Introduction to Nanoscience and Nanotechnology. Chris Binns
Чтение книги онлайн.

Читать онлайн книгу Introduction to Nanoscience and Nanotechnology - Chris Binns страница 12

Название: Introduction to Nanoscience and Nanotechnology

Автор: Chris Binns

Издательство: John Wiley & Sons Limited

Жанр: Отраслевые издания

Серия:

isbn: 9781119172253

isbn:

СКАЧАТЬ but for the moment consider Figure I.1, which shows, schematically, the size scale of interest in nanotechnology (The Nanoworld) with sizes plotted on a logarithmic scale. For reasons that will become clear in Chapter 1, the upper edge of the Nanoworld is set at about 100 nm. Even though this is hundreds of times smaller than the tiniest mote you can see with your eyes, and is smaller than anything that can be resolved by the most powerful optical microscope, a chunk of matter this size or bigger can be considered to be a “chip off the old block.” That is, a very tiny piece of ordinary material. If we were to assemble pieces of copper or iron this big into a large chunk, the resulting block would behave exactly as we would expect for the bulk material. Thus, nanotechnology does not consider pieces of matter larger than about 100 nm to be useful building blocks.

      As shown in Figure I.1, viruses are small enough to be inhabitants of the nanoworld whereas bacteria are much larger, being typically over 10 μm (10 000 nm) in size, though they are packed with “machinery” that falls into the size range of the nanoworld (see Chapter 8, Section 8.1.5.3). Going down in size, the figure shows typical sizes of metal particles, containing ~1000 atoms and bucky balls containing ~100 atoms that can be used to produce advanced materials. The properties of these (per atom) deviate significantly from the bulk material, and so assembling these into macroscopic chunks produces materials with novel behavior. Finally, the lower edge of the nanoworld is defined by the size of single atoms, whose diameters vary from 0.1 (hydrogen atom) to about 0.4 nm (uranium atom). We cannot build materials or devices with building blocks smaller than atoms and so these represent the smallest structures that can be used in nanotechnology.

      There are so many aspects to nanotechnology that one of the difficulties in writing about it is finding ways to organize the description into a coherent structure. This book will largely follow a classification scheme introduced by Richard Jones in his book Soft Machines [2] that helps to categorize nanotechnology into a logical framework. He defines three categories in order of increasing sophistication, that is, Incremental, Evolutionary and Radical nanotechnology. These are described below.

      Source: Reproduced under Creative Commons license CC BY‐SA 3.0.

      Most modern nanotechnologists would be proud of the size control of the particles in this picture. Whereas these days a process that involved nanoparticles such as this would be proudly claimed to be nanotechnology, and thus, open the door to research funding, spin‐off companies, etc. The ancients were developing processes that did something invisible to the materials, but nevertheless allowed them to achieve visible changes. In this sense, a lot of incremental nanotechnology can sometimes be considered to be a re‐branding of other more traditional lines of research such as materials science. The nanotechnology title is still useful, however, since nanotechnology is, by its nature, multi‐disciplinary and it encourages cross‐disciplinary communication between researchers.

      The aspect of incremental nanotechnology that has really changed in the modern world is the development of instruments (see Chapter 5) that can probe at the nanoscale and image the particles within materials or devices. Researchers can actually observe what is happening to the particles or grains in response to changes in processing. This not only makes development of new processes more efficient, but also leads to the discovery of completely new structures that were not known to exist and hence new applications. Nature is full of surprises when one studies sufficiently, small pieces of matter, as will be come clear throughout this book.

image

      Source: Reproduced with permission from [3].

      Whereas Incremental Nanotechnology is the business of assembling vast numbers of very tiny particles to produce novel substances, Evolutionary Nanotechnology attempts to produce nanoparticles that individually perform some kind of useful function. They may need to be assembled in vast numbers to form a macroscopic array in order to build a device, but a functionality is built into each one. Such nanoparticles are necessarily more complex than those used in incremental nanotechnology, and will often consist of more than one material and have a surface coating of organic molecules.

      An example of a single nanoparticle device is a single‐electron transistor (SET), that uses a phenomenon known as “Coulomb blockade” to effect transistor action on individual electrons (see Chapter 6). The device works in a similar manner to a field effect transistor (FET), that is, it is conducting or not conducting through the main terminals depending upon the value of a voltage applied to a third “gate” electrode. The difference is that the “on” and “off” states control single electrons hopping through the device, and the action is carried out by a single nanoparticle a few nanometers across. The smallest device that has exhibited transistor action this way is a 66‐atom aluminium nanoparticle with a diameter of about 1.5 nm [4].