Summary and Evaluation of NRC-Sponsored Stellite 6 Aging and Friction Tests

Watkins, J.C.; DeWall, K.G.; Bramwell, D.

doi:10.2172/766386

Cited by 1 publication

(1 citation statement)

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“…In the case of interstitials, our HSE calculations reveal that the H-H pathway is dominant with the migration barrier H m;H-H ¼ 0:47 eV (H m;H-X ¼ 0:75 eV, H m;H-T ¼ 0:53 eV, and H m;T-X ¼ 0:67 eV). In contrast to the defect formation energy, where HSE exhibits a good agreement with higher-level calculations and experimental values, there is a marked difference between HSE (0.47-0.75 eV) and experiment (0.20 eV [41]) for the migration barrier height. Upon including the vdW interactions, all HSE migration barriers are decreased when using the HSE þ vdW approach.…”

Section: H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 60%

Electronic Structure and van der Waals Interactions in the Stability and Mobility of Point Defects in Semiconductors

Wang

Tkatchenko

2013

Phys. Rev. Lett.

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We study the role of electronic structure (band gaps) and long-range van der Waals (vdW) interactions on the stability and mobility of point defects in silicon and heavier semiconductors. Density functional theory calculations with hybrid functionals that contain part of the Hartree-Fock exchange energy are essential to achieve a reasonable description of defect electronic levels, leading to accurate defect formation energies. However, these functionals significantly overestimate the experimental migration barriers. The inclusion of screened vdW interactions further improves the description of defect formation energies, significantly changes the barrier geometries, and brings migration barrier heights into close agreement with experimental values. These results suggest that hybrid functionals with vdW interactions can be successfully used for predictions in a broad range of materials in which the correct description of both the electronic structure and the long-range electron correlation is essential. The diffusion of defects in semiconductors is a fundamental process of matter transport. Defects are abundant in essentially all real materials and they often significantly modify the electronic, optical, and magnetic properties of solids. For example, the electron spin of donors in Si and vacancy defects in SiC have been investigated for their possible use as components of quantum devices [1,2]. Therefore, the study of defects is important from both fundamental and technological points of view.Here we focus on understanding the interplay between electronic structure and nonlocal correlation effects for the fundamental benchmark case of intrinsic point defects in bulk Si and heavier semiconductors. Two kinds of native point defects in Si, self-interstitials and vacancies, have been intensively investigated both experimentally and theoretically. However, the understanding of self-diffusion in Si remains incomplete, despite decades of seminal work on the subject . Using secondary ion mass spectrometry (SIMS), two groups obtained identical conclusions that the vacancies mechanism is preferred over the interstitials mechanism in self-diffusion at low temperature while the interstitials mechanism can be dominant at high temperature [5,6]. Correspondingly, the diffusion activation energies (sum of the formation energy and migration barrier [14][15][16][17][18][19][20][21][22][23]; however, the computation of point defect properties is still fraught with difficulties. Density functional theory (DFT) calculations with the local-density approximation (LDA) or generalized gradient approximation (GGA) usually underestimate defect formation energies due to the electron self-interaction error. Furthermore, both LDA and GGA miss the long-range van der Waals (vdW) interactions for nonhomogeneous electron densities. Nevertheless, it is remarkable that GGAs often produce fairly good results for migration barrier heights of point defects [24]. Hybrid DFT functionals mitigate the electron self-interaction error, and yield defect for...

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Section: H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 60%