Showing papers in "Surface and Interface Analysis in 2015"

Resolving ruthenium: XPS studies of common ruthenium materials

Abstract: X-ray photoelectron spectroscopy (XPS) utilising monochromatic Al Kα radiation has been employed to study metallic ruthenium and the catalytically and technologically important ruthenium compounds RuO2, RuCl3, Ru(NO)(NO3)3 and Ru(AcAc)3. The results improve on the accuracy of already published Ru(3d) binding energies, expand known Ru(3p) binding energies and also report spin-orbit splitting for the core levels. For RuO2, the difference between anhydrous and hydrated samples is explored, and the effect on curve fitting such spectra is discussed. Analysis of RuCl3 has allowed, for the first time, the positive identification of Ru(OH)3 by XPS. Copyright © 2015 John Wiley & Sons, Ltd.

Calculations of electron inelastic mean free paths. X. Data for 41 elemental solids over the 50 eV to 200 keV range with the relativistic full Penn algorithm

Abstract: We have calculated inelastic mean free paths (IMFPs) for 41 elemental solids (Li, Be, graphite, diamond, glassy C, Na, Mg, Al, Si, K, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Ge, Y, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Cs, Gd, Tb, Dy, Hf, Ta, W, Re, Os, Ir, Pt, Au, and Bi) for electron energies from 50 eV to 200 keV. The IMFPs were calculated from measured energy loss functions for each solid with a relativistic version of the full Penn algorithm. The calculated IMFPs could be fitted to a modified form of the relativistic Bethe equation for inelastic scattering of electrons in matter for energies from 50 eV to 200 keV. The average root-mean-square (RMS) deviation in these fits was 0.68%. The IMFPs were also compared with IMFPs from a relativistic version of our predictive Tanuma, and Powell and Penn (TPP-2M) equation that was developed from a modified form of the relativistic Bethe equation. In these comparisons, the average RMS deviation was 11.9% for energies between 50 eV and 200 keV. This RMS deviation is almost the same as that found previously in a similar comparison for the 50 eV to 30 keV range (12.3%). Relatively large RMS deviations were found for diamond, graphite, and cesium as in our previous comparisons. If these three elements were excluded in the comparisons, the average RMS deviation was 8.9% between 50 eV and 200 keV. The relativistic TPP-2M equation can thus be used to estimate IMFPs in solid materials for energies between 50 eV and 200 keV. We found satisfactory agreement between our calculated IMFPs and those from recent calculations and from measurements at energies of 100 and 200 keV. Copyright © 2015 John Wiley & Sons, Ltd.

Self‐assembled silane monolayers: an efficient step‐by‐step recipe for high‐quality, low energy surfaces

Abstract: Organosilane self-assembled monolayers (SAMs) are commonly used for modifying a wide range of substrates. Depending on the end group, highly hydrophobic or hydrophilic surfaces can be achieved. Silanization bases on the adsorption, self-assembly and covalent binding of silane molecules onto surfaces and results in a densely packed, SAM. Following wet chemical routines, the quality of the monolayer is often variable and, therefore, unsatisfactory. The process of self-assembly is not only affected by the chemicals involved and their purity but is also extremely sensitive to ambient parameters such as humidity or temperature and to contaminants. Here, a reliable and efficient wet-chemical recipe is presented for the preparation of ultra-smooth, highly ordered alkyl-terminated silane SAMs on Si wafers. The resulting surfaces are characterized by means of atomic force microscopy, X-ray reflectometry and contact angle measurements. Copyright © 2015 John Wiley & Sons, Ltd.

XPS study of Ni‐base alloys oxide films formed in primary conditions of pressurized water reactor

Abstract: The oxide scales formed on alloy 690 during its exposure to pressurized water reactor primary simulated media at 325 °C for different periods, ranging between 24 and 858 h have been characterized through XPS analysis. These results have been compared with the data obtained on Cr2O3, NiCr2O4, NiFe2O4, and Ni(OH)2 reference compounds. This comparison leads to the following conclusions about the scale formed on alloy 690: (i) the deconvolution of Cr-2p3/2 core level spectra seems to show that the internal oxide scale is made of a mix of chromite and chromia; (ii) the evolution of the height ratio between satellite and principal peaks, on the Ni-2p3/2 core level, has highlighted the presence of nickel hydroxide for all corrosion durations; and (iii) XPS analysis can be used to study the kinetics of nickel ferrite precipitation. In order to obtain a more complete description of such oxide scales based upon XPS measurements, reference data, obtained on nickel ferrites and chromites in which Fe is partially substituted to Ni, are needed. The comparison of published data and reference spectra performed in this work also leads to conclude that core level fits are dependent on the energy resolution, which can be achieved with specific spectrometer and analysis procedures. Therefore, reference compound spectra need to be recorded in the very identical analytical configuration before dealing with results obtained on corroded specimen.

Comparative XPS analysis of passive layers composition formed on AISI 304 L SS after standard and high‐current density electropolishing

Abstract: In the paper, there are described chemical compositions of passive surface layers formed on AISI 304 L (EN 1.4307) stainless steel after standard (EP50; i = 50 A/dm2) and high-current density (EP1000; i = 1000 A/dm2) electropolishing. For the studies, a mixture of orthophosphoric and sulfuric acid electrolyte in proportion 1:4 was used. The survey and high-resolution spectra of Cr 2p, Fe 2p, S 2p, P 2p, Ni 2p and C 1s are presented. On the basis of the obtained results it was noted that the chromium-to-iron ratio (Cr/Fe) after EP50 was about 3.5 times higher than that after EP1000 treatment. The phosphorus-to-sulfur ratios after EP50 and EP1000 electropolishing were 0.13 and 0.3, respectively, and nickel to the sum of chromium and iron coefficient (Ni/Cr + Fe) for both electrochemical polishing was equal to 0.04. Copyright © 2014 John Wiley & Sons, Ltd.

A new asymmetric Pseudo-Voigt function for more efficient fitting of XPS lines

Abstract: Asymmetric peak profiles for the application in spectroscopy can be obtained in a simple way by substituting the usually constant full width at half maximum parameter in Pseudo-Voigt functions with an energy-dependent expression, for instance of sigmoidal shape. While this approach has been successfully applied to vibrational spectra, we find that the resulting curves are less suitable for least-squares fits of X-ray photoelectron spectroscopy (XPS) data. However, if one additionally allows a variable displacement of the sigmoidal step relative to the peak, excellent fitting results can be obtained. We demonstrate the applicability of our extended approach on several inherently asymmetric XPS lines, i.e. the C 1s signal of graphite and C2H2/Pd(100), the 3d5/2–3d3/2 doublet of palladium, and the 4f7/2–4f5/2 doublet of platinum. Comparison of the corresponding fit results with the results obtained by the application of more elaborate, theory-based line profiles (Doniach-Sunjic and Mahan functions) shows that the modified Pseudo-Voigt function gives practically identical results in terms of peak shape and area, while requiring much less computational effort since no convolution procedures are required for its calculation. Thus, this function is most suitable for application in one of the following situations: (i) the peak shape of a given signal is known but cannot be calculated with ease, and (ii) the theoretical peak shape is not (yet) known, however, one wants to perform a first quantitative screening of the data at issue. Copyright © 2014 John Wiley & Sons, Ltd.

Surface structure and photoluminescence properties of AZO thin films on polymer substrates

Abstract: Al-doped zinc oxide (AZO) thin films were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method at room temperature. The effects of film thickness on the surface structure and the photoluminescencepropertiesofthe films were investigated by atomicforce microscopy (AFM),secondary ion massspectroscopy (SIMS) and room temperature photoluminescence (PL). AFM analysis showed that the surface of all films was extremely flat and uniform at nanoscale. Root mean square (RMS) value of the surface roughness which scanned the surface area of 3 μ mb y 3 μm andgrain size increased with increasing the filmthickness. Thus, the surfacemorphology ofthe films becamerough because of the coarse grains. The depth profile of AZO layers was analyzed by SIMS. It was found that the thickness of the AZO layer is almost same with the desired film thickness. The PL intensity of the dominant peak decreased and shifted slightly towards the shorter wavelengths with increasing the film thickness. According to the relationships between luminescence intensity and crystalline characteristics, it was observed that the intensity of the peak decreased by the increased surface area of the grains. Copyright © 2014 John Wiley & Sons, Ltd.

Formation of endogenous MgO and MgAl2O4 particles and their possibility of acting as substrate for heterogeneous nucleation of aluminum grains

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Effects of nitrogen composition on the resistivity of reactively sputtered TaN thin films

Abstract: Nanocrystalline tantalum nitride (TaN) thin films have been deposited by reactive direct current magnetron sputtering technique on Si/SiO2 (100) substrate with nitrogen flow rate ranging from 0, 3, 5, 7, 9 to 11 standard cubic centimeter per minute (sccm). Structural properties, surface morphology, chemical composition and and resistivity of the TaN films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy, X-ray photoemission spectroscopy (XPS) and four-point probe measurements, respectively. In the XRD spectra, a classical formation sequence of tantalum nitride phases in the order of Ta-Ta2N-TaN-Ta4N5 and decreasing amount of metallic Ta were observed with increasing nitrogen flow. The electrical resistivity of the TaN film was found to increase with increasing N/Ta ratio as a result of the increased electron scattering from interstitial N atoms. In the XPS analysis, two groups of Ta4f doublets relating to different TaN phases were observed in the core level spectra of TaN films. No strong coupling was observed between the Ta4f doublets and the Ta4p and the N1s groups. The appropriate nitrogen flow was believed to be helpful in the bonding and formation of stoichiometric TaN. Copyright © 2014 John Wiley & Sons, Ltd.

Influence of substrate temperature on the structural and optical properties of crystalline ZnO films obtained by pulsed spray pyrolysis

Abstract: This research was supported by the Ministry of Education and Science of Ukraine (Grant Numbers 0113U000131, 0112U000772, and the individual grant for D.O.).

High‐temperature oxidation behavior of Ni‐based superalloys with Nb and Y and the interface characteristics of oxidation scales

Abstract: Ni-based superalloys with niobium (Nb) or/and yttrium (Y) were prepared by vacuum melting. The oxidation kinetics of these alloys was studied by thermogravimetry at 800 °C for 100 h in static air. Morphology of oxides was studied using SEM, and the composition was analyzed by X-ray diffraction. Energy-dispersive X-ray spectrometer was employed to examine the linear element distribution of the cross section of the oxidation films. Results showed that the oxidation kinetics all followed a parabolic law at different stages. The oxide films were mainly comprised of Cr2O3, NiCr2O4, Al2O3 and TiO2. All the oxide films exhibited layered structure owing to different oxidation stages. With the addition of Nb or Y, the high-temperature oxidation resistance of the superalloy was improved significantly and the surface morphology of the oxidation film was ameliorated. The comprehensive effect of Nb and Y was remarkable in improving the high-temperature oxidation resistance of Ni-based alloys. Copyright © 2014 John Wiley & Sons, Ltd.

Surface characterization of standard cotton fibres and determination of adsorption isotherms of fragrances by IGC

Abstract: The surface characterizations of theWFK16000 standard cotton by dispersive, specific and total surface energy heterogeneity profiles with surface energy distributions and acid–base properties determined by surface energy analyser are presented in thiswork. The Dorris–Gray and Schultz methods for the determination of the dispersive surface energy component are compared, and their critical analysis is given. It is concluded that the Dorris–Gray method is more applicable at elevated temperature. Furthermore, Henry’s coefficient, standard free enthalpy, enthalpy and entropy data at infinite dilution and adsorption isotherms for some fragrances (benzyl acetate, Cyclal C, diphenyl oxide, eucalyptol, linalool and viridine) measured on dry cotton fibres by inverse gas chromatography at various temperatures are given. The temperature-dependent form of the Langmuir equation has been fitted to the multiple temperature adsorption isotherms with good agreement. Copyright © 2015 John Wiley & Sons, Ltd.

Photoemission investigation of the graphene surface cleaning by hydrogen/nitrogen plasma

Abstract: It is known that graphene surface contaminations by residues affect drastically its intrinsic properties and cannot be avoided when chemical vapor deposited (CVD) graphene is transferred on other substrates. In this work, we investigate by X‐ray photoelectron spectroscopy and work function measurements using X‐ray photoemission electron microscopy the capabilities of high‐density plasmas to clean graphene. The evolution of different chemical species at surface is monitored as a function of plasma exposure. H2 plasmas are shown to clean efficiently PMMA residues from CVD graphene on Cu. However, when the same plasma is used on graphene transferred on SiO2/Si substrate a liftoff of the graphene layer is observed before the end of cleaning procedure. These results are discussed in terms of H+ penetration through graphene and H2 formation between the SiO2 substrate and graphene. Using Cl‐based chemistries, we found that the plasma is able to etch polymeric contamination at the graphene surface. It is also found that the plasma induces spreading of the Si nanoparticle contamination that hampers the cleaning process.

Electrodeposition and characterization of Zn–Sn alloy coatings from a deep eutectic solvent based on choline chloride for corrosion protection

Abstract: With the aim of obtaining high corrosion resistant Zn–Sn alloy coatings from an ionic liquid, the effects of electrodeposition potential and electrolyte composition on the electrodeposition behavior, film composition, morphology and corrosion performance were investigated. Cyclic voltammograms indicate that Zn and Sn were co-deposited at distinct reduction potentials as pure Zn and Sn elements. In addition, the phase composition analysis also showed that the obtained Zn–Sn alloy deposits (8 wt.%–45 wt.% Zn) consist of a two-phase mechanical mixture of small aggregates of Zn and Sn metals. The Zn content of the alloy significantly increases as the electrodeposition potential and electrolyte Zn (II)/Sn (II) ratio increase. The corrosion performance study of the obtained Zn–Sn coatings showed that they have a passivation behavior and their corrosion resistance increases as the alloy-Sn content increases. To improve their morphological properties, ethylene diamine tetraacetic acid additive was introduced into the electrolyte and greatly improved the morphology and corrosion resistance of the deposits. For the first time, it was shown that high corrosion resistance Zn–Sn coatings can be obtained from ionic liquids. Copyright © 2014 John Wiley & Sons, Ltd.

Multivariate analysis of extremely large ToFSIMS imaging datasets by a rapid PCA method

Abstract: Principal component analysis (PCA) and other multivariate analysis methods have been used increasingly to analyse and understand depth profiles in X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). These methods have proved equally useful in fundamental studies as in applied work where speed of interpretation is very valuable. Until now these methods have been difficult to apply to very large datasets such as spectra associated with 2D images or 3D depth-profiles. Existing algorithms for computing PCA matrices have been either too slow or demanded more memory than is available on desktop PCs. This often forces analysts to 'bin' spectra on much more coarse a grid than they would like, perhaps even to unity mass bins even though much higher resolution is available, or select only part of an image for PCA analysis, even though PCA of the full data would be preferred.We apply the new 'random vectors' method of singular value decomposition proposed by Halko and co-authors to time-of-flight (ToF)SIMS data for the first time. This increases the speed of calculation by a factor of several hundred, making PCA of these datasets practical on desktop PCs for the first time. For large images or 3D depth profiles we have implemented a version of this algorithm which minimises memory needs, so that even datasets too large to store in memory can be processed into PCA results on an ordinary PC with a few gigabytes of memory in a few hours. We present results from ToFSIMS imaging of a citrate crystal and a basalt rock sample, the largest of which is 134GB in file size corresponding to 67 111 mass values at each of 512 × 512 pixels. This was processed into 100 PCA components in six hours on a conventional Windows desktop PC.

Surface characterization of untreated and hydro‐thermally pre‐treated Turkey oak woods after UV‐C irradiation

Abstract: The aim of this study was to determine the effect of UV-C irradiation on the Turkey oak wood surface (Quercus cerris L.). In order to compare the effect of irradiation, both untreated wood samples and those treated with steam and heat were analyzed. The steam treatments were carried out in an autoclave at 130 °C; samples were then heated in an oven for 2 h at 180 °C. The physical and chemical changes brought about in the untreated and treated wood samples by the UV-C light were monitored by colorimetry (color changes), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) (chemical composition) and scanning electron microscopy (SEM) (microstructure and morphology). A detailed analysis of the results indicates that the UV-C treatment caused irreversible changes in both the chemical composition and morphology of the wood samples via photooxidation and photodegradation processes. Depending on the type of pre-treatment used, these processes affected the wood samples differently. Copyright © 2014 John Wiley & Sons, Ltd.

Preparation and characterization of copper/silver bimetallic nanowires with core‐shell structure

Abstract: Core-shell copper/silver bimetallic nanowires were prepared by replacement reaction with citric acid and polyvinylpyrollidone at room temperature. A uniform silver coating was obtained by strictly controlling the molar ratio of Ag/Cu. The copper/silver composite was characterized by X-ray diffraction, scanning electron microscopy, electron probe microanalysis and X-ray photoelectron spectroscopy. Microscopic analysis shows that a well-copper/silver core-shell structure was formed. Thermo-gravimetry and differential thermal analysis to the composite nanowires show that the silver coatings efficiently inhibit the oxidation of Cu. Copyright © 2015 John Wiley & Sons, Ltd.

Corrosion inhibition by benzotriazole derivatives and sodium dodecyl sulphate as corrosion inhibitors for copper in ground water at different temperatures

Abstract: 1-(2-Pyrrole carbonyl) benzotriazole (PBTA) and 1-(2-thienyl carbonyl)-benzotriazole (TBTA) were synthesized. Different concentrations of PBTA, TBTA, sodium dodecyl sulphate (SDS), and molybdate (Mo) were evaluated as corrosion inhibitors for copper in ground water medium at different temperatures. The obtained results were compared with the effect of benzotriazole (BTA) on the inhibition of copper corrosion at the same condition. The study was performed using potentiodynamic polarization, electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy investigations. A good inhibition is ensured at elevated temperatures. All measurements indicated that PBTA, TBTA, and BTA act as good corrosion inhibitors and their inhibition efficiency (IE%) increased with combining them with optimum concentration of SDS and Mo. Furthermore, the best performance was recorded for the compound PBTA + SDS + Mo, which was found to offer increased IE% in a synergistic manner, thereby acting as a good corrosion inhibitor for copper in ground water medium. Copyright © 2015 John Wiley & Sons, Ltd.

Interfacial reactions of a MAX phase/superalloy hybrid

Abstract: Oxidation resistant, strain tolerant MAX phase coatings are of general interest for high temperature applications. Accordingly, Cr2AlC MAX phase coupons were vacuum diffusion bonded to an advanced turbine disk alloy at 1100 °C for compatibility studies. The interface revealed an inner diffusion zone consisting of ~10 µm of β-Ni(Co)Al, decorated with various γ′ (Ni,Co)3Al, Ta(Ti,Nb)C, and W(Cr,Mo)3B2 precipitates. On the Cr2AlC side, an additional ~40-µm Al-depletion zone of Cr7C3 formed an interconnected network with the β-Ni(Co)Al. On the superalloy side, enhanced carbide precipitation developed over a depth of ~80 µm. Subsequent annealing for 100 h and 1000 h at 800 °C coarsened some features, enhanced TCP precipitation in the superalloy, but only enlarged the diffusion layers by ~5 µm at most. Because of Al depletion from the MAX phase and corresponding Al enrichment of the alloy, the reaction zone displayed similarities to an oxidized Cr2AlC surface and an aluminized superalloy, respectively. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Characterisation and properties of magnetron sputtered nanoscale bi-layered Ni/Ti thin films and effect of annealing

Abstract: Single-bi-layer of Ni–Ti thin film was deposited using DC and RF magnetron sputtering technique by layer-wise deposition of Ni and Ti on Si(100) substrate in the order of Ni as the bottom layer and Ti as the top layer. The deposition of these amorphous as-deposited thin films was followed by annealing at 300 °C, 400 °C, 500 °C, and 600 °C temperature with 1-h annealing time for each to achieve crystalline thin films. This paper describes the fabrication processes and the novel characterization techniques of the as-deposited as well as the annealed thin films. Microstructures were analysed using FESEM and HRTEM. Nano-indentation and AFM were carried out to characterize the mechanical properties and surface profiles of the films. It was found that, for the annealing temperatures of 300 °C to 600 °C, the increase in annealing temperature resulted in gradual increase in atomic-cluster coarsening with improved ad-atom mobility. Phase analyses, performed by GIXRD, showed the development of silicide phases and intermetallic compounds. Cross-sectional micrographs exhibited the inter-diffusion between the two-layer constituents, especially at higher temperatures, which resulted either in amorphization or in crystallization after annealing at temperatures above 400 °C. Copyright © 2015 John Wiley & Sons, Ltd.

Sustainable natural adsorbents for heavy metal removal from wastewater: lead sorption on pine bark (Pinus radiata D.Don)

Abstract: Aqueous Pb(II) adsorption on pine bark (Pinus Radiata D.Don), an inexpensive and sustainable natural sorbent material, has been evaluated and the mechanism of metal retention characterized by scanning electron microscopy (SEM), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS). Bark pulp densities >1.5 g l−1 achieve near 100% Pb(II) removal from aqueous solutions containing 100 mg l−1 Pb(II). Adsorption rates increased with pulp density, although adsorption capacity diminished at high densities because of blockage of adsorption sites. The effects of washing and sulfuric acid activation were assessed and found to be less important than in previous metal sorption studies. Pb(II) sorption takes place mainly at the lignocellulosic C―O groups, with adsorption at phenolic sites appearing to be most significant. © 2016 The Authors. Surface and Interface Analysis published by John Wiley & Sons, Ltd.

Surface evaluation and electrochemical behavior of cerium conversion coating modified with silane on magnesium alloy

Abstract: A new cerium conversion coating modified with the hydrolysis silane is designed for AZ31 magnesium alloy, which aims at assessing the surface characterizations and electrochemical behaviors between the cerium conversion coating with and without the silane modified. The effect of the silane addictive is studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The adhesion of the coatings is undertaken according to the American Society for Testing and Materials (ASTM) standard D3359-08 cross tape test. The electrochemical behavior is evacuated by polarization experiment and electrochemical impedance spectroscopy (EIS) in NaCl electrolyte. The results show that the addition of bis-[triethoxysilylpropyl] tetrasulfide (BTESPT) to loosen and porous cerium conversion coating leads to the formation of a more compact and homogenous film, higher resistance to water uptake and better adhesion to substrate. Electrochemical measurements show that, compared with the non-modified cerium conversion coating, the coating modified with the silane exhibits better anticorrosion properties. Copyright © 2014 John Wiley & Sons, Ltd.

XPS and factor analysis study of initial stages of cerium oxide growth on polycrystalline tungsten

Abstract: The initial stages of growth of the nanostructured cerium oxide deposited on the polycrystalline tungsten surface by pulsed laser deposition are studied using XPS technique. The population of Ce (III) and Ce (IV) oxidation states in the deposited CeO2−x layers is determined applying factor analysis method. Tungsten atoms react with oxygen from the cerium oxide nanoparticles already at the room temperature, and a layer of tungsten trioxide is formed at the interface. Gradual heating of the samples up to 900 K leads to the increase of the thickness of WO3 oxide layer and a partial reduction of Ce (IV) to Ce (III). The spectra of O (1s) photoelectrons are composed from a signal originating from metal oxides and a signal of surface superoxide and hydroxyl groups. Factor analysis was performed on the spectra of Ce (3d) photoelectrons to determine the position, shape, and intensity of the spectral components belonging to Ce (III) and Ce (IV) oxidation states. We propose a new simple method to generate components of the spectroscopic meaning. The basic idea of our method consists in the use of the slightly positive values instead of zeros to the needle test vector. Two components are required to reproduce the original data within the experimental errors. Copyright © 2015 John Wiley & Sons, Ltd.