New Research Explores Making Electrical Contact with Nanotubes
14 Aug, 2007 11:26 am
With walls that can be just one atom thick, carbon nanotubes promise to enable technology that??s smaller, faster and more energy efficient than seems possible with today??s semiconductors.
But no one has yet come up with a standard means of making electrical contact with carbon nanotubes. We hope to solve that problem through a three-year project involving researchers at the University of Texas at Dallas, South Korea's Sungkyunkwan University and the University of Pittsburgh.
The challenge lies in establishing an approach for robust, low-resistance electrical contact between carbon nanotubes and metal electrodes. Perfecting that contact is crucial for optimizing the flow of current, which in turn will determine many properties of nanotube-based devices.
There's a particularly significant challenge in overcoming the high energy barrier at the nanotube-electrode contact that hinders electrons from jumping from a metal electrode to the carbon nanotube. It's thus important to understand the precise nature of the nanotube-metal contact, including the effect of the relatively rough surface of the metal on current density at the contact area.
We have just recently initiated our investigations into these matters, and our success could pave the way for a wide array of nanotube applications that have been discussed, including energy storage, energy conversion devices, biosensors, chemical sensors, field emission displays, radiation sources, hydrogen storage media, nanoscaled semiconductor devices and interconnectors. With an advantage of the nearly one-dimensional electronic structure, electronic transport in carbon nanotubes occurs ballistically over long nanotube lengths and enables them to carry high currents without heating. Previous experimental results show that nanotubes can carry much greater maximum current densities than normal metals, although, as noted, the large contact resistance must first be overcome.
A number of other researchers have previously explored this issue, however most have ignored the nanoscale and microscale description of the contact, which is strongly correlated to the chirality, or asymmetry, and diameter of the carbon nanotube. Therefore, in order to fully account for the charge transfer at the point of metal-nanotube contact, we are modeling various contact metals and studying the intrinsic properties of various nanotubes as well as the nature of nanotube-electrode contacts.
One of our goals is to unify previous studies on contact resistance and to develop a more comprehensive understanding of contact phenomenon. Our hypothesis is that the electrical properties of nanotube-electrode contacts depend strongly on the type of metal employed and on nanotube chirality and diameter, and that these contacts are distinctly different from those of metal-silicon contacts in today's semiconductors.
Ultimately we intend to identify the optimal combination of nanotube diameter and chirality and type of metal.
Ever since they emerged in the early 1990s, nanotubes have promised to enable a whole new wave of technology, including ultra-fast computers that leave today's machines in their dust. By fully understanding and resolving the bottleneck at the connection between tube and electrode we hope to help realize nanotubes promise.
NOTE: The $225,000 grant that is funding this research is one of eight awarded through the new Nano-Bio-Information Technology Symbiosis program, or NBIT, jointly operated by the South Korean Ministry of Science and Technology and the U.S. Air Force Office of Scientific Research. Key collaborators on the project are Young Hee Lee of Sungkyunkwan University and Minhee Yun of the University of Pittsburgh.
Reference: Moon, Kim et al. "Schottky Barrier Engineering in Carbon Nanotubes with Various Metal Electrodes" IEEE journal, 2007