A New Era in Surface Diffraction - In-Situ Pulsed Laser Deposition of Complex Thin Films
P.R. Willmott, C.M. Schlepuetz, R. Herger, and B.D. Patterson
Swiss Light Source
Subtle structural differences in complex metal oxides lead to fundamentally different properties, due to the strong coupling of the valence electrons. On the one hand, this suggests that surface effects (e.g., relaxations and/or reconstructions) can set a lower limit to "downsizing" of thin film devices that exploit bulk effects, while on the other, unexpected new phenomena, such as surface ferroelectricity may occur only in the surface region of such materials. In addition, interpretation of the electronic properties of strongly correlated systems, investigated with ARPES, strongly depends on the reliable determination of the atomic structure down to the electron escape depth, which in many cases is presently missing. There is therefore a need to obtain exact surface structural models, and how these change in thin films with the film thickness, to better understand such phenomena.
In this contribution, I will present initial structural and growth kinetics results obtained from the Surface Diffraction Station at the Swiss Light Source. The 5-circle surface diffractometer has been fit with a customized pulsed laser deposition (PLD) thin film growth chamber. Using this equipment, it has been possible to grow atomically flat layers of materials which have no preferred cleaving plane and are otherwise practically impossible to prepare with sufficient perfection. For example, heteroepitaxial La-Sr-Mn-O thin films were grown on SrTiO3 monolayer by monolayer and the evolution of the surface structure was followed in-situ at each step. The chemical and crystallographic complexity of such systems requires a concomitant increase in independent data points compared to "simpler" semiconductor or elemental systems most commonly studied using surface diffraction to date. This has only been made possible by the use of a novel photon-counting x-ray pixel detector, which allows the acquisition of reliable surface diffraction data sets at unprecedented rates, some 100 times faster than those possible using conventional point detectors.
Other specific examples, highlighting the capabilities of the setup at the Swiss Light Source, will include the growth of textured quasicrystals on sapphire, LaAlO3 grown on SrTiO3, and YBa2Cu3O7 grown on NdGaO3.
