Structure and Bonding in Amorphous Cr1-xCx Nanocomposite Thin Films: X-ray Absorption Spectra and First-Principles Calculation

TL;DR

This study combines X-ray absorption spectroscopy and first-principles calculations to analyze the local structure and bonding in amorphous Cr-C nanocomposite thin films, revealing insights into their complex atomic arrangements.

Contribution

It introduces the use of stochastic quenching and ab initio theory to accurately model and interpret the local structure of amorphous Cr-C materials, advancing understanding of their bonding.

Findings

Coordination in amorphous carbide resembles Cr7C3 structure at high carbon content

Excess carbon forms amorphous carbon phase

Ab initio modeling improves spectral fitting and structural insights

Abstract

The local structure and chemical bonding in two-phase amorphous Cr$_{1-x}$C$_{x}$ nanocomposite thin films are investigated by Cr $K$-edge ($1s$) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies in comparison to theory. By utilizing the computationally efficient \textit{stochastic quenching} (SQ) technique, we reveal the complexity of different Cr-sites in the transition metal carbides, highlighting the need for large scale averaging to obtain theoretical XANES and EXAFS spectra for comparison with measurements. As shown in this work, it is advantageous to use \textit{ab initio} theory as an assessment to correctly model and fit experimental spectra and investigate the trends of bond lengths and coordination numbers in complex amorphous materials. With sufficient total carbon content ($\geq$ 30 at\%), we find that the short-range coordination in the amorphous carbide phase exhibit similarities to that of a Cr$_{7}$C$_{3\pm{}y}$ structure, while excessive carbons assemble in the amorphous carbon phase.