Tuesday, November 25, 2008
What will be after Nanotechnology ?
Now the challenge is to push nanofabrication to the scale of single nanometers and even Angstroms.
Historically, the Ångström is named after the Swedish physicist Anders Jonas Ångström (1814–1874), who was one of the founders of spectroscopy. In 1868, Ångström introduced a spectrum chart to systematize solar radiation. The chart expressed the wavelength of electromagnetic radiation of the Sun in multiples of one ten-millionth of a millimeter, now called Angstrom. To give an example, the width of a human hair is typically about one million Angstroms.To make electronic devices with dimensions of a few Angstroms a new technology needs to be developed. Such Angstrom-resolution technology, or angotechnology, to be efficient, needs to provide tools to manipulate single atoms. Recently a possible approach to angotechnology was suggested in a paper by Aref, Remeika, and Bezryadin. Their idea is based on two facts: (1) Single atomic layers of graphite, known as graphene, are now available to scientists through the developments of Novoselov and collaborators. (2) The electron beam in a modern high-resolution Transmission Electron Microscope can be focused into a spot of only half an Angstrom. Remarkably, the electron focus spot diameter is smaller than the distance between neighboring atoms in graphene, which is 1.4 Angstroms. It is suggested by some researchers that if a highly focused e-beam of a TEM should be able to push single atoms from a suspended graphene layer. In order to illustrate the idea, Aref and collaborators focused an electron beam on a carbon nanotube, which is composed of a few rolled layers of graphene. It was indeed possible to remove atoms from the nanotube. The size of the resulting holes was about 20 or 30 Angstroms, which corresponds to hundreds of atoms removed. Although the power of the 2 00 keV e-beam to expel atoms from graphene is evident, the possibility to remove single atoms at will remains to be demonstrated in the experiment. The authors of the paper argue that further optimization of the method should allow the electron-beam expulsion of single atoms (EBESA) from the graphene. The EBESA, when achieved, will be the key to angofabrication and angotechnolgy. Many group compete to achieve the goal of a controlled expulsion of single atoms. This will allow one to fabricate devices with a truly atomic precision, simply by removing unwanted atoms from a monoatomic film, such as graphene.
The image given above illustrates the principle of EBESA, suggested as an approach to the development of angotechnology. There, a ficused beam of electrons (red) targets single atoms of graphene and expels them, on a one-by-one basis. Thus graphene-based electronic devices of any shape can be produced, with atomic precision. The figure above shows a prototype tripod device (green).