New insights into the transformation dynamics of antimony

At the Institute of Materials Physics at the University of Münster, researchers investigate materials that can transform their internal structure very rapidly, thereby significantly changing their optical properties. This behaviour is useful, for example, when processing information using photonic waveguides. Together with other researchers in Prof Martin Salinga’s team and cooperation partners from the University of Groningen, doctoral student Sebastian Walfort has shown for the first time which phases the chemical element antimony undergoes during its transformation.

As in many solids, the atoms of such materials arrange themselves stably as a regular (crystalline) lattice at room temperature. The atoms can be disorganised by melting the solid. If the material is then cooled so quickly that the atoms do not have enough time to rearrange themselves back into a crystalline structure, a disordered solid (a glass) is created, which can exhibit different electronic and optical properties despite having the same chemical composition.

Together with a team from IBM Research in Zurich, Martin Salinga had previously shown that such opposing states can be created in electronic components made of pure antimony within just a few nanoseconds (billionths of a second). Now, to characterise the transformation dynamics in antimony, experiments with ultrashort laser pulses were essential, enabling analysis with a temporal resolution in the femtosecond range (millionths of a billionth of a second).

By combining complex molecular dynamics simulations, it was possible to draw far-reaching conclusions. For one, the change between ordered and disordered solid states involves several transient intermediate states with very different properties. For example, the material changes to a metallic state before melting and becomes semiconducting again when the excited (hot) electrons transfer their energy to the atomic structure. The final optical contrast between crystal and glass, as observed in the refractive index, only forms after strong cooling in the supercooled liquid (in liquid antimony below the melting temperature), when the local atomic structure assumes a local distortion motif, which also characterises the arrangement of neighbouring atoms in the crystalline state.

As Sebastian Walfort explains, “the study not only improves our understanding of this class of materials, but also opens up new possibilities for use in photonic applications that can benefit from the complex short-term dynamics.”

 

 

Original publication

Sebastian Walfort, Nils Holle, Julia Vehndel, Daniel T. Yimam, Niklas Vollmar, Bart J. Kooi, Martin Salinga (2025): The Photoinduced Response of Antimony from Femtoseconds to Minutes. Advanced Materials; DOI: 10.1002/adma.202414687

Further information

• Original publication in “Advanced Materials”
• Cooperation project with Prof Dr Wolfram Pernice in the “Intelligent Matter” collaborative research centre
• Salinga, M., Kersting, B., Ronneberger, I. et al. Monatomic phase change memory. Nature Materials 17, 681-685 (2018)
• The research group of Prof. Martin Salinga at the University of Münster