Let us begin with the revised introduction of nanotechnology, and then we will get ahead with the heterogeneous properties of the nanoparticles and their structure.
Definition of Nanotechnology:
Nanotechnology is the collaboration of the physics, chemistry, biology, computer science and material science integrated with engineering entering the nanoscale. This means science and engineering focused on making the particles, things and devices at the atomic and molecular scale.
Definition of Nanoparticles:
Nanomaterials or the Nanoparticles are the set of particles or the substances where atlas one dimension is less than approximately 100 nm.
Classically, a Nanomaterial is an object that has at least one dimension in the nanometer scale, approximately 1 to100 nm.
Note: Richard Feynman is known as the father of nanotechnology.
Classification of the nanomaterials:
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Due to the reduction in the spatial dimension, or confinement of particles or quasi particles in a particular crystallographic direction within a structure generally leads to changes in physical properties of the system in that direction.
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Hence, classification of the nanostructure materials and systems essentially depends on the number of dimensions which lie within the nanometer range.
A. Systems confined in 3 dimensions [Zero dimension structures]
Examples: Nanoparticles, Nanograins; Nanoshells; Nanocapsule, Nanorings, Fullerenes, colloidal particles, activated carbon, nanoporous silicon;quasi crystals.
B. Systems confined in 2 dimensions [One dimension structures]
Examples: Nanorods, Nanofilaments, Nanotubes, quantum wires, nanowires.
C. Systems confined in 1 dimension [two dimension structures]
Examples: discs, platelets, ultrathin films, super lattices, quantum wells.
Now let us list out the various properties of the Nanoparticles
Magnetic properties:
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Magnetic nanoparticles are used in a wide range of applications, like imaging, bio-processing, refrigeration as well as high storage density magnetic memory media.
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The large surface area to volume ratio results in a substantial proportion of atoms having different magnetic coupling with neighboring atoms, leading to differing magnetic properties.
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Bulk gold and platinum are nonmagnetic, but at the nanoparticle size they act as magnetic particles. Gold nanoparticles become ferromagnetic when they are capped with the appropriate molecules, such as Thiol.
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Giant magnetoresistance (GMR) is a phenomenon observed in nanoscale multilayer consisting of strong ferromagnetic (Fe, Co,Ni ) and a weaker magnetic or nonmagnetic buffer (Cr, Cu). It is usually employed in data storage and sensing.
Optical properties:
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In small nanoclusters the effect of reduced dimensionality on electronic structure has the most profound effect on the energies of the highest occupied molecular orbital which is the valence band and the lowest unoccupied molecular orbital, essentially the conduction band.
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The optical emission and adsorption occurs when the transition of the electrons occur between these two states.
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Semiconductors and many metals show large changes in optical properties, such as color, as a function of particle size.
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Colloidal suspensions of gold nanoparticles have a deep red color, which becomes progressively more yellow as the particle size increases.
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Gold spheres of 10 to 20 nm exhibit red color.
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Gold spheres of 2 to 5 nm exhibit yellow color.
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Gold spheres of >20 nm exhibit purple color
Similarly,
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Silver particles of 40 nm exhibit blue color
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Silver particles of 100 nm exhibit yellow color
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Prism shaped silver particles red color.
Other properties which may be affected by reduced dimensionality include photocatalysis, photo-conductivity, photoemission and electroluminescence.
Electronic properties:
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The changes which occur in electronic properties as the system length scale is reduced are related mainly to the increasing influence of the wave-like property of the electrons (quantum mechanical effects) and the scarcity of scattering centers.
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As the size of the system becomes comparable with the de-Broglie wavelength of the electrons, the discrete nature of the energy states becomes apparent once again, although a fully discrete energy spectrum is only observed in systems that are confined in all three dimensions.
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In certain cases, conducting materials become insulators below a critical length scale, as the energy bands cease to overlap. Owing to their intrinsic wave-like nature, electrons can tunnel quantum mechanically between two closely adjacent nanostructures, and if a voltage is applied between two nanostructures which aligns the discrete energy levels in the DOS, resonant tunneling occurs, which abruptly increases the tunneling current.
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Conduction in highly confined structures, such as quantum dots, is very sensitive to the presence of other charge carriers and hence the charge state of the dot.
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These Coulomb blockade effects result in conduction processes involving single electrons and as a result they require only a small amount of energy to operate a switch, transistor or memory element.
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All these phenomena can be utilized to produce radically different types of components for electronic, optoelectronics and information processing applications, such as resonant tunneling transistors and single-electron transistors.
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