A5088592235- Advanced Chemical Physics Studies
- Atomic and Molecular Physics
- Laser-Matter Interactions and Applications
- Mass Spectrometry Techniques and Applications
- 2D Materials and Applications
- Topological Materials and Phenomena
- Graphene research and applications
- Quantum and electron transport phenomena
- Spectroscopy and Quantum Chemical Studies
- Photochemistry and Electron Transfer Studies
- Cold Atom Physics and Bose-Einstein Condensates
- Molecular Junctions and Nanostructures
- Physics of Superconductivity and Magnetism
- Electron and X-Ray Spectroscopy Techniques
- Molecular spectroscopy and chirality
- Nuclear physics research studies
- Perovskite Materials and Applications
- Semiconductor Quantum Structures and Devices
- X-ray Spectroscopy and Fluorescence Analysis
- Quantum, superfluid, helium dynamics
- Porphyrin and Phthalocyanine Chemistry
- Advanced Condensed Matter Physics
- Spectroscopy and Laser Applications
- Diamond and Carbon-based Materials Research
- Strong Light-Matter Interactions
Philipps University of Marburg
2016-2023
Goethe University Frankfurt
2008-2017
Johannes Gutenberg University Mainz
2016-2017
Technion – Israel Institute of Technology
2015
The dynamics of momentum-dark exciton formation in transition metal dichalcogenides is difficult to measure experimentally, as many momentum-indirect states are not accessible optical interband spectroscopy. Here, we combine a tunable pump, high-harmonic probe laser source with 3D momentum imaging technique map photoemitted electrons from monolayer WS2. This provides momentum-, energy- and time-resolved access excited on an ultrafast time scale. high temporal resolution the setup allows us...
Electron dynamics in time and space Following molecular excitation electron transfer processes within a single experiment is long-standing goal of spectroscopy the field chemistry. Wallauer et al. combined tomographic photoemission imaging with femtosecond pump-probe scheme to trace excited state orbitals surface-adsorbed molecules both spatial temporal resolution. The present demonstration opens new window for investigating ultrafast such as chemical reactions on surfaces intermolecular...
Using synchrotron radiation we simultaneously ionize and excite one helium atom of a dimer (He2) in shakeup process. The populated states the ion [i.e., He(*+)(n = 2, 3) - He] are found to deexcite via interatomic Coulombic decay. This leads emission second electron from neutral site subsequent Coulomb explosion. In this Letter present measurement momenta fragments that created during reaction. energy distribution kinetic release two He+ ions show pronounced oscillations which attribute...
During the past 15 years a novel decay mechanism of excited atoms has been discovered and investigated. This so-called interatomic Coulombic (ICD) involves chemical environment electronically atom: excitation energy is transferred (in many cases over long distances) to neighbor initially particle usually ionizing that neighbor. It turned out ICD very common route in nature as it occurs across van der Waals hydrogen bonds. The time evolution predicted be highly complex, its efficiency...
We report on the direct mapping of electron transfer in momentum space bulk MoS$_2$ by means time- and angle-resolved two-photon photoemission with a high-harmonic probe. For this purpose, we have combined high-repetition rate source tunable femtosecond pump pulses 3D ($k_x, k_y, E$) spectrometer. show that optical excitation slightly above A exciton resonance results an immediate occupation conduction band at $\overline{K}$ followed ultrafast ($< 50$~fs) to minimum $\overline{\Sigma}$. Both...
Most large molecules are chiral in their structure: they exist as two enantiomers, which mirror images of each other. Whereas the rovibronic sublevels enantiomers almost identical (neglecting a minuscular effect weak interaction), it turns out that photoelectric is sensitive to absolute configuration ionized enantiomer. Indeed, photoionization randomly oriented by left or right circularly polarized light results slightly different electron flux parallel antiparallel with respect photon...
We demonstrate a method for determining the full three-dimensional molecular-frame photoelectron angular distribution in polyatomic molecules using methane as prototype. Simultaneous double Auger decay and subsequent dissociation allow measurement of initial momentum vectors ionic fragments coincidence, allowing orientation by observing three-ion pathway, (H+, H+, CH2(+)). find striking result that at low energies molecule is effectively imaged focusing photoelectrons along bond directions.
We investigate the ionization of HeNe from below He $1s3p$ excitation to threshold. observe ${\mathrm{HeNe}}^{+}$ ions with an enhancement by more than a factor 60 when side couples resonantly radiation field. These are experimental proof two-center resonant photoionization mechanism predicted Najjari et al. [Phys. Rev. Lett. 105, 153002 (2010)]. Furthermore, our data provide electronic and vibrational state resolved decay widths interatomic Coulombic in dimers. find that lifetime strongly...
A comprehensive mapping of the spin polarization electronic bands in ferroelectric a-GeTe(111) films has been performed using a time-of-flight momentum microscope equipped with an imaging filter that enables simultaneous measurement more than 10.000 data points (voxels). Rashba type splitting both surface and bulk opposite helicity inner outer is found revealing complex texture at Fermi energy. The switchable electric field GeTe implies new functionalities for spintronic devices.
The absolute configuration of individual small molecules in the gas phase can be determined directly by light-induced Coulomb explosion imaging (CEI). Herein, this approach is demonstrated for ionization with a single X-ray photon from synchrotron light source, leading to enhanced efficiency and faster fragmentation as compared previous experiments femtosecond laser. In addition, it shown that even incomplete pathways racemic CHBrClF sample give access CEI. This leads significant increase...
We used cold target recoil ion momentum spectroscopy for a comprehensive study of the decay neon dimer $({\mathrm{Ne}}_{2})$ after removal $1s$ electron from one atoms dimer. Multiple pathways are found and identified, mostly being connected to different types interatomic Coulombic (ICD) such as ``direct'' ICD which happens via transfer virtual photon, ``exchange'' an mediated decay. A quantitative theoretical analysis these processes can be in preceding paper by Demekhin et al. [Phys. Rev....
Diffraction of a low energy (<4 eV) carbon-K-photoelectron wave that is created inside CO molecule by absorption circularly polarized photon investigated. The measurements resolve the vibrational states K-shell ionized CO+ and display photoelectron diffraction patterns in molecular frame. These show significant variation for different states. This effect stronger than predicted state-of-the-art theory. As this study performed close to C-K-threshold and, therefore, far below molecule's...
By employing the cold target recoil ion momentum spectroscopy technique, we have investigated (${\mathrm{He}}^{+}$, ${\mathrm{He}}^{+}$) breakup of a helium dimer (${\mathrm{He}}_{2}$) caused by transfer ionization and double capture in collisions with alpha particles ($E=150\text{ }\text{ }\mathrm{keV}/\mathrm{u}$). Surprisingly, results show two-step process as well one-step followed electron exchange. In addition, interatomic Coulombic decay [L. S. Cederbaum, J. Zobeley, F. Tarantelli,...
In the quest for detailed spectroscopic insight into electronic structure at solid surfaces in a large momentum range, we have developed an advanced experimental approach. It combines 3D detection scheme of time-of-flight microscope with optimized filling pattern BESSY II storage ring. Here, comprehensive data sets covering full surface Brillouin zone been used to study faint substrate-film hybridization effects graphene on Ir(111), revealed by pronounced linear dichroism angular...
We used cold target recoil ion momentum spectroscopy (COLTRIMS) to investigate the decay of Ne2 after K-shell photoionization. The breakup into Ne1+/Ne2+ shows interatomic Coulombic (ICD) occurring a preceding atomic Auger decay. molecular frame angular distributions photoelectron and ICD electron show distinct, asymmetric features, which imply localization K-vacancy created at one two sites an emission from localized site. experimental results are supported by calculations in frozen core...
We investigate the temporal evolution of molecular frame angular distributions Auger electrons emitted during ultrafast dissociation HCl following a resonant single-photon excitation. The electron emission pattern changes its shape from that σ orbital to an atomic p state as system evolves molecule into two separated atoms.
We find in the case of W(110) previously overlooked anomalous surface states having their spin locked at right angle to momentum using spin-resolved microscopy. In addition well known Dirac-like state with Rashba texture near -point, we observe a tilted Dirac cone circularly shaped cross section and crossing 0.28 × within projected bulk band gap tungsten. This has eye-catching similarities spin-locked topological insulator. The experiments are fortified by one-step photoemission calculation...
We show that a single photon can ionize the two helium atoms of dimer in distance up to 10 {\deg}A. The energy sharing among electrons, angular distributions ions and electrons as well comparison with electron impact data for suggest knock-off type double ionization process. Coulomb explosion imaging He_2 provides direct view nuclear wave function this by far most extended diffuse all naturally existing molecules.
At photon energies near the Ne K edge it is shown that for 1s ionization Auger electron, and 2s fast photoelectron, launch vibrational wave packets in a dimer. These then decay by emission of slow electron via interatomic Coulombic (ICD). The measured computed ICD spectra are to be significantly modified recoil induced nuclear motion.
We present experimental measurements and theoretical calculations for the photoionization of CH4 at carbon K-edge. Measurements performed using cold target recoil ion momentum spectroscopy (COLTRIMS) combined with complex Kohn variational photoelectron in molecular frame demonstrate surprising result that low energy photoelectrons effectively image molecule by emerging along bond axes. Furthermore, we observe a dynamic breakdown axial behaviour one dissociation pathways intermediate...
We doubly ionize H(2)O by single photon absorption at 43 eV leading to H(+) + OH(+). A direct double ionization and a sequential process in which is followed rapid dissociation into proton an autoionizing OH(*) are identified. The angular distribution of this delayed autoionization electron shows preferred emission the direction emitted proton. From diffraction feature we obtain internuclear distances 700 1100 a.u. occurs. experimental findings line with calculations excited potential energy...
We experimentally study 2p photoionization of neon dimers (Ne_{2}) at a photon energy hν=36.56 eV. By postselection ionization events which lead to dissociation into Ne^{+}+Ne we obtain the photoelectron angular emission distribution in molecular frame. This is symmetric with respect direction charged vs neutral fragment. It shows an inverted Cohen-Fano double slit interference pattern two spherical waves emitted coherently but opposite phases from atoms dimer.
How fast is the charge transfer between two layers of transition metal dichalcogenides and where does it take place in momentum space? Two-photon photoemission using high-harmonic probe pulses can answer this question, as authors demonstrate here for topmost MoS${}_{2}$. By tuning pump below topmost-layer gap, they excite electrons deeper only layer. GW-based tight-binding calculations support experimental findings explain why electron takes at $\overline{\mathrm{\ensuremath{\Sigma}}}$.