Question

What is nanotechnology? What is nanomaterial? What is atom, molecule, ion, and bond? Describe strong and weak bonds. Explain sp^2 hybridization using frames and arrows representing electrons, and principles of a semiconductor using a models of Si atom. What is conduction and valence band and what is energy gap? What would be the necessary energy and wavelength of photons to excite electrons in materials with energy gap of 5.5 eV (diamond), 1.1 eV(Si) and 0.57 eV(Ge)? What would be necessary temperature increase to make Si semiconductor? What are carbon nanotubes, what types do you know and what is their typical geometry (dimensions)? What is chirality, explain electrical conductivity and draw a schematic of zigzag, armchair and chiral arrangements. Explain the dependence of yield stress in nanograin-size materials. What is lithography and what are the limits of this method? Explain size of table feature depth of focus and resolution issues. What is self-assembly? Explain principle of single nanoparticle devices using carbon nanoelectronics examples.

Answer 1

1) Nanotechnology: The branch of technology that deals with study and application of small things of size less than 100 nanometres, especially the manipulation of individual atoms and molecules.

Nanomaterial: A material having particles or constituents of nanoscale dimensions, or one that is produced by nanotechnology.

2) Atom: The smallest particle of a chemical element that can exist.

Molecule: A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Bond: A bond is a lasting attraction between atoms that enables the formation of chemicalcompounds.

Strong bond: The attaraction between atoms is strong it forms strongest bond. Ex: Ionic bond.

Weak bond: The attaraction between atoms is weak it forms weakest bond. Ex: Vanderwall bond.

3)
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4) Conduction Band: A delocalized band of energy levels in a crystalline solid which is partly filled with electrons. These electrons have great mobility and are responsible for electrical conductivity.

Valance band: The valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states.

Bnad Gap: The band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors.

The necessary energy for diamond is greater than 5.5 eV, Si is >1.1 eV and Ge is > 0.6 eV. The wavelength is calculated by using formula E=hc/lambda, then corresponding wavelength lambda=1239 nm.eV/E(eV).

So for Diamond wavelength=225 nm, Si =1126 nm and Ge=2065 nm.

The band gap energy of semiconductors tends to decrease with increasing temperature. When temperature increases, the amplitude of atomic vibrations increase, leading to larger interatomic spacing. The interaction between the lattice phonons and the free electrons and holes will also affect the band gap a little. The relationship between band gap energy and temperature can be described by Varshni's empirical expression,

${\displaystyle E_{g}(T)=E_{g}(0)-{\frac {\alpha T^{2}}{T+\beta }}}$ where E_g(0), ? and ? are material constants.