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Thin films, surfaces and nanomaterials

Among thin-film growth modes, which correctly describes Stranski–Krastanov (SK) growth?

  1. AWith weak film–substrate bonding, three-dimensional islands scattered over the substrate grow from the very start
  2. BAfter layer-by-layer growth of a few atomic layers, three-dimensional islands grow, driven by accumulated strain and other factors
  3. CEven with lattice mismatch, growth proceeds layer by layer, one atomic layer at a time, to the end
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Answer: B. After layer-by-layer growth of a few atomic layers, three-dimensional islands grow, driven by accumulated strain and other factors

In SK growth, a few atomic layers called the wetting layer first grow layer by layer; then, as strain energy from lattice mismatch accumulates, three-dimensional islands grow to relax it. The self-assembly of quantum dots of InAs on GaAs (lattice mismatch of about 7%) is the classic example. Growth as three-dimensional islands from the start is Volmer–Weber (VW) growth, which occurs when the bonds among film atoms are stronger than the bonds between film and substrate, and is often seen for metal films on oxides. Layer-by-layer growth to the end is Frank–van der Merwe (FM) growth, which occurs ideally in lattice-matched epitaxial growth.

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