Evolutionary optimization of a charge transfer ionic potential model for Ta/Ta-oxide hetero-interfaces

摘要

Tantalum, tantalum oxide and their hetero-interfaces are of tremendoustechnological interest in several applications spanning electronics, thermalmanagement, catalysis and biochemistry. For example, local oxygen stoichiometryvariation in TaOx memristors comprising of metallic (Ta) and insulating oxide(Ta2O5) have been shown to result in fast switching on the sub-nanosecondtimescale over a billion cycles, relevant to neuromorphic computation. Despiteits broad importance, an atomistic scale understanding of oxygen stoichiometryvariation across Ta/TaOx hetero-interfaces, such as during early stages ofoxidation and oxide growth, is not well understood. This is mainly due to thelack of a variable charge interatomic potential model for tantalum oxides thatcan accurately describe the ionic interactions in the metallic (Ta) and oxide(TaOx) environment as well as at their interfaces. To address this challenge,we introduce a charge transfer ionic potential (CTIP) model for Ta/Ta-oxidesystem by training against lattice parameters, cohesive energies, equations ofstate, and elastic properties of various experimentally observed Ta2O5polymorphs. The best set of CTIP parameters are determined by employing asingle-objective global optimization scheme driven by genetic algorithmsfollowed by local Simplex optimization. Our newly developed CTIP potentialaccurately predicts structure, thermodynamics, energetic ordering ofpolymorphs, as well as elastic and surface properties of both Ta and Ta2O5, inexcellent agreement with DFT calculations and experiments. We employ our newlyparameterized CTIP potential to investigate the early stages of oxidation of Taat different temperatures and atomic/molecular nature of the oxidizing species.