This set of Multiple Choice Questions & Answers (MCQs) focuses on “Nanomaterials – Set 5”.
1. A chemical reaction follows: SiH4 (g) → Si(s) + 2H2 (g) at 650°C, which type of reaction is this?
a) Pyrolysis
b) Reduction
c) Oxidation
d) Compound formation
View Answer
Explanation: In this type of reaction, decomposition is done by thermal treatment which lies in pyrolysis reactions. Here reduction of one species and oxidation of another species is done, so it is a red-ox reaction. It is a decomposition reaction, not a formation reaction.
2. In chemical vapour deposition, what is the correct sequence of mechanism?
a) Generation-diffusion-deposition
b) Generation-reaction-deposition
c) Generation-reaction-diffusion
d) Generation-reaction-diffusion-deposition
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Explanation: Correct sequence of chemical vapour deposition is generation of different chemical species, reaction of these species in gas phase to give reactive growth species, these growth species then react with the substrate by chemical bonding and deposit there.
3. In chemical vapour deposition, _____
a) Volatile compounds react to give volatile growth species
b) Volatile compounds react to give non-volatile growth species
c) Non-volatile compounds react to give non-volatile growth species
d) Non-volatile compounds react to give volatile growth species
View Answer
Explanation: In chemical vapour deposition, first volatile compounds react with other volatile gases by chemical reactions to give growth species. These growth species are non-volatile in nature so that they don’t evaporate again.
4. If a pressure of 5torr is used in chemical vapour deposition, what kind of chemical vapour deposition it is?
a) Low pressure chemical vapour deposition
b) Plasma enhanced chemical vapour deposition
c) Metalorganic chemical vapour deposition
d) Simple chemical vapour deposition
View Answer
Explanation: Other chemical vapour deposition uses pressure in range of 0.5torr to 1torr while plasma enhanced chemical vapour deposition uses pressure in range between 0.5 to 5torr. Other chemical vapour deposition requires high mass flux of precursors so they use high pressure.
5. Which chemical vapour deposition technique is best?
a) Plasma enhanced chemical vapour deposition
b) Metalorganic chemical vapour deposition
c) Simple chemical vapour deposition
d) Low pressure chemical vapour deposition
View Answer
Explanation: Plasma enhanced chemical deposition uses plasma gas to enhance the deposition rate. Plasma activates the substrate surface and increase the speed of reaction, that is why plasma enhanced chemical vapour deposition is better than other chemical vapour techniques.
6. If a laser is used to provide thermal energy in pyrolytic chemical vapour deposition, where it should be focused?
a) Precursors
b) Chamber
c) Reactive mixture
d) Substrate
View Answer
Explanation: Thermal energy is required in chemical vapour deposition for the reactions between volatile precursors, as method is pyroelectric hence laser energy should be converted to temperature. Thus laser is applied to substrate so that it can heat and provide thermal energy to volatile mixture to react.
7. If a laser is used to provide thermal energy in photolytic chemical vapour deposition, where it should be focused?
a) Precursors
b) Chamber
c) Reactive mixture
d) Substrate
View Answer
Explanation: In photolytic chemical vapour deposition using laser, photons of laser should be used to give energy to precursor gases so that they can react. This can be achieved by focusing laser on precursor mixtures, so laser should be focused on precursors.
8. To deposit a substance which have no gaseous precursor, which technique should be used?
a) Plasma enhanced chemical vapour deposition
b) Metalorganic chemical vapour deposition
c) Aerosol chemical vapour deposition
d) Laser chemical vapour deposition
View Answer
Explanation: From plasma enhanced CVD to laser CVD gaseous precursors are used to obtain the growth species but in aerosol chemical vapour deposition, liquid or solid precursors are mystified in droplets or tiny particles, mixed with carrier gas and in the chamber these droplets decomposes and get deposited on substrate.
9. To deposit solid electrolyte film on a porous media, which method should be used?
a) Plasma enhanced chemical vapour deposition
b) Electrochemical vapour deposition
c) Aerosol chemical vapour deposition
d) Laser chemical vapour deposition
View Answer
Explanation: Other methods are used to deposit material on non-porous solid surface, in these method chemical reaction occurs in the chamber, generated growth species react with surface. In Electrochemical vapour deposition, precursors diffuse first to the pores of substrate separately, they react & get deposited.
10. To deposit non-electrolyte solid particles in porous substrate, which method should be used?
a) Plasma enhanced chemical vapour deposition
b) Electrochemical vapour deposition
c) Aerosol chemical vapour deposition
d) Chemical vapour Infiltration
View Answer
Explanation: Plasma method is used for non-porous substrate, aerosol method is also used to deposit solid particles which do not have gaseous precursors. Electrochemical method is for solid particles which are electrical conductor in nature, while chemical vapour infiltration is used to deposit solid non-electrolyte particles in pores of substrates for filling purposes.
Sanfoundry Global Education & Learning Series – Nanomaterials.
To practice all areas of Nanomaterials, here is complete set of Multiple Choice Questions and Answers.
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