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New method to obtain nanostructures with previously impossible geometries

Scientists at the CSIC and the Porto University have developed a method for obtaining nanostructures of diverse ferromagnetic materials, which can be applied to magnetic, nanophotonic and magnonic devices. The new procedure avoids the standard lithographic techniques, and shortens production time and economic cost.

Cubic symmetry, one of the geometric shapes obtained with this new method. Image: ICMM/CSIC.Nanostructured materials enable a high and precise control of a device’s performance. The tiniest difference in a material’s characteristics in an optical device can cause the response of light - be it diffraction, reflection or any other - to be different.

The possibility of controlling these nanometric structures is opening a wide range of possibilities for developing photonic, magnetic or magnonic devices. The latter are devices based on the use of electrons’ spin waves (magnons) to transmit, process and detect information.

Scientists at the CSIC and at the Porto University have developed a method to obtain nanoporous templates to produce metallic nanostructured coatings. The new procedure avoids the standard lithographic techniques, shortens production time and results in a more economic method. It is also more versatile as it enables to obtain templates with a wider variety of geometric shapes.

Companies from the nanotechnology sector interested in the commercial exploitation of this patented technology by means of a license are sought. 

Stamping a predefined pattern

The method starts with high-purity alumina layers, on which a mould is pressed in order to stamp a predefined pattern. In the experimental work, this stamping step has been carried out with a CD (a DVD or a BR could also be used), which are of common use and have a very low cost. The CD is used as a stamp to print the grooves that will "guide" the subsequent anodization of the aluminium. This stamping process can be carried out several times, thus changing the printing angle to obtain templates with different geometrical shapes.

With anodization, the aluminum oxidizes and by self-assembly produces a template with ordered nanopores. Subsequently, thanks to a sputtering process carried out on the surface, a metallic coating is obtained that follows the pattern. A single anodizing process is performed, which "increases corrosion resistance and creates better adhesion than bare metal," the scientists declare.

This method allows obtaining metallic nanostructures of different ferromagnetic materials with high applicability. The printing process is short, having a duration of approximately 2 hours, and it can be easily automated. 

As scientists clarify, "the commercial CD, DVD and BR discs are just an example we have used as they are the easiest materials to find for this method. But the proposed technique could be extended to any other type of disc or ‘printing label’ with different geometric shapes."

Examples of geometric shapes obtained with the new method. Image: ICMM/CSIC.

Nanostructures with previously impossible geometries

The greatest advantage, says Manuel Vázquez, principal researcher of the team responsible for the discovery at the Madrid Institute of Materials Science (ICMM-CSIC), “is mainly the possibility  to generate nanostructures with geometries that are impossible to obtain with the conventional method, such as squares, rectangles, triangles, or rhombus. The conventional method only makes it possible to obtain hexagonal shapes. Another advantageous difference between these two methods is that our proposal achieves a larger nanostructured section”.

"With a DVD or a CD, that is worth less than a euro, it is possible to obtain large porous structures", adds David González, another team researcher. "For example, we can obtain stripes of one centimetre and a thickness of 600 or 300 nanometers; square-sized structures of 600 to 300 nanometres and other non-conventional elements, such as triangles, which would be impossible to obtain with conventional lithography, especially in large quantities. This makes it possible to carry out experiments on a larger qualitative and quantitative scale”.

Other advantages include a decrease in time, as well as in economic costs of the process. On one hand, thanks to the stamping, anodization can be done in a single step: "without stamping, a ‘hard anodization’ or two anodization steps would be needed", clarifies David Navas, another scientist and developer of the project.

Regarding costs, "we certainly expect a reduction in the production expenses, although it is difficult to quantify it, since it will vary according to each specific case", he concludes.