Multi-technique Approach to Unravel the (Dis)order in Amorphous Materials

Abstract

The concept of order in disordered materials is the key to controlling the mechanical, electrical, and chemical properties of amorphous compounds widely exploited in industrial applications and daily life. Rather, it is far from being understood. Here, we propose a multi-technique numerical approach to study the order/disorder of amorphous materials on both the short- and the medium-range scale. We combine the analysis of the disorder level based on chemical and physical features with their geometrical and topological properties, defining a previously unexplored interplay between the different techniques and the different order scales. We applied this scheme to amorphous GeSe and GeSeTe chalcogenides, showing a modulation of the internal disorder as a function of the stoichiometry and composition: Se-rich systems are less ordered than Ge-rich systems at the short- and medium-range length scales. The present approach can be easily applied to more complex systems containing three or more atom types without any a priori knowledge about the system chemical–physical features, giving a deep insight into the understanding of complex systems.

Atomic-Layer-Deposited Aluminum Oxide Thin Films Probed with X-ray Scattering and Compared to Molecular Dynamics and Density Functional Theory Models

“…Simulated atomic configurations can be used to characterize bonding environments with greater detail than can be obtained from experiments. − The average coordination number of O atoms around Al as a function of the cutoff distance R c (Figure a) and the average coordination numbers (averaged over time and all Al atoms in the system, Table ) match well with previous studies, which used coordination cutoffs ( R c ) between 2.2 ( C N ̅ A l = 4.24) and 2.5 Å ( C N ̅ A l = 4.41). Examining coordination statistics for both of these cutoff distances shows that the coordination is dominated by fourfold-coordinated Al and threefold-coordinated O.…”

Persistent homology: A tool to understand medium-range order glass structure

“…These are connecting the ionic metal nodes, meaning that rings typically consist of more than two atomic types. Finally, dimension 1 PH has been used to discriminate the degree of disorder at the MRO scale in simulated chalcogenide glasses, involving the concept of "persistent entropy", which quantifies how "lattice-like" the obtained persistence diagram is [46]. Interestingly, in the same study, birth and death times are found to correlate well with the first and second coordination shell distances (from the RDF), respectively.…”

Device‐to‐Materials Pathway for Electron Traps Detection in Amorphous GeSe‐Based Selectors

“…Gray polyhedrons indicate ordered threefold and fourfold local‐order structures centered on Ge atoms, that are among the most frequent local arrangements found in these systems. [ 33 ] From the analysis of the spatial distribution of the in‐gap states, we draw a few important observations: i) at odd with the usual crystalline case, the localized states of these amorphous structures are not localized around the single atomic site (e.g., the point defect), but involve a few bonds. ii) The defect states often appear at interconnections among a few threefold and fourfold polyhedrons, indicating a key role of Ge coordination on the formation of trap states, in agreement with previous theory reports.…”

“…[ 28 ] The complete description of the adopted model and the analysis of the classical MD results were reported elsewhere. [ 32,33 ]…”

“…This approach allows the system to rearrange at the local-and medium-order structures avoiding unphysical "frozen-liquid" structures, and it has been demonstrated to generate a realistic model for the amorphous GeSe compound. [32,33] The increase of Ge content from 50% to 60% in Ge x Se 100−x causes a systematic change of the average coordination number of Ge and Se species that moves from 3:3 (as www.advelectronicmat.de in the crystal) to a phase where Ge has a mixed fourfold (as in Ge-bulk) and threefold coordination. The different short-range structures and their spatial arrangement in the medium range are expected to have a critical role in the formation/appearance of the electrical trap states (see below).…”