| 1. |
- Evertsson, Jonas, et al.
(author)
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The thickness of native oxides on aluminum alloys and single crystals
- 2015
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In: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 349, s. 826-832
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Journal article (peer-reviewed)abstract
- We present results from measurements of the native oxide film thickness on four different industrial aluminum alloys and three different aluminum single crystals. The thicknesses were determined using X-ray reflectivity, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. In addition, atomic force microscopy was used for micro-structural studies of the oxide surfaces. The reflectivity measurements were performed in ultra-high vacuum, vacuum, ambient, nitrogen and liquid water conditions. The results obtained using X-ray reflectivity and X-ray photoelectron spectroscopy demonstrate good agreement. However, the oxide thicknesses determined from the electrochemical impedance spectroscopy show a larger discrepancy from the above two methods. In the present contribution the reasons for this discrepancy are discussed. We also address the effect of the substrate type and the presence of water on the resultant oxide thickness.
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| 2. |
- Fernandes, V. R., et al.
(author)
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H-2 reduction of surface oxides on Pd-based membrane model systems - The case of Pd(100) and Pd75Ag25(100)
- 2014
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In: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 313, s. 794-803
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Journal article (peer-reviewed)abstract
- Reduction of the (root 5 x root 5)R27 degrees surface oxide on Pd(1 0 0) and Pd75Ag25(1 0 0) surfaces by H-2 has been studied using high-resolution photoelectron spectroscopy in situ at H-2 pressures 5 x 10(-9) mbar and 5 x 10(-8) mbar and selected temperatures in the range 30 degrees C to 170 degrees C. The reduction is slower on Pd75Ag25(1 0 0) compared to Pd(1 0 0) for all temperatures and pressures investigated. For Pd(1 0 0), the surface oxide reduction rate is rather independent of temperature, while for Pd75Ag25(1 0 0) a nonmonotonic variation is observed. As indicated by kinetic analysis, the complex reduction behavior is not well described by Avrami kinetics. Oxygen spillover effects contribute to this picture for Pd(1 0 0), while surface compositional effects appear to dominate the performance for Pd75Ag25(1 0 0). These findings may have implications for understanding the oxidation, reduction and hydrogen transport properties of Pd-Ag membranes. (C) 2014 Elsevier B.V. All rights reserved.
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| 3. |
- Larsson, Alfred, et al.
(author)
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In situ quantitative analysis of electrochemical oxide film development on metal surfaces using ambient pressure X-ray photoelectron spectroscopy : Industrial alloys
- 2023
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 611
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Journal article (peer-reviewed)abstract
- Ambient Pressure X-ray Photoelectron Spectroscopy combined with an electrochemical setup is used to study, in situ, the electrochemical oxide growth on an in-dustrial Ni-Cr-Mo alloy. The native oxide film was characterized in vacuum and in water vapor at 17 mbar, and was found to be 11.4 & ANGS; thick and rich in Cr3+. In 0.1 M NaCl electrolyte, anodic growth of the oxide film at potentials up to 700 mV vs Ag/AgCl nearly doubled the thickness of the oxide film. Moreover, a transformation of the oxide composition occurred, as the oxide became enriched in Mo6+ with a chemical fingerprint more like that of pure MoO3. Both thermodynamics and kinetics of the oxidation of the alloying elements dictate the oxide film growth and composition. Furthermore, we develop the quantitative analysis of oxide composition and thickness to take into account the attenuation through the liquid water and the water vapor atmosphere. Finally, we discuss the differences between ex situ, UHV, in situ, and operando measurements. Our approach is robust, fast, simple, and suitable for systematically probing metal surfaces after aqueous exposure and electro-chemical polarization, which promises wide applications for studies of solid-liquid interfaces in corrosion, batteries, fuel cells, and electrocatalysis.
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| 4. |
- Mikkelsen, Anders, et al.
(author)
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A study of the surface structure and composition of annealed Ga0.96Mn0.04As(100)
- 2004
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In: Applied Surface Science. - 1873-5584. ; 222:1-4, s. 23-32
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Journal article (peer-reviewed)abstract
- The surface structure and chemical composition of annealed Ga0.96Mn0.04As(1 0 0) have been studied by scanning tunneling microscopy (STM), auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The samples were As capped and subsequently transferred in-air from the MBE system to the STM chamber. After annealing to 600 K it is found that the Mn segregates to the surface and forms a compound, which is stable up to annealing temperatures of 790 K. For annealing temperatures above 825 K a well-ordered phase exists signified by a LEED pattern consisting of a superposition of a (1 x 6) and a (4 x 2) pattern. LEED and STM measurements demonstrate that the surface is dominated by (1 x 6) domains coexisting with small patches of (4 x 2) domains. By comparing the STM images of the high temperature phase found on Ga0.96Mn0.04As(1 0 0) with the high temperature phases found on ordinary GaAs(1 0 0), we demonstrate differences between annealed Ga0.96Mn0.04As(1 0 0) and GaAs(1 0 0) in both surface morphology and atomic structure. We argue that the Ga0.96Mn0.04As surface is more As rich than the GaAs surface prepared in a similar fashion. Reasons for these differences are discussed.
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