Nanotechnology research to offer new breed of electronics?
2 mins read
Researchers at Arizona State University have demonstrated a new way of controlling electrical conductance of a single molecule by exploiting its mechanical properties. The findings, which have been published in the journal Nature Nanotechnology, could offer advances in the design of ultra tiny electrical gadgets in biological and chemical sensing, as well as telecommunications and computer memory.
When electrical devices are shrunk to a molecular scale, both electrical and mechanical properties of a given molecule become critical. Specific properties may be exploited, depending on the needs of the application. Here, a single molecule is attached at either end to a pair of gold electrodes, forming an electrical circuit, whose current can be measured. Picture courtesy of Arizona State University.
According to Nongjian Tao, a researcher at the Biodesign Institute at the university, the team was able to examine the electromechanical properties of single molecules sandwiched between conducting electrodes. When a voltage was applied, a resulting flow of current could be measured. The team was then able to vary the conductance by as much as an order of magnitude, by changing the orientation of the molecule with respect to the electrode surfaces. The molecule's tilt angle was altered, with conductance rising as the distance separating the electrodes decreased and reached a maximum when the molecule was poised between the electrodes at 90°.
"Some molecules have unusual electromechanical properties which are unlike silicon based materials," said Tao. "A molecule can also recognise other molecules via specific interactions. These unique properties can offer tremendous functional flexibility to designers of nanoscale devices."
According to the researcher, the reason for the dramatic fluctuation in conductance was due to the so called pi orbitals of the electrons making up the molecules and their interaction with electron orbitals in the attached electrodes. "Pi orbitals may be thought of as electron clouds, protruding perpendicularly from either side of the plane of the molecule. When the tilt angle of a molecule trapped between two electrodes is altered, these pi orbitals can come in contact and blend with electron orbitals contained in the gold electrode - a process known as lateral coupling. This lateral coupling of orbitals has the effect of increasing conductance."
Tao said that in the case of the pentaphenylene molecule they used, the lateral coupling effect was pronounced, with conductance levels increasing up to 10 times as the lateral coupling of orbitals came into greater play. In contrast, the tetraphenyl molecule used as a control for the experiments did not exhibit lateral coupling and conductance values remained constant, regardless of the tilt angle applied to the molecule.
"This means molecules can now be designed to either exploit or minimise lateral coupling effects of orbitals, thereby permitting the fine tuning of conductance properties, based on an application's specific requirements," said Tao. "This modulation technique may also be broadly applied as a new method for evaluating conductance changes in molecular scale systems."
