Logo: to the web site of Uppsala University

uu.sePublications from Uppsala University
Change search
Link to record
Permanent link

Direct link
Alternative names
Publications (10 of 56) Show all publications
Svensson, P., Schwob, L., Grånäs, O., Unger, I., Björneholm, O., Timneanu, N., . . . Berholts, M. (2024). Heavy element incorporation in nitroimidazole radiosensitizers: molecular-level insights into fragmentation dynamics. Physical Chemistry, Chemical Physics - PCCP, 26(2), 770-779
Open this publication in new window or tab >>Heavy element incorporation in nitroimidazole radiosensitizers: molecular-level insights into fragmentation dynamics
Show others...
2024 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 26, no 2, p. 770-779Article in journal (Refereed) Published
Abstract [en]

The present study investigates the photofragmentation behavior of iodine-enhanced nitroimidazole-based radiosensitizer model compounds in their protonated form using near-edge X-ray absorption mass spectrometry and quantum mechanical calculations. These molecules possess dual functionality: improved photoabsorption capabilities and the ability to generate species that are relevant to cancer sensitization upon photofragmentation. Four samples were investigated by scanning the generated fragments in the energy regions around C 1s, N 1s, O 1s, and I 3d-edges with a particular focus on NO2+ production. The experimental summed ion yield spectra are explained using the theoretical near-edge X-ray absorption fine structure spectrum based on density functional theory. Born-Oppenheimer-based molecular dynamics simulations were performed to investigate the fragmentation processes.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2024
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-522697 (URN)10.1039/d3cp03800a (DOI)001090175100001 ()37888897 (PubMedID)
Funder
Swedish Research Council, 2019-03935Swedish Research Council, 2017-05128Swedish Research Council, 2018-00740Swedish Foundation for Strategic ResearchSwedish National Infrastructure for Computing (SNIC), 2022/1-36Swedish National Infrastructure for Computing (SNIC), 2022/22-597
Available from: 2024-02-08 Created: 2024-02-08 Last updated: 2024-02-08Bibliographically approved
Prasad, A. K., Sebesta, J., Esteban-Puyuelo, R., Maldonado, P., Ji, S., Sanyal, B., . . . Weissenrieder, J. (2023). Nonequilibrium Phonon Dynamics and Its Impact on the Thermal Conductivity of the Benchmark Thermoelectric Material SnSe. ACS Nano, 17(21), 21006-21017
Open this publication in new window or tab >>Nonequilibrium Phonon Dynamics and Its Impact on the Thermal Conductivity of the Benchmark Thermoelectric Material SnSe
Show others...
2023 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 17, no 21, p. 21006-21017Article in journal (Refereed) Published
Abstract [en]

Thermoelectric materials play a vital role in the pursuit of a sustainable energy system by allowing the conversion of waste heat to electric energy. Low thermal conductivity is essential to achieving high-efficiency conversion. The conductivity depends on an interplay between the phononic and electronic properties of the nonequilibrium state. Therefore, obtaining a comprehensive understanding of nonequilibrium dynamics of the electronic and phononic subsystems as well as their interactions is key for unlocking the microscopic mechanisms that ultimately govern thermal conductivity. A benchmark material that exhibits ultralow thermal conductivity is SnSe. We study the nonequilibrium phonon dynamics induced by an excited electron population using a framework combining ultrafast electron diffuse scattering and nonequilibrium kinetic theory. This in-depth approach provides a fundamental understanding of energy transfer in the spatiotemporal domain. Our analysis explains the dynamics leading to the observed low thermal conductivity, which we attribute to a mode-dependent tendency to nonconservative phonon scattering. The results offer a penetrating perspective on energy transport in condensed matter with far-reaching implications for rational design of advanced materials with tailored thermal properties.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023
Keywords
Photoinduced electron diffuse scattering (PDS), thermoelectric, nonequilibrium phonon dynamics, SnSe, Ultrafastelectron microscope (UEM), electron-phonon coupling, phonon-phonon scattering
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-516644 (URN)10.1021/acsnano.3c03827 (DOI)001092796200001 ()37862596 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, 2012.0321Swedish Research Council, VR 2021-00171Swedish Research Council, 2018-05973Swedish Research Council, 2019-03901Knut and Alice Wallenberg Foundation, 2018.0104Swedish National Infrastructure for Computing (SNIC)Swedish Foundation for Strategic Research, ICA16-0037EU, European Research Council, 854843Carl Tryggers foundation , CTS20:153
Available from: 2023-11-29 Created: 2023-11-29 Last updated: 2023-11-29Bibliographically approved
Ryan, S. A., Johnsen, P. C., Elhanoty, M. F., Grafov, A., Li, N., Delin, A., . . . Murnane, M. M. (2023). Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100-fs time scales. Science Advances, 9(45), Article ID eadi1428.
Open this publication in new window or tab >>Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100-fs time scales
Show others...
2023 (English)In: Science Advances, E-ISSN 2375-2548, Vol. 9, no 45, article id eadi1428Article in journal (Refereed) Published
Abstract [en]

The direct manipulation of spins via light may provide a path toward ultrafast energy-efficient devices. However, distinguishing the microscopic processes that can occur during ultrafast laser excitation in magnetic alloys is challenging. Here, we study the Heusler compound Co2MnGa, a material that exhibits very strong light-induced spin transfers across the entire M-edge. By combining the element specificity of extreme ultraviolet high-harmonic probes with time-dependent density functional theory, we disentangle the competition between three ultrafast light-induced processes that occur in Co2MnGa: same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast spin flips mediated by spin-orbit coupling. By measuring the dynamic magnetic asymmetry across the entire M-edges of the two magnetic sublattices involved, we uncover the relative dominance of these processes at different probe energy regions and times during the laser pulse. Our combined approach enables a comprehensive microscopic interpretation of laser-induced magnetization dynamics on time scales shorter than 100 femtoseconds.

Place, publisher, year, edition, pages
American Association for the Advancement of Science (AAAS), 2023
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-523905 (URN)10.1126/sciadv.adi1428 (DOI)001142520500002 ()37948525 (PubMedID)
Funder
Swedish Foundation for Strategic Research, ICA16-0037Swedish Research Council, 2019-03901Swedish Research Council, 2016-05980Swedish Research Council, 2019-05304Swedish Research Council, 2022.0108Swedish Research Council, 854843-FASTCORRKnut and Alice Wallenberg Foundation, 2022-06725Knut and Alice Wallenberg Foundation, 2018-05973Knut and Alice Wallenberg Foundation, 2018.0060Knut and Alice Wallenberg FoundationEU, European Research Council, 2021.0246StandUpSwedish National Infrastructure for Computing (SNIC)
Available from: 2024-02-26 Created: 2024-02-26 Last updated: 2024-02-26Bibliographically approved
Elhanoty, M. F., Eriksson, O., Knut, R., Karis, O. & Grånäs, O. (2022). Different fingerprints for the OISTR mechanism in the magnetic alloys experiments. In: Haacke, S Yakovlev, V (Ed.), ADVANCES IN ULTRAFAST CONDENSED PHASE PHYSICS III: . Paper presented at Conference on Advances in Ultrafast Condensed Phase Physics III, APR 03-MAY 20, 2022, ELECTR NETWORK. SPIE-Intl Soc Optical Eng SPIE - The International Society for Optics and Photonics, 12132, Article ID 121320B.
Open this publication in new window or tab >>Different fingerprints for the OISTR mechanism in the magnetic alloys experiments
Show others...
2022 (English)In: ADVANCES IN ULTRAFAST CONDENSED PHASE PHYSICS III / [ed] Haacke, S Yakovlev, V, SPIE-Intl Soc Optical Eng SPIE - The International Society for Optics and Photonics, 2022, Vol. 12132, article id 121320BConference paper, Published paper (Refereed)
Abstract [en]

The interplay between various degrees of freedom in laser induced ultrafast magnetization dynamics (LIUMD) of magnetic alloys is intricate due to the competition between different mechanisms and processes. In this work, we resolve the element specific magnetization dynamics of FePd alloy and further elucidate the dependency of the OISTR mechanism on the laser pulse parameters using ultrashort, short and relatively longer pulse duration with weak and strong fluence. Remarkably, our results illustrate potential discrepancies in experiments measuring the optical inter site spin transfer (OISTR) effect in magnetic alloys.

Place, publisher, year, edition, pages
SPIE - The International Society for Optics and PhotonicsSPIE-Intl Soc Optical Eng, 2022
Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X
Keywords
ultrafast magnetization dynamics, spin flips, magnetic alloys, LIUMD, OISTR, SOC
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-484241 (URN)10.1117/12.2621839 (DOI)000844424500008 ()978-1-5106-5141-8 (ISBN)978-1-5106-5140-1 (ISBN)
Conference
Conference on Advances in Ultrafast Condensed Phase Physics III, APR 03-MAY 20, 2022, ELECTR NETWORK
Funder
Swedish Research Council, 2018-05973Swedish Foundation for Strategic Research, ICA160037Swedish Research Council, 2019-03901EU, European Research Council, 854843-FASTCORR
Available from: 2022-09-12 Created: 2022-09-12 Last updated: 2024-01-15Bibliographically approved
Elhanoty, M. F., Eriksson, O., Knut, R., Karis, O. & Grånäs, O. (2022). Element-selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets. Physical Review B, 105(10), Article ID L100401.
Open this publication in new window or tab >>Element-selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets
Show others...
2022 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 10, article id L100401Article in journal (Refereed) Published
Abstract [en]

Stoner and Heisenberg excitations in magnetic materials are inherently different. The first involves an effective reduction of the exchange splitting, whereas the second comprises excitation of spin waves. In this work, we test the impact of these two excitations in the hybrid Stoner-Heisenberg system of FePd. We present a microscopic picture of ultrafast demagnetization dynamics in this alloy, which represents both components of strong local exchange splitting in Fe and induced polarization in Pd. We identify the spin-orbit coupling (SOC) and the optical intersite spin transfer (OISTR) as the two dominant factors for demagnetization at ultrashort timescales. Remarkably, the drastic difference in the origin of the magnetic moment of the Fe and Pd species is not deciding the initial magnetization dynamics in this alloy. By tuning the external laser pulse, the extrinsic OISTR can be manipulated for site-selective demagnetization on femtosecond timescales providing the fastest way for optical and selective control of the magnetization dynamics in alloys. Saliently, our results signify why various experiments demonstrating OISTR might obtain conflicting results.

Place, publisher, year, edition, pages
American Physical SocietyAmerican Physical Society (APS), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-470544 (URN)10.1103/PhysRevB.105.L100401 (DOI)000766660100003 ()
Funder
Swedish Research Council, 2018-05973Swedish Foundation for Strategic Research , ICA16-0037Swedish Research Council, 2019-03901EU, European Research Council, 854843-FASTCORR
Available from: 2022-03-28 Created: 2022-03-28 Last updated: 2024-01-15Bibliographically approved
Eliah Dawod, I., Timneanu, N., Mancuso, A. P., Caleman, C. & Grånäs, O. (2022). Imaging of femtosecond bond breaking and charge dynamics in ultracharged peptides. Physical Chemistry, Chemical Physics - PCCP, 24(3), 1532-1543
Open this publication in new window or tab >>Imaging of femtosecond bond breaking and charge dynamics in ultracharged peptides
Show others...
2022 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 3, p. 1532-1543Article in journal (Refereed) Published
Abstract [en]

X-ray free-electrons lasers have revolutionized the method of imaging biological macromolecules such as proteins, viruses and cells by opening the door to structural determination of both single particles and crystals at room temperature. By utilizing high intensity X-ray pulses on femtosecond timescales, the effects of radiation damage can be reduced. Achieving high resolution structures will likely require knowledge of how radiation damage affects the structure on an atomic scale, since the experimentally obtained electron densities will be reconstructed in the presence of radiation damage. Detailed understanding of the expected damage scenarios provides further information, in addition to guiding possible corrections that may need to be made to obtain a damage free reconstruction. In this work, we have quantified the effects of ionizing photon-matter interactions using first principles molecular dynamics. We utilize density functional theory to calculate bond breaking and charge dynamics in three ultracharged molecules and two different structural conformations that are important to the structural integrity of biological macromolecules, comparing to our previous studies on amino acids. The effects of the ultracharged states and subsequent bond breaking in real space are studied in reciprocal space using coherent diffractive imaging of an ensemble of aligned biomolecules in the gas phase.

Place, publisher, year, edition, pages
Royal Society of Chemistry (RSC), 2022
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-468649 (URN)10.1039/d1cp03419g (DOI)000733885500001 ()34939631 (PubMedID)
Funder
Swedish Research Council, 2018-05973Swedish Research Council, 2019-03935Swedish Research Council, 2018-00740Swedish Foundation for Strategic Research, ICA16-0037Swedish National Infrastructure for Computing (SNIC)
Available from: 2022-02-28 Created: 2022-02-28 Last updated: 2024-01-09Bibliographically approved
Droulias, S. A., Grånäs, O., Hartmann, O., Komander, K., Hjörvarsson, B., Wolff, M. & Pálsson, G. K. (2022). Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices. Physical Review B, 105(19), Article ID 195438.
Open this publication in new window or tab >>Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices
Show others...
2022 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 19, article id 195438Article in journal (Refereed) Published
Abstract [en]

The deuterium-induced changes of the optical transmission in Fe/V (001) and Cr/V (001) superlattices are found experimentally to be dominated by the volume changes of the vanadium layers and thus indirectly linked to concentration. The deuterium-induced expansion is 67% larger in Cr/V 2/14 monolayers (ML) as compared to Fe/V 2/14 ML. This large difference can be explained by a difference in the site of deuterium from tetrahedral in Fe/V to octahedral in Cr/V. First-principles calculations based on this assumption give quantitative agreement with both the measured optical transmission and the deuterium-induced expansion coefficient. Placing hydrogen in the middle of the vanadium layers results in total energies at 0 K that favor tetrahedral occupancy at low concentrations, although the energy difference is of the order of the thermal energy available in the experiments. Hence small changes in strain, defect concentration, and/or vibrational spectrum of the superlattices may tip the balance to octahedral occupancy at low concentrations. Given this link to concentration and the linear scaling, optical transmission can, therefore, be used in a straightforward way to obtain pressure-composition isotherms also in thin metal films that do not undergo metal-insulator transitions upon hydrogenation.

Place, publisher, year, edition, pages
American Physical SocietyAmerican Physical Society (APS), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-478582 (URN)10.1103/PhysRevB.105.195438 (DOI)000809498100007 ()
Funder
Swedish Foundation for Strategic Research, ICA16-0037Swedish Research Council, 2018-05973Swedish Research Council
Available from: 2022-06-27 Created: 2022-06-27 Last updated: 2024-03-22Bibliographically approved
Ji, S., Grånäs, O., Prasad, A. K. & Weissenrieder, J. (2022). Influence of strain on an ultrafast phase transition. Nanoscale, 15(1), 304-312
Open this publication in new window or tab >>Influence of strain on an ultrafast phase transition
2022 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 15, no 1, p. 304-312Article in journal (Refereed) Published
Abstract [en]

The flexibility of 2D materials combined with properties highly sensitive to strain makes strain engineering a promising avenue for manipulation of both structure and function. Here we investigate the influence of strain, associated with microstructural defects, on a photo-induced structural phase transition in Td–WTe2. Above threshold photoexcitation of uniform, non-strained, samples result in an orthorhombic Td to a metastable orthorhombic 1T* phase transition facilitated by shear displacements of the WTe2 layers along the b axis of the material. In samples prepared with wrinkle defects WTe2 continue its trajectory through a secondary transition that shears the unit cell along the c axis towards a metastable monoclinic 1T′ phase. The time scales and microstructural evolution associated with the transition and its subsequent recovery to the 1T* phase is followed in detail by a combination of ultrafast electron diffraction and microscopy. Our findings show how local strain fields can be employed for tailoring phase change dynamics in ultrafast optically driven processes with potential applications in phase change devices.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2022
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-493335 (URN)10.1039/d2nr03395j (DOI)000895070500001 ()36484465 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, 2018-0104Knut and Alice Wallenberg Foundation, 2012-0321Swedish Research Council, 2021-04379Swedish Foundation for Strategic Research, ICA7-0016Swedish Research Council, 2019-03901EU, European Research Council, 854843Swedish Research Council, 2018-05973Wenner-Gren FoundationsSwedish National Infrastructure for Computing (SNIC)
Available from: 2023-01-17 Created: 2023-01-17 Last updated: 2023-01-17Bibliographically approved
Wang, X., Engel, R. Y., Vaskivskyi, I., Turenne, D., Shokeen, V., Yaroslavtsev, A., . . . Dürr, H. (2022). Ultrafast manipulation of the NiO antiferromagnetic order via sub-gap optical excitation. Faraday discussions, 237(0), 300-316
Open this publication in new window or tab >>Ultrafast manipulation of the NiO antiferromagnetic order via sub-gap optical excitation
Show others...
2022 (English)In: Faraday discussions, ISSN 1359-6640, E-ISSN 1364-5498, Vol. 237, no 0, p. 300-316Article in journal (Refereed) Published
Abstract [en]

Wide-band-gap insulators such as NiO offer the exciting prospect of coherently manipulating electronic correlations with strong optical fields. Contrary to metals where rapid dephasing of optical excitation via electronic processes occurs, the sub-gap excitation in charge-transfer insulators has been shown to couple to low-energy bosonic excitations. However, it is currently unknown if the bosonic dressing field is composed of phonons or magnons. Here we use the prototypical charge-transfer insulator NiO to demonstrate that 1.5 eV sub-gap optical excitation leads to a renormalised NiO band-gap in combination with a significant reduction of the antiferromagnetic order. We employ element-specific X-ray reflectivity at the FLASH free-electron laser to demonstrate the reduction of the upper band-edge at the O 1s-2p core-valence resonance (K-edge) whereas the antiferromagnetic order is probed via X-ray magnetic linear dichroism (XMLD) at the Ni 2p-3d resonance (L-2-edge). Comparing the transient XMLD spectral line shape to ground-state measurements allows us to extract a spin temperature rise of 65 +/- 5 K for time delays longer than 400 fs while at earlier times a non-equilibrium spin state is formed. We identify transient mid-gap states being formed during the first 200 fs accompanied by a band-gap reduction lasting at least up to the maximum measured time delay of 2.4 ps. Electronic structure calculations indicate that magnon excitations significantly contribute to the reduction of the NiO band gap.

Place, publisher, year, edition, pages
Royal Society of Chemistry (RSC), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-493355 (URN)10.1039/d2fd00005a (DOI)000807019100001 ()35670419 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research, ICA16-0037Swedish Research Council, 2019-03901
Available from: 2023-01-16 Created: 2023-01-16 Last updated: 2023-01-16Bibliographically approved
Grånäs, O., Vaskivskyi, I., Wang, X., Thunström, P., Ghimire, S., Knut, R., . . . Dürr, H. (2022). Ultrafast modification of the electronic structure of a correlated insulator. Physical Review Research, 4(3), Article ID L032030.
Open this publication in new window or tab >>Ultrafast modification of the electronic structure of a correlated insulator
Show others...
2022 (English)In: Physical Review Research, E-ISSN 2643-1564, Vol. 4, no 3, article id L032030Article in journal (Refereed) Published
Abstract [en]

A nontrivial balance between Coulomb repulsion and kinematic effects determines the electronic structure of correlated electron materials. The use of electromagnetic fields strong enough to rival these native microscopic interactions allows us to study the electronic response as well as the time scales and energies involved in using quantum effects for possible applications. We use element-specific transient x-ray absorption spectroscopy and high-harmonic generation to measure the response to ultrashort off-resonant optical fields in the prototypical correlated electron insulator NiO. Surprisingly, fields of up to 0.22 V/angstrom lead to no detectable changes in the correlated Ni 3d orbitals contrary to previous predictions. A transient directional charge transfer is uncovered, a behavior that is captured by first-principles theory. Our results highlight the importance of retardation effects in electronic screening and pinpoints a key challenge in functionalizing correlated materials for ultrafast device operation.

Place, publisher, year, edition, pages
American Physical SocietyAmerican Physical Society (APS), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-486313 (URN)10.1103/PhysRevResearch.4.L032030 (DOI)000856584000004 ()
Funder
Swedish Foundation for Strategic Research, ICA16-0037Swedish Research Council, 2017- 06711Swedish Research Council, 854843-FASTCORRSwedish Research Council, 2018-04918Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic ResearchEU, European Research Council, 2018-05973EU, European Research Council, DE-AC02-76SF00515German Research Foundation (DFG), IT1249-19German Research Foundation (DFG)
Available from: 2022-10-07 Created: 2022-10-07 Last updated: 2024-01-15Bibliographically approved
Projects
Multiscale modeling of electron excitations and charge transfer in dye-sensitized solar cells [2013-07303_VR]; Uppsala UniversityAttendance to Future Leaders Program of STS Forum [2018-03046_ VINNOVA]; Uppsala UniversityCoherent Control of Materials Properties [2019-03901_VR]; Uppsala University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1482-2182

Search in DiVA

Show all publications