SKM 2023 – scientific programme

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O: Fachverband Oberflächenphysik

O 25: Poster: Metal Substrates

O 25.2: Poster

Monday, March 27, 2023, 18:00–20:00, P2/EG

2D Lattice Gas Order-Disorder Transition Observed by LEED and Vibrational Sum Frequency Generation Spectroscopy — •Zhipeng Huang, Tobias Roos, Yujin Tong, and R. Kramer Campen — Faculty of Physics, University of Duisburg-Essen

Order-disorder phase transition of monoatomic superstructures on single crystal surfaces is commonly described by Ising or lattice-gas model. The molecular orientation needs to be considered for modeling the order-disorder transition of diatomic superstructures on single crystal surfaces, but it is challenge to be accessed by experiments.

Here we present our studies on CO ordered overlayers on Pt(111) surface by the surface sensitive thermal desorption spectroscopy (TDS), low-energy electron diffraction (LEED) and polarization dependent sum-frequency generation spectroscopy (SFG). An order-disorder phase transition of CO overlayer is observed by LEED under in-situ heating. The CO stretch vibrational frequency shifts suddenly when the transition happens. Combining LEED superstructure patterns and polarization dependent sum-frequency generation spectroscopy results, we reveal the changes of CO molecular orientation on Pt(111) surface during the order-disorder phase transition. We model the sudden CO stretch frequency shift caused by phase transition and the systematic shift as a function of coverage. These results demonstrate how the CO intermolecular interactions influence the molecular orientation and the stretch vibrational frequency. They provide insights on the change of microscopic potential energy level during the order-disorder phase transition.