Ab-initio thermodynamics of deposition growth: surface terminations of CVD titanium carbide and nitride

TL;DR

This paper introduces a new ab-initio thermodynamic method combining DFT calculations and rate equations to predict surface terminations during CVD growth of titanium carbide and nitride, accounting for non-equilibrium conditions.

Contribution

The paper develops a novel approach integrating ab-initio calculations with thermodynamics and rate equations to predict surface terminations under realistic growth conditions.

Findings

Method accurately predicts surface terminations based on environment and growth rate.

Predictions align with equilibrium thermodynamics in the limit of dynamic equilibrium.

Surface termination control is feasible through environmental parameters.

Abstract

We present a calculational method to predict terminations of growing or as-deposited surfaces as a function of the deposition conditions. Such characterizations are valuable for understanding catalysis and growth phenomena. The method combines ab-initio density functional theory (DFT) calculations and experimental thermodynamical data with a rate-equations description of partial pressures in the reaction chamber. The use of rate equations enables a complete description of a complex gas environment in terms of a few, (experimentally accessible) parameters. The predictions are based on comparisons between free energies of reaction associated with the formation of surfaces with different terminations. The method has an intrinsic non-equilibrium character. In the limit of dynamic equilibrium (with equal chemical potential in the surface and the gas phase) we find that the predictions of the method coincide with those of standard ab-initio based equilibrium thermodynamics. We illustrate the method for chemical vapor deposition (CVD) of TiC(111) and TiN(111), and find that the emerging termination can be controlled both by the environment and the growth rate.