2D materials called molecular aggregates are effective light emitters. They work on a different principle than typical organic light-emitting diodes (OLEDs) or quantum dots. Their potential as components for new kinds of optoelectronic devices has been limited by their relatively slow response time. Researchers at MIT, the University of California at Berkely and Northeastern University have found a way to overcome this problem. This could open up a variety of applications for these materials.
The key to enhancing the response time of the 2D molecular aggregates (2DMA) is to couple the material with a thin layer of a metal-like silver. The interaction between 2DMA and the metal that is a few nanometers away boosts the speed of the material’s light pulsed by more than 10 times.
The 2DMA materials show a few unusual properties and have been used to create exotic forms of matter that are called the Bose-Einstein condensates, at room temperature. Other approaches have required extreme cooling. The new work identifies the strong influence that a close sheet of metal can have on the way the materials emit light.
For these materials to be used in devices like photonic chips — which are like semiconductor chips but their operations use light instead of electrons — “the challenge is to be able to switch them on and off quickly,” said Nicholas X. Fang, leader of the research team. This has not been possible before.
When the metal substrate is nearby, the response time for the light emission dropped from 60 picoseconds to 2 picoseconds. Fang said, “This is pretty exciting because we observed this effect even when the material is 5 to 10 nanometers away from the surface," with a spacing layer of polymer in between. That's enough of a separation that fabricating such paired materials in quantity should not be an overly demanding process. "This is something we think could be adapted to roll-to-roll printing," Fang added.
If this is used for signal processing, like sending data by light rather than radio waves, it could lead to a data transmission rate of about 40 gigahertz, eight times faster than the current devices. This is a promising step even though it is still in the early stages.
The team studied one of the many kinds of molecular aggregates that have been developed. There may be other opportunities to find even better variations of this method.
Due to the responsiveness of the material being so strongly influenced by the exact proximity of the nearby metal substrate, these systems could be used for precise measuring tools. "The interaction is reduced as a function of the gap size, so it could be used if we want to measure the proximity of a surface," Fang says.
As the study of these materials continues, one of the next steps is to study the effects that patterning of the metal surface might have because, so far, the tests have only used flat surfaces. Other questions that need to be addressed include determining useful lifetimes of these materials and how they may be extended.
According to Fang, a prototype of a device that uses this system may be produced within a year or so. A paper on this study was published in the journal Proceedings of the National Academy of Sciences.