Theoretical Investigations of the Reactions of N- and O-Containing Species on a C(100):H 2 × 1 Reconstructed Diamond Surface

Mark W Kelly,Jason D Pattle,Jeremy N Harvey,Sarah C Halliwell,Michael N R Ashfold,W Jeff Rodgers

doi:10.1021/acs.jpca.7b00466

Mark W Kelly, Jason D Pattle + Show 4 more

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https://doi.org/10.1021/acs.jpca.7b00466

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Abstract

Quantum mechanical and hybrid quantum mechanical/molecular mechanical cluster models were used to investigate possible reaction mechanisms whereby gas-phase NHx (x = 0-2), CNHx (x = 0, 1), and OH radicals can add to, and incorporate in, a C-C dimer bond on the C(100):H 2 × 1 diamond surface during chemical vapor deposition (CVD) from microwave-activated C/H containing gas mixtures containing trace amounts of added N or O. Three N incorporation routes are identified, initiated by N, NH, and CN(H) addition to a surface radical site, whereas only OH addition was considered as the precursor to O incorporation. Each is shown to proceed via a ring-opening/ring-closing reaction mechanism analogous to that identified previously for the case of CH3 addition (and CH2 incorporation) in diamond growth from a pure C/H plasma. On the basis of the relative abundances of N atoms and NH radicals close to the growing diamond surface, the former is identified as the more probable carrier of the N atoms appearing in CVD grown diamond, but fast H-shifting reactions postaddition encourage the view that NH is the more probable migrating and incorporating species. CN radical addition is deemed less probable but remains an intriguing prospect, since, if the ring-closed structure is reached, this mechanism has the effect of adding two heavy atoms, with the N atom sitting above the current growth layer and thus offering a potential nucleation site for next-layer growth.

Highlights

Modeling has played a key role in determining the feasibility and mechanisms of reactions whereby reactive gas-phase species incorporate into a growing diamond film during chemical vapor deposition (CVD).[1−14] Typical gas mixtures for growing high-quality diamond films contain 1−5% CH4 in H2, and the methyl (CH3) radical is generally considered to be the main species responsible for diamond growth from activated C/H gas mixtures
Analogous reaction sequences have been demonstrated for the case of B atom and/or BH radical addition to the surface of CVD diamond grown from C/H gas mixtures containing trace quantities of B2H6.16,17
The various elementary reaction sequences explored in this work with both quantum mechanical (QM) and QM/MM methods are reported in turn

Summary

Introduction

Modeling has played a key role in determining the feasibility and mechanisms of reactions whereby reactive gas-phase species incorporate into a growing diamond film during chemical vapor deposition (CVD).[1−14] Typical gas mixtures for growing high-quality diamond films contain 1−5% CH4 in H2, and the methyl (CH3) radical is generally considered to be the main species responsible for diamond growth from activated C/H gas mixtures. Resolved laser absorption studies of the diamond-growing plasma along with complementary plasma modeling confirm CH3 as the most abundant carbon containing radical species immediately above the growing diamond surface,[15] and theoretical studies have identified energetically favorable reaction sequences whereby a CH3 species can bind to a surface radical site, incorporate into the surface as a CH2 group and, if necessary, migrate to a step edge.[12] Analogous reaction sequences have been demonstrated for the case of B atom and/or BH radical addition to the surface of CVD diamond grown from C/H gas mixtures containing trace quantities of B2H6.16,17. Most recent interest in CVD growth from C/N/H gas mixtures on (111)-

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