Nanometres and nanoscale

A nanometre is a billionth of a metre. Nanoscale can refer to things less than 100 nanometres in size, or to materials so small that they behave differently to normal.

What is a nanometre?

Your fingernails grow about a nanometre every second. That means they grow 86,400 nanometres in a day, but that’s still too small for you to notice a difference.

Look at it another way. If a nanometre was as long as your foot, a centimetre would be the distance from New Zealand to Australia.

A nanometre is very, very small – there are a million of them in a millimetre.

‘Nano’ means ‘a billionth’ (a billion is a thousand million), so:

• a nanometre is a billionth of a metre
• a nanosecond is a billionth of a second.

Compare a nanometre with some measurements you are more familiar with:

• a metre
• a centimetre (a hundredth of a metre)
• a millimetre (a thousandth of a metre)
• a micrometre (a millionth of a metre)

As part of the International System of Units (SI), the standard symbol for nanometre is nm.

You can measure metres, centimetres and millimetres with a ruler, but measuring anything smaller than that is harder. In fact, it is hard trying to even imagine something as small as a billionth of a metre. It helps if you compare things of different sizes.

The head of a pin	1,000,000 nm across	You can see these with your eyes unaided
The page of a book	100,000 nm thick
A human hair	40,000 nm thick
A red blood cell	7000 nm across	You can see these using a light microscope
Bacteria	1000–10 000 nm
Transistor on latest computer chips (there are up to 100 million of them)	100 nm	You need an electron microscope or other device to see these
DNA molecule	2 nm wide
Most atoms	0.1–0.2 nm
10 hydrogen atoms side by side	1 nm long

What is nanoscale?

There is no fixed definition for what nanoscale is, but there are a couple of things that are very important – small size and different properties.

Nanoparticle size

At least one dimension (height, length or depth) is less than 100 nm:

• A nanotube can be much longer than 100 nm, but it is still called a nanoparticle because it is only about 3 nm wide.
• A very thin film of material can be many centimetres wide, but if it is less than 100 nm thick, it is still called a nanofilm.

This definition of nanoscale tends to be used by people who create tiny devices such as pumps and motors out of a few atoms, or by people who deal with very thin surface coatings.

Many nanoparticles are ball-shaped, so all dimensions are small.

Nanoparticle properties

To many scientists, things are at the nanoscale if they are so small that they display different properties to the large scale material. This mostly happens when particles are only a few nanometres across.

For example, you may know that water boils at 100ºC (at a pressure of 1 atmosphere), but that is only true for large amounts of water. A drop of water only 5 nm across boils at 95.9ºC.

One nanoparticle can behave differently to another nanoparticle even if it is only slightly a different size. It may be a different colour, it may have a different melting point, or it may conduct electricity differently.

So, there is more than one definition of what is meant by nanoscale. Learning to understand and make use of these different properties of matter at the nanoscale is what nanoscience is about.