Observed effects of a changing step-edge density on thin-film growth dynamics

We grew SrTiO3 on SrTiO3(001) by pulsed laser deposition, while observing x-ray diffraction at the (00 1/2) position. The drop DeltaI in the x-ray intensity following a laser pulse contains information about plume-surface interactions. Kinematic theory predicts DeltaI/I=-4sigma(1-sigma), so that DeltaI/I depends only on the amount of deposited material sigma. In contrast, we observed experimentally that \DeltaI/I|<4sigma(1-sigma) and that DeltaI/I depends on the phase of x-ray growth oscillations. The combined results suggest a fast smoothing mechanism that depends on surface step-edge density.