Researchers at St Petersburg University succeeded in synthesising the micro-spiral of iron compounds with a diameter of about 12 microns — almost ten times thinner than a human hair. They can be used, for example, to create sensors with high sensitivity, as well as miniature electromagnets or inductors.

Usually, the creation of complex microstructures requires a lot of laborious and precise operations. For example, to use a component in the form of a spiral in a micro device, it is first necessary to draw a wire of the desired diameter, and then form a spiral with the required number of turns. That is why the direct synthesis of microstructures of complex shapes is an important direction in the development of modern materials science.

The results of the research are published in the journal of the publishing house Wiley «Particle & Particle Systems Characterization».

In the work of scientists of St Petersburg University there is presented an original way of creating micro-spirals with a diameter from 10 to 20 microns. The researchers were able to show that with the help of simple chemical reactions, miniature «springs» made of iron oxide or metallic iron can be produced. This development can be used in a variety of areas. For example, a powder of such spiral has a large specific surface, which is important when creating effective catalysts or sensors with high sensitivity.

Thus, the electrocatalytic characteristics of iron oxide micro-spirals, despite their low cost, are comparable with the indices of catalysts based on a number of noble metals, which are widely used in the electrolysis of water. On the other hand, one spiral can serve as an independent component of microelectronics, for example, an oxide spiral is a microsensor electrode, and a metallic spiral, due to its shape and magnetic characteristics, is an electromagnet or inductor.

To obtain such microstructures, the research team of chemists at St Petersburg University is developing a simple and effective synthesis route based on the interaction of reagents at the interface between the aqueous solution and the gaseous medium. Earlier, using this method, it was possible to grow nanocrystals of inorganic compounds with one- and two-dimensional morphology (rods and sheets), as well as complex architectures in the form of nanocells. However, according to the researchers, the main advantage of the method is the possibility of obtaining micro- and nanotubes with the morphology of scrolls of various classes of inorganic compounds: oxides, fluorides, sulphides, etc.

The study was supported by a grant from the Russian Science Foundation No. 16-13-10223

The work shows for the first time how micro-twists can be divided into spirals, and with the help of heat treatment their height can be regulated. «Everyone knows the method of self-assembly of nanostructures,» said one of the authors of the study, Professor of St Petersburg University, Doctor of Chemistry Valery Tolstoy. «We want to justify a new approach to micro- and nanoscale materials creation, based on a controlled» self-assembly «of an array of larger objects, which opens up the possibility of» spontaneous «obtaining ordered nano-objects using the top-down methodology.»

The method of synthesis that our group develops, makes it easy to modify the composition of micro-helical blades by introducing other elements into the structure and, as a result, to obtain micro-helixes of a double oxide or alloy based on iron. This means that we can control the functional properties of micro-twisters in a wide range to improve the characteristics of products based on them.

One of the authors of the study was a senior research fellow of St Petersburg University, Candidate of Chemical Sciences Larisa Gulina.

The research also involved engineer-researcher Candidate of Chemical Sciences Artem Lobinsky and Associate Professor, Candidate of Physical and Mathematical Sciences Yuri Petrov. By the way, the unusual form of synthesised microstructures has attracted the attention of the editors of the journal of one of the most ranking journals in the field of biotechnology NanoToday. A photo of spirals was obtained with the help of unique equipment and experienced specialists of the interdisciplinary resource centre of St Petersburg University in the direction of «Nanotechnology». After artistic processing, it won the journal’s competition.. The image was placed on the cover of the 18th issue of the journal NanoToday (February 2018).