The first two-dimensional boron oxide crystal synthesised in Trieste
A joint research project carried out by the Institute of Materials Workshop of the National Research Council in Trieste (Cnr-Iom), the Universities of Trieste and Innsbruck, and Elettra Sincrotrone Trieste has synthesised a new crystalline form of diboron trioxide, entirely composed of structural units previously observed only in its vitreous form.
Boron oxide is commonly used as a key component in the manufacture of highly resistant glasses such as Pyrex and in enamels: in such industrial processes, it has been demonstrated that the addition of boron oxide significantly improves the glass’s ability to withstand thermal shock and chemical reactions, making it ideal for the most demanding applications. However, the vitrification process of boron oxide is still little understood, and presents anomalies not found in other oxides, such as silica, which exist in both crystalline and amorphous form.
“The key distinction between a crystal and a glass lies in the ordered arrangement of atoms in the former, which is absent in the latter,” explains Alessandro Sala, a Cnr-Iom researcher who conceived the project. “Both systems are normally made up of the same structural unit composed of a few atoms, repeated in space. In crystals this ‘building block’ repeats periodically in a geometrically ordered manner, whereas in glass it repeats in a disordered way. Boron is an exception to this rule, since its vitreous phase contains elementary units composed of a ring of three boron atoms and three oxygen atoms, which are not present in the crystal. Today, for the first time, we have succeeded in obtaining a two-dimensional crystalline phase composed exclusively of the ‘building blocks’ present in the vitreous phase”.
The research was based on the use of platinum as the base material to obtain this compound and to characterise its main physical properties in detail.
The scientific team was able not only to develop the “recipe” for obtaining this material, but also to study its principal physical properties in depth. Maria Peressi, Full Professor at the University of Trieste, comments: “Our numerical simulations indicate that this material, porous by construction, consists of a mesh of boron and oxygen atoms that is extremely flexible, to the point of being the most elastic monoatomic-thickness material ever reported – ten times more so than graphene! This peculiar characteristic is due to the fact that the rigid ‘building blocks’ of which it is made are linked by an oxygen atom that acts as a hinge, around which they can rotate within the plane. Experimental evidence and results from numerical simulations also indicate that this material interacts only very weakly with the platinum substrate on which it is produced, suggesting the possibility of using conventional methods to separate it in order to employ it in innovative devices”.
The crystalline structure of the two-dimensional material obtained was then analysed through scanning tunnelling microscopy: “The complementary measurements carried out in Trieste and Innsbruck enabled us to observe the material down to its most fundamental components,” continues Laerte Patera, Professor at the University of Innsbruck. “With the spatial resolution achieved, we are now able to determine the position of each atom within the two-dimensional mesh: in the future we will be able to observe how the atoms rearrange as the material passes from the crystalline form to the disordered form characteristic of glass”.
Andrea Locatelli, head of the Nanospectroscopy beamline at Elettra Sincrotrone Trieste, concludes: “The use of synchrotron light was crucial to precisely determine the relative abundance of the constituent elements, the absence of contaminants, and the crystallinity of the new material produced. We are already capable of producing homogeneous crystals of this material measuring tens of square microns. The complementarity of the experimental techniques and theoretical simulations employed in this study proved decisive for the success of the entire scientific project. The distinctive characteristics of this new material – a wide band-gap semiconductor, extremely flexible and porous – encourage exploration of its potential use in applications across very different sectors, from electronics to catalysis to quantum technologies”.
The first authors of this important work, Teresa Zio and Marco Dirindin, are two PhD students at the University of Trieste, who are brilliantly crowning a path of excellence in advanced training and introduction to research.