Fig. 3: Momentum-space model of photoelectron diffraction.
From: Momentum-transfer model of valence-band photoelectron diffraction
a, b Direct transitions fulfilling conditions for constructive interference in normal emission due to forward (a) and backward-scattering (b). c The general case, resembling the Ewald construction, a graphical way to find “spots” where the Laue condition (kf′ – kf = G) is fulfilled. d Details marking (EB, k)-sectors, where the final-state sphere intersects identical regions in different repeated Brillouin zones. Vectors kf, kf′ and kf″ are located on the same final-state sphere and reach equivalent points. Reciprocal lattice vectors G give their distances. e Schematic 3D view showing the vector structure of the transition; length of vector khν exaggerated for clarity. The spherical section is projected onto the planar screen. f Scheme illustrating that all reciprocal lattice vectors inside of the final-state sphere correspond to two specific (EB, k)-sectors on the sphere, fulfilling the Laue equation. BZ marks the Brillouin zone, G1−G4 denote reciprocal lattice vectors. g–i Example of the mechanism described in (c), measured for Mo at EF, hν = 1200 eV and kz close to the border of the Brillouin zone (plane through the high-symmetry points NHP): the V-shaped band on the right-hand side of the field of view is cut by the final-state sphere in two different Brillouin zones (g) and (h), leading to a strong enhancement of the observed intensity (i).
