Fig. 2: Photoinduced domain evolution observed in UED patterns.
From: Photoinduced anisotropic lattice dynamic response and domain formation in thermoelectric SnSe
a An intensity difference map between the UED patterns taken before time-zero and at 1.7 ps. The Brillouin zones around the (020) Bragg peak (Γ point) with the 1st, 2nd, and 3rd Brillouin zone boundaries marked by white, yellow and black lines, respectively. The (000) beam position is indicated by the circle. b The dots present the line profiles of the diffraction intensity along the Γ–Z (purple dots) and Γ–Y directions (green dots) in a, showing significant asymmetry of the intensity profiles. The solid lines are the intensity profiles from the simulated pattern in c. c Simulated intensity difference map calculated using Monte Carlo based multislice method with large supercell containing domain structure between t ≤ 0 (initial) and t > 0. d Line profiles along Γ-Z direction of the Bragg peak in the UED intensity difference pattern as a function of time. The squares are experimental data, the solid lines are simulation result. e Schematic of the domain formation and evolution after photoexcitation, showing the change of domain size (ξc) along the c direction with time, while the domain size (ξb) along the b direction remains unchanged. The domain size in b and c directions becomes equal in the metastable state. f Magnified drawing from the area marked by the blue rectangle in e, showing lattice distortion after forming domains. g Projected potential calculated based on the distorted lattice in f. The lattice distortion is exaggerated for clarity in e–g. h [100] projected electric potential calculated from the undistorted SnSe structure. The [100] projection of SnSe structure model is embedded with blue and yellow spheres representing Sn and Se, respectively.
