Any sufficiently advanced technology is indistinguishable from magic. Although that could apply to any scientific marvel, the field of nanotechnology is always a strong candidate, because the manipulation of individual atoms to create new structures still seems like witchcraft.
Straight off the back of a separate team managing to “sew” atomically thin lattices together, a team led by the University of California, Berkeley has managed to piece together what is essentially a minuscule light bulb using a specialized material just three atoms thick.
As noted in their Nature Communications paper, the device itself isn’t nanosized – it’s a few millimeters wide – but the tech that goes into it means that it’s practically invisible.
It’s nanoscale thickness means that “a majority of visible light penetrates the material… so the absorption is low,” co-first author Danny Lien, a postdoctoral fellow at UC Berkeley, told IFLScience. “We also switched out opaque components with transparent ones (quartz and indium tin oxide),” which means that when the device isn’t emitting light itself, it’s completely transparent.
Far from just being a fancy little light source, however, this proof-of-concept design could be a precursor to futuristic tech inventions, including invisible digital screens.
The seemingly magic material in question is a monolayer semiconductor (MS). The first half of that word just means that it’s made of a single layer of atoms; the latter half refers to its ability to moderately conduct electricity. Semiconductors are common features of electronic circuitry because they’re small, reliable, efficient and cheap – but they’re rarely atomically thin.
Light emitting diodes (LEDs) use semiconductors too. Impregnated with opposing electrical charges, light is produced when they encounter each other. In order to keep producing light, these opposing charges must continually be injected into the LED, and this requires two contact points.
MSs are usefully tiny, but this does also present engineers hoping to turn them into compact LEDs with a problem: their miniature dimensions mean it’s difficult to design contact points for them wherein these opposing charges are passed into the material uninterrupted and efficiently.
An MS-impregnated outline of UC Berkeley's Campanile in action. Lien et al./Nature Communications
MSs have cropped up in a few studies recently, including – as noted by a press release – one by the very same team that authored this new study. Back in 2015, the team were fiddling about with the ability of MS materials to generate electric currents using light, and vice versa. They managed to use an MS to emit light, but fell short of transforming it into a true miniature light bulb because of the physical trickiness.
A lot can happen in three years. The team’s new design, which features a sandwich of the MS and an insulator between various electrodes, neatly gets around the problem. Positive and negative charges appear simultaneously in the MS, which allows light to be emitted.
Using four different MS materials, the team showed that four different colors of light can be produced. It wasn’t easy making them, mind you: Making atomically thin, pristine materials required painstaking precision, involving the deposition of chemical vapors – via “mechanical exfoliation” – onto specific mats at high temperatures.
Using this method, the team managed to keep the MS just a handful of atoms thick, but make it magnitudes wider, thus leading to a massive uptick in light intensity. All said and done, the team have created one of the smallest sources of electroluminescence in the world – and it’s transparent when inactive to boot.
The small size does still cause some problems, one notable one being that the MS device is just 1 percent efficient – 25 to 30 times less than conventional LEDs. Still, it’s a step in the right direction, toward a future where, once again, magic emerges from the miniature.
