Growing thin films on nanosheets provides magnetic control

In two recent journal papers, scientists from the MESA+ research institute at the University of Twente (UT) have reported using two-dimensional (2D) crystals to create high-quality magnetic thin films. The researchers show that growing the magnetic layers on various 2D crystals, better known as nanosheets, gives them highly local control over the preferred direction of the magnetism.

In an article published in Advanced Functional Materials, they use this method to create magnetic patterns on the micrometer scale. In Angewandte Chemie, they demonstrate that the nanosheets can be made in less than a minute, whereas previous synthesis processes had been much slower. The resultant magnetic films can be deployed for many different applications, such as new generations of smartphones.

To grow thin layers on a substrate, scientists often use a technique known as pulsed laser deposition (PLD). This involves rapidly heating a material with a powerful laser beam to produce a plasma that is then deposited on the substrate.

By providing fine control over the thickness of the layer, PLD allows the formation of smooth and thin layers, often with special properties that are interesting for use in electronics and electro-mechanics. For such applications, however, it is essential that the thin layers can be fabricated in defined patterns. Unfortunately, this is not easy with PLD, especially as the substrate needs to be heated to temperatures above 500° C during the PLD process.

The UT researchers have now developed a new method for producing such patterns, based on using nanosheets obtained from three-dimensional crystals with a layered structure. If these crystals are dissolved in a special liquid, they spontaneously disintegrate into individual nanosheets, with nanosheets from different crystals possessing different crystal structures. It was long thought that this crystal disintegration process took weeks. However, the researchers have now shown that the nanosheets are able to form within a few seconds, which opens the way for the production of nanosheets on a large scale.

When the researchers used PLD to deposit layers of magnetic LaSrMnO₃ on the nanosheets, they found that their growth was influenced by the crystal structure of the nanosheets. Thus by using nanosheets with different structures, they were able to produce magnetic films with specific orientations, allowing them to control the magnetism of the film at micrometer scales. They monitored this process by means of an analytical technique called electron backscatter diffraction (EBSD), which makes it possible to 'reveal' the structure in the patterns.

In addition to magnetism, it is also possible to use this technique to pattern other properties at the micrometer scale. An important step has thus been taken in bridging the gap between scientific research into artificial layered crystals and their ultimate application.

This story is adapted from material from the University of Twente, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.