3.3.3 Summary to: 3.3 Nucleation and Growth

Deposition of a thin layer must start with a "clean" substrate surface on which the first atomic / molecular layer of the film must nucleate.

There are many possible interactions between the substrate and "first" incoming atoms.

As the interaction energy goes up we move from "some" absorption to physisorption (secondary bonds are formed) to chemisorption (full bonding)

The sticking coefficient is a measure of the likelihood to find an incoming atom in the thin film forming.

Immobilization by some bonding is more likely at defects (= more partners). The initial stage of nucleation is thus very defect sensitive.

Simple surface steps qualify as efficient "defects" for nucleation.

Small deviations from perfect orientation provide large step densities. Nucleation therefore can be very sensitive to the precise {hkl} of the surface

Intersections of (screw) dislocation lines with the surface also provide steps.

This may cause grain boundaries and other defects in the growing layer.

Scanning probe microscopy gives the experimental background

There is always a nucleation barrier that has to be overcome for the first B-clusters" to form on A

the three involved interface energies, all expressed in the "wetting angle", plus possibly some strain are the decisive inputs for the resulting growth mode.

Frank - van der Merve: Smooth layer-by-layer growth
Vollmer - Weber: Island growth
Stranski - Krastanov: Layer plus island growth

Exercise 3.3-1
All Questions to 3.3