Steinar Raaen

Minute synthesis of extremely stable gold nanoparticles

We describe a rapid environmentally friendly wet-chemical approach to synthesize extremely stable non-toxic, biocompatible, water-soluble monodispersed gold nanoparticles (AuNPs) in one step at room temperature. The particles have been successfully achieved in just a few minutes by merely adding sodium hydroxide (NaOH) acting as an initiator for the reduction of HAuCl(4) in aqueous solution in the presence of polyvinylpyrrolidone (PVP) without the use of any reducing agent. It is also proved to be highly efficient for the preparation of AuNPs with controllable sizes. The AuNPs show remarkable stability in water media with high concentrations of salt, various buffer solutions and physiological conditions in biotechnology and biomedicine. Moreover, the AuNPs are also non-toxic at high concentration (100 microM). Therefore, it provides great opportunities to use these AuNPs for biotechnology and biomedicine. This new approach also involved several green chemistry concepts, such as the selection of environmentally benign reagents and solvents, without energy consumption, and less reaction time.

Effects of thin cerium overlayers on the oxidation of tantalum and aluminium

Abstract Oxidation of aluminium and tantalum with thin (4–15 A) overlayers of cerium has been studied with X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. The cerium layer is found to induce a large enhancement in the oxidation of the Ta and Al substrates at room temperature. The catalytic oxidation of Ta exhibits growth characteristics identical with those previously reported for Nb. This enhanced growth was attributed to a mechanism in which a conversion from tetra- to trivalent Ce-oxide plays an important role. In contrast, the enhanced oxidation of Al is caused by formation of an intermetallic surface layer which enables increased oxygen uptake. The growth of bulk Ta- and Al-oxide follows logarithmic growth laws at room temperature. The absence of bulk oxide formation at liquid nitrogen temperature shows that the enhanced surface oxidation is limited by a thermally activated process and not by electron tunneling across the oxide barrier. Field assisted diffusion is assumed to be the rate determining mechanism for both systems investigated.

Towards a highly-efficient fuel-cell catalyst: optimization of Pt particle size, supports and surface-oxygen group concentration.

In the present work, methanol oxidation reaction was investigated on Pt particles of various diameters on carbon-nanofibers and carbon-black supports with different surface-oxygen concentrations, aiming for a better understanding of the relationship between the catalyst properties and the electrochemical performance. The pre-synthesized Pt nanoparticles in ethylene glycol, prepared by the polyol method without using any capping agents, were deposited on different carbon supports. Removal of oxygen-groups from the carbon supports had profound positive effects on not only the Pt dispersion but also the specific activity. The edge structures on the stacked graphene sheets in the platelet carbon-nanofibers provided a strong interaction with the Pt particles, significantly reconstructing them in the process. Such reconstruction resulted in the formation of more plated Pt particles on the CNF than on the carbon-black and exposure of more Pt atoms with relatively high co-ordination numbers, and thereby higher specific activity. Owing to the combined advantages of optimum Pt particle diameter, an oxygen-free surface and the unique properties of CNFs, Pt supported on heat-treated CNFs exhibited a higher mass activity twice of that of its commercial counterpart.

SEM, EDS and XPS Analysis of the Coatings Obtained on Titanium after Plasma Electrolytic Oxidation in Electrolytes Containing Copper Nitrate

In the paper, the Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) results of the surface layer formed on pure titanium after plasma electrolytic oxidation (micro arc oxidation) at the voltage of 450 V are shown. As an electrolyte, the mixture of copper nitrate Cu(NO3)2 (10–600 g/L) in concentrated phosphoric acid H3PO4 (98 g/mol) was used. The thickness of the obtained porous surface layer equals about 10 μm, and it consists mainly of titanium phosphates and oxygen with embedded copper ions as a bactericidal agent. The maximum percent of copper in the PEO surface layer was equal to 12.2 ± 0.7 wt % (7.6 ± 0.5 at %), which is the best result that the authors obtained. The top surface layer of all obtained plasma electrolytic oxidation (PEO) coatings consisted most likely mainly of Ti3(PO4)4∙nH3PO4 and Cu3(PO4)2∙nH3PO4 with a small addition of CuP2, CuO and Cu2O.

Hydrophobic monolayer preparation by Langmuir-Blodgett and chemical adsorption techniques.

Alkylsiloxane and perfluoroalkylsiloxane monolayers are prepared on siliceous surfaces using the techniques of Langmuir-Blodgett deposition and solid-liquid chemical adsorption. Acid-catalyzed hydrolysis and polycondensation reactions provide two-dimensional siloxane networks at the liquid-vapor interface, which can be compressed to mean molecular areas of approximately 22 and approximately 32 A(2) for pendent hydrocarbon and fluorocarbon chains, respectively. Subsequent Langmuir-Blodgett transfer onto glass substrates at moderate surface pressures leads to compact monolayers for single-component precursors, while mixed alkyl- and perfluoroalkylsilanes produce nonhomogeneous films characterized by transfer ratios greater than unity. As an alternate monolayer preparation technique, silane polymerization was performed directly on siliceous surfaces via a chemical adsorption mechanism. XPS analysis of a chemically adsorbed 1H,1H,2H,2H-perfluorodecylsiloxane film confirms a single adsorbed monolayer thickness in which the pendent fluoroalkyl chains align nonperpendicularly with respect to the surface. The surface free energy was determined to be 11.4 dyn cm(-1) based on static contact angle measurements. AFM imaging shows the presence of surface defects due to oligomer deposition during the drying process. The use of solubilized trichloro-based silane coupling agents under anhydrous conditions is shown to produce surfaces with a minimal number of surface defects. The presence of undissolved silane material in the bulk solution significantly increases the number of surface defects.

Preparation of stable cubic LaFeO3 nanoparticles using carbon nanotubes as templates

In the present study, the cubic lanthanum ferrite (LaFeO3) perovskite nanoparticles with a high surface area (30 m2 g−1) have been synthesized, which are stable at high temperatures up to 1173 K. Carbon nanotubes (CNTs) were used as hard templates. The advantages of this synthesis are evidenced in this study by comparing the phase, size and stability of the resulting LaFeO3 perovskite with those synthesized by using the well-established citrate method. CNTs can stabilize not only the perovskite cubic structure, but also the size.

XPS and GDOES Characterization of Porous Coating Enriched with Copper and Calcium Obtained on Tantalum via Plasma Electrolytic Oxidation

XPS and GDOES characterizations of porous coatings on tantalum after Plasma Electrolytic Oxidation (PEO) at 450 V for 3 minutes in electrolyte containing concentrated (85%) phosphoric acid with calcium nitrate and copper (II) nitrate are described. Based on the obtained data, it may be concluded that the PEO coating consists of tantalum (Ta5

Initial oxidation of pure and K doped NiTi shape memory alloys

Initial oxidation of pure and K doped nitinol has been studied by photoelectron spectroscopy. The composition of the TiOx layer that forms on the surface is found to depend on the temperature during oxidation. The oxidation at high temperatures results in enhanced formation of lower oxides, whereas TiO2 predominates for oxidation at lower temperatures, e.g., 70 °C. Submonolayer coverage of K on NiTi enhances the formation of TiO2 on the expense of lower oxides, which is of consequence for formation of a protective oxide layer and biocompatibility. Oxidation in the martensitic phase was found to be independent of temperature for temperatures between −40 and 10 °C, whereas in the austenitic phase the oxide growth is thermally activated.

Electronic properties of the Sm∕4H-SiC surface alloy

The formation of a samarium on silicon carbide (Sm∕SiC) alloy after deposition of 2–3 monolayers of Sm in ultrahigh vacuum on clean reconstructed carbon(000-1)- and silicon(0001)-terminated SiC surfaces is studied by x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, and low-energy electron diffraction (LEED). The measured work function together with core-level spectroscopy is used to differentiate the formation of samarium silicide carbide (Sm–Si–C) surface alloys on both polar faces of 4H-SiC. Both naturally n-type-doped bulk Si-face and low-doped epilayer Si-face SiC were studied. A (1×1) LEED pattern is obtained on the C-face Sm–Si–C alloy and on the Si-face epilayer Sm–Si–C alloy. Flatband voltages are estimated as a function of annealing, from the shift in the C1s and Si2p bulk core-level positions. The valency of Sm is estimated during the formation of the Sm–Si–C surface alloy. The valence of the Sm overlayer after deposition at room temperature is estimated to be approximat...

Interface formation in rare-earth overlayer systems

Abstract Photoemission studies reveal that intermixed interface layers form when rare earths are deposited onto various metallic substrates at room temperature. The following systems have been investigated: Ce on Au, Ce on Cu, Ce on Al, and La on Mg. Such intermixed regions are argued to be amorphous in nature, since they are being formed at temperatures that are well below those where nucleation and crystalline growth are expected to occur. Interactions between deposited and substrate material are witnessed by core level shifts in substrate photoemission peaks. Deviations from exponential attenuation of substrate emission indicate that even overlayers are not formed. Simplistic models for the mixed interface are used to estimate the extent of the interface and the average volume fraction of deposited and substrate material in the interface.