Nitrogen overgrowth as a catalytic mechanism during diamond chemical vapour deposition

TL;DR

This study reveals that surface-embedded nitrogen catalyzes diamond layer nucleation during chemical vapour deposition by reducing energy barriers and facilitating new layer formation, providing a detailed atomistic mechanism.

Contribution

The paper introduces a density functional theory model showing how surface nitrogen enhances diamond growth by lowering energy barriers for C insertion and enabling nitrogen defect formation.

Findings

Nitrogen reduces energy barriers for C insertion into surface dimers.

The presence of nitrogen increases the rate of key surface reactions 400-fold.

Surface nitrogen facilitates the formation of substitutional nitrogen defects.

Abstract

Nitrogen is frequently included in chemical vapour deposition feed gases to accelerate diamond growth. While there is no consensus for an atomistic mechanism of this effect, existing studies have largely focused on the role of sub-surface nitrogen and nitrogen-based adsorbates. In this work, we demonstrate the catalytic effect of surface-embedded nitrogen in nucleating new layers of (100) diamond. To do so we develop a model of nitrogen overgrowth using density functional theory. Nucleation of new layers occurs through C insertion into a C--C surface dimer. However, we find that C insertion into a C--N dimer has substantially reduced energy requirements. In particular, the rate of the key dimer ring-opening and closing mechanism is increased 400-fold in the presence of nitrogen. Full incorporation of the substitutional nitrogen defect is then facilitated through charge transfer of an electron from the nitrogen lone pair to charge acceptors on the surface. This work provides a compelling mechanism for the role of surface-embedded nitrogen in enhancing (100) diamond growth through the nucleation of new layers. Furthermore, it demonstrates a pathway for substitutional nitrogen formation during chemical vapour deposition which can be extended to study the creation of technologically relevant nitrogen-based defects.