EMSL: Don Baer's Publications

Baer DR, MH Engelhard, AR Felmy, JJ Ford, JZ Hu, AS Lea, P Nachimuthu, LV Saraf, JA Sears, and S Thevuthasan. 2009. "New Approaches for Characterizing Sensor and Other Modern Complex Materials." ECS Transactions 19(6):137-148. doi:10.1149/1.3118546 Abstract Advances in understanding of sensor and other modern complex materials are often enabled by new research tools. This paper highlights three capability development themes used to identify new research tools to be provided to users of the U. S. Department of Energy’s Environmental Molecular Sciences Laboratory. These capability development directions address the importance of dynamic measurements in realistic environments, the need for increased resolution in three dimensional analyses as well as the importance of linking theory and experiment. Capability development involves expanding the range of operation for a number of important techniques, developing and applying new capabilities, and advancing methods of data processing. Examples of current developments are provided including those related to magnetic resonance, x-ray diffraction, application of a focused beam capability to fuel cell aging, and near real time analysis of XPS spectra.

Wang CM, Z Yang, S Thevuthasan, J Liu, DR Baer, D Choi, D Wang, J Zhang, LV Saraf, and Z Nie. 2009. "Crystal and Electronic Structure of Lithiated Nanosized RutileTiO2 by Electron Diffraction and Electron Energy-loss Spectroscopy." Applied Physics Letters 94(23):Art. No.: 233116. doi:10.1063/1.3152783 Abstract The electronic structure of the nanosized rutile TiO2 before and after mechanical lithiation were studied using TEM and EELS. EELS reveals the Li K-edge at the energy-loss position of ~ 61 eV. After lithiation, the separation of the t2g-eg crystal-field splitting on both Ti L2,3-edge and O K-edge decreases, the O K-edge shifts towards a higher energy-loss position and the separation between the pre-edge peak and main peak on the O K-edge decreases. These results suggest that the lithiation of rutile TiO2 was accompanied by the reduction of Ti ion and a charge transfer from Li to Ti.

Wang CM, DR Baer, JE Amonette, MH Engelhard, J Antony, and Y Qiang. 2009. "Morphology and Electronic Structure of the Oxide Shell on the Surface of Iron Nanoparticles." Journal of the American Chemical Society 131(25):8824–8832. doi:10.1021/ja900353f Abstract A iron nanoparticle exposed to air at room temperature will be instantly covered by an oxide shell of typical thickness of ~ 3 nm. This native oxide shell in combination with an underlying iron core determines the physical and chemical behavior of this type of core-shell nanoparticles. One of the great challenges for characterizing this type of nanoparticles is determination of the structure of the oxide shell, as it is FeO, Fe3O4, -Fe2O3, -Fe2O3, or anything else. Significant research effort, mostly based on x-ray diffraction and spectroscopy and electron diffraction and transmission electron microscopy imaging, has been made to determine the structure of this thin layer of iron oxide. Most of the experimental results have been framed with one of the known iron oxide structures, although it is not necessarily true that this thin layer of iron oxide consists of a standard iron oxide. In this paper, the structure of the oxide shell on iron nanoparticle is probed using electron energy loss spectroscopy (EELS) at O K-edge with a spatial resolution of several nanometers (individual particle). Two types of representative particles were studied: particles that are fully oxidized and core-shell particle which possesses a Fe core. We found that the O K-edge spectra collected on the oxide shell in the nanoparticles shows distinctive differences as compared with that of the known iron oxide. Based on finger printing and quantum mechanical calculations results, we conclude that the distances between the absorbing oxygen and the next-nearest neighbor oxygens are more widely distributed than that in bulk Fe3O4 for both of these two types of particles. For smaller and fully oxidized particles, there is also a broadened distribution between the absorbing oxygen and the nearest neighbor oxygens. These results clearly demonstrate that the coordination configuration in the oxide shell on Fe nanoparticle is defective as compared with that of their bulk counterpart. Of the two types particles examined in this work, the degree of disorder is larger for the smaller fully oxidized particles.

Baer DR, JE Amonette, MH Engelhard, DJ Gaspar, AS Karakoti, SVNT Kuchibhatla, P Nachimuthu, J Nurmi, Y Qiang, V Sarathy, S Seal, A Sharma, PG Tratnyek, and CM Wang. 2008. "Characterization Challenges for Nanomaterials." Surface and Interface Analysis 40(3-4):529-537. doi:10.1002/sia.2726 Abstract Nanostructured materials are increasingly subject to nearly every type of chemical and physical analysis possible. Because of their small feature size there is a significant focus on tools with high spatial resolution. Because of their high surface area, it is also natural to characterize nanomaterials using tools designed to analyze surfaces. Regardless of the approach, nanostructured materials present a variety of obstacles to adequate, useful and needed analysis. This paper provides short overviews to some of the issues and complications including: particle stability, environmental effects, specimen handling, surface coating, contamination and time. Some specific examples are provided from a our work focused on ceria nanoparticles and iron metal-core/oxide-shell nanoparticles in which we use a combination of tools for routine analysis including XPS, TEM, and XRD and apply other methods as needed to obtain essential information.

Bera D, SVNT Kuchibhatla, S Azad, LV Saraf, CM Wang, V Shutthanandan, P Nachimuthu, DE Mccready, MH Engelhard, OA Marina, DR Baer, S Seal, and S Thevuthasan. 2008. "Growth and characterization of highly oriented gadolinia-doped ceria (111) thin films on zirconia (111)/sapphire (0001) substrates." Thin Solid Films 516(18):6088-6094. doi:10.1016/j.tsf.2007.11.007 Abstract Highly-oriented pure and gadolinia-doped ceria thin films have been grown on pure and ZrO2 (111)-buffered Al2O3 (0001) substrates using oxygen plasma-assisted molecular beam epitaxy (OPA-MBE) to understand the oxygen ionic transport processes in ceria based oxide thin films. Gadolinia-doped ceria films grown on pure Al2O3(0001) substrate show polycrystalline features due to structural deformations resulting from the large lattice mismatch between the Al2O3(0001) substrate and the films. However, the films, grown on a thin layer of ZrO2(111) buffered Al2O3 (0001) substrate, appears to be highly oriented. These films were characterized using high resolution transmission electron microscopy (HRTEM) and x-ray photoelectron spectroscopy (XPS) depth profiling. Oxygen ionic conductivity in gadolinia-doped ceria films was measured as a function of Gd concentration and these results were compared with the ion conductance data of the polycrystalline and single crystalline yttria-stabilized zirconia (YSZ).

Groves JF, Y Du, I Lyubinetsky, and DR Baer. 2008. "Focused ion beam directed self-assembly (Cu2O on SrTiO3 ): FIB pit and Cu2O nanodot evolution." Superlattices and Microstructures 44(4-5):677-685. doi:10.1016/j.spmi.2008.01.016 Abstract A gallium focused ion beam has been used to create discrete pits on the surface of a SrTiO3 (100) surface with the idea that these pits will serve as the nucleation sites for subsequent Cu2O quantum dot growth. Immediately after pit formation and following wet chemical etching and thermal annealing of the surface, the concentration of gallium within these pits has been analyzed using a high-resolution Auger system,. Using atomic force microscopy, the geometry of the pits has also been determined following etching and annealing. Growth of Cu2O quantum dots on the patterned surfaces has been performed. Growth of Cu2O quantum dots within the pits is the primary mode of dot formation. In several samples, dot growth within pits appears to occur by a two-step process with pits filling prior to initiation of a second, distinct phase of quantum dot growth above the plane of the original SrTiO3 surface.

Karakoti AS, SVNT Kuchibhatla, DR Baer, S Thevuthasan, DC Sayle, and S Seal. 2008. "Self-Assembly of Cerium Oxide Nanostructures in Ice Molds." Small 4(8):1210-1216. doi:10.1002/smll.200800219 Abstract The formation of nanorods, driven by the physico-chemical phenomena during the freezing of ceria nanoparticle suspension is reported. During freezing a dilute solution of CeO2 nanocrystals, some nuclei remain in solution while others are trapped inside the voids formed within the growing ice front. Over time the particles trapped within the constrained geometries combined by an oriented attachment process to form ceria nanorods. The experimental observations are further supported through Molecular Dynamics (MD) simulations. These observations suggest a new possible strategy for the templated formation of nanostructures through self assembly by exploiting natural phenomena such as freezing of water. "(A portion of) The research described in this paper (poster or presentation) was performed in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory."

Saheb AH, JA Smith, M Josowicz, J Janata, DR Baer, and MH Engelhard. 2008. "Controlling Size of Gold Clusters in Polyaniline from Top-Down and from Bottom-Up." Journal of Electroanalytical Chemistry 621(2):238-244. doi:10.1016/j.jelechem.2007.11.025 Abstract Polyaniline forms a strong complex with chloroaurate at the protonated imine sites. Here we report on electrochemical procedure that allows preparation of gold clusters by adding gold atoms one-by-one (“bottom up” approach). It is contrasted with the “top down” approach in which the growth of multi-atom Au clusters was also controlled electrochemically. Our results confirm that both the amount and the size of gold clusters affects the properties of the composite material.

Sarathy V, PG Tratnyek, J Nurmi, DR Baer, JE Amonette, CL Chun, RL Penn, and EJ Reardon. 2008. "Aging of Iron Nanoparticles in Aqueous Solution: Effects on Structure and Reactivity." Journal of Physical Chemistry C 112(7):2286-2293. doi:10.1021/jp0777418 Abstract Aging (or longevity) is one of the most important and potentially limiting factors in the use of nano-Fe0 to reduce groundwater contaminants. We investigated the aging of FeH2 (Toda RNIP-10DS) in water with a focus on changes in (i) the composition and structure of the particles (by XPS, XRD, TEM, and bulk Fe0 content), and (ii) the reactivity of the particles (by carbon tetrachloride reaction kinetics and electrochemical corrosion potentials). Our results show that the FeH2 becomes more reactive between 0 and ~2 days aging, and then gradually loses reactivity over the next few hundred days. These changes in reactivity correlate with evidence for rapid destruction of the original Fe(III) oxide film on FeH2 during immersion and the subsequent formation of a new passivating mixed-valence Fe(II)-Fe(III) oxide shell. The behavior of “unaged” nano-Fe0 in the laboratory may be similar to that in field-scale applications for source-zone treatment due to the short reaction times involved. Long-term aged FeH2 acquires properties that are relatively stable over weeks or even months.

Sharma A, Y Qiang, DR Meyer, R Souza, A Mcconnaughoy, L Muldoon, and DR Baer. 2008. "Biocompatible core-shell magnetic nanoparticles for cancer treatment." Journal of Applied Physics 103(7):Art. No.07A308. doi:10.1063/1.2831791 Abstract Non-toxic magnetic nanoparticles (MNPs) have expanded the treatment delivery options in the medical world. With a size range from 2 to 200 nm MNPs can be compiled with most of the small cells and tissues in living body. Monodispersive iron-iron oxide core shell nanoparticles were prepared in our novel cluster deposition system. This unique method of preparing the core shell MNPs gives nanoparticles very high magnetic moment. We tested the nontoxicity and uptake of MNPs coated with/without dextrin by incubating them with rat LX-1 small cell lung cancer cells (SCLC). Since core iron enhances the heating effect [7] the rate of oxidation of iron nanoparticles was tested in deionized water at certain time interval. Both coated and noncoated MNPs were successfully uptaken by the cells, indicating that the nanoparticles were not toxic. The stability of MNPs was verified by X-ray diffraction (XRD) scan after 0, 24, 48, 96, 204 hours. Due to the high magnetic moment offered by MNPs produced in our lab, we predict that even in low applied external alternating field desired temperature can be reached in cancer cells in comparison to the commercially available nanoparticles. Moreover, our MNPs do not require additional anti-coagulating agents and provide a cost effective means of treatment with significantly lower dosage in the body in comparison to commercially available nanoparticles.