Dresden 2026 – scientific programme

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O: Fachverband Oberflächenphysik

O 22: Surface dynamics – Poster

O 22.4: Poster

Monday, March 9, 2026, 18:00–20:00, P2

Extending Surface Phase Diagrams to Non-Equilibrium Plasmas — •Maximilian Wünschek, Alper T. Celebi, and Markus Valtiner — Institute of Applied Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10/E134, Vienna 1040, Austria

Surface phase diagrams are widely used to visualize the stability of surface reconstructions under equilibrium gas conditions. However, many growth and treatment processes use plasmas that operate far from equilibrium, where activated and ionized species are present in substantial concentrations. Examples such as ZnO have shown that unique reconstructions can be found outside the stability range defined by conventional chemical potential axes, highlighting the need to extend surface phase diagrams to non-equilibrium regimes.

Using GaN as a model system, we compile a large dataset of reconstructions for polar GaN surfaces under hydrogen, nitrogen, and oxygen environments. Building on these results, we introduce a framework for applying surface phase diagrams to plasma conditions by incorporating non-thermal species into the chemical potential landscape. A minimal kinetic model estimates plasma composition, and thermochemical properties of the constituent species are combined into an effective plasma chemical potential.

The resulting extended diagrams show how radicals and ions shift phase boundaries and stabilize surface structures inaccessible under equilibrium. This approach provides a basis for understanding and predicting surface configurations formed during plasma-assisted processing.

Keywords: Plasma; Surface Reconstructions; Surface Phase Diagrams; Non-Equilibrium Conditions; Density Functional Theory