A highly effective way to cope with the weak signals in hard X-ray angular-resolved photoelectron spectroscopy is introduced. Full-field momentum imaging combined with time-of-flight parallel energy recording constitute a 3D recording scheme, gaining two orders of magnitude in detection efficiency.

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.

The coupling of real and momentum space is utilized to tailor electronic properties of the collinear metallic antiferromagnet Mn 2 Au by aligning the real space Néel vector indicating the direction of the staggered magnetization. Pulsed magnetic fields of 60 T were used to orient the sublattice magnetizations of capped epitaxial Mn 2 Au(001) thin films perpendicular to the applied field direction by a spin-flop transition. The electronic structure and its corresponding changes were investigated by angular-resolved photoemission spectroscopy with photon energies in the vacuum-ultraviolet, soft and hard X-ray range. The results reveal an energetic rearrangement of conduction electrons propagating perpendicular to the Néel vector. They confirm previous predictions on the origin of the Néel spin-orbit torque and anisotropic magnetoresistance in Mn 2 Au, and reflect the combined antiferromagnetic and spin-orbit interaction in this compound leading to inversion symmetry breaking.

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...

The atomic structure of the cubic-SiC(001) surface during ultra-high vacuum graphene synthesis has been studied using scanning tunneling microscopy (STM) and low-energy electron diffraction. Atomically resolved STM studies prove the synthesis of a uniform, millimeter-scale graphene overlayer consisting of nanodomains rotated by ±13.5° relative to the 〈110〉-directed boundaries. The preferential directions of the domain boundaries coincide with the directions of carbon atomic chains on the SiC(001)-c(2 × 2) reconstruction, fabricated prior to graphene synthesis. The presented data show the correlation between the atomic structures of the SiC(001)-c(2 × 2) surface and the graphene/SiC(001) rotated domain network and pave the way for optimizing large-area graphene synthesis on low-cost cubic-SiC(001)/Si(001) wafers.