New theoretical studies of material properties as a function of thickness in chalcogenides

By August 18, 2020August 20th, 2020ICN2

Researchers from the Catalan Institute of Nanoscience and Nanotechnology (ICN2), a BIST centre, and the Institute for Theoretical Solid State Physics (Germany) reveal materials of two subfamilies of chalcogenides show different dependence on slab thickness. This is reflected in the ferroelectric characteristics, which are relevant to its information technology applications.

Following the discovery of the striking properties of graphene, a material made up of a single layer of carbon atoms, 2D and few-layer materials have been studied with increasing interest due to their possible applications in various fields. What makes them special is the fact that their properties differ from those of the corresponding bulk materials, which are composed of more layers of the same kind. These differences are strictly related to the type of links that hold the layers together.

In order to better understand their characteristics and predict the behaviour of possible novel 2D and few-layer materials, theoretical simulations and computational resources are largely employed. Among the recently discovered families of 2D compounds, group IV chalcogenides (which are composed of a group IV element, such as Ge or Sn, and a chalcogen, such as S, Se, or Te). They are particularly interesting as they exhibit remarkable electronic properties, including in-plane ferroelectric polarisation.

In a project developed in close collaboration with Dr. Ider Ronneberger (Institute for Theoretical Solid State Physics in Aachen, Germany) and Dr. Zeila Zanolli, (ICN2 Theory and Simulation Group), the properties of a few compounds, representative of two subfamilies of group IV chalcogenides, have been investigated as a function of the slab thickness, using thin-film computational models. The study focused on analysing the behaviour of thin films of two selenides, GeSe and SnSe, which are held together by covalent bonds in their bulk state, and that of thin films of two tellurides, GeTe and SnTe, which show an unconventional form of bonding called metavalent bonding (MVB). The work was recently published in Advanced Materials Communications.

The simulations showed that, in the case of the selenides, bulk properties are recovered, increasing the thickness of the material to just a few layers, while the structure of the tellurides thin films exhibits pronounced deviations from the bulk counterparts, even for thicknesses exceeding 18 bilayers (a bilayer is the “unit” of layers used in this research because more suitable to this study). As a result, these two groups of materials also present different ferroelectric properties. These are relevant to possible applications such as information technology.

This study provides crucial information about the characteristics and the bonding of few-layer structures from different families of compounds and allows for predicting the behaviour of other 2D materials. Such knowledge is key to developing tools to tune materials properties according to the desired application.

More information can be found on the ICN2 website