Pudell, J.-E.; Mattern, M.; Baltrusch, F.; Boariu, F. L.; Kronseder, M.; Shayduk, R.; Madsen, A.; Rössle, M.; Bargheer, M.; Schick, D.; von Reppert, A.: Ultrafast x-ray thermometry: Contrasting strain and Debye-Waller effects in platinum thin films. Physical Review B 113 (2026), p. L220301/1-9
10.1103/x46h-3kdb
Open Accesn Version
Abstract:
Thermal energy and temperature govern a wide range of physical properties and dynamics in solids. X-ray diffraction can be used to monitor material-specific temperatures on ultrafast timescales and within nanostructures by exploiting thermal expansion or the Debye-Waller effect. Here, we simultaneously track the intensity and position changes of different out-of-plane Bragg peaks of a 16nm thick Pt film on an MgO substrate upon equilibrium heating and upon femtosecond laser excitation to quantify the mean-square atomic displacement and the lattice expansion. Our comparison of these two x-ray thermometers experimentally verifies that the in-plane expansion of homogeneously excited continuous single-crystalline thin films is forbidden on picosecond timescales. This drastically changes the out-of-plane thermal expansion coefficient, i.e., the relationship between the observed lattice expansion and the corresponding temperature increase. Thus, considering the boundary conditions of in-plane lattice expansion is generally indispensable for extracting temperatures from the lattice expansion in diffraction experiments.