Stability and Migration of Small Copper Clusters in Amorphous Dielectrics

TL;DR

This study uses density functional theory to analyze the stability and migration of copper ions and clusters in amorphous silica, revealing their energetic favorability and migration energy distribution, relevant for electronic applications.

Contribution

It provides the first comprehensive DFT analysis of copper cluster stability and migration in amorphous silica, accounting for atomic-level variability.

Findings

Copper clusters are energetically favorable over isolated ions.

Formation energy of Cu ions is significantly lower than in crystalline silica.

Migration activation energies vary broadly from 0.4 to 1.1 eV.

Abstract

We use density functional theory (DFT) to study the thermodynamic stability and migration of copper ions and small clusters embedded in amorphous silicon dioxide. We perform the calculations over an ensemble of statistically independent structures to quantify the role of the intrinsic atomic-level variability in the amorphous matrix affect the properties. The predicted formation energy of a Cu ion in the silica matrix is 2.7+/-2.4 eV, significantly lower the value for crystalline SiO2. Interestingly, we find that Cu clusters of any size are energetically favorable as compared to isolated ions; showing that the formation of metallic clusters does not require overcoming a nucleation barrier as is often assumed. We also find a broad distribution of activation energies for Cu migration, from 0.4 to 1.1 eV. This study provides insights into the stability of nanoscale metallic clusters in silica of interest in electrochemical metallization cell memories and optoelectronics.