Molecular dynamics simulation of Cu deposition near a step on the Cu(001) surface showing steering effect (attraction to top layer of step)

Atom landing 'between' of step atoms:

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Notice how the depositing atom "slides in" between the two step-edge atoms after bouncing and is then attracted to the top terrace. This gives rise to a positive surface current (instability).

The depositing atom is initially close to the critical distance y = 0.3 b beyond the edge of the step, corresponding to attraction to the top terrace but is now 'between' of the neighboring step atoms.

(Atom initial kinetic energy = 0.1 eV, substrate temperature = 84 K)