Researchers Dr. Benjamin Lowe and Dr. Oleksandr Stetsovych from FZU have built a QR code more than 1000 times smaller than the width of a human hair and nearly 800 times smaller than the current Guiness World Record holder.
Teaming up with collaborator Dr. Julian Ceddia from Monash University, the researchers used the probe of a scanning tunnelling microscope to precisely arrange atoms, one by one, and create a QR code measuring just 50x50 nm2. An image of the resulting pattern was then acquired using the same microscope.
How was it achieved?
Scanning tunnelling microscopes measure tiny currents that flow when a probe as sharp as an atom is positioned very close to a flat, conductive sample (typically sub-nanometre distances away!). In this set-up, electrons can “jump” across the boundary to produce a current via the quantum mechanical phenomenon known as tunnelling. These microscopes are used by chemists, physicists, and materials scientists all over the world to image materials with atomic-scale resolution.
When operated under vacuum conditions at cryogenic temperatures, the precision offered by these microscopes can be used to interact with matter at the atomic scale. This precision allows atoms and molecules to be picked up, put down, or pushed and pulled across an atomically flat surface.
“We very gently brought our probe, coated in silver atoms, into contact with a silver surface,” explains Dr. Stetsovych. “With just the right parameters, such an interaction can be tuned to deposit a single silver atom on the surface.”
The researchers automated a procedure which performed this interaction at specified points of a 50x50nm2 region to produce the QR code.
“The automation got us most of the way there, but we still couldn’t make our phones read the QR code,” explains Dr. Lowe. “So then, we applied some finishing touches manually to correctly place and align the final few atoms. After this, we were very happy to find that microscope images of the QR code could be scanned from our phones.”
How can this precise control be useful?
The ability to controllably move single atoms around a surface is used by researchers with scanning tunnelling microscopes to precisely control and study interactions.
“Our image is a playful demonstration of the level of control scanning tunnelling microscopes give us,” explains Dr. Ceddia. “But researchers worldwide are using these techniques to build entirely new materials atom by atom - structures that can’t otherwise exist naturally.”
Precise positioning of atoms on surfaces is a potential route towards building qubits for quantum computing or engineering new electronic states by tuning many-body interactions – such as by building chains of magnetic atoms on superconducting surfaces.
So where does the QR code take you?
The researchers are using their new nano-QR code to promote their new competition for the scanning probe microscopy community: SPM Pro Tips.
The website is intended to be an platform for researchers to share more of their data with the community, and to explain their work to a broader audience. Each submission comes with an accessible description about the i platform for researchers to share more of their data with the community, and to explain their work to a broader audience.
“We wanted to create a fun way for scientists in the field to show their creativity and share the amazing capabilities of our microscopes,” explains Dr. Lowe. “We hope that both scientists and non-scientists can laugh at funny submissions, admire beautiful submissions, and maybe learn something about how we use these techniques to study materials at the smallest possible scale.”
Among the posts you will find single molecules that resemble teddy bears, flowers or gummy candies, molecular arrangements shaped like honeycombs or butterflies, and quasiparticles in 2D materials that look like van Gogh's The Starry Night. You can reach the website through the world's smallest QR code or at spmprotips.com.
Browse the gallery, vote for your favourite image and leave a comment. You can also try taking such images yourself with a scanning tunnelling microscope.