Scientific Breakthrough in Carbon Nanotube Photonics

Ultraclean carbon nanotubes hold promise for advances in optical fiber communications, solar cells and LEDs

8/7/2013

Dr. Stefan Strauf, Professor in the Department of Physics and Engineering Physics and Director of the NanoPhotonics Laboratory, and collaborators James Hone and Chee Wei Wong from Columbia University have published a paper in the July 11 edition of Nature Communications. Their article, titled “Prolonged Spontaneous Emission and Dephasing of Quantum Dot Excitons in Air-Bridged Carbon Nanotubes,” describes an improved fabrication process for carbon nanotubes, potentially leading to brighter light sources and more effective solar cells. They were able to increase the spontaneous light emission from an individual carbon nanotube by two orders of magnitude compared to previously reported experiments. They were also able to achieve a fourfold prolonged coherence time of the light emission.

“Dr. Strauf’s groundbreaking advances with carbon nanotubes represent a significant scientific breakthrough that could herald technological innovation in numerous important industries such as quantum computing and solar energy,” says Dr. Michael Bruno, Dean of the Charles V. Schaefer, Jr. School of Engineering and Science.

A carbon nanotube is a cylindrical carbon molecule that exhibits extraordinary strength, unique electrical properties, and efficient heat conduction. It has well-established applications in nanoelectronics and more recently has attracted tremendous interest as a nanomaterial for next-generation optoelectronics (electronic devices that source, detect and control light for optical fiber communications, solar cells and LEDs) and quantum photonic devices that have the potential to revolutionize information processing, telecommunications, sensing and measurement.

Carbon nanotubes have attracted enormous interest for optoelectronics due to the unique ability of the material to maintain the stability of electron states called excitons even at room temperature. An environment of extreme cold is usually required. An exciton comes about when a (negatively charged) electron in a carbon nanotube is excited (raised to a higher energy level) but remains bound to a positively charged “hole” in the lower energy level. The exciton thus carries energy but not a net electric charge. Photons are absorbed when the electron enters the exciton state and light emitted when the electron recombines with the hole. The absorption can be used to create solar cells, while the emission can be used to create devices like LEDs, lasers, and quantum light sources.

Despite the promise of this innovative material, its light emission has generally been dimmer than theorists had expected. The majority of experiments on carbon nanotubes to date reveal low quantum efficiencies as well as dependence on the environment and chemical processing. This is detrimental to their usefulness in devices and other applications. According to Dr. Strauf, “Understanding the intrinsic photophysical properties of carbon nanotubes is very interesting scientifically and also essential to realizing efficient devices.” To address these inefficiencies, Dr. Strauf and his collaborators devised an improved fabrication process for carbon nanotubes. They discovered that impurities introduced by the growth techniques and their proximity to a substrate masked the intrinsic optical properties. Their ultraclean and air-suspended carbon nanotubes can potentially lead to brighter light sources and more effective solar cells.

According to Dr. Rainer Martini, Director of the Department of Physics and Engineering Physics, “This work constitutes a major advance in carbon-nanotube based photonics and will generate even more interdisciplinary inquiry in this field.”

About the Department of Physics and Engineering Physics

The mission of the Department of Physics and Engineering Physics is to provide a world-class scientific research and academic environment that fosters creation of new knowledge while educating and inspiring students at all levels as well as motivating faculty and support staff, to acquire, use, and advance the competencies needed to lead in scientific discovery and in the creation, application and management of technology to solve complex problems, invent new processes and products, and build new enterprises.  The Department has broad research programs, with special emphasis on the fields of atomic, molecular, and optical physics (AMO), photonics technology, quantum optics, and quantum information science.

Learn more: www.stevens.edu/ses/physics