Researchers from Monash University’s School of Physics and Astronomy and the Czech Academy of Sciences say they have built what they believe is the world’s smallest scannable QR code by positioning individual silver atoms with a scanning tunnelling microscope.
The QR code measures 50 by 50 square nanometres, which the researchers said is more than 1,000 times smaller in width than a human hair and about 800 times smaller in area than the current Guinness World Record holder.
The team used an ultra-precise scanning tunnelling microscope, operating under ultra-high vacuum and cryogenic temperatures, to place silver atoms one by one on a surface. The method relies on quantum tunnelling, where electrons can tunnel between a needle-like probe and the surface when the probe is brought extremely close, enabling imaging and manipulation at atomic scale.
“This is a playful demonstration of the extraordinary level of control these microscopes give us at the atomic scale,” said Dr Julian Ceddia, a research fellow at Monash University’s School of Physics and Astronomy.
“But the same techniques are also being used by researchers around the world to build entirely new materials atom by atom, structures that simply don’t exist in nature.”
Dr Oleksandr Stetsovych from the Czech Academy of Sciences said the team brought a probe coated in silver atoms into contact with a silver surface. “With the right conditions, we can leave behind a single atom exactly where we want it,” he said.
According to the researchers, much of the construction process was automated, with atoms placed across the 50 x 50 square nanometre area to form the QR pattern, before final adjustments were made manually to ensure it remained scannable. “The automation got us most of the way there,” said Dr Benjamin Lowe from the Czech Academy of Sciences. “Then we manually adjusted and aligned the final atoms to make the QR code fully scannable.”
Beyond the demonstration, the researchers framed the work as an example of atomic-scale fabrication methods being used internationally to investigate quantum behaviours, engineer new electronic states, and explore future quantum materials and computing components.
The QR code also links to “SPM Pro Tips”, an international outreach initiative focused on scanning probe microscopy, inviting researchers to share microscopy images and explain their work for a broader audience via spmprotips.com.
