Comparative Evaluation of Some Properties of Native and Oxidized ...

African Journals Online (AJOL)

The study was designed to produce native starches from cassava, yam and rice, and to modify a portion of the native starches by oxidation and compare their properties. The modification process was carried out by treating the native starches with food grade sodium hypochlorite (NaOCl). The proximate, swelling index and ...

Immobilization of azurin with retention of its native electrochemical properties at alkylsilane self-assembled monolayer modified indium tin oxide

International Nuclear Information System (INIS)

Ashur, Idan; Jones, Anne K.

2012-01-01

Highlights: ► Immobilization of azurin at indium tin oxide causes modification of the native redox properties. ► Azurin was immobilized at alkylsilane self-assembled monolayer on indium tin oxide. ► Native, solution redox properties are retained for the immobilized protein on the SAM. ► Technique should be widely applicable to other redox proteins. - Abstract: Indium tin oxide (ITO) is a promising material for developing spectroelectrochemical methods due to its combination of excellent transparency in the visible region and high conductivity over a broad range of potential. However, relatively few examples of immobilization of redox proteins at ITO with retention of the ability to transfer electrons with the underlying material with native characteristics have been reported. In this work, we utilize an alkylsilane functionalized ITO surface as a biocompatible interface for immobilization of the blue copper protein azurin. Adsorption of azurin at ITO as well as ITO coated with self-assembled monolayers of (3-mercaptopropyl)trimethoxysilane (MPTMS) and n-decyltrimethoxysilane (DTMS) was achieved, and immobilized protein probed using protein film electrochemistry. The native redox properties of the protein were perturbed by adsorption directly to ITO or to the MPTMS layer on an ITO surface. However, azurin adsorbed at a DTMS covered ITO surface retained native electrochemical properties (E 1/2 = 122 ± 5 mV vs. Ag/AgCl) and could exchange electrons directly with the underlying ITO layer without need for an intervening chemical mediator. These results open new opportunities for immobilizing functional redox proteins at ITO and developing spectroelectrochemical methods for investigating them.

Novel Size and Surface Oxide Effects in Silicon Nanowires as Lithium Battery Anodes

KAUST Repository

McDowell, Matthew T.

2011-09-14

With its high specific capacity, silicon is a promising anode material for high-energy lithium-ion batteries, but volume expansion and fracture during lithium reaction have prevented implementation. Si nanostructures have shown resistance to fracture during cycling, but the critical effects of nanostructure size and native surface oxide on volume expansion and cycling performance are not understood. Here, we use an ex situ transmission electron microscopy technique to observe the same Si nanowires before and after lithiation and have discovered the impacts of size and surface oxide on volume expansion. For nanowires with native SiO2, the surface oxide can suppress the volume expansion during lithiation for nanowires with diameters <∼50 nm. Finite element modeling shows that the oxide layer can induce compressive hydrostatic stress that could act to limit the extent of lithiation. The understanding developed herein of how volume expansion and extent of lithiation can depend on nanomaterial structure is important for the improvement of Si-based anodes. © 2011 American Chemical Society.

Effect of surface oxidation on the nm-scale wear behavior of a metallic glass

International Nuclear Information System (INIS)

Caron, A.; Louzguine-Luzguin, D. V.; Sharma, P.; Inoue, A.; Shluger, A.; Fecht, H.-J.

2011-01-01

Metallic glasses are good candidates for applications in micromechanical systems. With size reduction of mechanical components into the micrometer and submicrometer range, the native surface oxide layer starts playing an important role in contact mechanical applications of metallic glasses. We use atomic force microscopy to investigate the wear behavior of the Ni 62 Nb 38 metallic glass with a native oxide layer and with an oxide grown after annealing in air. After the annealing, the wear rate is found to have significantly decreased. Also the dependency of the specific wear on the velocity is found to be linear in the case of the as spun sample while it follows a power law in the case of the sample annealed in air. We discuss these results in relation to the friction behavior and properties of the surface oxide layer obtained on the same alloy.

Evaluation of the nanomechanical properties of vanadium and native oxide vanadium thin films prepared by RF magnetron sputtering

International Nuclear Information System (INIS)

Mamun, M.A.; Zhang, K.; Baumgart, H.; Elmustafa, A.A.

2015-01-01

Graphical abstract: - Highlights: • V films of 50, 75, 100 nm thickness were deposited on Si by RF magnetron sputtering. • We studied structural/mechanical properties by XRD, FE-SEM, AFM, and nanoindentation. • The hardness increased from 9.0 to 14.0 GPa for 100 to 50 nm. • The modulus showed no correlation with thickness or native oxide formation. • Native oxide formation resulted in grain enlargement and roughness reduction. - Abstract: Polycrystalline vanadium thin films of 50, 75, and 100 nm thickness were deposited by magnetron sputtering of a vanadium metal target of 2 inch diameter with 99.9% purity on native oxide covered Si substrates. One set of the fabricated samples were kept in moisture free environment and the other set was exposed to ambient air at room temperature for a long period of time that resulted in formation of native oxide prior to testing. The crystal structure and phase purity of the vanadium and the oxidized vanadium thin films were characterized by X-ray diffraction (XRD). The XRD results yield a preferential (1 1 0), and (2 0 0) orientation of the polycrystalline V films and (0 0 4) vanadium oxide (V 3 O 7 ). The vanadium films thickness were verified using field emission scanning electron microscopy and the films surface morphologies were inspected using atomic force microscopy (AFM). AFM images reveal surface roughness was observed to increase with increasing film thickness and also subsequent to oxidation at room temperature. The nanomechanical properties were measured by nanoindentation to evaluate the modulus and hardness of the vanadium and the oxidized vanadium thin films. The elastic modulus of the vanadium and the oxidized vanadium films was estimated as 150 GPa at 30% film thickness and the elastic modulus of the bulk vanadium target is estimated as 135 GPa. The measured hardness of the vanadium films at 30% film thickness varies between 9 and 14 GPa for the 100 and 50 nm films, respectively, exhibiting size effects

Rapid Surface Oxidation as a Source of Surface Degradation Factor for Bi 2 Se 3

KAUST Repository

Kong, Desheng

2011-06-28

Bismuth selenide (Bi2Se3) is a topological insulator with metallic surface states (SS) residing in a large bulk bandgap. In experiments, synthesized Bi2Se3 is often heavily n-type doped due to selenium vacancies. Furthermore, it is discovered from experiments on bulk single crystals that Bi2Se3 gets additional n-type doping after exposure to the atmosphere, thereby reducing the relative contribution of SS in total conductivity. In this article, transport measurements on Bi2Se3 nanoribbons provide additional evidence of such environmental doping process. Systematic surface composition analyses by X-ray photoelectron spectroscopy reveal fast formation and continuous growth of native oxide on Bi2Se3 under ambient conditions. In addition to n-type doping at the surface, such surface oxidation is likely the material origin of the degradation of topological SS. Appropriate surface passivation or encapsulation may be required to probe topological SS of Bi2Se3 by transport measurements. © 2011 American Chemical Society.

Development of natively textured surface hydrogenated Ga-doped ZnO-TCO thin films for solar cells via magnetron sputtering

International Nuclear Information System (INIS)

Wang, Fei; Chen, Xin-liang; Geng, Xin-hua; Zhang, De-kun; Wei, Chang-chun; Huang, Qian; Zhang, Xiao-dan; Zhao, Ying

2012-01-01

Highlights: ► Natively textured surface hydrogenated gallium-doped zinc oxide (HGZO) thin films have been deposited via magnetron sputtering on glass substrates. ► The directly deposited HGZO thin films present rough crater-type surface morphology. ► Typical HGZO thin film exhibits a high electron mobility of 41.3 cm 2 /V s and a relative low sheet resistance of ∼7.0 Ω. ► These HGZO thin films have high optical transmittances in the visible and near infrared region (∼380–1100 nm). ► A gradient H 2 growth method for fabricating HGZO thin films has been proposed in magnetron sputtering process. - Abstract: The main purposes are to obtain high quality transparent conductive oxide (TCO) based on zinc oxide (ZnO) thin films with high optical transparency in the visible and near infrared spectral range, high electrical conductivity and good light-scattering capability to enhance the path of the light inside the Si-based thin film solar cells. Natively textured surface hydrogenated gallium-doped ZnO (HGZO) thin films have been deposited via pulsed direct current (DC) magnetron sputtering on glass substrates at a substrate temperature of 553 K. These natively textured HGZO thin films exhibit high optical transmittance (over 80%) in the visible and near infrared region (λ = 380–1100 nm) and excellent electrical properties. The optimized HGZO thin film with crater-type textured surface obtained at the hydrogen flow rate of ∼2.0 sccm exhibits a high electron mobility of 41.3 cm 2 /V s and a relatively low sheet resistance of ∼7.0 Ω. The influences of hydrogen flow rates on the surface morphology, electrical and optical properties of HGZO thin films were investigated in detail. In addition, we put forward a method of gradient H 2 growth technique for fabricating HGZO thin films so as to obtain rough surface structure with good light-scattering capability and high electrical conductivity. “Crater-like” surface feature size and optical transmittance

High-Resolution Electron Energy Loss Studies of Oxygen, Hydrogen, Nitrogen, Nitric Oxide, and Nitrous Oxide Adsorption on Germanium Surfaces.

Science.gov (United States)

Entringer, Anthony G.

The first high resolution electron energy loss spectroscopy (HREELS) studies of the oxidation and nitridation of germanium surfaces are reported. Both single crystal Ge(111) and disordered surfaces were studied. Surfaces were exposed to H, O_2, NO, N _2O, and N, after cleaning in ultra-high vacuum. The Ge surfaces were found to be non-reactive to molecular hydrogen (H_2) at room temperature. Exposure to atomic hydrogen (H) resulted hydrogen adsorption as demonstrated by the presence of Ge-H vibrational modes. The HREEL spectrum of the native oxide of Ge characteristic of nu -GeO_2 was obtained by heating the oxide to 200^circC. Three peaks were observed at 33, 62, and 106 meV for molecular oxygen (O_2) adsorbed on clean Ge(111) at room temperature. These peaks are indicative of dissociative bonding and a dominant Ge-O-Ge bridge structure. Subsequent hydrogen exposure resulted in a shift of the Ge-H stretch from its isolated value of 247 meV to 267 meV, indicative of a dominant +3 oxidation state. A high density of dangling bonds and defects and deeper oxygen penetration at the amorphous Ge surface result in a dilute bridge structure with a predominant +1 oxidation state for similar exposures. Molecules of N_2O decompose at the surfaces to desorbed N_2 molecules and chemisorbed oxygen atoms. In contrast, both oxygen and nitrogen are detected at the surfaces following exposure to NO molecules. Both NO and N_2O appear to dissociate and bond at the top surface layer. Molecular nitrogen (N_2) does not react with the Ge surfaces, however, a precursor Ge nitride is observed at room temperature following exposure to nitrogen atoms and ions. Removal of oxygen by heating of the NO-exposed surface to 550^circC enabled the identification of the Ge-N vibrational modes. These modes show a structure similar to that of germanium nitride. This spectrum is also identical to that of the N-exposed surface heated to 550^circC. Surface phonon modes of the narrow-gap semiconducting

Structure and nano-mechanical characteristics of surface oxide layers on a metallic glass.

Science.gov (United States)

Caron, A; Qin, C L; Gu, L; González, S; Shluger, A; Fecht, H-J; Louzguine-Luzgin, D V; Inoue, A

2011-03-04

Owing to their low elastic moduli, high specific strength and excellent processing characteristics in the undercooled liquid state, metallic glasses are promising materials for applications in micromechanical systems. With miniaturization of metallic mechanical components down to the micrometer scale, the importance of a native oxide layer on a glass surface is increasing. In this work we use TEM and XPS to characterize the structure and properties of the native oxide layer grown on Ni(62)Nb(38) metallic glass and their evolution after annealing in air. The thickness of the oxide layer almost doubled after annealing. In both cases the oxide layer is amorphous and consists predominantly of Nb oxide. We investigate the friction behavior at low loads and in ambient conditions (i.e. at T = 295 K and 60% air humidity) of both as-cast and annealed samples by friction force microscopy. After annealing the friction coefficient is found to have significantly increased. We attribute this effect to the increase of the mechanical stability of the oxide layer upon annealing.

Pre-treatments applied to oxidized aluminum surfaces to modify the interfacial bonding with bis-1,2-(triethoxysilyl)ethane (BTSE)

Energy Technology Data Exchange (ETDEWEB)

Teo, M. [Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1 (Canada); Kim, J. [Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1 (Canada); Wong, P.C. [Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1 (Canada); Wong, K.C. [Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1 (Canada); Mitchell, K.A.R. [Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1 (Canada)]. E-mail: karm@chem.ubc.ca

2005-12-15

A remote microwave-generated H{sub 2} plasma and heating to 250 deg. C were separately used to modify high-purity oxidized aluminum surfaces and to assess whether these treatments can help enhance adhesion with bis-1,2-(triethoxysilyl)ethane (BTSE) coatings. Different initial oxide surfaces were considered, corresponding to the native oxide and to surfaces formed by the Forest Products Laboratory (FPL) treatment applied for either 15 or 60 min. BTSE is applied from solution at pH 4, and competing processes of etching, protonation (to form OH groups) and coupling (to form Al-O-Si interfacial bonds) occur at the solid-liquid interface. Scanning electron microscopy (SEM) was used to determine how the topographies of the modified Al surfaces changed with the different pre-treatments and with exposure to a buffer solution of pH 4. Secondary-ion mass spectrometry (SIMS) was used to determine the direct amount of Al-O-Si interfacial bonds by measuring the ratio of peak intensities 71-70 amu, while X-ray photoelectron spectroscopy (XPS) was used to determine the overall strength of the silane coating adhesion by measuring the Si 2p signals before and after application of an ultrasonic rinse to the coated sample. Measured Al 2p and O 1s spectra helped assess how the different pre-treatments modified the various Al oxidized surfaces prior to BTSE coating. Pre-treated samples that showed increased Al-O-Si bonding after BTSE coating corresponded to surfaces, which did not show evidence of significant etching after exposure to a pH 4 environment. This suggests that such surfaces are more receptive to the coupling reaction during exposure to the BTSE coating solution. These surfaces include all H{sub 2} plasma-treated samples, the heated native oxide and the sample that only received the 15 min FPL treatment. In contrast, other surfaces that show evidence of etching in pH 4 environments are samples that received lower amounts of Al-O-Si interfacial bonding. Overall, heating

Fluorine-enhanced low-temperature wafer bonding of native-oxide covered Si wafers

Science.gov (United States)

Tong, Q.-Y.; Gan, Q.; Fountain, G.; Enquist, P.; Scholz, R.; Gösele, U.

2004-10-01

The bonding energy of bonded native-oxide-covered silicon wafers treated in the HNO3/H2O/HF or the HNO3/HF solution prior to room-temperature contact is significantly higher than bonded standard RCA1 cleaned wafer pairs after low-temperature annealing. The bonding energy reaches over 2000mJ/m2 after annealing at 100 °C. The very slight etching and fluorine in the chemically grown oxide are believed to be the main contributors to the enhanced bonding energy. Transmission-electron-microscopic images have shown that the chemically formed native oxide at bonding interface is embedded with many flake-like cavities. The cavities can absorb the by-products of the interfacial reactions that result in covalent bond formation at low temperatures allowing the strong bond to be retained.

Effect of surface finishing on the oxidation behaviour of a ferritic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Ardigo-Besnard, M.R., E-mail: maria-rosa.ardigo-besnard@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS—Université de Bourgogne Franche-Comté, BP 47870, 21078 Dijon Cedex (France); Popa, I.; Heintz, O.; Chassagnon, R. [Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS—Université de Bourgogne Franche-Comté, BP 47870, 21078 Dijon Cedex (France); Vilasi, M. [Institut Jean Lamour, UMR 7198 CNRS—Université de Lorraine, Parc de Saurupt, 54011 Nancy (France); Herbst, F. [Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS—Université de Bourgogne Franche-Comté, BP 47870, 21078 Dijon Cedex (France); Girardon, P. [APERAM, Centre de Recherche, BP15, 62330 Isbergues (France); Chevalier, S. [Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS—Université de Bourgogne Franche-Comté, BP 47870, 21078 Dijon Cedex (France)

2017-08-01

Highlights: • Study of surface finishing effect on the corrosion behaviour of a stainless steel. • Mirror polished samples were compared to as-rolled material. • Two oxidation mechanisms were identified depending on the surface finishing. • Before oxidation, native chemical phases are identical for both samples. • Subsurface dislocations generated by the polishing process promote Cr{sub 2}O{sub 3} formation. - Abstract: The corrosion behaviour and the oxidation mechanism of a ferritic stainless steel, K41X (AISI 441), were evaluated at 800 °C in water vapour hydrogen enriched atmosphere. Mirror polished samples were compared to as-rolled K41X material. Two different oxidation behaviours were observed depending on the surface finishing: a protective double (Cr,Mn){sub 3}O{sub 4}/Cr{sub 2}O{sub 3} scale formed on the polished samples whereas external Fe{sub 3}O{sub 4} and (Cr,Fe){sub 2}O{sub 3} oxides grew on the raw steel. Moreover, isotopic marker experiments combined with SIMS analyses revealed different growth mechanisms. The influence of surface finishing on the corrosion products and growth mechanisms was apprehended by means of X-ray photoelectron spectroscopy (XPS) and residual stress analyses using XRD at the sample surfaces before ageing.

The role of the native oxide shell on the microwave sintering of copper metal powder compacts

International Nuclear Information System (INIS)

Mahmoud, Morsi M.; Link, Guido; Thumm, Manfred

2015-01-01

Highlights: • Thin oxide native layer had a critical role on microwave sintering of copper. • Explain why microwaves interact with copper powder differently than its bulk. • Abnormal expansion in copper is due to the plastic deformation and crack formation. • In-situ setup gives important insight about the microwave sintering of metals. • Microwave sintering is a promising candidate technology in powder metallurgy. - Abstract: Successful microwave sintering of several metal powders had been reported by many researchers with remarkable improvements in the materials properties and/or in the overall process. However, the concept behind microwave heating of metal powders has not been fully understood till now, as it is well known that bulk metals reflect microwaves. The progress of microwave sintering of copper metal powder compacts was investigated via combining both in-situ electrical resistivity and dilatometry measurements that give important information about microstructural changes with respect to the inter-particle electrical contacts during sintering. The sintering behavior of copper metal powders was depending on the type of the gas used, particle size, the initial green density, the soaking sintering time and the thin oxide layer on the particles surfaces. The thin copper oxide native layer (ceramics) that thermodynamically formed on the particles surfaces under normal handling and ambient environmental conditions had a very critical and important role in the microwave absorption and interaction, the sintering behavior and the microstructural changes. This finding could help to have a fundamental understanding of why MW’s interact with copper metal powder in a different way than its bulk at room temperature, i.e. why a given metal powder could be heated using microwaves while its bulk reflects it

Systematic study of metal-insulator-metal diodes with a native oxide

KAUST Repository

Donchev, E.; Gammon, P. M.; Pang, J. S.; Petrov, P. K.; Alford, N. McN.

2014-01-01

© 2014 SPIE. In this paper, a systematic analysis of native oxides within a Metal-Insulator-Metal (MIM) diode is carried out, with the goal of determining their practicality for incorporation into a nanoscale Rectenna (Rectifying Antenna

Amylolytic hydrolysis of native starch granules affected by granule surface area.

Science.gov (United States)

Kim, J C; Kong, B W; Kim, M J; Lee, S H

2008-11-01

Initial stage of hydrolysis of native starch granules with various amylolytic enzymes, alpha-amylase from Bacillus subtilis, glucoamylase I (GA-I) and II (GA-II) from Aspergillus niger, and beta-amylase from sweet potato showed that the reaction was apparently affected by a specific surface area of the starch granules. The ratios of the reciprocal of initial velocity of each amylolytic hydrolysis for native potato and maize starch to that for rice with the amylolytic enzymes were nearly equivalent to the ratio of surface area per mass of the 2 starch granules to that of rice, that is, 6.94 and 2.25, respectively. Thus, the reciprocal of initial velocity of each enzymatic hydrolysis as expressed in a Lineweaver-Burk plot was a linear function of the reciprocal of surface area for each starch granule. As a result, it is concluded that amylolytic hydrolysis of native starch granules is governed by the specific surface area, not by the mass concentration, of each granule.

Oxidized epigallocatechin gallate inhibited lysozyme fibrillation more strongly than the native form

Directory of Open Access Journals (Sweden)

Ting-Ting An

2017-04-01

Full Text Available Epigallocatechin gallate (EGCG, the most abundant flavanoid in green tea, is currently being evaluated in the clinic due to its benefits in the treatment of amyloid disorders. Its anti-amyloidogenic effect has been attributed to direct interaction of the intact molecule with misfolded polypeptides. In addition, antioxidant activity is also involved in the anti-amyloidogenic role. The detailed molecular mechanism is still unclear and requires further investigation. In the present study, the kinetics of EGCG oxidation and the anti-amyloidogenic effect of the resultant oxidation substances have been examined. The results indicate that EGCG degrades in a medium at pH 8.0 with a half-life less than 2 h. By utilizing lysozyme as an in vitro model, the oxidized EGCG demonstrates a more potent anti-amyloidogenic capacity than the intact molecule, as shown by ThT and ANS fluorescence, TEM determination, and hemolytic assay. The oxidized EGCG also has a stronger disruptive effect on preformed fibrils than the native form. Ascorbic acid eliminates the disruptive role of native EGCG on the fibrils, suggesting that oxidation is a prerequisite in fibril disruption. The results of this work demonstrate that oxidized EGCG plays a more important role than the intact molecule in anti-amyloidogenic activity. These insights into the action of EGCG may provide a novel route to understand the anti-amyloidogenic activity of natural polyphenols.

Iron oxide surfaces

Science.gov (United States)

Parkinson, Gareth S.

2016-03-01

The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe3O4), maghemite (γ-Fe2O3), haematite (α-Fe2O3), and wüstite (Fe1-xO) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. Fe diffuses in and out from the bulk in response to the O2 chemical potential, forming sometimes complex intermediate phases at the surface. For example, α-Fe2O3 adopts Fe3O4-like surfaces in reducing conditions, and Fe3O4 adopts Fe1-xO-like structures in further reducing conditions still. It is argued that known bulk defect structures are an excellent starting point in building models for iron oxide surfaces. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe3O4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment. It is also an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed. The best understood iron oxide surface at present is probably Fe3O4(100); the structure is

Memory for non-native language: the role of lexical processing in the retention of surface form.

Science.gov (United States)

Sampaio, Cristina; Konopka, Agnieszka E

2013-01-01

Research on memory for native language (L1) has consistently shown that retention of surface form is inferior to that of gist (e.g., Sachs, 1967). This paper investigates whether the same pattern is found in memory for non-native language (L2). We apply a model of bilingual word processing to more complex linguistic structures and predict that memory for L2 sentences ought to contain more surface information than L1 sentences. Native and non-native speakers of English were tested on a set of sentence pairs with different surface forms but the same meaning (e.g., "The bullet hit/struck the bull's eye"). Memory for these sentences was assessed with a cued recall procedure. Responses showed that native and non-native speakers did not differ in the accuracy of gist-based recall but that non-native speakers outperformed native speakers in the retention of surface form. The results suggest that L2 processing involves more intensive encoding of lexical level information than L1 processing.

Decarboxylative alkylation for site-selective bioconjugation of native proteins via oxidation potentials

Science.gov (United States)

Bloom, Steven; Liu, Chun; Kölmel, Dominik K.; Qiao, Jennifer X.; Zhang, Yong; Poss, Michael A.; Ewing, William R.; MacMillan, David W. C.

2018-02-01

The advent of antibody-drug conjugates as pharmaceuticals has fuelled a need for reliable methods of site-selective protein modification that furnish homogeneous adducts. Although bioorthogonal methods that use engineered amino acids often provide an elegant solution to the question of selective functionalization, achieving homogeneity using native amino acids remains a challenge. Here, we explore visible-light-mediated single-electron transfer as a mechanism towards enabling site- and chemoselective bioconjugation. Specifically, we demonstrate the use of photoredox catalysis as a platform to selectivity wherein the discrepancy in oxidation potentials between internal versus C-terminal carboxylates can be exploited towards obtaining C-terminal functionalization exclusively. This oxidation potential-gated technology is amenable to endogenous peptides and has been successfully demonstrated on the protein insulin. As a fundamentally new approach to bioconjugation this methodology provides a blueprint toward the development of photoredox catalysis as a generic platform to target other redox-active side chains for native conjugation.

Decarboxylative alkylation for site-selective bioconjugation of native proteins via oxidation potentials.

Science.gov (United States)

Bloom, Steven; Liu, Chun; Kölmel, Dominik K; Qiao, Jennifer X; Zhang, Yong; Poss, Michael A; Ewing, William R; MacMillan, David W C

2018-02-01

The advent of antibody-drug conjugates as pharmaceuticals has fuelled a need for reliable methods of site-selective protein modification that furnish homogeneous adducts. Although bioorthogonal methods that use engineered amino acids often provide an elegant solution to the question of selective functionalization, achieving homogeneity using native amino acids remains a challenge. Here, we explore visible-light-mediated single-electron transfer as a mechanism towards enabling site- and chemoselective bioconjugation. Specifically, we demonstrate the use of photoredox catalysis as a platform to selectivity wherein the discrepancy in oxidation potentials between internal versus C-terminal carboxylates can be exploited towards obtaining C-terminal functionalization exclusively. This oxidation potential-gated technology is amenable to endogenous peptides and has been successfully demonstrated on the protein insulin. As a fundamentally new approach to bioconjugation this methodology provides a blueprint toward the development of photoredox catalysis as a generic platform to target other redox-active side chains for native conjugation.

On the growth of native oxides on hydrogen-terminated silicon surfaces in dark and under illumination with light

NARCIS (Netherlands)

Kovalgin, Alexeij Y.; Zinine, A.; Bankras, R.G.; Wormeester, Herbert; Poelsema, Bene; Schmitz, Jurriaan

2006-01-01

After a cleaning procedure, a silicon surface can be terminated by Si-OH groups which results in a high chemical activity. As it is accepted, after removing the wet-chemically grown oxide layer using an HF solution, the surface becomes terminated with Si-H groups. This results in a chemically stable

Thermal processing and native oxidation of silicon nanoparticles

International Nuclear Information System (INIS)

Winters, Brandon J.; Holm, Jason; Roberts, Jeffrey T.

2011-01-01

In this study, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS) were used to investigate in-air oxidation of silicon nanoparticles ca. 11 nm in diameter. Particle samples were prepared first by extracting them from an RF plasma synthesis reactor, and then heating them in an inert carrier gas stream. The resulting particles had varying surface hydrogen coverages and relative amounts of SiH x (x = 1, 2, and 3), depending on the temperature to which they had been heated. The particles were allowed to oxidize in-air for several weeks. FTIR, XPS, and EELS analyses that were performed during this period clearly establish that adsorbed hydrogen retards oxidation, although in complex ways. In particular, particles that have been heated to intermediate hydrogen coverages oxidize more slowly in air than do freshly generated particles that have a much higher hydrogen content. In addition, the loss of surface hydride species at high processing temperatures results in fast initial oxidation and the formation of a self-limiting oxide layer. Analogous measurements made on deuterium-covered particles show broadly similar behavior; i.e., that oxidation is the slowest at some intermediate coverage of adsorbed deuterium.

Alterations of markers of oxidative stress caused by environmental factors and their dynamics under impact of native biomodulators

International Nuclear Information System (INIS)

Stasytyte-Buneviciene, D.; Juozulynas, A.; Bunevicius, J.

2004-01-01

Intensified formation of free radicals is one of the most important harmful factors of ionizing radiation acting upon human organism. Under physiological conditions, anti oxidative system preserves from harmful influence of free radicals. To avoid a disturbing influence of oxidative stress upon the processes of human homeostasis, additional quantities of antioxidants are indispensable. Among native biomodulators, pollen are well known for their anti oxidative, antitoxic and radioprotective properties. Dynamics of alterations of markers of oxidative stress as well as possibilities of restitution of their qualitative and quantitative indices were studied using native pollen. Correction programme was performed on 50 persons, 9 males and 41 female, residing and working under impact of harmful factors of oxidative stress, who used pollen 10 g per day during a period of 30 days. Control group consisted of 57 persons, 10 males and 47 females living and working under the same conditions. Blood tests (diene conjugates, malonic dialdehyde and katalase) using standard spectrophotometric methodic were studied before and after the course of treatment. After the treatment, contents of metabolites of lipid peroxidation, diene conjugates and malonic dialdehyde in blood serum essentially reduced. Activity of catalase decreased significantly in blood serum of the males and regularly smoking females. In conclusion, data presented demonstrate anti oxidative efficiency of native pollen and suggest more often it's applying in cases with alterated processes of homeostasis under impact of harmful factors of oxidative stress including influence of ionizing radiation. (author)

Reliable wet-chemical cleaning of natively oxidized high-efficiency Cu(In,Ga)Se2 thin-film solar cell absorbers

Science.gov (United States)

Lehmann, Jascha; Lehmann, Sebastian; Lauermann, Iver; Rissom, Thorsten; Kaufmann, Christian A.; Lux-Steiner, Martha Ch.; Bär, Marcus; Sadewasser, Sascha

2014-12-01

Currently, Cu-containing chalcopyrite-based solar cells provide the highest conversion efficiencies among all thin-film photovoltaic (PV) technologies. They have reached efficiency values above 20%, the same performance level as multi-crystalline silicon-wafer technology that dominates the commercial PV market. Chalcopyrite thin-film heterostructures consist of a layer stack with a variety of interfaces between different materials. It is the chalcopyrite/buffer region (forming the p-n junction), which is of crucial importance and therefore frequently investigated using surface and interface science tools, such as photoelectron spectroscopy and scanning probe microscopy. To ensure comparability and validity of the results, a general preparation guide for "realistic" surfaces of polycrystalline chalcopyrite thin films is highly desirable. We present results on wet-chemical cleaning procedures of polycrystalline Cu(In1-xGax)Se2 thin films with an average x = [Ga]/([In] + [Ga]) = 0.29, which were exposed to ambient conditions for different times. The hence natively oxidized sample surfaces were etched in KCN- or NH3-based aqueous solutions. By x-ray photoelectron spectroscopy, we find that the KCN treatment results in a chemical surface structure which is - apart from a slight change in surface composition - identical to a pristine as-received sample surface. Additionally, we discover a different oxidation behavior of In and Ga, in agreement with thermodynamic reference data, and we find indications for the segregation and removal of copper selenide surface phases from the polycrystalline material.

Spectroscopic investigation of oxidized solder surfaces

International Nuclear Information System (INIS)

Song, Jenn-Ming; Chang-Chien, Yu-Chien; Huang, Bo-Chang; Chen, Wei-Ting; Shie, Chi-Rung; Hsu, Chuang-Yao

2011-01-01

Highlights: → UV-visible spectroscopy is successfully used to evaluate the degree of discoloring of solders. → The surface oxides of solders can also be identified by UV-visible absorption spectra. → The discoloration of solder surface can be correlated with optical characterization of oxides. → A strategy against discoloring by alloying was also suggested. - Abstract: For further understanding of the discoloration of solder surfaces due to oxidation during the assembly and operation of electronic devices, UV-vis and X-ray photoelectron spectroscopic analyses were applied to evaluate the degree of discoloring and identify the surface oxides. The decrease in reflectance of the oxidized solder surface is related to SnO whose absorption band is located within the visible region. A trace of P can effectively depress the discoloration of solders under both solid and semi-solid states through the suppression of SnO.

Oxidation of Ethylene Carbonate on Li Metal Oxide Surfaces

DEFF Research Database (Denmark)

Østergaard, Thomas M.; Giordano, Livia; Castelli, Ivano Eligio

2018-01-01

Understanding the reactivity of the cathode surface is of key importance to the development of batteries. Here, density functional theory is applied to investigate the oxidative decomposition of the electrolyte component, ethylene carbonate (EC), on layered LixMO(2) oxide surfaces. We compare...

Leaf gas exchange and water status responses of a native and non-native grass to precipitation across contrasting soil surfaces in the Sonoran Desert.

Science.gov (United States)

Ignace, Danielle D; Huxman, Travis E; Weltzin, Jake F; Williams, David G

2007-06-01

Arid and semi-arid ecosystems of the southwestern US are undergoing changes in vegetation composition and are predicted to experience shifts in climate. To understand implications of these current and predicted changes, we conducted a precipitation manipulation experiment on the Santa Rita Experimental Range in southeastern Arizona. The objectives of our study were to determine how soil surface and seasonal timing of rainfall events mediate the dynamics of leaf-level photosynthesis and plant water status of a native and non-native grass species in response to precipitation pulse events. We followed a simulated precipitation event (pulse) that occurred prior to the onset of the North American monsoon (in June) and at the peak of the monsoon (in August) for 2002 and 2003. We measured responses of pre-dawn water potential, photosynthetic rate, and stomatal conductance of native (Heteropogon contortus) and non-native (Eragrostis lehmanniana) C(4) bunchgrasses on sandy and clay-rich soil surfaces. Soil surface did not always amplify differences in plant response to a pulse event. A June pulse event lead to an increase in plant water status and photosynthesis. Whereas the August pulse did not lead to an increase in plant water status and photosynthesis, due to favorable soil moisture conditions facilitating high plant performance during this period. E. lehmanniana did not demonstrate heightened photosynthetic performance over the native species in response to pulses across both soil surfaces. Overall accumulated leaf-level CO(2) response to a pulse event was dependent on antecedent soil moisture during the August pulse event, but not during the June pulse event. This work highlights the need to understand how desert species respond to pulse events across contrasting soil surfaces in water-limited systems that are predicted to experience changes in climate.

Native oxidation of ultra high purity Cu bulk and thin films

International Nuclear Information System (INIS)

Iijima, J.; Lim, J.-W.; Hong, S.-H.; Suzuki, S.; Mimura, K.; Isshiki, M.

2006-01-01

The effect of microstructure and purity on the native oxidation of Cu was studied by using angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and spectroscopic ellipsometry (SE). A high quality copper film prepared by ion beam deposition under a substrate bias voltage of -50 V (IBD Cu film at V s = -50 V) showed an oxidation resistance as high as an ultra high purity copper (UHP Cu) bulk, whereas a Cu film deposited without substrate bias voltage (IBD Cu film at V s = 0 V) showed lower oxidation resistance. The growth of Cu 2 O layer on the UHP Cu bulk and both types of the films obeyed in principle a logarithmic rate law. However, the growth of oxide layer on the IBD Cu films at V s = 0 and -50 V deviated upward from the logarithmic rate law after the exposure time of 320 and 800 h, respectively. The deviation from the logarithmic law is due to the formation of CuO on the Cu 2 O layer after a critical time

Interaction of amines with native aluminium oxide layers in non-aqueous environment: Application to the understanding of the formation of epoxy-amine/metal interphases

International Nuclear Information System (INIS)

Mercier, D.; Rouchaud, J.-C.; Barthes-Labrousse, M.-G.

2008-01-01

Interaction of propylamine (PA), 1,2-diaminoethane (DAE) or 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophorone diamine, IPDA) with native aluminium oxide layers in non-aqueous environment has been studied using time-resolved inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The formation of several surface complexes has been evidenced. Monodentate and bidentate metal-bond surface complexes (MBSC) result from interactions between the amine terminations of the molecule and aluminium cations by donation of the N lone electron pair to the metal ion (Lewis-like mechanism leading to O-Al...N bonds). Monodentate and bidentate hydrogen-bond surface complexes (HBSC) are due to interaction of the amino group with surface hydroxyl groups by protonation of the amine termination (Bronsted-like mechanism leading to the formation of Al-OH...N bonds) or interaction with carbonaceous contamination (C x O y H z ...N bonds). Diamines can also form mixed complexes with one amino group forming an O-Al...N bond and the other group forming an Al-OH...N or C x O y H z ...N bond. Al-OH...N and C x O y H z ...N bonds are less stable under vacuum than O-Al...N bonds, leading to partial desorption of the DAE molecules in vacuum and modification of the interaction modes. Only DAE and IPDA can lead to partial dissolution of the aluminium native (hydr)oxide films. A detailed mechanism of dissolution has been proposed based on the formation of mononuclear bidentate (chelate) MBSC by ligand exchange between the terminal η 1 -OH and bridged μ 2 -OH surface sites and the amino terminations of the molecule. The detachment of this complex from the surface is likely to be the precursor step to the formation of the interphase in epoxy-amine/metal systems

Study on influence of native oxide and corrosion products on atmospheric corrosion of pure Al

International Nuclear Information System (INIS)

Liu, Yanjie; Wang, Zhenyao; Ke, Wei

2014-01-01

Highlights: •Corrosion products layer is only formed in coastal atmosphere. •In coastal atmosphere, rate controlling step is diffusion process. •In rural atmosphere, rate controlling step is charge transfer process. •Pitting area increases greatly in coastal site, but slightly in rural site. -- Abstract: Effects of native oxide and corrosion products on atmospheric corrosion of aluminium in rural and coastal sites were studied by electrochemical impedance spectroscopy (EIS), open-circuit potential (OCP) and scanning electron microscope (SEM) techniques after outdoor exposure. In the rural atmosphere, only the compact, adhesive native oxide layer exists, and the rate controlling step is diffusion process, while in the coastal atmosphere, another loose, inadhesive corrosion products layer exists, and a charge transfer process controls the corrosion process. The pitting area in the coastal atmosphere increases over time more obviously than that in the rural atmosphere

Surface and sub-surface thermal oxidation of thin ruthenium films

Energy Technology Data Exchange (ETDEWEB)

Coloma Ribera, R.; Kruijs, R. W. E. van de; Yakshin, A. E.; Bijkerk, F. [MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Kokke, S.; Zoethout, E. [FOM Dutch Institute for Fundamental Energy Research (DIFFER), P.O. Box 1207, 3430 BE Nieuwegein (Netherlands)

2014-09-29

A mixed 2D (film) and 3D (nano-column) growth of ruthenium oxide has been experimentally observed for thermally oxidized polycrystalline ruthenium thin films. Furthermore, in situ x-ray reflectivity upon annealing allowed the detection of 2D film growth as two separate layers consisting of low density and high density oxides. Nano-columns grow at the surface of the low density oxide layer, with the growth rate being limited by diffusion of ruthenium through the formed oxide film. Simultaneously, with the growth of the columns, sub-surface high density oxide continues to grow limited by diffusion of oxygen or ruthenium through the oxide film.

Oxide surfaces and metal/oxide interfaces studied by grazing incidence X-ray scattering

Science.gov (United States)

Renaud, Gilles

Experimental determinations of the atomic structure of insulating oxide surfaces and metal/oxide interfaces are scarce, because surface science techniques are often limited by the insulating character of the substrate. Grazing incidence X-ray scattering (GIXS), which is not subject to charge effects, can provide very precise information on the atomic structure of oxide surfaces: roughness, relaxation and reconstruction. It is also well adapted to analyze the atomic structure, the registry, the misfit relaxation, elastic or plastic, the growth mode and the morphology of metal/oxide interfaces during their growth, performed in situ. GIXS also allows the analysis of thin films and buried interfaces, in a non-destructive way, yielding the epitaxial relationships, and, by variation of the grazing incidence angle, the lattice parameter relaxation along the growth direction. On semi-coherent interfaces, the existence of an ordered network of interfacial misfit dislocations can be demonstrated, its Burger's vector determined, its ordering during in situ annealing cycles followed, and sometimes even its atomic structure can be addressed. Careful analysis during growth allows the modeling of the dislocation nucleation process. This review emphasizes the new information that GIXS can bring to oxide surfaces and metal/oxide interfaces by comparison with other surface science techniques. The principles of X-ray diffraction by surfaces and interfaces are recalled, together with the advantages and properties of grazing angles. The specific experimental requirements are discussed. Recent results are presented on the determination of the atomic structure of relaxed or reconstructed oxide surfaces. A description of results obtained during the in situ growth of metal on oxide surfaces is also given, as well as investigations of thick metal films on oxide surfaces, with lattice parameter misfit relaxed by an array of dislocations. Recent work performed on oxide thin films having

Effect of native oxide layers on copper thin-film tensile properties: A reactive molecular dynamics study

Energy Technology Data Exchange (ETDEWEB)

Skarlinski, Michael D., E-mail: michael.skarlinski@rochester.edu [Materials Science Program, University of Rochester, Rochester, New York 14627 (United States); Quesnel, David J. [Materials Science Program, University of Rochester, Rochester, New York 14627 (United States); Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627 (United States)

2015-12-21

Metal-oxide layers are likely to be present on metallic nano-structures due to either environmental exposure during use, or high temperature processing techniques such as annealing. It is well known that nano-structured metals have vastly different mechanical properties from bulk metals; however, difficulties in modeling the transition between metallic and ionic bonding have prevented the computational investigation of the effects of oxide surface layers. Newly developed charge-optimized many body [Liang et al., Mater. Sci. Eng., R 74, 255 (2013)] potentials are used to perform fully reactive molecular dynamics simulations which elucidate the effects that metal-oxide layers have on the mechanical properties of a copper thin-film. Simulated tensile tests are performed on thin-films while using different strain-rates, temperatures, and oxide thicknesses to evaluate changes in yield stress, modulus, and failure mechanisms. Findings indicate that copper-thin film mechanical properties are strongly affected by native oxide layers. The formed oxide layers have an amorphous structure with lower Cu-O bond-densities than bulk CuO, and a mixture of Cu{sub 2}O and CuO charge character. It is found that oxidation will cause modifications to the strain response of the elastic modulii, producing a stiffened modulii at low temperatures (<75 K) and low strain values (<5%), and a softened modulii at higher temperatures. While under strain, structural reorganization within the oxide layers facilitates brittle yielding through nucleation of defects across the oxide/metal interface. The oxide-free copper thin-film yielding mechanism is found to be a tensile-axis reorientation and grain creation. The oxide layers change the observed yielding mechanism, allowing for the inner copper thin-film to sustain an FCC-to-BCC transition during yielding. The mechanical properties are fit to a thermodynamic model based on classical nucleation theory. The fit implies that the oxidation of the

Oxidation of scandium thin films on tungsten surface

International Nuclear Information System (INIS)

Gorodetskij, D.A.; Martynyuk, A.V.

1988-01-01

Presence of Sc on the surface of W in amounts larger than a monolayer coverage leads to a decrease of the work function at the initial oxidation stage, which is attributed to oxygen implantation into the surface layer of the metal. A subsequent oxidation is followed by the formation on the surface of a thin oxide layer and an increase of the work function. An increase of the amount of Sc deposited on the surface before the oxidation decreases the work function of the obtained oxide from 5.8 (clean W surface) down to 3.3 eV (thick Sc layer on W)

Preferred hydride growth orientations on oxide-coated gadolinium surfaces

International Nuclear Information System (INIS)

Benamar, G.M.; Schweke, D.; Kimmel, G.; Mintz, M.H.

2012-01-01

Highlights: ► The preferred hydride growth orientations on gadolinium metal coated by a thin oxide layer are presented. ► A preferred growth of the (1 0 0) h plane of the face centered cubic (FCC) GdH 2 is observed for the hydride spots forming below the oxidation layer. ► A change to the (1 1 1) h plane of the cubic hydride dominates for the hydride's Growth Centers. ► The texture change is attributed to the surface normal compressive stress component exerted by the oxidation layer on the developing hydride. - Abstract: The initial development of hydrides on polycrystalline gadolinium (Gd), as on some other hydride forming metals, is characterized by two sequential steps. The first step involves the rapid formation of a dense pattern of small hydride spots (referred to as the “small family” of hydrides) below the native oxidation layer. The second stage takes place when some of the “small family” nucleants (referred to as “growth centers”, GCs) break the oxide layer, leading to their rapid growth and finally to the massive hydriding of the sample. In the present study, the texture of the two hydride families was studied, by combining X-ray diffraction (XRD) analysis with a microscopic analysis of the hydride, using scanning electron microscopy (SEM) and atomic force microscopy (AFM). It has been observed that for the “small family”, a preferred growth of the (1 0 0) h plane of the cubic GdH 2 takes place, whereas for the GCs, a change to the (1 1 1) h plane of the cubic hydride dominates. These preferred growth orientations were analyzed by their structure relation with the (0 0 .1) m basal plane of the Gd metal. It has been concluded that the above texture change is due to the surface normal compressive stress component exerted by the oxidation overlayer on the developing hydride, preventing the (0 0 .1) m ||(1 1 1) h growth orientation. This stress is relieved upon the rupture of that overlayer and the development of the GCs, leading to

Reliable wet-chemical cleaning of natively oxidized high-efficiency Cu(In,Ga)Se{sub 2} thin-film solar cell absorbers

Energy Technology Data Exchange (ETDEWEB)

Lehmann, Jascha [Renewable Energies, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Potsdam Institute for Climate Impact Research (PIK), 14473 Potsdam (Germany); Lehmann, Sebastian, E-mail: sebastian.lehmann@ftf.lth.se [Renewable Energies, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Solid State Physics, Lund University, Box 118, S-22100 Lund (Sweden); Lauermann, Iver; Rissom, Thorsten; Kaufmann, Christian A.; Lux-Steiner, Martha Ch. [Renewable Energies, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Bär, Marcus, E-mail: marcus.baer@helmholtz-berlin.de [Renewable Energies, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Institut für Physik und Chemie, Brandenburgische Technische Universität Cottbus-Senftenberg, Platz der Deutschen Einheit 1, 03046 Cottbus (Germany); Sadewasser, Sascha, E-mail: sascha.sadewasser@inl.int [Renewable Energies, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga s/n, 4715-330 Braga (Portugal)

2014-12-21

Currently, Cu-containing chalcopyrite-based solar cells provide the highest conversion efficiencies among all thin-film photovoltaic (PV) technologies. They have reached efficiency values above 20%, the same performance level as multi-crystalline silicon-wafer technology that dominates the commercial PV market. Chalcopyrite thin-film heterostructures consist of a layer stack with a variety of interfaces between different materials. It is the chalcopyrite/buffer region (forming the p-n junction), which is of crucial importance and therefore frequently investigated using surface and interface science tools, such as photoelectron spectroscopy and scanning probe microscopy. To ensure comparability and validity of the results, a general preparation guide for “realistic” surfaces of polycrystalline chalcopyrite thin films is highly desirable. We present results on wet-chemical cleaning procedures of polycrystalline Cu(In{sub 1-x}Ga{sub x})Se{sub 2} thin films with an average x = [Ga]/([In] + [Ga]) = 0.29, which were exposed to ambient conditions for different times. The hence natively oxidized sample surfaces were etched in KCN- or NH{sub 3}-based aqueous solutions. By x-ray photoelectron spectroscopy, we find that the KCN treatment results in a chemical surface structure which is – apart from a slight change in surface composition – identical to a pristine as-received sample surface. Additionally, we discover a different oxidation behavior of In and Ga, in agreement with thermodynamic reference data, and we find indications for the segregation and removal of copper selenide surface phases from the polycrystalline material.

Defects at oxide surfaces

CERN Document Server

Thornton, Geoff

2015-01-01

This book presents the basics and characterization of defects at oxide surfaces. It provides a state-of-the-art review of the field, containing information to the various types of surface defects, describes analytical methods to study defects, their chemical activity and the catalytic reactivity of oxides. Numerical simulations of defective structures complete the picture developed. Defects on planar surfaces form the focus of much of the book, although the investigation of powder samples also form an important part. The experimental study of planar surfaces opens the possibility of applying the large armoury of techniques that have been developed over the last half-century to study surfaces in ultra-high vacuum. This enables the acquisition of atomic level data under well-controlled conditions, providing a stringent test of theoretical methods. The latter can then be more reliably applied to systems such as nanoparticles for which accurate methods of characterization of structure and electronic properties ha...

Mechanism and Thermochemistry of Coal Char Oxidation and Desorption of Surface Oxides

DEFF Research Database (Denmark)

Levi, Gianluca; Causà, Mauro; Lacovig, Paolo

2017-01-01

The present study investigates the coal char combustion by a combination of thermochemical and X-ray photoemission spectroscopy (XPS) analyses. Thermoanalytical methods (differential thermogravimetry, differential scanning calorimetry, and temperature-programmed desorption) are used to identify...... the key reactive steps that occur upon oxidation and heating of coal char (chemisorption, structural rearrangement and switchover of surface oxides, and desorption) and their energetics. XPS is used to reveal the chemical nature of the surface oxides that populate the char surface and to monitor...... functionalities prevail. The rearrangement of epoxy during preoxidation goes together with activation of the more stable and less reactive carbon sites. Results are in good agreement with semi-lumped kinetic models of carbon oxidation, which include (1) formation of "metastable" surface oxides, (2) complex...

Effect of Ge surface termination on oxidation behavior

Science.gov (United States)

Lee, Younghwan; Park, Kibyung; Cho, Yong Soo; Lim, Sangwoo

2008-09-01

Sulfur-termination was formed on the Ge(1 0 0) surface using (NH 4) 2S solution. Formation of Ge-S and the oxidation of the S-terminated Ge surface were monitored with multiple internal reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. In the 0.5, 5, or 20% (NH 4) 2S solution, H-termination on the Ge(1 0 0) surface was substituted with S-termination in 1 min. When the S-terminated Ge(1 0 0) surface was exposed in air ambient, the oxidation was retarded for about 3600 min. The preservation time of the oxide layer up to one monolayer of S-terminated Ge(1 0 0) surface was about 120 times longer than for the H-terminated Ge(1 0 0) surface. However, the oxidation of S-terminated Ge(1 0 0) surface drastically increased after the threshold time. There was no significant difference in threshold time between S-terminations formed in 0.5, 5, and 20% (NH 4) 2S solutions. With the surface oxidation, desorption of S on the Ge surface was observed. The desorption behavior of sulfur on the S-terminated Ge(1 0 0) surface was independent of the concentration of the (NH 4) 2S solution that forms S-termination. Non-ideal S-termination on Ge surfaces may be related to drastic oxidation of the Ge surface. Finally, with the desulfurization on the S-terminated Ge(1 0 0) surface, oxide growth is accelerated.

Atomic profile imaging of ceramic oxide surfaces

International Nuclear Information System (INIS)

Bursill, L.A.; Peng JuLin; Sellar, J.R.

1989-01-01

Atomic surface profile imaging is an electron optical technique capable of revealing directly the surface crystallography of ceramic oxides. Use of an image-intensifier with a TV camera allows fluctuations in surface morphology and surface reactivity to be recorded and analyzed using digitized image data. This paper reviews aspects of the electron optical techniques, including interpretations based upon computer-simulation image-matching techniques. An extensive range of applications is then presented for ceramic oxides of commercial interest for advanced materials applications: including uranium oxide (UO 2 ); magnesium and nickel oxide (MgO,NiO); ceramic superconductor YBa 2 Cu 3 O 6.7 ); barium titanate (BaTiO 3 ); sapphire (α-A1 2 O 3 ); haematite (α-Fe-2O 3 ); monoclinic, tetragonal and cubic monocrystalline forms of zirconia (ZrO 2 ), lead zirconium titanate (PZT + 6 mol.% NiNbO 3 ) and ZBLAN fluoride glass. Atomic scale detail has been obtained of local structures such as steps associated with vicinal surfaces, facetting parallel to stable low energy crystallographic planes, monolayer formation on certain facets, relaxation and reconstructions, oriented overgrowth of lower oxides, chemical decomposition of complex oxides into component oxides, as well as amorphous coatings. This remarkable variety of observed surface stabilization mechanisms is discussed in terms of novel double-layer electrostatic depolarization mechanisms, as well as classical concepts of the physics and chemistry of surfaces (ionization and affinity energies and work function). 46 refs., 16 figs

CO oxidation on PdO surfaces

DEFF Research Database (Denmark)

Hirvi, Janne T.; Kinnunen, Toni-Jani J.; Suvanto, Mika

2010-01-01

Density functional calculations were performed in order to investigate CO oxidation on two of the most stable bulk PdO surfaces. The most stable PdO(100) surface, with oxygen excess, is inert against CO adsorption, whereas strong adsorption on the stoichiometric PdO(101) surface leads to favorable...... oxidation via the Langmuir–Hinshelwood mechanism. The reaction with a surface oxygen atom has an activation energy of 0.66 eV, which is comparable to the lowest activation energies observed on metallic surfaces. However, the reaction rate may be limited by the coverage of molecular oxygen. Actually...... adsorption, following the Eley–Rideal mechanism and taking advantage of the reaction tunnel provided by the adjacent palladium atom, has an activation energy of only 0.24 eV. The reaction mechanism and activation energy for the palladium activated CO oxidation on the most stable PdO(100)–O surface...

Heat-induced redistribution of surface oxide in uranium

International Nuclear Information System (INIS)

Swissa, E.; Shamir, N.; Bloch, J.; Mintz, M.H.; Israel Atomic Energy Commission, Beersheba. Nuclear Research Center-Negev)

1990-01-01

The redistribution of oxygen and uranium metal at the vicinity of the metal-oxide interface of native and grown oxides due to vacuum thermal annealing was studied for uranium and uranium-chromium alloy using Auger depth profiling and metallographic techniques. It was found that uranium metal is segregating out through the uranium oxide layer for annealing temperatures above 450deg C. At the same time the oxide is redistributed in the metal below the oxide-metal interface in a diffusion like process. By applying a diffusion equation of a finite source, the diffusion coefficients for the process were obtained from the oxygen depth profiles measured for different annealing times. An Arrhenius like behavior was found for the diffusion coefficient between 400 and 800deg C. The activation energy obtained was E a =15.4±1.9 kcal/mole and the pre-exponential factor, D 0 =1.1x10 -8 cm 2 /s. An internal oxidation mechanism is proposed to explain the results. (orig.)

Heat-induced redistribution of surface oxide in uranium

Science.gov (United States)

Swissa, Eli; Shamir, Noah; Mintz, Moshe H.; Bloch, Joseph

1990-09-01

The redistribution of oxygen and uranium metal at the vicinity of the metal-oxide interface of native and grown oxides due to vacuum thermal annealing was studied for uranium and uranium-chromium alloy using Auger depth profiling and metallographic techniques. It was found that uranium metal is segregating out through the uranium oxide layer for annealing temperatures above 450°C. At the same time the oxide is redistributed in the metal below the oxide-metal interface in a diffusion like process. By applying a diffusion equation of a finite source, the diffusion coefficients for the process were obtained from the oxygen depth profiles measured for different annealing times. An Arrhenius like behavior was found for the diffusion coefficient between 400 and 800°C. The activation energy obtained was Ea = 15.4 ± 1.9 kcal/mole and the pre-exponential factor, D0 = 1.1 × 10 -8cm2/ s. An internal oxidation mechanism is proposed to explain the results.

Calculations of oxide formation on low-index Cu surfaces

Energy Technology Data Exchange (ETDEWEB)

Lian, Xin; Liu, Renlong, E-mail: lrl@cqu.edu.cn, E-mail: henkelman@utexas.edu [College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030 (China); Xiao, Penghao; Yang, Sheng-Che; Henkelman, Graeme, E-mail: lrl@cqu.edu.cn, E-mail: henkelman@utexas.edu [Department of Chemistry and the Institute for Computational and Engineering Sciences, University of Texas at Austin, Austin, Texas 78712-0165 (United States)

2016-07-28

Density-functional theory is used to evaluate the mechanism of copper surface oxidation. Reaction pathways of O{sub 2} dissociation on the surface and oxidation of the sub-surface are found on the Cu(100), Cu(110), and Cu(111) facets. At low oxygen coverage, all three surfaces dissociate O{sub 2} spontaneously. As oxygen accumulates on the surfaces, O{sub 2} dissociation becomes more difficult. A bottleneck to further oxidation occurs when the surfaces are saturated with oxygen. The barriers for O{sub 2} dissociation on the O-saturated Cu(100)-c(2×2)-0.5 monolayer (ML) and Cu(100) missing-row structures are 0.97 eV and 0.75 eV, respectively; significantly lower than those have been reported previously. Oxidation of Cu(110)-c(6×2), the most stable (110) surface oxide, has a barrier of 0.72 eV. As the reconstructions grow from step edges, clean Cu(110) surfaces can dissociatively adsorb oxygen until the surface Cu atoms are saturated. After slight rearrangements, these surface areas form a “1 ML” oxide structure which has not been reported in the literature. The barrier for further oxidation of this “1 ML” phase is only 0.31 eV. Finally the oxidized Cu(111) surface has a relatively low reaction energy barrier for O{sub 2} dissociation, even at high oxygen coverage, and allows for facile oxidation of the subsurface by fast O diffusion through the surface oxide. The kinetic mechanisms found provide a qualitative explanation of the observed oxidation of the low-index Cu surfaces.

Terahertz emission from semi-insulating GaAs with octadecanthiol-passivated surface

International Nuclear Information System (INIS)

Wu, Xiaojun; Xu, Xinlong; Lu, Xinchao; Wang, Li

2013-01-01

Terahertz (THz) emission from octadecanthiol (ODT) passivated (1 0 0) surface of the semi-insulating GaAs was measured, and compared with those from the native oxidized and the fresh surfaces. It was shown that the self-assembled ODT monolayer can stabilize the GaAs (1 0 0) surface, and maintain a THz surface emission 1.4 times as efficient as the native oxidized surface under equal conditions. Surface passivation can reduce the built-in electric field in the depletion region of the GaAs (1 0 0), resulting in the suppression of the THz radiation to a different extent. Oxidation of GaAs surface reduces the THz amplitude mainly in the low-frequency region. These results indicate that GaAs can be made a more effective THz source by choosing molecular passivation technique. Conversely, the THz emission features such as polarity, amplitude, and phase from molecule-passivated surfaces may be used to characterize the attached molecules.

Surface oxide formation during corona discharge treatment of AA 1050 aluminium surfaces

DEFF Research Database (Denmark)

Minzari, Daniel; Møller, Per; Kingshott, Peter

2008-01-01

process modifies aluminium AA 1050 surface, the oxide growth and resulting corrosion properties. The corona treatment is carried out in atmospheric air. Treated surfaces are characterized using XPS, SEM/EDS, and FIB-FESEM and results suggest that an oxide layer is grown, consisting of mixture of oxide...

A Novel Investigation of the Formation of Titanium Oxide Nanotubes on Thermally Formed Oxide of Ti-6Al-4V.

Science.gov (United States)

Butt, Arman; Hamlekhan, Azhang; Patel, Sweetu; Royhman, Dmitry; Sukotjo, Cortino; Mathew, Mathew T; Shokuhfar, Tolou; Takoudis, Christos

2015-10-01

Traditionally, titanium oxide (TiO2) nanotubes (TNTs) are anodized on Ti-6Al-4V alloy (Ti-V) surfaces with native TiO2 (amorphous TiO2); subsequent heat treatment of anodized surfaces has been observed to enhance cellular response. As-is bulk Ti-V, however, is often subjected to heat treatment, such as thermal oxidation (TO), to improve its mechanical properties. Thermal oxidation treatment of Ti-V at temperatures greater than 200°C and 400°C initiates the formation of anatase and rutile TiO2, respectively, which can affect TNT formation. This study aims at understanding the TNT formation mechanism on Ti-V surfaces with TO-formed TiO2 compared with that on as-is Ti-V surfaces with native oxide. Thermal oxidation-formed TiO2 can affect TNT formation and surface wettability because TO-formed TiO2 is expected to be part of the TNT structure. Surface characterization was carried out with field emission scanning electron microscopy, energy dispersive x-ray spectroscopy, water contact angle measurements, and white light interferometry. The TNTs were formed on control and 300°C and 600°C TO-treated Ti-V samples, and significant differences in TNT lengths and surface morphology were observed. No difference in elemental composition was found. Thermal oxidation and TO/anodization treatments produced hydrophilic surfaces, while hydrophobic behavior was observed over time (aging) for all samples. Reduced hydrophobic behavior was observed for TO/anodized samples when compared with control, control/anodized, and TO-treated samples. A method for improved surface wettability and TNT morphology is therefore discussed for possible applications in effective osseointegration of dental and orthopedic implants.

Oxidation and photo-oxidation of water on TiO2 surface

DEFF Research Database (Denmark)

Valdes, A.; Qu, Z.W.; Kroes, G.J.

2008-01-01

The oxidation and photo-oxidation of water on the rutile TiO2(110) surface is investigated using density functional theory (DFT) calculations. We investigate the relative stability of different surface terminations of TiO2 interacting with H2O and analyze the overpotential needed for the electrol...

Surface effects in metal oxide-based nanodevices

KAUST Repository

Lien, Der Hsien; Duran Retamal, Jose Ramon; Ke, Jr Jian; Kang, Chen Fang; He, Jr-Hau

2015-01-01

As devices shrink to the nanoscale, surface-to-volume ratio increases and the surface-environment interaction becomes a major factor for affecting device performance. The variation of electronic properties, including the surface band bending, gas chemisorption or photodesorption, native surface defects, and surface roughness, is called "surface effects". Such effects are ambiguous because they can be either negative or beneficial effects, depending on the environmental conditions and device application. This review provides an introduction to the surface effects on different types of nanodevices, offering the solutions to respond to their benefits and negative effects and provides an outlook on further applications regarding the surface effect. This review is beneficial for designing nano-enabled photodetectors, harsh electronics, memories, sensors and transistors via surface engineering.

Surface effects in metal oxide-based nanodevices

KAUST Repository

Lien, Der Hsien

2015-10-29

As devices shrink to the nanoscale, surface-to-volume ratio increases and the surface-environment interaction becomes a major factor for affecting device performance. The variation of electronic properties, including the surface band bending, gas chemisorption or photodesorption, native surface defects, and surface roughness, is called "surface effects". Such effects are ambiguous because they can be either negative or beneficial effects, depending on the environmental conditions and device application. This review provides an introduction to the surface effects on different types of nanodevices, offering the solutions to respond to their benefits and negative effects and provides an outlook on further applications regarding the surface effect. This review is beneficial for designing nano-enabled photodetectors, harsh electronics, memories, sensors and transistors via surface engineering.

Antioxidant Enzyme Activity, Iron Content and Lipid Oxidation of Raw and Cooked Meat of Korean Native Chickens and Other Poultry

Directory of Open Access Journals (Sweden)

Muhlisin

2016-05-01

Full Text Available This study was conducted to observe antioxidant enzyme activity, iron content and lipid oxidation of Korean native chickens and other poultry. The breast and thigh meat of three Korean native chicken breeds including Woorimatdak, Hyunin black and Yeonsan ogye, and three commercial poultry breeds including the broiler, White Leghorn and Pekin duck (Anasplatyrhyncos domesticus were studied. The analyses of the antioxidant enzymes activity, iron content and lipid oxidation were performed in raw and cooked samples. The activity of catalase (CAT in the thigh meat was higher than that of the breast meat of three Korean native chickens and the broiler, respectively. The activity of glutathione peroxidase (GPx in the uncooked thigh meat of three Korean native chickens was higher than that of the breasts. The breast meat of Woorimatdak and Pekin duck had higher superoxide dismutase (SOD activity than the others, while only the thigh meat of Pekin duck had the highest activity. Cooking inactivated CAT and decreased the activity of GPx and SOD. The thigh meat of Woorimatdak, White Leghorn, Yeonsan ogye and Hyunin black contained more total iron than the breast meat of those breeds. The heme-iron lost during cooking ranged from 3.2% to 14.8%. It is noted that the thigh meat had higher thiobarbituric acid reactive substances values than the breast in all chicken breeds. Though Woorimatdak showed higher antioxidant enzyme activity and lower released-iron percentage among Korean native chickens, no differences were found on lipid oxidation. We confirm that the dark meat of poultry exhibited higher antioxidant enzyme activity and contained more iron than the white meat.

Control of Surface and Edge Oxidation on Phosphorene.

Science.gov (United States)

Kuntz, Kaci L; Wells, Rebekah A; Hu, Jun; Yang, Teng; Dong, Baojuan; Guo, Huaihong; Woomer, Adam H; Druffel, Daniel L; Alabanza, Anginelle; Tománek, David; Warren, Scott C

2017-03-15

Phosphorene is emerging as an important two-dimensional semiconductor, but controlling the surface chemistry of phosphorene remains a significant challenge. Here, we show that controlled oxidation of phosphorene determines the composition and spatial distribution of the resulting oxide. We used X-ray photoemission spectroscopy to measure the binding energy shifts that accompany oxidation. We interpreted these spectra by calculating the binding energy shift for 24 likely bonding configurations, including phosphorus oxides and hydroxides located on the basal surface or edges of flakes. After brief exposure to high-purity oxygen or high-purity water vapor at room temperature, we observed phosphorus in the +1 and +2 oxidation states; longer exposures led to a large population of phosphorus in the +3 oxidation state. To provide insight into the spatial distribution of the oxide, transmission electron microscopy was performed at several stages during the oxidation. We found crucial differences between oxygen and water oxidants: while pure oxygen produced an oxide layer on the van der Waals surface, water oxidized the material at pre-existing defects such as edges or steps. We propose a mechanism based on the thermodynamics of electron transfer to interpret these observations. This work opens a route to functionalize the basal surface or edges of two-dimensional (2D) black phosphorus through site-selective chemical reactions and presents the opportunity to explore the synthesis of 2D phosphorene oxide by oxidation.

Comparative diversity of ammonia oxidizer 16S rRNA gene sequences in native, tilled, and successional soils

NARCIS (Netherlands)

Bruns, M.A.; Stephen, J.R.; Kowalchuk, G.A.; Prosser, J.I.; Paul, E.A.

1999-01-01

Autotrophic ammonia oxidizer (AAO) populations in soils from native, tilled, and successional treatments at the Kellogg Biological Station Long-Term Ecological Research site in southwestern Michigan were compared to assess effects of disturbance on these bacteria. N fertilization effects on AAO

Removal of arsenic from groundwater by using a native isolated arsenite-oxidizing bacterium.

Science.gov (United States)

Kao, An-Chieh; Chu, Yu-Ju; Hsu, Fu-Lan; Liao, Vivian Hsiu-Chuan

2013-12-01

Arsenic (As) contamination of groundwater is a significant public health concern. In this study, the removal of arsenic from groundwater using biological processes was investigated. The efficiency of arsenite (As(III)) bacterial oxidation and subsequent arsenate (As(V)) removal from contaminated groundwater using bacterial biomass was examined. A novel As(III)-oxidizing bacterium (As7325) was isolated from the aquifer in the blackfoot disease (BFD) endemic area in Taiwan. As7325 oxidized 2300μg/l As(III) using in situ As(III)-contaminated groundwater under aerobic conditions within 1d. After the oxidation of As(III) to As(V), As(V) removal was further examined using As7325 cell pellets. The results showed that As(V) could be adsorbed efficiently by lyophilized As7325 cell pellets, the efficiency of which was related to lyophilized cell pellet concentration. Our study conducted the examination of an alternative technology for the removal of As(III) and As(V) from groundwater, indicating that the oxidation of As(III)-contaminated groundwater by native isolated bacterium, followed by As(V) removal using bacterial biomass is a potentially effective technology for the treatment of As(III)-contaminated groundwater. © 2013.

Oxidized zirconium versus cobalt-chromium against the native patella in total knee arthroplasty: Patellofemoral outcomes.

Science.gov (United States)

Matassi, Fabrizio; Paoli, Tommaso; Civinini, Roberto; Carulli, Christian; Innocenti, Massimo

2017-10-01

Oxidized zirconium (OxZr) has demonstrated excellent mechanical properties in vitro when used against articular cartilage; less coefficient of friction and less chondral damage have been found when compared with cobalt-chromium (CoCr) implants. However, controversy exists as to whether implants with a zirconium femoral component articulate safely with a native patella in total knee arthroplasty (TKA). To answer this question, the clinical and radiographic results were analysed from a group of patients who underwent a TKA with patella retention; the OxZr versus CoCr femoral components were compared. The present study prospectively evaluated 83 knees of 74 patients from 2009 to 2010. Each patient was evaluated clinically (visual analogue scale, Knee Society score, patellar score) and radiographically (long leg standing radiograph, anterior-posterior and latero-lateral projections, axial view of the patella) pre-operatively and postoperatively with a mean follow-up of 4.47years. The patellar tilt and shift, and progression of patellofemoral osteoarthritis were calculated with the axial view. There were no patient reported adverse reactions and none of the evaluated prostheses failed. Both the clinical and radiographic evaluations showed no statistically significant between-group differences. No adverse events were observed clinically or radiologically. These results justify pursuing the use of oxidized zirconium as an alternative bearing surface for a femoral component associated with patellar retention in TKA. Published by Elsevier B.V.

Effect of surface pretreatment on interfacial chemical bonding states of atomic layer deposited ZrO2 on AlGaN

International Nuclear Information System (INIS)

Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Ng, Serene Lay Geok; Ji, Rong; Liu, Zhi Hong

2015-01-01

Atomic layer deposition (ALD) of ZrO 2 on native oxide covered (untreated) and buffered oxide etchant (BOE) treated AlGaN surface was analyzed by utilizing x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy. Evidenced by Ga–O and Al–O chemical bonds by XPS, parasitic oxidation during deposition is largely enhanced on BOE treated AlGaN surface. Due to the high reactivity of Al atoms, more prominent oxidation of Al atoms is observed, which leads to thicker interfacial layer formed on BOE treated surface. The results suggest that native oxide on AlGaN surface may serve as a protecting layer to inhibit the surface from further parasitic oxidation during ALD. The findings provide important process guidelines for the use of ALD ZrO 2 and its pre-ALD surface treatments for high-k AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors and other related device applications

Fractionation of silver isotopes in native silver explained by redox reactions

Science.gov (United States)

Mathur, Ryan; Arribas, Antonio; Megaw, Peter; Wilson, Marc; Stroup, Steven; Meyer-Arrivillaga, Danilo; Arribas, Isabel

2018-03-01

Scant data exist on the silver isotope composition of native silver specimens because of the relative newness of the technique. This study increases the published dataset by an order of magnitude and presents 80 silver new isotope analyses from native silver originating from a diverse set of worldwide deposits (8 deposit types, 33 mining districts in five continents). The measured isotopic range (defined as δ109Ag/107Ag in per mil units compared to NIST 978 Ag isotope standard) is +2.1 to -0.86‰ (2σ errors less than 0.015); with no apparent systematic correlations to date with deposit type or even within districts. Importantly, the data centering on 0‰ all come from high temperature hypogene/primary deposits whereas flanking and overlapping data represent secondary supergene deposits. To investigate the causes for the more fractionated values, several laboratory experiments involving oxidation of silver from natural specimens of Ag-rich sulfides and precipitation and adsorption of silver onto reagent grade MnO2 and FeOOH were conducted. Simple leach experiments demonstrate little Ag isotope fractionation occurred through oxidation of Ag from native Ag (Δsolution-native109Ag = 0.12‰). In contrast, significant fractionation occurred through precipitation of native Ag onto MnO2 (up to Δsolution-MnO2109Ag = 0.68‰, or 0.3amu). Adsorption of silver onto the MnO2 and FeOOH did not produce as large fractionation as precipitation (mean value of Δsolution-MnO2109Ag = 0.10‰). The most likely cause for the isotopic variations seen relates to redox effects such as the reduction of silver from Ag (I) to Ag° that occurs during precipitation onto the mineral surface. Since many Ag deposits have halos dominated by MnO2 and FeOOH phases, potential may exist for the silver isotope composition of ores and surrounding geochemical haloes to be used to better understand ore genesis and potential exploration applications. Aside from the Mn oxides, surface fluid silver

Dynamics of Defects and Dopants in Complex Systems: Si and Oxide Surfaces and Interfaces

Science.gov (United States)

Kirichenko, Taras; Yu, Decai; Banarjee, Sanjay; Hwang, Gyeong

2004-10-01

Fabrication of forthcoming nanometer scale electronic devices faces many difficulties including formation of extremely shallow and highly doped junctions. At present, ultra-low-energy ion implantation followed by high-temperature thermal annealing is most widely used to fabricate such ultra-shallow junctions. In the process, a great challenge lies in achieving precise control of redistribution and electrical activation of dopant impurities. Native defects (such as vacancies and interstitials) generated during implantation are known to be mainly responsible for the TED and also influence significantly the electrical activation/deactivation. Defect-dopant dynamics is rather well understood in crystalline Si and SiO2. However, little is known about their diffusion and annihilation (or precipitation) at the surfaces and interfaces, despite its growing importance in determining junction profiles as device dimensions get smaller. In this talk, we will present our density functional theory calculation results on the atomic and electronic structure and dynamical behavior of native defects and dopant-defect complexes in disordered/strained Si and oxide systems, such as i) clean and absorbent-modified Si(100) surface and subsurface layers, ii) amorphous-crystalline Si interfaces and iii) amorphous SiO2/Si interfaces. The fundamental understanding and data is essential in developing a comprehensive kinetic model for junction formation, which would contribute greatly in improving current process technologies.

Surface characterization of low-temperature grown yttrium oxide

Science.gov (United States)

Krawczyk, Mirosław; Lisowski, Wojciech; Pisarek, Marcin; Nikiforow, Kostiantyn; Jablonski, Aleksander

2018-04-01

The step-by-step growth of yttrium oxide layer was controlled in situ using X-ray photoelectron spectroscopy (XPS). The O/Y atomic concentration (AC) ratio in the surface layer of finally oxidized Y substrate was found to be equal to 1.48. The as-grown yttrium oxide layers were then analyzed ex situ using combination of Auger electron spectroscopy (AES), elastic-peak electron spectroscopy (EPES) and scanning electron microscopy (SEM) in order to characterize their surface chemical composition, electron transport phenomena and surface morphology. Prior to EPES measurements, the Y oxide surface was pre-sputtered by 3 kV argon ions, and the resulting AES-derived composition was found to be Y0.383O0.465C0.152 (O/Y AC ratio of 1.21). The SEM images revealed different surface morphology of sample before and after Ar sputtering. The oxide precipitates were observed on the top of un-sputtered Y oxide layer, whereas the oxide growth at the Ar ion-sputtered surface proceeded along defects lines normal to the layer plane. The inelastic mean free path (IMFP) characterizing electron transport was evaluated as a function of energy in the range of 0.5-2 keV from the EPES method. Two reference materials (Ni and Au) were used in these measurements. Experimental IMFPs determined for the Y0.383O0.465C0.152 and Y2O3 surface compositions, λ, were uncorrected for surface excitations and approximated by the simple function λ = kEp at electron energies E between 500 eV and 2000 eV, where k and p were fitted parameters. These values were also compared with IMFPs resulting from the TPP-2 M predictive equation for both oxide compositions. The fitted functions were found to be reasonably consistent with the measured and predicted IMFPs. In both cases, the average value of the mean percentage deviation from the fits varied between 5% and 37%. The IMFPs measured for Y0.383O0.465C0.152 surface composition were found to be similar to the IMFPs for Y2O3.

Surface and sub-surface thermal oxidation of ruthenium thin films

NARCIS (Netherlands)

Coloma Ribera, R.; van de Kruijs, Robbert Wilhelmus Elisabeth; Zoethout, E.; Yakshin, Andrey; Bijkerk, Frederik

2014-01-01

For next generation Extreme UV photolithography, multilayer coatings may require protective capping layers against surface contamination. Ruthenium, as a low-oxidation metal, is often used as a reference material. The oxidation behaviour of Ru thin films has been studied using X-ray reflectometry

Surface and interfacial reaction study of half cycle atomic layer deposited HfO{sub 2} on chemically treated GaSb surfaces

Energy Technology Data Exchange (ETDEWEB)

Zhernokletov, D. M. [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States); Dong, H.; Brennan, B.; Kim, J. [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Yakimov, M.; Tokranov, V.; Oktyabrsky, S. [College of Nanoscale Science and Engineering, University at Albany - SUNY, Albany, New York 12203 (United States); Wallace, R. M. [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States); Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States)

2013-04-01

An in situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (XPS) study was conducted in order to investigate the evolution of the HfO{sub 2} dielectric interface with GaSb(100) surfaces after sulfur passivation and HCl etching, designed to remove the native oxides. With the first pulses of tetrakis(dimethylamido)hafnium(IV) and water, a decrease in the concentration of antimony oxide states present on the HCl-etched surface is observed, while antimony sulfur states diminished below the XPS detection limit on sulfur passivated surface. An increase in the amount of gallium oxide/sulfide is seen, suggesting oxygen or sulfur transfers from antimony to gallium during antimony oxides/sulfides decomposition.

Decontamination of U-metal surface by an oxidation etching system

Energy Technology Data Exchange (ETDEWEB)

Stout, R.B.; Kansa, E.J.; Shaffer, R.J.; Weed, H.C. [California Univ., Livermore, CA (United States). Lawrence Livermore National Lab

2001-07-01

A surface treatment to remove surface contamination from uranium (U) metal and/or hydrides of uranium and heavy metals (HM) from U-metal parts is described. In the case of heavy metal atomic contamination on a surface, and potentially several atomic layers beneath, the surface oxidation treatment combines both chemical and chemically driven mechanical processes. The chemical process is a controlled temperature-time oxidation process to create a thin film of uranium oxide (UO{sub 2} and higher oxides) on the U-metal surface. The chemically driven mechanical process is strain induced by the volume increase as the U-metal surface transforms to a UO{sub 2} surface film. These volume strains are significantly large to cause surface failure spalling/scale formation and thus, removal of a U-oxide film that contains the HM-contaminated surface. The case of a HM-hydride surface contamination layer can be treated similarly by using inert hot gas to decompose the U-hydrides and/or HM-hydrides that are contiguous with the surface. A preliminary analysis to design and to plan for a sequence of tests is developed. The tests will provide necessary and sufficient data to evaluate the effective implementation and operational characteristics of a safe and reliable system. The following description is limited to only a surface oxidation process for HM-decontamination. (authors)

Surface morphology study on chromium oxide growth on Cr films by Nd-YAG laser oxidation process

International Nuclear Information System (INIS)

Dong Qizhi; Hu Jiandong; Guo Zuoxing; Lian Jianshe; Chen Jiwei; Chen Bo

2002-01-01

Grain sized (60-100 nm) Cr 2 O 3 thin films were prepared on Cr thin film surfaces by Nd-YAG laser photothermal oxidation process. Surface morphology study showed crack-free short plateau-like oxide films formed. Increase of dislocation density after pulsed laser irradiation was found. Thin film external surfaces, grain boundaries and dislocations are main paths of laser surface oxidation. Pinning and sealing of grain boundary was the reason that deeper oxidation did not produce. Grain growth and agglomeration of Cr sub-layer yielded tensile stress on the surface Cr 2 O 3 thin film. It was the reason that short plateau-like surface morphology formed and cracks appeared sometimes. In oxygen annealing at 700 deg. C, grain boundaries were considered not to be pinned at the surface, mixture diffusion was main mechanism in growth of oxide. Compression stress development in whole film led to extrusion of grains that was the reason that multiple appearances such as pyramid-like and nutshell-like morphology formed

Photoinduced hydrophobic surface of graphene oxide thin films

International Nuclear Information System (INIS)

Zhang Xiaoyan; Song Peng; Cui Xiaoli

2012-01-01

Graphene oxide (GO) thin films were deposited on transparent conducting oxide substrates and glass slides by spin coating method at room temperature. The wettability of GO thin films before and after ultraviolet (UV) irradiation was characterized with water contact angles, which increased from 27.3° to 57.6° after 3 h of irradiation, indicating a photo-induced hydrophobic surface. The UV–vis absorption spectra, Raman spectroscopy, X-ray photoelectron spectroscopy, and conductivity measurements of GO films before and after UV irradiation were taken to study the mechanism of photoinduced hydrophobic surface of GO thin films. It is demonstrated that the photoinduced hydrophobic surface is ascribed to the elimination of oxygen-containing functional groups on GO molecules. This work provides a simple strategy to control the wettability properties of GO thin films by UV irradiation. - Highlights: ► Photoinduced hydrophobic surface of graphene oxide thin films has been demonstrated. ► Elimination of oxygen-containing functional groups in graphene oxide achieved by UV irradiation. ► We provide novel strategy to control surface wettability of GO thin films by UV irradiation.

Damage free Ar ion plasma surface treatment on In{sub 0.53}Ga{sub 0.47}As-on-silicon metal-oxide-semiconductor device

Energy Technology Data Exchange (ETDEWEB)

Koh, Donghyi; Shin, Seung Heon; Ahn, Jaehyun; Sonde, Sushant; Banerjee, Sanjay K. [Department of Electrical and Computer Engineering, Microelectronics Research Center, The University of Texas at Austin, 10100 Burnet Road, Austin, Texas 78758 (United States); Kwon, Hyuk-Min [SK Hynix, Icheon, 2091, Gyeongchung-daero, Bubal-eub, Icheon-si, Gyeonggi-do 136-1 (Korea, Republic of); Orzali, Tommaso; Kim, Tae-Woo, E-mail: twkim78@gmail.com [SEMATECH Inc., 257 Fuller Rd #2200, Albany, New York 12203 (United States); Kim, Dae-Hyun [Kyungpook National University, 80, Daehak-ro, Buk-gu, Daegu 702-701 (Korea, Republic of)

2015-11-02

In this paper, we investigated the effect of in-situ Ar ion plasma surface pre-treatment in order to improve the interface properties of In{sub 0.53}Ga{sub 0.47}As for high-κ top-gate oxide deposition. X-ray photoelectron spectroscopy (XPS) and metal-oxide-semiconductor capacitors (MOSCAPs) demonstrate that Ar ion treatment removes the native oxide on In{sub 0.53}Ga{sub 0.47}As. The XPS spectra of Ar treated In{sub 0.53}Ga{sub 0.47}As show a decrease in the AsO{sub x} and GaO{sub x} signal intensities, and the MOSCAPs show higher accumulation capacitance (C{sub acc}), along with reduced frequency dispersion. In addition, Ar treatment is found to suppress the interface trap density (D{sub it}), which thereby led to a reduction in the threshold voltage (V{sub th}) degradation during constant voltage stress and relaxation. These results outline the potential of surface treatment for III-V channel metal-oxide-semiconductor devices and application to non-planar device process.

Effect of CO on surface oxidation of uranium metal

International Nuclear Information System (INIS)

Wang, X.; Fu, Y.; Xie, R.

1997-01-01

The surface reactions of uranium metal with carbon monoxide at 25 and 200 deg C have been studied by X-ray photoelectron spectroscopy (XPS);respectively. Adsorption of carbon monoxide on the surface layer of uranium metal leads to partial reduction of surface oxide and results in U4f photoelectron peak shifting to the lower binding energy. The content of oxygen in the surface oxide is decreased and O1s/O4f ratio decreases with increasing the exposure of carbon monoxide. The investigation indicates the surface layer of uranium metal has resistance to further oxidation in the atmosphere of carbon monoxide. (author)

Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

NARCIS (Netherlands)

Weckhuysen, B.M.; Wachs, I.E.; Schoonheydt, R.A.

1996-01-01

Focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides. Characterization of the molecular structures of chromium; Mechanics of hydrogenation-dehydrogenation reactions; Mobility and reactivity on oxidic surfaces.

Surface functionalization of dopamine coated iron oxide nanoparticles for various surface functionalities

Energy Technology Data Exchange (ETDEWEB)

Sherwood, Jennifer; Xu, Yaolin; Lovas, Kira [Chemical and Biological Engineering, The University of Alabama, Tuscaloosa , AL 35487 (United States); Qin, Ying [Alabama Innovation and Mentoring of Entrepreneurs, The University of Alabama, Tuscaloosa, AL 35487 (United States); Bao, Yuping, E-mail: ybao@eng.ua.edu [Chemical and Biological Engineering, The University of Alabama, Tuscaloosa , AL 35487 (United States)

2017-04-01

We present effective conjugation of four small molecules (glutathione, cysteine, lysine, and Tris(hydroxymethyl)aminomethane) onto dopamine-coated iron oxide nanoparticles. Conjugation of these molecules could improve the surface functionality of nanoparticles for more neutral surface charge at physiological pH and potentially reduce non-specific adsorption of proteins to nanoparticles surfaces. The success of conjugation was evaluated with dynamic light scattering by measuring the surface charge changes and Fourier transform infrared spectroscopy for surface chemistry analysis. The stability of dopamine-coated nanoparticles and the ability of conjugated nanoparticles to reduce the formation of protein corona were evaluated by measuring the size and charge of the nanoparticles in biological medium. This facile conjugation method opens up possibilities for attaching various surface functionalities onto iron oxide nanoparticle surfaces for biomedical applications.

Surface functionalization of dopamine coated iron oxide nanoparticles for various surface functionalities

International Nuclear Information System (INIS)

Sherwood, Jennifer; Xu, Yaolin; Lovas, Kira; Qin, Ying; Bao, Yuping

2017-01-01

We present effective conjugation of four small molecules (glutathione, cysteine, lysine, and Tris(hydroxymethyl)aminomethane) onto dopamine-coated iron oxide nanoparticles. Conjugation of these molecules could improve the surface functionality of nanoparticles for more neutral surface charge at physiological pH and potentially reduce non-specific adsorption of proteins to nanoparticles surfaces. The success of conjugation was evaluated with dynamic light scattering by measuring the surface charge changes and Fourier transform infrared spectroscopy for surface chemistry analysis. The stability of dopamine-coated nanoparticles and the ability of conjugated nanoparticles to reduce the formation of protein corona were evaluated by measuring the size and charge of the nanoparticles in biological medium. This facile conjugation method opens up possibilities for attaching various surface functionalities onto iron oxide nanoparticle surfaces for biomedical applications.

Properties of InGaAs/GaAs metal-oxide-semiconductor heterostructure field-effect transistors modified by surface treatment

Energy Technology Data Exchange (ETDEWEB)

Gregušová, D., E-mail: Dagmar.Gregusova@savba.sk [Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava SK-84104 (Slovakia); Gucmann, F.; Kúdela, R. [Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava SK-84104 (Slovakia); Mičušík, M. [Polymer Institute of Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava SK-84541 (Slovakia); Stoklas, R.; Válik, L. [Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava SK-84104 (Slovakia); Greguš, J. [Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská dolina, Bratislava SK-84248 (Slovakia); Blaho, M. [Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava SK-84104 (Slovakia); Kordoš, P. [Institute of Electronics and Photonics, Faculty of Electrical Engineering and Information Technology STU, Ilkovičova 3, Bratislava SK-81219 (Slovakia)

2017-02-15

Highlights: • AlGaAs/InGaAs/GaAs-based metal oxide semiconductor transistors-MOSHFET. • Thin Al-layer deposited in-situ and oxidize in air – gate insulator. • MOSHFET vs HFET transistor properties, density of traps evaluated. - Abstract: GaAs-based heterostructures exhibit excellent carrier transport properties, mainly the high carrier velocity. An AlGaAs-GaAs heterostructure field-effect transistor (HFET) with an InGaAs channel was prepared using metal-organic chemical vapor deposition (MOVPE). An AlOx layer was formed on the AlGaAs barrier layer by the air-assisted oxidation of a thin Al layer deposited in-situ in an MOVPE reactor immediately after AlGaAs/InGaAs growth. The HFETs and MOSHFETs exhibited a very low trap state density in the order of 10{sup 11} cm{sup −2} eV{sup −1}. Capacitance measurement yielded no significant difference between the HFET and MOSHFET structures. The formation of an AlOx layer modified the surface by partially eliminating surface states that arise from Ga-and As-based native oxides. The presence of an AlOx layer reflected in a reduced gate leakage current, which was evidenced by the two-terminal transistor measurement. Presented preparation procedure and device properties show great potential of AlGaAs/InGaAs-based MOSHFETs.

Volcano Relations for Oxidation of Hydrogen Halides over Rutile Oxide Surfaces

DEFF Research Database (Denmark)

Toftelund, Anja; Man, Isabela C.; Hansen, Heine A.

2012-01-01

over a range of different rutile oxide surfaces. Based on the scaling relations, two descriptors are identified that describe the reactions uniquely. By combining scaling with the micro-kinetic model, activity volcanoes for the three different oxidation reactions are derived. It is found...

Structural and electronic properties of hydrosilylated silicon surfaces

Energy Technology Data Exchange (ETDEWEB)

Baumer, A.

2005-11-15

The structural and electronic properties of alkyl-terminated Si surfaces prepared by thermallyinduced hydrosilylation have been studied in detail in the preceding chapters. Various surfaces have been used for the functionalization ranging from crystalline Si over amorphous hydrogenated Si to nanoscaled materials such as Si nanowires and nanoparticles. In each case, the alkyl-terminated surfaces have been compared to the native oxidized and H-terminated surfaces. (orig.)

Study on the surface oxidation of uranium in different gaseous atmospheres

International Nuclear Information System (INIS)

Wang Xiaoling; Fu Yibei; Xie Renshou

1996-03-01

The studying for the surface oxidation of uranium and oxide by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and the surface oxidation of uranium in different gaseous atmospheres such as O 2 , H 2 , CO, CO 2 , H 2 O(v) and air were reviewed. The surface oxidation of uranium is greatly influenced by a number of parameters including atmospheric temperature, pressure, diffusion of adsorbed gas atoms through the oxide layer, surface and interface chemical component, and defect structure and electron nature of the oxide layer. The initial oxidation mechanism and kinetics have been discussed. Suggestions for future work have also been presented. (32 refs., 7 figs., 5 tabs.)

The structural and magnetic properties of Fe/native-oxide systems resolved by x-ray scattering and spectroscopy methods

International Nuclear Information System (INIS)

Couet, Sebastien

2008-12-01

Since the discovery of the giant magnetoresistance (GMR) effect in metallic magnetic multilayers and its industrial application in magnetic read heads, the data storage density and reading speed of hard disks steadily increased. But now the point is reached where conventional conductive multilayer structures suffer from parasitic eddy currents which decrease the signal to noise ratio of the system. To tackle this problem, new classes of materials have to be studied. One approach is to introduce ultra thin oxide layers in a metallic iron structure to reduce the conductivity while keeping a high net magnetization. This can be achieved by alternating metal deposition and controlled oxidation to produce metal/metal-oxide multilayers. However, the magnetic structure that forms in such multilayer is still rather unexplored. The aim of this work was to achieve a better understanding of the magnetic structure that forms in such iron/native-oxide multilayers. For that purpose, X-ray and neutron scattering experiments were carried out to determine the magnetic structure and its evolution in ex-situ and in-situ experiments, respectively. It was found that a non-collinear magnetic coupling appears between the metal layers, which is mediated by the antiferromagnetically ordered oxide layer in between. The use of isotope sensitive scattering techniques (namely nuclear resonant scattering and neutron reflectometry) allowed to resolve the magnetic depth profile of the system, showing that the buried oxide carries a net magnetic moment. The chemical and magnetic structure of the buried oxide was studied by in-situ X-ray absorption spectroscopy and nuclear resonant scattering. After oxidation, the layer exhibits a mixture of different oxide phases and incorporates 10 to 15% of Fe with metallic character. Upon deposition of only one atomic layer of metallic Fe, the layer reduces to a single phase FeO-like oxide. This structural change does not lead to a magnetically ordered oxide

The structural and magnetic properties of Fe/native-oxide systems resolved by x-ray scattering and spectroscopy methods

Energy Technology Data Exchange (ETDEWEB)

Couet, Sebastien

2008-12-15

Since the discovery of the giant magnetoresistance (GMR) effect in metallic magnetic multilayers and its industrial application in magnetic read heads, the data storage density and reading speed of hard disks steadily increased. But now the point is reached where conventional conductive multilayer structures suffer from parasitic eddy currents which decrease the signal to noise ratio of the system. To tackle this problem, new classes of materials have to be studied. One approach is to introduce ultra thin oxide layers in a metallic iron structure to reduce the conductivity while keeping a high net magnetization. This can be achieved by alternating metal deposition and controlled oxidation to produce metal/metal-oxide multilayers. However, the magnetic structure that forms in such multilayer is still rather unexplored. The aim of this work was to achieve a better understanding of the magnetic structure that forms in such iron/native-oxide multilayers. For that purpose, X-ray and neutron scattering experiments were carried out to determine the magnetic structure and its evolution in ex-situ and in-situ experiments, respectively. It was found that a non-collinear magnetic coupling appears between the metal layers, which is mediated by the antiferromagnetically ordered oxide layer in between. The use of isotope sensitive scattering techniques (namely nuclear resonant scattering and neutron reflectometry) allowed to resolve the magnetic depth profile of the system, showing that the buried oxide carries a net magnetic moment. The chemical and magnetic structure of the buried oxide was studied by in-situ X-ray absorption spectroscopy and nuclear resonant scattering. After oxidation, the layer exhibits a mixture of different oxide phases and incorporates 10 to 15% of Fe with metallic character. Upon deposition of only one atomic layer of metallic Fe, the layer reduces to a single phase FeO-like oxide. This structural change does not lead to a magnetically ordered oxide

Formation of Oxides in the Interior of Friction Stir Welds

Science.gov (United States)

Schneider, Judy; Chen, Po; Nunes, Arthur C., Jr.

2016-01-01

In friction stir welding (FSWing) the actual solid state joining takes place between the faying surfaces which form the weld seam. Thus the seam trace is often investigated for clues when the strength of the weld is reduced. Aluminum and its alloys are known to form a native, protective oxide on the surface. If these native surface oxides are not sufficiently broken up during the FSW process, they are reported to remain in the FSW interior and weaken the bond strength. This type of weld defect has been referred to as a lazy "S", lazy "Z", joint line defect, kissing bond, or residual oxide defect. Usually these defects are mitigated by modification of the process parameters, such as increased tool rotation rate, which causes a finer breakup of the native oxide particles. This study proposes that there may be an alternative mechanism for formation of oxides found within the weld nugget. As the oxidation rate increases at elevated temperatures above 400ºC, it may be possible for enhanced oxidation to occur on the interior surfaces during the FSW process from entrained air entering the seam gap. Normally, FSWs of aluminum alloys are made without a purge gas and it is unknown how process parameters and initial fit up could affect a potential air path into the interior during the processing. In addition, variations in FSW parameters, such as the tool rotation, are known to have a strong influence on the FSW temperature which may affect the oxidation rate if internal surfaces are exposed to entrained air. A series of FSWs were made in 3 different thickness panels of AA2219 (0.95, 1.27 and 1.56 cm) at 2 different weld pitches. As the thickness of the panels increased, there was an increased tendency for a gap to form in advance of the weld tool. If sufficient air is able to enter the workpiece gap prior to consolidation, the weld temperature can increase the oxidation rate on the interior surfaces. These oxidation rates would also be accelerated in areas of localized

Surface chemistry on interstellar oxide grains

International Nuclear Information System (INIS)

Denison, P.; Williams, D.A.

1981-01-01

Detailed calculations are made to test the predictions of Duley, Millar and Williams (1978) concerning the chemical reactivity of interstellar oxide grains. A method is established for calculating interaction energies between atoms and the perfect crystal with or without surface vacancy sites. The possibility of reactions between incident atoms and absorbed atoms is investigated. It is concluded that H 2 formation can occur on the perfect crystal surfaces, and that for other diatomic molecules the important formation sites are the Fsub(s)- and V 2- sub(s)-centres. The outline by Duley, Millar and Williams (1979) of interstellar oxide grain growth and destruction is justified by these calculations. (author)

Initial oxidation processes of Si(001) surfaces by supersonic O2 molecular beams. Different oxidation mechanisms for clean and partially-oxidized surfaces

International Nuclear Information System (INIS)

Teraoka, Yuden; Yoshigoe, Akitaka

2002-01-01

Potential energy barriers for dissociative chemisorption of O 2 molecules on Si(001) clean surfaces were investigated using supersonic O 2 molecular beams and photoemission spectroscopy. Relative initial sticking probabilities of O 2 molecules and the saturated oxygen amount on the Si(001) surface were measured as a function of incident energy of O 2 molecules. Although the probability was independent on the incident energy in the region larger than 1 eV, the saturated oxygen amount was dependent on the incident energy without energy thresholds. An Si-2p photoemission spectrum of the Si(001) surface oxidized by thermal O 2 gas revealed the oxygen insertion into dimer backbond sites. These facts indicate that a reaction path of the oxygen insertion into dimer backbonds through bridge sites is open for the clean surface oxidation, and the direct chemisorption probability at the backbonds is negligibly small comparing with that at the bridge sites. (author)

Characterization of SCC crack tips and surface oxide layers in alloy 600

Energy Technology Data Exchange (ETDEWEB)

Fujii, Katsuhiko; Fukuya, Koji [Inst. of Nuclear Safety System Inc., Mihama, Fukui (Japan)

2002-09-01

In order to investigate the mechanism of primary water stress corrosion cracking (SCC), direct observation of microstructures of SCC crack tips and surface oxide layers in alloy 600 were carried out. A focused-ion beam (FIB) micro-processing technique was applied to prepare electron transparent foils including the crack tip and the surface oxide layer without any damage to those microstructures. Transmission electron microscopy and analysis were used to characterize the crack tips and surface oxide layers. Cr-rich oxides and a metal-Ni phase were identified in the crack tips and grain boundaries ahead of the crack tips independent of dissolved hydrogen concentrations. >From the fact that the Cr-rich oxides and metal-Ni phase were observed in the inner surface oxide layer, the same oxidation mechanism as the surface is proposed for the crack tip region and internal oxidation accompanying selective Cr oxidation is suggested as the mechanism. (author)

Water reactivity with mixed oxide (U,Pu)O2 surfaces

International Nuclear Information System (INIS)

Gaillard, Jeremy

2013-01-01

The interaction of water with actinides oxide surfaces remains poorly understood. The adsorption of water on PuO 2 surface and (U,Pu)O 2 surface leads to hydrogen generation through radiolysis but also surface evolution. The study of water interaction with mixed oxide (U,Pu)O 2 and PuO 2 surfaces requires the implementation of non intrusive techniques. The study of the hydration of CeO 2 surface is used to study the effectiveness of different techniques. The results show that the water adsorption leads to the surface evolution through the formation of a hydroxide superficial layer. The reactivity of water on the surface depends on the calcination temperature of the oxide precursor. The thermal treatment of hydrated surfaces can regenerate the surface. The study on CeO 2 hydration emphasizes the relevancies of these techniques in studying the hydration of surfaces. The hydrogen generation through water radiolysis is studied with an experimental methodology based on constant relative humidity in the radiolysis cell. The hydrogen accumulation is linear for the first hours and then tends to a steady state content. A mechanism of hydrogen consumption is proposed to explain the existence of the steady state of hydrogen content. This mechanism enables to explain also the evolution of the oxide surface during hydrogen generation experiments as shown by the evolution of hydrogen accumulation kinetics. The accumulation kinetics depends on the dose rate, specific surface area and the relative humidity but also on the oxide aging. The plutonium percentage appears to be a crucial parameter in hydrogen accumulation kinetics. (author) [fr

Investigation of thin oxide layer removal from Si substrates using an SiO2 atomic layer etching approach: the importance of the reactivity of the substrate

International Nuclear Information System (INIS)

Metzler, Dominik; Oehrlein, Gottlieb S; Li, Chen; Lai, C Steven; Hudson, Eric A

2017-01-01

The evaluation of a plasma-based atomic layer etching (ALE) approach for native oxide surface removal from Si substrates is described. Objectives include removal of the native oxide while minimizing substrate damage, surface residues and substrate loss. Oxide thicknesses were measured using in situ ellipsometry and surface chemistry was analyzed by x-ray photoelectron spectroscopy. The cyclic ALE approach when used for removal of native oxide SiO 2 from a Si substrate did not remove native oxide to the extent required. This is due to the high reactivity of the silicon substrate during the low-energy (<40 eV) ion bombardment phase of the cyclic ALE approach which leads to reoxidation of the silicon surface. A modified process, which used continuously biased Ar plasma with periodic CF 4 injection, achieved significant oxygen removal from the Si surface, with some residual carbon and fluorine. A subsequent H 2 /Ar plasma exposure successfully removed residual carbon and fluorine while passivating the silicon surface. The combined treatment reduced oxygen and carbon levels to about half compared to as received silicon surfaces. The downside of this process sequence is a net loss of about 40 Å of Si. A generic insight of this work is the importance of the substrate and final surface chemistry in addition to precise etch control of the target film for ALE processes. By a fluorocarbon-based ALE technique, thin SiO 2 layer removal at the Ångstrom level can be precisely performed from an inert substrate, e.g. a thick SiO 2 layer. However, from a reactive substrate, like Si, complete removal of the thin SiO 2 layer is prevented by the high reactivity of low energy Ar + ion bombarded Si. The Si surfaces are reoxidized during the ALE ion bombardment etch step, even for very clean and ultra-low O 2 process conditions. (paper)

Modelling of low energy ion sputtering from oxide surfaces

International Nuclear Information System (INIS)

Kubart, T; Nyberg, T; Berg, S

2010-01-01

The main aim of this work is to present a way to estimate the values of surface binding energy for oxides. This is done by fitting results from the binary collisions approximation code Tridyn with data from the reactive sputtering processing curves, as well as the elemental composition obtained from x-ray photoelectron spectroscopy (XPS). Oxide targets of Al, Ti, V, Nb and Ta are studied. The obtained surface binding energies are then used to predict the partial sputtering yields. Anomalously high sputtering yield is observed for the TiO 2 target. This is attributed to the high sputtering yield of Ti lower oxides. Such an effect is not observed for the other studied metals. XPS measurement of the oxide targets confirms the formation of suboxides during ion bombardment as well as an oxygen deficient surface in the steady state. These effects are confirmed from the processing curves from the oxide targets showing an elevated sputtering rate in pure argon.

Layer Dependence of Graphene for Oxidation Resistance of Cu Surface

Institute of Scientific and Technical Information of China (English)

Yu-qing Song; Xiao-ping Wang

2017-01-01

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted,diminishing the influence induced by residue and transfer technology.It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate,compared to that coated with the bilayer graphene,which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene,respectively.We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection.Our finding indicates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects,depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.

Natively oxidized amino acid residues in the spinach cytochrome b 6 f complex.

Science.gov (United States)

Taylor, Ryan M; Sallans, Larry; Frankel, Laurie K; Bricker, Terry M

2018-01-29

The cytochrome b 6 f complex of oxygenic photosynthesis produces substantial levels of reactive oxygen species (ROS). It has been observed that the ROS production rate by b 6 f is 10-20 fold higher than that observed for the analogous respiratory cytochrome bc 1 complex. The types of ROS produced (O 2 •-, 1 O 2 , and, possibly, H 2 O 2 ) and the site(s) of ROS production within the b 6 f complex have been the subject of some debate. Proposed sources of ROS have included the heme b p , PQ p •- (possible sources for O 2 •- ), the Rieske iron-sulfur cluster (possible source of O 2 •- and/or 1 O 2 ), Chl a (possible source of 1 O 2 ), and heme c n (possible source of O 2 •- and/or H 2 O 2 ). Our working hypothesis is that amino acid residues proximal to the ROS production sites will be more susceptible to oxidative modification than distant residues. In the current study, we have identified natively oxidized amino acid residues in the subunits of the spinach cytochrome b 6 f complex. The oxidized residues were identified by tandem mass spectrometry using the MassMatrix Program. Our results indicate that numerous residues, principally localized near p-side cofactors and Chl a, were oxidatively modified. We hypothesize that these sites are sources for ROS generation in the spinach cytochrome b 6 f complex.

Influence of corrosive solutions on microhardness and chemistry of magnesium oxide /001/ surfaces

Science.gov (United States)

Ishigaki, H.; Miyoshi, K.; Buckley, D. H.

1982-01-01

X-ray photoelectron spectroscopy analyses and hardness experiments were conducted on cleaved magnesium oxide /001/ surfaces. The magnesium oxide bulk crystals were cleaved to specimen size along the /001/ surface, and indentations were made on the cleaved surface in corrosive solutions containing HCl, NaOH, or HNO3 and in water without exposing the specimen to any other environment. The results indicated that chloride (such as MgCl2) and sodium films are formed on the magnesium oxide surface as a result of interactions between an HCl-containing solution and a cleaved magnesium oxide surface. The chloride films soften the magnesium oxide surface. In this case microhardness is strongly influenced by the pH value of the solution. The lower the pH, the lower the microhardness. Sodium films, which are formed on the magnesium oxide surface exposed to an NaOH containing solution, do not soften the magnesium oxide surface.

Nanoparticles in natural systems I: The effective reactive surface area of the natural oxide fraction in field samples

Science.gov (United States)

Hiemstra, Tjisse; Antelo, Juan; Rahnemaie, Rasoul; van Riemsdijk, Willem H.

2010-01-01

Information on the particle size and reactive surface area of natural samples is essential for the application of surface complexation models (SCM) to predict bioavailability, toxicity, and transport of elements in the natural environment. In addition, this information will be of great help to enlighten views on the formation, stability, and structure of nanoparticle associations of natural organic matter (NOM) and natural oxide particles. Phosphate is proposed as a natively present probe ion to derive the effective reactive surface area of natural samples. In the suggested method, natural samples are equilibrated (⩾10 days) with 0.5 M NaHCO 3 (pH = 8.5) at various solid-solution ratios. This matrix fixes the pH and ionic strength, suppresses the influence of Ca 2+ and Mg 2+ ions by precipitation these in solid carbonates, and removes NOM due to the addition of activated carbon in excess, collectively leading to the dominance of the PO 4-CO 3 interaction in the system. The data have been interpreted with the charge distribution (CD) model, calibrated for goethite, and the analysis results in an effective reactive surface area (SA) and a reversibly bound phosphate loading Γ for a series of top soils. The oxidic SA varies between about 3-30 m 2/g sample for a large series of representative agricultural top soils. Scaling of our data to the total iron and aluminum oxide content (dithionite-citrate-bicarbonate extractable), results in the specific surface area between about 200-1200 m 2/g oxide for most soils, i.e. the oxide particles are nano-sized with an equivalent diameter in the order of ˜1-10 nm if considered as non-porous spheres. For the top soils, the effective surface area and the soil organic carbon fraction are strongly correlated. The oxide particles are embedded in a matrix of organic carbon (OC), equivalent to ˜1.4 ± 0.2 mg OC/m 2 oxide for many soils of the collection, forming a NOM-mineral nanoparticle association with an average NOM volume

The surface oxide as a source of oxygen on Rh(1 1 1)

Energy Technology Data Exchange (ETDEWEB)

Lundgren, E. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden)]. E-mail: edvin.lundgren@sljus.lu.se; Gustafson, J. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden); Resta, A. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden); Weissenrieder, J. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden); Mikkelsen, A. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden); Andersen, J.N. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden); Koehler, L. [Institut fuer Materialphysik and Centre for Computational Materials Science, Universitaet Wien, A-1090 Vienna (Austria); Kresse, G. [Institut fuer Materialphysik and Centre for Computational Materials Science, Universitaet Wien, A-1090 Vienna (Austria); Klikovits, J. [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Vienna (Austria); Biederman, A. [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Vienna (Austria); Schmid, M. [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Vienna (Austria); Varga, P. [Institut fuer Allgemeine Physik, Technische Universitaet Wien, A-1040 Vienna (Austria)

2005-06-15

The reduction of a thin surface oxide on the Rh(1 1 1) surface by CO is studied in situ by photoemission spectroscopy, scanning tunneling microscopy, and density functional theory. CO molecules are found not to adsorb on the surface oxide at a sample temperature of 100 K, in contrast to on the clean and chemisorbed oxygen covered surface. Despite this behavior, the surface oxide may still be reduced by CO, albeit in a significantly different fashion as compared to the reduction of a phase containing only chemisorbed on surface oxygen. The experimental observations combined with theoretical considerations concerning the stability of the surface oxide, result in a model of the reduction process at these pressures suggesting that the surface oxide behaves as a source of oxygen for the CO-oxidation reaction.

Influence of metallic surface states on electron affinity of epitaxial AlN films

Energy Technology Data Exchange (ETDEWEB)

Mishra, Monu; Krishna, Shibin; Aggarwal, Neha [Advanced Materials and Devices Division, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi110012 (India); Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Gupta, Govind, E-mail: govind@nplindia.org [Advanced Materials and Devices Division, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi110012 (India); Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, Dr. K.S. Krishnan Marg, New Delhi 110012 (India)

2017-06-15

The present article investigates surface metallic states induced alteration in the electron affinity of epitaxial AlN films. AlN films grown by plasma-assisted molecular beam epitaxy system with (30% and 16%) and without metallic aluminium on the surface were probed via photoemission spectroscopic measurements. An in-depth analysis exploring the influence of metallic aluminium and native oxide on the electronic structure of the films is performed. It was observed that the metallic states pinned the Fermi Level (FL) near valence band edge and lead to the reduction of electron affinity (EA). These metallic states initiated charge transfer and induced changes in surface and interface dipoles strength. Therefore, the EA of the films varied between 0.6–1.0 eV due to the variation in contribution of metallic states and native oxide. However, the surface barrier height (SBH) increased (4.2–3.5 eV) adversely due to the availability of donor-like surface states in metallic aluminium rich films.

Ellipsometry measurements of thickness of oxide and water layers on spherical and flat silicon surfaces

International Nuclear Information System (INIS)

Kenny, M.J.; Netterfield, R.; Wielunski, L.S.

1998-01-01

Full text: Ellipsometry has been used to measure the thickness of oxide layers on single crystal silicon surfaces, both flat and spherical and also to measure the extent of adsorption of moisture on the surface as a function of partial water vapour pressure. The measurements form part of an international collaborative project to make a precise determination of the Avogadro constant (ΔN A /N A -8 ) which will then be used to obtain an absolute definition of the kilogram, rather than one in terms of an artefact. Typically the native oxide layer on a cleaned silicon wafer is about 2 nm thick. On a polished sphere this oxide layer is typically 8 to 10 nm thick, the increased thickness being attributed to parameters related to the polishing process. Ellipsometry measurements on an 89 mm diameter polished silicon sphere at both VUW and CSIRO indicated a SiO 2 layer at 7 to 10 nm thick. It was observed that this thickness varied regularly. The crystal orientation of the sphere was determined using electron patterns generated from an electron microscope and the oxide layer was then measured through 180 arcs of great circles along (110) and (100) planes. It was observed that the thickness varied systematically with orientation. The minimum thickness was 7.4 nm at the axis (softest direction in silicon) and the greatest thickness was 9.5 nm at the axis (hardest direction in silicon). This is similar to an orientation dependent cubic pattern which has been observed to be superimposed on polished silicon spheres. At VUW, the sphere was placed in an evacuated bell jar and the ellipsometry signal was observed as the water vapour pressure was progressively increased up to saturation. The amount of water vapour adsorbed at saturation was one or two monolayers, indicating that the sphere does not wet

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces

International Nuclear Information System (INIS)

Flötotto, D.; Wang, Z. M.; Jeurgens, L. P. H.; Mittemeijer, E. J.

2014-01-01

The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al 2 O 3 films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively

Mechanical tearing of graphene on an oxidizing metal surface

International Nuclear Information System (INIS)

George, Lijin; Gupta, Aparna; Shaina, P R; Jaiswal, Manu; Gupta, Nandita Das

2015-01-01

Graphene, the thinnest possible anticorrosion and gas-permeation barrier, is poised to transform the protective coatings industry for a variety of surface applications. In this work, we have studied the structural changes of graphene when the underlying copper surface undergoes oxidation upon heating. Single-layer graphene directly grown on a copper surface by chemical vapour deposition was annealed under ambient atmosphere conditions up to 400 °C. The onset temperature of the surface oxidation of copper is found to be higher for graphene-coated foils. Parallel arrays of graphene nanoripples are a ubiquitous feature of pristine graphene on copper, and we demonstrate that these form crucial sites for the onset of the oxidation of copper, particularly for ∼0.3–0.4 μm ripple widths. In these regions, the oxidation proceeds along the length of the nanoripples, resulting in the formation of parallel stripes of oxidized copper regions. We demonstrate from temperature-dependent Raman spectroscopy that the primary defect formation process in graphene involves boundary-type defects rather than vacancy or sp"3-type defects. This observation is consistent with a mechanical tearing process that splits graphene into small polycrystalline domains. The size of these is estimated to be sub-50 nm. (paper)

Mechanical tearing of graphene on an oxidizing metal surface.

Science.gov (United States)

George, Lijin; Gupta, Aparna; Shaina, P R; Das Gupta, Nandita; Jaiswal, Manu

2015-12-11

Graphene, the thinnest possible anticorrosion and gas-permeation barrier, is poised to transform the protective coatings industry for a variety of surface applications. In this work, we have studied the structural changes of graphene when the underlying copper surface undergoes oxidation upon heating. Single-layer graphene directly grown on a copper surface by chemical vapour deposition was annealed under ambient atmosphere conditions up to 400 °C. The onset temperature of the surface oxidation of copper is found to be higher for graphene-coated foils. Parallel arrays of graphene nanoripples are a ubiquitous feature of pristine graphene on copper, and we demonstrate that these form crucial sites for the onset of the oxidation of copper, particularly for ∼0.3-0.4 μm ripple widths. In these regions, the oxidation proceeds along the length of the nanoripples, resulting in the formation of parallel stripes of oxidized copper regions. We demonstrate from temperature-dependent Raman spectroscopy that the primary defect formation process in graphene involves boundary-type defects rather than vacancy or sp(3)-type defects. This observation is consistent with a mechanical tearing process that splits graphene into small polycrystalline domains. The size of these is estimated to be sub-50 nm.

Characterization of Native and Modified Starches by Potentiometric Titration

OpenAIRE

Soto, Diana; Urdaneta, Jose; Pernia, Kelly

2014-01-01

The use of potentiometric titration for the analysis and characterization of native and modified starches is highlighted. The polyelectrolytic behavior of oxidized starches (thermal and thermal-chemical oxidation), a graft copolymer of itaconic acid (IA) onto starch, and starch esters (mono- and diester itaconate) was compared with the behavior of native starch, the homopolymer, and the acid employed as a graft monomer and substituent. Starch esters showed higher percentages of acidity, follo...

Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces

Science.gov (United States)

McBriarty, Martin E.

Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.

Negative secondary ion emission from oxidized surfaces

International Nuclear Information System (INIS)

Gnaser, H.; Kernforschungsanlage Juelich G.m.b.H.

1984-01-01

The emission of negative secondary ions from 23 elements was studied for 10 keV O 2 + and 10 keV In + impact at an angle of incidence of 45 0 . Partial oxidation of the sample surfaces was achieved by oxygen bombardment and/or by working at a high oxygen partial pressure. It was found that the emission of oxide ions shows an element-characteristic pattern. For the majority of the elements investigated these features are largely invariant against changes of the surface concentration of oxygen. For the others admission of oxygen strongly changes the relative intensities of oxide ions: a strong increase of MO 3 - signals (M stands for the respective element) is accompanied by a decrease of MO - and M - intensities. Different primary species frequently induce changes of both the relative and the absolute negative ion intensities. Carbon - in contrast to all other elements - does not show any detectable oxide ion emission but rather intense cluster ions Csub(n) - (detected up to n=12) whose intensities oscillate in dependence on n. (orig./RK)

Fiber optic hydrogen gas sensor utilizing surface plasmon resonance and native defects of zinc oxide by palladium

International Nuclear Information System (INIS)

Tabassum, Rana; Gupta, Banshi D

2016-01-01

We present an experimental study on a surface plasmon resonance (SPR) based fiber optic hydrogen gas sensor employing a palladium doped zinc oxide nanocomposite (ZnO (1−x) Pd x , 0 ≤ x ≤ 0.85) layer over the silver coated unclad core of the fiber. Palladium doped zinc oxide nanocomposites (ZnO (1−x) Pd x )  are prepared by a chemical route for different composition ratios and their structural, morphological and hydrogen sensing properties are investigated experimentally. The sensing principle involves the absorption of hydrogen gas by ZnO (1−x) Pd x , altering its dielectric function. The change in the dielectric constant is analyzed in terms of the red shift of the resonance wavelength in the visible region of the electromagnetic spectrum. To check the sensing capability of sensing probes fabricated with varying composition ratio (x) of nanocomposite, the SPR curves are recorded typically for 0% H 2 and 4% H 2 in N 2 atmosphere for each fabricated probe. On changing the concentration of hydrogen gas from 0% to 4%, the red shift in the SPR spectrum confirms the change in dielectric constant of ZnO (1−x) Pd x on exposure to hydrogen gas. It is noted that the shift in the SPR spectrum increases monotonically up to a certain fraction of Pd in zinc oxide, beyond which it starts decreasing. SEM images and the photoluminescence (PL) spectra reveal that Pd dopant atoms substitutionally incorporated into the ZnO lattice profoundly affect its defect levels; this is responsible for the optimal composition of ZnO (1−x) Pd x to sense the hydrogen gas. The sensor is highly selective to hydrogen gas and possesses high sensitivity. Since optical fiber sensing technology is employed along with the SPR technique, the present sensor is capable of remote sensing and online monitoring of hydrogen gas. (paper)

Novel (1 × 1)-reconstructions and native defects of TiO{sub 2} anatase (101) surface

Energy Technology Data Exchange (ETDEWEB)

Wang, Qinggao, E-mail: wangqinggao1984@126.com [Institute for Computational Materials Science, School of Physics and Electronics, Henan University, Kaifeng 475004 (China); Department of Physics and Electrical Engineering, Anyang Normal University, Anyang, Henan Province 455000 (China); Ren, Fengzhu [Institute for Computational Materials Science, School of Physics and Electronics, Henan University, Kaifeng 475004 (China); Dong, Huafeng [School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006 (China); Wang, Yuanxu, E-mail: wangyx@henu.edu.cn [Institute for Computational Materials Science, School of Physics and Electronics, Henan University, Kaifeng 475004 (China)

2017-05-31

Highlights: • Acceptor energy levels are induced by O interstitials; corresponding to a transition of indirect-to-direct band gap and a narrowing of band gap. • The Fermi levels of defected and reconstructed TiO{sub 2} anatse (101) can be modulated in a wide range. - Abstract: In this paper, reconstructions and native defects of TiO{sub 2} anatase (101) surface are studied using the state-of-the-art theoretical method. We find that O interstitials are dominated defects at an oxidization environment. These O interstitials induce acceptor energy levels, corresponding to an indirect-direct band transition and a bandgap narrowing. And thus, the experimental result that an O-rich anatase TiO{sub 2} has the higher photocatalytic activity can be understood. The formation of O vacancies and Ti interstitials becomes feasible at a reduced condition, and reconstructed TiO{sub 2} anatase (101)-(1 × 1) structures present with increasing reduction degree. Furthermore, the Fermi levels of defected and reconstructed TiO{sub 2} anatse (101) can be modulated in a wide range (i.e., nearly the whole band gap), which are different from those of TiO{sub 2} rutile (110).

Evolution of Near-Surface Internal and External Oxide Morphology During High-Temperature Selective Oxidation of Steels

Science.gov (United States)

Story, Mary E.; Webler, Bryan A.

2018-05-01

In this work we examine some observations made using high-temperature confocal scanning laser microscopy (HT-CSLM) during selective oxidation experiments. A plain carbon steel and advanced high-strength steel (AHSS) were selectively oxidized at high temperature (850-900°C) in either low oxygen or water vapor atmospheres. Surface evolution, including thermal grooving along grain boundaries and oxide growth, was viewed in situ during heating. Experiments investigated the influence of the microstructure and oxidizing atmosphere on selective oxidation behavior. Sequences of CSLM still frames collected during the experiment were processed with ImageJ to obtain histograms that showed a general darkening trend indicative of oxidation over time with all samples. Additional ex situ scanning electron microscopy and energy dispersive spectroscopy analysis supported in situ observations. Distinct oxidation behavior was observed for each case. Segregation, grain orientation, and extent of internal oxidation were all found to strongly influence surface evolution.

Hydrophobic cotton textile surfaces using an amphiphilic graphene oxide (GO) coating

International Nuclear Information System (INIS)

Tissera, Nadeeka D.; Wijesena, Ruchira N.; Perera, J. Rangana; Nalin de Silva, K.M.; Amaratunge, Gehan A.J.

2015-01-01

Graphical abstract: - Highlights: • Different GO dispersions were prepared by sonicating different amounts of GO in water. Degree of exfoliation of these GO sheets in water was analyzed using Atomic Force Microscopy (AFM). • AFM results obtained showed higher the GO concentration on water more the size of GO sheets and lesser the degree of exfoliation. • GO with different amounts was deposited on cotton fabric using simple dyeing method. • High GO loading on cotton increase the surface area coverage of the textile fibers with GO sheets. This led to less edge to mid area ratio of grafted GO sheets. • As contribution of mid area of GO increase on fiber surface cotton fabric becomes more hydrophobic. • Amphiphilic property of GO sheets was used to lower the surface energy of the cotton fibers leading to hydrophobic property. - Abstract: We report for the first time hydrophobic properties on cotton fabric successfully achieved by grafting graphene oxide on the fabric surface, using a dyeing method. Graphite oxide synthesized by oxidizing natural flake graphite employing improved Hummer's method showed an inter layer spacing of ∼1 nm from XRD. Synthesized graphite oxide was exfoliated in water using ultrasound energy to obtain graphene oxide (GO). AFM data obtained for the graphene oxide dispersed in an aqueous medium revealed a non-uniform size distribution. FTIR characterization of the synthesized GO sheets showed both hydrophilic and hydrophobic functional groups present on the nano sheets giving them an amphiphilic property. GO flakes of different sizes were successfully grafted on to a cotton fabric surface using a dip dry method. Loading different amounts of graphene oxide on the cotton fiber surface allowed the fabric to demonstrate different degrees of hydrophobicity. The highest observed water contact angle was at 143° with the highest loading of graphene oxide. The fabric surfaces grafted with GO also exhibits adhesive type hydrophobicity

Experimental investigation into the surface oxidation of lignite high temperature coke

Energy Technology Data Exchange (ETDEWEB)

Schaefer, H G; Dallmann, W [Technische Hochschule Aachen (Germany, F.R.). Lehrgebiet Kokerei und Brikettierung

1979-11-01

It was intended to produce lignite high temperature coke (BHFK) in the laboratory comparable to that produced with the Salem-Lurgi-open hearth process and quench them according to the prescribed condition. By this means, the surface oxide formation could be continually recorded gravimetrically. The self-sustaining reaction of the physical and chemical adsorption on the loose material were observed under consideration that the adsorption or surface oxide can exist in a gaseous as well as in a liquid aggregate. The established steam isotherms and electron-microscope photos identified the product BFHK as a material which shows in the range of high-humidity capillary condensation. The continuous gravimetric adsorption leads to 1,9 per cent by weight on dry surface oxides. On the other hand, oxidized coke in the presence of water builds up on the surface to 2,3 per cent by weight. It became apparent that the finest capillary water is not involved in the formation of the oxide. For the dry accumulation, which is a reaction of the first degree, the equation for the accumulation of the oxygen is given. From the BET surface, made up from the graphite-like ring structure of the carbon surface, as well as the dposited quantity of oxide, the surface density of the oxygen atoms is indicated in relation to the quantity of carbon atoms, or alternatively the six-ring. The dry deposition leads to a proportion of 1,5 oxygen atoms to 10 carbon atoms. In a wet reaction, the ratio is 1,8 to 10. With increasing quantities of oxide, the content of volatile matter, the sparking point and reactivity increase, while the porosity diminishes as a consequence.

Nano- and Micro-Scale Oxidative Patterning of Titanium Implant Surfaces for Improved Surface Wettability.

Science.gov (United States)

Kim, In-hye; Son, Jun Sik; Choi, Seok Hwa; Kim, Kyo-han; Kwon, Tae-yub

2016-02-01

A simple and scalable surface modification treatment is demonstrated, in which nano- and microscale features are introduced into the surface of titanium (Ti) substrates by means of a novel and eco-friendly oxidative aqueous solution composed of hydrogen peroxide (H202) and sodium bicarbonate (NaHCO3). By immersing mirror-polished Ti discs in an aqueous mixture of 30 wt% H2O2/5 wt% NaHCO3 at 23 +/- 3 degrees C for 4 h, it was confirmed that this mixture is capable of generating microscale topographies on Ti surfaces. It also simultaneously formed nanochannels that were regularly arranged in a comb-like pattern on the Ti surface, thus forming a hierarchical surface structure. Further, these nano/micro-textured Ti surfaces showed great surface roughness and excellent wettability when compared with control Ti surfaces. This study demonstrates that a H2O2/NaHCO3 mixture can be effectively utilized to create reproducible nano/microscale topographies on Ti implant surfaces, thus providing an economical new oxidative solution that may be used effectively and safely as a Ti surface modification treatment.

Temperature effect on surface oxidation of titanium

International Nuclear Information System (INIS)

Vaquilla, I.; Barco, J.L. del; Ferron, J.

1990-01-01

The effect of temperature on the first stages of the superficial oxidation of polycrystalline titanium was studied using both Auger electron spectroscopy (AES) and emission shreshold (AEAPS). The number of compounds present on the surface was determined by application of the factor analysis technique. Reaction evolution was followed through the relative variation of Auger LMM and LMV transitions which are characteristic of titanium. Also the evolution of the chemical shift was determined by AEAPS. The amount of oxygen on the surface was quantified using transition KLL of oxygen. It was found that superficial oxidation depends on temperature. As much as three different compounds were determined according to substrate temperature and our exposure ranges. (Author). 7 refs., 5 figs

Interactions of Graphene Oxide Nanomaterials with Natural Organic Matter and Metal Oxide Surfaces

Science.gov (United States)

Interactions of graphene oxide (GO) with silica surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration a...

Quasiparticle Interference on Cubic Perovskite Oxide Surfaces.

Science.gov (United States)

Okada, Yoshinori; Shiau, Shiue-Yuan; Chang, Tay-Rong; Chang, Guoqing; Kobayashi, Masaki; Shimizu, Ryota; Jeng, Horng-Tay; Shiraki, Susumu; Kumigashira, Hiroshi; Bansil, Arun; Lin, Hsin; Hitosugi, Taro

2017-08-25

We report the observation of coherent surface states on cubic perovskite oxide SrVO_{3}(001) thin films through spectroscopic-imaging scanning tunneling microscopy. A direct link between the observed quasiparticle interference patterns and the formation of a d_{xy}-derived surface state is supported by first-principles calculations. We show that the apical oxygens on the topmost VO_{2} plane play a critical role in controlling the coherent surface state via modulating orbital state.

In-situ oxidation study of Pd(100) by surface x-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Kilic, Volkan; Franz, Dirk; Stierle, Andreas [AG Grenzflaechen, Universitaet Siegen (Germany); Martin, Natalia; Lundgren, Edvin [Department of Synchrotron Radiation Research, Lund University (Sweden); Mantilla, Miguel [MPI fuer Metallforschung, Stuttgart (Germany)

2011-07-01

The oxidation of the Pd(100) surface at oxygen pressures in the 10{sup -6} mbar to 10{sup 3} mbar range and temperatures up to 1000 K has been studied in-situ by surface x-ray diffraction (SXRD). The SXRD experiments were performed at the MPI beamline at the Angstrom Quelle Karlsruhe (ANKA). We present the surface and crystal truncation rod (CTR) data from the ({radical}(5) x {radical}(5)) surface layer. We show that the transformation from the surface oxide to PdO bulk oxide can be observed in-situ under specific pressure and temperature conditions. We compare our results with previously proposed structure models based on low energy electron diffraction (LEED) I(V) curves and density functional theory calculations. Finally, we elucidate the question of commensurability of the surface oxide layer with respect to the Pd(100) substrate.

Thermally responsive silicon nanowire arrays for native/denatured-protein separation

International Nuclear Information System (INIS)

Wang Hongwei; Wang Yanwei; Yuan Lin; Wang Lei; Yang Weikang; Wu Zhaoqiang; Li Dan; Chen Hong

2013-01-01

We present our findings of the selective adsorption of native and denatured proteins onto thermally responsive, native-protein resistant poly(N-isopropylacrylamide) (PNIPAAm) decorated silicon nanowire arrays (SiNWAs). The PNIPAAm–SiNWAs surface, which shows very low levels of native-protein adsorption, favors the adsorption of denatured proteins. The amount of denatured-protein adsorption is higher at temperatures above the lower critical solution temperature (LCST) of PNIPAAm. Temperature cycling surrounding the LCST, which ensures against thermal denaturation of native proteins, further increases the amount of denatured-protein adsorption. Moreover, the PNIPAAm–SiNWAs surface is able to selectively adsorb denatured protein even from mixtures of different protein species; meanwhile, the amount of native proteins in solution is kept nearly at its original level. It is believed that these results will not only enrich current understanding of protein interactions with PNIPAAm-modified SiNWAs surfaces, but may also stimulate applications of PNIPAAm–SiNWAs surfaces for native/denatured protein separation. (paper)

Characterization of the thrombogenic potential of surface oxides on stainless steel for implant purposes

International Nuclear Information System (INIS)

Shih, C.-C.; Shih, C.-M.; Su, Y.-Y.; Chang, M.-S.; Lin, S.-J.

2003-01-01

Marketed stents are manufactured from various metals and passivated with different degrees of surface oxidation. The functional surface oxides on the degree of antithrombotic potential were explored through a canine femoral extracorporeal circuit model. Related properties of these oxide films were studied by open-circuit potential, current density detected at open-circuit potential, the electrochemical impedance spectroscopy, transmission electron microscopy, Auger spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. Experimental evidences showed that blood clot weight after a 30-min follow-up was significantly lower for the stainless steel wire passivated with amorphous oxide (AO) compared to the wire passivated with polycrystalline oxide (PO) or commercial as-received wire coils (AS). Surface characterizations showed that a stable negative current density at open-circuit potential and a significant lower potential were found for the wire surface passivated with AO than for the surface passivated with PO. Time constant of AO is about 25 times larger than that of polycrystalline oxide. Significant difference in oxide grain sizes was found between PO and AO. Surface chemistries revealed by the AES and XPS spectra indicated the presence of a Cr- and oxygen-rich surface oxide for AO, and a Fe-rich and oxygen-lean surface oxide for PO. These remarkable characteristics of AO surface film might have a potential to provide for excellent antithrombotic characteristics for the 316L stainless steel stents

Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

Directory of Open Access Journals (Sweden)

Noor A. Nama

2010-01-01

Full Text Available Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001-(1×1 surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.

Surfactant-assisted growth of anodic nanoporous niobium oxide with a grained surface

Energy Technology Data Exchange (ETDEWEB)

Yoo, Jeong Eun [Department of Chemical Engineering, Inha University, 253 Yonghyun Dong, Nam-Gu, Incheon 402-751 (Korea, Republic of); Choi, Jinsub, E-mail: jinsub@inha.ac.k [Department of Chemical Engineering, Inha University, 253 Yonghyun Dong, Nam-Gu, Incheon 402-751 (Korea, Republic of)

2010-07-15

Nanoporous niobium oxide film with a maximum thickness of 520 nm was prepared by anodizing niobium in a mixture of 1 wt% HF, 1 M H{sub 3}PO{sub 4}, and a small amount of Sodium Dodecyl Sulfate (SDS) surfactant. The porosity of the anodic niobium oxide prepared without SDS is irregular with the surface of the oxide suggesting a grained surface pattern rather than an ordered porous structure. A proper amount of SDS addition can prepare a pore arrangement with stripe patterns. The pore depth and surface pattern were strongly affected by the concentration of SDS and bath temperature. We found that the addition of SDS surfactant facilitated improvement in the chemical resistance of niobium oxide, leading to the formation of pores with a longer length compared to those prepared without a SDS surfactant. This can be in part ascribed to the protection of the surface by the physical adsorption of SDS on the surface due to a charge-charge interaction and be in part attributed to the formation of Nb=O bonding on the outermost oxide layer by SDS. When anodization was carried out for 4 h, the surface dissolution of niobium oxide was observed, which means that the maximum tolerance time against chemical dissolution was less than 4 h.

Regularities of radiation defects build up on oxide materials surface

International Nuclear Information System (INIS)

Bitenbaev, M.I.; Polyakov, A.I.; Tuseev, T.

2005-01-01

Analysis of experimental data by radiation defects study on different oxide elements (silicon, beryllium, aluminium, rare earth elements) irradiated by the photo-, gamma-, neutron-, alpha- radiation, protons and helium ions show, that gas adsorption process on the surface centers and radiation defects build up in metal oxide correlated between themselves. These processes were described by the equivalent kinetic equations for analysis of radiation defects build up in the different metal oxides. It was revealed in the result of the analysis: number of radiation defects are droningly increasing up to limit value with the treatment temperature growth. Constant of radicals death at ionizing radiation increases as well. Amount of surface defects in different oxides defining absorbing activity of these materials looks as: silicon oxide→beryllium oxide→aluminium oxide. So it was found, that most optimal material for absorbing system preparation is silicon oxide by it power intensity and berylium oxide by it adsorption efficiency

Biochemical and pharmacological studies of native and irradiated crotamine with gamma radiation of Co{sup 60}

Energy Technology Data Exchange (ETDEWEB)

Mitake, M.B. [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)]. E-mail: mbmitake@net.ipen.br

2000-07-01

Ionizing radiation has been widely employed to attenuate venoms and toxins, preserving and even enhancing their immunogenic properties. However, little is know about molecular changes in irradiated proteins. In this work, we compared native and irradiated bothropstoxin-1, with the aim of characterizing the structural modifications induced by radiation. Our results indicate that radiation promotes a transition from the multimeric to the monomeric state in a dose-dependent manner. Spectral and calorimetric analysis suggest that the irradiation molecules undergo oxidation and partially unfold the remaining elements being stabilized by the seven disulphide bonds. The binding pattern of monoclonal antibodies raised against irradiated bothropstoxin indicates that most of the recognized epitopes are linear present on the surface of both native and irradiated toxin. Also, irradiated toxin appears to be more immunogenic, inducing the formation of native toxin-binding antibodies. (author)

Oxidation behaviour of cast aluminium matrix composites with Ce surface coatings

International Nuclear Information System (INIS)

Pardo, A.; Merino, M.C.; Arrabal, R.; Feliu, S.; Viejo, F.

2007-01-01

The oxidation behaviour of SiC-reinforced aluminium matrix composites (A3xx.x/SiCp) has been studied after Ce-based treatments. Kinetics data of oxidation process were obtained from gravimetric tests performed at different temperatures (350, 425 and 500 o C). The nature of the oxidation layer was analyzed by scanning electron and atomic force microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and X-ray diffraction. The extent of oxidation degradation in untreated composites was preferentially localized in matrix/SiCp interfaces favouring the MgO formation. Ce coatings favoured a uniform oxidation of the composite surface with MgAl 2 O 4 spinel formation. This oxide increased the surface hardness of the materials

Pt-Si Bifunctional Surfaces for CO and Methanol Electro-Oxidation

DEFF Research Database (Denmark)

Permyakova, Anastasia A.; Han, Binghong; Jensen, Jens Oluf

2015-01-01

and storage. Here we report on Pt-Si bulk samples prepared by arc-melting, for the first time, with high activities toward the electro-oxidation of CO and methanol. Increasing the Si concentration on the surface was correlated with the shifts of onset oxidation potentials to lower values and higher activities...... for CO and methanol electro-oxidation. It is proposed that the reaction on the Pt-Si catalyst could follow a Langmuir-Hinshelwood type of mechanism, where substantially enhanced catalytic activity is attributed to the fine-tuning of the surface Pt-Si atomic structure....

Improved the Surface Roughness of Silicon Nanophotonic Devices by Thermal Oxidation Method

Energy Technology Data Exchange (ETDEWEB)

Shi Zujun; Shao Shiqian; Wang Yi, E-mail: ywangwnlo@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, No. 1037, Luoyu Street, Wuhan 430074 (China)

2011-02-01

The transmission loss of the silicon-on-insulator (SOI) waveguide and the coupling loss of the SOI grating are determined to a large extent by the surface roughness. In order to obtain smaller loss, thermal oxidation is a good choice to reduce the surface roughness of the SOI waveguide and grating. Before the thermal oxidation, the root mean square of the surface roughness is over 11 nm. After the thermal oxidation, the SEM figure shows that the bottom of the grating is as smooth as quartz surface, while the AFM shows that the root mean square of the surface is less than 5 nm.

Preparation of self-organized porous anodic niobium oxide microcones and their surface wettability

International Nuclear Information System (INIS)

Oikawa, Y.; Minami, T.; Mayama, H.; Tsujii, K.; Fushimi, K.; Aoki, Y.; Skeldon, P.; Thompson, G.E.; Habazaki, H.

2009-01-01

Porous anodic niobium oxide with a pore size of ∼10 nm was formed at 10 V in glycerol electrolyte containing 0.6 mol dm -3 K 2 HPO 4 and 0.2 mol dm -3 K 3 PO 4 at 433 K. After prolonged anodizing for 5.4 ks, niobium oxide microcones develop on the surface. X-ray diffraction patterns of the anodized specimens revealed that the initially formed anodic oxide is amorphous, but an amorphous-to-crystalline transition occurs during anodizing. As a consequence of the preferential chemical dissolution of the initially formed amorphous oxide, due to different solubility of the amorphous and crystalline oxides, crystalline oxide microcones appear on the film surface after prolonged anodizing. The surface is superhydrophilic. After coating with fluorinated alkylsilane, the surface becomes superhydrophobic with a contact angle of 158 o for water. The surface is also oil repellent, with a contact angle as high as 140 o for salad oil.

Facile preparation of superhydrophobic surfaces based on metal oxide nanoparticles

Science.gov (United States)

Bao, Xue-Mei; Cui, Jin-Feng; Sun, Han-Xue; Liang, Wei-Dong; Zhu, Zhao-Qi; An, Jin; Yang, Bao-Ping; La, Pei-Qing; Li, An

2014-06-01

A novel method for fabrication of superhydrophobic surfaces was developed by facile coating various metal oxide nanoparticles, including ZnO, Al2O3 and Fe3O4, on various substrates followed by treatment with polydimethylsiloxane (PDMS) via chemical vapor deposition (CVD) method. Using ZnO nanoparticles as a model, the changes in the surface chemical composition and crystalline structures of the metal oxide nanoparticles by PDMS treatment were investigated by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The results show that the combination of the improved surface roughness generated from of the nanoparticles aggregation with the low surface-energy of silicon-coating originated from the thermal pyrolysis of PDMS would be responsible for the surface superhydrophobicity. By a simple dip-coating method, we show that the metal oxide nanoparticles can be easily coated onto the surfaces of various textural and dimensional substrates, including glass slide, paper, fabric or sponge, for preparation of superhydrophobic surfaces for different purpose. The present strategy may provide an inexpensive and new route to surperhydrophobic surfaces, which would be of technological significance for various practical applications especially for separation of oils or organic contaminates from water.

Facile preparation of superhydrophobic surfaces based on metal oxide nanoparticles

International Nuclear Information System (INIS)

Bao, Xue-Mei; Cui, Jin-Feng; Sun, Han-Xue; Liang, Wei-Dong; Zhu, Zhao-Qi; An, Jin; Yang, Bao-Ping; La, Pei-Qing; Li, An

2014-01-01

A novel method for fabrication of superhydrophobic surfaces was developed by facile coating various metal oxide nanoparticles, including ZnO, Al 2 O 3 and Fe 3 O 4 , on various substrates followed by treatment with polydimethylsiloxane (PDMS) via chemical vapor deposition (CVD) method. Using ZnO nanoparticles as a model, the changes in the surface chemical composition and crystalline structures of the metal oxide nanoparticles by PDMS treatment were investigated by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The results show that the combination of the improved surface roughness generated from of the nanoparticles aggregation with the low surface-energy of silicon-coating originated from the thermal pyrolysis of PDMS would be responsible for the surface superhydrophobicity. By a simple dip-coating method, we show that the metal oxide nanoparticles can be easily coated onto the surfaces of various textural and dimensional substrates, including glass slide, paper, fabric or sponge, for preparation of superhydrophobic surfaces for different purpose. The present strategy may provide an inexpensive and new route to surperhydrophobic surfaces, which would be of technological significance for various practical applications especially for separation of oils or organic contaminates from water.

Facile preparation of superhydrophobic surfaces based on metal oxide nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Bao, Xue-Mei; Cui, Jin-Feng; Sun, Han-Xue; Liang, Wei-Dong; Zhu, Zhao-Qi; An, Jin; Yang, Bao-Ping; La, Pei-Qing; Li, An, E-mail: lian2010@lut.cn

2014-06-01

A novel method for fabrication of superhydrophobic surfaces was developed by facile coating various metal oxide nanoparticles, including ZnO, Al{sub 2}O{sub 3} and Fe{sub 3}O{sub 4}, on various substrates followed by treatment with polydimethylsiloxane (PDMS) via chemical vapor deposition (CVD) method. Using ZnO nanoparticles as a model, the changes in the surface chemical composition and crystalline structures of the metal oxide nanoparticles by PDMS treatment were investigated by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The results show that the combination of the improved surface roughness generated from of the nanoparticles aggregation with the low surface-energy of silicon-coating originated from the thermal pyrolysis of PDMS would be responsible for the surface superhydrophobicity. By a simple dip-coating method, we show that the metal oxide nanoparticles can be easily coated onto the surfaces of various textural and dimensional substrates, including glass slide, paper, fabric or sponge, for preparation of superhydrophobic surfaces for different purpose. The present strategy may provide an inexpensive and new route to surperhydrophobic surfaces, which would be of technological significance for various practical applications especially for separation of oils or organic contaminates from water.

Aspirin degradation in surface-charged TEMPO-oxidized mesoporous crystalline nanocellulose.

Science.gov (United States)

Carlsson, Daniel O; Hua, Kai; Forsgren, Johan; Mihranyan, Albert

2014-01-30

TEMPO-mediated surface oxidation of mesoporous highly crystalline Cladophora cellulose was used to introduce negative surface charges onto cellulose nanofibrils without significantly altering other structural characteristics. This enabled the investigation of the influence of mesoporous nanocellulose surface charges on aspirin chemical stability to be conducted. The negative surface charges (carboxylate content 0.44±0.01 mmol/g) introduced on the mesoporous crystalline nanocellulose significantly accelerated aspirin degradation, compared to the starting material which had significantly less surface charge (0.06±0.01 mmol/g). This effect followed from an increased aspirin amorphisation ability in mesopores of the oxidized nanocellulose. These results highlight the importance of surface charges in formulating nanocellulose for drug delivery. Copyright © 2013 Elsevier B.V. All rights reserved.

Decomposition of SnH{sub 4} molecules on metal and metal–oxide surfaces

Energy Technology Data Exchange (ETDEWEB)

Ugur, D. [TNO, Stieltjesweg 1, 2628 CK Delft (Netherlands); Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, 2628 CD Delft (Netherlands); Storm, A.J.; Verberk, R. [TNO, Stieltjesweg 1, 2628 CK Delft (Netherlands); Brouwer, J.C. [Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, 2628 CD Delft (Netherlands); Sloof, W.G., E-mail: w.g.sloof@tudelft.nl [Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, 2628 CD Delft (Netherlands)

2014-01-01

Atomic hydrogen cleaning is a promising method for EUV lithography systems, to recover from surface oxidation and to remove carbon and tin contaminants. Earlier studies showed, however, that tin may redeposit on nearby surfaces due to SnH{sub 4} decomposition. This phenomenon of SnH{sub 4} decomposition during tin cleaning has been quantified for various metallic and metal-oxide surfaces using X-ray photoelectron spectroscopy (XPS). It was observed that the metal oxide surfaces (TiO{sub 2} and ZrO{sub 2}) were significantly less contaminated than metallic surfaces. Tin contamination due to SnH{sub 4} decomposition can thus be reduced or even mitigated by application of a suitable metal-oxide coating.

Native Liquid Extraction Surface Analysis Mass Spectrometry: Analysis of Noncovalent Protein Complexes Directly from Dried Substrates

Science.gov (United States)

Martin, Nicholas J.; Griffiths, Rian L.; Edwards, Rebecca L.; Cooper, Helen J.

2015-08-01

Liquid extraction surface analysis (LESA) mass spectrometry is a promising tool for the analysis of intact proteins from biological substrates. Here, we demonstrate native LESA mass spectrometry of noncovalent protein complexes of myoglobin and hemoglobin from a range of surfaces. Holomyoglobin, in which apomyoglobin is noncovalently bound to the prosthetic heme group, was observed following LESA mass spectrometry of myoglobin dried onto glass and polyvinylidene fluoride surfaces. Tetrameric hemoglobin [(αβ)2 4H] was observed following LESA mass spectrometry of hemoglobin dried onto glass and polyvinylidene fluoride (PVDF) surfaces, and from dried blood spots (DBS) on filter paper. Heme-bound dimers and monomers were also observed. The `contact' LESA approach was particularly suitable for the analysis of hemoglobin tetramers from DBS.

Opposing effects of humidity on rhodochrosite surface oxidation.

Science.gov (United States)

Na, Chongzheng; Tang, Yuanzhi; Wang, Haitao; Martin, Scot T

2015-03-03

Rhodochrosite (MnCO3) is a model mineral representing carbonate aerosol particles containing redox-active elements that can influence particle surface reconstruction in humid air, thereby affecting the heterogeneous transformation of important atmospheric constituents such as nitric oxides, sulfur dioxides, and organic acids. Using in situ atomic force microscopy, we show that the surface reconstruction of rhodochrosite in humid oxygen leads to the formation and growth of oxide nanostructures. The oxidative reconstruction consists of two consecutive processes with distinctive time scales, including a long waiting period corresponding to slow nucleation and a rapid expansion phase corresponding to fast growth. By varying the relative humidity from 55 to 78%, we further show that increasing humidity has opposing effects on the two processes, accelerating nucleation from 2.8(±0.2) × 10(-3) to 3.0(±0.2) × 10(-2) h(-1) but decelerating growth from 7.5(±0.3) × 10(-3) to 3.1(±0.1) × 10(-3) μm(2) h(-1). Through quantitative analysis, we propose that nanostructure nucleation is controlled by rhodochrosite surface dissolution, similar to the dissolution-precipitation mechanism proposed for carbonate mineral surface reconstruction in aqueous solution. To explain nanostructure growth in humid oxygen, a new Cabrera-Mott mechanism involving electron tunneling and solid-state diffusion is proposed.

Enhanced magnetic properties of Fe soft magnetic composites by surface oxidation

Energy Technology Data Exchange (ETDEWEB)

Zhao, Guoliang; Wu, Chen, E-mail: chen_wu@zju.edu.cn; Yan, Mi, E-mail: mse_yanmi@zju.edu.cn

2016-02-01

Fe soft magnetic composites (SMCs) with low core loss were fabricated via surface oxidation of the Fe powders by H{sub 2}O and O{sub 2} at elevated temperatures. Surface oxidation prevents magnetic dilution due to the formation of the ferromagnetic iron oxide coating layer, giving rise to high magnetic flux density and effective permeability of the SMCs compared with those fabricated with traditional phosphate coating. Mechanism of the oxidation process has been investigated where Fe{sub 3}O{sub 4} forms by reactions of Fe with H{sub 2}O and O{sub 2}. The Fe{sub 3}O{sub 4} coating layer tends to convert into γ-Fe{sub 2}O{sub 3} with increased oxidation temperature and time. By controlling composition of the coating layer, low core loss of 688.9 mW/cm{sup 3} (measured at 50 mT and 100 kHz) and higher effective permeability of 88.3 can be achieved for the Fe SMCs. - Highlights: • Surface oxidation as a new method to fabricate Fe Soft magnetic composite (SMCs). • Oxidation mechanism revealed where Fe reacts with H2O and O2 at high temperatures. • Evolution of the iron oxide coating with growth temperature and time investigated. • The iron oxide insulation coating results in improved magnetic performance.

Evolution of a Native Oxide Layer at the a-Si:H/c-Si Interface and Its Influence on a Silicon Heterojunction Solar Cell.

Science.gov (United States)

Liu, Wenzhu; Meng, Fanying; Zhang, Xiaoyu; Liu, Zhengxin

2015-12-09

The interface microstructure of a silicon heterojunction (SHJ) solar cell was investigated. We found an ultrathin native oxide layer (NOL) with a thickness of several angstroms was formed on the crystalline silicon (c-Si) surface in a very short time (∼30 s) after being etched by HF solution. Although the NOL had a loose structure with defects that are detrimental for surface passivation, it acted as a barrier to restrain the epitaxial growth of hydrogenated amorphous silicon (a-Si:H) during the plasma-enhanced chemical vapor deposition (PECVD). The microstructure change of the NOL during the PECVD deposition of a-Si:H layers with different conditions and under different H2 plasma treatments were systemically investigated in detail. When a brief H2 plasma was applied to treat the a-Si:H layer after the PECVD deposition, interstitial oxygen and small-size SiO2 precipitates were transformed to hydrogenated amorphous silicon suboxide alloy (a-SiO(x):H, x ∼ 1.5). In the meantime, the interface defect density was reduced by about 50%, and the parameters of the SHJ solar cell were improved due to the post H2 plasma treatment.

Covalent Surface Modification of Silicon Oxides with Alcohols in Polar Aprotic Solvents.

Science.gov (United States)

Lee, Austin W H; Gates, Byron D

2017-09-05

Alcohol-based monolayers were successfully formed on the surfaces of silicon oxides through reactions performed in polar aprotic solvents. Monolayers prepared from alcohol-based reagents have been previously introduced as an alternative approach to covalently modify the surfaces of silicon oxides. These reagents are readily available, widely distributed, and are minimally susceptible to side reactions with ambient moisture. A limitation of using alcohol-based compounds is that previous reactions required relatively high temperatures in neat solutions, which can degrade some alcohol compounds or could lead to other unwanted side reactions during the formation of the monolayers. To overcome these challenges, we investigate the condensation reaction of alcohols on silicon oxides carried out in polar aprotic solvents. In particular, propylene carbonate has been identified as a polar aprotic solvent that is relatively nontoxic, readily accessible, and can facilitate the formation of alcohol-based monolayers. We have successfully demonstrated this approach for tuning the surface chemistry of silicon oxide surfaces with a variety of alcohol containing compounds. The strategy introduced in this research can be utilized to create silicon oxide surfaces with hydrophobic, oleophobic, or charged functionalities.

Patterning pentacene surfaces by local oxidation nanolithography

International Nuclear Information System (INIS)

Losilla, N.S.; Martinez, J.; Bystrenova, E.; Greco, P.; Biscarini, F.; Garcia, R.

2010-01-01

Sequential and parallel local oxidation nanolithographies have been applied to pattern pentacene samples by creating a variety of nanostructures. The sequential local oxidation process is performed with an atomic force microscope and requires the application of a sequence of voltage pulses of 36 V for 1 ms. The parallel local oxidation process is performed by using a conductive and patterned stamp. Then, a voltage pulse is applied between the stamp and the pentacene surface. Patterns formed by arrays of parallel lines covering 1 mm 2 regions and with a periodicity of less than 1 μm have been generated in a few seconds. We also show that the patterns can be used as templates for the deposition of antibodies.

Studies of high coverage oxidation of the Cu(100) surface using low energy positrons

Science.gov (United States)

Fazleev, N. G.; Maddox, W. B.; Weiss, A. H.

2012-02-01

The study of oxidation of single crystal metal surfaces is important in understanding the corrosive and catalytic processes associated with thin film metal oxides. The structures formed on oxidized transition metal surfaces vary from simple adlayers of chemisorbed oxygen to more complex structures which result from the diffusion of oxygen into subsurface regions. In this work we present the results of theoretical studies of positron surface and bulk states and annihilation probabilities of surface-trapped positrons with relevant core electrons at the oxidized Cu(100) surface under conditions of high oxygen coverage. Calculations are performed for various high coverage missing row structures ranging between 0.50 and 1.50 ML oxygen coverage. The results of calculations of positron binding energy, positron work function, and annihilation characteristics of surface trapped positrons with relevant core electrons as function of oxygen coverage are compared with experimental data obtained from studies of oxidation of the Cu(100) surface using positron annihilation induced Auger electron spectroscopy (PAES).

Work Function of Oxide Ultrathin Films on the Ag(100) Surface.

Science.gov (United States)

Sementa, Luca; Barcaro, Giovanni; Negreiros, Fabio R; Thomas, Iorwerth O; Netzer, Falko P; Ferrari, Anna Maria; Fortunelli, Alessandro

2012-02-14

Theoretical calculations of the work function of monolayer (ML) and bilayer (BL) oxide films on the Ag(100) surface are reported and analyzed as a function of the nature of the oxide for first-row transition metals. The contributions due to charge compression, charge transfer and rumpling are singled out. It is found that the presence of empty d-orbitals in the oxide metal can entail a charge flow from the Ag(100) surface to the oxide film which counteracts the decrease in the work function due to charge compression. This flow can also depend on the thickness of the film and be reduced in passing from ML to BL systems. A regular trend is observed along first-row transition metals, exhibiting a maximum for CuO, in which the charge flow to the oxide is so strong as to reverse the direction of rumpling. A simple protocol to estimate separately the contribution due to charge compression is discussed, and the difference between the work function of the bare metal surface and a Pauling-like electronegativity of the free oxide slabs is used as a descriptor quantity to predict the direction of charge transfer.

Oxidation of clean silicon surfaces studied by four-point probe surface conductance measurements

DEFF Research Database (Denmark)

Petersen, Christian Leth; Grey, Francois; Aono, M.

1997-01-01

We have investigated how the conductance of Si(100)-(2 x 1) and Si(111)-(7 x 7) surfaces change during exposure to molecular oxygen. A monotonic decrease in conductance is seen as the (100) surfaces oxidizes. In contract to a prior study, we propose that this change is caused by a decrease in sur...

Computerized infrared spectroscopic study of surface reactions on selected lanthanide oxides

International Nuclear Information System (INIS)

Dellisante, G.N.

1982-01-01

The natures of adsorption sites on La 2 O 3 , Nd 2 O 3 , and selected praseodymium oxides were investigated by examining surface reactions of probe molecules using computerized transmission ir spectroscopy on unsupported samples. Additionally, the rehydration/dehydration behavior and crystallographic phase transitions of these oxides were examined in pretreatment temperature experiments involving rehydration of the sesquioxides to hydroxides by water exposure. Following rehydration of La 2 O 3 to La(OH) 3 , the effect of increasing vacuum pretreatment temperature (350 to 1000 0 C) is to gradually remove surface hydroxyl and carbonate entities (up to 650 0 C), and increase the degree of A-type crystallinity. Increasing crystallinity causes a concomitant decrease in surface oxide basicity. The removal of hydroxyl and carbonate species, as well as increases in oxide basicity, strongly correlated to increases in certain catalytic activities. The adsorption of NH 3 , CO 2 , mixtures of NH 3 and CO 2 , formic acid, acetic acid, acetaldehyde, and ethanol on the oxides was determined to weakly coordinate in Ln 3 + sites, and the surface reactions are discussed. Heating was found to desorb the adsorbed compounds and/or causes changes of the originally adsorbed form into other compounds. The effects of temperature on both adsorption and desorption are reported

Surface Preparation and Deposited Gate Oxides for Gallium Nitride Based Metal Oxide Semiconductor Devices

Directory of Open Access Journals (Sweden)

Paul C. McIntyre

2012-07-01

Full Text Available The literature on polar Gallium Nitride (GaN surfaces, surface treatments and gate dielectrics relevant to metal oxide semiconductor devices is reviewed. The significance of the GaN growth technique and growth parameters on the properties of GaN epilayers, the ability to modify GaN surface properties using in situ and ex situ processes and progress on the understanding and performance of GaN metal oxide semiconductor (MOS devices are presented and discussed. Although a reasonably consistent picture is emerging from focused studies on issues covered in each of these topics, future research can achieve a better understanding of the critical oxide-semiconductor interface by probing the connections between these topics. The challenges in analyzing defect concentrations and energies in GaN MOS gate stacks are discussed. Promising gate dielectric deposition techniques such as atomic layer deposition, which is already accepted by the semiconductor industry for silicon CMOS device fabrication, coupled with more advanced physical and electrical characterization methods will likely accelerate the pace of learning required to develop future GaN-based MOS technology.

Fractional surface termination of diamond by electrochemical oxidation.

Science.gov (United States)

Hoffmann, René; Obloh, Harald; Tokuda, Norio; Yang, Nianjun; Nebel, Christoph E

2012-01-10

The crystalline form of sp(3)-hybridized carbon, diamond, offers various electrolyte-stable surface terminations. The H-termination-selective attachment of nitrophenyl diazonium, imaged by AFM, shows that electrochemical oxidation can control the fractional hydrogen/oxygen surface termination of diamond on the nanometer scale. This is of particular interest for all applications relying on interfacial electrochemistry, especially for biointerfaces.

Recombinant hepatitis B surface antigen production in Aspergillus niger: evaluating the strategy of gene fusion to native glucoamylase

CSIR Research Space (South Africa)

James, ER

2012-10-01

Full Text Available Microbiology and Biotechnology October 2012/ Vol. 96, No.2 Recombinant hepatitis B surface antigen production in Aspergillus niger: evaluating the strategy of gene fusion to native glucoamylase ER James a,c & WH van Zyl b & PJ van Zyl c & JF Görgens..., Pretoria 0001, South Africa Abstract This study demonstrates the potential of Aspergillus niger as a candidate expression system for virus- like particle production using gene fusion. Hepatitis B surface antigen (HBsAg) production, targeted...

Methane oxidation and methane fluxes in the ocean surface layer and deep anoxic waters

Science.gov (United States)

Ward, B. B.; Kilpatrick, K. A.; Novelli, P. C.; Scranton, M. I.

1987-01-01

Measured biological oxidation rates of methane in near-surface waters of the Cariaco Basin are compared with the diffusional fluxes computed from concentration gradients of methane in the surface layer. Methane fluxes and oxidation rates were investigated in surface waters, at the oxic/anoxic interface, and in deep anoxic waters. It is shown that the surface-waters oxidation of methane is a mechanism which modulates the flux of methane from marine waters to the atmosphere.

Reversible Compositional Control of Oxide Surfaces by Electrochemical Potentials

KAUST Repository

Mutoro, Eva

2012-01-05

Perovskite oxides can exhibit a wide range of interesting characteristics such as being catalytically active and electronically/ionically conducting, and thus, they have been used in a number of solid-state devices such as solid oxide fuel cells (SOFCs) and sensors. As the surface compositions of perovskites can greatly influence the catalytic properties, knowing and controlling their surface compositions is crucial to enhance device performance. In this study, we demonstrate that the surface strontium (Sr) and cobalt (Co) concentrations of perovskite-based thin films can be controlled reversibly at elevated temperatures by applying small electrical potential biases. The surface compositional changes of La 0.8Sr 0.2CoO 3-δ (LSC 113), (La 0.5Sr 0.5) 2CoO 4±δ (LSC 214), and LSC 214-decorated LSC 113 films (LSC 113/214) were investigated in situ by utilizing synchrotron-based X-ray photoelectron spectroscopy (XPS), where the largest changes of surface Sr were found for the LSC 113/214 surface. These findings offer the potential of reversibly controlling the surface functionality of perovskites. © 2011 American Chemical Society.

Surface composition of Cd{sub 1–x}Fe(Mn){sub x}Te{sub 1–y}Se{sub y} systems exposed to air

Energy Technology Data Exchange (ETDEWEB)

Bundaleski, Nenad [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia); Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Radisavljević, Ivana, E-mail: iva@vin.bg.ac.rs [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia); Trigueiro, João [Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Tolstogouzov, Alexander [Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Ryazan State Radio Engineering University, Gagarin 59/1, 390005 Ryazan (Russian Federation); Rakočević, Zlatko; Medić, Mirjana [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia); Teodoro, Orlando M.N.D. [Universidade Nova de Lisboa–Faculdade de Ciências e Tecnologia, Quinta da Torre, 2829–516 Caparica (Portugal); Romčević, Nebojša [University of Belgrade–Institute of Physics, Pregrevica 118, 11000 Belgrade (Serbia); Ivanović, Nenad [University of Belgrade–Vinča Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade (Serbia)

2017-03-01

Using X–ray induced Photoelectron Spectroscopy, Time–of–Flight Secondary Ion Mass Spectrometry and Atomic Force Microscopy we have investigated elemental composition, structure and oxidation process taking place at the surfaces of polycrystalline Cd{sub 0.99}Fe{sub 0.01}Te{sub 0.97}Se{sub 0.03} and Cd{sub 0.95}Mn{sub 0.05}Te{sub 0.97}Se{sub 0.03} systems stored in ambient conditions. The surface oxidation destroys the native CdTe matrix and provokes substantial atomic rearrangement in the first few atomic layers. The near–surface region of both systems is enriched in Cd and to some extent Te–deficient, but the surface structure, morphology and the native oxide composition are all found to be considerably different. In Cd{sub 0.99}Fe{sub 0.01}Te{sub 0.97}Se{sub 0.03} system both Fe and Se dopants diffuse into the bulk and oxidation of its surface results in formation of a thin CdTeO{sub 3} layer which covers the CdTe matrix. In Cd{sub 0.95}Mn{sub 0.05}Te{sub 0.97}Se{sub 0.03} system oxygen–rich atmosphere triggers Mn and Se out–diffusion and the nonuniform oxide layer predominantly consists of MnO and a small amount of Te–oxide which both lay underneath a thin layer of metallic Cd segregated at the top of the surface. - Highlights: • Nature of the CdFe(Mn)TeSe surfaces exposed to air is substantially different. • Near–surface region is enriched in Cd and to some extent Te–deficient. • Presence of Mn drastically changes the surface oxidation conditions. • The surface oxidation in ambient conditions undergoes different mechanisms. • Oxygen triggers Mn out–diffusion, while Fe diffuses into the bulk.

Surface and interface strains studied by x-ray diffraction

International Nuclear Information System (INIS)

Akimoto, Koichi; Emoto, Takashi; Ichimiya, Ayahiko

1998-01-01

The authors have developed a technique of X-ray diffraction in order to measure strain fields near semiconductor surface and interface. The diffraction geometry is using the extremely asymmetric Bragg-case bulk reflection of a small incident angle to the surface and a large angle exiting from the surface. The incident angle of the X-rays is set near critical angle of total reflection by tuning X-ray energy of synchrotron radiation at the Photon Factory, Japan. For thermally grown-silicon oxide/Si(100) interface, the X-ray intensity of the silicon substrate 311 reflection has been measured. From comparison of the full width at half maxima (FWHM) of X-ray rocking curves of various thickness of silicon oxides, it has been revealed that silicon substrate lattice is highly strained in the thin (less than about 5 nm) silicon oxide/silicon system. In order to know the original silicon surface strain, the authors have also performed the same kind of measurements in the ultra-high vacuum chamber. A clean Si(111) 7x7 surface gives sharper X-ray diffraction peak than that of the native oxide/Si(111) system. From these measurements, it is concluded that the thin silicon oxide film itself gives strong strain fields to the silicon substrates, which may be the reason of the existence of the structural transition layer at the silicon oxide/Si interface

Creation of hydrophobic surfaces using a paint containing functionalized oxide particles

Science.gov (United States)

Sino, Paul Albert L.; Herrera, Marvin U.; Balela, Mary Donnabelle L.

2017-05-01

Hydrophobic surfaces were created by coating various substrates (aluminum sheet, soda-lime glass, silicon carbide polishing paper, glass with double-sided adhesive) with paint containing functionalized oxide particles. The paint was created by functionalizing oxide particles (ground ZnO, TiO2 nanoparticles, or TiO2 microparticles) with fluorosilane molecules in absolute ethanol. Water contact angle of samples shows that the coated substrate becomes hydrophobic (water contact angle ≥ 90°). Among the oxides that were used, ground ZnO yielded contact angle exemplifying superhydrophobicity (water contact angle ≥ 150°). Scanning electron micrograph of paint-containing TiO2 nanoparticles shows rough functionalized oxides structures which probably increase the hydrophobicity of the surface.

Fabrication of long-term stable superoleophobic surface based on copper oxide/cobalt oxide with micro-nanoscale hierarchical roughness

Science.gov (United States)

Barthwal, Sumit; Lim, Si-Hyung

2015-02-01

We have demonstrated a simple and cost-effective technique for the large-area fabrication of a superoleophobic surface using copper as a substrate. The whole process included three simple steps: First, the copper substrate was oxidized under hot alkaline conditions to fabricate flower-like copper oxide microspheres by heating at a particular temperature for an interval of time. Second, the copper-oxide-covered copper substrate was further heated in a solution of cobalt nitrate and ammonium nitrate in the presence of an ammonia solution to fabricate cobalt oxide nanostructures. We applied this second step to increase the surface roughness because it is an important criterion for improved superoleophobicity. Finally, to reduce the surface energy of the fabricated structures, the surfaces were chemically modified with perfluorooctyltrichlorosilane. Contact-angle measurements indicate that the micro-nano binary (MNB) hierarchical structures fabricated on the copper substrate became super-repellent toward a broad range of liquids with surface tension in the range of 21.5-72 mN/m. In an attempt to significantly improve the superoleophobic property of the surface, we also examined and compared the role of nanostructures in MNB hierarchical structures with only micro-fabricated surfaces. The fabricated MNB hierarchical structures also displays thermal stability and excellent long-term stability after exposure in air for more than 9 months. Our method might provide a general route toward the preparation of novel hierarchical films on metal substrates for various industrial applications.

Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy

Directory of Open Access Journals (Sweden)

Thomas König

2011-01-01

Full Text Available Surfaces of thin oxide films were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001 and line defects in aluminum oxide on NiAl(110, respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM and the electronic structure by scanning tunneling spectroscopy (STS. On magnesium oxide, different color centers, i.e., F0, F+, F2+ and divacancies, have different effects on the contact potential. These differences enabled classification and unambiguous differentiation by KPFM. True atomic resolution shows the topography at line defects in aluminum oxide. At these domain boundaries, STS and KPFM verify F2+-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide films beyond imaging the topography of the surface atoms.

Theoretical aspects of studies of oxide and semiconductor surfaces using low energy positrons

Science.gov (United States)

Fazleev, N. G.; Maddox, W. B.; Weiss, A. H.

2011-01-01

This paper presents the results of a theoretical study of positron surface and bulk states and annihilation characteristics of surface trapped positrons at the oxidized Cu(100) single crystal and at both As- and Ga-rich reconstructed GaAs(100) surfaces. The variations in atomic structure and chemical composition of the topmost layers of the surfaces associated with oxidation and reconstructions and the charge redistribution at the surfaces are found to affect localization and spatial extent of the positron surface-state wave functions. The computed positron binding energy, work function, and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the surfaces. Theoretical positron annihilation probabilities with relevant core electrons computed for the oxidized Cu(100) surface and the As- and Ga-rich reconstructed GaAs(100) surfaces are compared with experimental ones estimated from the positron annihilation induced Auger peak intensities measured from these surfaces.

Does verbatim sentence recall underestimate the language competence of near-native speakers?

Directory of Open Access Journals (Sweden)

Judith eSchweppe

2015-02-01

Full Text Available Verbatim sentence recall is widely used to test the language competence of native and non-native speakers since it involves comprehension and production of connected speech. However, we assume that, to maintain surface information, sentence recall relies particularly on attentional resources, which differentially affects native and non-native speakers. Since even in near-natives language processing is less automatized than in native speakers, processing a sentence in a foreign language plus retaining its surface may result in a cognitive overload. We contrasted sentence recall performance of German native speakers with that of highly proficient non-natives. Non-natives recalled the sentences significantly poorer than the natives, but performed equally well on a cloze test. This implies that sentence recall underestimates the language competence of good non-native speakers in mixed groups with native speakers. The findings also suggest that theories of sentence recall need to consider both its linguistic and its attentional aspects.

Surface oxidization-reduction reactions in Columbia Plateau basalts

International Nuclear Information System (INIS)

White, A.F.; Yee, A.

1984-01-01

Results are presented which define principal oxidation-reduction reactions expected between ground water and iron in the Umtanum and Cohassett basalt flows of south central Washington. Data include kinetics of aqueous iron speciation, rates of O 2 uptake and nature of oxyhydroxide precipitates. Such data are important in predicting behavior of radionuclides in basalt aquifers including determination of valence states, speciation, solubility, sorption, and coprecipitation on iron oxyhydroxide substrates and colloids. Analyses of the basalt by XPS indicates that ferrous iron is oxidized to ferric iron on the surface and that the total iron decreases as a function of pH during experimental weathering. Iron oxyhydroxide phases did not form surface coating on basalt surfaces but rather nucleated as separate plases in solution. No significant increases in Cs or Sr sorption were observed with increased weathering of the basalt. Concurrent increases in Fe(II) and decreases in Fe(III) in slightly to moderately acid solutions indicated continued oxidization of ferrous iron in the basalt. At neutral to basic pH, Fe(II) was strongly sorbed onto the basalt surface (Kd = 6.5 x 10 -3 1 x m 2 ) resulting in low dissolved concentrations even under anoxic conditions. The rate of O 2 uptake increased with decreasing pH. Diffusion rates (-- 10 -14 cm 2 x s -1 ), calculated using a one-dimensional analytical model, indicate grain boundary diffusion. Comparisons of Eh values calculated by Pt electrode, dissolved O 2 and Fe(II)/Fe(III) measurements showed considerable divergence, with the ferric-ferrous couple being the preferred method of estimating Eh

DFT study of cyanide oxidation on surface of Ge-embedded carbon nanotube

Science.gov (United States)

Gao, Wei; Milad Abrishamifar, Seyyed; Ebrahimzadeh Rajaei, Gholamreza; Razavi, Razieh; Najafi, Meysam

2018-03-01

In recent years, the discovery of suitable catalyst to oxidation of the cyanide (CN) has high importance in the industry. In present study, in the first step, the carbon nanotube (CNT) with the Ge atom embedded and the surface of Ge-CNT via the O2 molecule activated. In second step, the oxidation of CN on surface of the Ge-CNT via the Langmuir Hinshelwood (LH) and the Eley Rideal (ER) mechanisms was investigated. Results show that O2-Ge-CNT oxidized the CN molecule via the Ge-CNT-O-O∗ + CN → Ge-CNT-O-O∗-CN → Ge-CNT-O∗ + OCN and the Ge-CNT-O∗ + CN → Ge-CNT + OCN reactions. Results show that oxidation of CN on surface of Ge-CNT via the LH mechanism has lower energy barrier than ER mechanism. Finally, calculated parameters reveal that Ge-CNT is acceptable catalyst with high performance for CN oxidation, form theoretical point of view.

Investigation of the Si(111) surface in uhv: oxidation and the effect of surface phosphorus

International Nuclear Information System (INIS)

Tom, H.W.K.; Zhu, X.D.; Shen, Y.R.; Somorjai, G.A.

1984-06-01

We have studied the initial stages of oxidation, the segregation of phosphorus, and the effect of phosphorus on oxidation of the Si(111) 7 x 7 surface using optical second-harmonic generation. We have also observed a (√3 x √3)R30 0 LEED pattern for P on Si

An ab initio study of plutonium oxides surfaces

International Nuclear Information System (INIS)

Jomard, G.; Bottin, F.; Amadon, B.

2007-01-01

By means of first-principles calculations, we have studied the atomic structure as well as the thermodynamic stability of various plutonium dioxide surfaces in function of their environment (in terms of oxygen partial pressure and temperature). All these simulations have been performed with the ABINIT code. It is well known that DFT fails to describe correctly plutonium-based materials since 5f electrons in such systems are strongly correlated. In order to go beyond DFT, we have treated PuO 2 and β-Pu 2 O 3 in a DFT+U framework. We show that the couple of parameters (U,J) that works well for pure Pu is also well designed for describing ground state (GS) properties of these two oxides. The major improvement with respect with DFT is that we are able to predict an insulating GS in agreement with experiments. The presence of a gap in the DOS (Density of States) of plutonium oxides should play a significant role in the predicted surface reactivity. However, performing DFT+U calculations on surfaces of plutonium oxide from scratch was too ambitious. That is why we decided, as a first step, to study the stability of the (100), (110) and (111) surfaces of PuO 2 in a DFT-GGA framework. For each of these orientations, we considered various terminations. These ab initio results have been introduced in a thermodynamic model which allows us to predict the relative stability of the different terminations as a function of temperature and oxygen partial pressure (p O 2 ). We conclude that at room temperature and for p O 2 ∼10 atm., the polar O 2 -(100) termination is favoured. The stabilization of such a polar stoichiometric surface is surprising and should be confirmed by DFT+U calculations before any final conclusion. (authors)

Adsorption and revaporisation studies on iodine oxide aerosols deposited on containment surface materials in LWR

International Nuclear Information System (INIS)

Tietze, S.; Foreman, M.R.StJ.; Ekberg, C.; Kaerkelae, T.; Auvinen, A.; Tapper, U.; Lamminmaeki, S.; Jokiniemi, J.

2012-12-01

During a hypothetical severe nuclear accident, the radiation field will be very high in the nuclear reactor containment building. As a result gaseous radiolysis products will be formed. Elemental iodine can react in the gaseous phase with ozone to form solid iodine oxide aerosol particles (iodine oxide). Within the AIAS (Adsorption of Iodine oxide Aerosols on Surfaces) project the interactions of iodine oxide (IOx) aerosols with common containment surface materials were investigated. Common surface materials in Swedish and Finnish LWRs are Teknopox Aqua V A paint films and metal surfaces such as Cu, Zn, Al and SS, as well as Pt and Pd surfaces from hydrogen recombiners. Non-radioactive and 131 I labelled iodine oxide aerosols were produced with the EXSI CONT facility from elemental iodine and ozone at VTT Technical Research Centre of Finland. The iodine oxide deposits were analysed with microscopic and spectroscopic measurement techniques to identify the kind of iodine oxide formed and if a chemical conversion on the different surface materials occurs. The revaporisation behaviour of the deposited iodine oxide aerosol particles from the different surface materials was studied under the influence of heat, humidity and gamma irradiation at Chalmers University of Technology, Sweden. Studies on the effects of humidity were performed using the FOMICAG facility, while heat and irradiation experiments were performed in a thermostated heating block and with a gammacell 22 having a dose rate of 14 kGy/h. The revaporisation losses were measured using a HPGe detector. The revaporisated 131 I species from the surfaces were chemically tested for elemental iodine formation. The parameter dominating the degradation of the produced iodine oxide aerosols was humidity. Cu and Zn surfaces were found to react with iodine from the iodine oxide aerosols to form iodides, while no metal iodides were detected for Al and SS samples. Most of the iodine oxide aerosols are assumed to be

Improved GaSb surfaces using a (NH4)2S/(NH4)2S04 solution

International Nuclear Information System (INIS)

Murape, D.M.; Eassa, N.; Nyamhere, C.; Neethling, J.H.; Betz, R.; Coetsee, E.; Swart, H.C.; Botha, J.R.; Venter, A.

2012-01-01

Bulk (1 0 0) n-GaSb surfaces have been treated with a sulphur based solution ((NH 4 ) 2 S/(NH 4 ) 2 SO 4 ) to which sulphur has been added, not previously reported for the passivation of GaSb surfaces. Au/n-GaSb Schottky barrier diodes (SBDs) fabricated on the treated material show significant improvement compared to that of the similar SBDs on the as-received material as evidenced by the lower ideality factor (n), higher barrier height (φ b ) and lower contact resistance obtained. Additionally, the reverse leakage current, although not saturating, has been reduced by almost an order of magnitude at −0.2 V. The sample surfaces were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The native oxide, Sb–O, present on the as-received material is effectively removed on treating with ([(NH 4 ) 2 S/(NH 4 ) 2 SO 4 ]+S) and (NH 4 ) 2 S. Analysis of the as-received surface by XPS, prior to and after argon sputtering, suggests that the native oxide layer is ≤8.5 nm.

High temperature oxidation behavior of aluminide on a Ni-based single crystal superalloy in different surface orientations

Institute of Scientific and Technical Information of China (English)

Fahamsyah H.Latief; Koji Kakehi; El-Sayed M.Sherif

2014-01-01

An investigation on oxidation behavior of coated Ni-based single crystal superalloy in different surface orientations has been carried out at 1100 1C. It has been found that the {100} surface shows a better oxidation resistance than the {110} one, which is attributed that the {110}surface had a slightly higher oxidation rate when compared to the {100} surface. The experimental results also indicated that the anisotropic oxidation behavior took place even with a very small difference in the oxidation rates that was found between the two surfaces. The differences of the topologically close packed phase amount and its penetration depth between the two surfaces, including the ratio of α-Al2O3 after 500 h oxidation, were responsible for the oxidation anisotropy.

Modification of polycarbonate surface in oxidizing plasma

Science.gov (United States)

Ovtsyn, A. A.; Smirnov, S. A.; Shikova, T. G.; Kholodkov, I. V.

2017-11-01

The properties of the surface of the film polycarbonate Lexan 8010 were experimentally studied after treatment in a DC discharge plasma in oxygen and air at pressures of 50-300 Pa and a discharge current of 80 mA. The contact angles of wetting and surface energies are measured. The topography of the surface was investigated by atomic force microscopy. The chemical composition of the surface was determined from the FT-IR spectroscopy data in the variant of total internal reflection, as well as X-ray photoelectron spectroscopy. Treatment in the oxidizing plasma leads to a change in morphology (average roughness increases), an increase in the surface energy, and the concentration of oxygen-containing groups (hydroxyl groups, carbonyl groups in ketones or aldehydes and in oxyketones) on the surface of the polymer. Possible reasons for the difference in surface properties of polymer under the action of oxygen and air plasma on it are discussed.

High temperature oxidation behavior of AISI 304L stainless steel—Effect of surface working operations

International Nuclear Information System (INIS)

Ghosh, Swati; Kumar, M. Kiran; Kain, Vivekanand

2013-01-01

Highlights: ► Surface working resulted in thinner oxide on the surface. ► Oxides on machined/ground surfaces richer in Cr, higher in specific resistivity. ► Additional ionic transport process at the metal-oxide for ground sample established. ► Presence of fragmented grains and martensite influenced oxide nature/morphology. - Abstract: The oxidation behavior of grade 304L stainless steel (SS) subjected to different surface finishing (machining and grinding) operations was followed in situ by contact electric resistance (CER) and electrochemical impedance spectroscopy (EIS) measurements using controlled distance electrochemistry (CDE) technique in high purity water (conductivity −1 ) at 300 °C and 10 MPa in an autoclave connected to a recirculation loop system. The results highlight the distinct differences in the oxidation behavior of surface worked material as compared to solution annealed material in terms of specific resistivity and low frequency Warburg impedance. The resultant oxide layer was characterized for (a) elemental analyses by glow discharge optical emission spectroscopy (GDOES) and (b) morphology by scanning electron microscopy (SEM). Oxide layers with higher specific resistivity and chromium content were formed in case of machined and ground conditions. Presence of an additional ionic transport process has also been identified for the ground condition at the metal/oxide interface. These differences in electrochemical properties and distinct morphological features of the oxide layer as a result of surface working were attributed to the prevalence of heavily fragmented grain structure and presence of martensite.

Oxide/water interfaces: how the surface chemistry modifies interfacial water properties

International Nuclear Information System (INIS)

Gaigeot, Marie-Pierre; Sprik, Michiel; Sulpizi, Marialore

2012-01-01

The organization of water at the interface with silica and alumina oxides is analysed using density functional theory-based molecular dynamics simulation (DFT-MD). The interfacial hydrogen bonding is investigated in detail and related to the chemistry of the oxide surfaces by computing the surface charge density and acidity. We find that water molecules hydrogen-bonded to the surface have different orientations depending on the strength of the hydrogen bonds and use this observation to explain the features in the surface vibrational spectra measured by sum frequency generation spectroscopy. In particular, ‘ice-like’ and ‘liquid-like’ features in these spectra are interpreted as the result of hydrogen bonds of different strengths between surface silanols/aluminols and water. (paper)

Oxidative Corrosion of the UO ₂ (001) Surface by Nonclassical Diffusion

Energy Technology Data Exchange (ETDEWEB)

Stubbs, Joanne E.; Biwer, Craig A.; Chaka, Anne M. [Pacific Northwest; Ilton, Eugene S. [Pacific Northwest; Du, Yingge [Pacific Northwest; Bargar, John R. [Stanford Synchrotron; Eng, Peter J.

2017-11-07

Uranium oxide is central to every stage of the nuclear fuel cycle, from mining through fuel fabrication and use, to waste disposal and environmental cleanup. Its chemical and mechanical stability are intricately linked to the concentration of interstitial O atoms within the structure and the oxidation state of U. We have previously shown that during corrosion of the UO2 (111) surface under either 1 atm O2 gas or oxygenated water at room temperature, oxygen interstitials diffuse into the substrate to form a superlattice with three-layer periodicity. In the current study, we present results from surface x-ray scattering that reveal the structure of the oxygen diffusion profile beneath the (001) surface. The first few layers below the surface oscillate strongly in their surface-normal lattice parameters, suggesting preferential interstitial occupation of every other layer below the surface, which is geometrically consistent with the interstitial network that forms below the oxidized (111) surface. Deeper layers are heavily contracted and indicate that the oxidation front penetrates ~52 Å below the (001) surface after 21 days of dry O2 gas exposure at ambient pressure and temperature. X-ray photoelectron spectroscopy indicates U is present as U(IV), U(V), and U(VI).

Influence of carbon monoxide to the surface layer of uranium metal and its oxides

International Nuclear Information System (INIS)

Wang Xiaoling; Fu Yibei; Xie Renshou; Huang Ruiliang

1996-09-01

The surface structures of uranium metal and triuranium octaoxide (U 3 O 8 ) and the influence of carbon monoxide to the surface layers have been studied by X-ray photoelectron spectroscopy (XPS). After exposure to carbon monoxide, contents of oxygen in the surface oxides of uranium metal and U 3 O 8 are decreased and O/U ratios decrease 7.2%, 8.0% respectively. The investigation indicated the surface layers of uranium metal and its oxides were forbidden to further oxidation in the atmosphere of carbon monoxide. (11 refs., 9 figs., 2 tabs.)

Surface Interrogation Scanning Electrochemical Microscopy for a Photoelectrochemical Reaction: Water Oxidation on a Hematite Surface.

Science.gov (United States)

Kim, Jae Young; Ahn, Hyun S; Bard, Allen J

2018-03-06

To understand the pathway of a photoelectrochemical (PEC) reaction, quantitative knowledge of reaction intermediates is important. We describe here surface interrogation scanning electrochemical microscopy for this purpose (PEC SI-SECM), where a light pulse to a photoactive semiconductor film at a given potential generates intermediates that are then analyzed by a tip generated titrant at known times after the light pulse. The improvements were demonstrated for photoelectrochemical water oxidation (oxygen evolution) reaction on a hematite surface. The density of photoactive sites, proposed to be Fe 4+ species, on a hematite surface was successfully quantified, and the photoelectrochemical water oxidation reaction dynamics were elucidated by time-dependent redox titration experiments. The new configuration of PEC SI-SECM should find expanded usage to understand and investigate more complicated PEC reactions with other materials.

Surface Characterization and Electrochemical Oxidation of Metal Doped Uranium Dioxide

Energy Technology Data Exchange (ETDEWEB)

Lee, Jeongmook; Kim, Jandee; Youn, Young-Sang; Kim, Jong-Goo; Ha, Yeong-Keong; Kim, Jong-Yun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

Trivalent element in UO{sub 2} matrix makes the oxygen vacancy from loss of oxygen for charge compensation. Tetravalent element alters lattice parameter of UO{sub 2} due to diameter difference between the tetravalent element and replaced U. These structural changes have significant effect on not only relevant fuel performance but also the kinetics of fuel oxidation. Park and Olander explained the stabilization of Ln (III)-doped UO{sub 2} against oxidation based on oxygen potential calculations. In this work, we have been investigated the effect of Gd{sup 3+} and Th{sup 4+} doping on the UO{sub 2} structure with Raman spectroscopy and X-ray diffraction to characterize the surface structure of nuclear fuel material. For Gd doped UO{sub 2}, its electrochemical oxidation behaviors are also investigated. The Gd and Th doped uranium dioxide solid solution pellets with various doping level were investigated by XRD, Raman spectroscopy, SEM, electrochemical experiments to investigate surface structure and electro chemical oxidation behaviors. The lattice parameter evaluated from XRD spectra indicated the formation of solid solutions. Raman spectra showed the existence of the oxygen vacancy. SEM images showed the grain structure on the surface of Gd doped uranium dioxide depending on doping level and oxygen-to-metal ratio.

Surface functionalization of carbon nanofibers by sol-gel coating of zinc oxide

Energy Technology Data Exchange (ETDEWEB)

Shao Dongfeng [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China); Changzhou Textile Garment Institute, Changzhou 213164 (China); Wei Qufu [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China)], E-mail: qfwei@jiangnan.edu.cn; Zhang Liwei; Cai Yibing; Jiang Shudong [Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University, Wuxi 214122 (China)

2008-08-15

In this paper the functional carbon nanofibers were prepared by the carbonization of ZnO coated PAN nanofibers to expand the potential applications of carbon nanofibers. Polyacrylonitrile (PAN) nanofibers were obtained by electrospinning. The electrospun PAN nanofibers were then used as substrates for depositing the functional layer of zinc oxide (ZnO) on the PAN nanofiber surfaces by sol-gel technique. The effects of coating, pre-oxidation and carbonization on the surface morphology and structures of the nanofibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM), respectively. The results of SEM showed a significant increase of the size of ZnO nanograins on the surface of nanofibers after the treatments of coating, pre-oxidation and carbonization. The observations by SEM also revealed that ZnO nanoclusters were firmly and clearly distributed on the surface of the carbon nanofibers. FTIR examination also confirmed the deposition of ZnO on the surface of carbon nanofibers. The XRD analysis indicated that the crystal structure of ZnO nanograins on the surface of carbon nanofibers.

Oxidation-reduction induced roughening of platinum (111) surface

International Nuclear Information System (INIS)

You, H.; Nagy, Z.

1993-06-01

Platinum (111) single crystal surface was roughened by repeated cycles of oxidation and reduction to study dynamic evolution of surface roughening. The interface roughens progressively upon repeated cycles. The measured width of the interface was fit to an assumed pow law, W ∼t β , with β = 0.38(1). The results are compared with a simulation based on a random growth model. The fraction of the singly stepped surface apparently saturates to 0. 25 monolayer, which explains the apparent saturation to a steady roughness observed in previous studies

Biomimetic PDMS-hydroxyurethane terminated with catecholic moieties for chemical grafting on transition metal oxide-based surfaces

Science.gov (United States)

de Aguiar, Kelen R.; Rischka, Klaus; Gätjen, Linda; Noeske, Paul-Ludwig Michael; Cavalcanti, Welchy Leite; Rodrigues-Filho, Ubirajara P.

2018-01-01

The aim of this work was to synthesize a non-isocyanate poly(dimethylsiloxane) hydroxyurethane with biomimetic terminal catechol moieties, as a candidate for inorganic and metallic surface modification. Such surface modifier is capable to strongly attach onto metallic and inorganic substrates forming layers and, in addition, providing water-repellent surfaces. The non-isocyanate route is based on carbon dioxide cycloaddition into bis-epoxide, resulting in a precursor bis(cyclic carbonate)-polydimethylsiloxane (CCPDMS), thus fully replacing isocyanate in the manufacture process. A biomimetic approach was chosen with the molecular composition being inspired by terminal peptides present in adhesive proteins of mussels, like Mefp (Mytilus edulis foot protein), which bear catechol moieties and are strong adhesives even under natural and saline water. The catechol terminal groups were grafted by aminolysis reaction into a polydimethylsiloxane backbone. The product, PDMSUr-Dopamine, presented high affinity towards inhomogeneous alloy surfaces terminated by native oxide layers as demonstrated by quartz crystal microbalance (QCM-D), as well as stability against desorption by rinsing with ethanol. As revealed by QCM-D, X-ray photoelectron spectroscopy (XPS) and computational studies, the thickness and composition of the resulting nanolayers indicated an attachment of PDMSUr-Dopamine molecules to the substrate through both terminal catechol groups, with the adsorbate exposing the hydrophobic PDMS backbone. This hypothesis was investigated by classical molecular dynamic simulation (MD) of pure PDMSUr-Dopamine molecules on SiO2 surfaces. The computationally obtained PDMSUr-Dopamine assembly is in agreement with the conclusions from the experiments regarding the conformation of PDMSUr-Dopamine towards the surface. The tendency of the terminal catechol groups to approach the surface is in agreement with proposed model for the attachment PDMSUr-Dopamine. Remarkably, the versatile

First principles studies of complex oxide surfaces and interfaces

International Nuclear Information System (INIS)

Noguera, Claudine; Finocchi, Fabio; Goniakowski, Jacek

2004-01-01

Oxides enter our everyday life and exhibit an impressive variety of physical and chemical properties. The understanding of their behaviour, which is often determined by the electronic and atomic structures of their surfaces and interfaces, is a key question in many fields, such as geology, environmental chemistry, catalysis, thermal coatings, microelectronics, and bioengineering. In the last decade, first principles methods, mainly those based on the density functional theory, have been frequently applied to study complex oxide surfaces and interfaces, complementing the experimental observations. In this work, we discuss some of these contributions, with emphasis on several issues that are especially important when dealing with oxides: the local electronic structure at interfaces, and its connection with chemical reactivity; the charge redistribution and the bonding variations, in relation to screening properties; and the possibility of bridging the gap between model and real systems by taking into account the chemical environments and the effect of finite temperatures, and by performing simulations on systems of an adequate (large) size

Adsorption and revaporisation studies on iodine oxide aerosols deposited on containment surface materials in LWR

Energy Technology Data Exchange (ETDEWEB)

Tietze, S.; Foreman, M.R.StJ.; Ekberg, C. [Chalmers Univ. of Technology, Goeteborg (Sweden); Kaerkelae, T.; Auvinen, A.; Tapper, U.; Lamminmaeki, S.; Jokiniemi, J. [VTT Technical Research Centre of Finland, Espoo (Finland)

2012-12-15

During a hypothetical severe nuclear accident, the radiation field will be very high in the nuclear reactor containment building. As a result gaseous radiolysis products will be formed. Elemental iodine can react in the gaseous phase with ozone to form solid iodine oxide aerosol particles (iodine oxide). Within the AIAS (Adsorption of Iodine oxide Aerosols on Surfaces) project the interactions of iodine oxide (IOx) aerosols with common containment surface materials were investigated. Common surface materials in Swedish and Finnish LWRs are Teknopox Aqua V A paint films and metal surfaces such as Cu, Zn, Al and SS, as well as Pt and Pd surfaces from hydrogen recombiners. Non-radioactive and {sup 131}I labelled iodine oxide aerosols were produced with the EXSI CONT facility from elemental iodine and ozone at VTT Technical Research Centre of Finland. The iodine oxide deposits were analysed with microscopic and spectroscopic measurement techniques to identify the kind of iodine oxide formed and if a chemical conversion on the different surface materials occurs. The revaporisation behaviour of the deposited iodine oxide aerosol particles from the different surface materials was studied under the influence of heat, humidity and gamma irradiation at Chalmers University of Technology, Sweden. Studies on the effects of humidity were performed using the FOMICAG facility, while heat and irradiation experiments were performed in a thermostated heating block and with a gammacell 22 having a dose rate of 14 kGy/h. The revaporisation losses were measured using a HPGe detector. The revaporisated {sup 131}I species from the surfaces were chemically tested for elemental iodine formation. The parameter dominating the degradation of the produced iodine oxide aerosols was humidity. Cu and Zn surfaces were found to react with iodine from the iodine oxide aerosols to form iodides, while no metal iodides were detected for Al and SS samples. Most of the iodine oxide aerosols are assumed to

Mechanism of glucose electrochemical oxidation on gold surface

KAUST Repository

Pasta, Mauro; La Mantia, Fabio; Cui, Yi

2010-01-01

The complex oxidation of glucose at the surface of gold electrodes was studied in detail in different conditions of pH, buffer and halide concentration. As observed in previous studies, an oxidative current peak occurs during the cathodic sweep showing a highly linear dependence on glucose concentration, when other electrolyte conditions are unchanged. The effect of the different conditions on the intensity of this peak has stressed the limitations of the previously proposed mechanisms. A mechanism able to explain the presence of this oxidative peak was proposed. The mechanism takes into account ion-sorption and electrochemical adsorption of OH-, buffer species (K2HPO4/KH2PO4) and halides. © 2010 Elsevier Ltd. All rights reserved.

Mechanism of glucose electrochemical oxidation on gold surface

KAUST Repository

Pasta, Mauro

2010-08-01

The complex oxidation of glucose at the surface of gold electrodes was studied in detail in different conditions of pH, buffer and halide concentration. As observed in previous studies, an oxidative current peak occurs during the cathodic sweep showing a highly linear dependence on glucose concentration, when other electrolyte conditions are unchanged. The effect of the different conditions on the intensity of this peak has stressed the limitations of the previously proposed mechanisms. A mechanism able to explain the presence of this oxidative peak was proposed. The mechanism takes into account ion-sorption and electrochemical adsorption of OH-, buffer species (K2HPO4/KH2PO4) and halides. © 2010 Elsevier Ltd. All rights reserved.

Iron oxidation kinetics and phosphorus immobilization at the groundwater-surface water interface

Science.gov (United States)

van der Grift, Bas; Rozemeijer, Joachim; Griffioen, Jasper; van der Velde, Ype

2014-05-01

Eutrophication of freshwater environments following diffuse nutrient loads is a widely recognized water quality problem in catchments. Fluxes of non-point P sources to surface waters originate from surface runoff and flow from soil water and groundwater into surface water. The availability of P in surface waters is controlled strongly by biogeochemical nutrient cycling processes at the soil-water interface. The mechanisms and rates of the iron oxidation process with associated binding of phosphate during exfiltration of anaerobic Fe(II) bearing groundwater are among the key unknowns in P retention processes in surface waters in delta areas where the shallow groundwater is typically pH-neutral to slightly acid, anoxic, iron-rich. We developed an experimental field set-up to study the dynamics in Fe(II) oxidation and mechanisms of P immobilization at the groundwater-surface water interface in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. The exfiltrating groundwater was captured in in-stream reservoirs constructed in the ditch. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and ditch water, we quantified Fe(II) oxidation kinetics and P immobilization processes across the seasons. This study showed that seasonal changes in climatic conditions affect the Fe(II) oxidation process. In winter time the dissolved iron concentrations in the in-stream reservoirs reached the levels of the anaerobic groundwater. In summer time, the dissolved iron concentrations of the water in the reservoirs are low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into the reservoirs. Higher discharges, lower temperatures and lower pH of the exfiltrated groundwater in winter compared to summer shifts the location of the redox transition zone

Novel exchange mechanisms in the surface diffusion of oxides

International Nuclear Information System (INIS)

Harris, Duncan J; Lavrentiev, Mikhail Yu; Harding, John H; Allan, Neil L; Purton, John A

2004-01-01

We use temperature-accelerated dynamics to show the importance of exchange mechanisms in surface diffusion and growth of simple oxides. Such mechanisms can dominate transport processes both on terraces and steps for both homoepitaxial and heteroepitaxial growth. We suggest that the mixing inevitable when an exchange mechanism is present must be considered when attempts are made to grow sharp interfaces in oxide nanostructures. (letter to the editor)

Surface Mn(II) oxidation actuated by a multicopper oxidase in a soil bacterium leads to the formation of manganese oxide minerals.

Science.gov (United States)

Zhang, Zhen; Zhang, Zhongming; Chen, Hong; Liu, Jin; Liu, Chang; Ni, Hong; Zhao, Changsong; Ali, Muhammad; Liu, Fan; Li, Lin

2015-06-03

In this manuscript, we report that a bacterial multicopper oxidase (MCO266) catalyzes Mn(II) oxidation on the cell surface, resulting in the surface deposition of Mn(III) and Mn(IV) oxides and the gradual formation of bulky oxide aggregates. These aggregates serve as nucleation centers for the formation of Mn oxide micronodules and Mn-rich sediments. A soil-borne Escherichia coli with high Mn(II)-oxidizing activity formed Mn(III)/Mn(IV) oxide deposit layers and aggregates under laboratory culture conditions. We engineered MCO266 onto the cell surfaces of both an activity-negative recipient and wild-type strains. The results confirmed that MCO266 governs Mn(II) oxidation and initiates the formation of deposits and aggregates. By contrast, a cell-free substrate, heat-killed strains, and intracellularly expressed or purified MCO266 failed to catalyze Mn(II) oxidation. However, purified MCO266 exhibited Mn(II)-oxidizing activity when combined with cell outer membrane component (COMC) fractions in vitro. We demonstrated that Mn(II) oxidation and aggregate formation occurred through an oxygen-dependent biotic transformation process that requires a certain minimum Mn(II) concentration. We propose an approximate electron transfer pathway in which MCO266 transfers only one electron to convert Mn(II) to Mn(III) and then cooperates with other COMC electron transporters to transfer the other electron required to oxidize Mn(III) to Mn(IV).

NRC Information No. 88-98: Electrical relay degradation caused by oxidation of contact surfaces

International Nuclear Information System (INIS)

Rossi, C.E.

1992-01-01

The NRC staff was recently informed by Clinton Power Station that a reactor scram on June 24, 1988, was caused by an electrical relay failure from oxide buildup on relay contact surfaces. Other information on relay failure from contact oxidation indicates that this problem may be more prevalent than previously thought. For example, a July 17, 1988, 10 CFR Part 21 report from Palo Verde, Unit 2, reported relay failures from contact oxidation that were due to the low current application of the relays. The relay contact surfaces in both of these examples are silver-nickel alloys, and both applications were for low current (i.e., milli-ampere current). Electrical relay contacts made of silver-nickel or silver-cadmium alloys will oxidize (tarnish) when used in low current applications because of the absence of contact surface sparking from the typical relay contact ''making and breaking'' functions. The sparking in the contact surfaces promotes a self-cleaning mechanism that reduces the tarnish buildup on the silver-nickel or silver-cadmium contacts. Discussions with one relay manufacturer revealed that the normal industry practice for low current circuit applications is either to use a contact surface material that will not oxidize or to compensate for the oxidation by increased maintenance activities to ensure reliability. The applied voltage may also influence contact oxidation

Friction stir processed Al - Metal oxide surface composites: Anodization and optical appearance

DEFF Research Database (Denmark)

Gudla, Visweswara Chakravarthy; Jensen, Flemming; Canulescu, Stela

2014-01-01

Multiple-pass friction stir processing (FSP) was employed to impregnate metal oxide (TiO2, Y2O3 and CeO2) particles into the surface of an Aluminium alloy. The surface composites were then anodized in a sulphuric acid electrolyte. The effect of anodizing parameters on the resulting optical...... dark to greyish white. This is attributed to the localized microstructural and morphological differences around the metal oxide particles incorporated into the anodic alumina matrix. The metal oxide particles in the FSP zone electrochemically shadowed the underlying Al matrix and modified the local...

Enhanced biogenic emissions of nitric oxide and nitrous oxide following surface biomass burning

Science.gov (United States)

Anderson, Iris C.; Levine, Joel S.; Poth, Mark A.; Riggan, Philip J.

1988-01-01

Recent measurements indicate significantly enhanced biogenic soil emissions of both nitric oxide (NO) and nitrous oxide (N2O) following surface burning. These enhanced fluxes persisted for at least six months following the burn. Simultaneous measurements indicate enhanced levels of exchangeable ammonium in the soil following the burn. Biomass burning is known to be an instantaneous source of NO and N2O resulting from high-temperature combustion. Now it is found that biomass burning also results in significantly enhanced biogenic emissions of these gases, which persist for months following the burn.

Effects of sucrose on rFVIIa aggregation and methionine oxidation

DEFF Research Database (Denmark)

Soenderkaer, Susanne; Carpenter, John F; van de Weert, Marco

2004-01-01

The aim of this study was to characterize the effects of sucrose on the stability of recombinant factor VIIa (rFVIIa), with special emphasis on aggregation and methionine oxidation, as well as to investigate the impact of various environmental conditions on the rFVIIa conformation. The stability...... of rFVIIa was studied at pH 5. Aggregation was monitored using size exclusion high-performance liquid chromatography (SE-HPLC), whereas formation of methionine oxidation products was measured by reversed-phase high-performance liquid chromatography (RP-HPLC). Fourier transform infrared (FTIR...... the protein's surface, which shifts the protein molecular population away from expanded aggregation competent species and toward the compact native state, is thought to account for these observations. rFVIIa is sensitive to methionine oxidation; two mono-oxidized and one di-oxidized product were formed upon...

Poly(organo phosphazene) nanoparticles surface modified with poly(ethylene oxide).

Science.gov (United States)

Vandorpe, J; Schacht, E; Stolnik, S; Garnett, M C; Davies, M C; Illum, L; Davis, S S

1996-10-05

The use of biodegradable derivatives of poly(organo phosphazenes) for the preparation of nanoparticles and their surface modification with the novel poly(ethylene oxide) derivative of poly(organo phosphazene) has been assessed using a range of in vitro characterization methods. The nanoparticles were produced by the precipitation solvent evaporation method from the derivative co-substituted with phenylalanine and glycine ethyl ester side groups. A reduction in particle size to less than 200 nm was achieved by an increase in pH of the preparation medium. The formation (and colloidal stability) of these nanoparticles seems to be controlled by two opposite effects: attractive hydrophobic interactions between phenylalanine ester groups and electrostatic repulsions arising from the carboxyl groups formed due to (partial) hydrolysis of the ester bond(s) at the high pH of the preparation medium. The poly[(glycine ethyl ester)phosphazene] derivative containing 5000-Da poly(ethylene oxide) as 5% of the side groups was used for the surface modification of nanoparticles. Adsorbed onto the particles, the polymer produced a thick coating layer of approximately 35 nm. The coated nanoparticles exhibited reduced surface negative potential and improved colloidal stability toward electrolyte-induced flocculation, relative to the uncoated system. However, the steric stabilization provided was less effective than that of a Poloxamine 908 coating. This difference in effectiveness of the steric stabilization might indicate that, although both the stabilizing polymers possess a 5000-Da poly(ethylene oxide) moiety, there is a difference in the arrangements of these poly(ethylene oxide) chains at the particle surface. (c) 1996 John Wiley & Sons, Inc.

Microarc Oxidation of Product Surfaces without Using a Bath

Directory of Open Access Journals (Sweden)

V. K. Shatalov

2015-01-01

Full Text Available While using an electrochemical method to cover the large-sized work-pieces, units, and products up to 6 м3 by protective coating, there is a certain difficulty to apply traditional anodizing techniques in a plating vat, and it is necessary to find various processing techniques.To use the existing micro-arc oxide coating (MOC methods for work-pieces of various forms and sizes in a plating vat is complicated in case it is required to provide oxide layers in separate places rather than over entire surface of a work-piece. The challenge is to treat flat surfaces in various directions, external and internal surfaces of rotation bodies, profiled surfaces, intersections, closed and through holes, pipes, as well as spline and thread openings for ensuring anti-seize properties in individual or small-scale production to meet technical requirements and operational properties of products.A design of tools to provide MOC-process of all possible surfaces of various engineering box-type products depends on many factors and can be considerably different even when processing the surfaces of the same forms. An attachment to be used is fixed directly on a large-sized design (a work-piece, a product or fastened in the special tool. The features of technological process, design shape, and arrangement of the processed surfaces define a fastening method of the attachment. Therefore it is necessary to pay much attention to a choice of the processing pattern and a design of tools.The Kaluga-branch of Bauman Moscow State Technical University is an original proposer of methods to form MOC-coatings on the separate surfaces of large-sized work-pieces using the moved and stationary electrodes to solve the above listed tasks.The following results of work will have an impact on development of the offered processing methods and their early implementation in real production:1. To provide oxide coatings on the surfaces of large-sized products or assemblies in a single or small

Analysis of anti-condensation mechanism on superhydrophobic anodic aluminum oxide surface

International Nuclear Information System (INIS)

Wu, Yanpeng; Zhang, Chaoying

2013-01-01

Wetting theory about superhydrophobic surfaces reveals that hydrophobicity of surfaces has great relationship with surface roughness and surface free energy. Adopt electrochemical plus fluorine silane modified method to prepare superhydrophobic surface on anodic aluminum oxide surface, which not only enhances surface roughness, but also reduces surface free energy, even the static contact angle can reach 159.2° and anti-condensation is authenticated. Based on the experimental findings, analyze the reason of anti-condensation on superhydrophobic surfaces: one is that the density of droplets formed on superhydrophobic surfaces is low and the number of droplets is little; the other is bigger static contact angle and smaller rolling angle on superhydrophobic surfaces make droplets easy to detach on smaller tilt angle. This research can solve some condensation problems of equipment using in HVAC systems, such as heat exchangers in air conditioning system, cold radiation boards, air supply outlets, and so on. Highlights: • Prepare superhydrophobic surface on anodic aluminum oxide surface. • Analyze the reason of anti-condensation on superhydrophobic surfaces. • The density of droplets formed on superhydrophobic surfaces is low. • Droplets on superhydrophobic surfaces are easy to detach. • This research can solve some problems of equipment using in HVAC systems

Native fruit traits may mediate dispersal competition between native and non-native plants

Directory of Open Access Journals (Sweden)

Clare Aslan

2012-02-01

Full Text Available Seed disperser preferences may mediate the impact of invasive, non-native plant species on their new ecological communities. Significant seed disperser preference for invasives over native species could facilitate the spread of the invasives while impeding native plant dispersal. Such competition for dispersers could negatively impact the fitness of some native plants. Here, we review published literature to identify circumstances under which preference for non-native fruits occurs. The importance of fruit attraction is underscored by several studies demonstrating that invasive, fleshy-fruited plant species are particularly attractive to regional frugivores. A small set of studies directly compare frugivore preference for native vs. invasive species, and we find that different designs and goals within such studies frequently yield contrasting results. When similar native and non-native plant species have been compared, frugivores have tended to show preference for the non-natives. This preference appears to stem from enhanced feeding efficiency or accessibility associated with the non-native fruits. On the other hand, studies examining preference within existing suites of co-occurring species, with no attempt to maximize fruit similarity, show mixed results, with frugivores in most cases acting opportunistically or preferring native species. A simple, exploratory meta-analysis finds significant preference for native species when these studies are examined as a group. We illustrate the contrasting findings typical of these two approaches with results from two small-scale aviary experiments we conducted to determine preference by frugivorous bird species in northern California. In these case studies, native birds preferred the native fruit species as long as it was dissimilar from non-native fruits, while non-native European starlings preferred non-native fruit. However, native birds showed slight, non-significant preference for non-native fruit

Methanol Oxidation on Model Elemental and Bimetallic Transition Metal Surfaces

DEFF Research Database (Denmark)

Tritsaris, G. A.; Rossmeisl, J.

2012-01-01

Direct methanol fuel cells are a key enabling technology for clean energy conversion. Using density functional theory calculations, we study the methanol oxidation reaction on model electrodes. We discuss trends in reactivity for a set of monometallic and bimetallic transition metal surfaces, flat...... sites on the surface and to screen for novel bimetallic surfaces of enhanced activity. We suggest platinum copper surfaces as promising anode catalysts for direct methanol fuel cells....

Non-activated high surface area expanded graphite oxide for supercapacitors

Energy Technology Data Exchange (ETDEWEB)

Vermisoglou, E.C.; Giannakopoulou, T.; Romanos, G.E.; Boukos, N.; Giannouri, M. [Institute of Nanoscience and Nanotechnology “Demokritos”, 153 43 Ag. Paraskevi, Attikis (Greece); Lei, C.; Lekakou, C. [Division of Mechanical, Medical, and Aerospace Engineering, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH (United Kingdom); Trapalis, C., E-mail: c.trapalis@inn.demokritos.gr [Institute of Nanoscience and Nanotechnology “Demokritos”, 153 43 Ag. Paraskevi, Attikis (Greece)

2015-12-15

Graphical abstract: - Highlights: • One-step exfoliation and reduction of graphite oxide via microwave irradiation. • Effect of pristine graphite (type, flake size) on the microwave expanded material. • Effect of pretreatment and oxidation cycles on the produced expanded material. • Expanded graphene materials with high BET surface areas (940 m{sup 2}/g–2490 m{sup 2}/g). • Non-activated graphene based materials suitable for supercapacitors. - Abstract: Microwave irradiation of graphite oxide constitutes a facile route toward production of reduced graphene oxide, since during this treatment both exfoliation and reduction of graphite oxide occurs. In this work, the effect of pristine graphite (type, size of flakes), pretreatment and oxidation cycles on the finally produced expanded material was examined. All the types of graphite that were tested afforded materials with high BET surface areas ranging from 940 m{sup 2}/g to 2490 m{sup 2}/g, without intervening an activation stage at elevated temperature. SEM and TEM images displayed exfoliated structures, where the flakes were significantly detached and curved. The quality of the reduced graphene oxide sheets was evidenced both by X-ray photoelectron spectroscopy and Raman spectroscopy. The electrode material capacitance was determined via electrochemical impedance spectroscopy and cyclic voltammetry. The materials with PEDOT binder had better performance (∼97 F/g) at low operation rates while those with PVDF binder performed better (∼20 F/g) at higher rates, opening up perspectives for their application in supercapacitors.

Synchrotron photoemission spectroscopy study of ammonium hydroxide etching to prepare well-ordered GaAs(1 0 0) surfaces

International Nuclear Information System (INIS)

Lebedev, Mikhail V.; Ensling, David; Hunger, Ralf; Mayer, Thomas; Jaegermann, Wolfram

2004-01-01

Synchrotron-induced photoelectron spectroscopy was used to investigate the native-oxide-covered GaAs(1 0 0) surface and changes induced by etching with aqueous ammonia solution and by annealing in vacuum. The etching step removes arsenic and gallium oxides from the surface and the surface gets covered by elemental arsenic and tiny amounts of gallium suboxide. The surface oxygen content is reduced by an order of magnitude after etching, whereas the surface carbon content is somewhat increased. Annealing of this surface at 450 deg. C results in the disappearance of elemental arsenic and a considerable decrease in surface carbon and oxygen contents. The valence band spectra exhibit clear features typical for As-terminated GaAs(1 0 0) surfaces, as also obtained after As decapping

Nanomorphology Effects in Semiconductors with Native Ferromagnetism: Hierarchical Europium (II) Oxide Tubes Prepared via a Topotactic Nanostructure Transition.

Science.gov (United States)

Trepka, Bastian; Erler, Philipp; Selzer, Severin; Kollek, Tom; Boldt, Klaus; Fonin, Mikhail; Nowak, Ulrich; Wolf, Daniel; Lubk, Axel; Polarz, Sebastian

2018-01-01

Semiconductors with native ferromagnetism barely exist and defined nanostructures are almost unknown. This lack impedes the exploration of a new class of materials characterized by a direct combination of effects on the electronic system caused by quantum confinement effects with magnetism. A good example is EuO for which currently no reliable routes for nanoparticle synthesis can be established. Bottom-up approaches applicable to other oxides fail because of the labile oxidation state +II. Instead of targeting a direct synthesis, the two steps-"structure control" and "chemical transformation"-are separated. The generation of a transitional, hybrid nanophase is followed by its conversion into EuO under full conservation of all morphological features. Hierarchical EuO materials are now accessible in the shape of oriented nanodisks stacked to tubular particles. Magnetically, the coupling of either vortex or onion states has been found. An unexpected temperature dependence is governed by thermally activated transitions between these states. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Universality in Oxygen Evolution Electrocatalysis on Oxide Surfaces

DEFF Research Database (Denmark)

Man, Isabela Costinela; Su, Hai-Yan; Vallejo, Federico Calle

2011-01-01

with the computational standard hydrogen electrode (SHE) model. We showed that by the discovery of a universal scaling relation between the adsorption energies of HOO* vs HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano......Trends in electrocatalytic activity of the oxygen evolution reaction (OER) are investigated on the basis of a large database of HO* and HOO* adsorption energies on oxide surfaces. The theoretical overpotential was calculated by applying standard density functional theory in combination...

Oxidation and reduction kinetics of eutectic SnPb, InSn, and AuSn: a knowledge base for fluxless solder bonding applications

DEFF Research Database (Denmark)

Kuhmann, Jochen Friedrich; Preuss, A.; Adolphi, B.

1998-01-01

: (1) SnPb; (2) InSn; (3) AuSn. The studies of the oxidation kinetics show that the growth of the native oxide, which covers the solder surfaces from the start of all soldering operations is self-limiting. The rate of oxidation on the molten, metallic solder surfaces is significantly reduced...... and reduction kinetics, are applied to flip-chip (FC) bonding experiments in vacuum with and without the injection of H2. Wetting in vacuum is excellent but the self-alignment during flip-chip soldering is restricted. The desired, perfectly self-aligned FC-bonds have been only achieved, using evaporated...

Determination of surface oxide compositions on Alloy 600 using Rutherford backscattering

International Nuclear Information System (INIS)

Hanson, A.L.; Kraner, H.W.

1984-01-01

The surface composition of oxides formed on Alloy 600 under conditions similar to those in the primary side of PWR heat exchangers has been studied as a function of potential using Rutherford backscattering and proton inelastic scattering. Electropolished samples of Alloy 600 were exposed at several potentials to a solution of 0.18M H 3 BO 3 (2000ppm B) with 0.21mM LiOH (1.5ppm Li) at 300 0 C for 450 hours. The potentials relative to an internal hydrogen electrode ranged from -.09 to 750 mV. RBS analysis showed little or no oxide formation on samples exposed at 0 mV. Above 0 mV oxide layers formed whose thicknesses increased with potential. In addition the RBS showed a significantly enhanced concentration of aluminum and silicon in oxide. Both the oxygen and the sum of the aluminum and silicon content appeared to maintain a fixed surface concentration independent of the oxide thickness. Boron and lithium concentrations were analyzed with proton inelastic scattering. No lithium was detected in any sample. The boron concentration was found to follow the thickness of the oxide

Determination of surface oxide compositions on Alloy 600 using Rutherford backscattering

International Nuclear Information System (INIS)

Hanson, A.L.; Isaacs, H.S.; Kraner, H.W.

1984-01-01

The surface composition of oxides formed on Alloy 600 under conditions similar to those in the primary side of PWR heat exchangers has been studied as a function of potential using Rutherford backscattering and proton inelastic scattering. Electropolished samples of Alloy 600 were exposed at several potentials to a solution of 0.18M H 3 BO 3 (2000 ppM B) with 0.28M LiOH (1.4 ppM Li) at 300 0 C for 450 hours. The potentials relative to an internal hydrogen electrode ranged from -.09 to 750 mV. RBS analysis showed little or no oxide formation on samples exposed at 0 mV. Above 0 mV oxide layers formed whose thicknesses increased with potential. In addition the RBS showed a significantly enhanced concentration of aluminum and silicon in oxide. Both the oxygen and the sum of the aluminum and silicon content appeared to maintain a fixed surface concentration independent of the oxide thickness. Boron and lithium concentration were analyzed with proton inelastic scattering. No lithium was found in any sample. The boron concentration was found to follow the thickness of the oxide

Oxidation characteristics of the electron beam surface-treated Alloy 617 in high temperature helium environments

International Nuclear Information System (INIS)

Lee, Ho Jung; Sah, Injin; Kim, Donghoon; Kim, Hyunmyung; Jang, Changheui

2015-01-01

The oxidation characteristics of the electron beam surface-treated Alloy 617, which has an Al-rich surface layer, were evaluated in high temperature helium environments. Isothermal oxidation tests were performed in helium (99.999% purity) and VHTR-helium (helium of prototypical VHTR chemistry containing impurities like CO, CO 2 , CH 4 , and H 2 ) environments at 900 °C for up to 1000 h. The surface-treated Alloy 617 showed an initial transient oxidation stage followed by the steady-state oxidation in all test environments. In addition, the steady-state oxidation kinetics of the surface-treated Alloy 617 was 2-order of magnitude lower than that of the as-received Alloy 617 in both helium environments as well as in air. The improvement in oxidation resistance was primarily due to the formation of the protective Al 2 O 3 layer on the surface. The weight gain was larger in the order of air, helium, and VHTR-helium, while the parabolic rate constants (k p ) at steady-state were similar for all test environments. In both helium environments, the oxide structure consisted of the outer transition Al 2 O 3 with a small amount of Cr 2 O 3 and inner columnar structured Al 2 O 3 without an internal oxide. In the VHTR-helium environment, where the impurities were added to helium, the initial transient oxidation increased but the steady state kinetics was not affected

Modification of implant material surface properties by means of oxide nano-structured coatings deposition

Science.gov (United States)

Safonov, Vladimir; Zykova, Anna; Smolik, Jerzy; Rogowska, Renata; Lukyanchenko, Vladimir; Kolesnikov, Dmitrii

2014-08-01

The deposition of functional coatings on the metal surface of artificial joints is an effective way of enhancing joint tribological characteristics. It is well-known that nanostructured oxide coatings have specific properties advantageous for future implant applications. In the present study, we measured the high hardness parameters, the adhesion strength and the low friction coefficient of the oxide magnetron sputtered coatings. The corrosion test results show that the oxide coating deposition had improved the corrosion resistance by a factor of ten for both stainless steel and titanium alloy substrates. Moreover, the hydrophilic nature of coated surfaces in comparison with the metal ones was investigated in the tensiometric tests. The surfaces with nanostructured oxide coatings demonstrated improved biocompatibility for in vitro and in vivo tests, attributed to the high dielectric constants and the high values of the surface free energy parameters.

Measuring Forces between Oxide Surfaces Using the Atomic Force Microscope

DEFF Research Database (Denmark)

Pedersen, Henrik Guldberg; Høj, Jakob Weiland

1996-01-01

The interactions between colloidal particles play a major role in processing of ceramics, especially in casting processes. With the Atomic Force Microscope (AFM) it is possible to measure the inter-action force between a small oxide particle (a few micron) and a surface as function of surface...

Synchrotron-based XPS studies of AlGaN and GaN surface chemistry and its relationship to ion sensor behaviour

Energy Technology Data Exchange (ETDEWEB)

Khir, Farah Liyana Muhammad, E-mail: 21001899@student.uwa.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Myers, Matthew, E-mail: Matt.Myers@csiro.au [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); CSIRO Earth Science and Resource Engineering, Kensington, Western Australia 6151 (Australia); Podolska, Anna [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Department of Exploration Geophysics, Curtin University of Technology, 26 Dick Perry Avenue, ARRC, Kensington, Western Australia 6151 (Australia); Sanders, Tarun Maruthi [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Baker, Murray V., E-mail: murray.baker@uwa.edu.au [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Nener, Brett D., E-mail: brett.nener@uwa.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Parish, Giacinta, E-mail: giacinta.parish@uwa.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia)

2014-09-30

Highlights: • Soft X-ray was used to study the surface chemistry of GaN and AlGaN. • The surface chemistry and sensor behaviour were investigated. • The oxide of aluminum is significantly more reactive than gallium. • The Cl{sup −} ions are greater in GaN samples compared to AlGaN samples. - Abstract: Soft X-ray photoelectron spectroscopy was used to investigate the fundamental surface chemistry of both AlGaN and GaN surfaces in the context of understanding the behaviour of AlGaN/GaN heterostructures as chemical field-effect transistor (CHEMFET) ion sensors. AlGaN and GaN samples were subjected to different methods of oxide growth (native oxide and thermally grown oxide) and chemical treatment conditions. Our investigations indicate that the etching of the oxide layer is more pronounced with AlGaN compared to GaN. Also, we observed that chloride ions have a greater tendency to attach to the GaN surface relative to the AlGaN surface. Furthermore, chloride ions are comparatively more prevalent on surfaces treated with 5% HCl acid solution. The concentration of chloride ions is even higher on the HCl treated native oxide surface resulting in a very clear deconvolution of the Cl 2p{sub 1/2} and Cl 2p{sub 3/2} peaks. For GaN and AlGaN surfaces, a linear response (e.g. source-drain current) is typically seen with variation in pH of buffered solutions with constant reference electrode voltage at the surface gate; however, an inverted bath-tub type response (e.g. a maximum at neutral pH and lower values at pH values away from neutral) and a general tendency to negative charge selectivity has been also widely reported. We have shown that our XPS investigations are consistent with the different sensor response reported in the literature for these CHEMFET devices and may help to explain the differing response of these materials.

Nano-oxides to improve the surface properties of ceramic tiles

International Nuclear Information System (INIS)

Rambaldi, E.; Tucci, A.; Esposito, L.; Naldi, D.; Timellini, G.

2010-01-01

The aim of the present work is to realise ceramic tiles with superior surface mechanical characteristics and chemical resistance, by the addition of nano-oxides, such as zirconia and alumina, since such advanced ceramics oxides are well known for their excellent mechanical properties and good resistance to chemical etching. In order to avoid any dangerousness, the nanoparticles were used in form of aqueous suspension and they were sprayed, by airbrush, directly onto the dried ceramic support, before firing. To observe the distribution of the nanoparticles and to optimise the surface treatment, SEM-EDS analyses were carried out on the fired samples. XRD analysis was conducted to assess the phases evolution of the different materials during the firing step. The surface mechanical characteristics of the samples have been evaluated by Vickers hardness and scratch test. In addition, also chemical resistance tests were performed. Microstructural observations allowed to understand how alumina and zirconia nanoparticles acted to improve the surface performances of the modified ceramic tiles. (Author) 20 refs.

Surface chemistry and cytotoxicity of reactively sputtered tantalum oxide films on NiTi plates

Energy Technology Data Exchange (ETDEWEB)

McNamara, K. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Department of Physics & Energy, University of Limerick, Limerick (Ireland); Kolaj-Robin, O.; Belochapkine, S.; Laffir, F. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Gandhi, A.A. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Department of Physics & Energy, University of Limerick, Limerick (Ireland); Tofail, S.A.M., E-mail: tofail.syed@ul.ie [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland); Department of Physics & Energy, University of Limerick, Limerick (Ireland)

2015-08-31

NiTi, an equiatomic alloy containing nickel and titanium, exhibits unique properties such as shape memory effect and superelasticity. NiTi also forms a spontaneous protective titanium dioxide (TiO{sub 2}) layer that allows its use in biomedical applications. Despite the widely perceived biocompatibility there remain some concerns about the sustainability of the alloy's biocompatibility due to the defects in the TiO{sub 2} protective layer and the presence of high amount of sub-surface Ni, which can give allergic reactions. Many surface treatments have been investigated to try to improve both the corrosion resistance and biocompatibility of this layer. For such purposes, we have sputter deposited tantalum (Ta) oxide thin films onto the surface of the NiTi alloy. Despite being one of the promising metals for biomedical applications, Ta, and its various oxides and their interactions with cells have received relatively less attention. The oxidation chemistry, crystal structure, morphology and biocompatibility of these films have been investigated. In general, reactive sputtering especially in the presence of a low oxygen mixture yields a thicker film with better control of the film quality. The sputtering power influenced the surface oxidation states of Ta. Both microscopic and quantitative cytotoxicity measurements show that Ta films on NiTi are biocompatible with little to no variation in cytotoxic response when the surface oxidation state of Ta changes. - Highlights: • Reactive sputtering in low oxygen mixture yields thicker better quality films. • Sputtering power influenced surface oxidation states of Ta. • Cytotoxicity measurements show Ta films on NiTi are biocompatible. • Little to no variation in cytotoxic response when oxidation state changes.

Effect of reacting surface density on the overall graphite oxidation rate

International Nuclear Information System (INIS)

Oh, Chang; Kim, Eung; Lim, Jong; Schultz, Richard; Petti, David

2009-01-01

Graphite oxidation in an air-ingress accident is presently a very important issue for the reactor safety of the very high temperature gas cooled-reactor (VHTR), the concept of the next generation nuclear plant (NGNP) because of its potential problems such as mechanical degradation of the supporting graphite in the lower plenum of the VHTR might lead to core collapse if the countermeasure is taken carefully. The oxidation process of graphite has known to be affected by various factors, including temperature, pressure, oxygen concentration, types of graphite, graphite shape and size, flow distribution, etc. However, our recent study reveals that the internal pore characteristics play very important roles in the overall graphite oxidation rate. One of the main issues regarding graphite oxidation is the potential core collapse problem that may occur following the degradation of graphite mechanical strength. In analyzing this phenomenon, it is very important to understand the relationship between the degree of oxidization and strength degradation. In addition, the change of oxidation rate by graphite oxidation degree characterization by burn-off (ratio of the oxidized graphite density to the original density) should be quantified because graphite strength degradation is followed by graphite density decrease, which highly affects oxidation rates and patterns. Because the density change is proportional to the internal pore surface area, they should be quantified in advance. In order to understand the above issues, the following experiments were performed: (1) Experiment on the fracture of the oxidized graphite and validation of the previous correlations, (2) Experiment on the change of oxidation rate using graphite density and data collection, (3) Measure the BET surface area of the graphite. The experiments were performed using H451 (Great Lakes Carbon Corporation) and IG-110 (Toyo Tanso Co., Ltd) graphite. The reason for the use of those graphite materials is because

The origin of native selenium microparticles during the oxidation of sideritic mudstones in the Veřovice Formation (Outer Western Carpathians

Directory of Open Access Journals (Sweden)

Matýsek Dalibor

2015-08-01

Full Text Available Microparticles of native selenium were detected in weathered sideritic mudstones of the Veřovice Formation (Aptian of the Silesian Unit (Outer Western Carpatians, NE part of the Czech Republic. This mineral forms small needle-like crystals with lengths of up to 20 μm, and is confined to fissures in sideritic mudstones covered by goethite or rarely also by hydrated Mn-oxide minerals. The oxidized sideritic mudstones show zonal structure and resemble the initial stage of the formation of the so-called rattle stones. From the superposition of phase diagrams of selenium and Fe-oxyhydroxides, Fe apparently occupies a large field in which Se(0 and FeOOH and/or Fe(OH3 can co-exist. The reduction of selenites or selenates by pyrite or by any other phase, capable of charge transfer, is likely to have been responsible for the formation of microparticles of native selenium. The crucial factor controlling the origin of these particles is the extremely low solubility of Se(0. The source of Se is not obvious. It can be released in trace concentrations during the weathering of pyrite. Sediments of the Veřovice Formation correspond to the anoxic event OAE1b and accumulation of siderophile elements in similar sediments is very probable. A probable mechanism for the origin of Se microcrystals is gradual crystallization from solution.

Study on the influence of carbon monoxide to the surface oxide layer of uranium metal

International Nuclear Information System (INIS)

Wang Xiaolin; Duan Rongliang; Fu Yibei; Xie Renshou; Zuo Changming; Zhao Chunpei; Chen Hong

1997-01-01

The influence of carbon monoxide to the surface oxide layer of uranium metal has been studied by X-ray photoelectron spectroscopy (XPS) and gas chromatography (GC). Carbon monoxide adsorption on the oxide layer resulted in U4f peak shifting to the lower binding energy. The content of oxygen in the oxide is decreased and the atomic ratio (O/U) is decreased by 7.2%. The amount of carbon dioxide in the atmosphere after the surface reaction is increased by 11.0%. The investigation indicates that the surface layer can prevent the further oxidation uranium metal in the atmosphere of carbon monoxide

Surface Passivation of CIGS Solar Cells Using Gallium Oxide

KAUST Repository

Garud, Siddhartha

2018-02-27

This work proposes gallium oxide grown by plasma-enhanced atomic layer deposition, as a surface passivation material at the CdS buffer interface of Cu(In,Ga)Se2 (CIGS) solar cells. In preliminary experiments, a metal-insulator-semiconductor (MIS) structure is used to compare aluminium oxide, gallium oxide, and hafnium oxide as passivation layers at the CIGS-CdS interface. The findings suggest that gallium oxide on CIGS may show a density of positive charges and qualitatively, the least interface trap density. Subsequent solar cell results with an estimated 0.5 nm passivation layer show an substantial absolute improvement of 56 mV in open-circuit voltage (VOC), 1 mA cm−2 in short-circuit current density (JSC), and 2.6% in overall efficiency as compared to a reference (with the reference showing 8.5% under AM 1.5G).

Study on the surface oxidation resistance of uranium metal in the atmosphere of carbon monoxide

International Nuclear Information System (INIS)

Wang Xiaolin; Fu Yibei; Xie Renshou

1999-01-01

The surface reactions of different layers on uranium metal with carbon monoxide at 25, 80 and 200 degree C are studied by X-ray photoelectron spectroscopy (XPS). The experimental results show that the carbon monoxide is adsorbed on the surface oxide layer of uranium and interacted each other. The content of oxygen in the surface oxide and O/U ratio are decreased with increasing the exposure of carbon monoxide to the surface layer. The effect of reduction on the metal surface is more obviously with a higher temperature and increasing of layer thickness. The investigation indicates the uranium metal has resistance to further oxidation in the atmosphere of carbon monoxide

A method of eliminating the surface defect in low-temperature oxidation powder added UO2 pellet

International Nuclear Information System (INIS)

Yoo, H. S.; Lee, S. J.; Kim, J. I.; Jeon, K. R.; Kim, J. W.

2002-01-01

A study on methods to eliminate surface defect shown in low-temperature oxidation powder added UO 2 pellet has been performed. Powders oxidized at 350 .deg. C for 4 hrs were prepared and mixed with UO 2 powder after crushing them. After being sintered, surfaces of the pellet were inspected both visually and optically. A large number of defects were observed on the surface of the specimens in which low-temperature oxidation powders were directly mixed or master mixed with UO 2 powder while both specimens produced from mixed powders including milled oxidation powders and powders that were milled totally after mixing had clean surfaces. However, optical examination showed considerably large defected pores in the milled oxidation powder added pellet and it was confirmed that the inner defects can be eliminated completely only when milling the entire mixture on UO 2 and low-temperature oxidation powder, but not by crushing only oxidation powder

Influence of surface treatment on the oxidation behavior of zirconium and zircaloy-4

International Nuclear Information System (INIS)

Costa, I.; Ramanathan, L.V.

1986-01-01

The influence of fluoride concentration in surface treatment solutions on the oxidation behavior of Zr and Zircaloy-4 in the temperature range 350-760 0 C have been studied by means of thermogravimetric analysis. Two solutions containing different concentrations of hydrofluoric acid have been used for surface treatments, following which surface roughness measurements were also carried out. The influence of fluoride ion concentration on oxidation behavior has been found to be significant at higher temperatures. (Author) [pt

Iron oxidation kinetics and phosphate immobilization along the flow-path from groundwater into surface water

Science.gov (United States)

van der Grift, B.; Rozemeijer, J. C.; Griffioen, J.; van der Velde, Y.

2014-11-01

The retention of phosphorus in surface waters through co-precipitation of phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich groundwater is not well understood. We developed an experimental field set-up to study Fe(II) oxidation and P immobilization along the flow-path from groundwater into surface water in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and surface water, we investigated Fe(II) oxidation kinetics and P immobilization processes. The oxidation rate inferred from our field measurements closely agreed with the general rate law for abiotic oxidation of Fe(II) by O2. Seasonal changes in climatic conditions affected the Fe(II) oxidation process. Lower pH and lower temperatures in winter (compared to summer) resulted in low Fe oxidation rates. After exfiltration to the surface water, it took a couple of days to more than a week before complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates were much higher. The Fe concentrations in the exfiltrated groundwater were low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into a ditch. While the Fe oxidation rates reduce drastically from summer to winter, P concentrations remained high in the groundwater and an order of magnitude lower in the surface water throughout the year. This study shows very fast immobilization of dissolved P during the initial stage of the Fe(II) oxidation process which results in P-depleted water before Fe(II) is completely depleted. This cannot be explained by surface complexation of phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox gradients

Pyrrolizidine alkaloid variation in Senecio vulgaris populations from native and invasive ranges

Science.gov (United States)

Nguyen, Viet-Thang; Ndihokubwayo, Noel; Ge, Jiwen; Mulder, Patrick P.J.

2017-01-01

Biological invasion is regarded as one of the greatest environmental problems facilitated by globalization. Some hypotheses about the invasive mechanisms of alien invasive plants consider the plant–herbivore interaction and the role of plant defense in this interaction. For example, the “Shift Defense Hypothesis” (SDH) argues that introduced plants evolve higher levels of qualitative defense chemicals and decreased levels of quantitative defense, as they are released of the selective pressures from specialist herbivores but still face attack from generalists. Common groundsel (Senecio vulgaris), originating from Europe, is a cosmopolitan invasive plant in temperate regions. As in other Senecio species, S. vulgaris contains pyrrolizidine alkaloids (PAs) as characteristic qualitative defense compounds. In this study, S. vulgaris plants originating from native and invasive ranges (Europe and China, respectively) were grown under identical conditions and harvested upon flowering. PA composition and concentration in shoot and root samples were determined using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). We investigated the differences between native and invasive S. vulgaris populations with regard to quantitative and qualitative variation of PAs. We identified 20 PAs, among which senecionine, senecionine N-oxide, integerrimine N-oxide and seneciphylline N-oxide were dominant in the roots. In the shoots, in addition to the 4 PAs dominant in roots, retrorsine N-oxide, spartioidine N-oxide and 2 non-identified PAs were also prevalent. The roots possessed a lower PA diversity but a higher total PA concentration than the shoots. Most individual PAs as well as the total PA concentration were strongly positively correlated between the roots and shoots. Both native and invasive S. vulgaris populations shared the pattern described above. However, there was a slight trend indicating lower PA diversity and lower total PA concentration in invasive S. vulgaris

Pyrrolizidine alkaloid variation in Senecio vulgaris populations from native and invasive ranges

Directory of Open Access Journals (Sweden)

Dandan Cheng

2017-08-01

Full Text Available Biological invasion is regarded as one of the greatest environmental problems facilitated by globalization. Some hypotheses about the invasive mechanisms of alien invasive plants consider the plant–herbivore interaction and the role of plant defense in this interaction. For example, the “Shift Defense Hypothesis” (SDH argues that introduced plants evolve higher levels of qualitative defense chemicals and decreased levels of quantitative defense, as they are released of the selective pressures from specialist herbivores but still face attack from generalists. Common groundsel (Senecio vulgaris, originating from Europe, is a cosmopolitan invasive plant in temperate regions. As in other Senecio species, S. vulgaris contains pyrrolizidine alkaloids (PAs as characteristic qualitative defense compounds. In this study, S. vulgaris plants originating from native and invasive ranges (Europe and China, respectively were grown under identical conditions and harvested upon flowering. PA composition and concentration in shoot and root samples were determined using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS. We investigated the differences between native and invasive S. vulgaris populations with regard to quantitative and qualitative variation of PAs. We identified 20 PAs, among which senecionine, senecionine N-oxide, integerrimine N-oxide and seneciphylline N-oxide were dominant in the roots. In the shoots, in addition to the 4 PAs dominant in roots, retrorsine N-oxide, spartioidine N-oxide and 2 non-identified PAs were also prevalent. The roots possessed a lower PA diversity but a higher total PA concentration than the shoots. Most individual PAs as well as the total PA concentration were strongly positively correlated between the roots and shoots. Both native and invasive S. vulgaris populations shared the pattern described above. However, there was a slight trend indicating lower PA diversity and lower total PA concentration in

Alloying Au surface with Pd reduces the intrinsic activity in catalyzing CO oxidation

KAUST Repository

Qian, Kun

2016-03-30

© 2016. Various Au-Pd/SiO2 catalysts with a fixed Au loading but different Au:Pd molar ratios were prepared via deposition-precipitation method followed by H2 reduction. The structures were characterized and the catalytic activities in CO oxidation were evaluated. The formation of Au-Pd alloy particles was identified. The Au-Pd alloy particles exhibit enhanced dispersions on SiO2 than Au particles. Charge transfer from Pd to Au within Au-Pd alloy particles. Isolated Pd atoms dominate the surface of Au-Pd alloy particles with large Au:Pd molar ratios while contiguous Pd atoms dominate the surface of Au-Pd alloy particles with small Au:Pd molar ratios. Few synergetic effect of Au-Pd alloy occurs on catalyzing CO oxidation under employed reaction conditions. Alloying Au with Pd reduces the intrinsic activity in catalyzing CO oxidation, and contiguous Pd atoms on the Au-Pd alloy particles are capable of catalyzing CO oxidation while isolated Pd atoms are not. These results advance the fundamental understandings of Au-Pd alloy surfaces in catalyzing CO oxidation.

Simple quantification of surface carboxylic acids on chemically oxidized multi-walled carbon nanotubes

Science.gov (United States)

Gong, Hyejin; Kim, Seong-Taek; Lee, Jong Doo; Yim, Sanggyu

2013-02-01

The surface of multi-walled carbon nanotube (MWCNT) was chemically oxidized using nitric acid and sulfuric-nitric acid mixtures. Thermogravimetric analysis, transmission electron microscopy and infrared spectroscopy revealed that the use of acid mixtures led to higher degree of oxidation. More quantitative identification of surface carboxylic acids was carried out using X-ray photoelectron spectroscopy (XPS) and acid-base titration. However, these techniques are costly and require very long analysis times to promptly respond to the extent of the reaction. We propose a much simpler method using pH measurements and pre-determined pKa value in order to estimate the concentration of carboxylic acids on the oxidized MWCNT surfaces. The results from this technique were consistent with those obtained from XPS and titration, and it is expected that this simple quantification method can provide a cheap and fast way to monitor and control the oxidation reaction of MWCNT.

Microstructure and optical appearance of anodized friction stir processed Al - Metal oxide surface composites

DEFF Research Database (Denmark)

Gudla, Visweswara Chakravarthy; Jensen, Flemming; Bordo, Kirill

2014-01-01

Multiple-pass friction stir processing (FSP) was employed to impregnate Ti, Y and Ce oxide powders into the surface of an Aluminium alloy. The FSP processed surface composite was subsequently anodized with an aim to develop optical effects in the anodized layer owing to the presence of incorporated...... oxide particles which will influence the scattering of light. This paper presents the investigations on relation between microstructure of the FSP zone and optical appearance of the anodized layer due to incorporation of metal oxide particles and modification of the oxide particles due to the anodizing...

[A method of temperature measurement for hot forging with surface oxide based on infrared spectroscopy].

Science.gov (United States)

Zhang, Yu-cun; Qi, Yan-de; Fu, Xian-bin

2012-05-01

High temperature large forging is covered with a thick oxide during forging. It leads to a big measurement data error. In this paper, a method of measuring temperature based on infrared spectroscopy is presented. It can effectively eliminate the influence of surface oxide on the measurement of temperature. The method can measure the surface temperature and emissivity of the oxide directly using the infrared spectrum. The infrared spectrum is radiated from surface oxide of forging. Then it can derive the real temperature of hot forging covered with the oxide using the heat exchange equation. In order to greatly restrain interference spectroscopy through included in the received infrared radiation spectrum, three interference filter system was proposed, and a group of optimal gap parameter values using spectral simulation were obtained. The precision of temperature measurement was improved. The experimental results show that the method can accurately measure the surface temperature of high temperature forging covered with oxide. It meets the requirements of measurement accuracy, and the temperature measurement method is feasible according to the experiment result.

New data on the Hyrkkoelae U-Cu mineralization: the behaviour of native copper in a natural environment

Energy Technology Data Exchange (ETDEWEB)

Marcos, N. [Helsinki Univ. of Technology, Espoo (Finland); Ahonen, L. [Geological Survey of Finland, Helsinki (Finland)

1999-05-01

The Hyrkkoelae Cu-U mineralisation (SW Finland) is studied as an analogue to the behaviour of copper canister in crystalline bedrock. Uranium-native copper and uranium-copper corrosion products interactions are also addressed in this study. The integration of uranium series disequilibrium (USD) studies gives an estimate of the time-scales of the corrosion processes. The mineral assemblages native copper-copper sulfide, copper sulfides - copper iron sulfides, and native copper-copper oxide (cuprite) occur in open fractures at several depth intervals within granite pegmatites (GP). The surfaces of these open fractures have accumulations of uranophane crystals and other unidentified uranyl compounds. The secondary uranium minerals are mainly distributed around copper sulfide grains. Microscopic intergrowths of copper sulfides and uranyl compounds also have been observed. The surface of the fracture where native copper and cuprite occur is covered with uranium-rich smectite. The very low {sup 234}U/{sup 238}U activity ratio (0.29 - 0.39) in the main uranium fraction in smectite indicates chemical stable conditions (e.g., oxidising) during at least a time period comparable to the half-life of the {sup 234}U isotope (T{sub 1/2} = 2.44 x 10{sup 5} a). Groundwater samples were collected from intervals where copper minerals occur within open fractures. The Eh and pH conditions were measured during long-term pumping (2-4 weeks per sample). Eh was measured both in situ and an the surface using three electrodes (Pt, Au, C). The actual groundwater conditions are oxidising and would not allow the sulfidization of native copper. Sulfidization may be considered as on old phenomenon, older than the precipitation of uranyl phases in the samples. The end of sulfidization may be earlier than the precipitation and/or remobilisation of U(VI) phases in a time span from about 2 x 10{sup 5} years (precipitation of uranophane) to 2.44 x 10{sup 5} (remobilisation of U from smectite). (orig.)

New data on the Hyrkkoelae U-Cu mineralization: the behaviour of native copper in a natural environment

International Nuclear Information System (INIS)

Marcos, N.; Ahonen, L.

1999-05-01

The Hyrkkoelae Cu-U mineralisation (SW Finland) is studied as an analogue to the behaviour of copper canister in crystalline bedrock. Uranium-native copper and uranium-copper corrosion products interactions are also addressed in this study. The integration of uranium series disequilibrium (USD) studies gives an estimate of the time-scales of the corrosion processes. The mineral assemblages native copper-copper sulfide, copper sulfides - copper iron sulfides, and native copper-copper oxide (cuprite) occur in open fractures at several depth intervals within granite pegmatites (GP). The surfaces of these open fractures have accumulations of uranophane crystals and other unidentified uranyl compounds. The secondary uranium minerals are mainly distributed around copper sulfide grains. Microscopic intergrowths of copper sulfides and uranyl compounds also have been observed. The surface of the fracture where native copper and cuprite occur is covered with uranium-rich smectite. The very low 234 U/ 238 U activity ratio (0.29 - 0.39) in the main uranium fraction in smectite indicates chemical stable conditions (e.g., oxidising) during at least a time period comparable to the half-life of the 234 U isotope (T 1/2 = 2.44 x 10 5 a). Groundwater samples were collected from intervals where copper minerals occur within open fractures. The Eh and pH conditions were measured during long-term pumping (2-4 weeks per sample). Eh was measured both in situ and an the surface using three electrodes (Pt, Au, C). The actual groundwater conditions are oxidising and would not allow the sulfidization of native copper. Sulfidization may be considered as on old phenomenon, older than the precipitation of uranyl phases in the samples. The end of sulfidization may be earlier than the precipitation and/or remobilisation of U(VI) phases in a time span from about 2 x 10 5 years (precipitation of uranophane) to 2.44 x 10 5 (remobilisation of U from smectite). (orig.)

Non-Native & Native English Teachers

Directory of Open Access Journals (Sweden)

İrfan Tosuncuoglu

2017-12-01

Full Text Available In many countries the primary (mother tongue language is not English but there is a great demand for English language teachers all over the world. The demand in this field is try to be filled largely by non-native English speaking teachers who have learned English in the country or abroad, or from another non native English peaking teachers. In some countries, particularly those where English speaking is a a sign of status, the students prefer to learn English from a native English speaker. The perception is that a non-native English speaking teacher is a less authentic teacher than a native English speaker and their instruction is not satifactory in some ways. This paper will try to examine the literature to explore whether there is a difference in instructional effectiveness between NNESTs and native English teachers.

Influence of surface oxidation on the radiative properties of ZrB{sub 2}-SiC composites

Energy Technology Data Exchange (ETDEWEB)

Li, Ning, E-mail: lncaep@163.com [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, 621900 (China); Xing, Pifeng; Li, Cui [Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, 621900 (China); Wang, Peng [School of Material Science and Engineering, Shandong University of Technology, Zibo 255049 (China); Jin, Xinxin [College of Materials Science and Engineering, Harbin University of Science and Technology, Harbin 150040 (China); Zhang, Xinghong [Science and Technology on Advanced Composites in Special Environments Laboratory, Harbin Institute of Technology, Harbin 150001 (China)

2017-07-01

Highlights: • Surface component affected radiative properties of ZrB{sub 2}-SiC composites significantly. • Emissivity in long-wave range gradually increased with the thickness of oxide scale. • The surface temperature had a little effect on radiative properties of composites. • Influence of surface roughness on emissivity could be negligible. • Covering the surface with glass is a method for improving radiative properties. - Abstract: The spectral emissivities of ZrB{sub 2}-20 vol.% SiC composites with various surface components of ZrB{sub 2}/SiC (ZS1), silica-rich glass (ZS2) and porous zirconia (ZS3) were measured using infrared spectrometer in the wavelength range from 2.5 to 25.0 μm. The relationship between surface oxidation (associated with surface component, thickness of oxide scale, testing temperature as well as roughness) and the radiative properties of ZrB{sub 2}-SiC composites were investigated systematically. Surface component affected the radiative properties of composites significantly. The total emissivity of ZS1 varied from 0.22 to 0.81 accompanied with surface oxidation in the temperature range 300–900 °C. The emissivity of ZS2 was about 1.5 times as that of ZS3 under the same testing conditions. The oxide scale on specimen surface enhanced the radiative properties especially in terms of short-wave range, and the emissivity in the long-wave range gradually increased with the thickness of oxide scale within a certain range. The influence of testing temperature and surface roughness was also investigated. The testing temperature had a little effect on radiative properties, whereas effect of surface roughness could be negligible.

Surface modification of PLGA nanoparticles to deliver nitric oxide to inhibit Escherichia coli growth

Energy Technology Data Exchange (ETDEWEB)

Reger, Nina A. [Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282 (United States); Meng, Wilson S. [Division of Pharmaceutical Sciences, Duquesne University, Pittsburgh, PA 15282 (United States); Gawalt, Ellen S., E-mail: gawalte@duq.edu [Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282 (United States); McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15219 (United States)

2017-04-15

Highlights: • Thin film functionalized PLGA nanoparticles were modified to release nitric oxide from an s-nitrosothiol donor. • The nitric oxide modified nanoparticles were bacteriostatic against Escherichia coli. • The nitric oxide modified nanoparticles increased the effectiveness of tetracycline against Escherichia coli. • The modified nitric oxide nanoparticles did not exhibit cytotoxic effects against fibroblasts. - Abstract: Polymer nanoparticles consisting of poly (DL-lactic-co-glycolic acid) were surface functionalized to deliver nitric oxide. These biodegradable and biocompatible nanoparticles were modified with an S-nitrosothiol molecule, S-nitrosocysteamine, as the nitric oxide delivery molecule. S-nitrosocysteamine was covalently immobilized on the nanoparticle surface using small organic molecule linkers and carbodiimide coupling. Nanoparticle size, zeta potential, and morphology were determined using dynamic light scattering and scanning electron microscopy, respectively. Subsequent attachment of the S-nitrosothiol resulted in a nitric oxide release of 37.1 ± 1.1 nmol per milligram of nanoparticles under physiological conditions. This low concentration of nitric oxide reduced Escherichia coli culture growth by 31.8%, indicating that the nitric oxide donor was effective at releasing nitric oxide even after attachment to the nanoparticle surface. Combining the nitric oxide modified nanoparticles with tetracycline, a commonly prescribed antibiotic for E. coli infections, increased the effectiveness of the antibiotic by 87.8%, which allows for lower doses of antibiotics to be used in order to achieve the same effect. The functionalized nanoparticles were not cytotoxic to mouse fibroblasts.

Surface modification of PLGA nanoparticles to deliver nitric oxide to inhibit Escherichia coli growth

International Nuclear Information System (INIS)

Reger, Nina A.; Meng, Wilson S.; Gawalt, Ellen S.

2017-01-01

Highlights: • Thin film functionalized PLGA nanoparticles were modified to release nitric oxide from an s-nitrosothiol donor. • The nitric oxide modified nanoparticles were bacteriostatic against Escherichia coli. • The nitric oxide modified nanoparticles increased the effectiveness of tetracycline against Escherichia coli. • The modified nitric oxide nanoparticles did not exhibit cytotoxic effects against fibroblasts. - Abstract: Polymer nanoparticles consisting of poly (DL-lactic-co-glycolic acid) were surface functionalized to deliver nitric oxide. These biodegradable and biocompatible nanoparticles were modified with an S-nitrosothiol molecule, S-nitrosocysteamine, as the nitric oxide delivery molecule. S-nitrosocysteamine was covalently immobilized on the nanoparticle surface using small organic molecule linkers and carbodiimide coupling. Nanoparticle size, zeta potential, and morphology were determined using dynamic light scattering and scanning electron microscopy, respectively. Subsequent attachment of the S-nitrosothiol resulted in a nitric oxide release of 37.1 ± 1.1 nmol per milligram of nanoparticles under physiological conditions. This low concentration of nitric oxide reduced Escherichia coli culture growth by 31.8%, indicating that the nitric oxide donor was effective at releasing nitric oxide even after attachment to the nanoparticle surface. Combining the nitric oxide modified nanoparticles with tetracycline, a commonly prescribed antibiotic for E. coli infections, increased the effectiveness of the antibiotic by 87.8%, which allows for lower doses of antibiotics to be used in order to achieve the same effect. The functionalized nanoparticles were not cytotoxic to mouse fibroblasts.

Electrochemical and morphological analyses on the titanium surface modified by shot blasting and anodic oxidation processes

Energy Technology Data Exchange (ETDEWEB)

Szesz, Eduardo M., E-mail: eszesz@neoortho.com.br [Neoortho Research Institute, Rua Ângelo Domingos Durigan, 607-Cascatinha, CEP 82025-100 Curitiba, PR (Brazil); Pereira, Bruno L., E-mail: brnl7@hotmail.com [Physics Department, Universidade Federal do Paraná, 81531-980 Curitiba, PR (Brazil); Kuromoto, Neide K., E-mail: kuromoto@fisica.ufpr.br [Physics Department, Universidade Federal do Paraná, 81531-980 Curitiba, PR (Brazil); Marino, Claudia E.B., E-mail: claudiamarino@yahoo.com [Mechanical Engineering Department, Universidade Federal do Paraná, 81531-980 Curitiba, PR (Brazil); Souza, Gelson B. de, E-mail: gelsonbs@uepg.br [Physics Department, Universidade Estadual de Ponta Grossa, 84051-510 Ponta Grossa, PR (Brazil); Soares, Paulo, E-mail: pa.soares@pucpr.br [Mechanical Engineering Department, Pontifícia Universidade Católica do Paraná, 80215-901 Curitiba, PR (Brazil)

2013-01-01

In recent years, many surface modification processes have been developed in order to induce the osseointegration on titanium surface and thus to improve the implants' biocompatibility. In this work, Ti surface has been modified by shot blasting followed by anodic oxidation process in order to associate the good surface characteristics of both processes to obtain a rough and porous surface able to promote the titanium surface bioactivity. Commercially pure titanium (grade 2) plates were used on the surface treatments that were as follows: Shot blasting (SB) performed using alumina (Al{sub 2}O{sub 3}) particles, and anodic oxidation (AO) using NaOH electrolyte. The morphology, structural changes and the open-circuit potentials (OCP) of the surfaces were analyzed. It can be observed that an increase on the roughness of the blasted surface and a rough and porous surface happens after the AO process. The anodic film produced is thin and followed the blasted surface topography. It can be observed that there are small pores with regular shape covering the entire surface. X-ray diffraction results showed the presence of the anatase and rutile phases on the blasted and anodized surface after heat treatment at 600 °C/1 h. Concerning electrochemical measurements, when the different samples were submitted to open-circuit conditions in a physiological electrolyte, the protective effect increases with the oxidation process due to the oxide layer. When the surface was blasted, the OCP was more negative when compared with the Ti surface without surface treatments. - Highlights: ► A combination of shot blasting and anodic oxidation surface treatments is proposed. ► Both processes produced an increase in roughness compared to the polished surface. ► The combination of processes produced a rough and porous surface. ► Open circuit results show that the protective effect increases with oxidation process. ► The combination of processes presents the better results in this

Oxidation of hydrogen terminated Ge(1 0 0) surface in the presence of iodine in methanol

International Nuclear Information System (INIS)

Lee, Younghwan; Park, Kibyung; Lim, Sangwoo

2008-01-01

Surface reaction on Ge(1 0 0) in liquid methanol (MeOH) was systematically studied. In particular, the characteristics of the Ge surface in the presence of iodine (I 2 ) in MeOH were investigated. MeOH treatment of the Ge surface in the presence of 0.05 or 0.005 mM of I 2 exhibited a similar result to that without I 2 , which produces a GeO x -dominant oxide structure. However, when the concentration of I 2 in MeOH increased to 0.5 mM, Ge surface revealed a GeO 2 -dominant oxide structure. Therefore, it is believed that the addition of enough I 2 in MeOH modifies the Ge oxidation mechanism. Hydroxide produced by the reaction between MeOH and the iodine radical may oxidize the Ge surface to form a Ge-O layer. Because MeOH is greatly consumed by chain and series reactions when I 2 concentration is high, a GeO 2 structure is not etched and a GeO 2 -dominant oxide structure is obtained with the addition of 0.5 mM I 2 in MeOH. The modified oxide layer prepared in MeOH with 0.5 mM I 2 exhibited an atomically smoother surface compared to a pure MeOH- or H 2 O 2 -treated Ge surface and a much thinner oxide layer than H 2 O 2 treatment.

Chemical state analysis of oxidation products on steel surface by conversion electron Moessbauer spectrometry

International Nuclear Information System (INIS)

Ujihira, Yusuke; Nomura, Kiyoshi

1978-01-01

The polished NT-70H steel (Fe: 95.97%, C: 0.56%, diameter: 5 cm, thickness: 0.5 cm) was immersed in deionized water or in solutions containing (0.25 -- 0.5) M of chloride, sulfate and nitrate ions. The chemical states of oxidation products of iron on the surface were identified through the analysis of conversion electron Moessbauer spectra (CEMS). CEMS of the steel surface, which had been dipped in deionized water, revealed that γ-FeOOH was formed on the surface. The thickness of γ-FeOOH layer increased with the increase of the duration of dipping. Dissolved oxygen in the solution played an essential role in the oxidation of iron to γ-FeOOH. Oxidation product of iron dipped in the 0.5 M sodium chloride solution was identified as γ-FeOOH. Amorphous paramagnetic iron (III) compound tended to form in the presence of hydrogen peroxide or ammonium ions in the solutions. The increase of alkalinity of the solution up to pH 12 suppressed the oxidation rate and assisted the formation of green rust, which was confirmed by the appearance of the quadrupole splitting peaks of the green rust. In the 0.25 M sodium sulfate solution, oxidation of the steel surface proceeded slowly and the quadrupole splitting peaks of Fe(OH) 2 were seen in the CEMS. The peak intensity of Fe(OH) 2 gradually decreased and that of γ-FeOOH increased by the extension of immersion of steel in the solution. Magnetite (Fe 3 O 4 ) layer was developed beneath the γ-FeOOH layer, when steel was dipped in 0.5 M sodium nitrate solution. However, the peaks of Fe 3 O 4 were not seen on CEMS of steel surface immersed in 0.5 M ammonium nitrate solution. Thus, applying the feasibility of CEMS for the characterization of oxidated compounds of iron on the steel surface formed by the immersion in solutions, the oxidation mechanism of the steel surface was discussed based upon the results of chemical state analyses. (author)

Spectroellipsometric detection of silicon substrate damage caused by radiofrequency sputtering of niobium oxide

Science.gov (United States)

Lohner, Tivadar; Serényi, Miklós; Szilágyi, Edit; Zolnai, Zsolt; Czigány, Zsolt; Khánh, Nguyen Quoc; Petrik, Péter; Fried, Miklós

2017-11-01

Substrate surface damage induced by deposition of metal atoms by radiofrequency (rf) sputtering or ion beam sputtering onto single-crystalline silicon (c-Si) surface has been characterized earlier by electrical measurements. The question arises whether it is possible to characterize surface damage using spectroscopic ellipsometry (SE). In our experiments niobium oxide layers were deposited by rf sputtering on c-Si substrates in gas mixture of oxygen and argon. Multiple angle of incidence spectroscopic ellipsometry measurements were performed, a four-layer optical model (surface roughness layer, niobium oxide layer, native silicon oxide layer and ion implantation-amorphized silicon [i-a-Si] layer on a c-Si substrate) was created in order to evaluate the spectra. The evaluations yielded thicknesses of several nm for the i-a-Si layer. Better agreement could be achieved between the measured and the generated spectra by inserting a mixed layer (with components of c-Si and i-a-Si applying the effective medium approximation) between the silicon oxide layer and the c-Si substrate. High depth resolution Rutherford backscattering (RBS) measurements were performed to investigate the interface disorder between the deposited niobium oxide layer and the c-Si substrate. Atomic resolution cross-sectional transmission electron microscopy investigation was applied to visualize the details of the damaged subsurface region of the substrate.

Surface oxidation: an effective way to induce piezoelectricity in 2D black phosphorus

Science.gov (United States)

Li, Jiabin; Zhao, Ting; He, Chaoyu; Zhang, Kaiwang

2018-03-01

In this letter, first-principles methods are employed to investigate the elastic stiffness and piezoelectric tensors of surface-oxidized black phosphorene. Our results show that the piezoelectric coefficients d 11 and d 12 for surface-oxidized black phosphorene are 88.54 pm V-1 and  -1.94 pm V-1, respectively, which are comparable to those of group-IV monochalcogenides and more remarkable than those of the experimentally viable h-BN and MoS2. These results indicate that surface-oxidization is an effective way to make black phosphorene into an excellent piezoelectric material for potential applications in sensors, actuators, electric field generators and any other applications requiring electrical and mechanical energy conversion. We expect further experimental exploration on this interesting result to confirm our predictions.

Evidence concerning oxidation as a surface reaction in Baltic amber

DEFF Research Database (Denmark)

Shashoua, Yvonne

2012-01-01

, obtained from pressed amber powder, were subjected to accelerated thermal ageing. Cross-sections of the pellets were analyzed by infrared micro-spectroscopy, in order to identify and quantify changes in chemical properties. The experimental results showed strong oxidation exclusively at the exterior part...... of cross-sections from samples subjected to long-term thermal ageing, confirming that oxidation of Baltic amber starts from the surface....

Local electrical properties of thermally grown oxide films formed on duplex stainless steel surfaces

Science.gov (United States)

Guo, L. Q.; Yang, B. J.; He, J. Y.; Qiao, L. J.

2018-06-01

The local electrical properties of thermally grown oxide films formed on ferrite and austenite surfaces of duplex stainless steel at different temperatures were investigated by Current sensing atomic force microscopy, X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). The current maps and XPS/AES analyses show that the oxide films covering austenite and ferrite surfaces formed at different temperatures exhibit different local electrical characteristics, thickness and composition. The dependence of electrical conductivity of oxide films covering austenite and ferrite surface on the formation temperature is attributed to the film thickness and semiconducting structures, which is intrinsically related to thermodynamics and kinetics process of film grown at different temperature. This is well elucidated by corresponding semiconductor band structures of oxide films formed on austenite and ferrite phases at different temperature.

Physics and Chemistry on Well-Defined Semiconductor and Oxide Surfaces

Science.gov (United States)

Chen, Peijun

High resolution electron energy loss spectroscopy (HREELS) and other surface spectroscopic techniques have been employed to investigate the following two classes of surface/interface phenomena on well-defined semiconductor and oxide surfaces: (i) the fundamental physical and chemical processes involved in gas-solid interaction on silicon single crystal surfaces, and (ii) the physical and chemical properties of metal-oxide interfaces. The particular systems reported in this dissertation are: NH_3, PH_3 and B_ {10}H_{14} on Si(111)-(7 x 7); NH_3 on Si(100) -(2 x 1); atomic H on Si(111)-(7 x 7) and boron-modified Si(111); Al on Al_2O_3 and Sn on SiO_2.. On silicon surfaces, the surface dangling bonds function as the primary adsorption sites where surface chemical processes take place. The unambiguous identification of surface species by vibrational spectroscopy allows the elementary steps involved in these surface chemical processes to be followed on a molecular level. For adsorbate molecules such as NH_3 and PH_3, the nature of the initial low temperature (100 -300 K) adsorption is found to be dissociative, while that for B_{10}H_ {14} is non-dissociative. This has been deduced based upon the presence (or absence) of specific characteristic vibrational mode(s) on surface. By following the evolution of surface species as a function of temperature, the elementary steps leading to silicon nitride thin film growth and doping of silicon are elucidated. In the case of NH_3 on Si(111)-(7 x 7) and Si(100)-(2 x 1), a detailed understanding on the role of substrate surface structure in controlling the surface reactivity has been gained on the basis of a Si adatom backbond-strain relief mechanism on the Si(111) -(7 x 7). The electronic modification to Si(111) surface by subsurface boron doping has been shown to quench its surface chemistry, even for the most aggressive atomic H. This discovery is potentially meaningful to the technology of gas-phase silicon etching. The

Strengthening of Zircaloy-4 with Oxide Particles by Surface Treatment using Laser Beam

Energy Technology Data Exchange (ETDEWEB)

Jung, Yang Il; Park, Jung Hwan; Park, Dong Jun; Kim, Hyun Gil; Yang, Jae Ho; Koo, Yang Hyun [KAERI, Daejeon (Korea, Republic of)

2016-05-15

Accident tolerant fuel (ATF) cladding is being developed globally after the Fukushima accident with the demands for the nuclear fuel having higher safety at normal operation conditions as well as even in a severe accident conditions. Korea Atomic Energy Research Institute (KAERI) is one of the leading organizations for developing ATF claddings. One concept is to form an oxidation-resistant layer on Zr cladding surface. The other is to increase high-temperature mechanical strength of Zr tube. High-power laser beam was exposed on the zirconium surface previously coated by oxides. Various oxides such as Y{sub 2}O{sub 3}, CeO{sub 2}, Gd{sub 2}O{sub 3}, Er{sub 2}O{sub 3} were used for the ODS treatment. In this study, the effect of strengthening by the ODS treatment was investigated. The oxide particles of Y{sub 2}O{sub 3} were dispersed well in the Zr matrix at the surface region.

Influence of surface oxidation on ion dynamics and capacitance in porous and nonporous carbon electrodes

Energy Technology Data Exchange (ETDEWEB)

Dyatkin, Boris [Drexel Univ., Philadelphia, PA (United States); Zhang, Yu [Vanderbilt Univ., Nashville, TN (United States); Mamontov, Eugene [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Kolesnikov, Alexander I. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Cheng, Yongqiang [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Meyer, III, Harry M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Cummings, Peter T. [Vanderbilt Univ., Nashville, TN (United States); Gogotsi, Yury G. [Drexel Univ., Philadelphia, PA (United States)

2016-04-07

Here, we investigate the influence of surface chemistry and ion confinement on capacitance and electrosorption dynamics of room-temperature ionic liquids (RTILs) in supercapacitors. Using air oxidation and vacuum annealing, we produced defunctionalized and oxygen-rich surfaces of carbide-derived carbons (CDCs) and graphene nanoplatelets (GNPs). While oxidized surfaces of porous CDCs improve capacitance and rate handling abilities of ions, defunctionalized nonporous GNPs improve charge storage densities on planar electrodes. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) probed the structure, dynamics, and orientation of RTIL ions confined in divergently functionalized pores. Oxidized, ionophilic surfaces draw ions closer to pore surfaces and enhance potential-driven ion transport during electrosorption. Molecular dynamics (MD) simulations corroborated experimental data and demonstrated the significance of surface functional groups on ion orientations, accumulation densities, and capacitance.

UO{sub 2} surface oxidation by mixtures of water vapor and hydrogen as a function of temperature

Energy Technology Data Exchange (ETDEWEB)

Espriu-Gascon, A., E-mail: alexandra.espriu@upc.edu [Department of Chemical Engineering, Universitat Politècnica Catalunya-Barcelona Tech, Diagonal 647, E-08028 Barcelona (Spain); Llorca, J.; Domínguez, M. [Institut de Tècniques Energètiques (INTE), Universitat Politècnica Catalunya-Barcelona Tech, Diagonal 647, E-08028 Barcelona (Spain); Centre for Research in NanoEngineering (CRNE), Universitat Politècnica Catalunya-Barcelona Tech, Diagonal 647, E-08028 Barcelona (Spain); Giménez, J.; Casas, I. [Department of Chemical Engineering, Universitat Politècnica Catalunya-Barcelona Tech, Diagonal 647, E-08028 Barcelona (Spain); Pablo, J. de [Department of Chemical Engineering, Universitat Politècnica Catalunya-Barcelona Tech, Diagonal 647, E-08028 Barcelona (Spain); Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, E-08243 Manresa (Spain)

2015-12-15

In the present work, X-Ray Photoelectron Spectroscopy (XPS) was used to study the effect of water vapor on the UO{sub 2} surface as a function of temperature. The experiments were performed in situ inside a high pressure chamber attached to the XPS instrument. UO{sub 2} samples were put in contact with either hydrogen or argon streams, saturated with water at room temperature, and the sample surface evolution was analyzed by XPS. In the case of the water vapor/argon experiments, one experiment at 350 °C was performed and, in the case of the water vapor/hydrogen experiments, the temperatures used inside the reactor were 60, 120, 200 and 350 °C. On one hand, in presence of argon, the results obtained showed that the water vapor in the argon stream oxidized 93% of the U(IV) in the sample surface. On the other hand, the degree of UO{sub 2} surface oxidation showed a different dependence on the temperature in the experiments performed in the presence of hydrogen: the maximum surface oxidation occurred at 120 °C, where 65.4% of U(IV) in the sample surface was oxidized, while at higher temperatures, the surface oxidation decreased. This observation is attributed to the increase of hydrogen reducing effect when temperature increases which prevents part of the oxidation of the UO{sub 2} surface by the water vapor. - Highlights: • UO{sub 2} surface has been oxidized by water vapor in an argon stream at 350 °C. • H{sub 2} reduced more uranium oxidation produced by water at 350 °C when compared to Ar. • In H{sub 2} presence, the uranium oxidation produced by water depends on the temperature.

The surface nanostructures of titanium alloy regulate the proliferation of endothelial cells

Directory of Open Access Journals (Sweden)

Min Lai

2014-02-01

Full Text Available To investigate the effect of surface nanostructures on the behaviors of human umbilical vein endothelial cells (HUVECs, surface nanostructured titanium alloy (Ti-3Zr2Sn-3Mo-25Nb, TLM was fabricated by surface mechanical attrition treatment (SMAT technique. Field emission scanning electron microscopy (FE-SEM, atomic force microscopy (AFM, transmission electron microscopy (TEM and X-ray diffraction (XRD were employed to characterize the surface nanostructures of the TLM, respectively. The results demonstrated that nano-crystalline structures with several tens of nanometers were formed on the surface of TLM substrates. The HUVECs grown onto the surface nanostructured TLM spread well and expressed more vinculin around the edges of cells. More importantly, HUVECs grown onto the surface nanostructured TLM displayed significantly higher (p < 0.01 or p < 0.05 cell adhesion and viabilities than those of native titanium alloy. HUVECs cultured on the surface nanostructured titanium alloy displayed significantly higher (p < 0.01 or p < 0.05 productions of nitric oxide (NO and prostacyclin (PGI2 than those of native titanium alloy, respectively. This study provides an alternative for the development of titanium alloy based vascular stents.

Band energy control of molybdenum oxide by surface hydration

Energy Technology Data Exchange (ETDEWEB)

Butler, Keith T., E-mail: k.t.butler@bath.ac.uk; Walsh, Aron [Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom); Crespo-Otero, Rachel [School of Biological and Chemical Sciences, Queen Mary University London, Mile End Road, London E1 4NS (United Kingdom); Buckeridge, John; Scanlon, David O. [University College London, Kathleen Lonsdale Materials Chemistry, 20 Gordon Street, London WC1H 0AJ (United Kingdom); Bovill, Edward; Lidzey, David [Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

2015-12-07

The application of oxide buffer layers for improved carrier extraction is ubiquitous in organic electronics. However, the performance is highly susceptible to processing conditions. Notably, the interface stability and electronic structure is extremely sensitive to the uptake of ambient water. In this study we use density functional theory calculations to asses the effects of adsorbed water on the electronic structure of MoO{sub x}, in the context of polymer-fullerene solar cells based on PCDTBT. We obtain excellent agreement with experimental values of the ionization potential for pristine MoO{sub 3} (010). We find that IP and EA values can vary by as much as 2.5 eV depending on the oxidation state of the surface and that adsorbed water can either increase or decrease the IP and EA depending on the concentration of surface water.

Plasma surface oxidation of 316L stainless steel for improving adhesion strength of silicone rubber coating to metal substrate

Energy Technology Data Exchange (ETDEWEB)

Latifi, Afrooz, E-mail: afroozlatifi@yahoo.com [Department of Biomaterials, Biomedical Engineering Faculty, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Imani, Mohammad [Novel Drug Delivery Systems Dept., Iran Polymer and Petrochemical Institute, P.O. Box 14965/115, Tehran (Iran, Islamic Republic of); Khorasani, Mohammad Taghi [Biomaterials Dept., Iran Polymer and Petrochemical Institute, P.O. Box 14965/159, Tehran (Iran, Islamic Republic of); Daliri Joupari, Morteza [Animal and Marine Biotechnology Dept., National Institute of Genetic Engineering and Biotechnology, P.O. Box 14965/161, Tehran (Iran, Islamic Republic of)

2014-11-30

Highlights: • Stainless steel 316L was surface modified by plasma surface oxidation (PSO) and silicone rubber (SR) coating. • On the PSO substrates, concentration of oxide species was increased ca. 2.5 times comparing to non-PSO substrates. • The surface wettability was improved to 12.5°, in terms of water contact angle, after PSO. • Adhesion strength of SR coating on the PSO substrates was improved by more than two times comparing to non-PSO ones. • After pull-off test, the fractured area patterns for SR coating were dependent on the type of surface modifications received. - Abstract: Stainless steel 316L is one of the most widely used materials for fabricating of biomedical devices hence, improving its surface properties is still of great interest and challenging in biomaterial sciences. Plasma oxidation, in comparison to the conventional chemical or mechanical methods, is one of the most efficient methods recently used for surface treatment of biomaterials. Here, stainless steel specimens were surface oxidized by radio-frequency plasma irradiation operating at 34 MHz under pure oxygen atmosphere. Surface chemical composition of the samples was significantly changed after plasma oxidation by appearance of the chromium and iron oxides on the plasma-oxidized surface. A wettable surface, possessing high surface energy (83.19 mN m{sup −1}), was observed after plasma oxidation. Upon completion of the surface modification process, silicone rubber was spray coated on the plasma-treated stainless steel surface. Morphology of the silicone rubber coating was investigated by scanning electron microscopy (SEM). A uniform coating was formed on the oxidized surface with no delamination at polymer–metal interface. Pull-off tests showed the lowest adhesion strength of coating to substrate (0.12 MPa) for untreated specimens and the highest (0.89 MPa) for plasma-oxidized ones.

Surface-Induced Frustration in Solid State Polymorphic Transition of Native Cellulose Nanocrystals.

Science.gov (United States)

Salminen, Reeta; Baccile, Niki; Reza, Mehedi; Kontturi, Eero

2017-06-12

The presence of an interface generally influences crystallization of polymers from melt or from solution. Here, by contrast, we explore the effect of surface immobilization in a direct solid state polymorphic transition on individual cellulose nanocrystals (CNCs), extracted from a plant-based origin. The conversion from native cellulose I to cellulose III crystal occurred via a host-guest inclusion of ethylene diamine inside the crystal. A 60% reduction in CNC width (height) in atomic force microscopy images suggested that when immobilized on a flat modified silica surface, the stresses caused by the inclusion or the subsequent regeneration resulted in exfoliation, hypothetically, between the van der Waals bonded sheets within the crystal. Virtually no changes in dimensions were visible when the polymorphic transition was performed to nonimmobilized CNCs in bulk dispersion. With reservations and by acknowledging the obvious dissimilarities, the exfoliation of cellulose crystal sheets can be viewed as analogous to exfoliation of 2D structures like graphene from a van der Waals stacked solid. Here, the detachment is triggered by an inclusion of a guest molecule inside a host cellulose crystal and the stresses caused by the firm attachment of the CNC on a solid substrate, leading to detachment of molecular sheets or stacks of sheets.

Using Iron-Manganese Co-Oxide Filter Film to Remove Ammonium from Surface Water.

Science.gov (United States)

Zhang, Ruifeng; Huang, Tinglin; Wen, Gang; Chen, Yongpan; Cao, Xin; Zhang, Beibei

2017-07-19

An iron-manganese co-oxide filter film (MeO x ) has been proven to be a good catalyst for the chemical catalytic oxidation of ammonium in groundwater. Compared with groundwater, surface water is generally used more widely and has characteristics that make ammonium removal more difficult. In this study, MeO x was used to remove ammonium from surface water. It indicated that the average ammonium removal efficiency of MeO x was greater than 90%, even though the water quality changed dramatically and the water temperature was reduced to about 6-8 °C. Then, through inactivating microorganisms, it showed that the removal capability of MeO x included both biological (accounted for about 41.05%) and chemical catalytic oxidation and chemical catalytic oxidation (accounted for about 58.95%). The investigation of the characterizations suggested that MeO x was formed by abiotic ways and the main elements on the surface of MeO x were distributed homogenously. The analysis of the catalytic oxidation process indicated that ammonia nitrogen may interact with MeO x as both ammonia molecules and ammonium ions and the active species of O₂ were possibly • O and O₂ - .

Metal/metal-oxide interfaces: A surface science approach to the study of adhesion

Energy Technology Data Exchange (ETDEWEB)

Peden, C.H.F.; Kidd, K.B.; Shinn, N.D. (Sandia National Laboratories, Albuquerque, New Mexico 87185-5800 (USA))

1991-05-01

Metal-oxide/metal interfaces play an important role, for example, in the joining of an oxide ceramic to a metal for sealing applications. In order to probe the chemical and physical properties of such an interface, we have performed Auger electron spectroscopic (AES) and temperature programed desorption (TPD) experiments on a model system composed of very thin films of Cr, Fe, Ni, or Cu evaporated onto a very thin thermally grown oxide on a W single crystal. Monolayer films of Fe and Cr were found (by AES) to completely wet the oxide surface upon deposition, and were stable up to temperatures at which the films desorbed ({approx}1300 K). In contrast, monolayer Ni and Cu films formed three-dimensional islands exposing the oxidized W surface either upon annealing (Ni) or even upon room-temperature deposition (Cu). The relative interfacial interaction between the overlayer metal and the oxide, as assessed by TPD, increases in the series Cu{lt}Ni{lt}Fe{lt}Cr. This trend follows the heats of formation of the various oxides of these metals.

Identifying active surface phases for metal oxide electrocatalysts: a study of manganese oxide bi-functional catalysts for oxygen reduction and water oxidation catalysis

DEFF Research Database (Denmark)

Su, Hai-Yan; Gorlin, Yelena; Man, Isabela Costinela

2012-01-01

Progress in the field of electrocatalysis is often hampered by the difficulty in identifying the active site on an electrode surface. Herein we combine theoretical analysis and electrochemical methods to identify the active surfaces in a manganese oxide bi-functional catalyst for the oxygen...... reduction reaction (ORR) and the oxygen evolution reaction (OER). First, we electrochemically characterize the nanostructured α-Mn2O3 and find that it undergoes oxidation in two potential regions: initially, between 0.5 V and 0.8 V, a potential region relevant to the ORR and, subsequently, between 0.8 V...

Dye-Sensitized Solar Cells Based on High Surface Area Nanocrystalline Zinc Oxide Spheres

Directory of Open Access Journals (Sweden)

Pavuluri Srinivasu

2011-01-01

Full Text Available High surface area nanocrystalline zinc oxide material is fabricated using mesoporous nanostructured carbon as a sacrificial template through combustion process. The resulting material is characterized by XRD, N2 adsorption, HR-SEM, and HR-TEM. The nitrogen adsorption measurement indicates that the materials possess BET specific surface area ca. 30 m2/g. Electron microscopy images prove that the zinc oxide spheres possess particle size in the range of 0.12 μm–0.17 μm. The nanocrystalline zinc oxide spheres show 1.0% of energy conversion efficiency for dye-sensitized solar cells.

Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

Energy Technology Data Exchange (ETDEWEB)

Angermann, Heike, E-mail: angermann@helmholtz-berlin.de

2014-09-01

Highlights: • Determination of electronic interface properties by contact-less surface photovoltage (SPV) technique. • Systematic correlations of substrate morphology and surface electronic properties. • Optimization of surface pre-treatment for flat, saw damage etched, and textured Si solar cell substrates. • Ultra-thin passivating Si oxide layers with low densities of rechargeable states by wet-chemical oxidation and subsequent annealing. • Environmentally acceptable processes, utilizing hot water, diluted HCl, or ozone low cost alternative to current approaches with concentrated chemicals. • The effect of optimized wet-chemical pre-treatments can be preserved during subsequent layer deposition. - Abstract: The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution D{sub it}(E), and density D{sub it,min} of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates. Based on previous findings and new research, a study of conventional and newly developed wet-chemical oxidation methods was established, correlating the interactions between involved oxidizing and etching solutions and the initial substrate morphology to the final surface conditioning. It is shown, which sequences of wet-chemical oxidation and oxide removal, have to be combined in order to achieve atomically smooth, hydrogen terminated surfaces, as well as ultra-thin oxide layers with low densities of rechargeable states on flat, saw damage etched, and textured Si substrates, as commonly applied in silicon device and solar cell manufacturing. These conventional strategies for wet-chemical pre-treatment are mainly

Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

International Nuclear Information System (INIS)

Angermann, Heike

2014-01-01

Highlights: • Determination of electronic interface properties by contact-less surface photovoltage (SPV) technique. • Systematic correlations of substrate morphology and surface electronic properties. • Optimization of surface pre-treatment for flat, saw damage etched, and textured Si solar cell substrates. • Ultra-thin passivating Si oxide layers with low densities of rechargeable states by wet-chemical oxidation and subsequent annealing. • Environmentally acceptable processes, utilizing hot water, diluted HCl, or ozone low cost alternative to current approaches with concentrated chemicals. • The effect of optimized wet-chemical pre-treatments can be preserved during subsequent layer deposition. - Abstract: The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution D it (E), and density D it,min of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates. Based on previous findings and new research, a study of conventional and newly developed wet-chemical oxidation methods was established, correlating the interactions between involved oxidizing and etching solutions and the initial substrate morphology to the final surface conditioning. It is shown, which sequences of wet-chemical oxidation and oxide removal, have to be combined in order to achieve atomically smooth, hydrogen terminated surfaces, as well as ultra-thin oxide layers with low densities of rechargeable states on flat, saw damage etched, and textured Si substrates, as commonly applied in silicon device and solar cell manufacturing. These conventional strategies for wet-chemical pre-treatment are mainly based on

Inhibition of methane oxidation in slurry surface crust by inorganic nitrogen

DEFF Research Database (Denmark)

Duan, Yun-Feng; Elsgaard, Lars; Petersen, Søren O

2013-01-01

Livestock slurry is an important source of methane (CH4). Depending on dry matter content, a floating crust may form where methane-oxidizing bacteria (MOB) and CH4 oxidation activity have been found, suggesting that surface crusts may reduce CH4 emissions from slurry. However, it is not known how...... MOB in this environment interact with inorganic nitrogen (N). We studied inhibitory effects of ammonium (NH4+), nitrate (NO3–) and nitrite (NO2–) on potential CH4 oxidation in a cattle slurry surface crust. Methane oxidation was assayed at salt concentrations up to 500 mM at 100 and 10,000 ppmv...... headspace CH4. First-order rate constants were used to evaluate the strength of inhibition. Nitrite was the most potent inhibitor, reducing methanotrophic activity by up to 70% at only 1 mM NO2–. MOB were least sensitive to NO3–, tolerating up to 30 mM NO3– at 100 ppmv CH4 and 50 mM NO3– at 10,000 ppmv CH4...

Grafting of diazonium salts on oxides surface: formation of aryl-O bonds on iron oxide nanoparticles

Science.gov (United States)

Brymora, Katarzyna; Fouineau, Jonathan; Eddarir, Asma; Chau, François; Yaacoub, Nader; Grenèche, Jean-Marc; Pinson, Jean; Ammar, Souad; Calvayrac, Florent

2015-11-01

Combining ab initio modeling and 57Fe Mössbauer spectrometry, we characterized the nature of the chemical linkage of aminoalkyl arenediazonium salt on the surface of iron oxide nanoparticles. We established that it is built through a metal-oxygen-carbon bonding and not a metal-carbon one, as usually suggested and commonly observed in previously studied metal- or carbon-based surfaces.

Grafting of diazonium salts on oxides surface: formation of aryl-O bonds on iron oxide nanoparticles

International Nuclear Information System (INIS)

Brymora, Katarzyna; Fouineau, Jonathan; Eddarir, Asma; Chau, François; Yaacoub, Nader; Grenèche, Jean-Marc; Pinson, Jean; Ammar, Souad; Calvayrac, Florent

2015-01-01

Combining ab initio modeling and 57 Fe Mössbauer spectrometry, we characterized the nature of the chemical linkage of aminoalkyl arenediazonium salt on the surface of iron oxide nanoparticles. We established that it is built through a metal–oxygen–carbon bonding and not a metal–carbon one, as usually suggested and commonly observed in previously studied metal- or carbon-based surfaces

Grafting of diazonium salts on oxides surface: formation of aryl-O bonds on iron oxide nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Brymora, Katarzyna [LUNAM Université du Maine, IMMM UMR CNRS 6283 (France); Fouineau, Jonathan; Eddarir, Asma; Chau, François [Université Paris Diderot, Sorbonne Paris Cité, ITODYS CNRS UMR 7086 (France); Yaacoub, Nader; Grenèche, Jean-Marc [LUNAM Université du Maine, IMMM UMR CNRS 6283 (France); Pinson, Jean; Ammar, Souad [Université Paris Diderot, Sorbonne Paris Cité, ITODYS CNRS UMR 7086 (France); Calvayrac, Florent, E-mail: florent.calvayrac@univ-lemans.fr [LUNAM Université du Maine, IMMM UMR CNRS 6283 (France)

2015-11-15

Combining ab initio modeling and {sup 57}Fe Mössbauer spectrometry, we characterized the nature of the chemical linkage of aminoalkyl arenediazonium salt on the surface of iron oxide nanoparticles. We established that it is built through a metal–oxygen–carbon bonding and not a metal–carbon one, as usually suggested and commonly observed in previously studied metal- or carbon-based surfaces.

Surface oxidation of porous ZrB2-SiC ceramic composites by continuous-wave ytterbium fibre laser

International Nuclear Information System (INIS)

Mahmod, Dayang Salyani Abang; Glandut, Nicolas; Khan, Amir Azam; Labbe, Jean-Claude

2015-01-01

Highlights: • Surface oxidation of ZrB 2 -SiC ceramic composites by Yb-fibre laser. • Round spiral laser pattern created for the surface oxidation. • Presence of laser-formed oxide scale and unaffected beneath regions. • Crazed but uncracked surface oxide. • A dense glassy SiO 2 -rich layer exhibited enhances oxidation resistance. - Abstract: Surface treatment of ceramic substrates by a laser beam can allow to incorporate interesting properties to these ceramics. In the present work, surface oxidation of ca. 30% porous ZrB 2 -SiC ceramic composites by using an ytterbium fibre laser was conducted. Oxidation of ceramic substrates through this process under ambient conditions has certain advantages compared to the classical oxidation method. A particular spiral laser pattern was created in order to produce an oxidized structure on ZrB 2 -SiC porous substrates. The laser parameters were as follows i.e., laser power of 50, 60 and 70 W, a beam diameter of 1.25 mm, velocity of 2 mm/s, acceleration and deceleration of 1 mm/s 2 . The microstructural and morphological changes in the laser-treated region was examined using scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. At laser power of 70 W, the sample exhibits uniform oxidation. It revealed that the very porous bulk beneath remained unaffected and unoxidized because this laser-formed oxide scale protects the substrate from oxidation. The presence of oxidized and unaffected regions indicated a high degree of heat localization. The dense glassy SiO 2 -rich layer prevents the inward oxygen diffusion into the inner bulk hence enhances the oxidation resistance.

Hydroxyapatite growth induced by native extracellular matrix deposition on solid surfaces

Directory of Open Access Journals (Sweden)

Pramatarova L.

2005-02-01

Full Text Available Biological systems have a remarkable capability to produce perfect fine structures such as seashells, pearls, bones, teeth and corals. These structures are composites of interacting inorganic (calcium phosphate or carbonate minerals and organic counterparts. It is difficult to say with certainty which part has the primary role. For example, the growth of molluscan shell crystals is thought to be initiated from a solution by the extracellular organic matrix (ECM. According to this theory, the matrix induces nucleation of calcium containing crystals. Recently, an alternative theory has been put forward, stating that a class of granulocytic hemocytes would be directly involved in shell crystal production in oysters. In the work presented here the surface of AISI 316 stainless steel was modified by deposition of ECM proteins. The ability of the modified substrates to induce nucleation and growth of hydroxyapatite (HA from simulated body fluid (SBF was examined by a kinetic study using two methods: (1 a simple soaking process in SBF and (2 a laser-liquid-solid interaction (LLSI process which allows interaction between a scanning laser beam and a solid substrate immersed in SBF. The deposited HA layers were investigated by Fourier transform infrared spectroscopy (FTIR and scanning electron microscopy (SEM. It was found that a coating of stainless steel surface with native ECM proteins induced nucleation and growth of HA and facilitated its crystallization. By the process of simple soaking of the samples, irrespective of their horizontal or vertical position in the solution, HA layers were grown due to the reactive ECM-coated stainless steel surface. It was shown that the process occurring in the first stages of the growth was not only a result of the force of gravity. The application of the LLSI process strongly influenced HA formation on the ECM-modified substrates by promoting and enhancing the HA nucleation and growth through a synergistic effect

Bulk-surface relationship of an electronic structure for high-throughput screening of metal oxide catalysts

International Nuclear Information System (INIS)

Kweun, Joshua Minwoo; Li, Chenzhe; Zheng, Yongping; Cho, Maenghyo; Kim, Yoon Young; Cho, Kyeongjae

2016-01-01

Graphical abstract: - Highlights: • Bulk-surface relationship was predicted by the ligand field nature of metal oxides. • Antibonding and bonding d-bands occupancy clarified the bulk-surface relationship. • Different surface relaxations were explained by the bulk electronic structures. • Transition from the bulk to the surface state was simulated by oxygen adsorption. - Abstract: Designing metal-oxides consisting of earth-abundant elements has been a crucial issue to replace precious metal catalysts. To achieve efficient screening of metal-oxide catalysts via bulk descriptors rather than surface descriptors, we investigated the relationship between the electronic structure of bulk and that of the surface for lanthanum-based perovskite oxides, LaMO_3 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu). Through density functional theory calculations, we examined the d-band occupancy of the bulk and surface transition-metal atoms (n_B_u_l_k and n_S_u_r_f) and the adsorption energy of an oxygen atom (E_a_d_s) on (001), (110), and (111) surfaces. For the (001) surface, we observed strong correlation between the n_B_u_l_k and n_S_u_r_f with an R-squared value over 94%, and the result was interpreted in terms of ligand field splitting and antibonding/bonding level splitting. Moreover, the E_a_d_s on the surfaces was highly correlated with the n_B_u_l_k with an R-squared value of more than 94%, and different surface relaxations could be explained by the bulk electronic structure (e.g., LaMnO_3 vs. LaTiO_3). These results suggest that a bulk-derived descriptor such as n_B_u_l_k can be used to screen metal-oxide catalysts.

Native State Mass Spectrometry, Surface Plasmon Resonance, and X-ray Crystallography Correlate Strongly as a Fragment Screening Combination.

Science.gov (United States)

Woods, Lucy A; Dolezal, Olan; Ren, Bin; Ryan, John H; Peat, Thomas S; Poulsen, Sally-Ann

2016-03-10

Fragment-based drug discovery (FBDD) is contingent on the development of analytical methods to identify weak protein-fragment noncovalent interactions. Herein we have combined an underutilized fragment screening method, native state mass spectrometry, together with two proven and popular fragment screening methods, surface plasmon resonance and X-ray crystallography, in a fragment screening campaign against human carbonic anhydrase II (CA II). In an initial fragment screen against a 720-member fragment library (the "CSIRO Fragment Library") seven CA II binding fragments, including a selection of nonclassical CA II binding chemotypes, were identified. A further 70 compounds that comprised the initial hit chemotypes were subsequently sourced from the full CSIRO compound collection and screened. The fragment results were extremely well correlated across the three methods. Our findings demonstrate that there is a tremendous opportunity to apply native state mass spectrometry as a complementary fragment screening method to accelerate drug discovery.

Surface development of a brazing alloy during heat treatment-a comparison between UHV and APXPS

Science.gov (United States)

Rullik, L.; Johansson, N.; Bertram, F.; Evertsson, J.; Stenqvist, T.; Lundgren, E.

2018-01-01

In an attempt to bridge the pressure gap, APXPS was used to follow the surface development of an aluminum brazing sheet during heating in an ambient oxygen-pressure mimicking the environment of an industrial brazing furnace. The studied aluminum alloy brazing sheet is a composite material consisting of two aluminum alloy standards whose surface is covered with a native aluminum oxide film. To emphasize the necessity of studies of this system in ambient sample environments it is compared to measurements in UHV. Changes in thickness and composition of the surface oxide were followed after heating to 300 °C, 400 °C, and 500 °C. The two sets presented in this paper show that the surface development strongly depends on the environment the sample is heated in.

Impact of Mg content on native point defects in MgxZn1−xO (0 ≤ x ≤ 0.56

Directory of Open Access Journals (Sweden)

J. Perkins

2015-06-01

Full Text Available We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the densities, energy levels, and spatial distributions of zinc/magnesium cation and oxygen vacancies in isostructural, single-phase, non-polar MgxZn1−xO alloys over a wide (0 ≤ x ≤ 0.56 range. Within this wide range, both defect types exhibit strong Mg content-dependent surface segregation and pronounced bulk density minima corresponding to unit cell volume minima, which can inhibit defect formation due to electrostatic repulsion. Mg in ZnO significantly reduces native defect densities and their non-polar surface segregation, both major factors in carrier transport and doping of these oxide semiconductors.

Mechanical Properties of Glass Surfaces Coated with Tin Oxide

DEFF Research Database (Denmark)

Swindlehurst, W. E.; Cantor, B.

1978-01-01

The effect of tin oxide coatings on the coefficient of friction and fracture strength of glass surfaces is studied. Experiments were performed partly on commercially treated glass bottles and partly on laboratory prepared microscope slides. Coatings were applied in the laboratory by decomposition...

Iron carbide on titania surface modified with group VA oxides as Fischer-Tropsch catalysts

International Nuclear Information System (INIS)

Wachs, I.E.; Fiato, R.A.; Chersich, C.C.

1986-01-01

A catalyst is described comprising iron carbide supported on a surface modified titania wherein the support comprises an oxide of a metal selected form the group consisting of niobium, vanadium, tantalum or mixture thereof supported on the titania wherein at least a portion of the supported oxide of niobium, vanandium, tantalum or mixture is in a non-crystalline form. The amount of the supported oxide ranges from about 0.5 to 25 weight percent metal oxide on the titania support based on the total support composition and the catalyst contains at least about 2 milligrams of iron, calculated as Fe/sub 2/O/sub 3/, per square meter of support surface

Effect of SUS316L stainless steel surface conditions on the wetting of molten multi-component oxides ceramic

Energy Technology Data Exchange (ETDEWEB)

Wang, Jin, E-mail: wangjinustb@gmail.com [Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Fukuoka, 808-0196 (Japan); Matsuda, Nozomu [Bar and Wire Product Unit, Nippon steel and Sumitomo Metal Corporation, Fukuoka, 802-8686 (Japan); Shinozaki, Nobuya [Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Fukuoka, 808-0196 (Japan); Miyoshi, Noriko [The Center for Instrumental Analysis, Kyushu Institute of Technology, Fukuoka, 804-8550 (Japan); Shiraishi, Takanobu [Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, 852-8588 (Japan)

2015-02-01

Highlights: • Multi-component oxides had a good wetting on stainless substrates with pretreatments. • Various substrates surface roughness caused the difference of final contact angles. • The wetting rate was slow on polished substrate due to the slow surface oxidation. - Abstract: A study on the effect of SUS316L stainless steel surface conditions on the wetting behavior of molten multi-component oxides ceramic was performed and aimed to contribute to the further understanding of the application of oxides ceramic in penetration treatment of stainless steel coatings and the deposition of stainless steel cermet coatings. The results show that at 1273 K, different surface pre-treatments (polishing and heating) had an important effect on the wetting behavior. The molten multi-component oxides showed good wettability on both stainless steel substrates, however, the wetting process on the polished substrate was significantly slower than that on the heated substrates. The mechanism of the interfacial reactions was discussed based on the microscopic and thermodynamic analysis, the substrates reacted with oxygen generated from the decomposition of the molten multi-component oxides and oxygen contained in the argon atmosphere, and the oxide film caused the molten multi-component oxides ceramic to spread on the substrates surfaces. For the polished substrate, more time was required for the surface oxidation to reach the surface composition of Heated-S, which resulted in relatively slow spreading and wetting rates. Moreover, the variance of the surface roughness drove the final contact angles to slightly different values following the sequence Polished-S > Heated-S.

Effect of surface oxidation on thermomechanical behavior of NiTi shape memory alloy wire

Science.gov (United States)

Ng, Ching Wei; Mahmud, Abdus Samad

2017-12-01

Nickel titanium (NiTi) alloy is a unique alloy that exhibits special behavior that recovers fully its shape after being deformed to beyond elastic region. However, this alloy is sensitive to any changes of its composition and introduction of inclusion in its matrix. Heat treatment of NiTi shape memory alloy to above 600 °C leads to the formation of the titanium oxide (TiO2) layer. Titanium oxide is a ceramic material that does not exhibit shape memory behaviors and possess different mechanical properties than that of NiTi alloy, thus disturbs the shape memory behavior of the alloy. In this work, the effect of formation of TiO2 surface oxide layer towards the thermal phase transformation and stress-induced deformation behaviors of the NiTi alloy were studied. The NiTi wire with composition of Ti-50.6 at% Ni was subjected to thermal oxidation at 600 °C to 900 °C for 30 and 60 minutes. The formation of the surface oxide layers was characterized by using the Scanning Electron Microscope (SEM). The effect of surface oxide layers with different thickness towards the thermal phase transformation behavior was studied by using the Differential Scanning Calorimeter (DSC). The effect of surface oxidation towards the stress-induced deformation behavior was studied through the tensile deformation test. The stress-induced deformation behavior and the shape memory recovery of the NiTi wire under tensile deformation were found to be affected marginally by the formation of thick TiO2 layer.

Thermal oxidative degradation of wood modified with aminophenylborates

Directory of Open Access Journals (Sweden)

Klyachenkova Olga

2016-01-01

Full Text Available Comparative thermal analysis in the presence of oxygen was carried out for samples of native pine wood and wood samples modified with aminophenylborates. Significant decrease in the amount of heat released during thermal decomposition of the modified samples was established, which is due to the increase of carbonaceous residues on the surface. Reduction of heat release during decomposition of the modified samples may be explained by the lower yield of combustible volatile products as well as by thin film of boron oxide, formed on the surface of the modified wood, that partially reflects heat flow. Produced upon the modifier decomposition water vapor and inert nitrogen oxides dilute gaseous mixture near the wood surface and isolate it from oxygen. This enhances fire-resistance of wood modified with mono- and diethanolamine(N→Bphenylborates. Hydroxyl group at the sixth carbon atom of the glucopyranose ring of cellulose participates in reactions of cellulose modification, which prevents formation of flammable levoglucosan and, consequently, improves the fire-resistance of the modified wood.

Effect of process parameters on surface oxides on chromium-alloyed steel powder during sintering

International Nuclear Information System (INIS)

Chasoglou, D.; Hryha, E.; Nyborg, L.

2013-01-01

The use of chromium in the PM steel industry today puts high demands on the choice and control of the atmosphere during the sintering process due to its high affinity to oxygen. Particular attention is required in order to control the surface chemistry of the powder which in turn is the key factor for the successful sintering and production of PM parts. Different atmosphere compositions, heating rates and green densities were employed while performing sintering trials on water atomized steel powder pre-alloyed with 3 wt.% Cr in order to evaluate the effect on surface chemical reactions. Fracture surfaces of sintered samples were examined using high resolution scanning electron microscopy combined with X-ray microanalysis. The investigation was complemented with thermogravimetric (TG) studies. Reaction products in particulate form containing strong-oxide forming elements such as Cr, Si and Mn were formed during sintering for all conditions. Processing in vacuum results in intensive inter-particle neck development during the heating stage and consequently in the excessive enclosure of surface oxide which is reflected in less good final mechanical properties. Enhanced oxide reduction was observed in samples processed in hydrogen-containing atmospheres independent of the actual content in the range of 3–10 vol.%. An optimum heating rate was required for balancing reduction/oxidation processes. A simple model for the enclosure and growth of oxide inclusions during the sinter-neck development is proposed. The obtained results show that significant reduction of the oxygen content can be achieved by adjusting the atmosphere purity/composition. - Highlights: ► A local atmosphere microclimate is very important for sintering of PM steels. ► High risk of surface oxide enclosure between 800 and 1000 °C. ► Coalescence and agglomeration of enclosed oxides take place during sintering. ► The effect of different process parameters on the oxide reduction is examined. ► A

NO oxidation on Zeolite Supported Cu Catalysts: Formation and Reactivity of Surface Nitrates

Energy Technology Data Exchange (ETDEWEB)

Chen, Hai-Ying; Wei, Zhehao; Kollar, Marton; Gao, Feng; Wang, Yilin; Szanyi, Janos; Peden, Charles HF

2016-04-18

The comparative activities of a small-pore Cu-CHA and a large-pore Cu-BEA catalyst for the selective catalytic reduction (SCR) of NOx with NH3, and for the oxidation of NO to NO2 and the subsequent formation of surface nitrates were investigated. Although both catalysts are highly active in SCR reactions, they exhibit very low NO oxidation activity. Furthermore, Cu-CHA is even less active than Cu-BEA in catalyzing NO oxidation but is clearly more active for SCR reactions. Temperature-programed desorption (TPD) experiments following the adsorption of (NO2 + NO + O2) with different NO2:NO ratios reveal that the poor NO oxidation activity of the two catalysts is not due to the formation of stable surface nitrates. On the contrary, NO is found to reduce and decompose the surface nitrates on both catalysts. To monitor the reaction pathways, isotope exchange experiments were conducted by using 15NO to react with 14N-nitrate covered catalyst surfaces. The evolution of FTIR spectra during the isotope exchange process demonstrates that 14N-nitrates are simply displaced with no formation of 15N-nitrates on the Cu-CHA sample, which is clearly different from that observed on the Cu-BEA sample where formation of 15N-nitrates is apparent. The results suggest that the formal oxidation state of N during the NO oxidation on Cu-CHA mainly proceeds from its original +2 to a +3 oxidation state, whereas reaching a higher oxidation state for N, such as +4 or +5, is possible on Cu-BEA. The authors at PNNL gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

Surface area of antimony oxide by isotope exchange and other methods

Energy Technology Data Exchange (ETDEWEB)

Rao, Y.K.; Acharya, B.V.; Rangamannar, B.

1985-06-17

Specific surface areas of antimony oxide samples, one commercial, the other prepared from antimony trichloride were measured by heterogeneous isotope exchange, gas adsorption, air permeability and microscopic methods. Specific surface areas obtained by these four methods for the two samples were compared and the observed differences are explained.

Barriers, invasion, and conservation of native salmonids in coldwater streams [Box 18.2

Science.gov (United States)

Bruce Rieman; Michael Young; Kurt Fausch; Jason Dunham; Douglas Peterson

2010-01-01

Habitat loss and fragmentation are threats to persistence of many native fish populations. Invading nonnative species that may restrict or displace native species are also important. These two issues are particularly relevant for native salmonids that are often limited to remnant habitats in cold, headwater streams. On the surface, reversing threats to native fishes...

A Classical Potential to Model the Adsorption of Biological Molecules on Oxidized Titanium Surfaces.

Science.gov (United States)

Schneider, Julian; Ciacchi, Lucio Colombi

2011-02-08

The behavior of titanium implants in physiological environments is governed by the thin oxide layer that forms spontaneously on the metal surface and mediates the interactions with adsorbate molecules. In order to study the adsorption of biomolecules on titanium in a realistic fashion, we first build up a model of an oxidized Ti surface in contact with liquid water by means of extensive first-principles molecular dynamics simulations. Taking the obtained structure as reference, we then develop a classical potential to model the Ti/TiOx/water interface. This is based on the mapping with Coulomb and Lennard-Jones potentials of the adsorption energy landscape of single water and ammonia molecules on the rutile TiO2(110) surface. The interactions with arbitrary organic molecules are obtained via standard combination rules to established biomolecular force fields. The transferability of our potential to the case of organic molecules adsorbing on the oxidized Ti surface is checked by comparing the classical potential energy surfaces of representative systems to quantum mechanical results at the level of density functional theory. Moreover, we calculate the heat of immersion of the TiO2 rutile surface and the detachment force of a single tyrosine residue from steered molecular dynamics simulations, finding good agreement with experimental reference data in both cases. As a first application, we study the adsorption behavior of the Arg-Gly-Asp (RGD) peptide on the oxidized titanium surface, focusing particularly on the calculation of the free energy of desorption.

Process for growing a film epitaxially upon an oxide surface and structures formed with the process

Science.gov (United States)

McKee, Rodney A.; Walker, Frederick J.

1995-01-01

A process and structure wherein a film comprised of a perovskite or a spinel is built epitaxially upon a surface, such as an alkaline earth oxide surface, involves the epitaxial build up of alternating constituent metal oxide planes of the perovskite or spinel. The first layer of metal oxide built upon the surface includes a metal element which provides a small cation in the crystalline structure of the perovskite or spinel, and the second layer of metal oxide built upon the surface includes a metal element which provides a large cation in the crystalline structure of the perovskite or spinel. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

Macromolecular surface design: photopatterning of functional stable nitrile oxides.

Science.gov (United States)

Altintas, Ozcan; Glassner, Mathias; Rodriguez-Emmenegger, Cesar; Welle, Alexander; Trouillet, Vanessa; Barner-Kowollik, Christopher

2015-05-04

The efficient trapping of photogenerated thioaldehydes with functional shelf-stable nitrile oxides in a 1,3-dipolar cycloaddition is a novel and versatile photochemical strategy for polymer end-group functionalization and surface modification under mild and equimolar conditions. The modular ligation in solution was followed in detail by electrospray ionization mass spectrometry (ESI-MS). X-ray photoelectron spectroscopy (XPS) was employed to analyze the functionalized surfaces, whereas time-of-flight secondary-ion mass spectrometry (ToF-SIMS) confirmed the spatial control of the surface functionalization using a micropatterned shadow mask. Polymer brushes were grown from the surface in a spatially confined regime by surface-initiated atom transfer radical polymerization (SI-ATRP) as confirmed by TOF-SIMS, XPS as well as ellipsometry. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Descriptors and Thermodynamic Limitations of Electrocatalytic Carbon Dioxide Reduction on Rutile Oxide Surfaces

DEFF Research Database (Denmark)

Bhowmik, Arghya; Vegge, Tejs; Hansen, Heine Anton

2016-01-01

A detailed understanding of the electrochemical reduction of CO2 into liquid fuels on rutile metal oxide surfaces is developed by using DFT calculations. We consider oxide overlayer structures on RuO2(1 1 0) surfaces as model catalysts to elucidate the trends and limitations in the CO2 reduction...... and it defines the left leg of the activity volcano for CO2RR. HCOOH* is a key intermediate for products formed through further reduction, for example, methanediol, methanol, and methane. The surfaces that do not bind HCOOH* are selective towards formic acid (HCOOH) production, but hydrogen evolution limits...

Influence of substrate preparation on the shaping of the topography of the surface of nanoceramic oxide layers

Science.gov (United States)

Bara, Marek; Kubica, Marek

2014-02-01

The paper discusses the shaping mechanism and changes occurring in the structure and topography of the surface of nanoceramic oxide layers during their formation. The paper presents the influence of substrate preparation on the surface topography of oxide layers. The layers were produced via hard anodizing on the EN AW-5251 aluminum alloy. The layers obtained were subjected to microscope examinations, image and chemical composition analyses, and stereometric examinations. Heredity of substrate properties in the topography of the surface of nanoceramic oxide layers formed as a result of electrochemical oxidation has been shown.

Growth of micrometric oxide layers to explore laser decontamination of metallic surfaces

Directory of Open Access Journals (Sweden)

Carvalho Luisa

2017-01-01

Full Text Available The nuclear industry produces a wide range of radioactive waste in terms of hazard level, contaminants and material. For metallic equipment like steam generators, the radioactivity is mainly located in the oxide surface. In order to study and develop safe techniques for dismantling and for decontamination, it is important to have access to oxide layers with a representative distribution of non-radioactive contaminants. In this paper we propose a method for the creation of oxide layers on stainless steel 304L with europium (Eu as contaminant. This technique consists in spraying an Eu-solution on stainless steel samples. The specimens are firstly treated with a pulsed nanosecond laser after which the steel samples are placed in a 873 K furnace for various durations in order to grow an oxide layer. The oxide structure and in-depth distribution of Eu in the oxide layer were analyzed by scanning electron microscopy coupled to an energy-dispersive X-ray microanalyzer, as well as by glow discharge optical emission or mass spectrometry. The oxide layers were grown to thicknesses in the range of 200 nm–4.5 μm depending on the laser treatment parameters and the heating duration. These contaminated oxides had a ‘duplex structure’ with a mean concentration of the order of 6 × 1016 atoms/cm2 (15 μg/cm2 of europium in the volume of the oxide layer. It appears that europium implementation prevented the oxide growth in the furnace. Nevertheless, the presence of the contamination had no impact on the thickness of the oxide layers obtained by preliminary laser treatment. These oxide layers were used to study the decontamination of metallic surfaces such as stainless steel 304L using a nanosecond pulsed laser.

Levels of protein hydroperoxides and carbonyl groups in guinea pigs native of high altitudes (Huancavelica, 3660 m)

OpenAIRE

Huayta, Roxana; Zúñiga, Haydée; Esquerre, Cynthia; Hernández, Luz; Carranza, Elizabeth

2014-01-01

The influence of hypobaric hypoxia on protein oxidation in lungs, heart, liver, kidneys and testicles of high altitude native guinea pigs (Huancavelica, 3660 m) in comparison to sea level (Lima, 150 m) native guinea pigs was evaluated. The concentration of protein hydroperoxides (POOH) and carbonyl groups (GC) as markers of protein oxidation, as well as total thiols (TT) concentration, powerful reducing agents that act as live antioxidants were determined. The results showed low concentration...

Photoelectron binding energy shifts observed during oxidation of group IIA, IIIA and IVA elemental surfaces

International Nuclear Information System (INIS)

Heide, P.A.W. van der

2006-01-01

An extensive re-evaluation of XPS binding energies (BE's) and binding energy shifts (ΔBE's) from metals, oxides and the carbonates of the group II, III and IVA elements (exceptions are Be, Mg and Hf) has been carried out using a substrate specific BE referencing approach. From this, O-1s BE's are found to fall into surface oxide, bulk oxide and carbonate groupings, with bulk oxides showing the lowest BE's followed by surface oxides (+∼1.5 eV) and then carbonates (+∼3.0 eV). The O-1s BE's from the bulk oxides also appear to scale with 1/d, where d is inter-atomic distance. The same is noted in the ΔBE's observed from the metallic counterparts during oxidation of the elemental surfaces. This, and the decreasing BE exhibited by Ca, Sr and Ba on oxidation is explained within the charge potential model as resulting from competing inter- and intra-atomic effects, and is shown to be consistent with partial covalency arguments utilizing Madulung potentials. The ΔBE's also fall into groups according to the elements location in the periodic table, i.e. s, p or d block. These trends open up the possibility of approximating ΔBE's arising from initial and final state effects, and bond distances

Surface properties of nanostructured NiO undergoing electrochemical oxidation in 3-methoxy-propionitrile

Science.gov (United States)

Bonomo, Matteo; Marrani, Andrea Giacomo; Novelli, Vittoria; Awais, Muhammad; Dowling, Denis P.; Vos, Johannes G.; Dini, Danilo

2017-05-01

Nanostructured nickel oxide (NiO) was deposited in the configuration of thin film (thickness, l = 2-6 μm) onto fluorine-doped tin oxide (FTO) substrates via plasma-assisted rapid discharge sintering (RDS). Electrochemical cycling of RDS NiO in 3-methoxy-propionitrile (3-MPN) revealed two characteristic peaks of NiO oxidation which were associated to the surface-confined redox processes Ni(II) → Ni(III) and Ni(III) → Ni(IV). Grazing angle X-ray photoelectron spectroscopy (XPS) was conducted ex-situ on NiO electrodes in both pristine and oxidized states. Oxidized NiO samples for XPS experiments were obtained in the potentiostatic mode through the polarization of NiO at its two characteristic potentials of oxidation. The XPS analysis allowed to ascertain the electronic structure of the nanoporous NiO framework, and verify the adsorption of perchlorate and chloride anions onto NiO surface due to the compensation of the charge stored in oxidized NiO. XPS also revealed that the spectrum within the region characteristic of Ni 2p ionization does not vary considerably with the state of charge of the nickel centres. This finding is in evident contrast to what has been observed for the same system when it undergoes electrochemical oxidation in aqueous electrolyte.

Catabolism of native and oxidized low density lipoproteins: in vivo insights from small animal positron emission tomography studies.

Science.gov (United States)

Pietzsch, J; Bergmann, R; Wuest, F; Pawelke, B; Hultsch, C; van den Hoff, J

2005-12-01

The human organism is exposed to numerous processes that generate reactive oxygen species (ROS). ROS may directly or indirectly cause oxidative modification and damage of proteins. Protein oxidation is regarded as a crucial event in the pathogenesis of various diseases ranging from rheumatoid arthritis to Alzheimer's disease and atherosclerosis. As a representative example, oxidation of low density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Data concerning the role of circulating oxidized LDL (oxLDL) in the development and outcome of diseases are scarce. One reason for this is the shortage of methods for direct assessment of the metabolic fate of circulating oxLDL in vivo. We present an improved methodology based on the radiolabelling of apoB-100 of native LDL (nLDL) and oxLDL, respectively, with the positron emitter fluorine-18 ((18)F) by conjugation with N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). Radiolabelling of both nLDL and oxLDL using [(18)F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively, in vitro. The method was further evaluated with respect to the radiopharmacological properties of both [(18)F]fluorobenzoylated nLDL and oxLDL by biodistribution studies in male Wistar rats. The metabolic fate of [(18)F]fluorobenzoylated nLDL and oxLDL in rats in vivo was further delineated by dynamic positron emission tomography (PET) using a dedicated small animal tomograph (spatial resolution of 2 mm). From this study we conclude that the use of [(18)F]FB-labelled LDL particles is an attractive alternative to, e.g., LDL iodination methods, and is of value to characterize and to discriminate the kinetics and the metabolic fate of nLDL and oxLDL in small animals in vivo.

Theoretical studies of positron states and annihilation characteristics at the oxidized Cu(100) surface

Energy Technology Data Exchange (ETDEWEB)

Fazleev, N. G. [Department of Physics, Box 19059, University of Texas at Arlington, Arlington Texas 76019 (United States) and Institute of Physics, Kazan Federal University, Kremlevskaya18, Kazan 420008 (Russian Federation); Weiss, A. H. [Department of Physics, Box 19059, University of Texas at Arlington, Arlington Texas 76019 (United States)

2013-04-19

In this work we present the results of theoretical studies of positron surface and bulk states and annihilation probabilities of surface-trapped positrons with relevant core electrons at the oxidized Cu(100) surface under conditions of high oxygen coverage. An ab-initio study of the electronic properties of the Cu(100) missing row reconstructed surface at various on surface and sub-surface oxygen coverages has been performed on the basis of the density functional theory (DFT) using the Dmol3 code and the generalized gradient approximation (GGA). Surface structures in calculations have been constructed by adding oxygen atoms to various surface hollow and sub-surface octahedral sites of the 0.5 monolayer (ML) missing row reconstructed phase of the Cu(100) surface with oxygen coverages ranging from 0.5 to 1.5 ML. The charge redistribution at the surface and variations in atomic structure and chemical composition of the topmost layers associated with oxidation and surface reconstruction have been found to affect the spatial extent and localization of the positron surface state wave function and annihilation probabilities of surface trapped positrons with relevant core electrons. Theoretical results are compared with experimental data obtained from studies of oxidation of the Cu(100) surface using positron annihilation induced Auger electron spectroscopy (PAES). It has been shown that positron annihilation probabilities with Cu 3s and 3p core electrons decrease when total (on-surface and sub-surface) oxygen coverage of the Cu(100) surface increases up to 1 ML. The calculations show that for high oxygen coverage when total oxygen coverage is 1. 5 ML the positron is not bound to the surface.

Characterization of the inside and outside oxide surfaces of irradiated pressure tubes of Embalse nuclear power plant

International Nuclear Information System (INIS)

Bordoni, Roberto A.; Olmedo, Ana M.

2004-01-01

The inside and outside surfaces of two pressure tubes (PT) removed from Embalse nuclear power plant (CNE) after 10 of effective full power years (EFPY) were characterized. The oxide thickness of both faces, in different zones, was also measured. The inside surfaces of both PTs, B-102 (A-14) and B-298 (L-12), were covered with a black oxide that replicates the original PT surface. A network of microcracks perpendicular to the inside surface in contact with the coolant was found. In some cases, near the outlet of the PT, some spalling of the oxide was also found. These small microcracks and spalling do not affect the protective character of the oxide since a thickness about 5 or 6 μm of an undamaged oxide is found at the metal/oxide interface side. The oxide thickness changes between approximately 6 to 12 μm for B-102 tube and around 7 to 15 μm for B-298 tube. The average corrosion rate is 1.16 μm/10 4 HH for B-102 tube and 1.35 μm/10 4 HH for B-298 tube at 5.8 m position for both PTs. These corrosion rates show good corrosion behaviour of CNE PTs. The average corrosion rate of the inside surface of the PTs depends on the coolant temperature but not on fast neutron flux. The outside oxide film is black, shiny, compact and protective, replicating also the original surface. The oxide thickness changes between 2 to 6.5 μm in B-102 tube and between 1.8 to 3.7 μm B-298 tube. These oxide thicknesses are within the values reported for PTs in CANDU Stations. (author) [es

Adsorption of poly(vinyl formamide-co-vinyl amine) (PVFA-co-PVAm) polymers on zinc, zinc oxide, iron, and iron oxide surfaces.

Science.gov (United States)

Seifert, Susan; Simon, Frank; Baumann, Giesela; Hietschold, Michael; Seifert, Andreas; Spange, Stefan

2011-12-06

The adsorption of poly(vinyl formamide) (PVFA) and the statistic copolymers poly(vinyl formamide-co-vinyl amine) (PVFA-co-PVAm) onto zinc and iron metal particles as well as their oxides was investigated. The adsorbates were characterized by means of XPS, DRIFT spectroscopy, wet chemical analysis, and solvatochromic probes. Dicyano-bis-(1,10-phenanthroline)-iron(II) (1), 3-(4-amino-3-methylphenyl)-7-phenyl-benzo-[1,2-b:4,5-b']difuran-2,6-dione (2), and 4-tert-butyl-2-(dicyano-methylene)-5-[4-(diethylamino)-benzylidene]-Δ(3)-thiazoline (3) as solvatochromic probes were coadsorbed onto zinc oxide to measure various effects of surface polarity. The experimental findings showed that the adsorption mechanism of PVFA and PVFA-co-PVAm strongly depends on the degree of hydrolysis of PVFA and pH values and also on the kind of metal or metal oxide surfaces that were employed as adsorbents. The adsorption mechanism of PVFA/PVFA-co-PVAm onto zinc oxide and iron oxide surfaces is mainly affected by electrostatic interactions. Particularly in the region of pH 5, the adsorption of PVFA/PVFA-co-PVAm onto zinc and iron metal particles is additionally influenced by redox processes, dissolution, and complexation reactions. © 2011 American Chemical Society

Reduction of a thin chromium oxide film on Inconel surface upon treatment with hydrogen plasma

Energy Technology Data Exchange (ETDEWEB)

Vesel, Alenka, E-mail: alenka.vesel@guest.arnes.si [Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana (Slovenia); Mozetic, Miran [Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana (Slovenia); Balat-Pichelin, Marianne [PROMES-CNRS Laboratory, 7 Rue du four solaire, 66120 Font Romeu Odeillo (France)

2016-11-30

Highlights: • Oxidized Inconel alloy was exposed to hydrogen at temperatures up to 1500 K. • Oxide reduction in hydrogen plasma started at approximately 1300 K. • AES depth profiling revealed complete reduction of oxides in plasma. • Oxides were not reduced, if the sample was heated just in hydrogen atmosphere. • Surface of reduced Inconel preserved the same composition as the bulk material. - Abstract: Inconel samples with a surface oxide film composed of solely chromium oxide with a thickness of approximately 700 nm were exposed to low-pressure hydrogen plasma at elevated temperatures to determine the suitable parameters for reduction of the oxide film. The hydrogen pressure during treatment was set to 60 Pa. Plasma was created by a surfaguide microwave discharge in a quartz glass tube to allow for a high dissociation fraction of hydrogen molecules. Auger electron depth profiling (AES) was used to determine the decay of the oxygen in the surface film and X-ray diffraction (XRD) to measure structural modifications. During hydrogen plasma treatment, the oxidized Inconel samples were heated to elevated temperatures. The reduction of the oxide film started at temperatures of approximately 1300 K (considering the emissivity of 0.85) and the oxide was reduced in about 10 s of treatment as revealed by AES. The XRD showed sharper substrate peaks after the reduction. Samples treated in hydrogen atmosphere under the same conditions have not been reduced up to approximately 1500 K indicating usefulness of plasma treatment.

Effect of ammonium-salt solutions on the surface properties of carbon fibers in electrochemical anodic oxidation

Energy Technology Data Exchange (ETDEWEB)

Qian Xin, E-mail: qx3023@nimte.ac.cn [National Engineering Laboratory of Carbon Fiber Preparation Technology, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Wang Xuefei; Ouyang Qin; Chen Yousi; Yan Qing [National Engineering Laboratory of Carbon Fiber Preparation Technology, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

2012-10-15

Highlights: Black-Right-Pointing-Pointer Longitudinal grooves on the fiber surface became more well-defined and much deeper after surface treatment. Black-Right-Pointing-Pointer The concentration of oxygen and nitrogen on the fiber surface increased after surface treatment. Black-Right-Pointing-Pointer The intensity of oxidative reaction varied with the change of ammonium-salt solutions. Black-Right-Pointing-Pointer The higher the concentration of OH{sup -} ions in the electrolytes, the violent the oxidative reaction happened. - Abstract: The surfaces of polyacrylonitrile-based carbon fibers were treated by an electrochemical anodic method. Three different kinds of ammonium-salt solutions namely NH{sub 4}HCO{sub 3}, (NH{sub 4}){sub 2}CO{sub 3} and (NH{sub 4}){sub 3}PO{sub 4} were respectively chosen as the electrolytes. The effect of these electrolytes on the surface structure was studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed that longitudinal grooves on the fiber surface became more well-defined and much deeper after surface treatment, and the root mean square roughness (RMS) of carbon fiber surface increased from 4.6 nm for untreated fibers to 13.5 nm for treated fibers in (NH{sub 4}){sub 3}PO{sub 4} electrolytes. The concentration of oxygen and nitrogen atomic on the fiber surface increased after surface treatment. The tensile strength of oxidized fibers had an obvious decrease, whereas the interlaminar shear strength (ILSS) value of corresponding carbon fiber reinforced polymers (CFRPs) increased in a large extent. The intensity of oxidative reaction varied with the change of ammonium-salt solutions and electrochemical oxidation in (NH{sub 4}){sub 3}PO{sub 4} electrolyte was of the most violence. The corresponding mechanism was also discussed and the result showed that the higher the concentration of OH{sup -} ions in the electrolytes, the violent the oxidative

Oxidative nanopatterning of titanium generates mesoporous surfaces with antimicrobial properties

Directory of Open Access Journals (Sweden)

Variola F

2014-05-01

Full Text Available Fabio Variola,1,2 Sylvia Francis Zalzal,3 Annie Leduc,3 Jean Barbeau,3 Antonio Nanci31Faculty of Engineering, Department of Mechanical Engineering, 2Faculty of Science, Department of Physics, University of Ottawa, Ottawa, ON, 3Faculty of Dental Medicine, Université de Montréal, Montreal, QC, CanadaAbstract: Mesoporous surfaces generated by oxidative nanopatterning have the capacity to selectively regulate cell behavior, but their impact on microorganisms has not yet been explored. The main objective of this study was to test the effects of such surfaces on the adherence of two common bacteria and one yeast strain that are responsible for nosocomial infections in clinical settings and biomedical applications. In addition, because surface characteristics are known to affect bacterial adhesion, we further characterized the physicochemical properties of the mesoporous surfaces. Focused ion beam (FIB was used to generate ultrathin sections for elemental analysis by energy-dispersive X-ray spectroscopy (EDS, nanobeam electron diffraction (NBED, and high-angle annular dark field (HAADF scanning transmission electron microscopy (STEM imaging. The adherence of Staphylococcus aureus, Escherichia coli and Candida albicans onto titanium disks with mesoporous and polished surfaces was compared. Disks with the two surfaces side-by-side were also used for direct visual comparison. Qualitative and quantitative results from this study indicate that bacterial adhesion is significantly hindered by the mesoporous surface. In addition, we provide evidence that it alters structural parameters of C. albicans that determine its invasiveness potential, suggesting that microorganisms can sense and respond to the mesoporous surface. Our findings demonstrate the efficiency of a simple chemical oxidative treatment in generating nanotextured surfaces with antimicrobial capacity with potential applications in the implant manufacturing industry and hospital setting

Role of surface chemistry in modified ACF (activated carbon fiber)-catalyzed peroxymonosulfate oxidation

Energy Technology Data Exchange (ETDEWEB)

Yang, Shiying, E-mail: ysy@ouc.edu.cn [Key Laboratory of Marine Environment and Ecology, Ministry of Education, Qingdao 266100 (China); College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China); Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering (MEGE), Qingdao 266100 (China); Li, Lei [College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China); Xiao, Tuo [College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China); China City Environment Protection Engineering Limited Company, Wuhan 430071 (China); Zheng, Di; Zhang, Yitao [College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100 (China)

2016-10-15

Highlights: • ACF can efficiently activate peroxymonosulfate to degrade organic pollutants. • Basic functional groups may mainly increase the adsorption capacity of ACF. • C1, N1, N2 have promoting effect on the ACF catalyzed PMS oxidation. • Modification by heat after nitric acid is also a way of ACF regeneration. - Abstract: A commercial activated carbon fiber (ACF-0) was modified by three different methods: nitration treatment (ACF-N), heat treatment (ACF-H) and heat treatment after nitration (ACF-NH), and the effects of textural and chemical properties on the ability of the metal-free ACF-catalyzed peroxymonosulfate (PMS) oxidation of Reactive Black 5 (RB5), an azo dye being difficultly adsorbed onto ACF, in aqueous solution were investigated in this work. Surface density of functional groups, surface area changes, surface morphology and the chemical state inside ACF samples were characterized by Boehm titration, N{sub 2} adsorption, scanning electron microscopy in couple with energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), respectively. XPS spectra deconvolution was applied to figure out the importance of surface nitrogen-containing function groups. We found that π-π, pyridine and amine have promoting effect on the catalytic oxidation while the −NO{sub 2} has inhibitory effect on the ACF/PMS systems for RB5 destroy. Sustainability and renewability of the typical ACF-NH for catalytic oxidation of RB5 were also discussed in detail. Information about our conclusions are useful to control and improve the performance of ACF-catalyzed PMS oxidation for organic pollutants in wastewater treatment.

In situ characterization of Ti-peroxy gel during formation on titanium surfaces in hydrogen peroxide containing solutions

International Nuclear Information System (INIS)

Muyco, Julie J.; Gray, Jeremy J.; Ratto, Timothy V.; Orme, Christine A.; McKittrick, Joanna; Frangos, John

2006-01-01

Three possible functions of Ti-peroxy gel are: reduction of the inflammatory response through the reduction of hydrogen peroxide and other reactive oxygen species; creation of a favorable surface for calcium phosphate nucleation; and as a transitional layer between the compliant surrounding tissue and the stiff titanium. Traditional surface characterization techniques operate in high vacuum environments that alter the actual sample-solution interface. Our studies used techniques that allowed samples to remain in solution and be observed over time. Atomic force microscopy (AFM) force-distance curves, electrochemical impedance spectroscopy (EIS), and Raman spectroscopy were each used in situ to define kinetic and mechanical properties of Ti-peroxy gel as it formed over time on titanium during exposure to hydrogen peroxide. Our studies enabled us to monitor real-time changes in the native oxide layer on titanium in hydrogen peroxide containing solution, including the formation of a Ti-peroxy gel layer above the native oxide. Peaks attributed to Ti-peroxy gel were seen to emerge over the course of several hours using in situ Raman spectroscopy. Force-distance curves suggest a layer that thickens with time on the titanium sample surface. EIS data showed that changes in the surface layers could be monitored in solution over time

Effect of dew point on the formation of surface oxides of twinning-induced plasticity steel

International Nuclear Information System (INIS)

Kim, Yunkyum; Lee, Joonho; Shin, Kwang-Soo; Jeon, Sun-Ho; Chin, Kwang-Geun

2014-01-01

The surface oxides of twinning-induced plasticity (TWIP) steel annealed at 800 °C for 43 s were investigated using transmission electron microscopy. During the annealing process, the oxygen potential was controlled by adjusting the dew point in a 15%H 2 –N 2 gas atmosphere. It was found that the type of surface oxides formed and the thickness of the oxide layer were determined by the dew point. In a gas mixture with a dew point of − 20 °C, a MnO layer with a thickness of ∼ 100 nm was formed uniformly on the steel surface. Under the MnO layer, a MnAl 2 O 4 layer with a thickness of ∼ 15 nm was formed with small Mn 2 SiO 4 particles that measured ∼ 70 nm in diameter. Approximately 500 nm below the MnAl 2 O 4 layer, Al 2 O 3 was formed at the grain boundaries. On the other hand, in a gas mixture with a dew point of − 40 °C, a MnAl 2 O 4 layer with a thickness of ∼ 5 nm was formed on most parts of the surface. On some parts of the surface, Mn 2 SiO 4 particles were formed irregularly up to a thickness of ∼ 50 nm. Approximately 200 nm below the MnAl 2 O 4 layer, Al 2 O 3 was found at the grain boundaries. Thermodynamic calculations were performed to explain the experimental results. The calculations showed that when a O2 > ∼ 1.26 × 10 −28 , MnO, MnAl 2 O 4 , and Mn 2 SiO 4 can be formed together, and the major oxide is MnO. When a O2 is in the range of 1.26 × 10 −28 –2.51 × 10 −31 , MnO is not stable but MnAl 2 O 4 is the major oxide. When a O2 < ∼ 2.51 × 10 −31 , only Al 2 O 3 is stable. Consequently, the effective activity of oxygen is considered the dominant factor in determining the type and shape of surface oxides of TWIP steel. - Highlights: • The surface oxides of TWIP steel annealed at 800 °C were investigated using TEM. • The surface oxides were determined by the dew point during the annealing process. • The activity of oxygen is the major factor determining the oxides of TWIP steel

Surface oxidation of porous ZrB{sub 2}-SiC ceramic composites by continuous-wave ytterbium fibre laser

Energy Technology Data Exchange (ETDEWEB)

Mahmod, Dayang Salyani Abang, E-mail: dygsalyani@gmail.com [Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak (Malaysia); Glandut, Nicolas [SPCTS, UMR 7315, CNRS, University of Limoges, European Ceramic Center, 12 Rue Atlantis, 87068 Limoges (France); Khan, Amir Azam [Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak (Malaysia); Labbe, Jean-Claude [SPCTS, UMR 7315, CNRS, University of Limoges, European Ceramic Center, 12 Rue Atlantis, 87068 Limoges (France)

2015-12-01

Highlights: • Surface oxidation of ZrB{sub 2}-SiC ceramic composites by Yb-fibre laser. • Round spiral laser pattern created for the surface oxidation. • Presence of laser-formed oxide scale and unaffected beneath regions. • Crazed but uncracked surface oxide. • A dense glassy SiO{sub 2}-rich layer exhibited enhances oxidation resistance. - Abstract: Surface treatment of ceramic substrates by a laser beam can allow to incorporate interesting properties to these ceramics. In the present work, surface oxidation of ca. 30% porous ZrB{sub 2}-SiC ceramic composites by using an ytterbium fibre laser was conducted. Oxidation of ceramic substrates through this process under ambient conditions has certain advantages compared to the classical oxidation method. A particular spiral laser pattern was created in order to produce an oxidized structure on ZrB{sub 2}-SiC porous substrates. The laser parameters were as follows i.e., laser power of 50, 60 and 70 W, a beam diameter of 1.25 mm, velocity of 2 mm/s, acceleration and deceleration of 1 mm/s{sup 2}. The microstructural and morphological changes in the laser-treated region was examined using scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. At laser power of 70 W, the sample exhibits uniform oxidation. It revealed that the very porous bulk beneath remained unaffected and unoxidized because this laser-formed oxide scale protects the substrate from oxidation. The presence of oxidized and unaffected regions indicated a high degree of heat localization. The dense glassy SiO{sub 2}-rich layer prevents the inward oxygen diffusion into the inner bulk hence enhances the oxidation resistance.

Effects of Oxidation and fractal surface roughness on the wettability and critical heat flux of glass-peened zirconium alloy tubes

International Nuclear Information System (INIS)

Fong, R.W.L.; Nitheanandan, T.; Bullock, C.D.; Slater, L.F.; McRae, G.A.

2003-05-01

Glass-bead peening the outside surfaces of zirconium alloy tubes has been shown to increase the Critical Heat Flux (CHF) in pool boiling of water. The CHF is found to correlate with the fractal roughness of the metal tube surfaces. In this study on the effect of oxidation on glass-peened surfaces, test measurements for CHF, surface wettability and roughness have been evaluated using various glass-peened and oxidized zirconium alloy tubes. The results show that oxidation changes the solid-liquid contact angle (i.e., decreases wettability of the metal-oxide surface), but does not change the fractal surface roughness, appreciably. Thus, oxidation of the glass-peened surfaces of zirconium alloy tubes is not expected to degrade the CHF enhancement obtained by glass-bead peening. (author)

Sorption processes affecting arsenic solubility in oxidized surface sediments from Tulare Lake Bed, California

Science.gov (United States)

Gao, S.; Goldberg, S.; Herbel, M.J.; Chalmers, A.T.; Fujii, R.; Tanji, K.K.

2006-01-01

Elevated concentrations of arsenic (As) in shallow groundwater in Tulare Basin pose an environmental risk because of the carcinogenic properties of As and the potential for its migration to deep aquifers that could serve as a future drinking water source. Adsorption and desorption are hypothesized to be the major processes controlling As solubility in oxidized surface sediments where arsenate [As(V)] is dominant. This study examined the relationship between sorption processes and arsenic solubility in shallow sediments from the dry Tulare Lake bed by determining sorption isotherms, pH effect on solubility, and desorption-readsorption behavior (hysteresis), and by using a surface complexation model to describe sorption. The sediments showed a high capacity to adsorb As(V). Estimates of the maximum adsorption capacity were 92 mg As kg- 1 at pH 7.5 and 70 mg As kg- 1 at pH 8.5 obtained using the Langmuir adsorption isotherm. Soluble arsenic [> 97% As(V)] did not increase dramatically until above pH 10. In the native pH range (7.5-8.5), soluble As concentrations were close to the lowest, indicating that As was strongly retained on the sediment. A surface complexation model, the constant capacitance model, was able to provide a simultaneous fit to both adsorption isotherms (pH 7.5 and 8.5) and the adsorption envelope (pH effect on soluble As), although the data ranges are one order of magnitude different. A hysteresis phenomenon between As adsorbed on the sediment and As in solution phase was observed in the desorption-readsorption processes and differs from conventional hysteresis observed in adsorption-desorption processes. The cause is most likely due to modification of adsorbent surfaces in sediment samples upon extensive extractions (or desorption). The significance of the hysteresis phenomenon in affecting As solubility and mobility may be better understood by further microscopic studies of As interaction mechanisms with sediments subjected to extensive leaching

Hydrophobic and optical characteristics of graphene and graphene oxide films transferred onto functionalized silica particles deposited glass surface

Science.gov (United States)

Yilbas, B. S.; Ibrahim, A.; Ali, H.; Khaled, M.; Laoui, T.

2018-06-01

Hydrophobic and optical transmittance characteristics of the functionalized silica particles on the glass surface prior and after transfer of graphene and graphene oxide films on the surface are examined. Nano-size silica particles are synthesized and functionalized via chemical grafting and deposited onto a glass surface. Graphene film, grown on copper substrate, was transferred onto the functionalized silica particles surface through direct fishing method. Graphene oxide layer was deposited onto the functionalized silica particles surface via spin coating technique. Morphological, hydrophobic, and optical characteristics of the functionalized silica particles deposited surface prior and after graphene and graphene oxide films transfer are examined using the analytical tools. It is found that the functionalized silica particles are agglomerated at the surface forming packed structures with few micro/nano size pores. This arrangement gives rise to water droplet contact angle and contact angle hysteresis in the order of 163° and 2°, respectively, and remains almost uniform over the entire surface. Transferring graphene and depositing graphene oxide films over the functionalized silica particles surface lowers the water droplet contact angle slightly (157-160°) and increases the contact angle hysteresis (4°). The addition of the graphene and graphene oxide films onto the surface of the deposited functionalized silica particles improves the optical transmittance.

Oxidation Behavior of Surface-modified Stainless Steel 316LN in Supercritical-CO{sub 2} Environment

Energy Technology Data Exchange (ETDEWEB)

Kim, Sung Hwan; Heo, Jin Woo; Kim, Hyunm Yung; Jang, Chang Heui [KAIST, Daejeon (Korea, Republic of)

2016-05-15

Compared to other working fluids such as helium or nitrogen, S-CO{sub 2} offers a higher efficiency at operating temperatures of advanced reactors above 550 .deg. C. Moreover, the S-CO{sub 2} cycle is expected to have a significantly smaller footprint compared to other power conversion cycles, resulting in a broader range of applications with lower capital costs. Currently, stainless steel 316 is considered as the candidate structural material for the SFR. In comparison, it is well known that alumina (Al{sub 2}O{sub 3}) have superior oxidation and carburization resistance specifically at higher temperatures where α-Al{sub 2}O{sub 3} may form. Thus, various surface modification techniques have been applied to mostly Ni-base alloys so that a protective and continuous Al-rich oxide layer forms on the surface, conferring superior oxidation and carburization resistance. In this study, SS 316LN was deposited with Al via physical vapor deposition (PVD) method followed by heat treatment processes to develop an Al-rich layer at the surface. The specimens are to be exposed to high temperature S-CO{sub 2} environment to evaluate the oxidation and carburization resistance. Stainless steel 316LN was surface-modified to develop an Al-rich layer for improvement of oxidation behavior in S-CO{sub 2} environment. As the test temperature of 600 .deg. C is not sufficiently high for the formation of protective α-Al{sub 2}O{sub 3} formation, pre-oxidation of surface modified SS 316LN was conducted.

Atomic layer-by-layer oxidation of Ge (100) and (111) surfaces by plasma post oxidation of Al2O3/Ge structures

International Nuclear Information System (INIS)

Zhang, Rui; Huang, Po-Chin; Lin, Ju-Chin; Takenaka, Mitsuru; Takagi, Shinichi

2013-01-01

The ultrathin GeO x /Ge interfaces formed on Ge (100) and (111) surfaces by applying plasma post oxidation to thin Al 2 O 3 /Ge structures are characterized in detail using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. It is found that the XPS signals assigned to Ge 1+ and the 2+ states in the GeO x layers by post plasma oxidation have oscillating behaviors on Ge (100) surfaces in a period of ∼0.3 nm with an increase in the GeO x thickness. Additionally, the oscillations of the signals assigned to Ge 1+ and 2+ states show opposite phase to each other. The similar oscillation behaviors are also confirmed on Ge (111) surfaces for Ge 1+ and 3+ states in a period of ∼0.5 nm. These phenomena can be strongly regarded as an evidence of the atomic layer-by-layer oxidation of GeO x /Ge interfaces on Ge (100) and (111) surfaces.

Pb, Cu, and Zn distributions at humic acid-coated metal-oxide surfaces

Science.gov (United States)

Wang, Yingge; Michel, F. Marc; Choi, Yongseong; Eng, Peter J.; Levard, Clement; Siebner, Hagar; Gu, Baohua; Bargar, John R.; Brown, Gordon E.

2016-09-01

Mineral surfaces are often coated by natural organic matter (NOM), which has a major influence on metal-ion sorption and sequestration because of the abundance of binding sites in such coatings and the changes they cause in local nanoscale environments. The effects of NOM coatings on mineral surfaces are, however, still poorly understood at the molecular level due to the complexity of these systems. In this study, we have applied long-period X-ray standing wave-fluorescence yield (LP-XSW-FY) spectroscopy to measure the partitioning of naturally present Cu(II) (0.0226%), Zn(II) (0.009%), and Pb(II) (∼0.0004%) between Elliott Soil Humic Acid (ESHA) coatings and three model single-crystal metal-oxide substrates: α-Al2O3 (0 0 0 1), α-Al2O3 (1 -1 0 2), and α-Fe2O3 (0 0 0 1). The competitive sorption effects among these metal ions for binding sites in the ESHA coatings and on the metal-oxide surfaces were investigated as a function of reaction time, calcium content, and solution pH. Pb(II) ions present in the ESHA coatings were found to redistribute to reactive α-Al2O3 (1 -1 0 2) and α-Fe2O3 (0 0 0 1) surfaces after 3 h of reaction (pH = 6.0, [Ca(II)] = 2 mM). Pb(II) partitioning onto these reactive metal-oxide surfaces increased with increasing reaction time (up to 7 d). In addition, the partitioning of Cu(II) and Zn(II) from the ESHA coating to the α-Fe2O3 (0 0 0 1) substrate increased slightly with reaction time (2.4% and 3.7% for Cu(II) and Zn(II), respectively, after 3 h and 6.4% and 7.7% for Cu(II) and Zn(II), respectively, after 72 h of reaction time). However, no changes in the partitioning of Cu(II) and Zn(II) onto the α-Al2O3 (1 -1 0 2) surface were observed with increasing reaction time, suggesting that these ions strongly complex with functional groups in the ESHA coatings. Similar results were obtained for Cu(II) and Zn(II) on the ESHA-coated α-Al2O3 (1 -1 0 2) surfaces in samples without the addition of calcium. However, the amounts of Pb

Growth of micrometric oxide layers to explore laser decontamination of metallic surfaces

OpenAIRE

Carvalho Luisa; Pacquentin Wilfried; Tabarant Michel; Maskrot Hicham; Semerok Alexandre

2017-01-01

The nuclear industry produces a wide range of radioactive waste in terms of hazard level, contaminants and material. For metallic equipment like steam generators, the radioactivity is mainly located in the oxide surface. In order to study and develop safe techniques for dismantling and for decontamination, it is important to have access to oxide layers with a representative distribution of non-radioactive contaminants. In this paper we propose a method for the creation of oxide layers on stai...

Interaction of dimethylamine with clean and partially oxidized copper surfaces

Science.gov (United States)

Kelber, J. A.; Rogers, J. W.; Banse, B. A.; Koel, B. E.

1990-05-01

The interaction of dimethylamine (DMA) with partially oxidized polycrystalline copper [Cu(poly)] and clean and partially oxidized Cu(110) between 110 and 500 K has been examined using electron stimulated desorption (ESD), high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). ESD mass spectra of the DMA adsorbed on O/Cu(poly) between 112 and 230 K consistently display peaks at 44 amu [(CH 3) 2N] + and 46 amu [(CH 3) 2NH-H] +, but no significant parent peak at 45 amu [(CH 3) 2NH] +, even though this last feature is prominent in the gas-phase mass spectrum. OH - is not observed at temperatures below 184 K and the yield at higher temperatures is much less than that of O +. HREELS of DMA on clean and oxygen covered Cu(110) obtained at temperatures between 100 and 320 K show characteristic vibrational spectra for molecular DMA and no OH(a) vibrational modes. TPD results show that the desorption profiles of all the major peaks in the DMA mass spectrum follow that of the parent peak with no evidence for production of H 2O. The ESD, HREELS and TPD results all indicate that DMA is molecularly and reversibly adsorbed, with no significant formation of surface hydroxyl species. The results indicate that preferential adsorption of amines from amine/epoxy mixtures onto metal oxide surfaces could passivate the surface and prevent subsequent bonding to the epoxy resin.

Micro-arc oxidation as a tool to develop multifunctional calcium-rich surfaces for dental implant applications.

Science.gov (United States)

Ribeiro, A R; Oliveira, F; Boldrini, L C; Leite, P E; Falagan-Lotsch, P; Linhares, A B R; Zambuzzi, W F; Fragneaud, B; Campos, A P C; Gouvêa, C P; Archanjo, B S; Achete, C A; Marcantonio, E; Rocha, L A; Granjeiro, J M

2015-09-01

Titanium (Ti) is commonly used in dental implant applications. Surface modification strategies are being followed in last years in order to build Ti oxide-based surfaces that can fulfill, simultaneously, the following requirements: induced cell attachment and adhesion, while providing a superior corrosion and tribocorrosion performance. In this work micro-arc oxidation (MAO) was used as a tool for the growth of a nanostructured bioactive titanium oxide layer aimed to enhance cell attachment and adhesion for dental implant applications. Characterization of the surfaces was performed, in terms of morphology, topography, chemical composition and crystalline structure. Primary human osteoblast adhesion on the developed surfaces was investigated in detail by electronic and atomic force microscopy as well as immunocytochemistry. Also an investigation on the early cytokine production was performed. Results show that a relatively thick hybrid and graded oxide layer was produced on the Ti surface, being constituted by a mixture of anatase, rutile and amorphous phases where calcium (Ca) and phosphorous (P) were incorporated. An outermost nanometric-thick amorphous oxide layer rich in Ca was present in the film. This amorphous layer, rich in Ca, improved fibroblast viability and metabolic activity as well as osteoblast adhesion. High-resolution techniques allowed to understand that osteoblasts adhered less in the crystalline-rich regions while they preferentially adhere and spread over in the Ca-rich amorphous oxide layer. Also, these surfaces induce higher amounts of IFN-γ cytokine secretion, which is known to regulate inflammatory responses, bone microarchitecture as well as cytoskeleton reorganization and cellular spreading. These surfaces are promising in the context of dental implants, since they might lead to faster osseointegration. Copyright © 2015 Elsevier B.V. All rights reserved.

Micro-arc oxidation as a tool to develop multifunctional calcium-rich surfaces for dental implant applications

Energy Technology Data Exchange (ETDEWEB)

Ribeiro, A.R., E-mail: arribeiro@inmetro.gov.br [Department of Periodontology, Araraquara Dental School, University Estadual Paulista, Rua Humaitá 1680, 14801-903 Araraquara, São Paulo (Brazil); Directory of Metrology Applied to Life Science, National Institute of Metrology Quality and Technology, Av. N. S. das Graças 50, Xerém, Duque de Caxias, Rio de Janeiro (Brazil); Brazilian Branch of Institute of Biomaterials, Tribocorrosion and Nanomedicine (IBTN/Br) (Brazil); Oliveira, F., E-mail: fernando@dem.uminho.pt [Brazilian Branch of Institute of Biomaterials, Tribocorrosion and Nanomedicine (IBTN/Br) (Brazil); Centre for Mechanical and Materials Technologies, University of Minho, Campus de Azurém, 4800-058 Guimarães (Portugal); Boldrini, L.C., E-mail: lcboldrini@inmetro.gov.br [Directory of Metrology Applied to Life Science, National Institute of Metrology Quality and Technology, Av. N. S. das Graças 50, Xerém, Duque de Caxias, Rio de Janeiro (Brazil); Leite, P.E., E-mail: leitepec@gmail.com [Directory of Metrology Applied to Life Science, National Institute of Metrology Quality and Technology, Av. N. S. das Graças 50, Xerém, Duque de Caxias, Rio de Janeiro (Brazil); Falagan-Lotsch, P., E-mail: prifalagan@gmail.com [Directory of Metrology Applied to Life Science, National Institute of Metrology Quality and Technology, Av. N. S. das Graças 50, Xerém, Duque de Caxias, Rio de Janeiro (Brazil); Linhares, A.B.R., E-mail: adrianalinhares@hotmail.com [Clinical Research Unit, Antonio Pedro Hospital, Fluminense Federal University, Niterói (Brazil); and others

2015-09-01

Titanium (Ti) is commonly used in dental implant applications. Surface modification strategies are being followed in last years in order to build Ti oxide-based surfaces that can fulfill, simultaneously, the following requirements: induced cell attachment and adhesion, while providing a superior corrosion and tribocorrosion performance. In this work micro-arc oxidation (MAO) was used as a tool for the growth of a nanostructured bioactive titanium oxide layer aimed to enhance cell attachment and adhesion for dental implant applications. Characterization of the surfaces was performed, in terms of morphology, topography, chemical composition and crystalline structure. Primary human osteoblast adhesion on the developed surfaces was investigated in detail by electronic and atomic force microscopy as well as immunocytochemistry. Also an investigation on the early cytokine production was performed. Results show that a relatively thick hybrid and graded oxide layer was produced on the Ti surface, being constituted by a mixture of anatase, rutile and amorphous phases where calcium (Ca) and phosphorous (P) were incorporated. An outermost nanometric-thick amorphous oxide layer rich in Ca was present in the film. This amorphous layer, rich in Ca, improved fibroblast viability and metabolic activity as well as osteoblast adhesion. High-resolution techniques allowed to understand that osteoblasts adhered less in the crystalline-rich regions while they preferentially adhere and spread over in the Ca-rich amorphous oxide layer. Also, these surfaces induce higher amounts of IFN-γ cytokine secretion, which is known to regulate inflammatory responses, bone microarchitecture as well as cytoskeleton reorganization and cellular spreading. These surfaces are promising in the context of dental implants, since they might lead to faster osseointegration. - Highlights: • A nanometric-structured calcium-rich amorphous layer with improved bioactivity was produced on titanium surfaces. �

Micro-arc oxidation as a tool to develop multifunctional calcium-rich surfaces for dental implant applications

International Nuclear Information System (INIS)

Ribeiro, A.R.; Oliveira, F.; Boldrini, L.C.; Leite, P.E.; Falagan-Lotsch, P.; Linhares, A.B.R.

2015-01-01

Titanium (Ti) is commonly used in dental implant applications. Surface modification strategies are being followed in last years in order to build Ti oxide-based surfaces that can fulfill, simultaneously, the following requirements: induced cell attachment and adhesion, while providing a superior corrosion and tribocorrosion performance. In this work micro-arc oxidation (MAO) was used as a tool for the growth of a nanostructured bioactive titanium oxide layer aimed to enhance cell attachment and adhesion for dental implant applications. Characterization of the surfaces was performed, in terms of morphology, topography, chemical composition and crystalline structure. Primary human osteoblast adhesion on the developed surfaces was investigated in detail by electronic and atomic force microscopy as well as immunocytochemistry. Also an investigation on the early cytokine production was performed. Results show that a relatively thick hybrid and graded oxide layer was produced on the Ti surface, being constituted by a mixture of anatase, rutile and amorphous phases where calcium (Ca) and phosphorous (P) were incorporated. An outermost nanometric-thick amorphous oxide layer rich in Ca was present in the film. This amorphous layer, rich in Ca, improved fibroblast viability and metabolic activity as well as osteoblast adhesion. High-resolution techniques allowed to understand that osteoblasts adhered less in the crystalline-rich regions while they preferentially adhere and spread over in the Ca-rich amorphous oxide layer. Also, these surfaces induce higher amounts of IFN-γ cytokine secretion, which is known to regulate inflammatory responses, bone microarchitecture as well as cytoskeleton reorganization and cellular spreading. These surfaces are promising in the context of dental implants, since they might lead to faster osseointegration. - Highlights: • A nanometric-structured calcium-rich amorphous layer with improved bioactivity was produced on titanium surfaces. �

Narrow titanium oxide nanowires induced by femtosecond laser pulses on a titanium surface

Energy Technology Data Exchange (ETDEWEB)

Li, Hui; Li, Xian-Feng [Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006 (China); Zhang, Cheng-Yun [School of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China); Tie, Shao-Long [School of Chemistry and Environment, South China Normal University, Guangzhou 510006 (China); Lan, Sheng, E-mail: slan@scnu.edu.cn [Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006 (China)

2017-02-28

Highlights: • Titanium oxide nanowires with a feature width as narrow as ∼20 nm were induced on a titanium surface by using femtosecond laser pulses at 400 nm. • An evolution of the surface structure from a high spatial frequency laser-induced periodic structure parallel to the laser polarization to a low spatial frequency one perpendicular to the laser polarization was observed with increasing irradiation pulse number. • The formation of the titanium oxide nanowires was confirmed by the energy dispersive spectroscopy measurements and the evolution of the surface structure was successfully interpreted by using the efficacy factor theory. - Abstract: The evolution of the nanostructure induced on a titanium (Ti) surface with increasing irradiation pulse number by using a 400-nm femtosecond laser was examined by using scanning electron microscopy. High spatial frequency periodic structures of TiO{sub 2} parallel to the laser polarization were initially observed because of the laser-induced oxidation of the Ti surface and the larger efficacy factor of TiO{sub 2} in this direction. Periodically aligned TiO{sub 2} nanowires with featured width as small as 20 nm were obtained. With increasing pulse number, however, low spatial frequency periodic structures of Ti perpendicular to the laser polarization became dominant because Ti possesses a larger efficacy factor in this direction. The competition between the high- and low-spatial frequency periodic structures is in good agreement with the prediction of the efficacy factor theory and it should also be observed in the femtosecond laser ablation of other metals which are easily oxidized in air.

Designing porous metallic glass compact enclosed with surface iron oxides

Energy Technology Data Exchange (ETDEWEB)

Cho, Jae Young; Park, Hae Jin; Hong, Sung Hwan; Kim, Jeong Tae; Kim, Young Seok; Park, Jun-Young; Lee, Naesung [Hybrid Materials Center (HMC), Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 143-747 (Korea, Republic of); Seo, Yongho [Graphene Research Institute (GRI) & HMC, Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 143-747 (Korea, Republic of); Park, Jin Man, E-mail: jinman_park@hotmail.com [Global Technology Center, Samsung Electronics Co., Ltd, 129 Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 443-742 (Korea, Republic of); Kim, Ki Buem, E-mail: kbkim@sejong.ac.kr [Hybrid Materials Center (HMC), Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 143-747 (Korea, Republic of)

2015-06-25

Highlights: • Porous metallic glass compact was developed using electro-discharge sintering process. • Uniform PMGC can only be achieved when low electrical input energy was applied. • Functional iron-oxides were formed on the surface of PMGCs by hydrothermal technique. - Abstract: Porous metallic glass compact (PMGC) using electro-discharge sintering (EDS) process of gas atomized Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10}Be{sub 22.5} metallic glass powder was developed. The formation of uniform PMGC can only be achieved when low electrical input energy was applied. Functional iron-oxides were formed on the surface of PMGCs by hydrothermal technique. This finding suggests that PMGC can be applied in the new area such as catalyst via hydrothermal technique and offer a promising guideline for using the metallic glasses as a potential functional application.

Suppression of Magnetoresistance in Thin WTe2 Flakes by Surface Oxidation.

Science.gov (United States)

Woods, John M; Shen, Jie; Kumaravadivel, Piranavan; Pang, Yuan; Xie, Yujun; Pan, Grace A; Li, Min; Altman, Eric I; Lu, Li; Cha, Judy J

2017-07-12

Recent renewed interest in layered transition metal dichalcogenides stems from the exotic electronic phases predicted and observed in the single- and few-layer limit. Realizing these electronic phases requires preserving the desired transport properties down to a monolayer, which is challenging. Surface oxides are known to impart Fermi level pinning or degrade the mobility on a number of different systems, including transition metal dichalcogenides and black phosphorus. Semimetallic WTe 2 exhibits large magnetoresistance due to electron-hole compensation; thus, Fermi level pinning in thin WTe 2 flakes could break the electron-hole balance and suppress the large magnetoresistance. We show that WTe 2 develops an ∼2 nm thick amorphous surface oxide, which shifts the Fermi level by ∼300 meV at the WTe 2 surface. We also observe a dramatic suppression of the magnetoresistance for thin flakes. However, due to the semimetallic nature of WTe 2 , the effects of Fermi level pinning are well screened and are not the dominant cause for the suppression of magnetoresistance, supported by fitting a two-band model to the transport data, which showed the electron and hole carrier densities are balanced down to ∼13 nm. However, the fitting shows a significant decrease of the mobilities of both electrons and holes. We attribute this to the disorder introduced by the amorphous surface oxide layer. Thus, the decrease of mobility is the dominant factor in the suppression of magnetoresistance for thin WTe 2 flakes. Our study highlights the critical need to investigate often unanticipated and sometimes unavoidable extrinsic surface effects on the transport properties of layered dichalcogenides and other 2D materials.

Photocatalytic oxidation of NOx gases using TiO2: a surface spectroscopic approach

International Nuclear Information System (INIS)

Dalton, J.S.; Janes, P.A.; Jones, N.G.; Nicholson, J.A.; Hallam, K.R.; Allen, G.C.

2002-01-01

X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to study surface reactions between nitrogen oxides and TiO 2 on surfaces. - The bandgap of solid-state TiO 2 (3.2 eV) enables it to be a useful photocatalyst in the ultraviolet (λ 2 surface in the presence of sunlight therefore enables the removal of harmful NO x gases from the atmosphere by oxidation to nitrates. These properties, in addition to the whiteness, relative cheapness and non-toxicity, make TiO 2 ideal for the many de-NOX catalysts that are currently being commercially exploited both in the UK and Japan for concrete paving materials in inner cities. There is need, however, for further academic understanding of the surface reactions involved. Hence, we have used surface specific techniques, including X-ray photoelectron spectroscopy and Raman spectroscopy, to investigate the NO x adsorbate reaction at the TiO 2 substrate surface

Generalized molybdenum oxide surface chemical state XPS determination via informed amorphous sample model

Energy Technology Data Exchange (ETDEWEB)

Baltrusaitis, Jonas, E-mail: job314@lehigh.edu [Department of Chemical Engineering, Lehigh University, B336 Iacocca Hall, 111 Research Drive, Bethlehem, PA 18015 (United States); PhotoCatalytic Synthesis group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, Meander 229, P.O. Box 217, 7500 AE Enschede (Netherlands); Mendoza-Sanchez, Beatriz [CRANN, Chemistry School, Trinity College Dublin, Dublin (Ireland); Fernandez, Vincent [Institut des Matériaux Jean Rouxel, 2 rue de la Houssinière, BP 32229, F-44322 Nantes Cedex 3 (France); Veenstra, Rick [PhotoCatalytic Synthesis group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, Meander 229, P.O. Box 217, 7500 AE Enschede (Netherlands); Dukstiene, Nijole [Department of Physical and Inorganic Chemistry, Kaunas University of Technology, Radvilenu pl. 19, LT-50254 Kaunas (Lithuania); Roberts, Adam [Kratos Analytical Ltd, Trafford Wharf Road, Wharfside, Manchester, M17 1GP (United Kingdom); Fairley, Neal [Casa Software Ltd, Bay House, 5 Grosvenor Terrace, Teignmouth, Devon TQ14 8NE (United Kingdom)

2015-01-30

Highlights: • We analyzed and modeled spectral envelopes of complex molybdenum oxides. • Molybdenum oxide films of varying valence and crystallinity were synthesized. • MoO{sub 3} and MoO{sub 2} line shapes from experimental data were created. • Informed amorphous sample model (IASM) developed. • Amorphous molybdenum oxide XPS envelopes were interpreted. - Abstract: Accurate elemental oxidation state determination for the outer surface of a complex material is of crucial importance in many science and engineering disciplines, including chemistry, fundamental and applied surface science, catalysis, semiconductors and many others. X-ray photoelectron spectroscopy (XPS) is the primary tool used for this purpose. The spectral data obtained, however, is often very complex and can be subject to incorrect interpretation. Unlike traditional XPS spectra fitting procedures using purely synthetic spectral components, here we develop and present an XPS data processing method based on vector analysis that allows creating XPS spectral components by incorporating key information, obtained experimentally. XPS spectral data, obtained from series of molybdenum oxide samples with varying oxidation states and degree of crystallinity, were processed using this method and the corresponding oxidation states present, as well as their relative distribution was elucidated. It was shown that monitoring the evolution of the chemistry and crystal structure of a molybdenum oxide sample due to an invasive X-ray probe could be used to infer solutions to complex spectral envelopes.

Water surface coverage effects on reactivity of plasma oxidized Ti films

International Nuclear Information System (INIS)

Pranevicius, L.; Pranevicius, L.L.; Vilkinis, P.; Baltaragis, S.; Gedvilas, K.

2014-01-01

Highlights: • The reactivity of Ti films immersed in water vapor plasma depends on the surface water coverage. • The adsorbed water monolayers are disintegrated into atomic constituents on the hydrophilic TiO 2 under plasma radiation. • The TiO 2 surface covered by water multilayer loses its ability to split adsorbed water molecules under plasma radiation. - Abstract: The behavior of the adsorbed water on the surface of thin sputter deposited Ti films maintained at room temperature was investigated in dependence on the thickness of the resulting adsorbed water layer, controllably injecting water vapor into plasma. The surface morphology and microstructure were used to characterize the surfaces of plasma treated titanium films. Presented experimental results showed that titanium films immersed in water vapor plasma at pressure of 10–100 Pa promoted the photocatalytic activity of overall water splitting. The surfaces of plasma oxidized titanium covered by an adsorbed hydroxyl-rich island structure water layer and activated by plasma radiation became highly chemically reactive. As water vapor pressure increased up to 300–500 Pa, the formed water multilayer diminished the water oxidation and, consequently, water splitting efficiency decreased. Analysis of the experimental results gave important insights into the role an adsorbed water layer on surface of titanium exposed to water vapor plasma on its chemical activity and plasma activated electrochemical processes, and elucidated the surface reactions that could lead to the split of water molecules

High temperature steam oxidation of Al3Ti-based alloys for the oxidation-resistant surface layer on Zr fuel claddings

International Nuclear Information System (INIS)

Park, Jeong-Yong; Kim, Il-Hyun; Jung, Yang-Il; Kim, Hyun-Gil; Park, Dong-Jun; Choi, Byung-Kwon

2013-01-01

We investigated the feasibility to apply Al 3 Ti-based alloys as the surface layer for improving the oxidation resistance of Zr fuel claddings under accident conditions. Two types of Al 3 Ti-based alloys with the compositions of Al–25Ti–10Cr and Al–21Ti–23Cr in atomic percent were prepared by arc-melting followed by homogenization annealing at 1423 K for 48 h. Al–25Ti–10Cr alloy showed an L1 2 quasi-single phase microstructure with a lot of needle-shaped minor phase and pores. Al–21Ti–23Cr alloy consisted of an L1 2 matrix and Cr 2 Al as the second phase. Al 3 Ti-based alloys showed an extremely low oxidation rate in a 1473 K steam for up to 7200 s when compared to Zircaloy-4. Both alloys exhibited almost the same oxidation rate in the early stage of oxidation, but Al–25Ti–10Cr showed a little lower oxidation rate after 4000 s than Al–21Ti–23Cr. The difference in the oxidation rate between two types of Al 3 Ti-based alloys was too marginal to distinguish the oxidation behavior of each alloy. The resultant oxide exhibited almost the same characteristics in both alloys even though the microstructure was explicitly distinguished from each other. The crystal structure of the oxide formed up to 2000 s was identified as Al 2 O 3 in both alloys. The oxide morphology consisted of columnar grains whose length was almost identical to the average oxide thickness. On the basis of the results obtained, it is considered that Al 3 Ti-based alloy is one of the promising candidates for the oxidation-resistant surface layer on Zr fuel claddings

Nonaqueous electrocatalytic water oxidation by a surface-bound Ru(bda)(L)₂ complex.

Science.gov (United States)

Sheridan, Matthew V; Sherman, Benjamin D; Wee, Kyung-Ryang; Marquard, Seth L; Gold, Alexander S; Meyer, Thomas J

2016-04-21

The rate of electrocatalytic water oxidation by the heterogeneous water oxidation catalyst [Ru(bda)(4-O(CH2)3P(O3H2)2-pyr)2], , (pyr = pyridine; bda = 2,2'-bipyridine-6,6'-dicarboxylate) on metal oxide surfaces is greatly enhanced relative to water as the solvent. In these experiments with propylene carbonate (PC) as the nonaqueous solvent, water is the limiting reagent. Mechanistic studies point to atom proton transfer (APT) as the rate limiting step in water oxidation catalysis.

Surface strontium enrichment on highly active perovskites for oxygen electrocatalysis in solid oxide fuel cells

KAUST Repository

Crumlin, Ethan J.; Mutoro, Eva; Liu, Zhi; Grass, Michael E.; Biegalski, Michael D.; Lee, Yueh-Lin; Morgan, Dane; Christen, Hans M.; Bluhm, Hendrik; Shao-Horn, Yang

2012-01-01

Perovskite oxides have high catalytic activities for oxygen electrocatalysis competitive to platinum at elevated temperatures. However, little is known about the oxide surface chemistry that influences the activity near ambient oxygen partial pressures, which hampers the design of highly active catalysts for many clean-energy technologies such as solid oxide fuel cells. Using in situ synchrotron-based, ambient pressure X-ray photoelectron spectroscopy to study the surface chemistry changes, we show that the coverage of surface secondary phases on a (001)-oriented La 0.8Sr 0.2CoO 3-δ (LSC) film becomes smaller than that on an LSC powder pellet at elevated temperatures. In addition, strontium (Sr) in the perovskite structure enriches towards the film surface in contrast to the pellet having no detectable changes with increasing temperature. We propose that the ability to reduce surface secondary phases and develop Sr-enriched perovskite surfaces of the LSC film contributes to its enhanced activity for O 2 electrocatalysis relative to LSC powder-based electrodes. © 2012 The Royal Society of Chemistry.

Surface adhesion properties of graphene and graphene oxide studied by colloid-probe atomic force microscopy

International Nuclear Information System (INIS)

Ding Yanhuai; Zhang Ping; Ren Huming; Zhuo Qin; Yang Zhongmei; Jiang Xu; Jiang Yong

2011-01-01

Surface adhesion properties are important to various applications of graphene-based materials. Atomic force microscopy is powerful to study the adhesion properties of samples by measuring the forces on the colloidal sphere tip as it approaches and retracts from the surface. In this paper we have measured the adhesion force between the colloid probe and the surface of graphene (graphene oxide) nanosheet. The results revealed that the adhesion force on graphene and graphene oxide surface were 66.3 and 170.6 nN, respectively. It was found the adhesion force was mainly determined by the water meniscus, which was related to the surface contact angle of samples.

Measurement of UO2 surface oxidation using grazing-incidence x-ray diffraction: Implications for nuclear forensics

Science.gov (United States)

Tracy, Cameron L.; Chen, Chien-Hung; Park, Sulgiye; Davisson, M. Lee; Ewing, Rodney C.

2018-04-01

Nuclear forensics involves determination of the origin and history of interdicted nuclear materials based on the detection of signatures associated with their production and trafficking. The surface oxidation undergone by UO2 when exposed to air is a potential signature of its atmospheric exposure during handling and transport. To assess the sensitivity of this oxidation to atmospheric parameters, surface sensitive grazing-incidence x-ray diffraction (GIXRD) measurements were performed on UO2 samples exposed to air of varying relative humidity (34%, 56%, and 95% RH) and temperature (room temperature, 50 °C, and 100 °C). Near-surface unit cell contraction was observed following exposure, indicating oxidation of the surface and accompanying reduction of the uranium cation ionic radii. The extent of unit cell contraction provides a measure of the extent of oxidation, allowing for comparison of the effects of various exposure conditions. No clear influence of relative humidity on the extent of oxidation was observed, with samples exhibiting similar degrees of unit cell contraction at all relative humidities investigated. In contrast, the thickness of the oxidized layers increased substantially with increasing temperature, such that differences on the order of 10 °C yielded readily observable crystallographic signatures of the exposure conditions.

Improved GaSb surfaces using a (NH{sub 4}){sub 2}S/(NH{sub 4}){sub 2}S0{sub 4} solution

Energy Technology Data Exchange (ETDEWEB)

Murape, D.M., E-mail: Davison.Murape@live.nmmu.ac.za [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Eassa, N.; Nyamhere, C.; Neethling, J.H. [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Betz, R. [Department of Chemistry, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Coetsee, E.; Swart, H.C. [Department of Physics, University of the Free State, PO Box 339, Bloemfontein 9300 (South Africa); Botha, J.R.; Venter, A. [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

2012-05-15

Bulk (1 0 0) n-GaSb surfaces have been treated with a sulphur based solution ((NH{sub 4}){sub 2}S/(NH{sub 4}){sub 2}SO{sub 4}) to which sulphur has been added, not previously reported for the passivation of GaSb surfaces. Au/n-GaSb Schottky barrier diodes (SBDs) fabricated on the treated material show significant improvement compared to that of the similar SBDs on the as-received material as evidenced by the lower ideality factor (n), higher barrier height ({phi}{sub b}) and lower contact resistance obtained. Additionally, the reverse leakage current, although not saturating, has been reduced by almost an order of magnitude at -0.2 V. The sample surfaces were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The native oxide, Sb-O, present on the as-received material is effectively removed on treating with ([(NH{sub 4}){sub 2}S/(NH{sub 4}){sub 2}SO{sub 4}]+S) and (NH{sub 4}){sub 2}S. Analysis of the as-received surface by XPS, prior to and after argon sputtering, suggests that the native oxide layer is {<=}8.5 nm.

Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

Energy Technology Data Exchange (ETDEWEB)

Guo, Yongling [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Bo, Maolin [Yangtze Normal University, College of Mechanical and Electrical Engineering, Chongqing 408100 (China); Wang, Yan [School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Liu, Yonghui [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Chang Q. [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Huang, Yongli, E-mail: huangyongli@xtu.edu.cn [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China)

2017-02-28

Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O{sup 2−} lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta{sup +} electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta{sup +}; the sp{sup 3}-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent

Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

International Nuclear Information System (INIS)

Guo, Yongling; Bo, Maolin; Wang, Yan; Liu, Yonghui; Sun, Chang Q.; Huang, Yongli

2017-01-01

Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O"2"− lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta"+ electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta"+; the sp"3-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent insight into the

Effect of dew point on the formation of surface oxides of twinning-induced plasticity steel

Energy Technology Data Exchange (ETDEWEB)

Kim, Yunkyum [Department of Materials Science and Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 136–713 (Korea, Republic of); Lee, Joonho, E-mail: joonholee@korea.ac.kr [Department of Materials Science and Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 136–713 (Korea, Republic of); Shin, Kwang-Soo [Research Institute of Industrial Science and Technology, Pohang 790–600 (Korea, Republic of); Jeon, Sun-Ho; Chin, Kwang-Geun [POSCO Technical Research Laboratories, Gwangyang 545–090 (Korea, Republic of)

2014-03-01

The surface oxides of twinning-induced plasticity (TWIP) steel annealed at 800 °C for 43 s were investigated using transmission electron microscopy. During the annealing process, the oxygen potential was controlled by adjusting the dew point in a 15%H{sub 2}–N{sub 2} gas atmosphere. It was found that the type of surface oxides formed and the thickness of the oxide layer were determined by the dew point. In a gas mixture with a dew point of − 20 °C, a MnO layer with a thickness of ∼ 100 nm was formed uniformly on the steel surface. Under the MnO layer, a MnAl{sub 2}O{sub 4} layer with a thickness of ∼ 15 nm was formed with small Mn{sub 2}SiO{sub 4} particles that measured ∼ 70 nm in diameter. Approximately 500 nm below the MnAl{sub 2}O{sub 4} layer, Al{sub 2}O{sub 3} was formed at the grain boundaries. On the other hand, in a gas mixture with a dew point of − 40 °C, a MnAl{sub 2}O{sub 4} layer with a thickness of ∼ 5 nm was formed on most parts of the surface. On some parts of the surface, Mn{sub 2}SiO{sub 4} particles were formed irregularly up to a thickness of ∼ 50 nm. Approximately 200 nm below the MnAl{sub 2}O{sub 4} layer, Al{sub 2}O{sub 3} was found at the grain boundaries. Thermodynamic calculations were performed to explain the experimental results. The calculations showed that when a{sub O2} > ∼ 1.26 × 10{sup −28}, MnO, MnAl{sub 2}O{sub 4}, and Mn{sub 2}SiO{sub 4} can be formed together, and the major oxide is MnO. When a{sub O2} is in the range of 1.26 × 10{sup −28}–2.51 × 10{sup −31}, MnO is not stable but MnAl{sub 2}O{sub 4} is the major oxide. When a{sub O2} < ∼ 2.51 × 10{sup −31}, only Al{sub 2}O{sub 3} is stable. Consequently, the effective activity of oxygen is considered the dominant factor in determining the type and shape of surface oxides of TWIP steel. - Highlights: • The surface oxides of TWIP steel annealed at 800 °C were investigated using TEM. • The surface oxides were determined by the dew point

Phenol by direct hydroxylation of benzene with nitrous oxide - role of surface oxygen species in the reaction pathways

Energy Technology Data Exchange (ETDEWEB)

Reitzmann, A.; Klemm, E.; Emig, G. [Erlangen-Nuernberg Univ., Erlangen (Germany). Lehrstuhl fuer Technische Chemie 1; Buchholz, S.A.; Zanthoff, H.W. [Bochum Univ. (Germany). Inst. of Technical Chemistry

1998-12-31

Transient experiments in a Temporal Analysis of Products (TAP) Reactor were performed to elucidate the role of surface oyxgen species in the oxidation of benzene to phenol on ZSM-5 type zeolites with nitrous oxide as a selective oxidant. It was shown by puls experiments with nitrous oxide that the mean lifetime of the generated surface oxygen species is between 0.2s at 500 C and about 4.2 s at 400 C. Afterwards the surface oxygen species desorb as molecular oxygen into the gas phase where total oxidation will take place if hydrocarbons are present. Dual puls experiments consisting of a nitrous oxide puls followed by a benzene puls allowed studying the reactivity of the surface oxygen species formed during the first puls. The observation of the phenol formation was impeded due to the strong sorption of phenol. Multipulse experiments were necessary to reach a pseudo steady state phenol yield. (orig.)

Fluorine-18 radiolabeling of low-density lipoproteins: a potential approach for characterization and differentiation of metabolism of native and oxidized low-density lipoproteins in vivo

International Nuclear Information System (INIS)

Pietzsch, Jens; Bergmann, Ralf; Rode, Katrin; Hultsch, Christina; Pawelke, Beate; Wuest, Frank; Hoff, Joerg van den

2004-01-01

Oxidative modification of low-density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Assessing the metabolic fate of oxidized LDL (oxLDL) in vivo with radiotracer techniques is hindered by the lack of suitable sensitive and specific radiolabeling methods. We evaluated an improved methodology based on the radiolabeling of native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 ( 18 F) by conjugation with N-succinimidyl-4-[ 18 F]fluorobenzoate ([ 18 F]SFB). We investigated whether radiolabeling of LDL induces adverse structural modifications. Results suggest that radiolabeling of both nLDL and oxLDL using [ 18 F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively. Thus, radiolabeling of LDL using [ 18 F]SFB could prove to be a promising approach for studying the kinetics of oxLDL in vivo

Fluorine-18 radiolabeling of low-density lipoproteins: a potential approach for characterization and differentiation of metabolism of native and oxidized low-density lipoproteins in vivo.

Science.gov (United States)

Pietzsch, Jens; Bergmann, Ralf; Rode, Katrin; Hultsch, Christina; Pawelke, Beate; Wuest, Frank; van den Hoff, Joerg

2004-11-01

Oxidative modification of low-density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Assessing the metabolic fate of oxidized LDL (oxLDL) in vivo with radiotracer techniques is hindered by the lack of suitable sensitive and specific radiolabeling methods. We evaluated an improved methodology based on the radiolabeling of native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 ((18)F) by conjugation with N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). We investigated whether radiolabeling of LDL induces adverse structural modifications. Results suggest that radiolabeling of both nLDL and oxLDL using [(18)F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively. Thus, radiolabeling of LDL using [(18)F]SFB could prove to be a promising approach for studying the kinetics of oxLDL in vivo.

Zinc (hydr)oxide/graphite oxide/AuNPs composites: role of surface features in H₂S reactive adsorption.

Science.gov (United States)

Giannakoudakis, Dimitrios A; Bandosz, Teresa J

2014-12-15

Zinc hydroxide/graphite oxide/AuNPs composites with various levels of complexity were synthesized using an in situ precipitation method. Then they were used as H2S adsorbents in visible light. The materials' surfaces were characterized before and after H2S adsorption by various physical and chemical methods (XRD, FTIR, thermal analysis, potentiometric titration, adsorption of nitrogen and SEM/EDX). Significant differences in surface features and synergistic effects were found depending on the materials' composition. Addition of graphite oxide and the deposition of gold nanoparticles resulted in a marked increase in the adsorption capacity in comparison with that on the zinc hydroxide and zinc hydroxide/AuNP. Addition of AuNPs to zinc hydroxide led to a crystalline ZnO/AuNP composite while the zinc hydroxide/graphite oxide/AuNP composite was amorphous. The ZnOH/GO/AuNPs composite exhibited the greatest H2S adsorption capacity due to the increased number of OH terminal groups and the conductive properties of GO that facilitated the electron transfer and consequently the formation of superoxide ions promoting oxidation of hydrogen sulfide. AuNPs present in the composite increased the conductivity, helped with electron transfer to oxygen, and prevented the fast recombination of the electrons and holes. Copyright © 2014 Elsevier Inc. All rights reserved.

Positron annihilation induced Auger electron spectroscopic studies of oxide surfaces

Science.gov (United States)

Nadesalingam, Manori

2005-03-01

Defects on oxide surfaces are well known to play a key role in catalysis. TiO2, MgO, SiO2 surfaces were investigated using Time-Of-Flight Positron induced Auger Electron Spectroscopy (TOF-PAES). Previous work in bulk materials has demonstrated that positrons are particularly sensitive to charged defects. In PAES energetic electron emission results from Auger transitions initiated by annihilation of core electrons with positrons trapped in an image-potential well at the surface. Annealed samples in O2 environment show a strong Auger peak of Oxygen. The implication of these results will be discussed

Synthesis of Graphite Oxide with Different Surface Oxygen Contents Assisted Microwave Radiation

Directory of Open Access Journals (Sweden)

Adriana Ibarra-Hernández

2018-02-01

Full Text Available Graphite oxide is synthesized via oxidation reaction using oxidant compounds that have lattice defects by the incorporation of unlike functional groups. Herein, we report the synthesis of the graphite oxide with diverse surface oxygen content through three (B, C, D different modified versions of the Hummers method assisted microwave radiation compared with the conventional graphite oxide sample obtained by Hummers method (A. These methods allow not only the production of graphite oxide but also reduced graphene oxide, without undergoing chemical, thermal, or mechanical reduction steps. The values obtained of C/O ratio were ~2, 3.4, and ~8.5 for methodologies C, B, and D, respectively, indicating the presence of graphite oxide and reduced graphene oxide, according to X-ray photoelectron spectroscopy. Raman spectroscopy of method D shows the fewest structural defects compared to the other methodologies. The results obtained suggest that the permanganate ion produces reducing species during graphite oxidation. The generation of these species is attributed to a reversible reaction between the permanganate ion with π electrons, ions, and radicals produced after treatment with microwave radiation.

Non-activated high surface area expanded graphite oxide for supercapacitors

Science.gov (United States)

Vermisoglou, E. C.; Giannakopoulou, T.; Romanos, G. E.; Boukos, N.; Giannouri, M.; Lei, C.; Lekakou, C.; Trapalis, C.

2015-12-01

Microwave irradiation of graphite oxide constitutes a facile route toward production of reduced graphene oxide, since during this treatment both exfoliation and reduction of graphite oxide occurs. In this work, the effect of pristine graphite (type, size of flakes), pretreatment and oxidation cycles on the finally produced expanded material was examined. All the types of graphite that were tested afforded materials with high BET surface areas ranging from 940 m2/g to 2490 m2/g, without intervening an activation stage at elevated temperature. SEM and TEM images displayed exfoliated structures, where the flakes were significantly detached and curved. The quality of the reduced graphene oxide sheets was evidenced both by X-ray photoelectron spectroscopy and Raman spectroscopy. The electrode material capacitance was determined via electrochemical impedance spectroscopy and cyclic voltammetry. The materials with PEDOT binder had better performance (∼97 F/g) at low operation rates while those with PVDF binder performed better (∼20 F/g) at higher rates, opening up perspectives for their application in supercapacitors.

Deposition of heated whey proteins on a chromium oxide surface.

NARCIS (Netherlands)

Jeurnink, Th.; Verheul, M.; Cohen Stuart, M.A.; Kruif, de C.G.

1996-01-01

Whey protein solutions were given different heat treatments after which their deposition on a chromium oxide surface (the outer layer of stainless steel) was measured by reflectometry. The deposition was studied under controlled flow conditions by using a stagnation point flow configuration. The

Impact of Mg content on native point defects in Mg{sub x}Zn{sub 1−x}O (0 ≤ x ≤ 0.56)

Energy Technology Data Exchange (ETDEWEB)

Perkins, J.; Foster, G. M. [Department of Physics, The Ohio State University, 191 West Woodruff Ave., Columbus, Ohio 43210 (United States); Myer, M.; Mehra, S. [Columbus School for Girls, 56 S. Columbia Ave., Columbus, Ohio 43209 (United States); Chauveau, J. M. [Centre de Recherche sur l’Hetero-Epitaxie et ses Applications, Centre National de la Recherche Scientifique (CRHEA-CNRS), Rue B. Gregory, F-06560 Valbonne Sophia Antipolis (France); University of Nice Sophia Antipolis, Parc Valrose, F-06102 Nice Cedex 2 (France); Hierro, A. [Dpto. Ingeniería Electrónica and ISOM, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Redondo-Cubero, A. [Dpto. Física Aplicada y Centro de Micro-Análisis de Materiales, Universidad Autónoma de Madrid, 28049 Madrid (Spain); Windl, W. [Department of Materials Science and Engineering, The Ohio State University, 2041 College Road N., Columbus, Ohio 43210 (United States); Brillson, L. J., E-mail: brillson.1@osu.edu [Department of Physics, The Ohio State University, 191 West Woodruff Ave., Columbus, Ohio 43210 (United States); Department of Electrical and Computer Engineering, The Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210-1272 (United States); Center for Materials Research, The Ohio State University, Columbus, Ohio 43210 (United States)

2015-06-01

We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the densities, energy levels, and spatial distributions of zinc/magnesium cation and oxygen vacancies in isostructural, single-phase, non-polar Mg{sub x}Zn{sub 1−x}O alloys over a wide (0 ≤ x ≤ 0.56) range. Within this wide range, both defect types exhibit strong Mg content-dependent surface segregation and pronounced bulk density minima corresponding to unit cell volume minima, which can inhibit defect formation due to electrostatic repulsion. Mg in ZnO significantly reduces native defect densities and their non-polar surface segregation, both major factors in carrier transport and doping of these oxide semiconductors.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

Science.gov (United States)

Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.

2011-06-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The PAES intensity then decreases monotonically as the annealing temperature is increased to ˜550 °C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M2,3VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 °C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

International Nuclear Information System (INIS)

Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.

2011-01-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The PAES intensity then decreases monotonically as the annealing temperature is increased to ∼550 deg. C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M 2,3 VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 deg. C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.

Effects of prior surface damage on high-temperature oxidation of Fe-, Ni-, and Co-based alloys

Energy Technology Data Exchange (ETDEWEB)

Blau, Peter Julian [ORNL; Lowe, Tracie M [ORNL; Pint, Bruce A [ORNL

2009-01-01

Multi-component metallic alloys have been developed to withstand high-temperature service in corrosive environments. Some of these applications, like exhaust valve seats in internal combustion engines, must also resist sliding, impact, and abrasion. The conjoint effects of temperature, oxidation, and mechanical contact can result in accelerated wear and the formation of complex surface layers whose properties differ from those of the base metal and the oxide scale that forms in the absence of mechanical contact. The authors have investigated the effects of prior surface damage, produced by scratch tests, on the localized reformation of oxide layers. Three high-performance commercial alloys, based on iron, nickel, and cobalt, were used as model materials. Thermogravimetric analysis (TGA) was used to determine their static oxidation rates at elevated temperature (850o C). A micro-abrasion, ball-cratering technique was used to measure oxide layer thickness and to compare it with TGA results. By using taper-sectioning techniques and energy-dispersive elemental mapping, a comparison was made between oxide compositions grown on non-damaged surfaces and oxides that formed on grooves produced by a diamond stylus. Microindentation and scratch hardness data revealed the effects of high temperature exposure on both the substrate hardness and the nature of oxide scale disruption. There were significant differences in elemental distribution between statically-formed oxides and those that formed on scratched regions

A TPD-MS study of glassy carbon surfaces oxidized by CO2 and O2

Directory of Open Access Journals (Sweden)

MILA D. LAUSEVIC

2002-11-01

Full Text Available The temperature-programmed desorption (TPD method combined with mass spectrometric (MS analysis has been applied to investigate the surface properties of carbon materials. The apparatus consisting of a temperature-programmed furnace and a quadrupole mass spectrometer was constructed in order to characterize the surface of differently treated glassy carbon samples. In this work, samples of glassy carbon exposed to air, CO2 and O2 were examined. The desorption of H2O, CO and CO2, as major products, indicated the presence of different oxide groups. The amount of these groups for all samples was calculated. It is concluded that oxidation affects the nature and the amount of the surface oxide groups and contributes to their increased stability.

The early stages of oxidation of magnesium single crystal surfaces

International Nuclear Information System (INIS)

Hayden, B.E.; Schweizer, E.; Koetz, R.; Bradshaw, A.M.

1981-01-01

The early stages of oxidation of Mg(001) and Mg(100) single crystal surfaces at 300 K have been investigated by LEED, ELS, work function and ellipsometric measurements. A sharp decrease in work function on both surfaces during the first 12 L exposure indicates the incorporation of oxygen in the earliest stages of the interaction. The incorporated oxygen on Mg(001) gives rise to a broadening of the integral order LEED spots for an exposure 3 L. (orig.)

Oxygen Reduction Kinetics Enhancement on a Heterostructured Oxide Surface for Solid Oxide Fuel Cells

KAUST Repository

Crumlin, Ethan J.

2010-11-04

Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of ∼85 nm thick La0.8Sr0.2CoO3-δ (LSC113) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia (YSZ) substrates is dramatically enhanced (∼3-4 orders of magnitude above bulk LSC113) by surface decorations of (La 0.5Sr0.5)2CoO4±δ (LSC214) with coverage in the range from ∼0.1 to ∼15 nm. Their surface and atomic structures were characterized by atomic force, scanning electron, and scanning transmission electron microscopy, and the ORR kinetics were determined by electrochemical impedance spectroscopy. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSC113/LSC214 regions, which were shown to be atomically sharp. © 2010 American Chemical Society.

Oxygen Reduction Kinetics Enhancement on a Heterostructured Oxide Surface for Solid Oxide Fuel Cells

KAUST Repository

Crumlin, Ethan J.; Mutoro, Eva; Ahn, Sung-Jin; la O’ , Gerardo Jose; Leonard, Donovan N.; Borisevich, Albina; Biegalski, Michael D.; Christen, Hans M.; Shao-Horn, Yang

2010-01-01

Heterostructured interfaces of oxides, which can exhibit transport and reactivity characteristics remarkably different from those of bulk oxides, are interesting systems to explore in search of highly active cathodes for the oxygen reduction reaction (ORR). Here, we show that the ORR of ∼85 nm thick La0.8Sr0.2CoO3-δ (LSC113) films prepared by pulsed laser deposition on (001)-oriented yttria-stabilized zirconia (YSZ) substrates is dramatically enhanced (∼3-4 orders of magnitude above bulk LSC113) by surface decorations of (La 0.5Sr0.5)2CoO4±δ (LSC214) with coverage in the range from ∼0.1 to ∼15 nm. Their surface and atomic structures were characterized by atomic force, scanning electron, and scanning transmission electron microscopy, and the ORR kinetics were determined by electrochemical impedance spectroscopy. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSC113/LSC214 regions, which were shown to be atomically sharp. © 2010 American Chemical Society.

Spectral force analysis using atomic force microscopy reveals the importance of surface heterogeneity in bacterial and colloid adhesion to engineered surfaces.

Science.gov (United States)

Ma, Huilian; Winslow, Charles J; Logan, Bruce E

2008-04-01

Coatings developed to reduce biofouling of engineered surfaces do not always perform as expected based on their native properties. One reason is that a relatively small number of highly adhesive sites, or the heterogeneity of the coated surface, may control the overall response of the system to initial bacterial deposition. It is shown here using an approach we call spectral force analysis (SFA), based on force volume imaging of the surface with atomic force microscopy, that the behavior of surfaces and coatings can be better understood relative to bacterial adhesion. The application of vapor deposited TiO(2) metal oxide increased bacterial and colloid adhesion, but coating the surface with silica oxide reduced adhesion in a manner consistent with SFA based on analysis of the "stickiest" sites. Application of a TiO(2)-based paint to a surface produced a relatively non-fouling surface. Addition of a hydrophilic layer coating to this surface should have decreased fouling. However, it was observed that this coating actually increased fouling. Using SFA it was shown that the reason for the increased adhesion of bacteria and particles to the hydrophilic layer was that the surface produced by this coating was highly heterogeneous, resulting in a small number of sites that created a stickier surface. These results show that while it is important to manufacture surfaces with coatings that are relatively non-adhesive to bacteria, it is also essential that these coatings have a highly uniform surface chemistry.

Graphite surface topography induced by Ta cluster impact and oxidative etching

International Nuclear Information System (INIS)

Reimann, C.T.; Olsson, L.; Erlandsson, R.; Henkel, M.; Urbassek, H.M.

1998-01-01

Freshly cleaved highly oriented pyrolytic graphite (HOPG), when baked in air at ∝630 C, forms one-monolayer(ML)-deep circular pits due to oxidation initiated at surface defect sites. We found that the areal density and depths of these pits could be modulated by deliberately introducing surface and sub-surface defects by energetic ion bombardment prior to baking. Bombardment by 555-eV/atom Ta 1 + , Ta 2 + , Ta 4 + , or Ta 9 + , always enhanced the areal density of etch pits, but only bombardment by Ta 4 + , or Ta 9 + significantly enhanced the depths of the pits. We performed molecular dynamics simulations of Ta n cluster bombardment of HOPG (n = 1, 2, 4, and 9) with the aim of characterizing the damage structures induced by the bombardment and correlating them with the experimental data. For Ta 9 + , the simulations showed a high level of damage extending from the surface down to nine MLs, in agreement with the most probable etch pit depth observed. For other cluster species, predicted etch pit depths were deeper than the observed ones. Annealing or steric requirements for initiating oxidation may account for some of the differences between simulations and experimental results. (orig.)

Indium tin oxide surface smoothing by gas cluster ion beam

CERN Document Server

Song, J H; Choi, W K

2002-01-01

CO sub 2 cluster ions are irradiated at the acceleration voltage of 25 kV to remove hillocks on indium tin oxide (ITO) surfaces and thus to attain highly smooth surfaces. CO sub 2 monomer ions are also bombarded on the ITO surfaces at the same acceleration voltage to compare sputtering phenomena. From the atomic force microscope results, the irradiation of monomer ions makes the hillocks sharper and the surfaces rougher from 1.31 to 1.6 nm in roughness. On the other hand, the irradiation of CO sub 2 cluster ions reduces the height of hillocks and planarize the ITO surfaces as smooth as 0.92 nm in roughness. This discrepancy could be explained by large lateral sputtering yield of the cluster ions and re-deposition of sputtered particles by the impact of the cluster ions on surfaces.

An evaluation of the effect of surface chromium concentration on the oxidation of a stainless steel

International Nuclear Information System (INIS)

Lobb, R.C.; Evans, H.E.

1983-01-01

Short-term oxidation tests have been performed at 850 deg C in a CO 2 -based atmosphere on 20Cr-25Ni-Nb-stabilized steels previously exposed to dynamic vacuum at 1000 deg C. This pre-treatment preferentially removes chromium from the metal surface and is always detrimental to the oxidation properties. It is shown that porous, iron-rich oxides initially form on specimens with surface chromium concentrations 18.5 w/o chromium, a protective surface layer is produced. It is suggested that the transition between these extremes is determined by nucleation conditions and, in the present steels, it is shown how the metal grain size plays a significant role. (author)

Emissions of nitrous oxide and methane from surface and ground waters in Germany

International Nuclear Information System (INIS)

Hiessl, H.

1993-01-01

The paper provides a first estimation of the contribution of inland freshwater systems (surface waters and ground waters) to the emission of the greenhouse gases nitrous oxide and methane in Germany. These amounts are compared to other main sources for the emission of nitrous oxide and methane. (orig.) [de

The Interface Structure of High-Temperature Oxidation-Resistant Aluminum-Based Coatings on Titanium Billet Surface

Science.gov (United States)

Xu, Zhefeng; Rong, Ju; Yu, Xiaohua; Kun, Meng; Zhan, Zhaolin; Wang, Xiao; Zhang, Yannan

2017-10-01

A new type of high-temperature oxidation-resistant aluminum-based coating, on a titanium billet surface, was fabricated by the cold spray method, at a high temperature of 1050°C, for 8 h, under atmospheric pressure. The microstructure of the exposed surface was analyzed via optical microscopy, the microstructure of the coating and elemental diffusion was analyzed via field emission scanning electron microscopy, and the interfacial phases were identified via x-ray diffraction. The Ti-Al binary phase diagram and Gibbs free energy of the stable phase were calculated by Thermo-calc. The results revealed that good oxidation resistant 50-μm-thick coatings were successfully obtained after 8 h at 1050°C. Two layers were obtained after the coating process: an Al2O3 oxidation layer and a TiAl3 transition layer on the Ti-based substrate. The large and brittle Al2O3 grains on the surface, which can be easily spalled off from the surface after thermal processing, protected the substrate against oxidation during processing. In addition, the thermodynamic calculation results were in good agreement with the experimental data.

Effect of emulsifiers on complexation and retrogradation characteristics of native and chemically modified White sorghum (Sorghum bicolor) starch

International Nuclear Information System (INIS)

Ali, Tahira Mohsin; Hasnain, Abid

2013-01-01

Highlights: ► Sorghum starches were chemically modified. ► Starch–lipid complexes were studied in the presence of emulsifiers. ► Type II complexes were also detected in native and oxidized starches on adding GMS. ► Starch–lipid complexes sharply reduced retrogradation in modified starches. - Abstract: The effect of emulsifiers on complexation and retrogradation characteristics of native and chemically modified white sorghum starches was studied. Complex forming tendency of white sorghum starch with commercially available emulsifiers GMS and DATEM improved after acetylation. Presence of emulsifiers reduced λ max (wavelength of maximum absorbance) both for native and modified sorghum starches suggesting lower availability of amylose chains to complex with iodine. In native white sorghum starch (NWSS) and oxidized white sorghum starch (OWSS), both Type I and Type II starch–lipid complexes were observed on addition of 1.0% GMS prior to gelatinization. Acetylated-oxidized white sorghum starch (AOWSS) formed weakest complexes among all the modified starches. The results revealed that antistaling characteristics of modified sorghum starches were enhanced when used in combination with emulsifiers. The most prominent decline in reassociative capability among modified starches was observed for acetylated starches.

Prediction of iodide adsorption on oxides by surface complexation modeling with spectroscopic confirmation.

Science.gov (United States)

Nagata, Takahiro; Fukushi, Keisuke; Takahashi, Yoshio

2009-04-15

A deficiency in environmental iodine can cause a number of health problems. Understanding how iodine is sequestered by materials is helpful for evaluating and developing methods for minimizing human health effects related to iodine. In addition, (129)I is considered to be strategically important for safety assessment of underground radioactive waste disposal. To assess the long-term stability of disposed radioactive waste, an understanding of (129)I adsorption on geologic materials is essential. Therefore, the adsorption of I(-) on naturally occurring oxides is of environmental concern. The surface charges of hydrous ferric oxide (HFO) in NaI electrolyte solutions were measured by potentiometric acid-base titration. The surface charge data were analyzed by means of an extended triple-layer model (ETLM) for surface complexation modeling to obtain the I(-) adsorption reaction and its equilibrium constant. The adsorption of I(-) was determined to be an outer-sphere process from ETLM analysis, which was consistent with independent X-ray absorption near-edge structure (XANES) observation of I(-) adsorbed on HFO. The adsorption equilibrium constants for I(-) on beta-TiO(2) and gamma-Al(2)O(3) were also evaluated by analyzing the surface charge data of these oxides in NaI solution as reported in the literature. Comparison of these adsorption equilibrium constants for HFO, beta-TiO(2), and gamma-Al(2)O(3) based on site-occupancy standard states permitted prediction of I(-) adsorption equilibrium constants for all oxides by means of the Born solvation theory. The batch adsorption data for I(-) on HFO and amorphous aluminum oxide were reasonably reproduced by ETLM with the predicted equilibrium constants, confirming the validity of the present approach. Using the predicted adsorption equilibrium constants, we calculated distribution coefficient (K(d)) values for I(-) adsorption on common soil minerals as a function of pH and ionic strength.

Photocatalysis of Modified Transition Metal Oxide Surfaces

Energy Technology Data Exchange (ETDEWEB)

Batzill, Matthias [Univ. of South Florida, Tampa, FL (United States). Dept. of Physics

2018-02-28

The goal of this project has been to establish a cause-effect relationship for photocatalytic activity variations of different structures of the same material; and furthermore gain fundamental understanding on modification of photocatalysts by compositional or surface modifications. The reasoning is that gaining atomic scale understanding of how surface and bulk modifications alter the photo reactivity will lead to design principles for next generation photocatalysts. As a prototypical photocatalyst the research focused on TiO₂ synthesized in well-defined single crystalline form to enable fundamental characterizations.We have obtained results in the following areas: (a) Preparation of epitaxial anatase TiO₂ samples by pulsed laser deposition. (b) Comparison of hydrogen diffusion on different crystallographic surface. (c) Determining the stability of the TiO₂(011)-2x1 reconstruction upon interactions with adsorbates. (d) Characterization of adsorption and (thermal and photo) reaction of molecules with nitro-endgroups, (e) Exploring the possibility of modifying planar model photocatalyst surfaces with graphene to enable fundamental studies on reported enhanced photocatalytic activities of graphene modified transition metal oxides, (f) gained fundamental understanding on the role of crystallographic polymorphs of the same material for their photocatalytic activities.

Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

Directory of Open Access Journals (Sweden)

Shutthanandan V

2008-06-01

Full Text Available Abstract Molybdenum disulfide (MoS2, a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM, scanning electron microscopy (SEM, transmission electron microscopy (TEM, Rutherford backscattering spectrometry (RBS, and nuclear reaction analysis (NRA. Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and

Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics.

Science.gov (United States)

Ramana, C V; Becker, U; Shutthanandan, V; Julien, C M

2008-06-05

Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia.The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA).Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400 degrees C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant

Handling a tricycle: Orthogonal versus random oxidation of the tricyclic inhibitor cystine knotted peptide gurmarin

DEFF Research Database (Denmark)

Eliasen, Rasmus; Andresen, Thomas L.; Conde-Frieboes, Kilian W.

2012-01-01

random oxidation strategy. We compared two oxidation procedures to form the three disulfide bridges. In the first, based on random oxidation, reduced gurmarin was synthesized using trityl for cysteine protection, and oxidized for 48h in a Tris–HCl buffer containing cystamine and reduced glutathione...... to facilitate disulfide scrambling. The second was based on step-wise deprotection followed by oxidation in which the cysteine pairs are orthogonally protected with tert-Butylthio, trityl and acetamidomethyl. To verify that the native gurmarin oxidation product was obtained, thermolysin cleavage was used...... UPLC. It was found that the random oxidation procedure leads to native gurmarin in high yield. Thus, the synthetic route was simple and significantly more efficient than previously reported syntheses of gurmarin and other cysteine rich peptides. Importantly, native gurmarin was obtained by random...

Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces

OpenAIRE

Jogikalmath, G.; Stuart, J.K.; Pungor, A.; Hlady, V.

1999-01-01

Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the μm-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of γ-glycidoxypropyltrimethoxy silane (GPS) to glass decreased the pull-off forces relative to the clean glass and made the surface mo...

Surface properties and catalytic performance of Pt/LaSrCoO4 catalysts in the oxidation of hexane

Directory of Open Access Journals (Sweden)

Hua Zhong

2007-08-01

Full Text Available Perovskite-type La2 –xSrxCoO4 mixed oxides have been prepared by calcination at various temperatures of precipitates obtained from aqueous solutions in the presence of citric or ethylenediamintetraacetic (EDTA acids, and have been studied by X-ray diffraction (XRD, surface area (BET measurements, temperature programmed desorption (TPD, temperature programmed reduction (TPR and X-ray photoelectron spectroscopy (XPS. These oxides are catalysts for hexane oxidation, with the greatest activity for LaSrCoO4 calcined at 750 C. This has extensive oxygen vacancies and large internal surface area. Pt-modified LaSrCoO4 catalysts are significantly more active than the Pt-free system. Both surface and bulk phases of the preovskitetype oxides contribute to hexane oxidation.

Prediction Surface Morphology of Nanostructure Fabricated by Nano-Oxidation Technology.

Science.gov (United States)

Huang, Jen-Ching; Chang, Ho; Kuo, Chin-Guo; Li, Jeen-Fong; You, Yong-Chin

2015-12-04

Atomic force microscopy (AFM) was used for visualization of a nano-oxidation technique performed on diamond-like carbon (DLC) thin film. Experiments of the nano-oxidation technique of the DLC thin film include those on nano-oxidation points and nano-oxidation lines. The feature sizes of the DLC thin film, including surface morphology, depth, and width, were explored after application of a nano-oxidation technique to the DLC thin film under different process parameters. A databank for process parameters and feature sizes of thin films was then established, and multiple regression analysis (MRA) and a back-propagation neural network (BPN) were used to carry out the algorithm. The algorithmic results are compared with the feature sizes acquired from experiments, thus obtaining a prediction model of the nano-oxidation technique of the DLC thin film. The comparative results show that the prediction accuracy of BPN is superior to that of MRA. When the BPN algorithm is used to predict nano-point machining, the mean absolute percentage errors (MAPE) of depth, left side, and right side are 8.02%, 9.68%, and 7.34%, respectively. When nano-line machining is being predicted, the MAPEs of depth, left side, and right side are 4.96%, 8.09%, and 6.77%, respectively. The obtained data can also be used to predict cross-sectional morphology in the DLC thin film treated with a nano-oxidation process.

Ceramic coated Y1 magnesium alloy surfaces by microarc oxidation

Indian Academy of Sciences (India)

The magnesium alloys occupy an important place in marine applications, but their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To meet these defects, some techniques are developed. Microarc oxidation is a one such recently developed surface treatment technology under ...

Surface oxidation phenomena of boride coatings grown on iron

International Nuclear Information System (INIS)

Carbucicchio, M.; Palombarini, G.; Sambogna, G.

1992-01-01

Very hard boride coatings are grown on various metals using thermochemical as well as chemical vapour deposition techniques. In this way many surface properties, and in particular the wear resistance, can be considerably improved. Usually, also the corrosion behaviour of the treated components is important. In particular, oxidizing atmospheres are involved in many applications where, therefore, coating-environment interactions can play a relevant role. In a previous work, the early stages of the oxidation of iron borides were studied by treating single phase compacted powders in flowing oxygen at low temperatures (300-450deg C). In the present paper, the attention is addressed to the oxidation of both single phase and polyphase boride coatings thermochemically grown on iron. The single phase boride coatings were constituted by Fe 2 B, while the polyphase coatings were constituted by an inner Fe 2 B layer and an outer FeB-base layer. All the boride layers displayed strong (002) preferred crystallographic orientations. (orig.)

Growth of micrometric oxide layers for the study of metallic surfaces decontamination by laser

Science.gov (United States)

Carvalho, Luisa; Pacquentin, Wilfried; Tabarant, Michel; Maskrot, Hicham; Semerok, Alexandre

2017-09-01

The nuclear industry produces a wide range of radioactive waste in term of level of hazard, contaminants and material. For metallic equipment like steam generators, the radioactivity is mainly located in the oxide surface. In order to study and develop techniques for dismantling and for decontamination in a safe way, it is important to have access to oxide layers with a representative distribution of non-radioactive contaminants. We propose a method of formation of oxide layer on stainless steel 304L with europium (Eu) as contaminant marker. In this method, an Eu-solution is sprayed on the stainless steel samples. The specimen are firstly treated with a pulsed nanosecond laser and secondly the steel samples are exposed to a 600°C furnace for various durations in order to grow an oxide layer. The oxide structure and in-depth distribution of Eu in the oxide layer are analysed by scanning electron microscopy coupled with energy dispersive X-ray microanalyzer, and by glow discharge optical emission or mass spectrometry. The oxide layers were grown to thicknesses in the range of 200 nm to 4.5 μm regarding to the laser treatment parameters and the heating duration. These contaminated oxides have a `duplex structure' with a mean weight percentage of 0.5% of europium in the volume of the oxide layer. It appears that europium implementation prevents the oxide growth by furnace but has no impact on laser heating. These oxide layers are used to study the decontamination of metallic surfaces such as stainless steel 304L using a nanosecond pulsed laser.

Fluorine-18 radiolabeling of low-density lipoproteins: a potential approach for characterization and differentiation of metabolism of native and oxidized low-density lipoproteins in vivo

Energy Technology Data Exchange (ETDEWEB)

Pietzsch, Jens [PET-Center, Institute of Bioinorganic and Radiopharmaceutical Chemistry, Research Center Rossendorf Dresden, P.O. Box 51 01 19, D-01314 Dresden (Germany); Bergmann, Ralf [PET-Center, Institute of Bioinorganic and Radiopharmaceutical Chemistry, Research Center Rossendorf Dresden, P.O. Box 51 01 19, D-01314 Dresden (Germany); Rode, Katrin [PET-Center, Institute of Bioinorganic and Radiopharmaceutical Chemistry, Research Center Rossendorf Dresden, P.O. Box 51 01 19, D-01314 Dresden (Germany); Hultsch, Christina [PET-Center, Institute of Bioinorganic and Radiopharmaceutical Chemistry, Research Center Rossendorf Dresden, P.O. Box 51 01 19, D-01314 Dresden (Germany); Pawelke, Beate [PET-Center, Institute of Bioinorganic and Radiopharmaceutical Chemistry, Research Center Rossendorf Dresden, P.O. Box 51 01 19, D-01314 Dresden (Germany); Wuest, Frank [PET-Center, Institute of Bioinorganic and Radiopharmaceutical Chemistry, Research Center Rossendorf Dresden, P.O. Box 51 01 19, D-01314 Dresden (Germany); Hoff, Joerg van den [PET-Center, Institute of Bioinorganic and Radiopharmaceutical Chemistry, Research Center Rossendorf Dresden, P.O. Box 51 01 19, D-01314 Dresden (Germany)

2004-11-01

Oxidative modification of low-density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Assessing the metabolic fate of oxidized LDL (oxLDL) in vivo with radiotracer techniques is hindered by the lack of suitable sensitive and specific radiolabeling methods. We evaluated an improved methodology based on the radiolabeling of native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 ({sup 18}F) by conjugation with N-succinimidyl-4-[{sup 18}F]fluorobenzoate ([{sup 18}F]SFB). We investigated whether radiolabeling of LDL induces adverse structural modifications. Results suggest that radiolabeling of both nLDL and oxLDL using [{sup 18}F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively. Thus, radiolabeling of LDL using [{sup 18}F]SFB could prove to be a promising approach for studying the kinetics of oxLDL in vivo.

Correlation between sub-micron surface roughness of iron oxide encrustations and trace element concentrations

International Nuclear Information System (INIS)

Fischer, Cornelius; Karius, Volker; Luettge, Andreas

2009-01-01

Iron oxide encrustations are formed on black slate surfaces during oxidative weathering of iron sulfide and phosphate bearing, organic matter-rich slates. Synchronously, trace elements are released during ongoing weathering. Laser ablation ICP-MS analyses of a weathered and encrusted slate showed that major portions of the V, Cu, As, Mo, Pb, Th, and U reside in the encrustation. Recently a potential relationship between several micrometer to 500 nm surface topography roughness of such encrustations and its uranium concentration was shown. Based on laser scanning microscopy measurements, the present study shows that this interrelation must be expanded to small submicron-sized half-pores with diameters between 100 nm and 500 nm. We demonstrate that the relationship is not limited to topography variations of a single encrustation in the hand-specimen scale. Surface topography and geochemical analyses of iron oxide encrustations from several locations but from the same geochemical environment and with similar weathering history showed that the concentrations of U, P, Cu, and Zn correlate inversely with the surface roughness parameter F. This parameter represents the total surface area and is - in this case - a proxy for the root-mean square surface roughness Rq. This study substantiates the environmental importance that micrometer- to submicrometer topography variations of fluid-rock interfaces govern the trapping of trace elements.

Correlation between sub-micron surface roughness of iron oxide encrustations and trace element concentrations

Energy Technology Data Exchange (ETDEWEB)

Fischer, Cornelius, E-mail: cornelius@rice.edu [Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 (United States); Geowissenschaftliches Zentrum der Universitaet Goettingen, Abt. Sedimentologie and Umweltgeologie, Goldschmidtstr. 3, D-37077 Goettingen (Germany); Karius, Volker [Geowissenschaftliches Zentrum der Universitaet Goettingen, Abt. Sedimentologie and Umweltgeologie, Goldschmidtstr. 3, D-37077 Goettingen (Germany); Luettge, Andreas [Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005 (United States); Department of Chemistry, Rice University, 6100 Main Street, Houston, TX 77005 (United States)

2009-08-01

Iron oxide encrustations are formed on black slate surfaces during oxidative weathering of iron sulfide and phosphate bearing, organic matter-rich slates. Synchronously, trace elements are released during ongoing weathering. Laser ablation ICP-MS analyses of a weathered and encrusted slate showed that major portions of the V, Cu, As, Mo, Pb, Th, and U reside in the encrustation. Recently a potential relationship between several micrometer to 500 nm surface topography roughness of such encrustations and its uranium concentration was shown. Based on laser scanning microscopy measurements, the present study shows that this interrelation must be expanded to small submicron-sized half-pores with diameters between 100 nm and 500 nm. We demonstrate that the relationship is not limited to topography variations of a single encrustation in the hand-specimen scale. Surface topography and geochemical analyses of iron oxide encrustations from several locations but from the same geochemical environment and with similar weathering history showed that the concentrations of U, P, Cu, and Zn correlate inversely with the surface roughness parameter F. This parameter represents the total surface area and is - in this case - a proxy for the root-mean square surface roughness Rq. This study substantiates the environmental importance that micrometer- to submicrometer topography variations of fluid-rock interfaces govern the trapping of trace elements.

Electrolysis of water on (oxidized) metal surfaces

DEFF Research Database (Denmark)

Rossmeisl, Jan; Logadottir, Ashildur; Nørskov, Jens Kehlet

2005-01-01

Density functional theory calculations are used as the basis for an analysis of the electrochemical process, where by water is split to form molecular oxygen and hydrogen. We develop a method for obtaining the thermochemistry of the electrochemical water splitting process as a function of the bias...... directly from the electronic structure calculations. We consider electrodes of Pt(111) and Au(111) in detail and then discuss trends for a series of different metals. We show that the difficult step in the water splitting process is the formation of superoxy-type (OOH) species on the surface...... by the splitting of a water molecule on top an adsorbed oxygen atom. One conclusion is that this is only possible on metal surfaces that are (partly) oxidized. We show that the binding energies of the different intermediates are linearly correlated for a number of metals. In a simple analysis, where the linear...

Thorium binding by biochar fibres derived from Luffa Cylindrica after controlled surface oxidation

Science.gov (United States)

Liatsou, Ioanna; Christodoulou, Eleni; Paschalidis, Ioannis

2017-04-01

Controlled surface modification of biochar fibres derived from Luffa Cylindrica sponges has been carried out by nitric acid and the degree of oxidation could be controlled by changing the acid concentration or the reaction time. The extent of surface oxidation has been quantified by acid-base titration and FTIR-spectroscopy. Furthermore, thorium binding has been studied as a function of various parameters and the experimental results show that even under strong acidic conditions the relative sorption is above 70% and the sorption capacity of the biochar fibres for Th(IV) at pH 3 is qmax= 70 gṡkg-1.

Effect of dynamic surface polarization on the oxidative stability of solvents in nonaqueous Li-O 2 batteries

Science.gov (United States)

Khetan, Abhishek; Pitsch, Heinz; Viswanathan, Venkatasubramanian

2017-09-01

Polarization-induced renormalization of the frontier energy levels of interacting molecules and surfaces can cause significant shifts in the excitation and transport behavior of electrons. This phenomenon is crucial in determining the oxidative stability of nonaqueous electrolytes in high-energy density electrochemical systems such as the Li-O2 battery. On the basis of partially self-consistent first-principles Sc G W0 calculations, we systematically study how the electronic energy levels of four commonly used solvent molecules, namely, dimethylsulfoxide (DMSO), dimethoxyethane (DME), tetrahydrofuran (THF), and acetonitrile (ACN), renormalize when physisorbed on the different stable surfaces of Li2O2 , the main discharge product. Using band level alignment arguments, we propose that the difference between the solvent's highest occupied molecular orbital (HOMO) level and the surface's valence-band maximum (VBM) is a refined metric of oxidative stability. This metric and a previously used descriptor, solvent's gas phase HOMO level, agree quite well for physisorbed cases on pristine surfaces where ACN is oxidatively most stable followed by DME, THF, and DMSO. However, this effect is intrinsically linked to the surface chemistry of the solvent's interaction with the surface states and defects, and depends strongly on their nature. We conclusively show that the propensity of solvent molecules to oxidize will be significantly higher on Li2O2 surfaces with defects as compared to pristine surfaces. This suggests that the oxidative stability of a solvent is dynamic and is a strong function of surface electronic properties. Thus, while gas phase HOMO levels could be used for preliminary solvent candidate screening, a more refined picture of solvent stability requires mapping out the solvent stability as a function of the state of the surface under operating conditions.

An ab initio study of plutonium oxides surfaces; Etude ab initio des surfaces d'oxydes de Pu

Energy Technology Data Exchange (ETDEWEB)

Jomard, G.; Bottin, F.; Amadon, B

2007-07-01

By means of first-principles calculations, we have studied the atomic structure as well as the thermodynamic stability of various plutonium dioxide surfaces in function of their environment (in terms of oxygen partial pressure and temperature). All these simulations have been performed with the ABINIT code. It is well known that DFT fails to describe correctly plutonium-based materials since 5f electrons in such systems are strongly correlated. In order to go beyond DFT, we have treated PuO{sub 2} and {beta}-Pu{sub 2}O{sub 3} in a DFT+U framework. We show that the couple of parameters (U,J) that works well for pure Pu is also well designed for describing ground state (GS) properties of these two oxides. The major improvement with respect with DFT is that we are able to predict an insulating GS in agreement with experiments. The presence of a gap in the DOS (Density of States) of plutonium oxides should play a significant role in the predicted surface reactivity. However, performing DFT+U calculations on surfaces of plutonium oxide from scratch was too ambitious. That is why we decided, as a first step, to study the stability of the (100), (110) and (111) surfaces of PuO{sub 2} in a DFT-GGA framework. For each of these orientations, we considered various terminations. These ab initio results have been introduced in a thermodynamic model which allows us to predict the relative stability of the different terminations as a function of temperature and oxygen partial pressure (p{sub O{sub 2}}). We conclude that at room temperature and for p{sub O{sub 2}}{approx}10 atm., the polar O{sub 2}-(100) termination is favoured. The stabilization of such a polar stoichiometric surface is surprising and should be confirmed by DFT+U calculations before any final conclusion. (authors)

Modification of aniline containing proteins using an oxidative coupling strategy.

Science.gov (United States)

Hooker, Jacob M; Esser-Kahn, Aaron P; Francis, Matthew B

2006-12-13

A new bioconjugation reaction has been developed based on the chemoselective modification of anilines through an oxidative coupling pathway. Aryl amines were installed on the surface of protein substrates through lysine acylation reactions or through the use of native chemical ligation techniques. Upon exposure to NaIO4 in aqueous buffer, the anilines coupled rapidly to the aromatic rings of N,N-dialkyl-N'-acyl-p-phenylenediamines. The identities of the reaction products were confirmed using ESI-MS and through comparison to small molecule analogs. Control experiments indicated that none of the native amino acids participated in the reaction. The resulting bioconjugates were found to be stable toward hydrolysis from pH 4 to pH 11 and in the presence of many commonly used oxidants, reductants, and nucleophiles. A fluorescent phenylenediamine reagent was synthesized for the selective detection of aniline labeled proteins in mixtures, and the reaction was used to append the C-terminus of the green fluorescent protein with a single PEG chain. When combined with techniques for the incorporation of unnatural amino acids into proteins, this bioorthogonal coupling method should prove useful for a number of applications requiring a high degree of labeling specificity.

Ozone Oxidation of Self-Assembled Monolayers on SiOx-Coated Zinc Selenide Surfaces

Science.gov (United States)

McIntire, T. M.; Ryder, O. S.; Finlayson-Pitts, B. J.

2008-12-01

Airborne particles are important for visibility, human health, climate, and atmospheric reactions. Atmospheric particles contain a significant fraction of organics and such compounds present on airborne particles are susceptible to oxidation by atmospheric oxidants, such as OH, ozone, halogen atoms, and nitrogen trioxide. Oxidized organics associated with airborne particles are thought to be polar, hygroscopic species with enhanced cloud-nucleating properties. Oxide layers on silicon, or SiO2-coated substrates, act as models of environmentally relevant surfaces such as dust particles upon which organics adsorb. We have shown previously that ozone oxidation of unsaturated self-assembled monolayers (SAMs) on silicon attenuated total reflectance (ATR) crystals leads to the formation of carbonyl groups and micron-sized, hydrophobic organic aggregates surrounded by carbon depleted substrate that do not have increased water uptake as previously assumed. Reported here are further ATR-FTIR studies of the oxidation of alkene SAMs on ZnSe and SiO2-coated ZnSe. These substrates have the advantage that they transmit below 1500 cm-1, allowing detection of additional product species. These experiments show that the loss of C=C and formation of carbonyl groups is also accompanied by formation of a peak at 1110 cm-1, attributed to the secondary ozonide. Details concerning the products and mechanism of ozonolysis of alkene SAMs on surfaces based on these new data are presented and the implications for the oxidation of alkenes on airborne dust particles are discussed.