Correction of the deterministic part of space–charge interaction in momentum microscopy of charged particles

Schönhense, G.; Medjanik, K.; Tusche, Christian; Loos, Marieke de; Geer, Bas van der; Scholz, Markus; Hieke, F.; Gerken, N.; Kirschner, J.; Würth, W.

doi:10.1016/j.ultramic.2015.05.015

Cited by 31 publications

(25 citation statements)

References 29 publications

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“…However, in addition, individual electron-electron scattering processes lead to stochastic (irreversible) heating of the electron ensemble, manifesting itself in a vertical broadening of the distribution. Momentum microscopy gives direct access to the three momentum coordinates, opening a path for a correction of the deterministic part of the Coulomb interaction (space-charge interaction) [116]. Further details on the space-charge problem in FEL experiments are discussed in [117].…”

Section: Summary and Outlook On Current Developmentsmentioning

confidence: 99%

“…(d-f) Point-spread functions calculated for a bimodal electron distribution with total charge of 1, 10 and 100 fC. Dashed lines denote curves of best fit, defining a new k ॥ -dependent energy scale (following [116]). …”

Section: Momentum Microscopy Towards Higher Energiesmentioning

confidence: 99%

“…Simulations using the GPT code [118,119] revealed that under realistic conditions, an order of magnitude gain in resolution can be achieved when the space-charge shift is properly corrected for [116]. The simulation Fig.…”

Section: Momentum Microscopy Towards Higher Energiesmentioning

confidence: 99%

“…The dashed lines denote best-fits of the point-spread functions and can be used for a renormalization of the energy scales. Since a substantial part of the Coulomb interaction is deterministic, it can be partially corrected for in a momentum microscope (for details, see [116]). In common ARPES or ToF spectrometers, the secondary electrons fly along with the fast electrons in all directions.…”

Section: Momentum Microscopy Towards Higher Energiesmentioning

confidence: 99%

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Space-, time- and spin-resolved photoemission

Schoenhense

Medjanik

Elmers

2015

Journal of Electron Spectroscopy and Related Phenomena

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This article reviews photoemission experiments that simultaneously resolve at least two of the following degrees of freedom: space (real and momentum space), time (intrinsic time scale of a fast experiment or time-of-flight) and spin. In the spatiotemporal domain, imaging of fast processes by PEEM gives direct insight into plasmon dynamics or magnetization processes. In the category real space & spin the novel concept of imaging spin filters is discussed. In the time & spin chapter we address time-of-flight spin detectors and ultrafast spin processes that are accessible by pump-and-probe techniques. A main part of the paper is devoted to the resolution of momentum-space & time. This is implemented in form of the time-of-flight momentum microscope, a very recent development of which the first instrument has been in operation since 2014. In an extended outlook chapter, the potential of new developments and of a novel, highly parallelized delay-line type electron detector will be discussed. The combination of all three degrees of freedom k-space, time & spin is emerging through the combination of the ToF momentum microscope with imaging spin filter. Outline

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Section: Summary and Outlook On Current Developmentsmentioning

confidence: 99%

Section: Momentum Microscopy Towards Higher Energiesmentioning

confidence: 99%

Section: Momentum Microscopy Towards Higher Energiesmentioning

confidence: 99%

Section: Momentum Microscopy Towards Higher Energiesmentioning

confidence: 99%

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Space-, time- and spin-resolved photoemission

Schoenhense

Medjanik

Elmers

2015

Journal of Electron Spectroscopy and Related Phenomena

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“…The high density of electrons released by intense, short photon pulses in a small area on the sample leads to significant Coulomb interaction, which alters the energy and angular distribution and sets the ultimate limit to the performance of photoemission experiments. Depending on the number of electrons in the cloud and their spatio-temporal distribution, this effect can deteriorate the photoelectron spectra dramatically [1][2][3][4][5][6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Multidimensional photoemission spectroscopy—the space-charge limit

et al. 2018

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Photoelectron spectroscopy, especially at pulsed sources, is ultimately limited by the Coulomb interaction in the electron cloud, changing energy and angular distribution of the photoelectrons. A detailed understanding of this phenomenon is crucial for future pump-probe photoemission studies at (x-ray) free electron lasers and high-harmonic photon sources. Measurements have been performed for Ir(111) at hν=1000 eV with photon flux densities between ∼10 2 and 10 4 photons per pulse and μm 2 (beamline P04/PETRA III, DESY Hamburg), revealing space-charge induced energy shifts of up to 10 eV. In order to correct the essential part of the energy shift and restore the electron distributions close to the Fermi energy, we developed a semi-analytical theory for the space-charge effect in cathode-lens instruments (momentum microscopes, photoemission electron microscopes). The theory predicts a Lorentzian profile of energy isosurfaces and allows us to quantify the charge cloud from measured energy profiles. The correction is essential for the determination of the Fermi surface, as we demonstrate by means of 'k-space movies' for the prototypical high-Z material tungsten. In an energy interval of about 1 eV below the Fermi edge, the bandstructure can be restored up to substantial shifts of ∼7 eV. Scattered photoelectrons strongly enhance the inelastic background in the region several eV below E F , proving that the majority of scattering events involves a slow electron. The correction yields a gain of two orders of magnitude in usable intensity compared with the uncorrected case (assuming a tolerable shift of 250 meV). The results are particularly important for future experiments at SASE-type free electron lasers, since the correction also works for strongly fluctuating (but known) pulse intensities.

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