The team of the 海角社区 Multiscale Modelling of Multicomponent Functional Materials Laboratory have made an important step towards the understanding of the properties of two-dimensional silicon carbide. The scientists have studied how point defects (vacancies) in monolayers of this material influence its electronic and magnetic characteristics. Their work has a fundamental significance for the development of nanoelectronics and spintronics.
“This research is part of a bigger fundamental project on studying the properties of the so-called “tetrel bonds”, the noncovalent interactions that are formed by the carbon group atoms (carbon, silicon, germanium, stannic),” shares Ekaterina Bartashevich, project head and leading research fellow at the Multiscale Modelling of Multicomponent Functional Materials Laboratory. “The understanding of these weak interatomic interactions is crucial for predicting the properties of silicon-carbon materials: from the capability of sorbents, based on them, to capture the functionally important molecules, to the activation of interfacial regions for chemical reactions.
We tried to focus namely on the properties of chemical bonds in order to be able to predict the strong and weak interactions of silicon-carbon materials with various components. We paid our attention to defects, that is, the situations when one of the atoms in the monolithic grid of silicon carbide is lost. We have found that sometimes such “vacancies” make a material more active, and sometimes quite the opposite, its structure reconstructs and “heals” itself, and the required activation does not happen.”
Understanding the mechanisms of emerging of magnetism in defect monolayers has become the key result of this work. Using quantum-chemical modelling, the project co-authors, physicists Sergey Sozykin and Vladimir Tsirelson, demonstrated that the effect fundamentally depends of the type of the removed atom.
If a silicon atom is removed from the grid, the neighbouring carbon atoms turn out to be in an excited state and with unpaired electrons. This leads to stable spin-polarized states: the material acquires local magnetism.
And if the grid loses a carbon atom, its structure, as a rule, reconfigures itself, new chemical bonds are formed, and magnetism is inhibited.
“We have demonstrated that the emergence of magnetism cannot be described by simply stating the presence of a defect. We need to take into consideration exactly how the electron density rearranges. Silicon vacancies is an effective method of “switching on” the magnetic properties in two-dimensional silicon carbide,” comments Sergey Sozykin, Candidate of Sciences (Physics and Mathematics), Associate Professor of the Department of Physics of Nanoscale Systems and senior research fellow at the Innovations Office.
Professor Vladimir Tsirelson, who is a specialist in the fields of quantum chemistry, crystal chemistry and chemical bond theory, Doctor of Sciences (Physics and Mathematics) and Head of the Department of Quantum Chemistry at D.I. Mendeleev Russian University of Chemical Technology, played a special role in this research study. The electronic descriptors, developed and proposed by him, allowed the scientists not only to simulate the behaviour of silicon-carbon monolayers with two-dimensional periodicity, but also to push closer to making accurate predictions of the properties of materials.
“At this stage, we are mostly interested in predicting the increase of the reactivity of silicon and carbon atoms in such two-dimensional structures. We can already say how defects would interact with various organic molecules,” adds Ekaterina Bartashevich.
The team stresses that the main difficulty and at the same time the main advantage of their work is the intersection of theory and experiments. Researchers often do not have enough experimental data in order to validate their complex models. The scientists are open for partnerships and seek collaboration with experimenting Physics and Chemistry groups, so that they could test their predictions and jointly advance in creating new hybrid materials.
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The obtained data open up prospects for using silicon carbide monolayers in nanoelectronics and spintronics, where it is important to control the spin states at the atomic level. Defects that have traditionally been considered as unwanted structure imperfections can now be seen as a tool for fine tuning of the functional properties of the materials of the future.
The research data have been published in a paper on in Physical Chemistry Chemical Physics publication, Q2 (Scopus), Q2 (White List).