This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Production of Graphene – Set 2”.
1. Mention the incorrect option with respect to the disadvantages of top-down methods for graphene production?
a) Poor yield of graphene sheets
b) Production of unoxidized sheets
c) Expensive ionic liquids used in electrochemical exfoliation
d) Small scale production of graphene films
View Answer
Explanation: Top-down production process for graphene has few drawbacks. These include very small scale production of graphene films, poor yield of graphene sheets, use of expensive ionic liquids in electrochemical exfoliation and hazardous acids in super acid dissolution of graphite respectively.
2. What is the method used for the production of defect-free graphene?
a) Sonication
b) Pyrolysis
c) Shear exfoliation
d) Chemical Vapour deposition
View Answer
Explanation: There are various methods used for the preparation of graphene. Shear exfoliation is one of them. It uses rotor-stator mixer, producing local shear rates greater than 104, for scalable production of defect-free, unoxidized graphene.
3. Select the correct sequence of steps occurring in the epitaxial growth process of graphene production.
a) SiC is heated at high temperature ➜ Carbon atoms accumulate ➜ Si atoms evaporate ➜ Graphene layers are controlled ➜ Thermionic emission
b) Carbon atoms accumulate ➜ Si atoms evaporate ➜ Thermionic emission ➜ Graphene layers are controlled ➜ SiC is heated at high temperature
c) Si atoms evaporate ➜ Thermionic emission ➜ Carbon atoms accumulate ➜ SiC is heated at high temperature ➜ Graphene layers are controlled
d) SiC is heated at high temperatures ➜ Thermionic emission ➜ Si atoms evaporate ➜ Carbon atoms accumulate ➜ Graphene layers are controlled
View Answer
Explanation: Initially, SiC wafers are heated at temperatures around 1000°C. Thermionic emission occurs leading to evaporation of silicon from the substrate, leaving behind carbon atoms. These atoms accumulate to form graphene layers on the remaining substrate. Multilayer, bilayer or single layer graphene can be grown by controlling the temperature and pressure.
4. Which of the following is sprayed onto the substrate in a supersonic spray method for graphene production?
a) Hydrocarbons
b) Buckyballs
c) Metal carbonyls
d) Carbon dioxide
View Answer
Explanation: Supersonic spray method uses a graphene spray gun inorder to deposit layers of graphene onto the substrate. Apart from reduced graphene oxide, bucky balls are also sprayed at supersonic speeds onto the substrate. These balls crack open upon impact. Subsequently unzipped cages bond together to form a graphene layer.
5. Find out the correct statement with respect to the epitaxial growth of graphene on silicon carbide.
a) Graphene layers on the substrate can be controlled by regulating temperature and pressure
b) Thermionic emission leaves behind silicon atoms on the substrate
c) Method operates at very low temperatures
d) Ultra-high vacuum favors the uniform growth of multi-layer graphene
View Answer
Explanation: Epitaxial growth of graphene is based on the concept that vapour pressure of silicon is higher than carbon. Thus, on heating the silicon carbon (SiC) substrate at extremely high temperatures, the silicon (Si) evaporates leaving behind the graphene layers on the remaining substrate. Ultra high vacuum used might hinder the uniform growth of multi-layer graphene.
6. In which method, sugar is used for the preparation of graphene?
a) Hydrothermal self-assembly
b) Exfoliation
c) Supersonic spray
d) Hydrothermal reduction of graphene oxide
View Answer
Explanation: Hydrothermal self assembly method of graphene production makes use of sugar for its preparation. This process uses glucose, fructose, sucrose etc. It is a substrate-free, safe, simple and eco-friendly process.
7. Which among the following is not an advantage for graphene production using epitaxial growth method?
a) Patterning of graphene is easy due to the use of insulating SiC substrate
b) Process requires temperatures as high as 1000°C
c) High quality graphene is obtained
d) Graphene layer thickness can be controlled by regulating temperature
View Answer
Explanation: Epitaxial growth of graphene is a highly advantageous method for graphene synthesis. This is because it produces high quality graphene on large scale. Moreover it is possible to control the thickness of layers by regulating various parameters. But there are few limitations to this process. First it requires very high temperature for production. Second, problems arise in growing uniform multilayer graphene in ultra-high vacuum. Finally lattice mismatch leads to various defects.
8. Why cannot isolated 2D structures be synthesized using chemical methods beyond small sizes?
a) Phonon density reduces rapidly
b) Two dimensional crystallites bend into three dimensional structures
c) Lateral forces reduce phonon density
d) Lateral size decreases with increasing phonon density
View Answer
Explanation: Chemical synthesis cannot be applied for the production of isolated two-dimensional crystals beyond small sizes. This is because rapid growth of phonon density with rising lateral size, forces 2D (two-dimensional) crystallites to bend into 3D (three dimensional structures).
9. Choose from the given options the bottom-up process that is applied for graphene production.
a) Mechanical Exfoliation
b) Epitaxial Growth
c) Sonication
d) Chemical exfoliation
View Answer
Explanation: Bottom-up process of graphene production is an additive process which involves the atoms and molecules to build up the desired objects. Bottom-up methods include chemical vapour deposition (CVD), epitaxial growth etc.
10. Choose the incorrect option with respect to the various types of chemical vapour deposition processes.
a) Cold wall
b) Plasma enhanced CVD
c) Hot wall
d) Arc discharge of Graphite
View Answer
Explanation: There are various types of CVD processes used for graphene production depending upon the precursors, material quality, structure and the thickness required. These include plasma enhanced CVD, cold wall, hot wall and so on.
11. Identify the mistake in the given diagram for epitaxial growth of graphene.
a) Incompatible substrate used
b) Graphene is formed on the upper surface of substrate
c) Arrows are in the reverse direction
d) Diagram has no mistake
View Answer
Explanation: Graphene production by the epitaxial growth method is conducted in three major steps. First, the silicon carbide substrate is heated at high temperature and pressure. Second, the silicon atoms evaporate owing to their greater vapour pressure than carbon. This leaves behind the carbon atoms on the remaining substrate. Third, the carbon layers accumulating on the substrate are controlled via regulating the temperature and pressure.
12. This method of graphene production is highly exothermic and involves an oxidation-reduction reaction to produce carbon nanoparticles. Which method is it?
a) Spin coating
b) Mechanical exfoliation
c) Sonication
d) Carbon dioxide reduction
View Answer
Explanation: It is scientifically proven that burning magnesium in an oxidation-reduction reaction with carbon dioxide produces carbon nanoparticles. The formation of this carbon with few layer graphene is the major product along with side products like fullerene.
13. What is the molar ratio of sodium and ethanol taken for the production of graphene using the method of pyrolysis?
a) 1:1
b) 1:2
c) 2:3
d) 3:1
View Answer
Explanation: A solvo-thermal based process is used for the production of sodium ethoxide. The molar ratio of sodium and ethanol taken in a closed vessel for the thermal reaction is 1:1. This compound formed undergoes pyrolysis, resulting in graphene foams that have great structural quality, high purity and high specific surface area.
14. How can macro-scale graphene films be produced?
a) Heavily centrifuging the dispersing liquid medium
b) Restacking thoroughly
c) Sonication of graphite at the interface of two immiscible liquids
d) Chemically treating the graphene solution
View Answer
Explanation: Macro-scale graphene films can be produced by sonicating graphite at the interface of two immiscible liquids. The graphene sheets are adsorbed to the high energy interface between the materials and are kept from restacking. The resulting sheets are extremely conductive and transparent.
15. Find out the sequential order for the graphene production using mechanical exfoliation.
a) Tape is pressed onto the target surface ➜ Tape is peeled off when layers stick to target surface ➜ Adhesive tape is pressed on graphite ➜ Tape is gently peeled off with some layers stuck to the surface
b) Adhesive tape is pressed on graphite ➜ Tape is gently peeled off with some layers stuck to the surface ➜ Tape is pressed onto the target surface ➜ Tape is peeled off when layers stick to target surface
c) Adhesive tape is pressed on graphite ➜ Tape is peeled off when layers stick to target surface ➜ Tape is pressed onto the target surface ➜ Tape is gently peeled off with some layers stuck to the surface
d) Tape is pressed onto the target surface ➜ Tape is gently peeled off with some layers stuck to the surface ➜ Tape is peeled off when layers stick to target surface ➜ Adhesive tape is pressed on graphite
View Answer
Explanation: Mechanical exfoliation employs scotch tape to carry out the entire process. First, the adhesive tape is pressed onto the graphite for few seconds. Second, the tape is peeled off with thick layers of graphite stuck to it. Third, the graphite layers from the tape are transferred to the substrate, generally Si/SiO2 wafers, by gently pressing the tape onto target surface. Finally, the tape is peeled off when layers stick to the target surface.
Sanfoundry Global Education & Learning Series – Nanotechnology.
To practice all areas of Nanotechnology, here is complete set of 1000+ Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
