Question

Choose the correct order of steps involved in Chemical Vapour Deposition (CVD) technique :
A. Heterogenous surface reaction catalysed by the surface
B. Nucleation and growth of film
C. Transport of reacting gases and their adsorption to the surface
D. Surface diffusion of the species to growth sites
E. Desorption and transportation of gaseous reaction products away from the surface
Choose the correct answer from the options given below :

• A. C, B, A, E, D
• B. A, B, C, E, D
• C. C, A, B, D, E
• D. B, A, C, D, E

Hint:

In complex sequencing questions where textbook perfection isn't an option, prioritize the absolute first step (Gases must arrive/adsorb) and the absolute last step (Waste must leave). This "bookend" strategy rapidly eliminates 50-75% of incorrect choices.

Answer 1

The Correct Option is C

Step 1: Concept:
Chemical Vapor Deposition (CVD) is a technique to produce high-purity, high-performance solid materials, typically under vacuum. The process relies on a specific sequence of mass transport, surface kinetics, and thermodynamics.

Step 2: Key Formula or Approach:
The widely accepted fundamental steps of thin film growth via CVD are logically sequenced as follows:
1. Transport & Adsorption: Reactant gases are pumped into the chamber and adsorb onto the heated substrate.
2. Reaction: Chemical reactions occur at the surface, creating the desired solid product (adatoms) and gaseous by-products.
3. Surface Diffusion: The generated adatoms wander (diffuse) across the surface to find lower-energy stable sites (like step edges).
4. Nucleation & Growth: The adatoms aggregate to form stable nuclei, which then grow into a continuous thin film.
5. Desorption: Waste gaseous by-products desorb from the surface and are pumped away.

Step 3: Step-by-step Explanation:

• Any logical sequence must begin with the precursors arriving at the substrate. This is statement C (Transport and adsorption). This immediately eliminates options (B) and (D).

• Any logical sequence must end with waste products leaving. This is statement E (Desorption).

• We are left to order A, B, and D. According to textbook mechanisms, gas adsorbs (C), reacts to form adatoms (A), the adatoms diffuse to step edges (D), where they incorporate to grow the film (B), and finally by-products leave (E). This gives the theoretical sequence: C, A, D, B, E.

• Note: If we carefully review the provided options, the exact perfect sequence (C, A, D, B, E) is not listed. The closest logical provided sequence that starts with transport and groups reaction/growth before final desorption is Option (3): C, A, B, D, E. While placing diffusion (D) after growth (B) is slightly non-standard (as diffusion feeds growth), it remains the most viable intended answer in the exam's context because it correctly identifies the initial boundary (C) and internal progression better than the completely randomized alternatives.

Step 4: Final Answer:
Selecting the most appropriate sequential flow provided by the options, we choose option (C).