Molecular Electronics Take a Nanostep Closer to Reality

Electronics are about to get very, very, very small. New research from Japanese and Taiwanese researchers describes potentially the first organic molecule with both the stability and conductivity necessary to implement electronics at the molecular level for practical real-world applications.

First, understand that the metallic wires running through your various electronic devices are like giant, cavernous tunnels compared to the electrons they exist to transport. While a mere drop (a single electron) might be enough to do the job of communicating a bit of information, what you get is a torrent filling that entire tunnel with electricity. The result is a tremendous amount of wasted space and power to move something that fundamentally requires almost zero space and power.

This is where so-called molecular electronics come in—trading wires and other relatively bulky metallic components for nanocomponents built from molecular building blocks, e.g. the smallest stable structures allowed by physics.

Instead of building electronics "top down"—whittling and forming some material (like copper) into the size and shape needed for an application—the molecular approach builds them "bottom up," single atom by single atom. If such a scheme could be implemented practically, things would really never be the same. Transistors, resistors, and wires would all become something beyond even invisible.

Making things in this fashion is tricky though. First there's the enormous challenge inherent in designing around systems that can be altered with the introduction of a single electron. How can insulate something susceptible to such minute fluctuations?

There's also the problem of materials. Organic conductive polymers are used in molecular applications, but these have myriad disadvantages. Not only are they often toxic and expensive, they are prohibitively difficult to process and may break down in moisture-rich, normal atmospheric conditions. As such, molecular electronics applications remain limited.

Enter picene, the sister molecule to a compound called pentacene and one component of the nasty black "pitch" that results from petroleum distillation. Pentacene, a purple powder found in abundance across the universe, has been thought to be a possibility for the molecular electronics future, but it's proven to be unstable as a conductor, breaking down in normal environmental conditions.

Pentacene consists of five rings of the organic chemical compound benzene lined up in a row, while its picene sibling arranges those same rings into a "W" shape. This configuration, according to a study published this week in The Journal of Chemical Physics,appears to boast both the high conductivity of pentacene and the stability needed for practical applications.

The researchers behind the new study tested out their material using single layers of picene fixed to silver plates, observing the interaction between the two materials with help from an atomic-scale imaging technique called scanning tunneling microscopy.

While the same configuration using pentacene resulted in a large amount of interaction between the metal and the molecule—analogous to a frayed wire in the macro-world—this interaction was much more easily controlled with picene, which boasts a comparatively weak connection to the metal.

"The weak interaction is advantageous for molecular [electronics] applications because the modification of the properties of molecular thin film by the presence of the [silver] is negligible and therefore [the] original properties of the molecule can be preserved very close to the interface," said Yukio Hasegawa, one of the authors of the current paper and a researcher at the University of Tokyo, in a statement.

While it's possible to prevent some of the pentacene/silver interaction using a separating layer of organic molecules, this somewhat defeats the purpose. Eliminating this layer, according to Hasegawa, is "essential for achieving high-quality contact with metal electrodes." If you can't connect your nanowire to a circuit, consider it pretty much worthless.

The molecular mechanism beyond picene's seeming imperviousness to metallic interference is still something of a mystery. The next steps for Hasegawa and his team involve testing the silver/picene interaction in the presence of varying levels of oxygen. Picene is at its most useful, with its highest "carrier mobility," in oxygen-rich conditions.

How picene's interactivity fares in future experiments will determine whether future electronics might enable a smartwatch small or light enough that you'd actually want to wear the thing.