Single-molecule LED breakthrough opens molecular computer opportunities
The device is formed from a single polythiophene wire placed between the tip of a scanning tunneling microscope and a gold surface. The LED emits light only when the current passes in a certain direction. The development, which reveals the interactions between electrons and photons at the smallest scales, paves the way for the creation of components for a molecular computer. The researchers have published their work in the journal Physical Review Letters.
A major benefit of LEDs is that it is possible to make them very small point light sources. This development overcomes a final miniaturization hurdle because the researchers at IPCMS in Strasbourg, in collaboration with a team from the Institut Parisien de Chimie Moléculaire (CNRS/UPMC) claim to have produced the first ever single-molecule LED.
To achieve this, the researchers used a single polythiophene wire which is 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 light emitting diode: 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.
In collaboration with a theoretical team from the Service de Physique de l’Etat Condensé (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 new 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.
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