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The pump-probe X-ray diffraction and scattering techniques have now been fully established as a powerful method to investigate molecular structural dynamics. We have employed the techniques to study structural dynamics and spatiotemporal kinetics of a wide variety of molecular systems including diatomic molecules, haloalkanes, organometallic complexes and protein molecules over timescales from femtoseconds to milliseconds. To emphasize that structural information can be obtained from the liquid phase, this time-resolved X-ray solution scattering technique is named time-resolved X-ray liquidography (TRXL) in analogy to time-resolved X-ray crystallography where the structural information of reaction intermediates is obtained from the crystalline phase. TRXL has been successfully used to reveal the structural dynamics of various biological reactions as well as small molecules. We will present our results obtained with femtosecond TRXL at PAL X-ray free-electron laser (PAL-XFEL), including the direct observation of bond formation process, roaming-mediated isomerization, optical Kerr effect, and protein structural dynamics. (Acknowledgement: This work was supported by the Institute for Basic Science (IBS-R033)).
The properties of quantum materials are increasingly being manipulated by light to induce new functionalities such as light-induced superconductivity. Understanding how such materials change is vital for determining how such properties arise. While we have many sophisticated probes that can track material changes on the ultrafast timescale, most lack spatial resolution and thus only provide the average dynamics of the sampled area. However, many quantum materials are either heterogeneous in their initial state or are believed to be heterogenous in their transient state, which makes it challenging to interpret exactly how the material is changing.
In this talk, I will show how coherent soft X-ray imaging can be used to image heterogenous dynamics of the light-induced insulator-metal phase transition with 150 fs time resolution and ~25 nm spatial resolution. I will show how soft X-ray absorption spectroscopy, combined with time-resolved imaging can be used as a nanoscale spectroscopic tool to directly measure the properties of the heterogenous state. By using spatially, temporally and spectrally resolved imaging, we show that the light-induced metallic phase in VO2 is different from the thermal phase transition, due to the presence of strain [1]. This work opens up the opportunity to directly measure dynamics heterogenous systems, or the formation of heterogenous dynamics in the time-domain.
The giant impact-driven redox processes in the atmosphere and magma ocean played a crucial role in the evolution of the early Earth. However, due to the absence of rock records from that time, understanding these processes have proven challenging. Here, we present experimental results that simulate the reaction between iron and volatile components (H2O and CO2) under giant impact conditions using high-brilliance X-ray free electron laser (XFEL) as a fast heat pump and structural probe. Our results show that under XFEL pump on a compressed mixture of iron and volatiles, iron is oxidized to wüstite (FeO), while the volatiles are reduced to H2 and CO. Furthermore, iron oxidation proceeds into the formation of hydrides (γ-FeHx) and siderite (FeCO3), with an indication of a possible redox boundary near 300 km depth. Through quantitative analysis of the reaction products, we estimate theoretical constraints on the mass of the impactor and its heliocentric origin, as well as the volatile and FeO budgets in the bulk silicate Earth, supporting the Theia hypothesis. Our findings shed light on the fast and short-lived process that led to a reduced atmosphere, which is required for the emergence of prebiotic organic molecules.
Language : Korean
Topics : HX2 빔라인 구축시 실험 장치 구성에 관한 이용자 의견 수렴
Posting poster presentations during the banquet
(via Zoom)
Recent progress in ultrafast science using X-ray free electron lasers has opened up new research opportunities. These advances allow for detailed examination of structural dynamics in materials, element-specific analysis of electronic structure, and exploration of the relationship between electronic and atomic structural dynamics. By combining pump-probe techniques with coherence applications, one can gain valuable information about the structural dynamics of complex material systems. In addition, the interation between the carriers and lattice can be explored by pumping with laser above the bandgap in the semiconducing materials. In my talk, some recent results include the study of band inversion-related topological phase transition in Bi2Se3 and the generation and evolution of polarons in perovskite oxides will be discussed.
This work is supported by supported by the National Research Foundation of Korea (NRF-2021R1A3B1077076), Samsung Electronics and Samsung Display.
(via Zoom)
Ultrafast optical excitation has recently emerged as a powerful means to control and induce new functionalities in quantum materials. One of the most ambitious goals is to selectively drive structural or electronic degrees of freedom to bring about nonequilibrium superconductivity at temperatures far above the equilibrium critical temperature Tc. While this phenomenon has been observed in a variety of systems ranging from copper oxides to organic molecular metals [1,2,3,4], the microscopic physics of these dynamics is still largely unexplored. In layered copper oxides, resonant scattering experiments have revealed that transient superconductivity is accompanied by a suppression of charge order correlations [5] and that the following dynamics at sub-meV scales are overdamped and diffusive [6,7]. Further, the CO phase exhibits dynamical critical scaling, a universal behavior arising from the propagation of topological defects. In order to explore whether these dynamics are universal among cuprate families and peculiar to the two-dimensional limit, we investigate charge order in light-driven Sr14Cu24O41 (SCO). SCO is a quasi-1D cuprate compound with a ladder-like structural subunit that is superconducting when doped with Ca and at high pressure (TC ~ 9 K, 3 GPa). The stoichiometric compound exhibits a robust charge order with a Tc of about 210 K and a (0, 0, 0.2) modulation wavevector [8]. When excited with 1.55 eV pulses, we find that the stripe phase behaves in markedly distinct ways than what found in La2-xBaxCuO4 and does not show the hydrodynamic fluctuation behavior observed in the 214 compounds [9]. We discuss the implications of our experiments for the origin of charge order in the cuprates and for the physics of light-induced superconductivity in these materials.
Antibiotics have had a tremendous impact on human medical technology and life expectancy. Since their discovery, many antibiotics have been developed and used in various fields, such as research, medicine, and animal husbandry. Beta-lactam antibiotics, which are derived from fungi in the Penicillium genus, are among the most commonly used antibiotics due to their ability to effectively inhibit the formation of microorganisms' peptidoglycan layer. However, the emergence of antibiotic-resistant strains has posed a threat to the "golden age" of antibiotic use. The rate of emergence of antibiotic-resistant bacteria has surpassed the rate of antibiotic development, and no new antibiotics have been approved since the early 2000s due to the significant challenges associated with antibiotic discovery. Recently, there have been reports of "super bacteria" that are resistant to carbapenem antibiotics containing beta-lactam structures, which has made antibiotic research an urgent need. The transporter X is a 14-transmembrane protein located in the inner membrane of Gram-negative bacteria that plays a critical role in the peptidoglycan cycle and the beta-lactamase signaling pathway of antibiotic-resistant bacteria. Our research objective is to identify the structure of transporter X and investigate its function. We also aim to develop "antibiotic adjuvants" by discovering and developing antagonists that can inhibit the function of transporter based on its structure. These inhibitors of the transporter X are expected to restore the effectiveness of beta-lactam antibiotics against previously resistant strains, making them susceptible to beta-lactam treatment. By reusing beta-lactam antibiotics through the use of these inhibitors, our research may contribute to combating antibiotic resistance.