Nanotechnology - definition

                        

Nanotechnology is a theoretical and experimental field of applied science and technology. It covers a broad range of topics and is focused on controlling and exploiting the structure of matter on a scale below 100 nanometers.[1] Nanotechnology has as its goal the realization of novel materials and devices with features on the nanoscale, drawing from fields such as colloidal science, device physics, and supramolecular chemistry. Much speculation exists as to what new technologies might be invented based upon these lines of research and what the implications for society might be if these become commonplace. In some regards, the term nanotechnology is a marketing term that has been used to sell existing lines of research in a new package. Although there are very high expectations as to what nanotechnology could be able to achieve, much of the actual progress in this field has yet to meet these expectations.

Despite the apparent simplicity of this definition, nanotechnology actually encompasses a very diverse group of lines of inquiry, each taking different approaches and using different methods to progress towards different applications. Nanotechnology cuts across many disciplines, including colloidal science, chemistry, applied physics, biology, and other scientific fields. It could variously be seen as an extension of existing sciences into the nanoscale, or as a recasting of existing sciences using a newer, more modern term. Two main approaches are used in nanotechnology: one is a "bottom-up" approach where materials and devices are built from smaller (molecular) components which assemble themselves chemically using principles such as molecular recognition; the other being a "top-down" approach where they are synthesized or constructed from larger entities through an externally-controlled process.

The impetus for nanotechnology has stemmed from a renewed interest in 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, these instruments allow the deliberate manipulation of nanostructures, and in turn led to the observation of novel phenomena. Nanotechnology is also used as an umbrella term to describe emerging or novel technological developments associated with microscopic dimensions. Despite the great promise of numerous nanotechnologies such as quantum dots and nanotubes, real applications that have moved out of the lab and into the marketplace have mainly utilized the advantages of colloidal nanoparticles in bulk form, such as suntan lotion, cosmetics, protective coatings, and stain resistant textiles.

 

Nanomaterials

This includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions.

  • Colloid science has given rise to many materials which may be useful in nanotechnology, such as carbon nanotubes and other fullerenes, and various nanoparticles and nanorods.
  • Nanoscale materials can also be used for bulk applications; most present commercial applications of nanotechnology are of this flavor.
  • Headway has been made in using these materials for medical applications; see Nanomedicine.            

 

Top-down approaches

These seek to create smaller devices by using larger ones to direct their assembly.

Bottom-up approaches

These seek to arrange smaller components into more complex assemblies.

Functional approaches

These seek to develop components of a desired functionality without regard to how they might be assembled.

  • Molecular electronics seeks to develop molecules with useful electronic properties. These could then be used as single-molecule components in a nanoelectronic device. For an example see rotaxane.
  • Synthetic chemical methods can also be used to create synthetic molecular motors, such as in a so-called nanocar.

Tools and techniques

Nanoscience and nanotechnology only became possible in the 1910's with the development of the first tools to measure and make nanostructures. But the actual development started with the discovery of electrons and neutrons which showed scientists that matter can really exist on a much smaller scale than what we normally think of as small, and/or what they thought was possible at the time. It was at this time when curiosity for nanostructures had originated.

The atomic force microscope (AFM) and the Scanning Tunneling Microscope (STM) are two early versions of scanning probes that launched nanotechnology. There are other types of scanning probe microscopy, all based on the idea of the STM, that make it possible to see structures at the nanoscale. The tip of scanning probes can also be used to manipulate nanostructures (a process called positional assembly). However, this is a very slow process. This led to the development of various techniques of nanolithography such as dip pen nanolithography, electron beam lithography or nanoimprint lithography. Lithography is a top-down fabrication technique where a bulk material is reduced in size to nanoscale pattern.

The top-down approach anticipates nanodevices that must be built piece by piece in stages, much as manufactured items are currently made. Scanning probe microscopy is an important technique both for characterization and synthesis of nanomaterials. Atomic force microscopes and scanning tunneling microscopes can be used to look at surfaces and to move atoms around. By designing different tips for these microscopes, they can be used for carving out structures on surfaces and to help guide self-assembling structures. Atoms can be moved around on a surface with scanning probe microscopy techniques, but it is cumbersome, expensive and very time-consuming. For these reasons, it is not feasible to construct nanoscaled devices atom by atom. Assembling a billion transistor microchip at the rate of about one transistor an hour is inefficient. However, these techniques may eventually be used to make primitive nanomachines, which in turn can be used to make more sophisticated nanomachines.

In contrast, bottom-up techniques build or grow larger structures atom by atom or molecule by molecule. These techniques include chemical synthesis, self-assembly and positional assembly.

Newer techniques such as Dual Polarisation Interferometry are enabling scientists to measure quantitatively the molecular interactions that take place at the nano-scale.

 

 

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