Time-Resolved Surface X-ray Diffraction at the Advanced Photon Source: Pulsed Laser Deposition Growth of SrTiO3

Knowledge of atomic structural arrangements and composition at surfaces and buried interfaces is fundamental to our understanding of the function and properties of fabricated thin-film structures. Because of favorable cross sections, x-rays offer a unique opportunity to penetrate through gas, liquid, or solid thin-film overlayers to probe the structure and chemistry of surfaces and internal boundaries on the atomic length scale. The brilliance of the Advanced Photon Source at the Argonne National Laboratory enables these in situ studies, permits real-time investigations to elucidate thin-film growth mechanisms, and allows for molecular scale studies of important chemical interactions at internal boundaries. In this talk, I will illustrate several important x-ray scattering techniques that are routinely exploited in the study of 2-dimensional surface or interface structures and demonstrate these with the example of homoepitaxial growth of SrTiO3 by Pulsed Laser Deposition (PLD). PLD is a widely used technique for the growth of complex oxide thin films and heterostructures of complex stoichiometry. In these studies, we used time-resolved surface x-ray diffraction measurements with microsecond-range resolution to study the growth kinetics of pulsed laser deposited SrTiO3. Time-dependent surface coverages corresponding to single laser shots were determined from crystal truncation rod intensity transients. Analysis of the surface growth evolution demonstrates that extremely fast non-equilibrium interlayer transport, which occurs concurrently with the arrival of the laser plume, dominates the deposition process. A much smaller fraction of material, which is governed by the dwell time between successive laser shots, is transferred by slow, thermally driven interlayer transport processes. I will also discuss new x-ray methods for the study of growth surfaces and internal interfaces, and I will describe initiatives for new surface & interface science facilities that are planned at the Advanced Photon Source.