New material can rewire itself

It is a well-known fact that computers become more advanced each year. But could computers one day become advanced enough to rewire themselves? This is the hope of researchers at Northwestern University, who have recently created a material for use in electronics that can conceivably alter its function based on the operation that the electronic device is carrying out in a particular moment. This could lead to computers with the ability to morph into completely different devices.

Other efforts to create these kinds of materials have used molecular changes. This strategy works, but it takes a long time for the reconfiguration to occur. The team at Northwestern, led by Bartosz A. Grzybowski, Professor of Chemical and Biological Engineering and Biology, tried a different approach, using electrical currents instead.

They have combined silicon and polymer-based electronics to create a new type of electronic material. Silicon-based electronics are devices such as cell phones that use silicon as a semiconductor in transistors. Polymer-based electronics contrast with silicon-based ones in that they use organic, carbon-based molecules to conduct electricity. The researchers refer to the combination of the two as nanoparticle-based electronics.

The material works by redirecting streams of electrons through its different parts. The nanoparticle-based material is composed of particles of gold, referred to as nanoionic nanoparticles, which can conduct electricity because they are coated with a layer of positively charged molecules called ligands. Each particle is about five nanometers wide. The particles were combined by being placed onto a substrate from a methanol solution to form layers that are approximately 100 nanometers thick.

In their experiments, the researchers also added gold electrodes that were attached to an electrometer, which was how a current was applied to the material. The gold particles were then surrounded by smaller, negatively charged atoms, called counterions, that gave the material as a whole a neutral charge. The negatively charged atoms can reconfigure themselves when an electrical charge is applied, but the larger particles are unable to move.

Different electrical charges can be applied to the material in such a way that they can only pass through certain regions. When the negatively charged atoms reconfigure themselves, they create gradients of charge and electric fields. These gradients are very unusual because they continue throughout the entire material and last for a very long time. They dictate where the electric current can run through, blocking or deflecting it so that it can only pass through select regions of the material. The different paths created by the charges are what allow the material to change its function.

So far, the team has only created very basic electronic components, like rectifiers, switches and diodes, which are devices that switch alternating current to direct current and keep the current running in a specific direction. They want to work their way up, however, to building components that can allow computers to change their own circuitry based on what operation is required of them in that moment.

The direction for the future that the researchers hope to take is to eventually start building transistors, and eventually to create entire circuits based on reconfigurable nanoparticles. The researchers believe that particles made up of different metals, different ligands and different types of counterions could alter the response time, how long the material takes to change.

The team's discovery appeared in Nature Nanotechnology under the title "Dynamic Internal Gradients Control and Direct Electric Currents within Nanostructured Materials." It will be the cover story in their November issue.