Jean-Michel Beuken

First-principles computation of material properties: the ABINIT software project

The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a DFT software project can benefit enormously from widespread collaboration, if handled properly. Also, modern software engineering concepts can considerably ease its development. The ABINIT project relies upon these ideas: freedom of sources, reliability, portability, and self-documentation are emphasised, in the development of a sophisticated plane-wave pseudopotential code. We describe ABINITv3.0, distributed under the GNU General Public License. The list of ABINITv3.0 capabilities is presented, as well as the different software techniques that have been used until now: PERL scripts and CPP directives treat a unique set of FORTRAN90 source files to generate sequential (or parallel) object code for many different platforms; more than 200 automated tests secure existing capabilities; strict coding rules are followed; the documentation is extensive, including online help files, tutorials, and HTML-formatted sources

A brief introduction to the ABINIT software package

Abstract A brief introduction to the ABINIT software package is given. Available under a free software license, it allows to compute directly a large set of properties useful for solid state studies, including structural and elastic properties, prediction of phase (meta)stability or instability, specific heat and free energy, spectroscopic and vibrational properties. These are described, and corresponding applications are presented. The emphasis is also laid on its ease of use and extensive documentation, allowing newcomers to quickly step in.

Perpendicular giant magnetoresistance of NiFe/Cu multilayered nanowires

We have prepared by electrodeposition Ni80Fe20/Cu multilayered nanowires into the pores of polymer membranes and performed giant magnetoresistance (GMR) measurements in the current perpendicular to the layer planes geometry. GMR ratios as high as 80% have been obtained at 4.2 K. Two types of structure have been studied: conventional Ni80Fe20/Cu multilayers and multilayers composed of Ni80Fe20/Cu/Ni80Fe20 trilayers magnetically isolated by long Cu rods

Perpendicular giant magnetoresistance of NiFe/Cu and Co/Cu multilayered nanowires

We report a comparative study of the giant magnetoresistance (GMR) in CPP (current perpendicular to the planes) geometry in two different types of multilayered nanowire systems: Co/Cu and Ni80Fe20/Cu. The nanowires were produced in the cylindrical pores of a polymer membrane using a pulsed electrodeposition technique. A GMR ratio as large as 78% was obtained for Ni80Fe20/Cu multilayered nanowires. Using the results of the Valet-Fert model for perpendicular transport we deduce the bulk and interface spin asymmetry coefficients and comparison is made between the two systems.

Perpendicular magnetoresistance in Co/Cu multilayered nanowires

We have carried out magnetoresistance measurements in the CPP (current perpendicular to the planes) geometry of electrodeposited Co/Cu multilayered nanowires with Cu and Co layer thicknesses varying over wide ranges. The data are compared with the results of the Valet-Fert model for perpendicular transport. The observed behaviour agrees with the corresponding predictions in various limits of the layers thicknesses. The interface and bulk spin-dependent scattering parameters as well as the spin diffusion lengths in the nonmagnetic and ferromagnetic layers are extracted from this analysis.

A Surface-composition Study of Sulfided Cobalt Molybdenum Catalysts By Low-energy Ion-scattering Spectrometry (iss)

Low energy ion scattering was used to analyse the surface composition of sulfided cobalt-molybdenum catalysts supported on γ-alumina powders (CoMoS/γ-Al2O3). A method is proposed for the correct interpretation of the ISS spectra of this complex system. It is based on a curve synthesis procedure using the spectra obtained on pure phase materials (MoS2, Co9S8 and γ-Al2O3). The results confirm a model of sintering of the MoS2 dispersed phase occuring when the samples are activated at a high reduction-sulfidation temperature.

Modification of polymer (PET) surface reactivity by low energy ion bombardment

The surface of polyethylene terephthalate (PET) was studied by low energy He/sup +/ ion scattering (ISS). Modifications of the surface composition induced by the He/sup +/ and Ar/sup +/ bombardments are observed. The ion bombardment causes surface damages with bond breaking and it results a highly activated surface for the chemisorption of nitrogen from the residual gas phase. Similar effects were observed on highly oriented pyrolytic graphite when analyzed in the same beam conditions.

Simulation of the trajectory-dependent neutralisation probability of low-energy He+ scattered from NaCl

A simple model of local neutralisation is proposed to simulate the variation of the intensity of He+ ions scattered from the (001) surface of NaCl as a function of the polar and azimuthal angles. For the neutralisation on Cl, it is necessary to introduce a transition rate with two contributions for long and close distance of separation which reflects the electronic density. The results are in good agreement with the experimental results of Souda et al..

Low energy He, Ne and Ar ion scattering from metal surfaces: Background and inelastic effects

Abstract The 139° ion scattering spectra of He, Ne and Ar ions incident on polycrystalline W, Ta and Au are measured for incident energies ranging from 0.8 keV to 4 keV. The He+ and Ar+ scattering behaviour from W is found to be very similar to that from Ta and different from that from Au. The single collision peak is shifted of about 20 eV to lower energy when calibrated with the Au single collision peak and for He+ scattering an important background contribution increasing with the incident energy is observed. These results cannot be explained by structure effects in the first atomic planes is revealed by simulation. They relate rather to differences in the charged fraction of ions scattered from inside the solid. This is interpreted on the basis of reionization at metal surfaces having a high density of electronic states above the Fermi level.

Computer-simulation of Low-energy He+ Scattering From Au and W

Abstract He + scattering from gold and tungsten is simulated by the MARLOWE code for incident energies ranging from 1 to 4 keV, and compared to experimental results. A good agreement is obtained when introducing a local neutralization model together with a reionization mechanism based on the electron promotion model.