Carbon nanotubes could one day be used to make electronic devices, ranging from night vision goggles and motion detectors to more powerful solar panels, thanks to techniques developed by Duke University researchers. Their findings were reported in the journal Proceedings of the National Academy of Sciences.
By wrapping a carbon nanotube with a ribbon-like polymer, Duke researchers were able to create nanotubes that conduct electricity when struck with low-energy light that our eyes cannot see. In the future, the approach could make it possible to optimize semiconductors for applications ranging from night vision to new forms of computing. Image Credit: Francesco Mastrocinque
Carbon nanotubes, first found in the early 1990s, are made up of single sheets of carbon atoms rolled up like straws.
Carbon is not precisely a new material, as it serves as the foundation for all life on Earth and is the same substance found in diamonds, charcoal, and pencil lead. Carbon nanotubes are unique because of their extraordinary characteristics. These small cylinders are stronger than steel yet so thin that 50,000 of them would equal the thickness of one human hair.
Since carbon nanotubes are great heat and electricity conductors, they have long been suggested as a possible silicon substitute in the search for quicker, more compact, and more effective electronics.
However, producing nanotubes with desired characteristics is not simple.
Certain nanotubes are categorized as metallic depending on how they are rolled up, which allows electrons to pass through them at any energy. The inability to turn them off is the issue. This restricts their application in digital electronics, where binary states are stored via electrical impulses that are either on or off, much as silicon semiconductor transistors, which alternate between 0 and 1 bits to do computations.
Michael Therien, a Duke chemistry professor, and his colleagues claim to have identified an alternative. The technique converts a metallic nanotube, which always allows current through, into a semiconducting form that can be turned on and off.
The key is in unique polymers—substances whose molecules are joined together in long chains—that coil around the nanotube in an orderly spiral, “like wrapping a ribbon around a pencil,” according to first author Francesco Mastrocinque, who received his chemistry Ph.D. in Therien’s lab at Duke.
They discovered that the effect is reversible. The nanotube’s electronic properties shift from conductor to semiconductor when it is wrapped in a polymer. However, the nanotube returns to its metallic state after being unwrapped.
Additionally, the researchers demonstrated that they could create multiple types of semiconducting nanotubes by modifying the type of polymer that surrounds a nanotube. Only when the proper quantity of external energy is introduced can they conduct electricity.
This method provides a subtle new tool. It allows you to make a semiconductor by design.
Michael Therien, Professor, Duke University
The method’s practical uses are probably a long way off.
Therien added, “We are a long way from making devices.”
Mastrocinque and his co-authors say the work is important because it is a way to design semiconductors that can conduct electricity when struck by light of certain low-energy wavelengths that are common but invisible to human eyes.
The findings of the Duke team, for example, might one day assist others in designing nanotubes that can identify objects concealed in the shadows, such as vehicles or people, by detecting heat released as infrared radiation. One of these nanotube-polymer hybrids would produce an electric signal in response to infrared light, such as that released by warm-blooded animals.
Consider solar cells: With this method, more solar energy can be captured by creating nanotube semiconductors that can convert a wider variety of wavelengths into electricity.
These structures could also be perfect materials for novel computing and data storage systems that process and transport information using electron spins in addition to their charge due to the spiral wrapper on the nanotube surface.
Journal Reference:
Mastrocinque, F., et. al. (2024) Band gap opening of metallic single-walled carbon nanotubes via noncovalent symmetry breaking. Proceedings of the National Academy of Sciences. doi:10.1073/pnas.2317078121.