Atomic mechanisms of fracture in silicon: Ab initio quantum molecular dynamics calculations
The aim of this work is to understand the energetics and the atomic mechanism of cleavage in brittle fracture. The method of ab-initio molecular dynamics investigates various problems in brittle fracture. The electronic structure of stacking faults in silicon is also examined. A modified quantum molecular dynamics method is used to study hydrogen embrittlement in silicon. The surface reconstructions which occur when a parallel-sided gap opens up between the (111) planes of silicon are computed. The Haneman (2 X 1) buckled row reconstruction is found to occur at a critical gap, d[sub c], and acts as a precursor for the Pandey (2 x 1) [pi]-bonded chain reconstructed Si(111) is calculated to be 1340 erg/cm[sup 2], in good agreement with experiment. Shuffle and glide terminations are compared and found to differ in energy by 0.24 eV/(surface atom) with shuffle termination having lower energy. The interface band gap states associated with the cleavage process are observed. The top states in the valence-band will transform into occupied interface states if the applied strain is large enough. The dependence of lattice trapping energies on applied load for cracks is determined. A type of flexible boundary condition is used in which outer atom positions are relaxed using an empirical interatomic potential, while inner atoms are treated ab-initio. The fractional range of loads K[sub max]/K[sub min] for lattice trapping is found to be 1.31 and the energy barrier to the advance of a straight crack line along [110] is found to be 0.24 eV/(surface atom). For the hydrogen embrittlement problem in silicon, the hydrogen atoms are found to channel along the [110] tunnel nearest and parallel to the crack line. Finally, the intrinsic stacking fault energy is found to be 106 erg/cm[sup 2] which is in close agreement to the results of others. The calculated defect state located at 0.128 eV above the valence-band maximum is also in good agreement with photoluminescence data.
- Research Organization:
- Arizona State Univ., Tempe, AZ (United States)
- OSTI ID:
- 7102950
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
SILICON
BRITTLENESS
FRACTURE PROPERTIES
BAND THEORY
DUCTILE-BRITTLE TRANSITIONS
DYNAMICS
HYDROGEN EMBRITTLEMENT
QUANTUM MECHANICS
ELEMENTS
EMBRITTLEMENT
MECHANICAL PROPERTIES
MECHANICS
SEMIMETALS
360603* - Materials- Properties
665400 - Quantum Physics Aspects of Condensed Matter- (1992-)