Decreasing the distance between the graphene quantum dots by 0.35 nanometers increased the device's conductivity by 43-fold, Berry said. Furthermore, because air contains water, reducing air pressure decreased its water content and caused the graphene quantum dots to get closer together, which increased conductivity. Quantum mechanics suggests that electrons have a finite probability to tunnel from an electrode to a nonconnected electrode, Berry said. This probability is inversely and exponentially proportional to the tunneling distance, or the gap between the electrodes.
The research has numerous applications, particularly in improving sensors for humidity, pressure or temperature.
"These devices are unique because, unlike most humidity sensors, these are more responsive in vacuum," Berry said. "For example, these devices can be incorporated into space shuttles, where low humidity measurements are required. These sensors might also be able to detect trace amounts of water on Mars, which has 1/100th of the earth's atmospheric pressure. This is because the device measures humidity at a much higher resolution in vacuum."
While the heart of the device is the modulation of electron tunneling, the response of the device is through the polymer microfiber, Berry said. His team also is looking at changing the polymer to find other applications for this research.
"If you replace this polymer with a polymer that is responsive to other stimuli, you can make a different kind of sensor," Berry said. "I envision this project to have a broad impact on sensing."
The research is supported by Berry's five-year, $400,000 National Science Foundation CAREER award. The research results appear in a recent issue of the journal Nano Letters in an article titled "Electron-tunneling modulation in percolating-network of graphene quantum dots: fabrication, phenomenologi
|Contact: Vikas Berry|
Kansas State University