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Wednesday, 18 September 2019
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Raw materials & technologies, Technologies, Nanotechnology

Zigzag structured nanomaterials

Wednesday, 14 August 2013

Nanostructures can be produced very precisely and in large numbers with a new method - interesting for new effectpigments and totally new embedded functions for coatings.

Nanohelix as a light antenna: The miniscule nanostructures can be produced very precisely and in large numbers with a new method. The colour of light they absorb can be controlled by their dimensions and composition. They are suited to filtering circularly polarized light.

Source: Andrew G. Mark
Nanohelix as a light antenna: The miniscule nanostructures can be produced very precisely and in large numbers with a new method. The colour of lig...

Combining chemical and physical properties on a small scale

The realization of nanomachines is inching ever closer to reality. Researchers at the Max Planck Institute for Intelligent Systems in Stuttgart, Germany are helping make one of the grand challenges of nanoscience become reality. They have developed a method that makes it possible to manufacture an assortment of unusually shaped and functionalizable nanostructures. It lets them combine materials with widely varying chemical and physical properties at the smallest of scales.

Vapor depositing onto a super-cool surface is the way

The team of scientists headed by Peer Fischer have even grown helical light antennas that are less than 100 nm in length from materials which can typically not be shaped at the nanoscale. This is achieved by vapor depositing the material onto a super-cooled rotating disk. Not only does the process allow for the fabrication of nanostructures more exactly than previous methods, several billion of such nanoparticles can be produced in parallel in a rapid manner.
"We’ve developed a versatile, precise, and efficient process with which three-dimensional nanostructures can be custom fabricated from various materials,” says Fischer. "Up to now, structures less than 100 nm could only be created in very symmetrical, primarily spherical or cylindrical shapes.”

New light reflections possible

With their new method, the researchers are now able to produce hybrid nanoscopic hooks, screws, and zigzag structures by processing materials with very diverse physical properties—metals, semiconductors, magnetic materials, and insulators.

As an example of the possible applications, the researchers produced helices of gold that are suitable as nanoantennas for light. The colour of light that the antennas absorb can be controlled by their shape and material composition. With them, circularly polarised light can for instance be filtered, a process used in projectors for 3D movies. Also, the plane of oscillation of an electromagnetic wave—which is what polarized light is—is rotated either clockwise or anticlockwise depending upon the rotational sense of the metal nanohelix. The effect is orders of magnitude larger per helix than what is seen with naturally occurring materials.

Despite the versatility of the method, not all shapes can be created with it. "Because the structure always grows away from the wafer, no rings, closed triangles or squares can form,” says Fischer. "We are not able to build a nanoscale Eiffel Tower.” Nevertheless, wide-ranging opportunities are open to him and his team.

Nanostructures from a stream of vapor onto gold nanodot islands

Exact control over the shape and structure of the nanocomponents was achieved by the researchers in Stuttgart by means of their elegant method, which can produce several hundred billion copies of a complex structure in about an hour.

With the help of micellar nanolithography, which has been available for several years, they first place billions of regularly arranged nanoparticles of gold onto the surface of a silicon or glass wafer. They deposit gold particles covered in a polymeric shell onto the substrate, which then arrange themselves into a tightly packed, regular pattern. After removing the polymer shell with a plasma, the gold dots remain behind bound to the substrate.

The scientists then place the pre-patterned wafer into what is essentially a stream of metallic vapour at an angle oblique enough that the metallic atoms can only see the tiny gold islands and deposit themselves only at those points. Thus, they quickly grow into nanostructures which can have feature sizes as small as 20 nm.

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