This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Characteristics of Nanowires”.
1. Why is the quantization of conductivity more pronounced in semiconductors?
a) Higher effective mass
b) Lower threshold voltage
c) Lower gate voltage
d) Lower electron density
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Explanation: Nanowires undergo a quantization in energy. This effect is more prominent in semiconductors such as the silicon and GaAs in comparison to metals. The lower electron density and effective mass can be attributed for this prominence in quantization of energy in semiconductors.
2. Choose the incorrect statement from the following.
a) Nanowire conductivity undergoes a quantization of energy
b) Nanowires electrical conductivity falls under the regime of ballistic transport
c) Nanowires have unbounded atoms that are often a source of defects within the wires
d) Nanowires shrink in size with simultaneous increase in edge effects
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Explanation: The conductivity of nanowires undergoes quantization in energy, assuming discrete values. Electrical conductivity of nanowires is strongly influenced by edge effects and do not fall under the regime of ballistic transport. These nanowires have unbounded atoms that are often a source of defects within them. Nanowires whenever shrink in size; the surface atoms increase in number compared to the atoms within the nanowire which results in increase of edge effects.
3. Why do gold nanowires have such high yield strength upon decreasing their size?
a) Increased defects in solids
b) Poor gate control over the channel
c) Lack of dislocations
d) Dielectrophoretic manipulation
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Explanation: Gold nanowires are known to have ultra-high strength owing to the extreme increase in the yield strength approaching the theoretical value of E/10. This occurs due to the lack of dislocation in solid. Without dislocation motion, a ‘dislocation starvation’ mechanism is in operation. This leads to huge material stresses accordingly before dislocation motion and then material begins to strain-harden.
4. Why are rough cylindrical wires preferred to the smooth ones for catalytic applications?
a) Increased electrodeposition
b) Reduced electrical conductivity
c) Increased surface area
d) Reduced thermal conductivity
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Explanation: Smooth cylindrical nanowires are suitable for several applications such as sensing of optical or electrical signals. However, in some cases an increased surface roughness is more desired. In catalysts, a larger roughness has effective increase in available surface thus making the catalyst more efficient.
5. The nanocones electrodeposited with CuSO4 based electrolyte have poor mechanical stability.
a) True
b) False
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Explanation: Mechanically stable nanocones, having good electrical contact to the substrate, can be generated via the method of electrodeposition using CuSO4 – based electrolyte in a two-electrode configuration. These have improved mechanical stability and solid contact interface which increase emission current values to a great extent in comparison to metallic cylindrical nanowires.
6. How is it possible to tune the surface roughness of the electrodeposited nanowires?
a) Increasing the available surface
b) Selecting suitable polymer membranes
c) Smoothening the nanowires
d) Increasing the electrodeposition
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Explanation: The surface roughness of the electrodeposited nanowires can be altered or tuned by selecting suitable polymer membranes: etched tracks in PC result in smooth channel walls however channels in PET have a rough surface.
7. Why is the conductivity of a nanowire much less than that of the corresponding bulk material?
a) Due to scattering from wire boundaries
b) Due to greater mean free path
c) Due to precise control of the heating mechanism
d) Due to the response of nanowires to an applied load
View Answer
Explanation: The conductivity of a nanowire is much less than that of the corresponding bulk material due to the scattering from the wire boundaries. This has a very significant effect upon reducing the wire width below the free electron mean free path of the bulk material. The decrease in conductivity is also attributed to the quantization in energy in nanowires.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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