The technology for the growth of thin oxide films or heterostructures is approaching the same level of atomic control as in the case of semiconductors. Yet, whereas semiconductors are usually described within the single-electron approach, the high electron densities in oxides can be the source of novel phases and functionalities. This includes phenomena like long-range magnetic or electric order, but also exotic behaviour like colossal magnetoresistance. Aside from multiple technological advantages in working with thin films instead of single crystals, one of their outstanding assets is the rich variety of functionalities that emerge when different constituents are combined into a multilayer heterostructure. The fascinating properties of oxide heterostructures continue to infatuate and drive materials scientists to master synthesis, understanding, and control of these systems with the goal of exploiting their properties in devices. The functionality of a heterostructure depends critically on the choice of constituents, design parameters and growth conditions. The iteration procedure is tedious: A heterostructure is grown and characterized and from small deliberate variations in subsequent batches conclusions are drawn on the parameters that determine quality and functionality. This process is greatly sped up if quality and functionality can be observed while the heterostructure is growing. So far, reflection high-energy electron diffraction is the only widely established technique for monitoring the structure and homogeneity of multilayers in-situ, while they are growing, and provide direct feedback information on how to optimise the growth process. However, any insight about the spin- and charge-related phenomena just constituting the extraordinary potential of oxide electronics are inaccessible using this technique. With our proposal we will introduce second harmonic generation (SHG) as new in-situ technique that allows us to track spin-and charge-related phenomena such as ferroelectricity, (anti-) ferromagnetism, insulator-metal transitions, domain coupling effects or interface states in a non-invasive way throughout the deposition process. We are pursuing two goals: first, to establish SHG as new in-situ property-monitoring tool characterization technique for physical vapor deposition which monitors strong spin-charge correlation effects while they emerge during growth; second, to apply in-situ SHG for tailoring novel functionalities in exemplary chosen types of transition-metal-oxide heterostructures of great current interest. These model systems are (i) proper ferroelectrics tuned to high-k dielectric response and improper ferroelectrics whose behavior is determined by the unusual nature of the polar state; (ii) compounds in which the interplay of strain and defects leads to novel and reversibly tunable states of matter; (iii) heterostructures with functionalities originating from the interaction across interfaces. All our objectives will allow us to answer fundamental questions of contemporary condensed-matter research. What are the mechanisms stabilizing the spontaneous polarization in textbook ferroelectrics, but also in those novel types of ferroelectrics that are presently discovered in multiferroics and other complex oxides? What types of new functionalities can be derived from these ferroelectrics? Answers to any of these questions will have great impact beyond specialist communities.
