This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Nanofabrication of Nanoscale Material”.
1. Which of the following statement is incorrect about self-assembly process?
a) Self-assembly may be a result of weak forces like hydrogen bond, static charges etc.
b) Self-assembly can occur in presence of external driving force
c) Molecules having definite shape and size, present in low energy state are unfit for self-assembly
d) Nanoparticles can undergo self-assembly using organic molecules
View Answer
Explanation: Self-assembly can occur if the molecules have definite shape, size and number of atoms. They should also be in the state of low energy. The driving force behind this process has been recognized as an attempt of a system to go to the lowest energy state.
2. What is the advantage of using negative photoresists in optical lithography?
a) Limited resolution
b) Line width is limited to nearly 3µm
c) Resists absorb developer solvent
d) Greater process latitude
View Answer
Explanation: Negative photoresists have a lot of drawbacks in comparison to positive resists. These include limited resolution due to swelling in the exposed cross linked areas, upon absorption of developer solvent. Also, their line width is limited to nearly 3µm. As opposed to positive photoresists, negative resists provide faster photo speed, wider process latitude and considerably lower operating cost.
3. What is the rate of coating in PVD (Physical Vapour Deposition) process?
a) Ultra-high
b) High
c) Medium
d) Very Slow
View Answer
Explanation: The rate of coating in PVD process is very slow. It is a time consuming method aimed at improving abrasion resistance, durability and impact strength of the material coating.
4. What is the function of the RHEED gun in a Molecular Beam Epitaxy (MBE) system?
a) Creates and maintains ultra high vacuum in MBE
b) Heats elements to sublime them slowly
c) Monitors the growth of crystal layers
d) Condense gaseous elements on the substrate
View Answer
Explanation: RHEED stands for Reflection high energy electron diffraction. It is used to monitor the growth of crystal layers. It also assesses the crystal quality that forms the epitaxial layer on the substrate.
5. Which of the following statement does not hold well in the top down approach?
a) Molding small materials by using larger objects
b) Creation of nanoscale devices by using larger ones
c) Frequent use of traditional workshops
d) Involves concepts of self-assembly or molecular recognition
View Answer
Explanation: The basic idea of top down approach is the miniaturization of bulk materials, whereas bottom up approach refers to creation of bulk materials. This is done by integrating atoms, molecules that are used as building blocks for complex objects.
6. Which among the following considerations is not an important one for Ball Milling?
a) Size of the milling media
b) Shape of the feed
c) Density of the milling media
d) Speed of rotation of the milling media
View Answer
Explanation: Ball Milling is a top down process involving crushing of the coarse-grained materials into fine powder. There are certain things that need to be considered during this process which include size, density and speed of rotation of the milling media.
7. Which of the following option denotes the conditions in an Molecular beam epitaxy system?
a) Low vacuum
b) Presence of carrier gases
c) Ultra high vacuum
d) Super cool temperatures
View Answer
Explanation: MBE is a technique for growing thin epitaxial structures on the substrate. MBE takes place in ultra high vacuum (10-8 to 10-12 torr), in the absence of carrier gases, resulting in high purity of the grown films. In solid source MBE high temperatures are required to sublime elements like gallium and arsenic to eventually condense them on to the substrate.
8. What do physical vapour deposition coatings involve?
a) High capital cost
b) Medium capital cost
c) Very low capital cost
d) Moderately low capital cost
View Answer
Explanation: PVD incurs high capital cost. This is because of the requirement of complex machineries that can operate at high temperature and vacuum. Moreover, these machineries have high maintenance cost.
9. Chemical vapour deposition apparatus comprises of several basic components. Which of the following is not one of them?
a) Gas delivery system
b) RHEED Gun
c) Vacuum system
d) Exhaust system
View Answer
Explanation: RHEED Gun (Reflection High Energy Electron diffraction) is an important component in a MBE system. Gas delivery, Vacuum and Exhaust systems are present in a CVD apparatus.
10. Which of the following statement is incorrect regarding the projection lithography?
a) No contact
b) No deterioration
c) No shadow projection
d) Poor resolution
View Answer
Explanation: Projection lithography is a photo lithography process that uses light to produce patterns. This method uses photoresists as casting solvents that have excellent resolution.
11. Choose the incorrect statement with respect to the objective behind reduction of solvent concentration in soft baking.
a) Avoids mask contamination
b) Prevents bubble formation
c) Improves the resist adhesion
d) Maximizes the dark erosion
View Answer
Explanation: Soft baking decreases the solvent concentration in order to: i. Avoid the contamination of masks, ii. Prevent foaming or bubbling by nitrogen during exposure, iii. Improve adhesion of the resist to the substrate, iv. Minimize the dark erosion during development.
12. The performance of a lithographic exposure is not determined by which of the following parameters?
a) Resolution
b) Repeatability
c) Instrument cost
d) Throughput
View Answer
Explanation: The performance is majorly determined by three parameters –Repeatability, Resolution and Throughput. Repeatability measures the accuracy of alignment of patterns on successive masks. Throughput measures the rate of exposure that is the number of wafers exposed per hour for a given mask level. Finally, resolution specifies the minimum dimension that can be transferred to a resist film.
13. Why is physical vapour deposition coating done?
a) To improve hardness of the substrate
b) To increase friction of the substrate
c) To reduce oxidation resistance
d) To improve the efficiency through the reduction of component life
View Answer
Explanation: PVD coatings are deposited for multiple reasons. These include friction reduction, wear resistance, improved hardness and increased efficiency through improved performance and longer component life.
14. What process involves the structural organization or pattern formation from the pre-existing components of a disordered system?
a) Optical Lithography
b) Molecular beam epitaxy
c) Ball Milling
d) Self-assembly
View Answer
Explanation: Self-assembly technique is the spontaneous organization of a disordered system from pre-existing components, usually without external direction. It generates structural organization on all scales from molecules to galaxies.
15. What kind of metal organic compound is Ni(CO)4?
a) Metal carbonyls
b) Metal alkyls
c) Metal alkoxides
d) Metal diketonates
View Answer
Explanation: Nickel tetracarbonyl [Ni(CO4)] is an organo-nickel compound. It is often used as a precursor in chemical vapour deposition process. It has other applications too, such as obtaining pure nickel for industrial purposes, as a catalyst in carboxylation process etc.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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