EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Structures of amorphous CNx, SiCN, BCN and SiBCN materials are predicted by extensive ab-initio molecular-dynamics simulations (over 10 000 trajectories) in a wide range of compositions and densities [1,2]. When and only when the structures are allowed to include unbonded N2 molecules, the predicted lowest-energy densities are in agreement with the experiment. The main attention is paid to the N2 formation, with the aim to predict and explain the relationships between Si/B/C ratios and the maximum achievable content of N bonded in stable amorphous networks ([N]network). The results reveal that N2-free networks are characterized by maximum [N]network between 34% (CNx) and 57% (SiNx). Networks formed in parallel to the formation of unbonded N2 molecules (which subsequently either diffuse out or stay trapped in the material) are characterized by maximum [N]network between 42% (CNx) and 57% (SiNx). The measured N contents in SiCN films prepared in our laboratories by reactive magnetron sputtering are in an excellent agreement with the prediction. Further analysis shows that while the N2 formation at a given total N content and in a wide range of Si/B/C ratios is given only by the packing factor, the lowest-energy packing factor depends on these ratios. The presented methodology constitutes a new way how to support the experiment by ab-initio simulations. The results are important for the design of amorphous nitrides for various technological applications, prediction of their stability, design of pathways for their preparation, and identification of what may or may not be achieved in this field.

[1] J. Houska, Acta Mater. 174, 189-194 (2019), 10.1016/j.actamat.2019.05.048

[2] J. Houska, ACS Appl. Mater. Inter. 12, 41666-41673 (2020), 10.1021/acsami.0c08300