Theoretical investigation of carbon defects and diffusion in α-quartz

Abstract

The geometries, formation energies, and diffusion barriers of carbon point defects in silica (␣-quartz͒ have been calculated using a charge-self-consistent density-functional based nonorthogonal tight-binding method. It is found that bonded interstitial carbon configurations have significantly lower formation energies ͑on the order of 5 eV͒ than substitutionals. The activation energy of atomic C diffusion via trapping and detrapping in interstitial positions is about 2.7 eV. Extraction of a CO molecule requires an activation energy Ͻ3.1 eV but the CO molecule can diffuse with an activation energy Ͻ0.4 eV. Retrapping in oxygen vacancies is hindered-unlike for O 2 -by a barrier of about 2 eV.

Thermal decomposition mechanisms of hafnium and zirconium silicates at the atomic scale

“…DFT is now well established as an accurate and efficient parameter-free way to compute the properties of crystalline materials, similar computations having been validated on zircon 20,25 and silicates of Mg. 26 By calculating the most stable forms of the MSO component oxides ͑␣-quartz SiO 2 and monoclinic MO 2 -as well as other silica polymorphs and the tetragonal and cubic MO 2 phases͒, we confirm structures and energetics agreeing to Ͻ2% with other theoretical [27][28][29][30][31] and experimental 32 work-well within the accuracy expected from DFT.…”

Defects inSiO2as the possible origin of near interface traps in theSiC∕SiO2system: A systematic theoretical study

“…49 ͑Slater-Koster files tested previously in Ref. 30 were applied.͒ The configurations of lowest energy were then relaxed with ab initio DFT in the SIESTA code. The maximum forces calculated by the hybrid functional are about twice as large as obtained by the LDA calculations.…”

“…An investigation of interstitial carbon and CO molecules has shown 30 that both are mobile ͑with activation energies below 2.7 and 0.4 eV, respectively͒. It was also shown 31 that on occasional encounter of CO molecules, oxygen deficient carbon clusters ͑up to four atoms͒ can be formed.…”

Theoretical study of the mechanism of dry oxidation of4H-SiC

“…For the energies of the CO and O 2 molecules, the energies of the free molecules were chosen, since they can diffuse fast through SiO 2 . 30,31 In addition to the interface model described above, a 243-atom 3 ϫ 3 ϫ 3 supercell of ␣-quartz ͑in the ⌫-point approximation͒ was used to model defects in the oxide layer, further away from the interface, for the purpose of calculating the energies of reactions leading to C or Si emission into the oxide or for correction purposes ͑cf. Sec.…”

“…A set of Slater-Koster files, tested for the Si-O-C system, 30 was employed. The geometry optimizations were performed using a conjugate gradient ͑CG͒ algorithm, until the interatomic forces fell below 10 −4 a.u.͑ϳ0.016 eV/ Å͒.…”