Satyesh Kumar Yadav

Heterostructure interfaces play a major role in defining the performance of thin-film devices. High-k dielectric oxide-semiconductor heterostructures are being extensively investigated as promising candidates for future integrated circuits, thus it becomes important to precisely probe the interfaces at the atomic scale for technological advancements. In this work, a high-k dielectric oxide (Gd2O3)-semiconductor (Ge) interface was characterized at the atomic scale using complex-valued exit wave reconstructed from a set of focal series high-resolution transmission electron microscopy (HRTEM) images acquired without objective lens spherical aberration correction. The complexity of this characterization lies in removing image artefacts produced by amorphous layer deposited on the imaged region during ion milling which was successfully solved using an algorithm to remove amorphous background developed recently. The final result reveals that the interface of the present study is atomically sharp and flat. The thickness of the imaged region along viewing direction was estimated from channelling map. Comparing reconstructed amplitude of experimental data with that of simulated one generated using Density Functional Theory (DFT) optimized interface structure, it was found that the Gd2O3 layers were terminated at the Gd atoms in the interface.

Using first-principles density functional theory (DFT), we separate the distortion energy (DE) on Fe due to the introduction of solute atoms like B, C, N, and O at different sites from the electronic binding energy (EBE) of a solute atom with Fe. Contrary to the belief that distortion energy alone dictates the preference of solute atoms for a site in bulk, we show that EBE dictates the preference of the O for the octahedral site in Fe, with DE being the highest at the site. The site preference for C and N in bulk Fe is dictated by both DE and EBE. However, DE alone dictates site preference for B. The DE of solute atoms cannot be predicted by calculated radius, which is highest for B and lowest for O. We find that O and B have similar distortion energy due to large charge transfer to the O atom from Fe.