Experimental Transmission Electron Microscopy Data Research Articles

Atomistic modelling of diamond-type SixGeyCzSn1−x−y−z crystals for realistic transmission electron microscopy image simulations

The realistic simulation of transmission electron microscopy (TEM) images requires an accurate definition of the positions of all atoms, which are linked to the mechanical properties of the material. This paper proposes an optimized atomistic modeling approach to model the lattice parameters and elastic properties of Si, Ge, diamond, alpha-tin, and related diamond alloys, with an approach compatible with systems bigger than 50000 atoms. In order to compute precisely the elastically strained SixGeyCzSn1−x−y−z diamond crystals, a dedicated parameterization of the Keating force field is provided. An original periodic boundary strategy is provided. Our tool is successfully used to interpret experimental TEM data with a reasonable accuracy and precision in a time scale about 10000 times faster than ab initio methods. The method predicts the correct lattice parameters and elastic constants of elementary compounds and alloys with a deviation inferior to 8.1%. We show that subsequent Monte-Carlo simulations predict original self-ordering effects in C in good agreement with the theory. An original approach is used to quantify the short-range and long-range order in comparison with high-resolution cross-sectional TEM experiments: the projected radial distribution function (p-RDF) appears to be a universal and very sensitive analytical tool to quantify the matching between our atomistic model and the experimental HR(S)TEM results. For our reference Si-Ge multilayer with 20 millions of atoms, a maximum broadening of 100 pm is obtained for the third-nearest neighbor (3nn) simulated peak of the p-RDF compared to the experimental one. The same value is obtained from a template matching analysis of the maximum local displacements between the projected experimental atomic positions and the corresponding simulation.

A theoretical study of ELNES spectra of [formula omitted] using Wien2k and Telnes programs

Several aspects of the modelling of the energy loss near edge structure (ELNES) using the Wien2k code and the Telnes program are discussed in this paper. A comparison of spectra calculated by an older Telnes.1 version and a recently released Telnes.2 program was carried out and some differences in the N K-edge ELNES were found. Subsequently, a case study with ground state, partial and full core-hole calculations of wurtzite AlN was performed and the results were compared with experimental transmission electron microscopy data. A good agreement with the experimental observations was obtained for the full core-hole case with a 2×2×1 supercell. Preliminary results on a compositional study of AlxGa1-xN are discussed.

Electron energy loss near edge structure (ELNES) spectra of AlN and AlGaN: A theoretical study using the Wien2k and Telnes programs

Several aspects of the modelling of the energy loss near edge structure (ELNES) using the Wien2k code and the Telnes program are discussed in this paper. A case study with ground state, partial and full core-hole calculations of wurtzite AlN was performed and the results were compared with experimental transmission electron microscopy data. The best agreement with the experimental observations was obtained for the full core-hole case. Changes in the ELNES spectra for various core-hole charges are explained by investigating the site and symmetry projected density of states. Directionally resolved N K-edge ELNES of AlN are discussed and the magic angle β ≈ 2.5 mrad is identified which is in a good agreement with other theoretical predictions. Finally, preliminary results on a compositional study of Al x Ga 1− x N are explored.

Temperature effects on defect production and disordering by displacement cascades in Ni3Al

Abstract Molecular dynamics simulations are used to obtain detailed information on defect production and disordering produced in the primary cascade state of radiation damage in Ni3Al as a function of irradiation temperature Tirr, Although the number of Frenkel pairs decreases with increasing Tirr, the size of interstitial clusters and the interstitial clustering fraction increase with temperature. Temperature has a strong effect in enhancing the production of antisite defects, for the number per cascade increases by about 20% as Tirr increases from 100 K to 600 K, and then by about 90% as it increases further to 900 K. These effects are believed to be due to the increase in the intensity and lifetime of the thermal spike. The average size of disordered zones at different temperatures in the simulations is compared with experimental transmission electron microscopy data and the results are in reasonable agreement. The long range order parameter in the cascade region is found to be consistent with values o...

Md Investigation of Thermal Spike Effects on Defect Production and Disordering by Displacement Cascades in Nl3AL

AbstractMolecular dynamics (MD) simulations are used to obtain detailed information on defect production and disordering produced in the primary cascade state of radiation damage in Ni3AI as a function of irradiation temperature, Tirr Although the number of Frenkel pairs decreases with increasing Tirr, the size of interstitial clusters and the interstitial clustering fraction increase with Tirr. The number of antisites defects per cascade increases by about 20% as Tir increases from 100 to 600K, and then by about 90% from 600 to 900K due to the increase in the intensity and lifetime of the thermal spike. The average size of disordered zones at different Tir, is compared with experimental transmission electron microscopy data and the results are in reasonable agreement. The long-range order parameter in the cascade region is found to be consistent with values obtained experimentally on Ni3A1 irradiated by ions to a similar dose. The chemical short-range order parameter is about 0.6 over the whole range of Tirr, considered, suggesting that the cascade core retains some short-range order at high temperature due to local reordering.

A model of disordered zone formation in Cu3Au under cascade-producing irradiation

Abstract A model to describe the disordering of ordered Cu3Au under irradiation is proposed. For the thermal spike phase of a displacement cascade, the processes of heat evolution and conduction in the cascade region are modelled by solving the thermal conduction equation by a discretization method for a medium that can melt and solidify under appropriate conditions. The model considers disordering to result from cascade core melting, with the final disordered zone corresponding to the largest molten zone achieved. The initial conditions for this treatment are obtained by simulation of cascades by the MARLOWE code. The contrast of disordered zones imaged in a superlattice dark-field reflection and projected on the plane parallel to the surface of a thin foil was calculated. The average size of images from hundreds of cascades created by incident Cu+ ions were calculated for different ion energies and compared with experimental transmission electron microscopy data. The model is in reasonable quantitative ...