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Tiny All-Rounder

Nanowires produced under vacuum have huge potential

More effective solar panels, faster computers, more precise medical diagnostic equipment – semiconductor nanowires could contribute to all of them. Materials scientists grow them using very high vacuum levels.

Wire drawn from iron, copper or steel is a practical material that humanity has used since the Middle Bronze Age. Nanowire is only similar in form and name. In addition to metal, nanowire can also be made from a semimetal or pure carbon and is synthesized instead of being pulled from solid raw materials during manufacturing. The crucial difference, however, is the size: several micrometers long at most, with a diameter between five and 100 nanometers. A human hair is about 50,000 nanometers thick and, in comparison, seems like a thick rope one might find on a ship.

High-performance and versatile building blocks

The long structures were discovered at the beginning of the 1990s. Researchers and material scientists soon recognized the potential of such long objects. For example, the tiny snippets are considered to be especially useful in forging ahead with the miniaturization of electronics, taking them from the micro level to the nanoscopic scale.

The tiny dimensions of the nanoworld are ruled by very particular physical laws. Electric current can be more easily controlled in nanowire than in conventional materials because electrons move more quickly – an important aspect for building innovative microchips or rather nanochips. In the future, it will likely be possible to build particularly powerful computers or highly precise sensors for medical diagnostic equipment using nanowires.

Photovoltaics represent a further promising area of application. Conventional solar cells can absorb around 60 percent of sunlight. Nanowires packed side by side could absorb 90 percent. The mini structures can also bundle and emit light. If installed in chips, they could be used as small semiconductor lasers.

Vacuum establishes environment for pure growth

Nanowires need to consist of extremely pure material, free from any contamination in order to display their unique characteristics. This is why they are manufactured using very high vacuum levels. Busch is also active in this field.

First, various atoms or small molecules are shot at silicon carrier plates. The semiconductor crystals subsequently self-organize and grow upward to create the desired wire form. It is even possible to create customized multilayer semiconductor nanowires for specific purposes using this procedure. The individual layers can handle different tasks and additionally expand the technical possibilities. Research is in full swing.
Why do different physical laws apply in the nanoworld?

Classical laws of physics are by no means as universal as we long assumed. As researchers delved deeper into the tiny worlds of the nanoscopic scale, they found something surprising: they crossed a threshold at 50 nanometers. Below it, substances follow quantum-physical laws.

Because nanoparticles are so small, their surface area is very large compared to their volume. These relatively large surfaces make the nanoparticles more prone to chemical reactions. Inertial forces lose their influence while the effect of surface forces like Van der Waals force increases. Surface charges and thermodynamic effects like Brownian movement also play a role – the smaller the particle, the stronger the effect.

This gives nanoparticles much different optical, magnetic and electrical properties than larger particles or solids. For example, gold gleams red to crimson in the nanoworld. Nano-sized water droplets remain stable for hours and can even hover in the air without evaporating. Carbon nanotubes are extremely tear-resistant and elastic. They conduct heat and, depending on the structure, can also conduct current with minimal losses.