Important Questions in Nano Devices

Important Questions in Nano Devices

Part- A '2' Marks Q & A

1. Define nano materials.

Nanophase materials are newly developed materials with grain size at the nanometre range (10^-9 m), i.e., in the order of 1 - 100 nm. The particle size in a nano material is 1 - 100 nm.

2. Define density of states.

It is defined as the number of available electron states per unit volume in an energy interval E and E + dE. It is denoted by Z (E).

3. Define Fermi energy.

It is defined as the highest energy level occupied by the electron at OK in metal.

4. What is a quantum confinement?

It is a process of reduction of the size of the solid such that the energy levels inside become discrete.

5. What is quantum structure?

When a bulk material is reduced in its size, atleast one of its dimension, in the order of few nanometres, then the structure is known as quantum structure.

6. What is quantum size-effect?

When the size of a nanocrystal becomes smaller than the de Broglie wavelength, electrons and holes get spatially confined, electrical dipoles get generated, the discrete energy levels are formed.

As the size of the material decreases, the energy separation between adjacent levels increases. The density of states of nanocrystals is positioned in between discrete (as that of atoms and molecules) and continuous (as in crystals).

Quantum size effect is most significant for semiconductor nanoparticles.

7. What is single electron phenomena?

Present day, transistors require 10,000 electrons. Rather than moving many electrons through transistors, it may very well be practical and necessary to move electrons one at a time. The phenomena in known as single electron phenomena.

8. Define Coulomb - Blockade effect.

The charging effect which blocks the injection or rejection. of a single charge into or from a quantum dot is called Coulomb blockade effect.

9. What is single electron tunneling?

The quantization of charge can dominate and tunneling of single electrons across leaky capacitors carries the current. This is called single electron tunneling.

10. What is a Single Electron Transistor?

SET is three-terminal switching devices which can transfer electrons from source to drain one by one.

11. What are the advantages of single electron transistor?

i. The fast information transfer velocity between cells (almost near optic velocity) is carried out via electrostatic interactions only.

ii. No wire is needed between arrays. The size of each cell guille can be as small as 2.5 nm. This made them very suitable for high density memory.

iii. This can be used for the next generation quantum computer.

12. What are the limitations of single electron transistor?

i. In order to operate SET circuit at room temperature, the size of the quantum dot should be smaller than 10 nm.

ii. It is very hard to fabricate by traditional optical lithography and semiconductor process.

iii. The methods must be developed for connecting the individual structures into logic circuits and these circuits must be arranged into larger 2D patterns.

13. What are the applications of single electron Transistor?

i. A variety of digital logic functions, including AND or NOR gates, is obtained based on SET operating at room temperature.

ii. It is used for mass data storage.

iii. It is used in highly sensitive electrometer.

iv. SET can be used as a temperature probe, particularly aidTo in the range of very low temperatures.

v. SET is a suitable measurement set-up for single electron spectroscopy.

vi. It is used for the fabrication of a homo-dyn receiver operating at frequencies between 10 and 300 MHz.

14. What is a carbon nano tube?

The carbon nanotubes are the wires of pure carbon like rolled sheets of graphite or like soda straws.

15. What are the types of carbon nano tube structure?

Three types of nanotube structures are considered by rolling a graphite sheet with different orientations about the axis.

They are

(i) Armchair structure

(ii) Zig-zag structure

(iii) Chiral structure luc

16. How carbon nanotubes are classified

Based on the number of layers, the carbon nanotubes are classified as

(i) Single-walled (SWNTs)

(ii) Multi-walled (MWNTs).

In multi-walled nanotubes, more than one CNTs are coaxially arranged.

PART B (16 Marks Questions)

1. Explain the electron density in bulk material and size dependence of fermi energy.

2. Explain quantum confinement and quantum structures in Nano material.

3. Discuss density of states in quantum well, quantum wire and quantum dot structure.

4. Discuss quantum size effect and band structure of nanocrystals.

5. Describe construction and working of single electron transistor.

6. Write short notes on conductivity of metallic nanowires ballistic transport, quantum resistance and conductance.

7. Describe the carbon nano tubes with their properties and applications.