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International audience; ITER will use beryllium as a plasma-facing material in the main chamber, covering a total surface area of about 620 m. Given the importance of beryllium erosion and co-deposition for tritium retention in ITER, significant efforts have been made to understand the behaviour of beryllium under fusion-relevant conditions with high particle and heat loads. This paper provides a comprehensive report on the state of knowledge of beryllium behaviour under fusion-relevant conditions: the erosion mechanisms and their consequences, beryllium migration in JET, fuel retention and dust generation. The paper reviews basic laboratory studies, advanced computer simulations and experience from laboratory plasma experiments in linear simulators of plasma–wall interactions and in controlled fusion devices using beryllium plasma-facing components. A critical assessment of analytical methods and simulation codes used in beryllium studies is given. The overall objective is to review the existing set of data with a broad literature survey and to identify gaps and research needs to broaden the database for ITER.

Combining experimental and ab initio core-level photoelectron spectroscopy (periodic DFT and quantum chemistry calculations), we elucidated how ammonia molecules bond to the hydroxyls of the (H,OH)-Si(001) model surface at a temperature of 130 K. Indeed, theory evaluated the magnitude and direction of the N 1s (and O 1s) chemical shifts according to the nature (acceptor or donor) of the hydrogen bond and, when confronted to experiment, showed unambiguously that the probe molecule makes one acceptor and one donor bond with a pair of hydroxyls. The consistency of our approach was proved by the fact that the identified adsorption geometries are precisely those that have the largest binding strength to the surface, as calculated by periodic DFT. Real-time core-level photoemission enabled measurement of the adsorption kinetics of H-bonded ammonia and its maximum coverage (0.37 ML) under 1.5 x 10(-9) mbar. Experimental desorption free energies were compared to the magnitude of the adsorption energies provided by periodic DFT calculations. Minority species were also detected on the surface. As in the case of H-bonded ammonia, DFT core-level calculations were instrumental to attribute these minority species to datively bonded ammonia molecules, associated with isolated dangling bonds remaining on the surface, and to dissociated ammonia molecules, resulting largely from beam damage.

The electronic and structural properties of the Ge/GeO2 interface are addressed through a density functional simulation scheme which includes the use of hybrid functionals for achieving accurate band gaps, band offsets and defect levels. The present work discusses the germanium dangling bond levels, the thermodynamics of GeOx, the stability of the oxygen vacancy across Ge/HfO2 interfaces, the atomic structure of GeOx, electron and hole trapping in GeOx, and the band alignment at the Ge/GeO2 interface. (C) 2011 Elsevier B.V. All rights reserved.

Core level photoelectron spectroscopy has been used to investigate the effect of substrate doping on the binding energies of 1 nm HfO2/0.6 nm SiO2/Si films. A characteristic 0.26-0.30 nm Hf0.35Si0.65O2 silicate interface is formed between the gate oxide and the SiO2 layer with an equivalent oxide thickness of 0.5 nm. High substrate doping shifts the Fermi level upwards by 0.5 eV. An interface dipole forms giving rise to a shift in the local work function. Screening from substrate electrons is confined to the SiO2/Si interface. The principal contributions modifying the core level binding energies in the oxide are the doping dependant Fermi level position and the interface dipole strength. (c) 2007 Elsevier B.V. All rights reserved.

The Fe62Ni20Cr18 valence band was studied by scanning the photon energy across the 2p(3/2) core-level threshold of each element of the alloy. A resonant enhancement of the weak 3d-like features was observed. In pure transition metals, similar valence band resonances are explained by a radiation-less Raman de-excitation emission, which is active at threshold and degenerate with the two-hole satellite of direct photoemission. Present structures are associated to satellite features occurring in Fe62Ni20Cr18, and their intensities and binding energies are compared to those of the pure metal components. The alloy satellite resonant behaviour reveals some peculiar modi. cations of: a) the crossover between the radiationless Raman scattering and the Auger emission regimes; b) the ratio of the relative intensities of the main and satellite peaks. We mainly assign these differences to the hetero-nuclear bonds in the alloy.

In X-ray photoelectron spectroscopy (XPS) core-level shifts of an atom in different chemi-cal environments, including the atom-free ion chemical change, result from both initial- and final-state effects (Egelhoff, 1987). The initial state effect is a static shift in the orbital energies in the ground state of the atom before core ionization. It is directly related to the nature of the chemical bonds in which the atom is involved. The charge distribution of an atom in molecules or solids, or as a free ion, in fact, changes the potentials of core electrons, even though the spa-tial character of the core electron wave function remains strongly localized within the atom. Instead, the final state effects are related to the degree to which core and valence electrons and the environment of the atom can polarize in response to ionization.

We present a database of $24\ifmmode\times\else\texttimes\fi{}24$ surface segregation energies of single transition metal impurities in transition-metal hosts obtained by a Green's-function linear-muffin-tin-orbitals method in conjunction with the coherent potential and atomic sphere approximations including a multipole correction to the electrostatic potential and energy. We use the database to establish the major factors which govern surface segregation in transition metal alloys. We find that the calculated trends are well described by Friedel's rectangular state density model and that the few but significant deviations from the simple trends are caused by crystal structure effects.

We report results from ab initio cluster-model calculations on the O(1s) binding energy (BE) in the alkaline-earth oxides, MgO, CaO, SrO, and BaO; all these oxides have a cubic lattice structure. We have obtained values for both the initial- and final-state BE's. A simple point-charge model, where an O2-anion is surrounded by point charges, accounts for the observed shift in the O(1s) BE by about 2.5 eV to lower energy going from MgO (largest BE) to BaO (smallest BE). This point-charge model only describes the effect of the Madelung potential at the 1s ionized O2- anion; it does not allow any covalent bonding between the metal (M) cations and the oxygen anions. Once the effect of the O2 --> M2+ covalent bonding is included explicitly by using O(m)M(n) cluster models of the MO crystal, the trend in the O(1s) BE to smaller values for heavier metals does not change significantly. This shows that the main contribution to the shift is not the different amount of covalent mixing in the alkaline-earth oxides but rather the change in the Madelung potential along the group.

In this thesis, quantum-mechanical calculations within density-functional theory on metallic systems are presented. The overarching goal has been to investigate effects of disorder. In particular, one of the properties investigated is the bindingenergy shifts for core electrons in binary alloys using different theoretical methods. These methods are compared with each other and with experimental results. One such method, the so-called Slater-Janak transition state method relies on the assumption that the single-particle eigenvalues within density-functional theory are linear functions of their respective occupation number. This assumption is investigated and it is found that while the eigenvalues to a first approximation show linear behavior, there are also nonlinearities which can influence the core-level binding energy shifts. Another area of investigation has been iron based alloys at pressures corresponding to those in the Earth’s inner core. This has been done for the hexagonal close packed and face entered cubic structures. The effects of alloying iron with magnesium and nickel on the equation of state as well on the elastic properties have been investigated. The calculations have shown that the hexagonal close packed structure in FeNi is more isotropic than the face-centered cubic structure, and that adding Mg to Fe has a large impact on the elastic properties. Finally, the effects of disorder due to thermal motion of the atoms have been investigated through ab-initio molecular dynamics simulations. Within the limits of this method and the setup, it is found that the face-centered cubic structure of molybdenum can be dynamically stabilized at high temperature, leading to a metastable structure, on the average. The dynamical stabilization of face-centered cubic molybdenum also rendered it possible to accurately calculate the lattice stability relative to the body-centered cubic phase. Inclusion of temperature effects for the lattice stability using ab-initio molecular dynamics simulations resolves the disagreement between ab-initio calculations and thermochemical methods.

The bulk properties of SiON films grown on n-Si substrates by CVD are examined by means of electrical measurements and Rutherford backscattering spectroscopy (RBS). The main aim of this project was to investigate the performance of the films in order to test their suitability for the construction of CMOS devices with SiON being the gate insulator. The CVD technique was used to produce the films and subsequent metallization leads to the creation of MOS devices. Rutherford backscattering spectroscopy (RBS) was used to verify the film bulk properties. Electrical measurements including current-voltage, capacitance-conductance-voltage (C-G-V) measurements and admittance spectroscopy were performed allowing determination of the bulk trapped charges and the dielectric constant of the films. These charges were calculated to have values between 0.76 nCb and 2.54 nCb, while the dielectric constant of the films was found to be quite high, with values greater than 5 and as high as 34. The RBS concluded that the films were uniform, and the nitrogen concentration was not higher than 10%. Semiconductor Science and Technology

We report results from ab initio cluster-model calculations on the O(1s) binding energy (BE) in the alkaline-earth oxides, MgO, CaO, SrO, and BaO; all these oxides have a cubic lattice structure. We have obtained values for both the initial- and final-state BE's. A simple point-charge model, where an O2-anion is surrounded by point charges, accounts for the observed shift in the O(1s) BE by about 2.5 eV to lower energy going from MgO (largest BE) to BaO (smallest BE). This point-charge model only describes the effect of the Madelung potential at the 1s ionized O2- anion; it does not allow any covalent bonding between the metal (M) cations and the oxygen anions. Once the effect of the O2 --> M2+ covalent bonding is included explicitly by using O(m)M(n) cluster models of the MO crystal, the trend in the O(1s) BE to smaller values for heavier metals does not change significantly. This shows that the main contribution to the shift is not the different amount of covalent mixing in the alkaline-earth oxides but rather the change in the Madelung potential along the group.

Electron and hole trapping in substoichiometric germanium oxides are investigated through the use of hybrid density functionals. We consider disordered model structures generated by Monte-Carlo bond switching and by ab initio molecular dynamics (MD). The Monte-Carlo model consists of fourfold coordinated Ge atoms and of twofold coordinated O atoms, and does not show trap levels neither for electron nor for holes. At variance, the MD model shows threefold coordinated O and Ge atoms forming valence alternation pairs and is found to present trap states for both carriers. The trapping states correspond to the formation and breaking of Ge-Ge bonds. The associated defect levels are determined within a band diagram of the Ge/GeO2 interface. (C) 2011 Elsevier B.V. All rights reserved.

Using hybrid density functional calculations, we investigate possible origins for the large variation of band offsets measured at Ge/GeO2 interfaces. We consider atomistic model interfaces with both amorphous and crystalline oxides, in which the bond density reduction accounts for the mass densities of the two interface components. To the extent that all the Ge atoms are fourfold coordinated and all the O atoms are twofold coordinated, the band offsets are found to remain constant within 0.1 eV. We then investigate the role of valence alternation pairs consisting of negatively charged Ge dangling bonds and positively charged threefold coordinated O atoms, which have been suggested to occur in sizeable concentrations in substoichiometric germanium oxide. A valence alternation pair is introduced in one of the atomistic models and is found to affect the band alignment by contributing to the interface dipole. The calculated band offsets shift by 0.7 eV for an areal concentration of valence alternation pairs corresponding to one pair per 8 Ge interface atoms. These pairs would act as fixed charges and are not expected to directly contribute to the defect density in the germanium band gap. The occurrence of such bonding patterns offers a possible explanation for the large range of valence band offsets measured at this interface. (C) 2011 Elsevier B.V. All rights reserved.

An atomistic model of substoichiometric germanium oxide is generated through ab initio molecular dynamics. The resulting structure shows a predominance of threefold coordinated Ge and O atoms. We also generate substoichiometric models through bond-switching Monte-Carlo simulations, which preserve the fourfold Ge and the twofold O coordinations. These differing structures are energetically competitive. Alignment of their electron densities of states to that of GeO2 reveals that the band-gap reduction is similar for both structures, mainly occurring through a shift of the valence band edge. (C) 2010 Elsevier B.V. All rights reserved.