First Single-Molecule LED

Researchers have made the smallest possible organic light-emitting diode

1 min read
First Single-Molecule LED
APS

Illustration: APS
Artist illustration of a single-molecule organic light-emitting diode

By coaxing light out of a single polymer molecule, researchers have made the world’s tiniest light-emitting diode. This work is part of an interdisciplinary effort to make molecular scale electronic devices, which hold the potential for creating smaller but more powerful and energy-efficient computers.

Guillaume Schull and his colleagues at the University of Strasbourg in France made the device with the conducting polymer polythiophene. They used a scanning tunneling microscope tip to locate and grab a single polythiophene molecule lying on a gold substrate. Then they pulled up the tip to suspend the molecule like a wire between the tip and the substrate.

The researchers report in the journal Physical Review Letters that when they applied a voltage across the molecule, they were able to measure a nanoampere-scale current passing through it and to record light emitted from it.

Conventional organic light-emitting diodes are semiconductors sandwiched between two electrodes. A voltage applied between the electrodes creates electrons and holes. When these two oppositely charged particles meet, photons are emitted.

The same thing happens here, except on a much tinier, single-molecule level. When the microscope tip had a large negative voltage, the researchers calculate that one photon was emitted for every 100 000 electrons that surged from the tip and into the molecule. The photon had a red wavelength. When the researchers flipped the voltage bias, the light emission was negligible.

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The Ultimate Transistor Timeline

The transistor’s amazing evolution from point contacts to quantum tunnels

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A chart showing the timeline of when a transistor was invented and when it was commercialized.
LightGreen

Even as the initial sales receipts for the first transistors to hit the market were being tallied up in 1948, the next generation of transistors had already been invented (see “The First Transistor and How it Worked.”) Since then, engineers have reinvented the transistor over and over again, raiding condensed-matter physics for anything that might offer even the possibility of turning a small signal into a larger one.

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