Ledges and jogs can be supplied by which of the following mechanisms?

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BlackTom AI · Accepted Answer

Question context: Ledges and jogs in crystal surfaces are features that can be introduced by several growth mechanisms. 
Option 1: 'by repeated surface nucleation' — This mechanism involves new atomic layers beginning at various sites on a surface, creating steps or ledges as layers advance. It contributes to the formation of stepped features and jogs when nucleation happens at multiple positions along the surface. 
Option 2: 'by spiral growth' — Spiral growth occurs around a screw dislocation, generating a continuous step that winds upward like a spiral staircase. This readily creates ledges and can introduce jog-like discontinuities along the growth front. 
Option 3: 'from twin boundaries' — Twin boundaries create crystallographic discontinuities that can act as preferential sites for new step formation or modification of existing steps, thereby supplying additional ledges or jogs during growth or annealing processes. 
Option 4: 'all of the above' — Since each of the first three mechanisms can independently contribute to the creation or modification of ledges and jogs, combining them, the comprehensive option encompasses all valid pathways by which ledges and jogs can be supplied. 
Putting it together, understanding crystal surface morphology shows that layer-by-layer nucleation, screw-dislocation-driven spirals, and structural defects like twin boundaries each play a role in supplying stepped features. Consequently, the mechanism set that covers all possibilities is the most complete explanation. 
Note: A common point of confusion is to assume only one pathway operates in a given system; in practice, multiple pathways can operate simultaneously to shape the stepped landscape of a surface.

2251-1_20MTEN6070001 Lecture 20 Pre-Class Reading Quiz

Ledges and jogs can be supplied by which of the following mechanisms?

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