Major Milestone in Molecular Electronics Scored by Berkeley Lab and Columbia University Team
A team of researchers from Columbia University and Berkeley Lab’s Molecular Foundry has passed a major milestone in molecular electronics with the creation of a single-molecule diode that outperforms the best of its predecessors by a factor of 50.
“Using an ionic solution, two gold electrodes of dramatically different exposed surface areas, and a single symmetric molecule specially designed by the Luis Campos’ group at Columbia, we were able to create a diode that resulted in a rectification ratio, the ratio of forward to reverse current at fixed voltage, in excess of 200, a record for single-molecule devices,” says Latha Venkataraman, Associate Professor of Applied Physics at Columbia University.
“The asymmetry necessary for diode behavior originates with the different exposed electrode areas and the ionic solution,” says Jeff Neaton, Director of the Molecular Foundry, a U.S. Department of Energy (DOE) Office of Science User Facility. “This leads to different electrostatic environments surrounding the two electrodes and superlative single-molecule device behavior.”
Venkataraman, Campos and Neaton are the corresponding authors of a paper describing this research in Nature Nanotechnology. The paper is titled “Single-molecule diodes with high rectification ratios through environmental control.” The lead author is Brian Capozzi, a member of Venkataraman’s group who discovered the environmental asymmetric technique. Other co-authors are Jianlong Xia, Olgun Adak, Emma Dell, Zhen-Fei Liu and Jeffrey Taylor
With “smaller and faster” as the driving mantra of the electronics industry, single-molecule devices represent the ultimate limit in electronic miniaturization. In 1974, molecular electronics pioneers Mark Ratner and Arieh Aviram theorized that an asymmetric molecule could act as a rectifier, a one-way conductor of electric current. Since then, development of functional single-molecule electronic devices has been a major pursuit with diodes – one of the most widely used electronic components – being at the top of the list.
A typical diode consists of a silicon p-n junction between a pair of electrodes (anode and cathode) that serves as the “valve” of an electrical circuit, directing the flow of current by allowing it to pass through in only one “forward” direction. The asymmetry of a p-n junction presents the electrons with an “on/off” transport environment. Scientists have previously fashioned single-molecule diodes either through the chemical synthesis of special asymmetric molecules that are analogous to a p-n junction; or through the use of symmetric molecules with different metals as the two electrodes. However, the resulting asymmetric junctions yielded low rectification ratios, and low forward current. The Columbia University groups, working together with Neaton and his group, have discovered a way to address both deficiencies.