Oxygen-induced atomic desorptions in oxynitrides: Density functional calculations

Abstract

The role of atomic oxygen, O 2 , and NO molecules in the nitrogen and oxygen removal processes observed during the thermal growth of oxynitride ͑SiO x N y ͒ films is addressed by spin density functional calculations. Our results show that the energetically most favorable N-desorption mechanism would be induced by O 2 reacting with the Si-͓NO͔-Si structure in SiO 2 , where nitrogen is released from the network as an interstitial NO molecule, leaving a peroxy linkage ͑Si-O-O-Si͒ in its place. Atomic O diffusing via peroxy linkage also removes nitrogen from the Si-͓NO͔-Si structure. However, this reaction has an occurrence rate of about 10 4 times smaller that the most favorable one. We also identify an oxygen exchange mechanism occurring through the annihilation of two peroxyl O atoms when they approach each other, where oxygen is released from the network as an O 2 molecule leaving a perfect SiO 2 structure. The energetics of other possible scenarios for atomic desorptions in SiO x N y are also discussed.

How Does Thermal Poling Produce Interstitial Molecular Oxygen in Silicate Glasses?

“…The sequence of the conversations, reaction , describes the diffusion of the peroxide bridge through the matrix and is a prerequisite for reaction to occur. In accordance with existing estimates, the barrier of atomic oxygen (or peroxide bridge) diffusion in reaction is equal to 1.3 eV (first-principles molecular dynamic calculation and α-quartz supercell model) or 1.9 eV (the density functional theory calculations).…”

“…The authors of ref relate this difference to the account of singlet–triplet character of the diffusion in their model: the fundamental state of the peroxide bridge is the singlet one, while the fundamental state of the oxygen atom is the triplet. It was shown that reaction is exothermic with the barrier of ∼1.6 eV. Reaction was not discussed in literature.…”

High-Temperature Oxidation of SiC-Based Composite: Rate Constant Calculation from ReaxFF MD Simulations, Part II

“…15,[47][48][49][50]53 In our simulations, the fluid oxidizer molecules actually chemisorb onto the numerous dangling bonds exposed on the entire surface due to the many defects present, 46,52 similar to the O atom lattice incorporation found in DFT studies. 48,50,51,54,55 Since this initial penetration process is exactly how the bulk SiO 2 transport mechanism proceeds, it can be posited that the surface chemisorption can be treated as a part of the bulk SiO 2 transport, and hence the surface barrier is effectively set to zero.…”

“…15,47 In the simulations the O atoms already incorporated into the lattice directly proceeded into the SiC slab region by breaking a number of Si−O bonds and displacing C atoms further downstream. 49,55,56 It is questionable to model this step as a standalone first-order reaction when it should be interpreted as the final hopping step in the SiO 2 slab. Hence, this third resistance can be incorporated into the bulk SiO 2 transport and also effectively set to zero; i.e., the O atoms rapidly react with the Si−C bonds.…”

“…Hence, this third resistance can be incorporated into the bulk SiO 2 transport and also effectively set to zero; i.e., the O atoms rapidly react with the Si−C bonds. 55,56 It should be noted that these assumptions are made for this particular system. For other SiO 2 slab structures with porous structures and a more passivated and thicker slab, the above assumptions could be relaxed and other transport/reaction parameters possibly included.…”