Danish nanophysicists have developed a new method for manufacturing the cornerstone of nanotechnology research — nanowires. The discovery has great potential for the development of nanoelectronics and highly efficient solar cells.

A nanowire made of the two semi- conductors (GaInAs and InAs) with gold (Au) as a catalyst. To the right a schematic illustration of the new cultivation method, where the semi- conductor materials can move both from the top of the gold droplet and from the underside. (Credit: Image courtesy of University of Copenhagen)

It is PhD student Peter Krogstrup, Nano-Science Center, the Niels Bohr Institute at the University of Copenhagen, who developed the method during his dissertation.

“We have changed the recipe for producing nanowires. This means that we can produce nanowires that contain two different semiconductors, namely gallium indium arsenide and indium arsenide. It is a big breakthrough, because for first time on a nanoscale, we can combine the good characteristics of the two materials, thus gaining new possibilities for the electronics of the future,” explains Peter Krogstrup.

We can capture more of the sun’s light

Today only approximately 1 % of the world’s electricity comes from solar energy. This is because it is difficult to convert solar energy into electricity. It is a great advantage for the researchers to be able to combine different semiconductors in the same nanowire.

“Different materials capture energy from the sun in different and quite specific absorption areas. When we manufacture nanowires of gallium indium arsenide and indium arsenide, which each have their own absorption area, they can collectively capture energy from a much wider area.

“We can therefore utilize more solar energy, if we produce nanowires from the two superconductors and use them for solar cells,” explains Peter Krogstrup

The nanowires of gallium indium arsenide and indium arsenide also have great potential in nanoelectronics. They can, for example, be used in the new OLED displays and LEDs. But it requires sharp transitions between the two materials in the nanowire.

No soft transitions

The cultivation of nanowires takes place in a vacuum chamber. The researchers lay a gold droplet on a thin disc comprising of the semiconductor and the nanowire grows up from below. In the transition between the two semiconductor materials in the gold droplet there was previously a mixing between the materials in the gold droplet and there was a soft transition between the materials. With the new method both of the materials can go from the top of the gold droplet or from the underside of the gold droplet. When the material comes from the underside, there is no mixing of the semiconductor materials. There is therefore a sharp transition on the atomic level between the gallium indium arsenide and indium arsenide.

“This sharp transition between the two semiconductors is necessary for the current — in the form of electrons, to be able to travel with high efficiency between the two materials. If the transition is soft, the electrons can easily get caught in the border area. The new mixed nanowire can be beneficial for many areas of nano research around the world,” says Peter Krogstrup, who has been working at the Danish III-V Nanolab, operated in collaboration between the University of Copenhagen and the Technical University of Denmark.

A new collaboration between the company SunFlake A/S and The Danish National Advanced Technology Foundation has recently begun. SunFlake A/S uses nanowires to develop prototypes of solar cells and they can also benefit from the new method in their continuing work. The nanophysicists’ discovery has just been published in the scientific journal Nano Letters.

Nano carbon Graphene is already being produced in decidedly non-nano quantities by Ohio-based Angstron. Yet the atom-thick nano-material was discovered so recently that researchers are still in the process of discovering what to use it for.

Graphene is an extremely low density material, almost an atomic-scale chicken wire made of carbon atoms and their bonds. It has been the focus of much research because of its exceptional electrical, mechanical and optical properties. It holds great promise in renewable energies.

Among the so far underutilized advantages Graphene offers are that it is fifty times stronger than steel, and it has five times the conductivity of copper, with only one quarter of the density.

There’s lots of possible uses for material with these properties, in renewable energy, aerospace, automotive, marine, electronics, construction, medical and telecommunications. And Graphene is a cost effective yet high quality alternative to carbon nanotubes, which were once the wonder nanomaterial, but which tended to stick together in clumps so was extremely difficult to form into composites.

Because of its light weight Graphene is the ideal substitute for copper for aerospace defense against emerging weapons technologies such as electromagnetic pulse as well as lightning strike protection for the aerospace market.

Graphene holds the promise of improving battery technology for hybrid cars and EVs. Adding Graphene to lithium batteries has recently been shown to prolong lithium battery life while increasing usable charge.

Angstron has a 22,000 square foot manufacturing facility in Dayton devoted to making this stuff, and is the first company to isolate single-layer and multi-layer graphene structures and successfully produce nano graphene sheets in large quantities.