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

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

THIS is a microscope image of tiny implanted atomic-scale structures in a silicon chip, illustrating the design capabilities of quantum devices. Various implants are illustrated with false colors. The smallest features in the image have a resolution of about 30 nanometers, about 1,000 times smaller than a human hair, and comparable in size to the smallest features used in the X-ray study. Image credits: University of Surrey

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

Now the team predicts that X-rays will detect a single atom in a solid sample within about a year.

Dr. Mateus Masteghin, who led the study at the University of Surrey, said:

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

“It’s like combining the capabilities of the Marvel characters Ant-Man and Superman to see through materials and into the smallest structures. This gives us a new tool for developing the ultimate nanotechnology devices, one atom at a time.”

On a regular chest x-ray, heavier and lighter elements are visible differently. This allows us to see metal screws or bones. Density changes contrast, allowing us to distinguish air-filled lungs.

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

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

At Surrey’s Ion Beam Center they implanted just 350 zeptograms of gallium atoms into 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 small cluster of gallium atoms.

Professor Ben Murdin, Head of the Photonics and Quantum Sciences Group at the University of Surrey, said:

“Far from being undesirable, crystal impurities are crucial to the operation of all kinds of technology, from lasers to computer chips.

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

“At the same time, detecting trace elements with this level of precision could lead to exciting new possibilities in chemistry, biology and medicine.”

Dr. Yong Chu, manager of the Imaging and Microscopy Program at NSLS-II, said:

“Detecting such a small impurity deep within a silicon crystal offers many exciting possibilities.

“We are excited to see how much further we can push the detection limit of X-ray microscopes.

“It is possible that with this technique they will be able to detect a single atom in the near future.”

The study was published in the journal Small Methods.