This set of Multiple Choice Questions & Answers (MCQs) focuses on “Nanomaterials – Set 4”.
1. If influx rate of growth species is very high and growth temperature is low, which form of thin films will be formed?
a) Amorphous
b) Single crystalline
c) Poly-crystalline
d) Liquid
View Answer
Explanation: For single crystalline growth influx rate should be small and temperature should be high so that thermodynamic deposition takes place. For poly crystalline growth temperature should be moderate and flux should be high and for amorphous, flux should be high and temperature very low. Liquid thin film is not formed in any case.
2. If there is a lattice mismatch, which growth will take place?
a) Island growth
b) Layer growth
c) Island-layer growth
d) Wire growth
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Explanation: When there is lattice mismatch, elastic strain comes in picture which increases with layers. First layers are formed thermodynamically but when layers are stacked upon each other, elastic strain develops which favours island growth. There is no growth such as wire growth as that is thermodynamically unfavourable.
3. In which physical vapour deposition process, thermal means are used to generate the growth species to deposit on substrate?
a) Evaporation
b) Sputtering
c) Chemical vapour infiltration
d) Electrochemical vapour deposition
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Explanation: Chemical vapour infiltration and electrochemical vapour deposition are the processes in which chemical reactions are used to generate growth species. In sputtering ion beam is used to generate the growth species from the source In evaporation high temperature is used to generate growth species by evaporation.
4. In sputtering method, which species knock down the neutral growth species from the source?
a) Positive ions of gas
b) Electrons
c) Negative ions of gas
d) Neutral accelerated molecules of gas.
View Answer
Explanation: In sputtering method, ejected electrons from cathode ionise the gas molecules. Generated positive gas ions, when accelerated gas ions gain momentum and knock down the growth species from source.
5. There are many sputtering methods, what is the name of sputtering method in which magnetic field is used?
a) DC sputtering
b) RF sputtering
c) Magnetron sputtering
d) Reactive sputtering
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Explanation: In dc sputtering and RF sputtering, electric field is used to produce gas ions and in reactive sputtering some reactive chemicals are used to knock down the growth species. In magnetron sputtering, magnetic field is used to produce such gas ions to knock down the target.
6. What is the pressure range used sputtering based physical vapour deposition?
a) 100torr
b) 10torr
c) 1torr
d) 0.1torr
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Explanation: In sputtering a moderate pressure of gas is required else there will be no ionization of the gas. 100torr is moderate enough to achieve this experimentally.
7. Which process has smaller grain size and better adhesion to substrate?
a) Sputtering
b) Evaporation
c) Lithography
d) Sol-gel
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Explanation: Evaporation uses thermodynamic approach and thus there is enough time to decrease surface energy and this results in larger grain size. Lithography uses tools which are sophisticated to generate smaller grains. Sol-gel method is also suitable for this, only sputtering can give smaller grain size as it uses kinetic approach.
8. Which method has highly activated substrate surface?
a) Sputtering
b) Evaporation
c) Lithography
d) Micro-emulsion
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Explanation: In all other methods surfaces are not subjected to any kind of radiation or high thermal treatment, there are under temperature but moderate temperature. In sputtering substrate is highly bombarded by electrons which results in active substrate.
9. Sputtering is a thermodynamic approach.
a) True
b) False
View Answer
Explanation: Sputtering is a kinetic approach, in sputtering there are large influx of growth species so there is not enough time for proper settling of species. On surface of substrate, bombardment of electrons also activates every site of substrate.
10. Molecular beam epitaxy is a _________
a) Chemical vapour deposition
b) Lithography
c) Physical vapour deposition
d) Template based synthesis
View Answer
Explanation: Chemical vapour deposition uses chemical reactivity to generate growth species. Molecular beam epitaxy method uses thermal energy to generate growth species. Template based synthesis is used to generate nanowires and molecular beam epitaxy gives thin films. Lithography is a method in which tailoring of dimensions is done, no such generation of growth species is done.
Sanfoundry Global Education & Learning Series – Nanomaterials.
To practice all areas of Nanomaterials, here is complete set of Multiple Choice Questions and Answers.
