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French researchers develop first ever single-molecule LED

Posted: 07 Feb 2014 ?? ?Print Version ?Bookmark and Share

Keywords:IPCMS? LED? polythiophene? photon?

A team of researchers at the Institut de Physique et de Chimie des Materiaux de Strasbourg (IPCMS, CNRS/Universite de Strasbourg), together with UPMC and CEA, has developed what they say is the first ever single-molecule LED. The LED emits light only when the current passes in a certain direction, noted the researchers.

To achieve this, the researchers used a single polythiophene wire that is considered a good electricity conductor. The wire is made of hydrogen, carbon and sulfur, and is used to make larger LEDs that are already on the market. The polythiophene wire was attached at one end to the tip of a scanning tunneling microscope, and at the other end to a gold surface. The scientists recorded the light emitted when a current passed through this nanowire. The scientists observed that the thiophene wire acts as a LED: light was only emitted when electrons went from the tip of the microscope towards the gold surface. When the polarity was reversed, light emission was negligible.

single-molecule LED

In collaboration with a theoretical team from the Service de Physique de l'Etat Condense (CNRS-CEA/IRAMIS/SPEC), the researchers showed that this light was emitted when a negative charge (an electron) combined with a positive charge (a hole) in the nanowire and transmitted most of its energy to a photon. For every 100,000 electrons injected into the thiophene wire, a photon was emitted. The wavelength was in the red range.

The device offers researchers a tool to probe phenomena that are produced when an electrical conductor emits light and it does so at a scale where quantum physics takes precedence over classical physics. Scientists will also be able to optimize substances to produce more powerful light emissions. The research marks a first step towards making molecule-sized components that combine electronic and optical properties.

- Paul Buckley
??EE Times Europe

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