Question

Surface and interfacial energies are critical in determining the thin film growth modes. Imagine that you are growing a bilayer film: material A is first deposited on substrate S, then material B is deposited. The amount of A and B being deposited is equivalent to a few monolayers of coverage, respectively. Sketch the side-view schematics of the structure of the deposited film, for the following scenarios:

(a) γs large, γA small, γB small, γAB small, γAS small, γBS small
(b) γs intermediate, γA large, γB small, γAB small, γAS large, γBS small
(c) γs intermediate, γA large, γB small, γAB small, γAS large, γBS large

Answer 1

Different combinations of surface and interfacial energies determine how materials A and B will deposit on substrate S to form a bilayer film. Scenarios vary from uniform layering to the formation of islands or non-uniform coverage.

Step-by-step explanation:

Understanding the growth modes of bilayer thin films involves analyzing the surface and interfacial energies between the materials and the substrate. Different interfacial energies lead to variations in the film's structure. Here's how different energy scenarios affect the bilayer film growth:

• (a) When γs is large, γA is small, γB is small, γAB is small, γAS is small, and γBS is small: Material A and B will likely spread evenly over the substrate S, leading to a uniform layering of A on S, followed by B on A, as there are no large surface tension disparities driving aggregation or separation.
• (b) When γs is intermediate, γA is large, γB is small, γAB is small, γAS is large, and γBS is small: Material A, with its large surface tension relative to the substrate, might not spread well on it, leading to the formation of islands or non-uniform coverage. A small γB allows material B to spread on top of A smoothly.
• (c) When γs is intermediate, γA is large, γB is small, γAB is small, γAS is large, and γBS is large: Both materials A and B, with their large surface tensions relative to the substrate, are likely to form aggregated islands on top of S. This could result in uneven layering and possibly separate domains of A and B depending on their relative surface tensions with each other.