| 1. |
- Airiskallio, E., et al.
(author)
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High temperature oxidation of Fe-Al and Fe-Cr-Al alloys : The role of Cr as a chemically active element
- 2010
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In: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 52:10, s. 3394-3404
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Journal article (peer-reviewed)abstract
- Good high-temperature corrosion resistance of Fe-Al alloys in oxidizing environments is due to the alpha-Al2O3 film which is formed on the surface provided temperature is above 900 degrees C and the Al-content of the alloy exceeds the critical value. Ab initio calculations combined with experiments on Fe-13Al, Fe-18Al, Fe-23Al and Fe-10Cr-10Al alloys show that the beneficial effect of Cr on the oxidation resistance is significantly related to bulk effects. The comparison of experimental and calculated results indicates a clear correlation between the Fe-Cr chemical potential difference and the formation of the protective oxide scales. (C) 2010 Elsevier Ltd. All rights reserved.
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| 2. |
- Airiskallio, E., et al.
(author)
-
Magnetic origin of the chemical balance in alloyed Fe-Cr stainless steels : First-principles and Ising model study
- 2014
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In: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 92, s. 135-140
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Journal article (peer-reviewed)abstract
- Iron-chromium is the base material for most of the stainless steel grades. Recently, new insights into the origins of fundamental physical and chemical characteristics of Fe-Cr based alloys have been achieved. Some of the new results are quite unexpected and call for further investigations. The present study focuses on the magnetic contribution in the atomic driving forces related to the chemical composition in Fe-Cr when alloyed with Al, Ti, V, Mn, Co, Ni, and Mo. Using the ab initio exact muffin-tin orbitals method combined with an Ising-type spin model, we demonstrate that the magnetic moment of the solute atoms with the induced changes in the magnetic moments of the host atoms form the main factor in determining the mixing energy and chemical potentials of low-Cr Fe-Cr based alloys. The results obtained in the present work are related to the designing and tuning of the microstructure and corrosion protection of low-Cr steels.
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| 3. |
- Airiskallio, E., et al.
(author)
-
Third element effect in the surface zone of Fe-Cr-Al alloys
- 2010
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:3
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Journal article (peer-reviewed)abstract
- The third element effect to improve the high temperature corrosion resistance of the low-Al Fe-Cr-Al alloys is suggested to involve a mechanism that boosts the recovering of the Al concentration to the required level in the Al-depleted zone beneath the oxide layer. We propose that the key factor in this mechanism is the coexistent Cr depletion that helps to maintain a sufficient Al content in the depleted zone. Several previous experiments related to our study support that conditions for such a mechanism to be functional prevail in real oxidation processes of Fe-Cr-Al alloys.
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| 4. |
- Airiskallio, E., et al.
(author)
-
Tuning the surface chemistry of Fe-Cr by V doping
- 2009
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:15
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Journal article (peer-reviewed)abstract
- The reversal of the magnitudes of the bulk and surface chemical-potential differences induces the outburst of Cr on the otherwise pure Fe surface of Fe-Cr alloys. This threshold value for the Cr content is about 10 at. %. It is found that vanadium addition to Fe-Cr shifts the Cr threshold to a substantially lower value suggesting V having a positive effect on the corrosion resistance of low Cr steels. The obtained shift in the Cr threshold is shown to be connected to the change in volume of the alloy.
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| 5. |
- Kuzmin, M., et al.
(author)
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Atomic structure of Yb/Si(100)(2X6) : Interrelation between the silicon dimer arrangement and Si 2p photoemission line shape
- 2010
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:11, s. 113302-
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Journal article (peer-reviewed)abstract
- Combining photoelectron spectroscopy and density-functional theory calculations, we have studied the atomic geometry of Yb/Si(100)(2 X 6) reconstruction and the mechanisms responsible for its stabilization as well as the influence of this reconstruction on Si 2p core-level photoemission. The analysis of measured and calculated surface core-level shifts supports the recently proposed model of the Yb/Si(100)(2 X 6). It involves, in agreement with valence-band measurements, unbuckled (symmetrical) silicon dimers, leading to unusually narrowed Si 2p line shape as compared to those of related systems. The origin of the symmetrical dimers in the (2 X 6) structure is discussed in the context of previous results in literature.
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| 6. |
- Kuzmin, M., et al.
(author)
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Surface core-level shifts on Ge(111)c(2 x 8) : Experiment and theory
- 2011
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:24, s. 245319-
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Journal article (peer-reviewed)abstract
- Combining high-resolution photoelectron spectroscopy and density functional theory (DFT) calculations, 3d photoemission line shape and surface core-level shifts have been reinvestigated on the Ge(111)c(2 x 8) surface. It is found that 3d spectra include, in addition to the bulk and three surface-shifted components reported in literature, a component that was not identified in earlier measurements with a lower resolution. The detailed interpretation of these spectra and their line shape is made on the basis of DFT calculations. It is shown that the lowest binding energy component is due to the rest atoms. The higher binding energy emission is caused by the adatoms and the third-layer atoms that are below the adatoms. Finally, the two other surface components originate from the first- and second-layer atoms. The screening effects in the Ge(111)c(2 x 8) are discussed.
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| 7. |
- Lang, J. J. K., et al.
(author)
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Ab initio and scanning tunneling microscopy study of an indium-terminated GaAs(100) surface : An indium-induced surface reconstruction change in the c(8x2) structure
- 2010
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:24, s. 245305-
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Journal article (peer-reviewed)abstract
- Technologically useful indium- (In) terminated c(8 x 2)-reconstructed GaAs(100) substrate surface has been studied by first-principles calculations and scanning tunneling microscopy (STM) measurements. Our total-energy calculations demonstrate the stability of four different so-called zeta a structures with In monomer rows and In coverage between 0.5 and 2 monolayers on the GaAs(100) substrate. Thus, we introduce a surface system, which stabilizes the zeta a reconstruction. Furthermore, an interesting trend is found. Atomic structure of the c(8 x 2) reconstruction depends on the surface-layer cation and substrate volumes, which, in principle, allows to tune the surface structure by cation adsorption. This phenomenon is related to the peculiar c(8 x 2) atomic surface structure, which shows mixed surface layer, including both anions and cations, and uncommon metallic-type cations in the zeta a structure, which do not show covalent bonds. Our results predict a structural transition from the zeta structure to the zeta a structure as the surface cation size is increased at 0 K. The found transition is probably related to the disordered surface structures (consisting of zeta and zeta a building blocks) found experimentally by x-ray diffraction at room temperature. Comparison of the STM images, calculated for various c(8 x 2) models, with the former and present measured STM images of In/GaAs(100) c(8 x 2) supports the presence of stable zeta a reconstructions.
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| 8. |
- Lang, J. J. K., et al.
(author)
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Tin-stabilized (1 x 2) and (1 x 4) reconstructions on GaAs(100) and InAs(100) studied by scanning tunneling microscopy, photoelectron spectroscopy, and ab initio calculations
- 2011
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In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 605:9-10, s. 883-888
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Journal article (peer-reviewed)abstract
- Tin (Sn) induced (1 x 2) reconstructions on GaAs(100) and InAs(100) substrates have been studied by low energy electron diffraction (LEED), photoelectron spectroscopy, scanning tunneling microscopy/spectroscopy (STM/STS) and ab initio calculations. The comparison of measured and calculated STM images and surface core-level shifts shows that these surfaces can be well described with the energetically stable building blocks that consist of Sn-III dimers. Furthermore, a new Sn-induced (1 x 4) reconstruction was found. In this reconstruction the occupied dangling bonds are closer to each other than in the more symmetric (1 x 2) reconstruction, and it is shown that the (1 x 4) reconstruction is stabilized as the adatom size increases.
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| 9. |
- Laukkanen, P., et al.
(author)
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Anomalous bismuth-stabilized (2x1) reconstructions on GaAs(100) and InP(100) surfaces
- 2008
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 100, s. 086101-
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Journal article (peer-reviewed)abstract
- First-principles phase diagrams of bismuth-stabilized GaAs- and InP(100) surfaces demonstrate for the first time the presence of anomalous (2 x 1) reconstructions, which disobey the common electron counting principle. Combining these theoretical results with our scanning-tunneling-microscopy and photoemission measurements, we identify novel (2 x 1) surface structures, which are composed of symmetric Bi-Bi and asymmetric mixed Bi-As and Bi-P dimers, and find that they are stabilized by stress relief and pseudogap formation.
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| 10. |
- Laukkanen, P., et al.
(author)
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Bismuth-stabilized c(2X6) reconstruction on a InSb(100) substrate : Violation of the electron counting model
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 81:3
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Journal article (peer-reviewed)abstract
- By means of scanning tunneling microscopy/spectroscopy (STM/STS), photoelectron spectroscopy, and first-principles calculations, we have studied the bismuth (Bi) adsorbate-stabilized InSb(100) substrate surface which shows a c(2X6) low-energy electron diffraction pattern [thus labeled Bi/InSb(100)c(2X6) surface] and which includes areas with metallic STS curves as well as areas with semiconducting STS curves. The first-principles phase diagram of the Bi/InSb(100) surface demonstrates the presence of the Bi-stabilized metallic c(2X6) reconstruction and semiconducting (4X3) reconstruction depending on the chemical potentials, in good agreement with STS results. The existence of the metallic c(2X6) phase, which does not obey the electron counting model, is attributed to the partial prohibition of the relaxation in the direction perpendicular to dimer rows in the competing reconstructions and the peculiar stability of the Bi-stabilized dimer rows. Based on (i) first-principles phase diagram, (ii) STS results, and (iii) comparison of the measured and calculated STM and photoemission data, we show that the measured Bi/InSb(100)c(2X6) surface includes metallic areas with the stable c(2X6) atomic structure and semiconducting areas with the stable (4X3) atomic structure.
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