“Nothing exists except atoms and empty space,” said Democritus (460-370 BC). Perhaps it was the whiff of baking bread that led Democritus to imagine that matter was composed of tiny, indivisible building blocks. Atoms, he called them, meaning something that cannot be cut.
If only the Greek philosopher could take a peek through today’s scanning transmission electron microscopes. The above image peers inside garnet, a semi-precious mineral found throughout Earth’s crust, to see neat stacks of yttrium atoms. On the left-hand side of the image, we’re looking down the stacks; on the right-hand side we see the stacks side-on.
Some elements diffused throughout the garnet record the pressure and temperature at which the rocks around them formed. Read these patterns and you can read the Earth’s geological history.
Rare Earth Elements
More than 7,000 years ago Neolithic metallurgists created the first man-made alloy when they toughened copper by adding a little arsenic. Modern alloys, like this one based on magnesium (pictured), form the basis of most of our heavy machinery.
On its own magnesium is light but weak. Add the exotic-sounding atoms neodymium and yttrium to the molten metal, and they lock neighbouring stacks of magnesium atoms together, hardening it.
The patterns of bright yellow spots in the above image show the type of reinforcing structures neodymium and yttrium form when mixed with magnesium.
“If we know how they form, we can start thinking about changing that,” says Monash University microscopist Matthew Weyland. That’s where tomorrow’s alloys could come from.
Pure aluminium is easy to bend – think of kitchen foil. To give this metal the rigidity and strength it needs for buildings, cars, bicycles and planes, you need to mix the aluminium with copper. Once mixed into molten aluminium, it deposits into plates only a few atoms thick (above brightly coloured in yellow). Each cubic millimetre of alloy has thousands of these plates scattered in all directions, reinforcing the aluminium, in the same way steel rods reinforce concrete. When the metal is stressed, the plates act like roadblocks to moving atoms.
Above, we see a section of aluminium alloy revealing one of these plates. The zigzags of brighter spots form where more copper atoms have stacked on top of each other.
Aerospace engineers want ultra-strong, light-weight materials to build planes. Magnesium is light and its alloys are top candidates. But can they be stronger? Yes, by spiking magnesium with 1% of calcium and indium by weight. When added to molten metal, calcium and indium form wafer-thin plates throughout the magnesium, strengthening it. Above we see a cross-section of one such plate. Despite being a mere four atoms wide, they increase the strength of magnesium 10-fold.
Think of the hot gases pouring from your car’s exhaust pipe: burning fossil fuels waste a lot of energy as heat. Researchers are designing ‘thermoelectric’ materials that can turn this heat into electricity. The more heat the material traps, the bigger the temperature difference between hot and cold components in a thermoelectric device and the higher the voltage it can generate. The above image is of a neodymium-titanium oxide thermoelectric material and was used to study a region thought to act as a heat barrier within it. Understanding the arrangement of atoms will help researchers improve the material’s performance. Quentin Ramasse, scientific director of the UK SuperSTEM Laboratory, says: “These images are beautiful but also extremely meaningful.”