Progress in HAXPES performance combining full-field <i>k</i>-imaging with time-of-flight recording

Medjanik, K.; Babenkov, S.; Chernov, S.; Vasilyev, Dmitry; Schönhense, B.; Schlueter, Christoph; Gloskovskii, A.; Matveyev, Yu.; Drube, W.; Elmers, H. J.; Schoenhense, G.

doi:10.1107/s1600577519012773

Cited by 41 publications

(67 citation statements)

References 73 publications

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“…For Graphite we take the value V 0 * =13 eV from [45] and assume m eff /m e =1. Measurements for tungsten yielded m eff /m e =1.07 at 1 keV [38] and 1 at 6 keV [46]. For Mo we found m eff /m e =1.03 at 460 eV and m eff /m e =1 already at 1.7 keV [47].…”

Section: Carbon 1s Diffractogramsmentioning

confidence: 68%

“…For most measurements we used the Si(111) double crystal monochromator (ΔE/E ∼1.3 × 10 −4 , bandwidth 450 meV at hν = 5 keV), a few measurements were done with the Si(311) crystal (ΔE/E ∼3 × 10 −5 , flux ∼2 × 10 12 hv/s, bandwidth 155 meV at 5 keV). A bandwidth of ∼50 meV is already available using a single Si(333) channel-cut crystal operating close to 6 keV [38]. A similar small bandwidth will be possible in the full energy range using an additional post-monochromator.…”

Section: Experimental and Theoretical Detailsmentioning

confidence: 99%

“…For the present geometry maximum k-fields of 14-16 Å −1 are recorded, limited by the 80 mm diameter of the detector. For valence-band k-mapping this covers the central Brillouin zone (BZ) and two rings of repeated BZs (in total 19 BZs in parallel for the hcp metal Re [38]).…”

Section: Experimental and Theoretical Detailsmentioning

confidence: 99%

“…So, if certain angular intervals are particularly sensitive on structural changes, e.g. in phase transitions, these intervals can be selected using zero-field mode and off-normal emission [38]. An example of such an off-normal hXPD pattern is shown in the supplemental information is available online at stacks.iop.org/NJP/21/113031/ mmedia.…”

Section: Experimental and Theoretical Detailsmentioning

confidence: 99%

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High-resolution hard-x-ray photoelectron diffraction in a momentum microscope—the model case of graphite

et al. 2019

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Hard x-ray photoelectron diffraction (hXPD) patterns recorded with a momentum microscope with high k-resolution (0.025 Å −1 equivalent to an angular resolution of 0.034°at 7 keV) reveal unprecedented rich fine structure. We have studied hXPD of the C 1s core level in the prototypical low-Z material Graphite at 20 photon energies between 2.8 and 7.3 keV. Sharp bright and dark lines shift with energy; regions of Kikuchi band crossings near zone axis exhibit a filigree structure which varies rapidly with energy. Calculations based on the Bloch wave approach to electron diffraction from lattice planes show excellent agreement with the experimental results throughout the entire energy range. The main Kikuchi bands in the [001] zone axis appear fixed on the momentum scale with a width of the corresponding reciprocal lattice vector, allowing to reconstruct the size of the projected Brillouin zone. The newly developed high-energy k-microscope allows full-field imaging of (k x , k y )-distributions in large k-fields (up to >22 Å −1 dia.) and time-of-flight energy recording.XPD cluster picture and dynamical electron scattering from lattice planes showed that the latter is more appropriate for very high energies. Hence, for the present study of hard x-ray photoelectron diffraction (hXPD) the dynamical scattering approach for bulk crystals is expected to be the more efficient theoretical description. By exploiting exchange scattering and multiplet splittings, even antiferromagnetic short-range order has been probed by XPD [17,18].Experimentally, XPD is studied using angular-resolved photoelectron spectroscopy. Large polar angular ranges of typically 0°-60°can be observed, mostly by rotating the sample about its surface normal (e.g. [8,10,11]). But also display-type electron analysers were developed [19][20][21] which give direct 2D full-field angular distributions in a wide angular range [22][23][24][25]. One main emphasis was to observe the pronounced forward scattering along atom rows in off-normal directions [4,8], hence the trend to observe a maximum polar angular range. Typical angular resolutions in both angular-scanning and display-type recording modes are ∼1°, but in some cases higher resolutions (<1°FWHM) have been reached [26][27][28].Here we present the first study of XPD using the new technique of momentum microscopy. In this type of photoelectron analyser, a cathode-lens (usually with an electrostatic extractor field) yields a reciprocal image in its backfocal plane (BFP), which is magnified on the image detector. This recording mode bears several essential differences in comparison with previous approaches: The diffractograms are observed in reciprocal space (i.e. on a momentum scale) instead of real-space polar coordinates. The k-field of view in the present study is up to ∼14 Å −1 at 7 keV, corresponding to a small polar angular range of 0°-9°. The k-resolution of ∼0.03 Å −1 corresponds to an angular resolution of 0.03°. For the small angular range, full-field imaging works without sample rotation, similar to...

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Section: Carbon 1s Diffractogramsmentioning

confidence: 68%

Section: Experimental and Theoretical Detailsmentioning

confidence: 99%

Section: Experimental and Theoretical Detailsmentioning

confidence: 99%

Section: Experimental and Theoretical Detailsmentioning

confidence: 99%

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High-resolution hard-x-ray photoelectron diffraction in a momentum microscope—the model case of graphite

et al. 2019

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“…The momentum coordinate k z results from scanning the photon energy, exploiting the concept of direct transitions as described in Refs. [42,53]. The constant-energy cuts for E = E F measured for 19 different photon energies in the range of (500-700) eV have been concatenated along k z to form the three-dimensional Fermi surface.…”

Section: Resultsmentioning

confidence: 99%

Rashba splitting of the Tamm surface state on Re(0001) observed by spin-resolved photoemission and scanning tunneling spectroscopy

Elmers

Regel

Mashoff

et al. 2020

Phys. Rev. Research

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Using spin-resolved time-of-flight momentum microscopy, the Rashba splitting of the Tamm surface state is investigated. This state resides at the Fermi level in a projected bulk band gap of the close-packed (0001) surface of hcp Re. The Rashba splitting amounts to 0.4 Å −1. The state with smaller parallel momentum is fully separated from bulk states, whereas the Rashba branch with larger momentum hybridizes with bulk states, which leads to a suppression of spin-momentum locking. We find a good agreement of the experimental results with one step photoemission calculations that are based on ab initio theory within the local density approximation. The spin polarization of the inner Rashba state is not complete, which manifests in the occurrence of quantum interference patterns as observed by scanning tunneling microscopy. A one-to-one agreement of scanning tunneling spectroscopy and photoemission results is observed, suggesting that the quantum interference pattern originates from the inner Rashba state.

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Electron‐ and X‐Ray Spectroscopies of Organic Charge‐Transfer Complexes

Medjanik

Elmers

Schönhense

et al. 2019

Physica Status Solidi (b)

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Recent work aiming at a deeper understanding of the electronic properties of classical and novel charge‐transfer (CT) complexes is reviewed herein. From a variety of studied CT salts, the prototypical examples TTF‐TCNQ, (TMTTF)2SbF6, (TMTSF)2PF6, and TMP/HMP‐TCNQ have been selected. Three different types of electron and X‐ray spectroscopies were applied, namely ultraviolet photoelectron spectroscopy (UPS), hard X‐ray photoelectron spectroscopy (HAXPES), and near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy. Using UPS, the development of the valence band structure during co‐deposition of the donor and acceptor moieties TMP/HMP and TCNQ has been studied. The spectra reveal characteristic level shifts and a strong reduction of the HOMO–LUMO gap upon formation of the complex. HAXPES probes the core levels and reveals characteristic shifts of the binding energies in (TMTTF)2SbF6 at the phase transition to the low‐temperature charge‐ordered state. NEXAFS is a local, element‐specific probe for the unoccupied bands above the Fermi level and reveals changes in the population of specific orbitals when the CT complex is formed. As an outlook, the novel method of photoelectron momentum microscopy is presented, giving access to the valence bands and core‐levels and in particular to high‐resolution X‐ray photoelectron diffraction patterns.

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Progress in HAXPES performance combining full-field k-imaging with time-of-flight recording

Cited by 41 publications

References 73 publications

High-resolution hard-x-ray photoelectron diffraction in a momentum microscope—the model case of graphite

High-resolution hard-x-ray photoelectron diffraction in a momentum microscope—the model case of graphite

Rashba splitting of the Tamm surface state on Re(0001) observed by spin-resolved photoemission and scanning tunneling spectroscopy

Electron‐ and X‐Ray Spectroscopies of Organic Charge‐Transfer Complexes

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