Posted in | Quantum Physics

Mechanical Setup for Evaluating Electrical Conductance across Individual Molecules

When an aliphatic thiol, such as alkanethiol, is used to treat noble metals (for example, gold), a uniform monolayer (i.e. a layer with a depth of just one molecule) gets self-organized on the surface. Each individual molecule has the ability to conduct electrons.

This phenomenon is intriguing as the conducting molecules generate distinctive quantum characteristics that could be prospectively applied in electronics such as superconducting switches, transistors, and gas sensors.

Efforts to evaluate the current across such thin layer of molecules have resulted in differing outcomes. Scientists from the Aix-Marseille University, France, have created an innovative, stable mechanical framework for evaluating conductance across individual molecules with a higher success rate. The outcomes of the study have been reported in the Journal of Applied Physics, published by AIP Publishing.

This is really a fundamental study concerning the behavior of one or a few molecules,” stated Hubert Klein, one of the co-authors of the paper, who is an assistant professor at Aix-Marseille University. “The results provide some fresh ideas to people interested in its applications in electronic devices.”

Earlier research works investigated break junction and scanning tunneling microscopy methods to evaluate electrical conductance through individual molecules. Those studies reiterated the effect of temperature on conductance over the molecular layer. As a result of the restrictions in experimental conditions, the outcomes of both methods led to a large spread in the evaluated current.

Klein and his colleagues devised an innovative method based on this observation. Their mechanical framework includes a notched alkanethiol-treated gold wire fixed to a phosphorous bronze bending plate. At ambient conditions, the molecules get self-assembled on the gold wire.

Klein said that the design for this research was developed from an earlier study that produced picometer resolution and mandated the use of a stable framework to prevent drifting of the electrodes at ambient temperature. Simultaneously, he continued his analyses of observations of single molecules by adopting near-field microscopy methods.

We thus naturally had the idea to apply our new custom device to questions of single-molecule conductance,” stated Klein said.

By using the new framework, the researchers could evaluate the impulsive evolution of current near the notch across the gold wire between two metallic electrodes. The researchers ascertained the conductance over an individual molecule by evaluating current jumps from the impulsive connection and de-connection of molecules that are in contact with the electrodes. “Temporal evolution” was brought about by the temperature when mechanical strain no longer had an effect on the molecule.

The team admits to the fact that the mechanical framework adopted in this study cannot necessarily be achieved under standard laboratory conditions. Yet, the stability of this innovative strategy opens the door for further research on nanocontacts and the transport and dynamics of molecules at ambient conditions.

It’s exciting to see that we have access to the behavior of individual nanometric objects at room temperature,” stated Klein. “It’s a great reward to see the efforts of your intuition become a reality.”

The Agence Nationale de la Recherche funded the study. M. Gil, T. Malinowski, M. Iazykov, and H.R. Klein are the authors of the article titled “Estimating single molecule conductance from spontaneous evolution of a molecular contact.”

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