Nanotechnology – taking it to the people
Glossary
atom. The fundamental unit of all matter consisting of a nucleus of protons and neutrons surrounded by orbiting electrons (or in the case of hydrogen, just one electron). For more information see Back to Basics: Atoms and molecules (Australian Academy of Science).
catalyst. A substance that increases the rate of a chemical reaction without actually undergoing any change itself.
composites. Composite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart – they do not dissolve or blend into each other. One material (the matrix or binder) surrounds and binds together a cluster of fibres or fragments of a much stronger material (the reinforcement). For more information see our Nova topic Putting it together – the science and technology of composite materials.
electrical conductivity. When a voltage is applied across a substance, an electric current will only flow if the substance conducts electricity. When salts dissolve in water, ions are formed and the solution (the electrolyte) will conduct electricity. As a general rule, the higher the concentration of ions in solution (ie, the higher the salt concentration) the better the solution conducts electricity; in other words, its electrical conductivity increases. Electrical conductivity is often expressed in units such as deciSeimens per metre (dS/m). Rain water, for example, has a conductivity of 0.02-0.05 dS/m, while sea water has a conductivity of 50-60 dS/m.
fuel cell. A device that converts energy from chemical reactions directly into electrical energy. The simplest fuel cell 'burns' hydrogen in a flameless chemical reaction to produce electricity. In order to 'burn' the hydrogen a fuel cell needs a source of oxygen and this is usually obtained from air. The only by-product from this type of fuel cell is water. For more information about fuel cells see our Nova topic Fuelling the 21st century.
molecule. The smallest unit of a chemical compound that can exist. It consists of two or more atoms held together by chemical bonds. Molecules can vary greatly in size and complexity.
nanometre (nm). One-millionth of a millimetre (or one-billionth of a metre). This is the scale at which we measure atoms and the molecules they make. For example, ten hydrogen atoms laid side by side measure a nanometre across and a pin head is around a million nanometres wide. The 'machines' inside our cells and the molecular constructions they put together are measured in nanometres.
nanopowders. Nano-sized particles exhibit a range of physical, chemical and biological properties that are quite different to bulk materials of the same substance. Industry is now making use of these changed properties to enhance the functionality of many products.
nanotubes. Extremely small tubes made from atoms such as carbon nanotubes or boron nitride nanotubes. For more information see IPE nanotube primer (Institut de Physique des Nanostructures, Switzerland).
solar cells. Convert light energy into electrical energy. Also known as photovoltaic cells. A solar cell is made of thin wafers of two slightly different types of silicon. One, doped with tiny quantities of boron, is called P-type (P for positive) and contains positively charged 'holes', which are missing electrons. The other type of silicon is doped with small amounts of phosphorus and is called N-type (N for negative). It contains extra electrons. Putting these two thin P and N materials together produces a junction (often refered to as P-N junction) which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Though most widely used solar cells are made of silicon, other materials could also be used to create P-N junctions.
ultraviolet (UV). A form of electromagnetic radiation. UV radiation has shorter wavelengths than visible light and it therefore carries more energy. It is divided into three broad categories: A, B and C. UV-A has the longest wavelength and is the least damaging form, although sufficient exposure will cause sunburn. UV-B damages proteins in unprotected organisms and can cause cancer, while UV-C is extremely dangerous because it can cause mutations in DNA.
visible light. The wavelength of visible light ranges from 400 to 700 nanometres while the wavelength of X-rays ranges from about 0.01 to 10 nanometres. The relatively long wavelength of visible light sets the limit of how small an image it can produce. For more information see Electromagnetic radiation (Back to basics, Australian Academy of Science).
wavelength. The distance between two adjacent wave crests. Visible light and X-rays are both electromagnetic waves and differ from each other only in the length of the wave. The wavelength of visible light ranges from 400 to 700 nanometres while the wavelength of X-rays ranges from about 0.01 to 10 nanometres. The relatively long wavelength of visible light sets the limit of how small an image it can produce. For more information see Electromagnetic radiation (Back to basics, Australian Academy of Science).
Posted March 2006.