In an article published in the magazine Nature Nanotechnology On September 2, 2012, scientists from the Brookhaven National Laboratory of the US Department of Energy and the departments of Chemistry and Applied Physics of Columbia University explore the laws that govern the electronic conductance of circuits at the molecular scale.
Conductance measures the degree to which a circuit conducts electricity. In a simple circuit, if the resistors are connected in parallel, the electrons can flow through two different pathways and the conductance of the entire circuit will simply be the sum of the conductance of each resistor.
However, in a molecular circuit, the rules governing the flow of current follow the fundamental principles of quantum mechanics. In most unimolecular circuits, the molecules do not behave like conventional resistors; instead, electrons pass through the molecule. For several years now, nanotechnology experts have suspected, but not proven, that quantum interference effects make the conductance of a two-way circuit up to four times higher than the conductance of a single-way circuit.
Using a new approach, the scientists found that molecules with two built-in pathways had a conductance greater than the sum of the conductance of each pathway, although the increase was not as great as expected.
The group suspects that when calculating the conductance of a molecular circuit, other factors must be taken into account, such as the nature of the bond between the molecule and the electrodes. Currently, they are studying other important questions in molecular electronics, including how the device changes when different metals are used.