May 2, 2014
Controlling carbon nanotube photoluminescence
Silicon microring resonators can control the way a semiconducting single-walled carbon nanotube (s-SWNT) emits light. When polyfluorene (PFO)-extracted s-SWNTs are deposited on these resonators, emission peaks are exhibited that are not only sharp, but tunable. Reporting in Nanotechnology, this is a first step towards a carbon nanotube-based light source integrated on silicon; the next step is working out how to integrate them into more complex devices.
Using the evanescent field from a narrow strip waveguide, carbon nanotube photoluminescence is coupled with a microring resonator. The resonance of a microring can be easily tuned by adjusting the ring diameter, making it easy to match the emission wavelength of the carbon nanotubes. In a typical experiment, microrings have a diameter of 5 or 10 µm, and the carbon nanotubes will emit light around 1300 nm.
Highest quality yet
By depositing a thin layer of around 5 nm thick of PFO-extracted SWNTs on top of these microrings, and using a microphotoluminescence set-up, researchers from the Université Paris-Sud find that very sharp emission peaks are superimposed to the nanotube broad emission peaks. The quality factor (Q) of these emission peaks range from 3000 to 4000, which is the highest values reported so far for integrated silicon cavities coupled to carbon nanotubes.
Photoluminescence excitation spectroscopy is used to further investigate the origins of these peaks. Researchers show that these peaks disappear when the carbon nanotube emission intensity drops, demonstrating the coupling of nanotube light with silicon microrings.
A range of possibilities for future photonic circuits is open, such as electrically driven carbon nanotube networks to produce light in the telecom wavelength range. The next step towards integration of carbon nanotubes into more complex photonic devices will be to investigate the electroluminescent properties of carbon nanotubes integrated into such devices.
More information about the research can be found in the journal Nanotechnology 25 215201.
About the author
Dr Nicolas Izard is the principal investigator at the Institute of Fundamental Electronics at the Université Paris-Sud in France. With a background in material science and carbon nanotube science, his current research interests focus on photonics-based applications.
Adrien Noury is a PhD candidate in the same laboratory.