Question

A student aims to deposit a thin metallic film on SiO\(_2\) substrate, with an adhesion layer between the metal film and substrate, in a contiguous planar fashion. Island type of growth must be avoided. The student performs an extensive optimization exercise. Which one of the following steps is in the right direction?

• A. Choose a metallic adhesion layer with very low interfacial energy with the deposited thin film
• B. Choose a metallic adhesion layer with very low interfacial energy with SiO\(_2\), irrespective of its interaction with metal film to be deposited
• C. Increase the substrate temperature and decrease the deposition rate
• D. Use intermittent stages of deposition followed by annealing

Hint:

To avoid island growth in thin films, ensure strong wetting by minimizing interfacial energy between the deposited film and adhesion layer.

Answer 1

The Correct Option is A

To obtain a smooth, continuous, planar metallic film on a substrate, the metal atoms must wet the surface effectively. Island growth (Volmer–Weber growth) occurs when the interfacial energy between the deposited metal and the underlying layer is high, causing atoms to cluster instead of spreading.
Using a metallic adhesion layer with low interfacial energy with the deposited metal film promotes good wetting and continuous layer formation. This suppresses island formation and encourages layer-by-layer growth.
Option (B) focuses only on SiO\(_2\)–adhesion-layer interaction but ignores metal–adhesion-layer compatibility, so it is not optimal. Options (C) and (D) may affect morphology but do not guarantee prevention of island growth. Hence, (A) is the correct direction.