TY - JOUR
T1 - Structural pathways for ultrafast melting of optically excited thin polycrystalline Palladium films
AU - Antonowicz, Jerzy
AU - Olczak, Adam
AU - Sokolowski-Tinten, Klaus
AU - Zalden, Peter
AU - Milov, Igor
AU - Dzięgielewski, Przemysław
AU - Bressler, Christian
AU - Chapman, Henry N.
AU - Chojnacki, Michał
AU - Dłużewski, Piotr
AU - Rodriguez-Fernandez, Angel
AU - Fronc, Krzysztof
AU - Gawełda, Wojciech
AU - Georgarakis, Konstantinos
AU - Greer, Alan L.
AU - Jacyna, Iwanna
AU - van de Kruijs, Robbert W.E.
AU - Kamiński, Radosław
AU - Khakhulin, Dmitry
AU - Klinger, Dorota
AU - Kosyl, Katarzyna M.
AU - Kubicek, Katharina
AU - Migdal, Kirill P.
AU - Minikayev, Roman
AU - Panagiotopoulos, Nikolaos T.
AU - Sikora, Marcin
AU - Sun, Peihao
AU - Yousef, Hazem
AU - Zajkowska-Pietrzak, Wiktoria
AU - Zhakhovsky, Vasily V.
AU - Sobierajski, Ryszard
N1 - Publisher Copyright:
© 2024
PY - 2024/9/1
Y1 - 2024/9/1
N2 - Due to its extremely short timescale, the non-equilibrium melting of metals is exceptionally difficult to probe experimentally. The knowledge of melting mechanisms is thus based mainly on the results of theoretical predictions. This work reports on the investigation of ultrafast melting of thin polycrystalline Pd films studied by optical laser pump – X-ray free-electron laser probe experiments and molecular-dynamics simulations. By acquiring X-ray diffraction snapshots with sub-picosecond resolution, we capture the sample's atomic structure during its transition from the crystalline to the liquid state. Bridging the timescales of experiments and simulations allows us to formulate a realistic microscopic picture of the crystal-liquid transition. According to the experimental data, the melting process gradually accelerates with the increasing density of deposited energy. The molecular dynamics simulations reveal that the transition mechanism progressively varies from heterogeneous, initiated inside the material at structurally disordered grain boundaries, to homogenous, proceeding catastrophically in the crystal volume on a picosecond timescale comparable to that of electron-phonon coupling. We demonstrate that the existing models of strongly non-equilibrium melting, developed for systems with relatively weak electron-phonon coupling, remain valid even for ultrafast heating rates achieved in femtosecond laser-excited Pd. Furthermore, we highlight the role of pre-existing and transiently generated crystal defects in the transition to the liquid state.
AB - Due to its extremely short timescale, the non-equilibrium melting of metals is exceptionally difficult to probe experimentally. The knowledge of melting mechanisms is thus based mainly on the results of theoretical predictions. This work reports on the investigation of ultrafast melting of thin polycrystalline Pd films studied by optical laser pump – X-ray free-electron laser probe experiments and molecular-dynamics simulations. By acquiring X-ray diffraction snapshots with sub-picosecond resolution, we capture the sample's atomic structure during its transition from the crystalline to the liquid state. Bridging the timescales of experiments and simulations allows us to formulate a realistic microscopic picture of the crystal-liquid transition. According to the experimental data, the melting process gradually accelerates with the increasing density of deposited energy. The molecular dynamics simulations reveal that the transition mechanism progressively varies from heterogeneous, initiated inside the material at structurally disordered grain boundaries, to homogenous, proceeding catastrophically in the crystal volume on a picosecond timescale comparable to that of electron-phonon coupling. We demonstrate that the existing models of strongly non-equilibrium melting, developed for systems with relatively weak electron-phonon coupling, remain valid even for ultrafast heating rates achieved in femtosecond laser-excited Pd. Furthermore, we highlight the role of pre-existing and transiently generated crystal defects in the transition to the liquid state.
KW - Laser processing
KW - Melting
KW - Metals
KW - Molecular dynamics simulation
KW - X-ray diffraction
UR - http://www.scopus.com/inward/record.url?scp=85195816664&partnerID=8YFLogxK
U2 - 10.1016/j.actamat.2024.120043
DO - 10.1016/j.actamat.2024.120043
M3 - Article
AN - SCOPUS:85195816664
SN - 1359-6454
VL - 276
JO - Acta materialia
JF - Acta materialia
M1 - 120043
ER -