A novel printing method that involves positioning individual nanoparticles with great accuracy could make smaller electronic circuits, and might eventually help prevent banknote counterfeiting, researchers say.
Heiko Wolf and colleagues at IBM’s Zurich research lab devised the printing technique with collaborators at the Swiss Federal Institute of Technology, also in Zurich, Switzerland. They used the method to position particles just 60 nanometres in diameter with an accuracy of 100 nm. The printing method was used to form a complete picture containing about 20,000 particles (see image).
The approach is similar to traditional press printing. A printing plate is used to pick up the nanoparticles in a reversed pattern and they are then pressed onto the target surface.
The researchers are able to precisely control where the particles stick to their printing plate by patterning it with tiny indentations – dots or grooves – not much larger than the particles themselves. These grooves were created using established silicon-chip manufacturing techniques.
A drop of liquid containing thousands of nanoparticles is then drawn across the plate. Surface tension forces are particularly strong near the patterned cavities, and this draws the nanoparticles into them. As the drop of liquid moves on, some of the "ink" remains the indented pattern. The plate can then be pressed onto a suitable substrate and the image produced.
The method could perhaps provide a way to foil counterfeiters by marking banknotes with carefully positioned nanoparticles, which could be detected with the right equipment. "This is an interesting application for an every small-scale, advanced printing method," Wolf says, "although it was not the motivation behind our research."
The resulting patterns can also form connected lines to make nanoscale circuitry and could perhaps be used to fabricate other nanoscale features, Wolf says.
In one such experiment, silicon nanowires were created using the same method. Other researchers are developing electronic circuits using nanowires, but it is not yet possible to mass-produce such devices.
The team hopes the method can be used to position smaller nanoparticles, perhaps down to just 2 nm.