume with a high signal-to-noise ratio. Such a 3D diffraction volume can then be phased using standard crystallographic techniques."Indexing" algorithms used in crystallography enable orientation determination of a diffraction data from a single crystal when a relatively large number of reflections are recorded. Here we show that it is possible to obtain the exact lattice geometry from a smaller number of measurements than standard approaches using a basis pursuit solver.
Date: September 20, 2010
Creator: Maia, Filipe; Yang, Chao & Marchesini, Stefano
Partner: UNT Libraries Government Documents Department

Nuclear quantum effects in the structure and lineshapes of the N2 NEXAFS spectrum

Description: We study the relative ability of several models of the X-ray absorption spectrum to capture the Franck-Condon structure apparent from an experiment on gaseous nitrogen. In doing so, we adopt the Born-Oppenheimer approximation and a constrained density functional theory method for computing the energies of the X-ray-excited molecule. Starting from an otherwise classical model for the spectrum, we systematically introduce more realistic physics, first by substituting the quantum mechanical nuclear radial density in the bond separation R for the classical radial density, then by adding the effect of zero-point energy and other level shifts, and finally by including explicit rovibrational quantization of both the ground and excited states. The quantization is determined exactly, using a discrete variable representation. We show that the NEXAFS spectrum can be predicted semiquantiatively within this framework. We also address the possibility of non-trivial temperature dependence in the spectrum. Finally, we show that it is possible to improve the predicted spectrum by using constrained DFT in combination with more accurate potentials.
Date: December 4, 2009
Creator: Fatehi, Shervin; Schwartz, Craig P.; Saykally, Richard J. & Prendergast, David
Partner: UNT Libraries Government Documents Department

Enhanced Magnetism in Epitaxial SrRuO3 Thin Films

Description: We have observed enhanced magnetization in epitaxial SrRuO{sub 3} thin films compared to previously reported bulk and thin film values of 1.1-1.6 {mu}{sub B}/Ru ion. The degree of enhancement is strongly dependent on the lattice distortions imposed on the SrRuO{sub 3} films by SrTiO{sub 3}, (LaAlO{sub 3}){sub 0.3}(SrTaO{sub 3}){sub 0.7} (LSAT), and LaAlO{sub 3} substrates. A larger enhancement of magnetization for coherently strained SrRuO{sub 3} films on SrTiO{sub 3} and LSAT compared to fully relaxed films on LaAlO{sub 3} confirms the importance of the strain state in determining the magnetic ground state of the Ru ion. In particular, SrRuO{sub 3} films on (111) SrTiO{sub 3} exhibit exhanced moments as high as 3.8 {mu}{sub B}/Ru ion, thus suggesting the stabilization of a high-spin Ru{sup 4+} state.
Date: November 20, 2009
Creator: Grutter, A.J.; Wong, F.; Arenholz, E.; Liberati, M.; Vailionis, A. & Suzuki, Y.
Partner: UNT Libraries Government Documents Department

Calix[4]arene Based Single-Molecule Magnets

Description: Single-molecule magnets (SMMs) have been the subject of much interest in recent years because their molecular nature and inherent physical properties allow the crossover between classical and quantum physics to be observed. The macroscopic observation of quantum phenomena - tunneling between different spin states, quantum interference between tunnel paths - not only allows scientists to study quantum mechanical laws in great detail, but also provides model systems with which to investigate the possible implementation of spin-based solid state qubits and molecular spintronics. The isolation of small, simple SMMs is therefore an exciting prospect. To date almost all SMMs have been made via the self-assembly of 3d metal ions in the presence of bridging/chelating organic ligands. However, very recently an exciting new class of SMMs, based on 3d metal clusters (or single lanthanide ions) housed within polyoxometalates, has appeared. These types of molecule, in which the SMM is completely encapsulated within (or shrouded by) a 'protective' organic or inorganic sheath have much potential for design and manipulation: for example, for the removal of unwanted dipolar interactions, the introduction of redox activity, or to simply aid functionalization for surface grafting. Calix[4]arenes are cyclic (typically bowl-shaped) polyphenols that have been used extensively in the formation of versatile self-assembled supramolecular structures. Although many have been reported, p-{sup t}But-calix[4]arene and calix[4]arene (TBC4 and C4 respectively, Figure 1A) are frequently encountered due to (a) synthetic accessibility, and (b) vast potential for alteration at either the upper or lower rim of the macrocyclic framework. Within the field of supramolecular chemistry, TBC4 is well known for interesting polymorphic behavior and phase transformations within anti-parallel bi-layer arrays, while C4 often forms self-included trimers. The polyphenolic nature of calix[n]arenes (where n = 4-8) also suggests they should be excellent candidates as ligands for the isolation of molecular magnets, but to ...
Date: June 4, 2009
Creator: Karotsis, Georgios; Teat, Simon J.; Wernsdorfer, Wolfgang; Piligkos, Stergios; Dalgarno, Scott J. & Brechin, Euan K.
Partner: UNT Libraries Government Documents Department

Strain Induced Magnetism in SrRuO3 Epitaxial Thin Films

Description: Epitaxial SrRuO{sub 3} thin films were grown on SrTiO{sub 3}, (LaAlO{sub 3}){sub 0.3}(SrAlO{sub 3}){sub 0.7} and LaAlO{sub 3} substrates inducing different biaxial compressive strains. Coherently strained SrRuO{sub 3} films exhibit enhanced magnetization compared to previously reported bulk and thin film values of 1.1-1.6 {micro}{sub B} per formula unit. A comparison of (001) and (110) SrRuO{sub 3} films on each substrate indicates that films on (110) oriented have consistently higher saturated moments than corresponding (001) films. These observations indicate the importance of lattice distortions in controlling the magnetic ground state in this transitional metal oxide.
Date: January 10, 2010
Creator: Grutter, A.; Wong, F.; Arenholz, E.; Liberati, M. & Suzuki, Y.
Partner: UNT Libraries Government Documents Department

Microstructural analyses of Cr(VI) speciation in chromite ore processing Residue (COPR)

Description: The speciation and distribution of Cr(VI) in the solid phase was investigated for two types of chromite ore processing residue (COPR) found at two deposition sites in the United States: gray-black (GB) granular and hard brown (HB) cemented COPR. COPR chemistry and mineralogy were investigated using micro-X-ray absorption spectroscopy and micro-X-ray diffraction, complemented by laboratory analyses. GB COPR contained 30percent of its total Cr(VI) (6000 mg/kg) as large crystals(>20 ?m diameter) of a previously unreported Na-rich analog of calcium aluminum chromate hydrates. These Cr(VI)-rich phases are thought to be vulnerable to reductive and pH treatments. More than 50percent of the Cr(VI) was located within nodules, not easily accessible to dissolved reductants, and bound to Fe-rich hydrogarnet, hydrotalcite, and possibly brucite. These phases are stable over a large pH range, thus harder to dissolve. Brownmilleritewasalso likely associated with physical entrapment of Cr(VI) in the interior of nodules. HB COPR contained no Cr(VI)-rich phases; all Cr(VI) was diffuse within the nodules and absent from the cementing matrix, with hydrogarnet and hydrotalcite being the main Cr(VI) binding phases. Treatment ofHBCOPRis challenging in terms of dissolving the acidity-resistant, inaccessible Cr(VI) compounds; the same applies to ~;;50percent of Cr(VI) in GB COPR.
Date: March 1, 2010
Creator: CHRYSOCHOOU, MARIA; FAKRA, SIRINE C .; Marcus, Matthew A.; Moon, Deok Hyun & Dermatas, Dimitris
Partner: UNT Libraries Government Documents Department

Site Determination and Magnetism of Mn Doping in Protein Encapsulated Iron Oxide Nanoparticles

Description: Soft-X-ray absorption spectroscopy, soft-X-ray magnetic circular dichroism, and alternating current magnetic susceptibility were performed on 6.7 nm iron oxide nanoparticles doped with (5-33%) Mn grown inside the horse-spleen ferritin protein cages and compared to similarly protein encapsulated pure Fe-oxide and Mn-oxide nanoparticles to determine the site of the Mn dopant and to quantify the magnetic behavior with varying Mn concentration. The Mn dopant is shown to substitute preferentially as Mn{sup +2} and prefers the octahedral site in the defected spinel structure. The Mn multiplet structure for the nanoparticles is simpler than for the bulk standards, suggesting that the nanoparticle lattices are relaxed from the distortions present in the bulk. Addition of Mn is found to alter the host Fe-oxide lattice from a defected ferrimagnetic spinel structure similar to {gamma}-Fe{sub 2}O{sub 3} to an non-ferromagnetic spinel structure with a local Fe environment similar to Fe{sub 3}O{sub 4}.
Date: January 11, 2010
Creator: Pool, V.; Klem, M.; Jolley, J.; Arenholz, E.A.; Douglas, T.; Young, M. et al.
Partner: UNT Libraries Government Documents Department

Strain engineering to control the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films

Description: This work studies the control of the magnetic and magnetotransport properties of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin films through strain engineering. The strain state is characterized by the tetragonal distortion (c/a ratio), which can be varied continuously between a compressive strain of 1.005 to a tensile strain of 0.952 by changing the type of substrate, the growth rate, and the presence of an underlying La{sub 0.67}Sr{sub 0.33}FeO{sub 3} buffer layer. Increasing tensile tetragonal distortion of the La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin film decreases the saturation magnetization, changes the temperature dependence of the resistivity and magnetoresistance, and increases the resistivity by several orders of magnitude.
Date: June 15, 2010
Creator: Yang, F.; Kemik, N.; Biegalski, M.D.; Christen, H.M.; Arenholz, E. & Takamura, Y.
Partner: UNT Libraries Government Documents Department

Iron oxyhydroxide mineralization on microbial extracellular polysaccharides

Description: Iron biominerals can form in neutral pH microaerophilic environments where microbes both catalyze iron oxidation and create polymers that localize mineral precipitation. In order to classify the microbial polymers that influence FeOOH mineralogy, we studied the organic and mineral components of biominerals using scanning transmission X-ray microscopy (STXM), micro X-ray fluorescence ({mu}XRF) microscopy, and high-resolution transmission electron microscopy (HRTEM). We focused on iron microbial mat samples from a creek and abandoned mine; these samples are dominated by iron oxyhydroxide-coated structures with sheath, stalk, and filament morphologies. In addition, we characterized the mineralized products of an iron-oxidizing, stalk-forming bacterial culture isolated from the mine. In both natural and cultured samples, microbial polymers were found to be acidic polysaccharides with carboxyl functional groups, strongly spatially correlated with iron oxyhydroxide distribution patterns. Organic fibrils collect FeOOH and control its recrystallization, in some cases resulting in oriented crystals with high aspect ratios. The impact of polymers is particularly pronounced as the materials age. Synthesis experiments designed to mimic the biomineralization processes show that the polysaccharide carboxyl groups bind dissolved iron strongly but release it as mineralization proceeds. Our results suggest that carboxyl groups of acidic polysaccharides are produced by different microorganisms to create a wide range of iron oxyhydroxide biomineral structures. The intimate and potentially long-term association controls the crystal growth, phase, and reactivity of iron oxyhydroxide nanoparticles in natural systems.
Date: June 22, 2010
Creator: Chan, Clara S.; Fakra, Sirine C.; Edwards, David C.; Emerson, David & Banfield, Jillian F.
Partner: UNT Libraries Government Documents Department