Question

For my lab on depositing thin films on a surface via thermal evaporation I was asked hat would have happened if we had obtained different color metals on the samples after the thermal evaporation? The only thing I can think of is there was a leak in the vacuum chamber so a nonintended product could have formed via chemical reaction or chemical mixing. Can someone please give me a clearer answer. Thanks!

Answer 1

1. High vacuum is critical for evaporation process. When gas is evacuated from a chamber, vapor molecules inside it can travel longer distances before they collide with a gas. Collision with gas molecules are undesirable as they change the direction and affects the absorption on the surface.

2. Background gases in the chamber can lead to contaminatio of the film because of presence of oxygen, moisture which are responsible for the light emission or absorption property.

3. Vapou presure of deposit material should be much higher than the resistive boat material otherwise it can contaminate the metal. When choosing a resistive boat for a given material, it is critical to ensure a high melting point differential and low solubility.

4. The size of the particle is also important as their property changes with change in the size. The thickness of the film also plays a role in deciding the color because the reflectivity property changes.