Transmission Electron Microscopy on Interface Engineered Superconducting Thin Films

Transmission electron microscopy is used to evaluate different deposition techniques, which optimize the microstructure and physical properties of superconducting thin films. High-resolution electron microscopy proves that the use of an YBa2Cu2O buffer layer can avoid a variable interface configuration in YBa2Cu3O7 thin films grown on SrTiO3. The growth can also be controlled at an atomic level by using sub-unit cell layer epitaxy, which results in films with high quality and few structural defects. Epitaxial strain in Sr0 85La0 15CuO2 infinite layer thin films influences the critical temperature of these films, as well as the microstructure. Compressive stress is released by a modulated or a twinned microstructure, which eliminates superconductivity. On the other hand, also tensile strain seems to lower the critical temperature of the infinite layer

Superconducting single-phase Sr1-xLaxCuO2 thin films with improved crystallinity grown by pulsed laser deposition

Sr1-xLaxCuO2-delta (x=0.10-0.20) thin films exhibiting an oxygen-deficient 2V2ap x 2V2ap x c structure ap and c represent the cell parameters of the perovskite subcell were epitaxially grown by means of pulsed laser deposition in low-pressure oxygen ambient. (001) KTaO3 and (001) SrTiO3 single crystals were used as substrates, with BaTiO3 as buffer layer. The Sr1-xLaxCuO2-delta films were oxidized during cooling down in order to yield the infinite-layer-type structure. By applying this method, high quality single-phase Sr1-xLaxCuO2 thin films could be obtained for 0.10<x<0.175 doping range. The films grown on BaTiO3 /KTaO3 show superconductivity for 0.15<x<0.175 with optimum doping at x=0.15, in contrast with previously reported data

Structure and properties of (Sr, Ca)CuO2-BaCuO2 superlattices grown by pulsed laser interval deposition

We report on the preparation of CuBa2(SrxCa1¿x)nCun¿1Oy compounds by fabrication of (Ba,Sr,Ca)CuO2 superlattices with pulsed laser deposition (PLD). A technique called interval deposition is used to suppress multi-level or island growth resulting in high-quality superlattice structures. Both, the applicability of PLD to atomic engineering as well as the fabrication of artificial superconductors is demonstrated. The (Sr,Ca)CuO2¿BaCuO2 superlattices are characterized by X-ray diffraction, high-resolution electron microscopy (HREM) and selected area electron diffraction. The superlattice period has been deduced from electron diffraction patterns and XRD measurements. For Sr containing films, the best growth behavior is observed and films with the highest degree of crystallinity are obtained, whereas superconductivity is only found in less crystalline, Ca containing films. Under some deposition conditions and depending on the amount of Ba containing layers in the superlattice, it was observed that the BaCuO2 material is converted to Ba2CuO4¿¿. Image simulations to interpret the HREM contrast are performed

Electronically coupled complementary interfaces between perovskite band insulators

Perovskite oxides exhibit a plethora of exceptional\ud properties, providing the basis for novel concepts of\ud oxide-electronic devices. The interest in these materials\ud is even extended by the remarkable characteristics of\ud their interfaces. Studies on single epitaxial connections\ud between the wide-bandgap insulators LaAlO3 and SrTiO3\ud have revealed them to be either high-mobility electron\ud conductors or insulating, depending on the atomic\ud stacking sequences. For device applications, as well as\ud for a basic understanding of the interface conduction\ud mechanism, it is important to investigate the electronic\ud coupling of closely spaced complementary interfaces.\ud Here we report the successful realization of such coupled\ud interfaces in SrTiO3–LaAlO3 thin-film multilayer structures.\ud We found a critical separation distance of six perovskite\ud unit cell layers, corresponding to approximately 23 A˚ ,\ud below which a decrease of the interface conductivity\ud and carrier density occurs. Interestingly, the high\ud carrier mobilities characterizing the separate conducting\ud interfaces are found to bemaintained in coupled structures\ud down to subnanometre interface spacing

Growth mechanism of epitaxial SrTiO3 on a (1 x 2) + (2 x 1) reconstructed Sr(1/2 ML)/Si(001) surface

Sub-monolayer control over the growth at silicon–oxide interfaces is a prerequisite for epitaxial integration of complex oxides with the Si platform, enriching it with a variety of functionalities. However, the control over this integration is hindered by the intense reaction of the constituents. The most suitable buffer material for Si passivation is metallic strontium. When it is overgrown with a layer of SrTiO3 (STO) it can serve as a pseudo-substrate for the integration with functional oxides. In our study we determined a mechanism for epitaxial integration of STO with a (1 × 2) + (2 × 1) reconstructed Sr(1/2 ML)/Si(001) surface using all-pulsed laser deposition (PLD) technology. A detailed analysis of the initial deposition parameters was performed, which enabled us to develop a complete protocol for integration, taking into account the peculiarities of the PLD growth, STO critical thickness, and process thermal budget, in order to kinetically trap the reaction between STO and Si and thus to minimize the thickness of the interface layer. The as-prepared oxide layer exhibits STO(001)‖Si(001) out-of-plane and STO[110]‖Si[100] in-plane orientation and together with recent advances in large-scale PLD tools these results represent a new technological solution for the implementation of oxide electronics on demand