TY  - JOUR
A1  - Beye, Martin
A1  - Öberg, Henrik
A1  - Xin, Hongliang
A1  - Dakovski, Georgi L.
A1  - Föhlisch, Alexander
A1  - Gladh, Jorgen
A1  - Hantschmann, Markus
A1  - Hieke, Florian
A1  - Kaya, Sarp
A1  - Kühn, Danilo
A1  - LaRue, Jerry
A1  - Mercurio, Giuseppe
A1  - Minitti, Michael P.
A1  - Mitra, Ankush
A1  - Moeller, Stefan P.
A1  - Ng, May Ling
A1  - Nilsson, Anders
A1  - Nordlund, Dennis
A1  - Norskov, Jens
A1  - Öström, Henrik
A1  - Ogasawara, Hirohito
A1  - Persson, Mats
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Wolf, Martin
A1  - Abild-Pedersen, Frank
A1  - Pettersson, Lars G. M.
A1  - Wurth, Wilfried
T1  - Chemical Bond Activation Observed with an X-ray Laser
JF  - The journal of physical chemistry letters
N2  - The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free electron laser to directly observe the decreased bonding antibonding splitting following bond-activation using an ultrashort optical laser pulse.
Y1  - 2016
U6  - https://doi.org/10.1021/acs.jpclett.6b01543
SN  - 1948-7185
VL  - 7
SP  - 3647
EP  - 3651
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - THES
A1  - Kühn, Danilo
T1  - Synchrotron-based angle-resolved time-of-flight electron spectroscopy for dynamics in dichalogenides
Y1  - 2018
ER  - 
TY  - GEN
A1  - Kühn, Danilo
A1  - Sorgenfrei, Florian
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Musazayb, Abdurrahman
A1  - Ovsyannikov, Ruslan
A1  - Stråhlman, Christian
A1  - Svensson, Svante
A1  - Mårtensson, Nils
A1  - Föhlisch, Alexander
T1  - Capabilities of angle resolved time of flight electron spectroscopy with the 60 degrees wide angle acceptance lens
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - The simultaneous detection of energy, momentum and temporal information in electron spectroscopy is the key aspect to enhance the detection efficiency in order to broaden the range of scientific applications. Employing a novel 60 degrees wide angle acceptance lens system, based on an additional accelerating electron optical element, leads to a significant enhancement in transmission over the previously employed 30 degrees electron lenses. Due to the performance gain, optimized capabilities for time resolved electron spectroscopy and other high transmission applications with pulsed ionizing radiation have been obtained. The energy resolution and transmission have been determined experimentally utilizing BESSY II as a photon source. Four different and complementary lens modes have been characterized. (C) 2017 The Authors. Published by Elsevier B.V.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 782 
KW  - Artof
KW  - electron spectroscopy
KW  - wide angle
KW  - time of flight
KW  - energy resolution
KW  - synchrotron
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436629
SN  - 1866-8372
IS  - 782
SP  - 45
EP  - 50
ER  - 
TY  - JOUR
A1  - Kühn, Danilo
A1  - Sorgenfrei, Florian
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael
A1  - Musazay, Abdurrahman
A1  - Ovsyannikov, Ruslan
A1  - Strahlman, Christian
A1  - Svensson, Svante
A1  - Mårtensson, Nils
A1  - Föhlisch, Alexander
T1  - Capabilities of angle resolved time of flight electron spectroscopy with the 60 degrees wide angle acceptance lens
JF  - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy
N2  - The simultaneous detection of energy, momentum and temporal information in electron spectroscopy is the key aspect to enhance the detection efficiency in order to broaden the range of scientific applications. Employing a novel 60 degrees wide angle acceptance lens system, based on an additional accelerating electron optical element, leads to a significant enhancement in transmission over the previously employed 30 degrees electron lenses. Due to the performance gain, optimized capabilities for time resolved electron spectroscopy and other high transmission applications with pulsed ionizing radiation have been obtained. The energy resolution and transmission have been determined experimentally utilizing BESSY II as a photon source. Four different and complementary lens modes have been characterized. (C) 2017 The Authors. Published by Elsevier B.V.
KW  - Artof
KW  - Electron spectroscopy
KW  - Wide angle
KW  - Time of flight
KW  - Energy resolution
KW  - Synchrotron
Y1  - 2018
U6  - https://doi.org/10.1016/j.elspec.2017.06.008
SN  - 0368-2048
SN  - 1873-2526
VL  - 224
SP  - 45
EP  - 50
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Kühn, Danilo
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Sorgenfrei, Florian
A1  - Föhlisch, Alexander
T1  - The influence of x-ray pulse length on space-charge effects in optical pump/x-ray probe photoemission
JF  - New journal of physics : the open-access journal for physics
N2  - Pump-probe photoelectron spectroscopy (PES) is a versatile tool to investigate the dynamics of transient states of excited matter. Vacuum space-charge effects can mask these dynamics and complicate the interpretation of electron spectra. Here we report on space-charge effects in Au 4f photoemission from a polycrystalline gold surface, excited with moderately intense 90 ps (FWHM) soft x-ray probe pulses, under the influence of the Coulomb forces exerted by a pump electron cloud, which was produced by intense 40 fs laser pulses. The experimentally observed kinetic energy shift and spectral broadening of the Au 4f lines, measured with highly-efficient time-of-flight spectroscopy, are in good agreement with simulations utilizing a mean-field model of the electrostatic pump electron potential. This confirms that the line broadening is predominantly caused by variations in the take-off time of the probe electrons without appreciable influence of local scattering events. Our findings might be of general interest for pump-probe PES with picosecond-pulse-length sources.
KW  - space-charge effects
KW  - mean-field model
KW  - x-ray photoemission
KW  - electron spectroscopy
KW  - pump-probe
KW  - ARTOF
Y1  - 2019
U6  - https://doi.org/10.1088/1367-2630/ab2f5c
SN  - 1367-2630
VL  - 21
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Kühn, Danilo
A1  - Müller, Moritz
A1  - Sorgenfrei, Florian
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Ovsyannikov, Ruslan
A1  - Martensson, Nils
A1  - Sanchez-Portal, Daniel
A1  - Föhlisch, Alexander
T1  - Directional sub-femtosecond charge transfer dynamics and the dimensionality of 1T-TaS2
JF  - Scientific reports
N2  - For the layered transition metal dichalcogenide 1T-TaS2, we establish through a unique experimental approach and density functional theory, how ultrafast charge transfer in 1T-TaS2 takes on isotropic three-dimensional character or anisotropic two-dimensional character, depending on the commensurability of the charge density wave phases of 1T-TaS2. The X-ray spectroscopic core-hole-clock method prepares selectively in-and out-of-plane polarized sulfur 3p orbital occupation with respect to the 1T-TaS2 planes and monitors sub-femtosecond wave packet delocalization. Despite being a prototypical two-dimensional material, isotropic three-dimensional charge transfer is found in the commensurate charge density wave phase (CCDW), indicating strong coupling between layers. In contrast, anisotropic two-dimensional charge transfer occurs for the nearly commensurate phase (NCDW). In direct comparison, theory shows that interlayer interaction in the CCDW phase - not layer stacking variations - causes isotropic three-dimensional charge transfer. This is presumably a general mechanism for phase transitions and tailored properties of dichalcogenides with charge density waves.
Y1  - 2019
U6  - https://doi.org/10.1038/s41598-018-36637-0
SN  - 2045-2322
VL  - 9
IS  - 488
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Haverkamp, Robert
A1  - Sorgenfrei, Nomi L. A. N.
A1  - Giangrisostomi, Erika
A1  - Neppl, Stefan
A1  - Kühn, Danilo
A1  - Föhlisch, Alexander
T1  - Directional charge delocalization dynamics in semiconducting 2H-MoS2 and metallic 1T-LixMoS2
JF  - Scientific reports
N2  - The layered dichalcogenide MoS2 is relevant for electrochemical Li adsorption/intercalation, in the course of which the material undergoes a concomitant structural phase transition from semiconducting 2H-MoS2 to metallic 1T-LixMoS2. With the core hole clock approach at the S L1 X-ray absorption edge we quantify the ultrafast directional charge transfer of excited S3p electrons in-plane () and out-of-plane (perpendicular to) for 2H-MoS2 as tau 2H,=0.38 +/- 0.08 fs and tau 2H,perpendicular to =0.33 +/- 0.06 fs and for 1T-LixMoS2 as tau 1T,=0.32 +/- 0.12 fs and tau 1T,perpendicular to =0.09 +/- 0.07 fs. The isotropic charge delocalization of S3p electrons in the semiconducting 2H phase within the S-Mo-S sheets is assigned to the specific symmetry of the Mo-S bonding arrangement. Formation of 1T-LixMoS2 by lithiation accelerates the in-plane charge transfer by a factor of similar to 1.2 due to electron injection to the Mo-S covalent bonds and concomitant structural repositioning of S atoms within the S-Mo-S sheets. For excitation into out-of-plane orbitals, an accelerated charge transfer by a factor of similar to 3.7 upon lithiation occurs due to S-Li coupling.
Y1  - 2021
U6  - https://doi.org/10.1038/s41598-021-86364-2
SN  - 2045-2322
VL  - 11
IS  - 1
PB  - Macmillan Publishers Limited, part of Springer Nature
CY  - London
ER  - 
TY  - JOUR
A1  - Sorgenfrei, Nomi
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Kühn, Danilo
A1  - Neppl, Stefan
A1  - Ovsyannikov, Ruslan
A1  - Sezen, Hikmet
A1  - Svensson, Svante
A1  - Föhlisch, Alexander
T1  - Photodriven transient picosecond top-layer semiconductor to metal phase-transition in p-doped molybdenum disulfide
JF  - Advanced materials
N2  - Visible light is shown to create a transient metallic S-Mo-S surface layer on bulk semiconducting p-doped indirect-bandgap 2H-MoS2. Optically created electron-hole pairs separate in the surface band bending region of the p-doped semiconducting crystal causing a transient accumulation of electrons in the surface region. This triggers a reversible 2H-semiconductor to 1T-metal phase-transition of the surface layer. Electron-phonon coupling of the indirect-bandgap p-doped 2H-MoS2 enables this efficient pathway even at a low density of excited electrons with a distinct optical excitation threshold and saturation behavior. This mechanism needs to be taken into consideration when describing the surface properties of illuminated p-doped 2H-MoS2. In particular, light-induced increased charge mobility and surface activation can cause and enhance the photocatalytic and photoassisted electrochemical hydrogen evolution reaction of water on 2H-MoS2. Generally, it opens up for a way to control not only the surface of p-doped 2H-MoS2 but also related dichalcogenides and layered systems. The findings are based on the sensitivity of time-resolved electron spectroscopy for chemical analysis with photon-energy-tuneable synchrotron radiation.
KW  - catalysis
KW  - dichalcogenides
KW  - hydrogen evolution reaction
KW  - phase transitions
KW  - photoelectron spectroscopy
Y1  - 2021
U6  - https://doi.org/10.1002/adma.202006957
SN  - 0935-9648
SN  - 1521-4095
VL  - 33
IS  - 14
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Andersson, Edvin K. W.
A1  - Sångeland, Christofer
A1  - Berggren, Elin
A1  - Johansson, Fredrik O. L.
A1  - Kühn, Danilo
A1  - Lindblad, Andreas
A1  - Mindemark, Jonas
A1  - Hahlin, Maria
T1  - Early-stage decomposition of solid polymer electrolytes in Li-metal batteries
JF  - Journal of materials chemistry : A, Materials for energy and sustainability
N2  - Development of functional and stable solid polymer electrolytes (SPEs) for battery applications is an important step towards both safer batteries and for the realization of lithium-based or anode-less batteries. The interface between the lithium and the solid polymer electrolyte is one of the bottlenecks, where severe degradation is expected. Here, the stability of three different SPEs - poly(ethylene oxide) (PEO), poly(epsilon-caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC) - together with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, is investigated after they have been exposed to lithium metal under UHV conditions. Degradation compounds, e.g. Li-O-R, LiF and LixSyOz, are identified for all SPEs using soft X-ray photoelectron spectroscopy. A competing degradation between polymer and salt is identified in the outermost surface region (<7 nm), and is dependent on the polymer host. PTMC:LiTFSI shows the most severe decomposition of both polymer and salt followed by PCL:LiTFSI and PEO:LiTFSI. In addition, the movement of lithium species through the decomposed interface shows large variation depending on the polymer electrolyte system.
Y1  - 2021
U6  - https://doi.org/10.1039/d1ta05015j
SN  - 2050-7488
SN  - 2050-7496
VL  - 9
IS  - 39
SP  - 22462
EP  - 22471
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  -