Glossary

Atom

The smallest unit of a chemical element, about a third of a nanometer in diameter. Atoms make up molecules and solid objects.

Metrology and Standards

Metrology and standards underpin everything we take for granted in modern society. For example, they ensure that we can compare one object or material with another, that devices we use are safe, and that they will operate in the manner for which they were designed.

However, most existing standards and measurement techniques are designed for the macroscale. At the macroscale the fundamental properties of a material do not change if you divide it, you simply have less of it. At the nanoscale this is no longer true. Surface area plays a much bigger role in determining physical properties. As an analogy, take a cube of sugar and the same amount of sugar but in granulated form; the granulated sugar will dissolve much more quickly in a hot cup of coffee. At the nanoscale more of the atoms are at the surface of the material and these do not have the same “constraints” as those inside. For example, a particle that has a diameter of 20 nanometres (nm) has 20% of its atoms at the surface, compared with 5% for a 30 nm particle. In quantum dots this difference in size means that the smaller particle will fluoresce with a blue colour, while the larger will be red (even though they are both made from the same material).

The measurements required for nanotechnology include:

• particles- number, surface area, shape, range, whether they are free or stuck together, and proportions of particles with different sizes, shapes etc, within a sample
• larger materials- surface nanoscale characteristics such as indentations, raised features etc
• chemical composition
• physical characteristics- electrical conductivity, magnetism, optical qualities, etc

To achieve this, nanometrologists use a variety of equipment, such as scanning probe microscopes (that can detect nanoscale features and can even add these to a surface), particle counters (that measure the number and size ranges of particles within a sample), and other instruments which can measure the surface area of a particle (by the amount of gas it can bind) and chemical composition.

Glossary

Scanning Probe Microscopy (SPM)

Generic name for different scanning microscopes. These use micro or nano-sized probes to collect information on the surface of a material (e.g. chemical composition, magnetic and electrical properties, topography) through specific interactions between the tip of the probe and the surface under study. For example, this can be electrical measurement (the tunnel current) for a scanning tunnelling microscope (STM) or the attractive or repulsive force in the case of an atomic force microscope (AFM).

Glossary

Quantum Dot

This is a nanoscale object (a diameter of a few tens of nanometres) constructed from metallic or semiconductor material. Quantum dots have unique electrical properties, which can be used for example to store electrons or to transform the colour of light (depending on its size, a quantum dot of the same material will emit (fluoresce) different coloured light). Quantum dots have applications in medical diagnostics, optoelectronics (where light is used to process information) and in energy conversion such as solar cells. They are made from a variety of different compounds, such as cadmium selenide.