Figure 7.

2D diffraction patterns recorded using 83 keV photons for (a) the metallic Fe(110) surface in pure H₂ at 150 °C after the cleaning procedure and (b) the Θ-Fe₃C-covered surface at 350 °C after a set of measurements in a 1CO:4H₂ reaction gas mixture at a 150 mbar total pressure; (c) circularly integrated representation of the 2D pattern in panel b, with the indicated reference values for metallic iron (black lines) and Θ-Fe₃C (red lines). Axes in panels (a) and (b) are given in reciprocal lattice units (RLUs) (see Section S2 in the Supporting information for more details).