This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Nanotribology”.
1. Wear of a nanoscale surface is measured by determining the volume of material loss.
a) True
b) False
View Answer
Explanation: Wear of a nanoscale surface cannot be measured by determining the volume of material loss. This is because of the extremely small size of the nano materials which makes the measurement of volume extremely difficult. Wear of a macro scale surface can be measured by determining the volume of the material loss.
2. Why are problems of friction and wear more critical in case of nanodevices?
a) High surface to volume ratio
b) Good conductor of electricity
c) Lubrication is impossible
d) Surface topology
View Answer
Explanation: Micro and nano-devices have high surface to volume ratio that makes the problems of friction and wear more critical. This can be solved by coating the movable parts of these devices with super lubricants.
3. Friction tends to be zero at nanoscale. Which of the following is not a reason for the given statement?
a) Lattice surfaces are commensurable
b) Friction is non-isotropic
c) Disproportionate surface lattice structures
d) Forces offset each other
View Answer
Explanation: Friction tends to be non-isotropic at nanoscale. If two surfaces sliding over each other have disproportionate lattice structures, each atom is subject to different amount of force from different directions. Thus, these forces balance each and net friction amounts to almost zero.
4. Surface analysis equipments like AFM, FFM are used for the detection of wear at nanoscale.
a) False
b) True
View Answer
Explanation: Nanotribology is the science that deals with friction, wear, lubrication and adhesion at nanoscale. Hence, characterization, analysis and modification of interacting surfaces at nanoscale are an integral part of this discipline.
5. What are the factors on which friction depends at nanoscale?
a) Atomic radius and Humidity
b) Interatomic potential energy & Lattice Parameters
c) Lattice Parameters and Density
d) Atomic interaction and Density
View Answer
Explanation: Friction at nanoscale occurs due to interaction of atoms. Factors such as atomic radius, Lattice Parameters, Interatomic potential energy play vital roles in atomic interaction. Temperature and relative motion speed also affect friction.
6. Which of the following is not used as a tool for Nanotribology studies?
a) STM (Scanning Tunneling Microscope)
b) AFM (Atomic Force Microscope)
c) Compound Microscope
d) SPM (Scanning Probe Microscope)
View Answer
Explanation: Compound microscope provides a magnification 1000 times but has very less resolution. Nanotribology studies require high resolution measurements which can be provided by STM, AFM and SPM microscopes.
7. Choose one option that doesn’t fall under the mechanisms of super lubricity.
a) Thermal fluctuations resulting in repulsion
b) Applied electrical voltage causing electrical repulsion
c) Thermal effects cause tip of probe to take multiple jumps in different directions
d) Grafted macromolecules cause thermodynamics repulsion
View Answer
Explanation: Super lubricity involves mechanisms such as: i) Thermodynamic repulsion occurring due to the presence of a layer of free or grafted macromolecules between the bodies; ii) Applied electrical voltage causing electrical repulsion; iii) Repulsion due to electrical double layer; iv) Thermal fluctuations generating repulsion. Thermo lubricity is observed at atomic scale. Thermal effects result in multiple jumps of the tip of atomic force microscope in backward and forward directions.
8. Which of the following material does not manifest exceptional tribological behavior of low friction and wear?
a) Diamond
b) Graphite
c) Graphene
d) Iron
View Answer
Explanation: There are many carbon based nanomaterials like Diamond, DLC (Diamond – like carbon), Graphite, Graphene and others which show exceptional tribological behavior of low friction and wear. Hard carbon materials that possess sharp surfaces usually are resistant to wear.
9. Choose the correct order of working of Atomic Force Microscope (AFM).
a) Deflection of cantilever ➔ Feedback adjusts height of probe ➔ Tip of the cantilever is brought near sample ➔ Feedback output is equal to sample surface topography
b) Tip of the cantilever is brought near sample ➔ Deflection of cantilever ➔ Feedback adjusts height of probe ➔ Feedback output is equal to sample surface topography
c) Feedback output is equal to sample surface topography ➔ Feedback adjusts height of probe ➔ Deflection of cantilever ➔ Tip of the cantilever is brought near sample
d) Tip of the cantilever is brought near sample ➔ Feedback output is equal to sample surface topography ➔ Feedback adjusts height of probe ➔ Deflection of cantilever
View Answer
Explanation: AFM uses a cantilever to which a probe (tip) of nanometer dimensions is fixed. When the tip is brought into proximity of the sample surface, forces acting between the tip and the surface deflect the cantilevers. The feedback adjusts the height of the probe in order to restore the deflection to a user-defined value. The feedback loop now adjusts the separation between the tip and sample continuously during scanning. This keeps the deflection approximately constant. In this position the feedback gives the output as the images of the sample surface topography.
10. Choose one of the following options that comply with the given statement “This microscope can only be used to study conductive surfaces”.
a) Lateral Force Microscope (LFM)
b) Transmission Electron Microscope (TEM)
c) Friction Force Microscope (FFM)
d) Scanning Tunneling Microscope (STM)
View Answer
Explanation: STM is a high resolution microscope that produces images of conductive surfaces at their atomic level. It is based on the principle of tunneling effect. It uses a conducting tip that is brought very close to the surface under examination. Electrons from the sample that is applied with a voltage, tunnel through the gap and reaches the tip of probe causing a flow of tunneling current. This information is utilized to display the images of the surface.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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