Search

Abstract: Variations in the local crystallographic orientation due to the presence of geometrically necessary dislocations and dislocation boundaries smear the distribution of intensity near Laue reflections. Here, some simple model distributions of geometrically necessary dislocations, GNDs, are used to estimate the dislocation tensor field from the intensity distribution of Laue peaks. Streaking of the Laue spots is found to be quantitatively and qualitatively distinct depending on the ratio between the absorption coefficient and the GND density gradient. In addition, different slip systems cause distinctly different Laue-pattern streaking. Experimental Laue patterns are therefore sensitive to stored dislocations and GNDs. As an example, white beam microdiffraction was applied to characterize the dislocation arrangement in a deformed polycrystalline Ni grain during in situ uniaxial tension. [Copyright &y& Elsevier]

Electromigration-induced failure in metal interconnect constitutes a major reliability problem in the semiconductor industry. Recently, experimental techniques capable of probing grain orientation and stress with a spatial resolution compatible with the dimensions of the lines have emerged. White beam X-ray microdiffraction is particularly well suited to the in situ study of electromigration. The technique was used to probe microstructure in interconnects and recently unambiguously unveiled the plastic nature of the deformation induced by mass transport during electromigration in Al(Cu) interconnect lines even before macroscopic damage. The aim of the present research is to understand the complex dislocation structure arising from electromigration-induced plastic deformation by simulating the shape of the reflections and comparing them with the shape observed in the experimental data. We provide a first quantitative analysis of the dislocation structure generated in individual micron-sized Al grains during an in situ electromigration experiment. Custom software allows us to determine the orientation of the predominant dislocation network in each sample subgrain. [Copyright &y& Elsevier]

Abstract: This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence (μ-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation of complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent. [Copyright &y& Elsevier]

Abstract: We compare experimental measurements of inhomogeneous plastic deformation in a Ni bicrystal with crystal plasticity simulations. Polychromatic X-ray microdiffraction, orientation imaging microscopy and scanning electron microscopy, were used to characterize the geometrically necessary dislocation distribution of the bicrystal after uniaxial tensile deformation. Changes in the local crystallographic orientations within the sample reflect its plastic response during the tensile test. Elastic strain in both grains increases near the grain boundary. Finite element simulations were used to understand the influence of initial grain orientation and structural inhomogeneities on the geometrically necessary dislocations arrangement and distribution and to understand the underlying materials physics. [Copyright &y& Elsevier]