The electronics are getting smaller and that causes big problems

Your TV, computer, smartphone, or other electronic device would not work if you were unable to conduct electrical charges across the circuits.

As these devices become more powerful, however, it becomes increasingly difficult to direct these electrical charges exactly where they are needed, as their individual components get smaller and smaller until they reach the nanoscale.

In fact, some of these nanoscale components behave very strangely, to the point where even a single atom can affect or disturb the flow of electrons. Better understanding and control of this nanoscale dynamics is therefore crucial to improving their function.

At the edge

Transistors are the building blocks of microchips and are used in computers, smartphones and amplifiers. Their function depends essentially on how electrons flow near or at the interfaces between their metallic, insulating, and semiconductor materials.

Nowadays, transistors can be up to 10 nanometers wide and get smaller and smaller. If you have a smartphone in your pocket, it probably contains more than a billion transistors.

As this miniaturization trend persists, the performance of electronic components is increasingly affected by the processes of electrons at the material boundaries because the likelihood of an electron approaching an interface increases with decreasing size.

When you are in a room, the smaller the room, the higher the probability that you are standing next to a wall.

A similar phenomenon also affects solar cells, which generate electricity when positive and negative charges are separated within a few nanometers at the boundary between electron-donating and electron-accepting materials.

Light-emitting diodes can work in reverse: they can generate light when positive and negative charges recombine at these boundaries.

Organic molecules - similar to those responsible for photosynthesis in bio-organisms - with semiconducting properties are promising materials for devices such as transistors, solar cells and light-emitting diodes.

They are inexpensive, lightweight, flexible and versatile. Their electronic properties are adjustable and their production consumes less energy than that of silicon.

To the islands

Nano-islands

Recently, we investigated two-dimensional nano-clusters - or "nano-islands" - of different size and shape composed of organic semiconducting molecules on a thin insulator to determine how the electronic properties differ at different locations on them.

We used a scanning tunneling microscope to determine the atomic structure and electronic properties of the organic nano-islands.

Measuring these currents allows us to create an image of the surface of the material to understand where atoms and electrons are located. These measurements were so sensitive that we had to perform them in a laboratory with extremely low vibration at the University of British Columbia in Canada.

Our experiments have shown that the electrons of the molecules at the edge of the nano-islands behave dramatically differently than in the middle. Importantly, these differences in electronic behavior are highly dependent on subtle variations in the position and orientation of nearby molecules.

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We found that when an electron is removed at a certain point in the center of a nano-island, the electrons of the surrounding material react and move in the direction of the positive charge generated by the removal of the electrons.

Similarly, the surrounding electrons moved away from the negative charge generated by the electron addition when an electron was added. This collective movement of electrons polarizes the environment and stabilizes the generated charge: the charge is shielded.

In contrast, the generated charge is much less efficiently shielded when an electron is removed or added at the nano-island interface - where electron transfer becomes important for technological applications.

Imagine a crowded party where someone suddenly leaves the middle of the room and creates an empty space. The people who dance around will occupy that spot much faster than if the person had left the edge of the room.

That's not surprising. What is surprising, however, is the extent of the effect. Our results show that the associated energies are very large.

Tuning in the nano range

Our work proposes a problem for the design of efficient nanoelectronic devices. Subtle features of the nanoscale structure of components not only cause severe electronic effects at their interfaces, but the influence of these effects becomes increasingly important with decreasing component size.

Therefore, it is crucial to control the arrangement of atoms and molecules at the interfaces between these components with incredible precision to develop new technologies with optimal efficiency and functionality.

Our findings open the door to new technical approaches that allow the electronic properties of nanodevices to be tuned by small and precise variations of their atomic structure.

This could be achieved by moving atoms and molecules in a controlled manner on a material surface. Another possibility is the use of supramolecular self-assembly, in which atoms and molecules interact and automatically arrange themselves in desired patterns in the nanoscale.

The effects we have discovered pose a challenge to the future of nanoelectronic devices, but also provide an excellent opportunity to develop faster and more efficient communication, information and electronic technologies.