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Research & Development

French researchers develop ‘single-molecule’ LED

12 Feb 2014

First achievement of "OLED-like" emission by one molecule of sulfur-hydrocarbon.

What its developers are calling “the ultimate challenge in the race to miniaturize LEDs” has now been solved by a team led by the Institut de Physique et de Chimie des Matériaux de Strasbourg, France, in collaboration with the Institut Parisien de Chimie Moléculaire and the French Atomic Agency: they have developed the first ever single-molecule LED.

The device is formed from a single polythiophene wire placed between the tip of a scanning tunneling microscope (STM) and a gold surface. It emits light only when the current passes in a certain direction.

The team of Guillaume Schull says this experimental achievement represents “another step towards creating components for a molecular computer in the future”. The work was recently published in the journal Physical Review Letters.

How it works

The polythiophene wire is a good electrical conductor. It comprises hydrogen, carbon and sulfur, and is used to make larger LEDs already on the market. The wire is attached at one end to the tip of a scanning tunneling microscope, and at the other end to the gold surface.

The scientists collect and analyse the light emitted when a current passes through this nanowire. They observe that the thiophene wire acts as a light emitting diode: light is only emitted when electrons pass from the tip of the microscope towards the gold surface. When the polarity is reversed, light emission is negligible.

In collaboration with a theoretical team from the Service de Physique de l'Etat Condensé, the researchers show that this red light is emitted when an electron combines with a positive charge (a hole) in the nanowire and transmits most of its energy into a photon. For every 100,000 electrons injected into the thiophene wire, a photon is emitted in the “red wavelength range”.

Schull added, “From a fundamental viewpoint, this achievement gives researchers a new tool to probe phenomena produced when an electrical conductor emits light and it does so at a scale where quantum physics takes precedence over classical physics. Scientists will be able to optimize certain substances to produce more powerful light emissions. Finally, this work is a first step towards making molecule-sized components that combine electronic and optical properties, which could form the basis of a molecular computer.”

About the Author

Matthew Peach is a contributing editor to optics.org.

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