Momentum-transfer model of valence-band photoelectron diffraction

Schönhense, G.; Medjanik, K.; Babenkov, S.; Vasilyev, Dmitry; Ellguth, Martin; Fedchenko, O.; Чернов, С. В.; Schönhense, B.; Elmers, H. J.

doi:10.1038/s42005-020-0311-9

Cited by 20 publications

(34 citation statements)

References 75 publications

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“…2m-p reveals that there are still various regions of significant local intensity enhancement. This resembles our earlier result found in the soft X-ray range 29 . We will come back to this point in the Discussion section.…”

Section: Resultssupporting

confidence: 92%

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High-accuracy bulk electronic bandmapping with eliminated diffraction effects using hard X-ray photoelectron momentum microscopy

et al. 2019

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A key benefit of angle-resolved photoelectron spectroscopy (ARPES) in the X-ray range is the significant increase of the information depth, thanks to the large inelastic mean-free-path of the escaping photoelectrons. In practice hard X-ray ARPES (HARPES) faces severe challenges by low cross sections, large photon momentum transfer, and in particular strong phonon scattering and photoelectron diffraction effects. Here, we show that these challenges can be overcome by extending ultra-efficient time-of-flight momentum microscopy into the hard X-ray regime. Phonon scattering destroys the initial momentum distribution but subsequent diffraction at the lattice imprints a pronounced Kikuchi-type pattern on the background signal. Moreover, the pattern of the valence electrons is modulated by diffraction as well. For the examples of the medium-weight element materials Mo and layered TiTe2, we demonstrate how comprehensive valence-band and core-level photoemission data taken under identical conditions can be used to effectively remove photoelectron diffraction effects in HARPES band maps.

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Section: Resultssupporting

confidence: 92%

“…It can be described in terms of Umklapp processes on the displaced final-state sphere involving reciprocal lattice vectors. We have discussed and quantified this effect in the soft X-ray range 29 . The intensity enhancement can reach a factor of 5.…”

Section: Discussionmentioning

confidence: 99%

High-accuracy bulk electronic bandmapping with eliminated diffraction effects using hard X-ray photoelectron momentum microscopy

et al. 2019

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“…In that work the dichroism asymmetry has been derived from a single measurement at fixed photon polarization, exploiting the symmetry properties of the setup. [50]). In the following, we neglect this phenomenon because we believe that the normalization of the CDAD signal to the sum intensity removes most of the diffraction effect.…”

Section: Experimental Results For the Cdadmentioning

confidence: 99%

4D texture of circular dichroism in soft-x-ray photoemission from tungsten

et al. 2019

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Photoemission-intensity distributions I RCP/LCP (E B , k) measured for right-and left-circularly polarized soft x-rays revealed a large circular dichroism in angular distribution (CDAD) in the 4D parameter space (E B binding energy, k momentum vector). Full-field k-imaging combined with timeof-flight energy recording at a high-brilliance soft x-ray beamline allowed mapping the CDAD in the bulk Brillouin zone of tungsten and the entire d-band complex within a few hours. CDADasymmetries are very high (up to 90%), persist throughout the whole photon-energy range (300-1300 eV) and show a pronounced dependence on momentum k and binding energy E B , visualized as movies or sequences of cuts through the 4D object. One-step photoemission calculations for the same photon energies show fair agreement with the measured results. In addition to the requirement of a 'handed' experimental geometry, known from previous experiments on adsorbates and surface states, we find an anti-symmetric behavior of the CDAD with respect to two bulk mirror planes. A new symmetry condition along the perpendicular momentum k z makes CDAD a valuable tool for an unambiguous identification of high-symmetry planes in direct transitions in the periodic zone scheme. Technically, the method provides a circular polarimeter for soft, tender and hard x-rays. being sensitive to their phase-shift differences. The differential photoemission cross section is proportional to the squared total dipole matrix element that contains interference terms between different final-state partial waves. Upon reversal of the photon helicity (in case of CDAD) or switching of the electric vector between orthogonal directions (for LDAD), interference terms with odd symmetry change their signs. This is the origin of the dichroism in the photoelectron angular distribution. This phenomenon exists in the pure electric dipole approximation and thus it differs from the 'natural' CD of chiral molecules, which is described by higher-order terms in the electron-photon operator [14].In the present work we employ the technique of time-of-flight (ToF) k-microscopy for a comprehensive study of the CDAD in the soft-x-ray spectral range. This new method captures simultaneously more than one full Brillouin zone (BZ) for binding energies in a range of several eV, yielding full information from the valence bands. In the vacuum ultraviolet (VUV) range, this instrument was previously used for the study of LDAD in photoemission from Mo(110) surface states and surface resonances [15]. These states are characterized by their 2D character and their location at the surface, wherefore they fulfill the criteria discussed for adsorbate systems [13]. Earlier work on graphite [16] and Pd [17] revealed that a CDAD also exists in photoemission from crystalline samples. However, the low photon energies used essentially probe the surface character of the bands. Hence, these results cannot be considered representative for true 3D bulk states. Moreover, no information on the dependence of the CDAD on the electro...

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“…Publications since the pilot studies have continued to exploit the microscope to study the valence band structure or to acquire XPD information of a range of materials and some are discussed in detail below. [137,198,[201][202][203][204][205][206] Initial studies in the HAXPES regime were conducted by Medjanik et al and presented proof of principle of the instrument by successfully mapping the electronic structure of Re(0001) at hν = 3.83 keV in a similar manner to the soft X-ray measurements conducted on W(110) prior. [197] Space-charge effects stemming from the Coloumb interaction of the photoelectron cloud induced an energy shift and an anisotropic acceleration of the electrons, which led to a Lorentzian deformation of the spectra.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020

Kalha

Fernando

Bhatt

et al. 2021

J. Phys.: Condens. Matter

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Hard X-ray photoelectron spectroscopy (HAXPES) is establishing itself as an essential technique for the characterisation of materials. The number of specialised photoelectron spectroscopy techniques making use of hard X-rays is steadily increasing and ever more complex experimental designs enable truly transformative insights into the chemical, electronic, magnetic, and structural nature of materials. This paper begins with a short historic perspective of HAXPES and spans from developments in the early days of photoelectron spectroscopy to provide an understanding of the origin and initial development of the technique to state-of-the-art instrumentation and experimental capabilities. The main motivation for and focus of this paper is to provide a picture of the technique in 2020, including a detailed overview of available experimental systems worldwide and insights into a range of specific measurement modi and approaches. We also aim to provide a glimpse into the future of the technique including possible developments and opportunities.

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Momentum-transfer model of valence-band photoelectron diffraction

Cited by 20 publications

References 75 publications

High-accuracy bulk electronic bandmapping with eliminated diffraction effects using hard X-ray photoelectron momentum microscopy

High-accuracy bulk electronic bandmapping with eliminated diffraction effects using hard X-ray photoelectron momentum microscopy

4D texture of circular dichroism in soft-x-ray photoemission from tungsten

Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020

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