Self-Healing Nanomaterials
By TECHNION-ISRAEL INSTITUTE OF
TECHNOLOGY
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| Abstract artist’s concept. |
From the Terminator to Spiderman’s suit, self-repairing robots and devices abound in sci-fi movies. In reality, though, wear and tear reduce the effectiveness of electronic devices until they need to be replaced. What is the cracked screen of your mobile phone healing itself overnight, or the solar panels providing energy to satellites continually repairing the damage caused by micro-meteorites?
The field of self-repairing materials is rapidly expanding, and what used to be science fiction might soon become reality, thanks to Technion – Israel Institute of Technology scientists who developed eco-friendly nanocrystal semiconductors capable of self-healing.
Their findings, recently published in Advanced Functional Materials, describe the process, in which a group of materials called double perovskites display self-healing properties after being damaged by the radiation of an electron beam.
The perovskites, first discovered in 1839, have recently
garnered scientists’ attention due to unique electro-optical characteristics
that make them highly efficient in energy conversion, despite inexpensive
production. A special effort has been put into the use of lead-based
perovskites in highly efficient solar cells.
The Technion research group of Professor Yehonadav Bekenstein from the Faculty of Material Sciences and Engineering and the Solid-State Institute at the Technion is searching for green alternatives to the toxic lead and engineering lead-free perovskites. The team specializes in the synthesis of nano-scale crystals of new materials. By controlling the crystals’ composition, shape, and size, they change the material’s physical properties.
Nanocrystals are the smallest material particles that remain
naturally stable. Their size makes certain properties more pronounced and
enables research approaches that would be impossible on larger crystals, such
as imaging using electron microscopy to see how atoms in the materials move.
This was, in fact, the method that enabled the discovery of self-repair in the
lead-free perovskites.
The perovskite nanoparticles were produced in Prof. Bekenstein’s lab using a short, simple process that involves heating the material to 100°C for a few minutes. When Ph.D. students Sasha Khalfin and Noam Veber examined the particles using a transmission electron microscope, they discovered the exciting phenomenon.
The high voltage electron beam used by this type of
microscope caused faults and holes in the nanocrystals. The researchers were
then able to explore how these holes interact with the material surrounding
them and move and transform within it.
They saw that the holes moved freely within the nanocrystal, but avoided its edges. The researchers developed a code that analyzed dozens of videos made using the electron microscope to understand the movement dynamics within the crystal. They found that holes formed on the surface of the nanoparticles, and then moved to energetically stable areas inside.
The reason
for the holes’ movement inwards was hypothesized to be organic molecules
coating the nanocrystals’ surface. Once these organic molecules were removed,
the group discovered the crystal spontaneously ejected the holes to the surface
and out, returning to its original pristine structure – in other words, the
crustal repaired itself.
This discovery is an important step towards understanding the
processes that enable perovskite nanoparticles to heal themselves, and paves
the way to their incorporation in solar panels and other electronic devices.
Reference: “Self-Healing of Crystal Voids in Double Perovskite
Nanocrystals Is Related to Surface Passivation” by Sasha Khalfin, Noam Veber,
Shaked Dror, Reut Shechter, Saar Shaek, Shai Levy, Yaron Kauffmann, Leonid
Klinger, Eugen Rabkin and Yehonadav Bekenstein, 23 December 2021, Advanced Functional Materials.
DOI: 10.1002/adfm.202110421