The melange of definitions of nanomaterials is discussed. Terminology laid down by the International Organization for Standardization (ISO) and European Commission (EC) concerning nanomaterials is described. Ultrafine grained materials with grain size in nanoscale range show unusually higher mechanical strength than coarse-grained materials. Two vital characterizing parameters representing the degree of dominance of surface effects in materials are dispersion and coordination number. Due to predominance of surface effects, nanoparticles are efficient catalytic agents. Melting points of these particles are lower than those of the bulk material, and phase transitions are hazily defined. The onset of quantum size effect in nanomaterials depends on the dimension of the nanomaterial compared to exciton Bohr radius. Due to quantum confinement, the bandgap of a semiconductor nanocrystal is wider than that of the bulk semiconductor. Dependence of bandgap on nanocrystal size leads to emission of light of different wavelengths from these quantum dots. In metals, interaction of light with surface plasmons leads to resonance oscillations at particular frequencies, thereby producing different color effects. Notable magnetic properties of nanomaterials include the display of superparamagnetic behavior, the exhibition of magnetism in materials that are generally believed to be nonmagnetic, and the giant magnetoresistance effect.
Coordination Number External Dimension Bulk Semiconductor Bulk Gold Confinement Energy
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