► We have found a correlation between chemical potentials in surface–bulk atomic exchanges and oxides formed on the surface of Fe–Cr–Al alloys in high temperature ► In Fe–Cr–Al alloys the addition of ...Cr changes the chemical potentials to drive Al to the surface to improve the formation of protective Al-oxide scales ► The described mechanism sheds light on the phenomenon called Third Element Effect (TEE), which does not have a generally accepted explanation so far ► Our research deals with the analysis of the experimental results from the point of view of atomic scale quantum mechanics, which represents a new kind of approach to the problem ► Our first-principles computational investigation covers also an exceptionally wide concentration range of Fe–Cr–Al alloys
Good high-temperature corrosion resistance of Fe–Al alloys in oxidizing environments is due to the
α-Al
2O
3 film which is formed on the surface provided temperature is above 900
°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.
X-ray photoelectron spectroscopy (XPS) is one of the most used methods in a diverse field of materials science and engineering. The elemental core-level binding energies (BE) and core-level shifts ...(CLS) are determined and interpreted in the XPS. Oxidation is commonly considered to increase the BE of the core electrons of metal and semiconductor elements (i.e., positive BE shift due to O bonds), because valence electron charge density moves toward electronegative O atoms in the intuitive charge-transfer model. Here we demonstrate that this BE hypothesis is not generally valid by presenting XPS spectra and a consistent model of atomic processes occurring at HfO2/InP interface including negative In CLSs. It is shown theoretically for abrupt HfO2/InP model structures that there is no correlation between the In CLSs and the number of oxygen neighbors. However, the P CLSs can be estimated using the number of close O neighbors. First native oxide model interfaces for III-V semiconductors are introduced. The results obtained from ab initio calculations and synchrotron XPS measurements emphasize the importance of complementary analyses in various academic and industrial investigations where CLSs are at the heart of advancing knowledge.
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•Interface energies of the III-V native oxide (quasi-)coherent interfaces are small.•Interface energy may stabilize oxide structures not found in bulk form.•Relatively small strain ...energy and configurational match imply a small interface energy.•Partially oxidized substrate P atoms induce distinct gap states.•Interface models presented can be used to study various properties of the interfaces.
III-V semiconductor - oxide interfaces have attracted huge interest due to their substantial potential in electronic applications. However, due to the extreme complexity of the modeling of the interfaces, there are only few ab initio studies of these interfaces.
Several model interfaces of native InPO4 oxides are designed in this study. It is shown that energies of the (quasi-)coherent interfaces are much smaller than energies of the incoherent interfaces. Furthermore, it is pointed out that the interface energy can stabilize oxide structures not found in bulk form. Relatively small strain energy and configurational match imply a small interface energy.
It is estimated that the gap state density of the In-terminated quasi-coherent interfaces is small or zero. However, partial oxidation of the substrate P atoms, which can be induced, e.g., by non-stoichiometry of the oxide, causes distinct gap states. This is a mechanism to explain Fermi level pinning of the III-V – oxide interfaces. Non-stoichiometric compositions are also investigated. Experimental results on InP native oxide growth are discussed. The models can be used to study various properties of the interfaces and more complex models including, e.g., dislocations or non-planar surfaces can be based on the models.
•Ab initio calculation of the surface relaxation of metals.•Surface energy and surface stress of transition metals.•Surface energy and surface stress of simple metals and light actinides.
We ...investigated surface properties of metals by performing first-principles calculations. A systematic database was established for the surface relaxation, surface energy (γ), and surface stress (τ) for metallic elements in the periodic table. The surfaces were modeled by multi-layered slab structures along the direction of low-index surfaces. The surface energy γ of simple metals decreases as the atomic number increases in a given group, while the surface stress τ has its minimum in the middle. The transition metal series show parabolic trends for both γ and τ with a dip in the middle. The dip occurs at half-band filling due to a long-range Friedel oscillation of the surface charge density, which induces a strong stability to the Peierls-like transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for γ and τ, respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative τ for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing γ trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.
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•Nickel can diffuse to the Si(1 0 0) surface from the sample holder at 1230°C.•The unit mesh of (2 × n) DVL structure on Si(1 0 0) includes one Ni atom.•The single missing-dimer ...defect is absent in the (2 × n) DVL structure.•Minimization of sample sizes is reasonable to avoid the unwanted Ni contamination.
Using scanning tunneling microscopy, x-ray photoelectron spectroscopy, and low-energy electron diffraction, we have studied clean and Ni-containing Si(1 0 0) surfaces and shown that the Ni contamination can easily appear at the Si(1 0 0) during its annealing at high temperature (1230 °C) because of migration of this impurity from heated parts of the sample holder, even though they are nominally Ni-free. The difference of dimer-vacancy (DV) defects, which are common features of Si(1 0 0), and their patterns on both surfaces is examined. It is also found that the density of DV defects on the Ni-contaminated surface is proportional to the number of Ni atoms. The analysis indicates that the fully saturated DV structure, i.e., Ni-induced Si(1 0 0)(2 × n) phase contains one metal atom per defect. The findings are valuable for constructing atomic models of defects on the Si(1 0 0) as well as preparation of clean Si(1 0 0) substrate and monitoring the Ni segregation on its surface. In addition, the results can be useful for Ni silicide metal-contact formation in metal-oxide-semiconductor field-effect transistor technology.”
We determine the atomic surface structure of the Bi-terminated GaAs(001) (1×3) reconstruction for the first time using scanning probe microscopies, photoemission spectroscopy, and ab initio ...calculations. The proposed kinked-dimer (4×3) model is consistent with experimental characterization and can accommodate a variety of species configurations due to an availability of low-energy sites for Bi substitution, accounting for the significant observed local disorder. In addition, experiments show that stability of this reconstruction coincides with a dramatic change in surface step morphology, giving rise to strong up/down step interaction and a counterintuitive smoothing effect on the micrometer length scale.
► Deposited 2.4ML (or 6ML with As4) of Bi onto GaAs(001) β2(2×4) surface. ► Reflective high-energy electron diffraction shows (1×3) and (4×3) patterns. ► Scanning tunneling microscopy (STM) reveals β(4×3) reconstruction. ► High number of up-down step edge pairs in STM suggest origin of Bi smoothing effect. ► Synchrotron photoemission spectra indicate α(4×3) and γ(4×3) reconstructions.
Using the projector augmented wave method within density functional theory, we present a systematic study of the layer relaxation, surface energy and surface stress of 3d transition metals. Comparing ...the calculated trends for the surface energy and stress with those obtained for 4d and 5d metals we find that magnetism has a significant effect on the surface properties. Enhanced surface magnetic moments decrease the size of the surface relaxation, lower the surface energy and surface stress, leading to compressive stress in Cr and Mn.
The surface properties of Fe-rich ferromagnetic Fe-Cr alloys are investigated using a first-principles quantum-mechanical method. In dilute alloys, the surfaces are dominated by Fe, whereas the ...Cr-containing surfaces become favorable when the bulk Cr concentration exceeds the limit of ∼ 10 atomic per cent. The abrupt change in the surface behavior is the consequence of complex competing magneto-chemical interactions between the alloying atoms. Considering the quantities of various features: equilibrium surface profiles, chemical potentials, segregation energies, surface energies, magnetic moments, mixing energies and pair interactions, within a wider range of bulk and surface concentrations enables us to build a comprehensive picture of the physics of Fe-Cr surfaces. Using the present achievements many previously controversial results can now be merged into a consistent model of Fe-rich Fe-Cr alloys.
Atomic structure of the Sr-adsorbed Si(100)(1×2) surface has been investigated by scanning tunneling microscopy (STM) and ab initio calculations. This surface reveals rows of Sr atoms between ...unbuckled Si dimer rows as well as an abundance of vacancy defects in the metal rows. The density of such defects can be minimized by the optimization of growth procedure; however, they cannot be avoided completely, forming vacancy lines along the 021 directions, where the neighboring vacancies are connected via the Si dimer. The origin of vacancy defects is discussed in the context of Sr/Si(100)(1×2) and related surfaces. In addition, the interaction of Sr/Si(100)(1×2) with oxygen is examined by STM directly during the exposure in the O2 gas.
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•A structural model of Sr/Si(100)(1×2) is proposed based on STM and DFT.•Vacancies in Sr rows agglomerate in the lines along the directions.•Sr/Si(100)(1×2) protects the Si crystal against oxidation.
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