What is nanotechnology

1 INTRODUCTION:
The emerging fields of nanoscience and nanoengineering are leading to
unprecedented understanding and control over the fundamental building blocks of all physical matter. This is likely to change the way almost everything —from vaccines to computers to automobile tires to objects not yet imagined —is designed and made.
The word “Nano” means dwarf in Greek language. Use it as a prefix for any unit like a second or a meter and it means a billionth of that unit. A nanosecond is one billionth of a second. And a nanometer is one billionth of a meter—about the length of a few atoms lined up shoulder to shoulder. A world of things is built up from the tiny scale of nanometers. The thousands of cellular proteins and enzymes that constitute eg. The human body are a few nanometers thick. Enzymes typically are constructions of thousands of atoms in precise molecular structures that span some tens of nanometers.
That kind of natural nanotechnology is about ten times smaller than some of the smallest synthetic nanotechnology that has been prepared until now. The individual components of an Intel Pentium III microprocessor span about 200 nanometers. This is the reason that computing is so powerful and easy these days. Nanotechnology makes microelectronics to be mere hints of what will come from engineering that begins on the even smaller scales of nanostructures.



What is nanotechnology?:
This is a term that has entered into the general and scientific vocabulary only
recently but has been used at least as early as 1974 by Taniguchi.1 nanotechnology is defined as a technology where dimensions and tolerances are in the range of 0.1-100 nm (from size of the atom to about the wavelength of light) play a critical role. This definition is however too general to be of practical value because it could as well include, for example, topics as diverse as X-ray crystallography, atomic physics, microbial biology and include the whole of chemistry! The field covered down by nanotechnology is narrowed down to manipulation and machining within the defined dimensional range by technological means, as opposed to those used by craftsman, and thus excludes, for example, traditional glass polishing or glass colouring
techniques.


1.3 History of nanomaterials:
The history of nanomaterials began immediately after the big bang when
Nanostructures were formed in the early meteorites. Nature later evolved many other Nanostructures like seashells, skeletons etc. Nanoscaled smoke particles were formed during the use of fire by early humans. The scientific story of nanomaterials however began much later. One of the first scientific report is the colloidal gold particles synthesised by Michael Faraday as early
as 1857.2 Nanostructured catalysts have also been investigated for over 70 years.3 By the early 1940’s, precipitated and fumed silica nanoparticles were being manufactured and sold in USA and Germany as substitutes for ultrafine carbon black for rubber reinforcements. Nanosized amorphous silica particles have found large-scale applications in many every-day consumer products, ranging from non-diary coffee creamer to automobile tires, optical fibers and catalyst supports. In the 1960s and 1970s metallic nanopowders for magnetic recording tapes were developed.4 In 1976, for the first time, nanocrystals produced by the now popular inert- gas evaporation technique was published by Granqvist and Buhrman.5 Recently it has been found that the Maya blue paint is a nanostructured hybrid material.6 The origin of its color and its resistance to acids and biocorrosion are still not understood but studies of authentic samples from Jaina Island show that the material is made of needle-shaped.



1.4.2 Why so much interest in nanomaterials?:
These materials have created a high interest in recent years by virtue of their
unusual mechanical, electrical, optical and magnetic properties. Some examples are
given below:

??Nanophase ceramics are of particular interest because they are more ductile at elevated temperatures as compared to the coarse-grained ceramics.
??Nanostructured semiconductors are known to show various non-linear optical properties. Semiconductor Q-particles also show quantum confinement effects which may lead to special properties, like the luminescence in silicon powders and silicon germanium quantum dots as infrared optoelectronic devices Nanostructured semiconductors are used as window layers in solar cells.
??Nanosized metallic powders have been used for the production of gas tight
materials, dense parts and porous coatings. Cold welding properties combined with the ductility make them suitable for metal-metal bonding especially in the electronic industry.
??Single nanosized magnetic particles are mono-domains and one expects that also in magnetic nanophase materials the grains correspond with domains, while boundaries on the contrary to disordered walls. Very small particles have special atomic structures with discrete electronic states, which give rise to special properties in addition to the super-paramagnetism behaviour. Magnetic nanocomposites have been used for mechanical force transfer (ferrofluids), for high density information storage and magnetic refrigeration.
??Nanostructured metal clusters and colloids of mono- or plurimetallic composition have a special impact in catalytic applications. They may serve as precursors for new type of heterogeneous catalysts (Cortex-catalysts) and have been shown to offer substantial advantages concerning activity, selectivity and lifetime in chemical transformations and electrocatalysis (fuel cells). Enantioselective catalysis were also achieved using chiral modifiers on the surface of nanoscale metal particles.
??Nanostructured metal-oxide thin films are receiving a growing attention for the realisation of gas sensors (NOx, CO, CO2, CH4 and aromatic hydrocarbons) with enhanced sensitivity and selectivity. Nanostructured metal-oxide (MnO2) find application for rechargeable batteries for cars or consumer goods. Nanocrystalline silicon films for highly transparent contacts in thin film solar cell and nano-structured titanium oxide porous films for its high transmission and significant surface area enhancement leading to strong absorption in dye sensitized solar cells.

??Polymer based composites with a high content of inorganic particles leading to a high dielectric constant are interesting materials for photonic band gap structure produced by the LIGA.



1.4.3 Influence on properties by "nano-structure induced effects":
For the synthesis of nanosized particles and for the fabrication of nanostructured materials, laser or plasma driven gas phase reactions, evaporation-condensation mechanisms, sol-gel-methods or other wet chemical routes like inverse micelle preparation of inorganic clusters have been used, that will be discussed later. Most of these methods result in very fine particles which are more or less agglomerated. The powders are amorphous, crystalline or show a metastable or an unexpected phase, the
reasons for which is far from being clear. Due to the small sizes any surface coating of the nano-particles strongly influences the properties of the particles as a whole. Studies have shown that the crystallisation behaviour of nano-scaled silicon particles is quite different from micron-sized powders or thin films. It was observed that tiny polycrystallites are formed in every nano-particle, even at moderately high temperatures.
Roughly two kinds of "nano-structure induced effects" can be distinguished:
??First the size effect, in particular the quantum size effects where the normal bulk electronic structure is replaced by a series of discrete electronic levels,
??and second the surface or interface induced effect, which is important because of the enormously increased specific surface in particle systems.
While the size effect is mainly considered to describe physical properties, the
surface or interface induced effect, plays an eminent role for chemical processing, in particular in connection with heterogeneous catalysis. Experimental evidence of the quantum size effect in small particles has been provided by different methods, while the surface induced effect could be evidenced by measurement of thermodynamic properties like vapour pressure, specific heat, thermal conductivity and melting point of small metallic particles. Both types of size effects have also been clearly separated inthe optical properties of metal cluster composites. Very small semiconductor (<10 nm), or metal particles in glass composites, and semiconductor/polymer composites show interesting quantum effects and non-linear electrical and optical properties. The numerous examples, which are not complete, by far, indicate that these materials will most probably gain rapidly increasing importance in the near future. In general, properties, production and characterisation methods and their inter-relations are however not yet satisfactorily understood. Hence, efforts need to be made to enable the directed tailoring of nanophase, nanoscopic and nanocomposite materials needed for future technical and industrial applications.