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Catch the sun in its rays

Researchers have created a metallic sponge that increases light energy and can adsorb substances to it

Nanotechnology to improve solar panels. Illustration:
Nanotechnology to improve solar panels. Illustration:

Solar energy is, as we know, clean, green, alternative and renewable energy. Installations that produce solar energy, convert the electromagnetic radiation that comes from the sun into thermal fuel or electricity and thus it can be a significant component of the global energy market.

Prof. Adi Salomon and her team from the Institute for Nanotechnology and Advanced Materials and the Department of Chemistry at Bar-Ilan University are studying the interaction between sunlight and nanometer structures (thousandths of the diameter of a hair) in metals. Thanks to these structures, the light interacts with the free electrons in the metal. This is how strong electromagnetic fields are created on the metallic material, or, in other words, this is how small "antennas" are built in metal surfaces and electromagnetic fields are concentrated on them, which can be used, among other things, for the production of green, environmentally friendly fuel.

Broadly speaking, the idea of ​​Prof. Salomon and her team is to control chemical processes and energy transitions in molecules that are near the nanoscale structures in metals. In fact, these surfaces can be compared to an artificial leaf with energy receptors on it, which absorb the sunlight and transfer it efficiently from one reaction center to another and produce energy from it. This is similar to the process of photosynthesis, where the plant absorbs carbon dioxide, light and water and produces sugar (fuel) from them.

"Thanks to the nanometer structures in the metal, the light manages to sway the free electrons in it. This is how energy centers are created in it that can amplify any optical phenomenon. In this state, the electrons move together like soldiers in an army, at a certain frequency, depending on the shape and size of the nanometer structure, and therefore the electromagnetic field is increased and concentrated in small areas. Nanoscale structures in metals also have a different color and not just a silvery sheen. They can be any color, depending on the shape of the nanometer structure," explains Prof. Salomon.

The latest research done in Prof. Salomon's laboratory, with the support of the National Science Foundation, is Dr. Racheli Ron's thesis. As part of it, the researchers built a structure consisting of nanometer-sized metal particles, woven together into a three-dimensional network - that is, a kind of metallic sponge (the size of which is measured in centimeters). This, through the evaporation of atoms (in an industrial device) on an electrically charged surface. The atoms that were pushed towards the surface of the charged surface changed their trajectory due to repulsive or attractive forces and thus the network structure was created.

The goal of the researchers was to create a new metallic structure whose interaction with light would be increased by several orders of magnitude, so that it would be able to concentrate even more light energy on it and also be able to absorb materials. In the case of the metallic sponge, in addition to the fact that the nano particles cause the scattering of light and the increase of the electromagnetic field, its hollow and light structure, and the huge surface area, allow molecules to penetrate through it and be absorbed by it. So it can be used for a variety of applications. For example, as an optical detector to detect pollutants (such as pesticides in water) and as a catalyst (catalyst capable of accelerating chemical reactions) in the chemical and pharmaceutical industry. In addition, when it is illuminated, "hot electrons" are created - charge carriers that can be used for chemical reactions such as splitting water to produce hydrogen (used for fuel). Moreover, it can be used as electrodes for batteries or electronic capacitors.

Says Prof. Salomon: "Our goal was to produce a structure that combines many structures and holes on a nanometer scale and weave them together so that they serve as an antenna for light. In professional language this is called a porosive structure. In the end we created a structure with very low density, extremely light, electrically conductive (like an electrode), and having a strong interaction with light. Thus it can be used for a variety of applications in the field of chemistry, physics, biology and medicine. In addition, its size is a few centimeters, so it can be seen without a microscope. This is how he combines the nano world with the real world."

Life itself:

Prof. Adi Salomon, married and lives in Tel Aviv. A mountain climber, a lover of French literature and played in the theater group of the Weizmann Institute.