Showing 1–6 of 6 results for author: Khakhulin, D

Crystallisation kinetics of supercooled liquid palladium

Authors: Zuzanna Kostera, Christian Bressler, Przemyslaw Dziegielewski, Wojciech Gawelda, Konstantinos Georgarakis, Dmitry Khakhulin, Oleksii I. Liubchenko, Adam Olczak, Angel Rodriguez-Fernandez, Ryszard Sobierajski, Klaus Sokolowski-Tinten, Peihao Sun, Robert W. E. van de Kruijs, Hazem Yousef, Peter Zalden, Jerzy Antonowicz

Abstract: In this study, we employ classical molecular dynamics (MD) simulations to investigate the crystallisation kinetics of supercooled liquid palladium and relate the results to time-resolved X-ray diffraction measurements on rapidly quenched Pd thin films. Crystal nucleation and growth rates are determined over the temperature range $700$--$1150~\mathrm{K}$ ($0.38$--$0.65 T_{\mathrm{m}}$) by analysing… ▽ More In this study, we employ classical molecular dynamics (MD) simulations to investigate the crystallisation kinetics of supercooled liquid palladium and relate the results to time-resolved X-ray diffraction measurements on rapidly quenched Pd thin films. Crystal nucleation and growth rates are determined over the temperature range $700$--$1150~\mathrm{K}$ ($0.38$--$0.65 T_{\mathrm{m}}$) by analysing the evolution of the microstructure during the liquid-to-crystal transition. The self-diffusion coefficient of Pd, obtained from the atomic mean-squared displacement, follows Arrhenius behaviour over the investigated temperature range, with an activation energy of $467(6)~\mathrm{meV/atom}$, consistent with available data for supercooled liquid metals. The steady-state homogeneous nucleation rate exhibits a maximum of approximately $4 \times 10^{35}~\mathrm{m^{-3} s^{-1}}$ near $0.5 T_{\mathrm{m}}$. Crystal growth occurs at velocities of the order of metres per second, with a temperature dependence consistent with diffusion-limited Wilson-Frenkel kinetics rather than the collision-limited regime. Based on multiple statistically independent simulations, a time-temperature-transformation (TTT) diagram for crystallisation onset is constructed. The TTT curve exhibits a nose near $0.5 T_{\mathrm{m}}$ and $100~\mathrm{ps}$, corresponding to a critical cooling rate for vitrification on the order of $10^{13}~\mathrm{K s^{-1}}.$ The simulations reproduce the crystallisation onset time and temperature observed in time-resolved X-ray diffraction experiments on optically molten Pd thin films quenched at $5 \times 10^{11}~\mathrm{K s^{-1}}.$ These results indicate that homogeneous, rather than heterogeneous, nucleation governs the achievable supercooling in the experimentally studied films. △ Less

Submitted 2 June, 2026; v1 submitted 29 May, 2026; originally announced May 2026.

Comments: 27 pages, 6 figures plus 4 pages of Supplementary Material

Laser-induced ultrafast structural transformations in thin Fe layer revealed by time-resolved X-ray diffraction

Authors: O. Liubchenko, J. Antonowicz, K. Sokolowski-Tinten, P. Zalden, R. Minikayev, I. Milov, T. J. Albert, C. Bressler, M. Chojnacki, P. Dłużewski, P. Dzięgielewski, A. Rodriguez-Fernandez, K. Fronc, W. Gawelda, K. Georgarakis, A. L. Greer, I. Jacyna, R. W. E. van de Kruijs, R. Kamiński, D. Khakhulin, D. Klinger, K. Kosyl, K. Kubicek, A. Olczak, N. T. Panagiotopoulos , et al. (5 additional authors not shown)

Abstract: The ultrafast structural response of a thin iron film to sub-ps pulsed laser-induced heating has been investigated using time-resolved X-ray diffraction in the partial melting regime. A tetragonal distortion of the bcc-phase emerges at ~6 ps. Its formation is delayed relative to the initial heating (1-2 ps) and partial melting (2-5 ps) of the material, and controlled by the stress release in the q… ▽ More The ultrafast structural response of a thin iron film to sub-ps pulsed laser-induced heating has been investigated using time-resolved X-ray diffraction in the partial melting regime. A tetragonal distortion of the bcc-phase emerges at ~6 ps. Its formation is delayed relative to the initial heating (1-2 ps) and partial melting (2-5 ps) of the material, and controlled by the stress release in the quasi-instantaneously pressurized film. The distortion persists for at least 60 ps indicating the formation of a metastable bct phase between the equilibrium bcc and fcc phases. △ Less

Submitted 8 August, 2025; v1 submitted 23 June, 2025; originally announced June 2025.

Comments: The revised manuscript features an upgraded discussion and conclusion parts, with particular emphasis on the role of stress-release mechanisms. The text has been substantially shortened and refined, with careful language improvements to ensure clarity and precision. Additionally, the manuscript has been formatted in accordance with PRL submission guidelines

Structural pathways for ultrafast melting of optically excited thin polycrystalline Palladium films

Authors: Jerzy Antonowicz, Adam Olczak, Klaus Sokolowski-Tinten, Peter Zalden, Igor Milov, Przemysław Dzięgielewski, Christian Bressler, Henry N. Chapman, Michał Chojnacki, Piotr Dłużewski, Angel Rodriguez-Fernandez, Krzysztof Fronc, Wojciech Gawełda, Konstantinos Georgarakis, Alan L. Greer, Iwanna Jacyna, Robbert W. E. van de Kruijs, Radosław Kamiński, Dmitry Khakhulin, Dorota Klinger, Katarzyna M. Kosyl, Katharina Kubicek, Kirill P. Migdal, Roman Minikayev, Nikolaos T. Panagiotopoulos , et al. (6 additional authors not shown)

Abstract: 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… ▽ More 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 melting. 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. △ Less

Submitted 19 September, 2023; originally announced September 2023.

Comments: main manuscript 33 pages, 9 figures; supplemental material 19 pages, 13 figures - all in one file

Ultrafast two-colour X-ray emission spectroscopy reveals excited state landscape in a base metal dyad

Authors: Michal Nowakowski, Marina Huber-Gedert, Hossam Elgabarty, Jacek Kubicki, Ahmet Kertem, Natalia Lindner, Dmitry Khakhulin, Frederico Alves Lima, Tae-Kyu Choi, Mykola Biednov, Natalia Piergies, Peter Zalden, Katerina Kubicek, Angel Rodriguez-Fernandez, Mohammad Alaraby Salem, Thomas Kühne, Wojciech Gawelda, Matthias Bauer

Abstract: Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light induced proton reduction systems. For a more sustainable future, development of competitive base metal dyads is mandatory. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored. We study a… ▽ More Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light induced proton reduction systems. For a more sustainable future, development of competitive base metal dyads is mandatory. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored. We study a Fe-Co dyad that exhibits photocatalytic H2 production activity using femtosecond X-ray emission spectroscopy, complemented by ultrafast optical spectroscopy and theoretical time-dependent DFT calculations, to understand the electronic and structural dynamics after photoexcitation and during the subsequent charge transfer process from the FeII photosensitizer to the cobaloxime catalyst. Using this novel approach, the simultaneous measurement of the transient Kalpha X-ray emission at the iron and cobalt K-edges in a two-colour experiment is enabled making it possible to correlate the excited state dynamics to the electron transfer processes. The methodology, therefore, provides a clear and direct spectroscopic evidence of the Fe->Co electron transfer responsible for the proton reduction activity. △ Less

Submitted 11 January, 2023; originally announced January 2023.

Doming and spin cascade in Ferric Haems: Femtosecond X-ray Absorption and X-ray Emission Studies

Authors: Camila Bacellar, Dominik Kinschel, Giulia F. Mancini, Rebecca A. Ingle, Jérémy Rouxel, Oliviero Cannelli, Claudio Cirelli, Gregor Knopp, Jakub Szlachetko, Frederico A. Lima, Samuel Menzi, Georgios Pamfilidis, Katharina Kubicek, Dmitry Khakhulin, Wojciech Gawelda, Angel Rodriguez-Fernandez, Mykola Biednov, Christian Bressler, Christopher A. Arrell, Philip J. M. Johnson, Christopher Milne, Majed Chergui

Abstract: The structure-function relationship is at the heart of biology and major protein deformations are correlated to specific functions. In the case of heme proteins, doming is associated with the respiratory function in hemoglobin and myoglobin, while ruffling has been correlated with electron transfer processes, such as in the case of Cytochrome c (Cyt c). The latter has indeed evolved to become an i… ▽ More The structure-function relationship is at the heart of biology and major protein deformations are correlated to specific functions. In the case of heme proteins, doming is associated with the respiratory function in hemoglobin and myoglobin, while ruffling has been correlated with electron transfer processes, such as in the case of Cytochrome c (Cyt c). The latter has indeed evolved to become an important electron transfer protein in humans. In its ferrous form, it undergoes ligand release and doming upon photoexcitation, but its ferric form does not release the distal ligand, while the return to the ground state has been attributed to thermal relaxation. Here, by combining femtosecond Fe K-edge X-ray absorption near-edge structure (XANES) studies and femtosecond Fe Kalpha and Kbeta X-ray emission spectroscopy (XES), we demonstrate that the photocycle of ferric Cyt c is entirely due to a cascade among excited spin states of the Iron ion, causing the ferric heme to undergo doming, which we identify for the first time. We also argue that this pattern is common to all ferric haems, raising the question of the biological relevance of doming in such proteins. △ Less

Submitted 1 June, 2020; originally announced June 2020.

Femtosecond X-ray emission study of the spin cross-over dynamics in haem proteins

Authors: Dominik Kinschel, Camila Bacellar, Oliviero Cannelli, Boris Sorokin, Tetsuo Katayama, Giulia F. Mancini, Jeremy R. Rouxel, Yuki Obara, Junichi Nishitani, Hironori Ito, Terumasa Ito, Naoya Kurahashi, Chika Higashimura, Shotaro Kudo, Theo Keane, Frederico A. Lima, Wojciech Gawelda, Peter Zalden, Sebastian Schulz, James Budarz, Dmitry Khakhulin, Andreas Galler, Christian Bressler, Christopher J. Milne, Thomas Penfold , et al. (4 additional authors not shown)

Abstract: In haemoglobin (consisting of four globular myoglobin-like subunits), the change from the low-spin (LS) hexacoordinated haem to the high spin (HS) pentacoordinated domed form upon ligand detachment and the reverse process upon ligand binding, represent the transition states that ultimately drive the respiratory function. Visible-ultraviolet light has long been used to mimic the ligand release from… ▽ More In haemoglobin (consisting of four globular myoglobin-like subunits), the change from the low-spin (LS) hexacoordinated haem to the high spin (HS) pentacoordinated domed form upon ligand detachment and the reverse process upon ligand binding, represent the transition states that ultimately drive the respiratory function. Visible-ultraviolet light has long been used to mimic the ligand release from the haem by photodissociation, while its recombination was monitored using time-resolved infrared to ultraviolet spectroscopic tools. However, these are neither element- nor spin-sensitive. Here we investigate the transition state in the case of Myoglobin-NO (MbNO) using femtosecond Fe Kalpha and Kbeta non-resonant X-ray emission spectroscopy (XES) at an X-ray free-electron laser upon photolysis of the Fe-NO bond. We find that the photoinduced change from the LS (S = 1/2) MbNO to the HS (S = 2) deoxy-myoglobin (deoxyMb) haem occurs in ca. 800 fs, and that it proceeds via an intermediate (S = 1) spin state. The XES observables also show that upon NO recombination to deoxyMb, the return to the planar MbNO ground state is an electronic relaxation from HS to LS taking place in ca. 30 ps. Thus, the entire ligand dissociation-recombination cycle in MbNO is a spin cross-over followed by a reverse spin cross-over process. △ Less

Submitted 12 May, 2020; originally announced May 2020.