Dislocation Nucleation and Multiplication at Crack Tips in Silicon
✍ Scribed by Scandian, C. ;Azzouzi, H. ;Maloufi, N. ;Michot, G. ;George, A.
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 591 KB
- Volume
- 171
- Category
- Article
- ISSN
- 0031-8965
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✦ Synopsis
The brittle±ductile transition (BDT) has been studied in silicon single crystals of different orientations and purities. It is shown that the BDT temperature at a given loading rate can be significantly varied depending on structural parameters, especially the density of cleavage defects (steps, F F F). The critical BDT temperature is raised when the cleavage defect density is lowered. This is explained by observations at crack tips which prove that dislocation nucleation is highly inhomogeneous. A first preliminary attempt to identify nucleation sites by AFM is reported. In crystals containing highly perfect cleavage cracks, dislocation formation prior to fracture in mode I loading could be suppressed. In such cases, a very small number of dislocations created on purpose from remote sources, sufficed to trigger the formation of a plastic zone as soon as they touched the crack front. Experimental results are compared to theoretical models and recent numerical computations.
La transition fragile±ductile a e  te  e  tudie  e dans des monocristaux de silicium de diffe  rentes orientations et purete  s. A une vitesse de chargement donne  e, la tempe  rature de transition de  pend fortement de parame Á tres structuraux, en particulier de la densite  de de  fauts que pre  sente la surface de clivage. La tempe  rature de transition fragile±ductile augmente quand la densite  de ces de  fauts diminue. Ceci est explique  par des observations au voisinage du front de fissure qui montrent que la nucle  ation des dislocations est tre Á s inhomoge Á ne. Un premier essai de caracte  risation par microscopie a Á force atomique en vue d'identifier les sites de nucle  ation est rapporte Â. Dans des cristaux contenant des fissures de clivage de grande qualite Â, la formation des dislocations avant rupture sous un chargement en mode I peut e à tre supprime  e. Dans de tels cas, un tout petit nombre de dislocations cre  e  es a Á dessein a Á partir de sources distantes du front de fissure suffit a Á de  clencher la formation de la zone plastique au moment ou Á elles touchent le front de fissure. Ces re  sultats expe  rimentaux sont compare  s aux mode Á les the  oriques et a Á des simulations nume  riques re  centes.