Part 1 - Thin films

Question 1

What are the two general ways of growing thin films?

Answer 1

Vapor-phase deposition and liquid-based growth.

Question 2

For vapor-phase deposition of 2D-materials, what kind of environment is required?

Answer 2

Vacuum.

Question 3

What are the three ways thin films can nucleate?

Answer 3

Island, or Volmer-Weber growth.
Layer, or Frank-van der Merwe growth
Intermediate, or Stranski-Krastonov growth.

Question 4

What is the difference between homoepitaxy and heteroepitaxy?

Answer 4

Homoepitaxy is the epitaxial growth of the same compound with the same crystal structure. Heteroepitaxy is when a compound is grown on a substrate of comparable crystal lattice.

Question 5

What is the reason one may get island growth when depositing a thin film?

Answer 5

Due to elastic strain at the interface. The addition of new atoms on top of the strained deposit is more favored than introducing even more strain by depositing more onto the substrate.

Question 6

When can we get a layered epitaxial growth instead of island growth?

Answer 6

This all depends on the free energy balance. If the interfacial energy between the deposit and the substrate is lower than the combined energy of the interface of the islands and the strain, as well as the surface free energy associated with the deposit/vapor interface, layered growth will occur. An intermediate growth mechanism (Stranski-Krastonov) can occur if first layered growth is preferred, then later island growth.

Question 7

What are the two most important factors governing the degree of crystallinity of a thin film?

Answer 7

Temperature and impinging rate of the growth species.

Question 8

What does a single crystal thin film require to be able to grow?

Answer 8

• a single crystal substrate with a close lattice match
• clean substrate as to not facilitate secondary nucleation
• a high growth temperature so as to ensure diffusion mobility of growth species across surface
• low impinging rate of growth species so that there is enough time for growth species to diffuse to the lowest energy sites, and for structural relaxation to occur between adsorption events.

Question 9

What does an amorphous thin film usually result from?

Answer 9

• Low growth temperature

- influx of growth species is very high

Question 10

What does polycrystalline thin films usually result from?

Answer 10

• moderate growth temperature

- moderately high influx of growth species.