Science of Interfacial Phenomena Publications

2009

Wang H, D Wingett, MH Engelhard, K Feris, KM Reddy, P Turner, J Layne, C Hanley, J Bell, D Tenne, CM Wang, and A Punnoose. 2009. "Fluorescent Dye Encapsulated ZnO Particles with Cell-specific Toxicity for Potential use in Biomedical Applications." Journal of Materials Science. Materials in Medicine 20(1):11-22. Abstract Fluorescein isothiocyanate (FITC)-encapsulated core-shell particles with a nanoscale ZnO finishing layer have been synthesized for the first time as multifunctional “smart” nanostructures for particle tracking and cell imaging using the visible fluorescence emission of the dye or UV fluorescence emission of ZnO, and anti-cancer/antibacterial treatments using the selective toxicity of the nanoscale ZnO outer surface. The chemical phase composition, morphology, size, and the layered core-shell architecture of the particles were characterized using detailed transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis-NIR spectrophotometry. Systematic XPS studies after removing nanometer thick layers confirmed the expected layered structure in the order ZnO-SiO2-APTMS-FITC proceeding from the surface to the core of the ~200 nm sized particles. Detailed investigation of the fluorescence properties of these hydrophilic particles in bio-compatible media using fluorescence spectroscopy, flow cytometry and fluorescence confocal microscopy demonstrated that the silica/ZnO outer layer offers considerable protection to the encapsulated dye molecules from photobleaching and quenching due to reactive species such as oxygen in the solvent. These particles showed promise toward cell imaging, for example when the bacterium Escherichia coli was used as a test system, the green fluorescence of the particles allowed confocal microscopy to image the cells. The FITC encapsulated ZnO (FITC-ZnO) particles demonstrated excellent selectivity in preferentially killing Jurkat cancer cells (18% cell viability) without any significant toxicity to normal primary immune cells (75% cell viability) at 60 g/mL concentrations and inhibited the growth of both gram-positive and gram negative bacteria at concentrations ≥ 250-500 g/mL (for Staphylococcus aureus and Escherichia coli, respectively). These results indicate that the novel FITC encapsulated multifunctional particles with nanoscale ZnO surface layer are smart nanostructures for particle tracking, cell imaging, antibacterial treatments and cancer therapy.
Bell RC, K Wu, MJ Iedema, GK Schenter, and JP Cowin. 2009. "The Oil-Water Interface: Mapping the Solvation Potential." Journal of the American Chemical Society 131(3):1037-1042. doi:10.1021/ja805962x Abstract Ions moving across the oil water interface are strongly impacted by the continuous changes in solvation. The solvation potential for Cs+ is directly measured as they approach the oil-water interface (“oil” = 3-methylpentane), from 0.4 to 4 nm away. The oil-water interfaces are created at 40K using molecular beam epitaxy and a softlanding ion beam, with pre-placed ions. The solvation potential slope was determined at each distance by balancing it against an increasing electrostatic potential made by increasing the number of imbedded ions at that distance, and monitoring the resulting ion motion. The potential approaches the Born model for greater than z>0.4nm, and shows the predicted reduction of the polarizability at z<0.4nm.
Barry RC, Y Lin, J Wang, G Liu, and C Timchalk. 2009. "Nanotechnology-Based Electrochemical Sensors for Biomonitoring Chemical Exposures ." Journal of Exposure Science and Environmental Epidemiology 19:1-18. doi:10.1038/jes.2008.71 Abstract This manuscript highlights research focused on the development of field-deployable analytical instruments based on EC detection. Background information and a general overview of EC detection methods and integrated use of nanomaterials in the development of these sensors are provided. New developments in EC sensors using various types of screen-printed electrodes, integrated nanomaterials, and immunoassays are discussed. Recent applications of EC sensors for assessing exposure to pesticides or detecting biomarkers of disease are highlighted to demonstrate the ability to monitor chemical metabolites, enzyme activity, or protein biomarkers of disease. In addition, future considerations and opportunities for advancing the use of EC platforms for dosimetric studies are covered.
Jiang W, and WJ Weber. 2009. "Anisotropy of disorder accumulation and recovery in 6H-SiC irradiated with Au2+ ions at 140 K." Journal of Nuclear Materials 389(2):332-335. doi:10.1016/j.jnucmat.2009.02.023 Abstract Single crystal <0001>-oriented 6H-SiC was irradiated with Au2+ ions to fluences of 0.032, 0.058 and 0.105 ions/nm2 at 140 K and was subsequently annealed at various temperatures up to 500 K. The relative disorder on both the Si and C sublattices has been determined simultaneously using in-situ D+ ion channeling along the <0001> and <2-201> axes. A higher level of disorder on both the Si and C sublattices is observed along the <2-201>. There is a preferential C disordering and more C interstitials are aligned with <0001>. Room-temperature recovery along <2-201> occurs, which is associated with the <0001>-aligned interstitials that annihilate due to close-pair recombination. Disorder recovery between 400 and 500 K is primarily attributed to annihilation of interstitials that are misaligned with <0001>. Effects of stacking order in SiC on disorder accumulation are insignificant; however, noticeable differences of low-temperature recovery in Au2+-irradiated 6H-SiC and 4H-SiC are observed.
Kwak JH, D Mei, CWW Yi, DH Kim, CHF Peden, L Allard, and J Szanyi. 2009. "Understanding the nature of surface nitrates in BaO/gamma-Al2O3 NOx storage materials: A combined experimental and theoretical study ." Journal of Catalysis 261(1):17-22. Abstract The special role of the interface between the active catalytic phase (metal or metal oxide) and the oxide support in determining the properties of practical catalysts has long been recognized; however, it is still very poorly understood in most systems
Smith RS, T Zubkov, Z Dohnalek, and BD Kay. 2009. "The Effect of the Incident Collision Energy on the Porosity of Vapor Deposited Amorphous Solid Water Films." Journal of Physical Chemistry B 113(13):4000-4007. Abstract Molecular beam techniques are used to grow water films on Pt(111) with various incident angles and collision energies from 5 to 205 kJ/mole. The effect of the incident angle and collision energy on the porosity and surface area of the vapor deposited water films was studied using nitrogen physisorption and infrared spectroscopy. At low incident energy (5 kJ/mole), the infrared spectra, which provide a direct measure of the surface area, show that the surface area increases with incident angle and levels-off at angles > 65°. This is in contrast to the nitrogen uptake data which display a maximum near 70° due to the decrease in nitrogen condensation in the larger pores that develop at high incident angles. Both techniques show that the morphology of vapor deposited water films depends strongly on the incident kinetic energy. These observations are consistent with a ballistic deposition-shadowing model used to describe the growth of highly porous materials at glancing angle. The dependence of film morphology on incident energy may have important implications for the growth of porous materials via glancing angle deposition and for the structure of interstellar ices.
Petrik NG, and GA Kimmel. 2009. "Nonthermal Water Splitting on Rutile TiO2: Electron-Stimulated Production of H-2 and O-2 in Amorphous Solid Water Films on TiO2(110)." Journal of Physical Chemistry C 113(11):4451-4460. Abstract Electron-stimulated desorption (ESD) of H2, O2 and H2O from 0 - 60 ML films of amorphous solid water (ASW) adsorbed on TiO2(110) are investigated as function of film thickness and isotopic composition. For 100 eV incident electrons, both the H2 and O2 ESD yields have maxima when the ASW coverage is ~ 20 monolayer (ML), while the H2O ESD yield increases monotonically with water coverage. All the products reach a coverage-independent yield above 40 - 50 ML. Experiments using isotopically layered films of H2O and D2O demonstrate that the molecular hydrogen is produced in reactions that occur preferentially at or near both the ASW/TiO2 interface and the ASW/vacuum interface. However, electronic excitations or ionic defects created within the interior of the ASW films by the energetic electrons can subsequently migrate to the interfaces where they initiate reactions. Electron irradiation of ASW films results in the formation of bridge-bonded hydroxyls on the TiO2(110). These hydroxyls do not contribute to the H2 produced near the ASW/TiO2 interface. Instead, the results suggest that this H2 is produced from a stable precursor, trapped near the substrate. The proposed mechanism for the H2 production near the ASW/TiO2(110) interface is supported by a kinetic model that semi-quantitatively reproduces the main features of the non-thermal reactions.
Johnson BR, BJ Riley, SK Sundaram, JV Crum, CH Henager, Jr, Y Zhang, V Shutthanandan, CE Seifert, RM Van Ginhoven, CE Chamberlin, A Rockett, D Hebert, and A Aquino. 2009. "Synthesis and Characterization of Bulk Vitreous Cadmium Germanium Arsenide." Journal of the American Ceramic Society 92(6):1236-1243. doi:10.1111/j.1551-2916.2009.03001.x Abstract Abstract Cadmium-germanium-diarsenide (“CGA”) glasses were synthesized in bulk form (~2.4 cm3) using the procedures adapted from the literature. Several issues involved in the fabrication and quenching of amorphous CdGexAs2 (x = 0.45, 0.65, 0.85, 1.00) are described. An innovative processing route is presented to enable quenching of vitreous, crack-free ingots with sizes up to 10 mm diameter, and 30 – 40 mm long. Specimens from selected ingots were characterized using thermal analysis, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, particle-induced X-ray emission, Rutherford backscattering, secondary ion mass spectrometry, X-ray diffraction, density, and optical spectroscopy. Variations in properties as a function of processing conditions and composition are described. Results show that the density of defect states in the middle of the band gap and near the band edges can be decreased three ways: through suitable control of the processing conditions, by doping the material with hydrogen, and by increasing the concentration of Ge in the glass.
Fernandez CA, JG Roberts, EM Hoppes, RJ Wiacek, GE Fryxell, JT Bays, MG Warner, CM Wang, JE Hutchinson, and RS Addleman. 2009. "Advancements Toward the Greener Processing of Engineered Nanomaterials -- Effect of Core Size on the Dispersibility and Transport of Gold Nanocrystals in Near-Critical Solvents." Small 5(8):961-969. doi:10.1002/smll.200801207 Abstract In this work, we explore the dispersibility of octanethiol-stabilized gold nanocrystals of different core sizes in compressed ethane and propane over a wide range of fluid conditions. The dispersibility of the nanocrystals was obtained through the Surface Plasmon Resonance (SPR) absorption spectra of solutions. Three models, the total interaction theory, the sedimentation coefficient equation, and the Chrastil method, are briefly discussed as tools to interpret the experimental results. Nanoparticle dispersibility-versus-density plots are strongly dependent on nanoparticle size and solvent conditions, with the dispersion of larger nanocrystals more dependant on changes of pressure or density at a given temperature. These results showed a notable correlation with the calculated sedimentation coefficients of the nanocrystals in both solvents. The Chrastil equation was successfully applied to predict and describe the dispersibility of the gold nanocrystals as a function of density, showing that the high stabilities of the nanocrystals dispersions are a result of the very strong solvent-nanocrystal interactions. For the range of nanoparticle sizes studied, compressed ethane at 25 ºC led to a greater tunability of nanoparticle dispersion when compared with compressed propane at 65 ºC. On the other hand, for equivalent pressures compressed propane was found to provide better solubility than ethane due to its higher density. The results of this study quantitatively demonstrate that compressed fluids can offer pressure tunable, size selective control of nanoparticle solvation and transport. This ability has clear advantages over conventional solvents and direct application to various nanomaterials processes, such as separation, transport and purification of nanocrystals.
Du Y, NA Deskins, Z Zhang, Z Dohnalek, M Dupuis, and I Lyubinetsky. 2009. "Imaging Consecutive Steps of O2 Reaction with Hydroxylated TiO₂(110): Identification of HO₂ and Terminal OH Intermediates." Journal of Physical Chemistry C 113(2):666-671. Abstract We report results of the combined experimental and theoretical investigation of the molecular oxygen reaction with a partially hydroxylated TiO₂(110) surface. The consecutive steps of both primary and secondary site-specific reactions have been tracked with high-resolution scanning tunneling microscopy (STM). For the first time, we have directly imaged stable, adsorbed hydroperoxyl (HO₂) species, which is believed to be a key intermediate in many heterogeneous photochemical processes but generally metastable and “elusive” until now. We also found terminal hydroxyl groups, another critical but never directly observed intermediates. A conclusive evidence that O₂ reacts spontaneously with a single bridging OH group as an initial reaction step is provided. The experimental results are supported by density functional theory (DFT) calculations that have determined species energies and configurations. Reported observations provide a basis for a consistent description of the elementary reaction steps and offer molecular-level insight into the underlying reaction mechanisms. In a broader perspective, the results are expected to have far reaching implications for various catalytic systems involving the interconversion of O₂ and H₂O.

Next Displaying results 1 - 10 of 221