Seeing atoms

Nanotechnology is possible partly because tools have been developed to ‘see’ particles of matter a nanometre (nm) across, or smaller. That’s less than a billionth of a metre.

When the idea of nanotechnology was developed in the 1960s, it was just that – an idea. Scientists couldn’t do much to make nanotechnology happen, as they didn’t have the tools to see or work at the nanoscale. So, in some ways, nanotechnology has advanced alongside developments of microscopes.

Optical microscopes

Optical (light) microscopes have been around for many years. You can get magnifications of over 2000 times with a modern light microscope. This is enough to see inside plant and animal cells, but not in much detail. The main limit is the wavelength of light. In effect, many nanoscale objects are so small that light aimed at them misses, and so is not reflected back for us to see. This means that objects of less than 300 nm are distorted under a light microscope.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Transmission electron microscope

Dr Richard Tilley using the transmission electron microscope of the MacDiarmid Institute. The sample is placed in the base of the grey column in front of Richard, and the image is viewed on the computer screen on the right.

Electron microscopes

To magnify things more, a new tool was developed. This came in 1931, with the invention of the electron microscope. Beams of electrons are focused on a sample. When they hit it, they are scattered, and this scattering is used to recreate an image. An electron microscope can be used to magnify things over 500,000 times, enough to see lots of details inside cells. There are several types of electron microscope. A transmission electron microscope can be used to see nanoparticles and atoms.

Scanning probe microscopes

To see atoms in detail, a tool was needed that did not rely on light or beams of electrons. This came in the 1980s, with the development of scanning probe microscopes. When you run your finger over a surface, say paper or carpet, you can tell how smooth or rough it is. A scanning probe microscope works in a similar mechanical way, but using a nanoscale ‘finger’.

There are different kinds of scanning probe microscope that work in slightly different ways:

• An atomic force microscope has a very fine tip, sometimes only an atom wide, which is dragged across a sample surface. The tip rises over atoms and falls into the spaces between. The rise and fall are so small that a laser is used to record the movement. A computer uses the information to produce 3D images of atoms. You see the image on a computer screen, not through an eyepiece like you do in optical microscopes.

• The scanning tunnelling microscope measures changes in electrical current between the probe tip and the atoms on a sample surface.

• In a magnetic force microscope, the tip senses changes in the magnetic structure of the surface at the atomic level.

These scanning probe microscopes were the tools scientists had been waiting for. Nanotechnology now took off. Not only could atoms be seen, it was found that the tips of the microscopes could be used to snag individual atoms and move them around. Scientists were able to make images out of a few atoms, such as letters and smiley faces. More seriously, this new tool meant that it was possible to start working on one of the dreams of some nanotechnologists – the building of nanoscale objects atom by atom. Explore this further in From Faraday to nanotubes – timeline.