Columbia University scientists announced that they have built a 2.6 nanometer-long nanowire with a high conductance showing an unusual increase in its previous record. The nanowire also exhibits quasi-metallic characteristics. The scientists considered the remarkable conductivity to offer great potential for the field of molecular electronics.
Engineer developing a new process in cleanroom
Nanowire Design Improvement
A team of researchers from Columbia Engineering and the department of chemistry at Columbia University, as well as theorists from Germany and synthetic chemists from China, investigated molecular wire designs that would support unpaired electrons on either end. The research was conducted to create one-dimensional analogs of topological insulators (TI). These insulators are insulating in the center and highly conducting through their edges.
Although the most basic 1D TI is composed only of carbon atoms. Its terminal carbons support the radical states (unpaired electrons). However, carbon does not prefer to have unpaired electrons, which makes the nanowire unstable. To increase the molecule's stability, substituting nitrogen for the terminal carbons solved the problem.
Latha Venkataraman, Lawrence Gussman Professor of Applied Physics and professor of chemistry said that ID TI with nitrogen was more stable than the previous composition. He noted they could work with the nanowire at room temperature under ambient conditions.
The experiment broke the potential decay rule when they developed a series of one-dimensional TIs. The decay rule is a formula for the process of a quantity declining at a rate proportional to its current value.
The researchers created a highly conducting channel across the molecules using the two radical-edge states and they achieved reversed conductance decay, especially in a system exhibiting an increasing conductance with increasing wire length.
"What's exciting is that our wire had a conductance at the same scale as that of a gold metal-metal point contacts, suggesting that the molecule itself shows quasi-metallic properties," Venkataraman said.
He added that the work demonstrates that organic molecules can behave like metals at the single-molecule level in contrast to what had been done in the past where they were primarily weakly conducted.
A bis(triarylamines) molecular series was designed and synthesized exhibiting the properties of a one-dimensional TI by chemical oxidation. Single-molecule junctions with molecules attached to the source and drain electrodes were used to assess conductance.
When the wire was longer than 2.5 nanometers, the diameter of a strand of human DNA, the team's measurements revealed that the longer molecules had a higher conductance.
The study is published today in Nature Chemistry.
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Nanowire Challenges and Future Potential
For the past 10 years, researchers attempted using single molecules as conducting wires. These wires had high tunability and distinct electronic characteristic. However, the wire's efficiency decreases when it gets longer.
Liang Li, a Ph.D. student in the lab and a co-first author of the study, said that The Venkataraman lab is continually working on understanding the interplay of physics, chemistry, and engineering of single-molecule electrical devices. Li said they were quite thrilled about the discoveries since they shed insight not just on fundamental physics, but also on potential applications in the future. Developing these specific wires will create the foundation for major scientific advances in understanding transport across innovative systems.
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