Nano means 10-9. A nanometer is 1 billionth or 10-9 of a meter. Nanomaterials could be defined as those materials which have structured components with size less than 100nm.


Properties of Nano particles:

Most of properties of solid depends on size of solid. The properties of nanoscale materials are very much different from those at a larger scale. Two principal factors cause the properties of nanomaterials to differ significantly from other materials: (1). Increased surface to volume ratio and (2) quantum effects. These factors can change or enhance the properties such as reactivity, strength and electrical characteristics.

Nanoscience and nano technology

Nano technology is an emerging engineering discipline that applies methods from nanoscience to create products. The difference between nanoscience and nano technology is that between theory and practice. Nanoscience is the study of phenomena and objects at the nanoscale and nano technology deals with the ability to develop and use the technology to manipulate and observe at nanoscale. Nano science is the study of nano structures and nano technology is the application of these knowledge in different industries.

Increase in surface to volume ratio.

Nano materials have a relatively large surface area when compared to the larger form of the materials of same volume (or mass)
Let us consider a sphere of radius r


When the radius of sphere decreases its surface area to volume ratio increases. When size decreased the surface area increases and properties like surface reactivity, catalytic activity, electrical and thermal conductivity melting point, mechanical strength, magnetic property change remarkably.

Given volume is divided into smaller pieces, the surface area increases. When particle size decreased, a greater proportion of atom are found at the surface compared to those inside.

30nm 5% of atoms at its surface 10nm 20% of atoms at its surface 3nm 50% of atoms at its surface

Thus nano particles have a much greater surface area per given volume compared with larger particles. It makes material more chemically reactive as chemical reaction occurs at surfaces.

Quantum confinement effect (Reduction of dimensionality)

Quantum effects can begin to dominate the behaviour of matter at the nanoscale effecting optical, electrical and magnetic behaviour of materials. Quantum confinement is the restricted motion of randomly moving electron in specific energy levels, when the dimension of a material approaches the de- Broglie wavelength of electron. When this occurs the properties change significantly because energy levels become discrete and motion of electrons becomes restricted. Based on the number of dimension that are confined, nanostructures are classified as quantum well (nanosheet), quantum wire(nanowire), and quantum dots.

a) Nanosheets

In nanosheets confinement is present in only one dimension. That is carriers are allowed to move freely along a two dimensional plane.
Suppose the confinement is present along z direction to a small distance L
z and free to move along X and Y directions/ Schrodinger equation in this case is


b) NanoWire

In a nanowire, carriers are confined in tow dimension and allowed to move freely along one diemesion. Suppose the carriers are confined in Y and Z directions to small distance Ly and Lz respectively and free to move in X direction then the wave function and energy will be.


c) Quantumdot

If the carriers are confined in three dimensions, then the nanostructure is called a quantum dot. In this case Schrodinger equation is



The physical, chemical, electronic and magnetic properties depend on the size of the material.

1. Electrical properties:

In nanoscale electrical properties depend on size. The resistance of a material is due to the scattering of conduction electrons with vibrating atoms and impurities. The mean distance travelled between two successive collision is called mean free path and scattering length. When the dimension of solid become comparable to this quantity, the scattering probability decreases and hence electrical properties change. When its size is in the order or mean free path or deBroglie wavelength of electrons or holes which carry current, electronic structure of the system changes completely.

2. Optical properties:

Depending on particle’s size, different colours are seen. Gold nanospheres of 100 nm appears orange in colour while 50nm nanosphere appear green in colour. In nano sized semiconductors particles quantum effects come in to play and optical properties are varied by controlling its size. This particle can be made to emit or absorb specific wavelength of light according to their size.

3. Mechanical properties:

In nanomaterials mechanical properties like hardness, young’s modules, yield strength, fracture toughness etc. show significant variation. At nanoscale, strength of metal enhances. For instance nanocrystalline nickel is as strong as hardened steel. Copper with average grain size of 6mm has five times higher micro hardness compared to a sample having grain size of 50