Nanotechnology refers broadly to a field of applied science and technology whose unifying theme is the control of matter on the atomic and molecular scale,normally 1 to 100 nanometers (1-10 nm called narrow and 1-100 broad nanotechnology),and the fabrication of devices with critical dimensions that lie within that size range. It is a highly multidisciplinary field,drawing from fields such as applied physics,material science,device physics,super molecular chemistry,self-replicating machines and robotics,chemical engineering,mechanical engineering and electrical engineering. Much speculation exists as to what may result from these lines of research. Nanotechnology can be seen as an extension of existing sciences into the nanoscale,or as a recasting of existing sciences using a newer,more modern term.
The term nanotechnology has evolved over the years via terminology drift to mean anything smaller than microtechnology,such as nano powders,and other things that are nanoscale in size,but not referring to mechanisms that have been purposefully built from nanoscale components. This evolved version of the term is more properly labeled nanoscale bulk technology,while the original meaning is now more properly labeled molecular nanotechnology (MNT),or nanoscale engineering,or molecular mechanics,or molecular machine systems,or molecular manufacturing.
In abstract Nanotechnology is the engineering of functional systems at the molecular scale. This covers current work and concepts that are more advanced. Basically the word nano means one billionth and anything between 1 nm to 100 nm will refer to nanotechnology. In its original sense,nanotechnology refers to the ability to construct items from the bottom-up or top-down methods,using techniques and tools being developed today to make highly advanced products.
Nanotechnology is often referred to as a general-purpose technology. That is because in its natural form it will have significant impact on almost all industries and all areas of society. It offers better built,longer lasting,cleaner,safer,and smarter products for the home,for communications,for medicine,for transportation,for agriculture,for environment,and for industry in general.
A key understanding of nanotechnology is that it offers not just better products,but a vastly improved means of production. A computer can make copies of data files essentially as many copies as you want at little cost. It may be only a matter of time until the manufacture of products becomes as cheap as the copying of files. That is the real meaning of nanotechnology,and why it is sometimes seen as the next industrial revolution.
Two main approaches are used in nanotechnology. In the bottom-up approach,materials and devices are built from molecular components which assemble themselves chemically by principles of molecular recognition. In the top-down approach,nano objects are constructed from larger entities without atomic-level control. The impetus for nanotechnology comes from a renewed interest in interface and colloidal science,coupled with a new generation of analytical tools such as the atomic force microscope (AFM),and the scanning tunneling microscope (STM). Combined with refined processes such as electron beam lithography and molecular beam epitaxy,these instruments allow the deliberate manipulation of nanostructures,and led to the observation of novel phenomena.
Examples of nanotechnology in modern use are the manufacture of polymers based on molecular structure,and the design of computer chip layouts based on surface science. Despite the great promise of numerous nanotechnologies such as quantum dots and nanotubes,real commercial applications have mainly used the advantages of colloidal nanoparticles in bulk form,such as suntan lotion,cosmetics,protective coatings,drug delivery and stain resistant clothing.
 Different chemical and physical approaches were developed for nanosilver preparation such as:ball milling,a flame by vapor phase reaction and condensation,chemical reduction and coprecipitation has been employed to control the particle size (up to 10 nm) and morphology. More recently,new preparation methods have been developed such as sonochemical reactions,gel-sol,microwave plasma and low energy cluster beam deposition.