Ant-Man and Superman techniques expose tiny hidden impurities in crystals

A breakthrough in atomic-scale X-ray imaging, detecting the presence of just a few hundred gallium atoms inside an otherwise pure silicon crystal, is being celebrated at the University of Surrey.

closeup of a crystal implanted into a silicon chip

Spotting such tiny impurities could help build more efficient and powerful quantum computers.

Now, the team predicts that X-ray imaging will detect a single atom inside a solid sample within the next year or so.

It has long been possible to image single atoms on surfaces or in very thin membranes. Yet, our findings showed we can approach single-atom sensitivity when the impurities are hidden inside a thick sample.

It’s like combining the capabilities of the Marvel characters Ant-Man and Superman to see through materials to the tiniest structures. This gives us a new tool for engineering the ultimate in nanotechnology devices, atom by atom. Dr Mateus Gallucci Masteghin, Research Fellow

In a regular chest X-ray, heavier and lighter elements show up differently. This allows us to see metal screws or bones. Density alters the contrast, which is how we can pick out air-filled lungs.

The Surrey scientists wondered how small a density the X-ray could detect.

They developed an experiment with colleagues at DESY (Germany), UCL, and Madison-Wisconsin to find out. They used the X-ray facilities at the National Synchotron Light Source II at Brookhaven National Laboratory (USA).

At Surrey’s Ion Beam Centre, they implanted just 350 zeptogrammes of gallium atoms in an otherwise pure silicon crystal. That’s about a million billion times less than the mass of an ant or about a billion times less than that of a single cell.

Remarkably, the X-rays were sensitive enough to find the tiny cluster of gallium atoms.

Far from being unwanted, crystal impurities are crucial for the function of all kinds of technology from lasers to computer chips.

This level of detail in impurity detection is critical for advancing quantum computing and could lead to more efficient and powerful quantum devices.

At the same time, trace element detection with this level of precision could lead to exciting new opportunities in chemistry, biology and medicine. Professor Benedict Murdin, Professor of Physics, Head of the Photonics and Quantum Sciences Group