Y. Ferro

Adsorption of beryllium atoms and clusters both on graphene and in a bilayer of graphite investigated by DFT

We herein investigate the interaction of beryllium with a graphene sheet and in a bilayer of graphite by means of periodic DFT calculations. In all cases, we find the beryllium atoms to be more weakly bonded on graphene than in the bilayer. Be(2) forms both magnetic and non-magnetic structures on graphene depending on the geometrical configuration of adsorption. We find that the stability of the Be/bilayer system increases with the size of the beryllium clusters inserted into the bilayer of graphite. We also find a charge transfer from beryllium to the graphite layers. All these results are analysed in terms of electronic structure.

Study of hydrogen isotopes behavior in tungsten by a multi trapping macroscopic rate equation model

Density functional theory (DFT) studies show that in tungsten a mono vacancy can contain up to six hydrogen isotopes (HIs) at 300 K with detrapping energies varying with the number of HIs in the vacancy. Using these predictions, a multi trapping rate equation model has been built and used to model thermal desorption spectrometry (TDS) experiments performed on single crystal tungsten after deuterium ions implantation. Detrapping energies obtained from the model to adjust temperature of TDS spectrum observed experimentally are in good agreement with DFT values within a deviation below 10%. The desorption spectrum as well as the diffusion of deuterium in the bulk are rationalized in light of the model results.

Hydrogen retention in beryllium: concentration effect and nanocrystalline growth

We herein report on the formation of BeD2 nanocrystalline domes on the surface of a beryllium sample exposed to energetic deuterium ions. A polycrystalline beryllium sample was exposed to D ions at 2 keV/atom leading to laterally averaged deuterium areal densities up to 3.5 10(17) D cm(-2), and studied using nuclear reaction analysis, Raman microscopy, atomic force microscopy, optical microscopy and quantum calculations. Incorporating D in beryllium generates a tensile stress that reaches a plateau at  ≈1.5 10(17) D cm(-2). For values higher than 2.0 10(17) cm(-2), we observed the growth of  ≈90 nm high dendrites, covering up to 10% of the surface in some zones of the sample when the deuterium concentration was 3  ×  10(17) D cm(-2). These dendrites are composed of crystalline BeD2, as evidenced by Raman microscopy and quantum calculations. They are candidates to explain low temperature thermal desorption spectroscopy peaks observed when bombarding Be samples with D ions with fluencies higher than 1.2 10(17) D cm(-2).

The interaction of beryllium with benzene and graphene: a comparative investigation based on DFT, MP2, CCSD(T), CAS-SCF and CAS-PT2.

The interaction of beryllium with benzene, graphene and graphitic compounds involves multi-reference electronic states, Jahn-Teller distortion, charge transfer and van der Waals interactions. This is investigated herein using periodic and molecular models at different levels of theory: (i) the second-order Møller-Plesset (MP2) perturbation theory, (ii) the coupled cluster method with inclusion of single double and perturbative triple excitations (CCSD(T)), (iii) the complete active space self-consistent field (CAS-SCF) and (iv) the complete active space with perturbation theory truncated at the 2nd order (CAS-PT2). Molecular and periodic Density Functional Theory (DFT) methods are also used. The two major failures of DFT are addressed with regard to the beryllium benzene and graphene interaction: the degeneracy problem is the source of no specific problem while the delocalization error causes DFT with the Perdew Burke, Ernzerhof functional plus the Grimme correction (DFT/PBE-D2) to be over-binding by about 0.4 eV at a short-range. The agreement between DFT/PBE-D2 and wave-function based methods is nevertheless good; DFT/PBE-D2 provides an accurate description of the electronic structure of the system. By the end of this work, we shall get a better insight into the mechanisms leading beryllium to physisorb on graphene and to chemisorb into the bilayer of graphite.

Hydrogen retention and diffusion in?tungsten beryllide

Beryllide compounds are often used in various domains because they are more resilient to oxidation than pure beryllium and at the same time they keep some of the properties of this metal. Nevertheless, the data about their properties during atomic hydrogen exposure are very scarce: numerous experiments have been conducted in the past few years on solid hydride deposition under beryllium-seeded plasma action or on energetic hydrogen implantation into metallic beryllium; many others have been devoted to hydrogen retention and diffusion in tungsten. There have been fewer studies about hydrogen interaction with the alloys of these metals, although the beryllium-tungsten mixed compounds have been experimentally detected in laboratory experiments. This article reports on calculations carried out using first-principles density functional theory (DFT) on tungsten beryllide crystal (Be12W) taken as a model alloy. The formation and reactivity of atomic vacancies are investigated in the domain of temperature ranging from 0 to 500 K, together with atomic hydrogen retention and diffusivity in the bulk and in/out vacancies.

Ion energy distributions measured inside a high-voltage cathode in a BF3 pulsed dc plasma used for plasma doping: experiments and ab initio calculations

The purpose of this paper is the characterization of a plasma-doping system in BF3. Energy distributions (IEDs) of boron ions crossing a high-voltage sheath (up to 1 kV) are measured in a BF3 plasma under different experimental conditions. It is demonstrated that relative percentages of boron ions reaching the cathode and IED shapes are governed by the number of collisions inside the sheath. Heavy molecular ions , are dissociated inside the sheath and light boron ions (B+, BF+) are created. Based on experimental results and ab initio calculations of boron ion structures, the mechanisms occurring in the sheath are discussed. Furthermore, the charge exchange cross-section between and BF3 is estimated to be 8.8 × 10−19 m2.