In a recently published study Nature CommunicationResearchers at Columbia Engineering announced the creation of high-conductivity tunable single-molecule devices in which the molecule attaches to wires through direct metal-to-metal contacts. Their new approach uses light to control the electronic properties of devices and opens the door to broader use of metal-metal contacts that could facilitate electron transport through a single-molecule device.

Competition

As devices continue to get smaller, their electronic components must also be miniaturized. Single-molecule devices that use organic molecules as conduction channels have the potential to solve the miniaturization and functionality challenges faced by traditional semiconductors. Such devices offer the exciting possibility of being controlled from the outside using light, but so far researchers have not been able to prove this.

“With this work, we have opened a new dimension in molecular electronics in which light can be used to control how a molecule binds to the gap between two metal electrodes,” said Latha Venkataraman, molecular electronics pioneer and Lawrence Guzman Professor. Professor of Applied Physics and Chemistry at Columbia Engineering. “This is like flipping a switch at the nanoscale, opening up all kinds of possibilities for designing smarter, more efficient electronic components.”

Approach

Venkataraman’s group has been investigating the interaction between physics, chemistry, and engineering at the nanometer scale by studying the fundamental properties of single-molecule devices for nearly two decades. The main focus is on the construction of single-molecule circuits, which are molecules bound to two electrodes with various functions, where the circuit structure is determined with atomic precision.

His group and those building functional devices with graphene, a two-dimensional carbon-based material, know that making good electrical contacts between metal electrodes and carbon systems is a major challenge. One solution might be to use organometallic molecules and develop methods to attach electrical wires to the metal atoms in the molecule.

To achieve this goal, they decided to explore the use of ferrocene, an iron-containing organometallic molecule that is also considered small building blocks in the world of nanotechnology. Just as LEGO pieces can be put together to create complex structures, ferrocene molecules can be used as building blocks to create ultra-small electronic devices. The team used a ferrocene-terminated molecule consisting of two carbon-based cyclopentadienyl rings containing an iron atom.

They then used light to exploit the electrochemical properties of ferrocene-based molecules to form a direct bond between the ferrocene iron center and the gold (Au) electrode while the molecule is in an oxidized state (i.e., when the iron atom loses one). electron). ). In this case, they found that ferrocene could bind to gold electrodes, which were used to connect the molecule to an external circuit. Technically, oxidation of ferrocene enabled the binding of Au0 to the Fe3+ center.

“Using light-induced oxidation, we found a way to manipulate these tiny building blocks at room temperature, opening the door to a future in which light can be used to control the behavior of electronic devices at the molecular level,” the study leader said. The author, Woojung Lee, holds a Ph.D. student in Venkararaman’s laboratory.

Potential impact

Venkataraman’s new approach will allow his team to expand the types of molecular termination (contact) chemistry they can use to create single-molecule devices. This work also demonstrates the ability to open and close this contact with light to change the oxidation state of ferrocene, revealing a photoswitchable ferrocene-based single-molecule device. Light-controlled devices could pave the way for the development of sensors and switches that respond to specific wavelengths of light, offering more versatile and efficient components for a wide range of technologies.

Set

This work was a collaborative effort involving synthesis, measurement, and calculation. The synthesis was primarily carried out at Columbia University by Michael Inkpen, who was a graduate student in Venkataraman’s group and is now an associate professor at the University of Southern California. All measurements were made by Wujung Li, a graduate student in Venkataraman’s group. The calculations were carried out by both graduate students in Venkataraman’s group and collaborators from the University of Regensburg in Germany.

what’s next

Researchers are now examining practical applications of light-controlled single-molecule devices. This may include optimizing the performance of devices, examining their behavior in different environmental conditions, and developing additional features offered through the metal-metal interface.