Time-of-flight photoelectron momentum microscopy with 80–500 MHz photon sources: electron-optical pulse picker or bandpass pre-filter

Schönhense, G.; Medjanik, K.; Fedchenko, O.; Zymaková, A.; Chernov, S.; Kutnyakhov, D.; Vasilyev, D.; Babenkov, S.; Elmers, H.J.; Baumgärtel, P.; Goslawski, P.; Öhrwall, G.; Grunske, T.; Kauerhof, T.; von Volkmann, K.; Kallmayer, M.; Ellguth, M.; Oelsner, A.

doi:10.1107/S1600577521010511

Figure 3
Time-of-flight spectra and momentum patterns recorded at BESSY II (U125-2_NIM) in multi-bunch hybrid-mode (with camshaft pulse). The spectrum of Au(111) without HF deflector (a) is dominated by the multi-bunch pulse train; the camshaft pulse (arrow) is visible in the center of the gap at 840 ns. After activating the HF deflector as blanking unit (b), the multi-bunch signal (b1) and camshaft signal (b2) are separated and the former is suppressed by the selector aperture, dashed circle in (b2). The auxiliary grid (b3) is located in the backfocal plane of the objective and serves for precise adjustment of the k-image on the delay-line detector. The time spectra (c, d) for Re(0001) and Au(111) are reduced to the camshaft pulse plus two adjacent small solitaire pulses at the lower and upper edge of the time gap, serving for reference (different filling for Re and Au). On the expanded time scale of (c, d) the `pulses' appear as full valence-band spectra. Rows (e–g) show momentum sections through data arrays I(E_B,k_x,k_y), recorded for Re(0001) in the pulse-picking mode at photon energies between hν = 12 and 32 eV as marked on top. (e–g) k_x–k_y cuts at E_F (e) and other binding energies as given in panels (f) and corresponding E_B-versus-k_x sections (g) showing the band dispersions. In (e), SS, SR1 and SR2 mark a surface state and two surface resonances. $[{\bar\Gamma}]$ , $[{\bar{M}}]$ and $[{\bar{K}}]$ denote high-symmetry points in the surface Brillouin zone; arrows mark regions of local intensity enhancement by photoelectron diffraction.

JOURNAL OF
SYNCHROTRON
RADIATION

ISSN: 1600-5775

Volume 28| Part 6| November 2021| Pages 1891-1908

https://doi.org/10.1107/S1600577521010511

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