Ultrafast Cluster Electronics

Hokkaido University researchers have developed a computational method that can predict how clusters of molecules behave and interact over time, providing critical insight for future electronics. This could lead to the creation of a new field of science called cluster molecular electronics.

Single molecule electronics is a relatively new, rapidly progressing branch of nanotechnology using individual molecules as electronic components in devices. Now, Hiroto Tachikawa and colleagues at Hokkaido University in Japan have developed a computational approach that can predict how clusters of molecules behave over time, which could help launch a new field of study for cluster molecule electronics. Their approach combines two methods traditionally used for quantum chemical and molecular dynamic calculations.

They used their method to predict the changes in a computer-simulated cluster of benzene molecules over time. When light is applied to the T-shaped benzene clusters, they reorganize themselves into a single stack; an interaction known as pi-stacking. This modification from one shape to another changes the cluster’s electrical conductivity, making it act like an on-off switch. The team then simulated the addition of a molecule of water to the cluster and found that pi-stacking happened significantly faster. This pi-stacking is also reversible, which would allow switching back and forth between the on and off modes.

Nature Scientific Reports – Water-accelerated π-Stacking Reaction in Benzene Cluster Cation

Abstract

Single molecule electron devices (SMEDs) have been widely studied through both experiments and theoretical calculations because they exhibit certain specific properties that general macromolecules do not possess. In actual SMED systems, a residual water molecule strongly affects the electronic properties of the SMED, even if only one water molecule is present. However, information about the effect of H2O molecules on the electronic properties of SMEDs is quite limited. In the present study, the effect of H2O on the ON-OFF switching property of benzene-based molecular devices was investigated by means of a direct ab initio molecular dynamics (AIMD) method. T- and H-shaped benzene dimers and trimers were examined as molecular devices. The present calculations showed that an H2O molecule accelerates the π-stacking formation in benzene molecular electronic systems. The times of stacking formation in a benzene dimer cation (n = 2) were calculated to be 460 fs (H2O) and 947 fs (no-H2O), while those in a trimer cation (n = 3) were 551 fs (H2O) and 1019 fs (no-H2O) as an average of the reaction time. This tendency was not dependent on the levels of theory used. Thus, H2O produced positive effects in benzene-based molecular electronics. The mechanism of π-stacking was discussed based on the theoretical results.

Conclusion

The calculations presented herein revealed that a H2O molecule accelerates the time of π-stacking formation in a benzene molecular system. The times of stacking formation in the benzene dimer (n = 2) and trimer (n = 3) cations were calculated to be 594 fs (H2O) and 922 fs (no-H2O), and 566 fs (H2O) and 1155 fs (no-H2O), respectively. Thus, H2O showed a positive effect in benzene-based molecular electronics. This tendency was not dependent on the level of theory used for calculations. The acceleration primarily originated from the re-orientation of H2O on benzene cluster cation following the hole capture.

While previous studies have shown that H2O suppresses the conductance and destroys the circuit of electron transport in molecular electronics (i.e., has negative effects) the present study demonstrated that H2O produces positive effects in benzene-based molecular electronics.

SOURCES- Nature Scientific Reports, Hakkaido University
Written By Brian Wang, Nextbigfuture.com

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