This set of Multiple Choice Questions & Answers (MCQs) focuses on “Nanomaterials – Set 2”.
1. In anisotropic spontaneous growth, which of these reasons is not correct?
a) Different planes of a crystal have different growth rate
b) Presence of imperfections in specific crystal directions
c) Poisoning of some crystal directions by substitution with some impurities
d) Using a catalyst does not give confinement in that surface
View Answer
Explanation: In anisotropic growth, presence of imperfections reduces the growth rate and different crystal planes have different atomic density so they have different growth rate. Using a catalyst enhances the growth of that surface.
2. Which one is not a method for anisotropic spontaneous growth?
a) Evaporation- condensation
b) Vapour-liquid-Solid growth
c) Stress induced recrystallization
d) Electroplating
View Answer
Explanation: All top three methods follows reduction in Gibbs free energy mechanism, it can be achieved by chemical reaction, new phase generation and stress, thus the process becomes spontaneous. Electroplating is template based synthesis.
3. Which site is thermodynamically unfavourable for growth of surfaces?
a) Terrace
b) Step
c) Ledge-kink
d) Kink
View Answer
Explanation: Terrace site forms only one bond with growth species. Step, ledge-kink & kink sites forms 2, and 4 bonds respectively which is thermodynamically stable.
4. Which anisotropic spontaneous growth mechanism is a top-down approach for nanowire synthesis?
a) Evaporation condensation
b) Template based synthesis
c) Electrospinning
d) Lithography
View Answer
Explanation: In all three methods other than lithography, crystals are produced from precursor solution and then their growth takes place molecule by molecule. In lithography bulk is broken down to nanostructures.
5. In which method of synthesis an impurity or catalyst is introduced for confinement of growth?
a) Lithography
b) Evaporation- condensation
c) Vapour-liquid-solid growth
d) Sol-gel
View Answer
Explanation: In sol-gel and evaporation condensation method simple growth takes place without any external phase material use as they are confined naturally. Lithography technique is about tailoring the dimensions. In vapour-liquid-solid growth a catalyst is used to bind to some crystal planes and enhance the growth rate at that surface.
6. The growth surface of a flat surface is due to the advancement of the _________
a) Terrace
b) Steps
c) Ledge-kink
d) Kink
View Answer
Explanation: ledge-kink and kink sites are the sites where growth species ends at last but first, molecules goes to steps and by surface diffusion they go to kinks. Terrace are the sites which are thermodynamically unfavourable.
7. In vapour-liquid-solid method catalyst should be _______
a) Chemically inert
b) Chemically active
c) Physically inert
d) Bigger than growth species in size
View Answer
Explanation: Catalyst should be physically active so that it can attach by weak forces to growth surface but it should be chemically inert so that its bond with growth surface becomes irreversible. There is no rule regulation for the size of catalyst but it should be according to the diameter of nanowire desired.
8. A catalyst in vapour-liquid-solid method forms with a large wetting angle will results in ______
a) Large diameter nanowire
b) Small diameter nanowire
c) Large diameter quantum dot
d) Small diameter quantum dot
View Answer
Explanation: Vapour-liquid-solid method is used for synthesis of nanowires, not for quantum dot. A large wetting angle means small surface area for growth and thus small diameter nanowire.
9. In stress induced recrystallization method, growth is confined in some directions by applying pressures but Growth takes place from a different site. Which site it is?
a) Tip
b) Base
c) Side opposite to pressure application side
d) Side matching to pressure application side
View Answer
Explanation: Pressure is applied to all sites but the dislocation is produced at base and from there the growth starts to take place.
10. In which method, precursor is used in solution form along with a catalyst?
a) Solution-liquid-solid method
b) Vapour-liquid-solid method
c) Lithography
d) Evaporation- condensation
View Answer
Explanation: Evaporation-condensation method and lithography do not uses catalyst for confined growth. In vapour-liquid-solid method vapour form precursor is used for synthesis with a catalyst for confinement of growth while in solution-liquid-solid method a catalyst is used for confined growth and solution form precursor is used.
Sanfoundry Global Education & Learning Series – Nanomaterials.
To practice all areas of Nanomaterials, here is complete set of Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
