Based on first principles quantum mechanics (DFT/GGA with pseudopotentials) calculations, we propose a new mechanism for monovacancy annihilation and single missing dimer creation. Our study shows that an isolated monovacancy can exist fairly stable, rather than liberating the remaining atom of the 'defect' dimer readily. The liberation barrier is calculated to be 1.3 eV. However, the monovacancy can diffuse rapidly along a dimer row by overcoming a barrier of 0.3 eV, leading to vacancy-vacancy pairing at elevated temperatures. These results suggest that the vacancy-vacancy pairing may play a major role in creating a single missing-dimer vacancy (which is ≈1.8 eV more stable than two isolated monovacancies). We also present the pathways and barriers of (i) the remaining atom hopping between the buckled-up and down site of the 'defect' dimer and (ii) the vacancy diffusion into the subsurface layer.
Bibliographical noteFunding Information:
We thank Dr. Yun Wang and Ms. Devina Pillay for helpful discussions and suggestions. GSH acknowledges the Welch Foundation (grant no.: F-1535) for their partial financial support. Most of our calculations were performed using IBM IA-32 and IBM IA-64 clusters in the Texas Advanced Computing Center.
- Ab initio quantum chemical methods and calculations
- Diffusion and migration
- Surface defects