Oh developed the process for manufacturing the new nano-OLEDs together with Tommaso Marcato. "In just one single step, the maximum pixel density is now around 2500 times greater than before," adds Marcato, who is active as a postdoc in Shih's group.
By way of comparison: up to the 2000s, the miniaturisation pace of computer processors followed Moore's Law, according to which the density of electronic elements doubled every two years.
Moreover, these tiny light sources could also help to focus on the sub-micrometre range by way of high-resolution microscopes. "A nano-pixel array as a light source could illuminate the most minute areas of a sample - the individual images could then be assembled on a computer to deliver an extremely detailed image," explains the professor of technical chemistry. He also perceives nano-pixels as potential tiny sensors that could detect signals from individual nerve cells, for example.
The basic principle of interacting waves can be aptly illustrated by throwing two stones next to each other into a mirror-smooth lake. Where the circular water waves meet, a geometric pattern of wave crests and troughs is created.
In a similar manner, intelligently arranged nano-OLEDs can produce optical wave effects in which the light from neighbouring pixels mutually reinforces or cancels each other out.
Polarised light - which is light that oscillates in only one plane - can also be generated by means of interactions, as the researchers have already demonstrated. Today, this is at work in medicine, for example, in order to distinguish healthy tissue from cancerous tissue.
Modern radio and radar technologies give us an idea of the potential of these interactions. They use wavelengths ranging from millimetres to kilometres and have already been exploiting these interactions for some time. So-called phased array arrangements allow antennas or transmitter signals to be precisely aligned and focused.
In the optical spectrum, such technologies could, among other things, help to further accelerate the transmission of information in data networks and computers.
As Oh explains, the drive towards miniaturisation is now being enabled by a special ceramic material: "Silicon nitride can form very thin yet resilient membranes that do not sag on surfaces measuring just a few square millimetres."
Consequently, the researchers were able to produce templates for placing the nano-OLED pixels that are around 3,000 times thinner. "Our method also has the advantage that it can be integrated directly into standard lithography processes for the production of computer chips," as Oh underlines.
"Our aim is to connect the OLEDs in such a way that we can control them individually," as Shih relates. This is necessary in order to leverage the full potential of the interactions between the light pixels. Among other things, precisely controllable nano-pixels could open the door to novel applications of phased array optics, which can electronically steer and focus light waves.
In the 1990s, it was postulated that phased array optics would enable holographic projections from two-dimensional screens. But Shih is already thinking one step ahead: in future, groups of interacting OLEDs could be bundled into meta-pixels and positioned precisely in space. "This would allow 3D images to be realised around viewers," says the chemist, with a look to the future.
Research Report: Scalable nanopatterning of organic light-emitting diodes beyond the diffraction limit
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