Investigating Local Structure of Ion-Implanted (Ni²⁺) and Thermally Annealed Rock Salt CoO Film by EXAFS Simulation Using Evolutionary Algorithm

Abstract

The CoO film deposited on the surface of F-doped SnO2 (FTO) conductive glass was prepared via drop casting technique. The effects of Ni2+-ion implantation at 700 keV energy and postannealing in vacuum at 450 °C temperature on the local structure of the CoO film was systematically explored. The XAFS study revealed the substitution of octahedral Co2+ by Ni2+ ion (Co1–x Ni x O) as a result of ion implantation. The existence of defects in local structure around the octahedral Co for the Co1–x Ni x O film after thermal annealing in vacuum was demonstrated by the theoretical EXAFS [χ­(k)] simulation via evolutionary algorithm implemented in reverse Monte Carlo method in rationale with EXAFS fitting. Nevertheless, the cubic rock salt structure for the Co1–x Ni x O was conserved, corroborated through XRD patterns, suggesting a remarkable candidate for application as an electrocatalyst in fuel cells.

Strategy to Probe the Local Atomic Structure of Luminescent Rare Earth Complexes by X-ray Absorption Near-Edge Spectroscopy Simulation Using a Machine Learning-Based PyFitIt Approach

“…Generally, theoretical EXAFS χ( k ) can be described as χ( k ) = ∑ i χ i ( k ), where summation includes single-scattering and multiple-scattering path contributions. For single-scattering path i , the familiar EXAFS equation can be presented as χ i ( k ) = ( false( N i S 0 2 false) F i false( k false) k R i 2 sin false( 2 k R i + normalΦ i ( k ) false) exp false( prefix− 2 σ i 2 k 2 false) exp true( prefix− 2 R i λ ( k ) true) ) where S 0 2 is the passive electrons’ amplitude reduction factor, N i is the number of backscattering neighbor atoms, R i is the average distance between the central photoabsorber and the backscatterers, F i ( k ) is the effective scattering amplitude, σ i 2 is the correlated Debye–Waller factor, measuring the mean-square relative displacement (MSRD) along the equilibrium path length, Φ i ( k ) is the effective total phase shift, including contributions from the central atom and all scattering atoms, and λ is the mean free path of the photoelectron.…”

A morphology-dependent lattice stability investigation in ZnS nanostructures by high-pressure XAFS studies

“…The fitting package (IFEFFIT) employs both the real and imaginary parts of the Fourier transformed w(k) to minimize the difference between the experimental data and the theoretical EXAFS. 52,53 Accordingly, we used three known crystalline phases of ZnS that exist at different pressures: wurtzite, zinc blende, and rock salt, as the theoretical models. Backscattering amplitudes and phases were calculated using the FEFF6 code for wurtzite, zinc blende, and rock salt ZnS of the local structure around the zinc atom.…”

Synthesis and Characterization of a Carbon‐Supported Cobalt Nitride Nano‐Catalyst

“…The continuous Cauchy wavelet transform (CCWT) analysis was applied to the k 2 ‐weighted EXAFS data of Co 4 N, in order to more clearly detect as colored two‐dimensional images the local coordination environment around Co in Co 4 N, using a high programing language MATLAB R2020a based code, developed by Muñoz and coworkers in 2003 [53] . CCWT modulus is clearly visualized the various coordination shells of the neighboring atoms around the photoabsorber in form of different RGB colored maps in the 2D CCWT image, [54] concurrently analyzing the EXAFS data of the material into respective two‐dimensional k and R spaces. Thus, the CCWT 2D‐image of Co 4 N thin film (Figure 9d) demonstrated the distinct yellowish green colored map associated with the N back‐scatterer in first coordination shell and dark red colored map corresponded to the Co atoms in second coordination shell, by decomposing the EXAFS signal of Co 4 N in related k‐and R‐spaces.…”