Fig. 1
Schematic of the experiment and coherent mixing effects during C60 thin film deposition. a X-rays from the synchrotron source are focused by a kinoform lens (KL) and a collimating slit system into an ultra-high vacuum sample enclosure. A polycrystalline thin film is deposited, which causes (111)-oriented crystalline mounds to form via nucleation at the top of each mound and local step-flow towards the mound edges. Scattered coherent X-rays form speckle patterns that correspond to the detailed configuration of the surface and are recorded versus time by a high-resolution photon sensitive X-ray area detector. b In addition to scattering from the surface (green lines and equation), the X-rays scatter from the average mounds structure (blue). The functions gA(1)(Δt) and gS(1)(Δt) correspond to the intermediate scattering functions for the average and surface mound contributions respectively. c The two signals interfere coherently, creating temporal correlations in the speckle pattern that can oscillate with the frequency \(\omega _1\), which is directly related to the step-edge velocity. This effect occurs even when the averaged intensity is nearly static. The second-order correlation function g(2)(Δt) is extracted from intensity data, as described in the main text
