Diffusion

� The diagram shows steps involved in a single jump of an atom in the vacancy mechanism.
� The vacancy (yellow) moves in a random walk on the lattice.

From: Guy, "Introduction to Materials Science," McGraw Hill (19972)

� When the vacancy is next to the marker atom, this can jump and exchange places with the vacancy if it has enough energy to overcome the saddle point barrier.
� The next jump may either reverse this (step 3') or cause the vacancy to move away from the marker atom, the latter having now completed a jump in the +x direction.