Light used to probe layered materials

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AGI – Scientists from the Institute of Nanoscience of the National Research Council in Modena (Cnr-Nano), in collaboration with colleagues from Paris-Saclay University, have demonstrated a method to reveal otherwise indistinguishable differences in the crystalline structure of materials. “layered” semiconductorsi.e. composed of very compact, stacked atomic layers.

Thanks to the detailed analysis light emitted by the material, known as luminescence spectroscopyIn fact, the team was able to understand the differences in the crystal structure of the two-layer semiconductor materials, which represent virtually indistinguishable differences, hexagonal and rhombohedral boron nitride. The study is published in Physical Review Letters.

“Despite the fact that the two forms of the investigated material consist of the same elements, boron and nitrogen, they differ only in how the atomic layers are stacked on top of each other,” explains Daniele Varsano, a Cnr-Nano researcher among the authors of the study. . “Based on these differences electronic and structural properties change, as well as possible applications: from use in optoelectronic devices such as LEDs to use in ceramic materials”.

Scientists have shown that the light emitted by these materials, when excited by an electric current, is a powerful tool for clearly and unambiguously distinguishing two similar shapes to separate the version with the desired properties from the other. A combination of experiment and theory was necessary to achieve the result.

Experimental physicists from Paris-Saclay University measured and analyzed with extreme precision the spectrum of light emitted by two versions of boron nitride. The observed differences were explained thanks to a theoretical study carried out by Cnr-Nano researchers Fulvio Paleari, Daniele Varsano, Elisa Molinari and Matteo Zanfrognini. “The simulations show that the emitted light is affected by the symmetry of the crystal lattice, which differs in hexagonal and rhombohedral shapes.

In particular, the differences in the spectra result from another way in which the atomic nuclei, vibrating, bump into the electrons of the material, causing them to emit light” explains Fulvio Paleari. “The study shows that, when measured precisely, the emission spectrum is much more sensitive to small structural differences than other commonly used experimental techniques. This may allow crystal structures to be easily distinguished when designing new materials, while providing greater control over the final optoelectronics.” features of the device From a theoretical point of view, the study highlightsand the determining role of the interaction between atomic nuclei and excited electrons in layered materials“.

“The emission of light by a material is a process of a quantum nature that involves a complex series of interactions between photons, electrons, nuclei of atoms that make up the crystalline structure. The Cnr-Nano theoretical group is able to perform simulations that include the effects of all these interactions thanks to advanced software for quantum mechanics developed within the framework of the MaX European Center of Excellence for the Theoretical Study of Materials and the National Research Center in HPC, Big Data and Quantum Computing ICSC and using high-performance supercomputers thanks to the collaboration with Cineca of Bologna,” concludes Varsano.

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