Searching for ultrathin materials through data mining — ScienceDaily
Two-dimensional (2D) materials have extraordinary properties. They usually consist of atomic layers only a few nanometers thick and are particularly good at conducting heat and electricity, for example. To the astonishment of many scientists, it was recently learned that 2D materials could also exist based on certain metal oxides. These oxides are of great interest in fields such as nanoelectronic applications. A German-American research team, led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), has now succeeded in predicting twenty-eight representatives of this new class of materials using data-driven methods.
There is a substantial difference between conventional 2D materials such as graphene and new materials that can be synthesized from metal oxides such as ilmenite and chromite. The latter do not form weak interactions – so-called van der Waals forces – in their crystal structure, but rather form stronger ionic bonds that point in all directions. For this reason, only a few experiments have so far succeeded in detaching new 2D materials from blocks of 3D materials. The results of the study can now lead to the success of other experiments of this type. Using theoretical methods, scientists predict which compounds are actually of interest for experimental research.
“With our data-driven method, we relied on the first available information from initial experiments. From this information, we developed structural prototypes and then analyzed them in a huge database of materials as a criterion filtering,” says study leader Dr. Rico Friedrich of the HZDR Institute for Ion Beam Physics and Materials Research. “The main challenge was to understand why these materials so easily form 2D systems with particular oxides. From this information, we were able to develop a valid generalized search criterion and systematically characterize the identified candidates based on their properties.”
To this end, the researchers mainly applied the so-called “density functional theory”, a practical computational method for electronic structures widely used in quantum chemistry and condensed matter physics. They collaborated with several German high-performance data centers for the necessary computational steps. A decisive factor was the determination of the exfoliation energy: this defines the amount of energy that must be spent to remove a 2D layer from the surface of a material.
Materials database with approximately 3.5 million entries
The study also used the materials database AFLOW (Automatic Flow for Materials Discovery). It has been under development for more than twenty years by Professor Stefano Curtarolo of Duke University (USA), who also contributed as an author of the study. AFLOW is considered one of the largest materials science databases and classifies approximately 3.5 million compounds with over 700 million calculated material properties.
Together with the associated software, the database ultimately provided researchers with not only the chemical composition of twenty-eight 2D-compatible materials, but also allowed them to study their properties, which are remarkable both electronically and magnetically as well as topological. According to Rico Friedrich, their specific magnetic surface structures could make them particularly attractive for spintronic applications, such as data storage in computers and smartphones.
“I’m sure we can find more 2D materials like this,” says the physicist from Dresden, looking to the future. “With enough candidates, perhaps even a dedicated database could be created that specializes entirely in this new class of materials.” HZDR scientists maintain close contact with colleagues at a subject-related collaborative research center (Sonderforschungsbereich) at TU Dresden as well as with the leading research group for the synthesis of new 2D systems in the USA. Together with the two partners, they plan to continue the study of the most promising compounds.