Nanoscale organization by elastic interactions between H and He platelets in Si
Résumé
We used ion implantation of H and He in Si and thermal treatments to produce two systems allowing to study the effects of global and local mechanical stress fields on the formation energy of H-precipitates called H-platelets. In the first part of the work, the depth-distribution of different crystallographic orientations of the precipitates formed along the implanted layer was characterized by transmission electron microscopy. The global strain in the region was measured by X-ray diffraction, and the depth distribution of strain was reconstructed using a dynamical-theory-based code. Elasticity theory was used to develop a model based on mechanical interactions, explaining the preferential presence of (001)-oriented precipitates in the more stressed region of the implanted layer. In a second part, local sources of stress of nanometer size and cylindrical symmetry were introduced in a deeper region of the matrix, before the nucleation of H-platelets. The local stresses were embodied by (001) He-plate precipitates. Upon annealing, a specific arrangement of crystallographic variants of {111}-oriented H-platelets in a four-fold configuration was observed. To explain these experimental observations, and to calculate the variations of the formation energy of the precipitates under the presence of local stress tensors components, analytical and numerical (finite element method) approaches were used to develop 2D and 3D models based on elasticity theory. The concepts and modeling strategy developed here paves the way for determining the required conditions to create controlled architecture of precipitates at the nanoscale using local stress engineering.
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