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The ternary iron arsenide compound BaFe2As2 exhibits a structural phase transition from tetragonal to orthorhombic at a temperature of about 140 K. The twin lamellae arising below this transition temperature were studied in undoped single crystalline bulk and epitaxial thin film samples using electron backscatter diffraction in a scanning electron microscope equipped with a helium cryostat. Applying this technique on bulk single crystals a characteristic twin lamella size in the range of 0.1 μm up to a few μm was observed. In contrast, in epitaxially strained thin films the phase transition is not observed at temperatures above 19 K.

Substantial efforts are dedicated worldwide to use lead-free materials for environmentally friendly processes in electrocaloric cooling. Whereas investigations on bulk materials showed that Na0.5Bi0.5TiO3 (NBT)-based compounds might be suitable for such applications, our aim is to clarify the feasibility of epitaxial NBT-based thin films for more detailed investigations on the correlation between the composition, microstructure, and functional properties. Therefore, NBT-based thin films were grown by pulsed laser deposition on different single crystalline substrates using a thin epitaxial La0.5Sr0.5CoO3 layer as the bottom electrode for subsequent electric measurements. Structural characterization revealed an undisturbed epitaxial growth of NBT on lattice-matching substrates with a columnar microstructure, but high roughness and increasing grain size with larger film thickness. Dielectric measurements indicate a shift of the phase transition to lower temperatures compared to bulk samples as well as a reduced permittivity and increased losses at higher temperatures. Whereas polarization loops taken at −100 °C revealed a distinct ferroelectric behavior, room temperature data showed a significant resistive contribution in these measurements. Leakage current studies confirmed a non-negligible conductivity between the electrodes, thus preventing an indirect characterization of the electrocaloric properties of these films.

We performed a detailed structural, magnetotransport, and superconducting analysis of thin epitaxial Ba(Fe1&minus, xNix)2As2 films with Ni doping of x = 0.05 and 0.08, as prepared by pulsed laser deposition. X-ray diffraction studies demonstrate the high crystalline perfection of the films, which have a similar quality to single crystals. Furthermore, magnetotransport measurements of the films were performed in magnetic fields up to 9 T. The results we used to estimate the density of electronic states at the Fermi level, the coefficient of electronic heat capacity, and other electronic parameters for this compound, in their dependence on the dopant concentration within the framework of the Ginzburg&ndash, Landau&ndash, Abrikosov&ndash, Gorkov theory. The comparison of the determined parameters with measurement data on comparable Ba(Fe1&minus, xNix)2As2 single crystals shows good agreement, which confirms the high quality of the obtained films.

The basic aim of our study is to investigate the correlation between structural parameters and the electrocaloric effect in lead-free epitaxial Ba1−xSrxTiO3 (BSTO) based thin film architectures. Therefore, BSTO thin films with Sr contents of x = 0 to x = 0.3 were grown on SrRuO3 buffered SrTiO3 single crystalline substrates by pulsed laser deposition. Structural characterization verified an epitaxial growth for all Sr contents with an additional tetragonal distortion compared to bulk material. Temperature and frequency-dependent measurements of dielectric properties revealed increased permittivity values for thicker films with broad maxima indicating a diffuse phase transition. The temperature of maximum permittivity decreases with increasing Sr content, whereas polarization measurements indicate a relaxor-like behaviour in particular above room temperature. Adiabatic temperature changes were determined with the indirect method resulting in |ΔT| values of up to 2.9 K for a 680 nm thick BSTO layer with x = 0.3 at an applied electric field of 750 kV cm−1.

Pb(Mg1/3Nb2/3)O3-PbTiO3 is known for its excellent ferroelectric and electrocaloric properties. Epitaxial films, which allow applying high voltages, can be grown in a much broader parameter range when depositing them on miscut substrates than on those without miscut. To understand the influence of substrate miscut, here the structure and microstructure of two films, with and without miscut, is compared in detail. In both cases the epitaxial strain is relaxed, but while in films without miscut perfect misfit dislocations are observed, the film with miscut exhibits many partial dislocations and stacking faults. The stacking faults may play an important role for the stabilization of the pure perovskite Pb(Mg1/3Nb2/3)O3-PbTiO3 phase in thin films on miscut substrates.

In this paper we report on the structural and superconducting properties of an epitaxially grown Ba(Fe 1-x Ni x ) 2 As 2 thin film using pulsed laser deposition. As target we used an optimally Ni-doped single crystal prepared from self-flux. The superconducting transition temperature of 21.4 K is among the highest values reported for Ni doping exceeding the critical temperature of the single-crystal target. The upper critical field shows a very high slope, which is connected to two-dimensional effect. Transmission electron microscopy investigations indicate planar defects, which might be the origin of this behavior.

We studied the impact of soft ferromagnetic permalloy (Py) on the shielding currents in a strong-pinning superconductor—YBa2Cu3O7−δ with Ba2Y(Nb/Ta)O6 nano-precipitates—by means of scanning transmission x-ray microscopy. Typically and in particular when in the thin film limit, superconductor/ferromagnet (SC/FM) bilayers exhibit isotropic properties of the flux line ensemble at all temperatures. However, in elements with small aspect ratio a significant anisotropy in flux penetration is observed. We explain this effect by local in-plane fields arising from anisotropic magnetic stray fields originated by the ferromagnet. This leads to direction-dependent motion of magnetic vortices inside the SC/FM bilayer. Our results demonstrate that small variations of the magnetic properties can have huge impact on the superconductor.

Elastic strain fields based on single crystal piezoelectric elements represent an effective way for engineering the quantum dot (QD) emission with unrivaled precision and technological relevance. However, pioneering researches in this direction were mainly based on bulk piezoelectric substrates, which prevent the development of chip-scale devices. Here, we present a monolithically integrated Microelectromechanical systems (MEMS) device with great potential for on-chip quantum photonic applications. High-quality epitaxial PMN-PT thin films have been grown on SrTiO3 buffered Si and show excellent piezoelectric responses. Dense arrays of MEMS with small footprints are then fabricated based on these films, forming an on-chip strain tuning platform. After transferring the QD-containing nanomembranes onto these MEMS, the nonclassical emissions (e.g., single photons) from single QDs can be engineered by the strain fields. We envision that the strain tunable QD sources on the individually addressable and monolithically integrated MEMS pave the way toward complex quantum photonic applications on chip.

Epitaxial films are a useful tool to study the interplay between the microstructure and the electrocaloric properties in order to optimize the performance of these materials. Therefore, epitaxial 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMN-PT) films were grown by pulsed laser deposition on (001)-oriented single crystalline SrTiO3 (STO) substrates using an epitaxial La0.7Sr0.3CoO3 buffer as bottom electrode and additional Au top electrodes on the surface of the PMN-PT layer. The main goal of our study was to characterize the influence of the laser fluence on the structural properties. Our data show that pyrochlore-free PMN-PT films can be realized for low fluences. The relative permittivity and the polarization were determined as a function of temperature to verify the ferroelectric quality of our films.

Thin films of Yb3 +/Er3 + codoped Pb(Zr,Ti)O3 (PZT:Yb/Er) have been epitaxially grown on the SrTiO3 buffered Si wafer by pulsed laser deposition. Strong upconversion photoluminescence was observed in the PZT:Yb/Er thin film. Using piezoresponse force microscopy, polar domains in the PZT:Yb/Er film can be reversibly switched with a phase change of 180°. Ferroelectric hysteresis loop shape with a well-saturated response was observed. The epitaxially grown lanthanide-doped PZT on silicon opens up a promising route to the integration of luminescent functional oxides on the silicon platform.

A new approach for the deposition of layers for coated conductors has been developed. High-frequency surface acoustic waves (SAWs) were applied for the atomization of precursor solutions into an ultrafine aerosol. The deposition via aerosol droplet condensation offers several advantages over existing deposition methods including ink jet printing and dip coating, e.g., a variable droplet size and the possibility of gel condensation in the aerosol phase due to solvent evaporation. In the future, a combination of two or more SAW atomizers might enable the simultaneous deposition of separate solutions and even nanoparticle dispersions. First, experiments were performed using water-based and propionic-acid-based mixed lanthanum and zirconium precursor solutions. These solutions are supplied to a SAW device via a stainless steel capillary, leading to continuous aerosol production. The aerosol droplets of the precursor solution were deposited on biaxial textured Ni-5 at.%W tapes having an area of 1-cm width and about 5-cm length and were subsequently crystallized into a continuous thin La 2 Zr 2 O 7 buffer layer in a tube furnace. X-ray diffraction studies showed that the La 2 Zr 2 O 7 films have high crystalline quality with a strong (001)-orientation. Furthermore, microstructural analysis on the deposited films showed homogeneous and dense layers.

Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PMN–PT) is one of the most promising ferroelectric material for actuator, dielectric and electrocaloric applications. However, oriented and phase pure thin films are essential to use the outstanding properties of these compounds. In this work it is demonstrated that the use of miscut substrates influences the growth mechanism leading to a significantly broader deposition window to achieve the required film quality. Therefore, epitaxial 0.68Pb(Mg 1/3 Nb 2/3 )O 3 –0.32PbTiO 3 films were grown by pulsed laser deposition on (001)-oriented single crystalline SrTiO 3 (STO) substrates with a miscut angle between 0 and 15° towards the [100] direction using a conducting La 0.7 Sr 0.3 CoO 3 buffer layer. The influence of the vicinal angle on the PMN–PT structure was studied by high resolution X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. A nearly pure perovskite phase growth with a cube-on-cube epitaxial relationship was obtained on all miscut STO substrates, whereas a significant volume fraction of the pyrochlore phase was present on the standard substrate. Reciprocal space measurements revealed a peak split of the perovskite reflections indicating structural variants of PMN–PT with different c / a ratios. An additional tilting of the PMN–PT planes with respect to the buffer layer was observed on some samples, which might be explained with the incorporation of dislocations according to the Nagai model. Polarization loops were measured in a temperature range between room temperature and 150 °C showing a sharp drop of the remanent polarization above 65 °C on vicinal substrates.

Tuning functional properties of thin caloric films by mechanical stress is currently of high interest. In particular, a controllable magnetisation or transition temperature is desired for improved usability in magnetocaloric devices. Here, we present results of epitaxial magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMN-PT) substrates. Utilizing X-ray diffraction measurements, we demonstrate that the strain induced in the substrate by application of an electric field can be transferred to the thin film, resulting in a change of the lattice parameters. We examined the consequences of this strain on the magnetic properties of the thin film by temperature- and electric field-dependent measurements. We did not observe a change of martensitic transformation temperature but a reversible change of magnetisation within the austenitic state, which we attribute to the intrinsic magnetic instability of this metamagnetic Heusler alloy. We demonstrate an electric field-controlled entropy change of about 31 % of the magnetocaloric effect - without any hysteresis.

Achieving low cost, safe, reproducible, and high performance superconducting thin films of YBa2Cu3O7-delta is essential to bring this material to the energy market. Here, we report on the chemical solution deposition of YBa2Cu3O7-delta nanocomposites from environmentally benign precursors with a low fluorine content. Preformed ZrO2 nanocrystals (3.5 nm) were stabilized in a methanolic precursor solution via two strategies: charge stabilization and steric stabilization. Counter-intuitively, charge stabilization did not result in high quality superconducting layers, while the steric stabilization resulted in highly reproducible nanocomposite thin films with a self-field J(c) of 4-5 MA cm(-2) (77 K) and a much smaller decay of J(c) with magnetic field compared to YBa2Cu3O7-delta without nanocrystals. In addition, these nanocomposite films show a strong pinning force enhancement and a reduced J(c) anisotropy compared to undoped YBa2Cu3O7-delta films. Given the relationship between the nanocrystal surface chemistry and final nanocomposite performance, we expect these results to be also relevant for other nanocomposite research.

We grow BaHfO3 (BHO) nanorods in REBa2Cu3O7-x (REBCO, RE: Gd or Y) thin films on metal tapes coated with the inclined substrate deposited (ISD)-MgO template by both electron beam physical vapour deposition and pulsed laser deposition. In both cases the nanorods are inclined by an angle of 21 degrees-29 degrees with respect to the sample surface normal as a consequence of the tilted growth of the REBCO film resulting from the ISD-MgO layer. We present angular critical current density (J(c)) anisotropy as well as field- and temperature-dependant J(c) data of the BHO nanorod-containing GdBCO films demonstrating an increase in J(c) over a wide range of temperatures between 30 and 77 K and magnetic fields up to 8 T. In addition, we show that the angle of the peak in the J(c) anisotropy curve resulting from the nanorods is dependent both on temperature and magnetic field. The largest J(c) enhancement from the addition of the nanorods was found to occur at 30 K, 3 T, resulting in a J(c) of 3.0 MA cm(-2).

We report on electrical transport properties of epitaxial Ba(Fe1-xNix)2As2 thin films grown by pulsed laser deposition in static magnetic fields up to 35 T. The thin film shows a critical temperature of 17.2 K and a critical current density of 5.7x10^5 A/cm^2 in self field at 4.2 K while the pinning is dominated by elastic pinning at two-dimensional nonmagnetic defects. Compared to single-crystal data, we find a higher slope of the upper critical field for the thin film at a similar doping level and a small anisotropy. Also an unusual small vortex liquid phase was observed at low temperatures, which is a striking difference to Co-doped BaFe2As2 thin films., Comment: Accepted for publication in Applied Physics Letters, 5 figures

In this work we present multilayers consisting of Fe and Co-doped BaFe 2 As 2 fabricated by UHV pulsed laser deposition. Employing the advantage of a coherent interfacial bonding between the FeAs tetrahedra of the iron pnictide and bcc Fe enables the growth of epitaxial bi- and multilayers of Fe and the new Fe-based superconductors with high crystalline quality. Epitaxial growth of the multilayers was controlled in situ by reflection high energy electron diffraction (RHEED) and after film growth by X-ray diffraction and TEM analysis. The stoichiometry determined by Auger electron spectroscopy (AES) indicated As-deficient layers of Co-doped Ba-122. The multilayers exhibit critical temperatures of T c,90 = 29 K which is so far the highest critical temperature reported for Co-doped Ba-122. We propose that the T c -enhancement is caused by As-vacancies.

The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O7−δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m3 at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.

Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) compounds, which are typically used for high performance actuator applications due to their outstanding piezoelectric properties, show, in addition, a pronounced electrocaloric (EC) effect. The study of epitaxial films is a useful tool to analyze the correlation between the microstructure and EC properties in order to optimize the performance of these materials. Therefore, the 0.9PMN-0.1PT films were grown by a pulsed laser deposition on (001) as well as (111) oriented SrTiO3 single crystalline substrates using a La0.7Sr0.3CoO3 buffer as the bottom electrode and additional Au top electrodes. The structural properties determined by a high resolution X-ray and electron microscopy techniques indicated an undisturbed epitaxial growth. The anisotropy of the ferroelectric domain structure was investigated by a vertical and lateral piezoresponse force microscopy showing clear differences between the two orientations. A significant reduction of the thermal hysteresis was observed in the T-dependent polarization measurements for (111) oriented PMN-PT films, whereas the indirectly determined EC properties yield a maximum DT of around 15 K at 40 °C for a field of about 400 kV/cm for both film orientations.

Pulsed laser deposition was used in combination with real time reflection high energy electron diffraction to prepare layer-by-layer grown La 1 − x Sr x CoO 3 films on single terminated substrates. The films exhibit an epitaxially and completely strained film growth resulting in an atomic flat surface with terrace structure. The films were compared to similar layers grown by off-axis laser deposition under higher oxygen partial pressure. With decreasing oxygen pressure an increased unit cell volume and decreasing magnetic moment was observed. Furthermore, we exemplarily show the preparation of layer-by-layer grown LaCoO 3 |SrTiO 3 multilayers.

Biaxially textured LuNi 2 B 2 C thin films with high T c up to 15.8 K and a residual resistivity ratio up to 15 have been prepared on MgO(1 1 0) substrates using pulsed laser deposition from a stoichiometric target. Via the precise control of the deposition rate, a biaxial texture is favored within a broad range of deposition temperatures, with an epitaxial relationship between the borocarbide film, the Lu 2 O 3 interface layer and the substrate of (0 1 1)[0 0 1]MgO || (0 1 1)[0 0 1]Lu 2 O 3 || (0 0 1)[1 0 0]LuNi 2 B 2 C. A very sharp in-plane alignment of about 1 ° and an out-of-plane order of about 2.5 ° was achieved in the LuNi 2 B 2 C layer. It is shown that the temperature is crucial for phase formation and superconducting properties. Applying optimized deposition conditions, critical temperatures of up to 15.8 K and steep superconducting transitions of about 0.3 K are reproducibly obtained. The upper critical field H c 2 of the optimized films was resistively measured along the [0 0 1] direction and fitted with a power law. The resulting value of H c 2 (0) = 9.82 T is in very good agreement with single crystal data, whereas the power exponent describing the positive curvature for small external magnetic fields α = 0.19 indicates a relatively low intraband scattering in the films.

Through dip-coating Ni-5%W substrates in a water-based sol-gel solution, thin films of La2Zr2O7 (LZO) were produced. This method yields highly crystalline and epitaxial films. The surface of the LZO film was found to be smooth and homogeneous. Subsequently, CeO2 layers followed by an YBa2Cu3O7-y layer were deposited via Pulsed Laser Deposition (PLD) onto the LZO film. The crystallinity and biaxial texture of the LZO layer was successfully transferred to the next layers, as demonstrated by pole figures and RHEED measurements. Resistive Tc-measurements were carried out on these samples and showed a Tc of 85 K.

Thin films of La2Zr2O7 (LZO) are highly regarded as possible buffer layers in the coated conductor configuration. This report describes a new synthesis for thin crystalline LZO films, based on a largely water-based solution, mainly containing metal acetates, acetic acid and an organic amine-base: triethanolamine. Initially, a thin layer of amorphous material is deposited on the textured Ni-5 at%W substrate by means of dip-coating. Only by careful control of the thermal treatment can the layer be transformed into a crystalline layer. Important parameters in this respect are the heating rate and the dwell time. The amorphous gel is analysed by HR-TGA/DTA and HR-TEM. The textured layers are analysed by XRD, pole figures, RHEED, AFM and SEM.

The appearance of new functionalities and devices arising from sizeand shape-dependent properties has triggered the interest in creating well-defined structures at the nanometricscale. While conventional lithography is used to fabricate structures in the range of hundreds of nanometers, self-organizing and self-assembling processes following a bottom-up approach can easily decrease this size limit and also cover cost-effectively much larger surfaces. Semiconductors, metals, oxides and molecular materials are different areas where such principles are intensively pursued to generate nanostructures. In particular, self-assembling based on the stress associated to heteroepitaxial growth is an attractive fabrication route in which the generation of semiconductor nanostructures has been extensively investigated and, recently, it has spread to other emerging fields such as oxide-based nanotechnology. Complex oxides attract a great interest for a wealth of different physical and chemical properties and applications such as ferromagnetism, ferroelectricity, colossal magnetoresistance, high dielectric constants, catalysis, optical properties, high temperature superconductivity, solar cells, etc. Based on these properties, many device concepts are under investigation requiring lateral confinement at the nanometric scale, therefore, it constitutes a real scientific challenge to understand the formation mechanisms of nanometric structures. So far the mechanisms that drive self-organized nanodot growth have been studied in certain detail in epitaxial materials prepared from vapor deposition techniques, including oxides, and either Stranski–Krastanov or Volmer–Weber mechanisms were found to apply. On the other hand, vicinal substrates have been widely considered as templates for growing low dimensional nanostructures. The role of lattice steps on the growth mechanism of oxide films has been analyzed by several authors, though the formation of self-organized nanostructures using the terraces as templates has been very scarce. Much less attention has been devoted to investigate the capabilities of Chemical Solution Deposition (CSD), a preparation methodology bearing a high interest for many functionalities and practical applications requiring the use of large areas or long lengths. Particularly, CeO2 is a key material which is being extensively investigated because of its very high intrinsic interest in many areas such as catalysis, ionic conductivity, optical and dielectric properties, buffer layer for oxide superconductors, or nanotemplates to manipulate the vortex properties in superconducting materials. In the last case, the use of self-organized templates in combination with superconducting films could lead to a wealth of new superconducting phenomena. It appears then as highly demanding, scientifically and technologically, the study of the mechanisms generating nanostructured networks of CeO2. Very thin films grown by CSD have been found to be unstable under high temperature annealings and so they can become the source of nanostructure generation, though under these conditions the size and morphology control may become problematic. In this work, a new methodology of general validity has been devised for the formation of quasi one-dimensional arrays of nanodots based on the control of the interfacial energy of heteroepitaxial structures grown from ultradiluted chemical solutions. The terraces of vicinal single crystals of LaAlO3 (LAO) or SrTiO3 (STO) perovskite substrates have been used as templates where CeO2 and Ce1–xGdxO2–y (CGO) nanostructures have been grown by CSD. We have been able to confine within the terraces rows of nanodots with heights ∼ 20 times higher than the unit cell steps of the vicinal substrate. We will show that the underlying mechanism leading to nanodot self-organization is grounded on an enhanced energy barrier at the surface steps due to the structural dissimilarity of the heterostructure. Figure 1a displays a typical image of a heat treated LAO vicinal substrate where the straightness of the lattice steps is clearly appreciated and Figure 1b shows the corresponding line scan where single perovskite unit cell steps are distinguished, thus demonstrating that only one type of crystal termination has been achieved. From the width of the terraces we have determined that the miscut angles of the substrates used in this work were in the range h = 0.2 ± 0.1°. A reproC O M M U N IC A IO N

Y2O3 nanoparticles prepared by an inert gas phase condensation process were used to introduce artificial pinning centres in YBa2Cu3O7−δ thin films. The areal density of the particles was varied between 120 and 4200 particles µm−2 without changing the mean particle diameter of approximately 9 nm. Y2O3 particles were deposited on TiO2 terminated SrTiO3 (100) single-crystal substrates with areal densities up to 1654 particles µm−2 and subsequently covered with YBa2Cu3O7−δ by off-axis pulsed laser deposition (PLD). The areal density of the room temperature deposited particles is not changed by the substrate heating during PLD although their height on the substrate decreases. An influence on Jc is demonstrated for particle densities above 1588 particles µm−2, indicating that the substrate decoration with Y2O3 nanoparticles from the gas phase affects the formation of artificial pinning centres in the YBa2Cu3O7−δ films and can be applied to further study of the effect of particle size and areal density on defect formation in YBa2Cu3O7−δ.

By controlling pulse number of laser ablation, we prepared a series of quasi-multilayers of YBa2Cu3O7-δ/M (M=incomplete oxide layer) namely 70×(40/n) (n = 2, 5, 10 and 20, pulse number of M) which were characterised with nano-scale precipitates. While the texture properties of Y123 inside qusi-multilayer hardly change, its Tc appeared much different depending on the doping level of M. X-ray θ-2θ scanning and pole figures indicated that the different growth-controlled precipitates occured inside Y123 films. In the case of M=YSZ (Yttria Stabilized Zirconia), nanosized perovskite precipitates of BaZrO3 formed as a result of solid state reaction of YSZ with Y123, leading to Tc obviously decreasing with increasing of n. In the case of M=Y2O3, however, Tc did not decrease so much at the studied range of n due to no solid state reaction mentioned above. Magneto-transport and field angular dependence showed that the critical current density in films with lower doping content (such as n = 2) was improved in large ranges of field and temperature, suggesting tailorable enhancement and anisotropy of flux pinning force.

Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1−xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1−xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1−xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1−xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1−xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C–320 °C) on MgO using PLD. This offers a broad scope of various applications.

FeSe0.5Te0.5 thin films were grown by pulsed laser deposition on CaF2, LaAlO3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe0.5Te0.5 bulk and the substrates shows no influence on the lattice parameters of the films, whereas the type of substrates affects the crystalline quality of the films and, therefore, the superconducting properties. The film on MgO showed an extra peak in the angular dependence of critical current density Jc({\theta}) at {\theta} = 180{\deg} (H || c), which arises from c-axis defects as confirmed by transmission electron microscopy. In contrast, no Jc({\theta}) peaks for H || c were observed in films on CaF2 and LaAlO3. Jc({\theta}) can be scaled successfully for both films without c-axis correlated defects by the anisotropic Ginzburg-Landau (AGL) approach with appropriate anisotropy ratio {\gamma}J. The scaling parameter {\gamma}J is decreasing with decreasing temperature, which is different from what we observed in FeSe0.5Te0.5 films on Fe-buffered MgO substrates., Comment: accepted for publication in SUST

Chemical solution deposition (CSD) is a promising way to realize REBa2Cu3O7−x (REBCO; RE = rare earth (here Y, Gd))-coated conductors with high performance in applied magnetic fields. However, the preparation process contains numerous parameters which need to be tuned to achieve high-quality films. Therefore, we investigated the growth of REBCO thin films containing nanometre-scale BaHfO3 (BHO) particles as pinning centres for magnetic flux lines, with emphasis on the influence of crystallization temperature and substrate on the microstructure and superconductivity. Conductivity, microscopy and x-ray investigations show an enhanced performance of BHO nano-composites in comparison to pristine REBCO. Further, those measurements reveal the superiority of GdBCO to YBCOe.g. by inductive critical current densities, J c, at self-field and 77 K. YBCO is outperformed by more than 1 MA cm−2 with J c values of up to 5.0 MA cm−2 for 265 nm thick layers of GdBCO(BHO) on lanthanum aluminate. Transport in-field J c measurements demonstrate high pinning force maxima of around 4 GN m−3 for YBCO(BHO) and GdBCO(BHO). However, the irreversibility fields are appreciably higher for GdBCO. The critical temperature was not significantly reduced upon BHO addition to both YBCO and GdBCO, indicating a low tendency for Hf diffusion into the REBCO matrix. Angular-dependent J c measurements show a reduction of the anisotropy in the same order of magnitude for both REBCO compounds. Theoretical models suggest that more than one sort of pinning centre is active in all CSD films.

The preparation of cube textured NiO buffer layers on biaxially textured Ni tapes using surface oxidation epitaxy (SOE) offers a cheap and scalable route for the production of long-length YBCO coated conductors. A second buffer layer is necessary to ensure epitaxial growth of the YBCO as well as to prevent Ni contamination of the superconducting layer. Zirconate buffer layers offer a close lattice misfit to NiO as well as a high stability during the YBCO deposition. BaZrO/sub 3/ and SrZrO/sub 3/ buffers were successfully deposited on NiO using pulsed laser deposition. Additionally, BaZrO/sub 3/ films were prepared on NiO using metal-organic decomposition. All buffers show a high quality epitaxial growth with an in-plane orientation similar to the underlying NiO. The subsequent deposition of YBCO on top of these buffers resulted in epitaxial layers with a T/sub c/ above 85 K and j/sub c/ up to 1 MA/cm/sup 2/ on NiO if a thin intermediate SrTiO/sub 3/ layer is used. Microstructural investigations showed that the roughness and the surface topography of the buffer layers is mainly determined by the quality of the NiO layer.

We report on the growth of epitaxial Fe1+δ Se0.5Te0.5 thin films on 0°, 5°, 10°, 15° and 20° vicinal cut CaF2 single crystals by pulsed laser deposition. In situ electron and ex situ x-ray diffraction studies reveal a tilted growth of the Fe1+δ Se0.5Te0.5 films, whereby under optimized deposition conditions the c-axis alignment coincides with the substrate [001] tilted axis up to a vicinal angle of 10°. Atomic force microscopy shows a flat island growth for all films. From resistivity measurements in longitudinal and transversal directions, the ab- and c-axis components of resistivity are derived and the mass anisotropy parameter is determined. Analysis of the critical current density indicates that no effective c-axis correlated defects are generated by vicinal growth, and pinning by normal point core defects dominates. However, for Hab the effective pinning centers change from surface defects to point core defects near the superconducting transition due to the vicinal cut. Furthermore, we show in angular-dependent critical current density data a shift of the ab-planes maxima position with the magnetic field strength.

Pulsed laser deposition was used for the preparation of thin meander shaped platinum strain gauges on piezoelectric single crystalline (001) Pb(Mg 1/3 Nb 2/3 ) 0.72 Ti 0.28 O 3 substrates to study in-situ the temperature dependence of the applied strain in thin films even for small samples. A strong decrease of the strain with temperature was revealed at constant electric fields with a plateau like behavior for temperatures in the range of 100 K. The electrical field induced strain leads to a shift in the super-conducting transition temperature of La 1.85 Sr 0.15 CuO 4 .A detailed study of the transition was used to prove a linear and reversible behavior of the strain with the applied electric field.

Biaxially textured MgO thin films were deposited on amorphous substrates using ion beam assisted pulsed laser deposition. The development of the texture and microstructure was investigated with electron diffraction and atomic force microscopy. After the first few nanometers of growth, a sharp nucleation texture is observed. During further growth a texture change takes place, leading to two texture components, one in the 〈220〉 direction and the other in the 〈111〉 direction parallel to the substrate normal. In both cases the 〈200〉 direction is parallel to the ion beam. This texture change can be explained in terms of the highly anisotropic sputter rate observed in experiments on single crystals, leading to grains having a 〈200〉 direction parallel to the ion beam during growth being preferred. Without ion beam assistance during further growth, one of the two texture components dominates.

MgO thin films were deposited on amorphous substrates using pulsed laser deposition. Without an assisting ion beam, strong fibre textures are observed changing with temperature. Using an ion beam at 55° with respect to the substrate normal and energies of more than 400 eV, biaxially textured films are grown with the direction parallel to the ion beam. Decreasing the deposition rate the texture changes towards the desired cube texture and resputtering becomes more important. Investigations of the surface topography show an increase in roughness and grain size with increasing film thickness. Preliminary ideas of texture and microstructure development in this deposition process are presented.

The anisotropy of the critical current density Jc depends in general on both the properties of the flux lines (such as line tension, coherence length and penetration depth) and the properties of the defects (such as density, shape, orientation etc.). Whereas the Jc anisotropy in microstructurally clean films can be scaled to an effective magnetic field containing the Ginzburg-Landau anisotropy term, it is in general not possible (or only in a limited field range) for samples containing extended defects. Here, the Jc anisotropy of a Co-doped BaFe2As2 sample with 45{\deg} [001] tilt grain boundaries (GBs), i.e. grain boundaries created by 45{\deg} in-plane rotated grains, as well as extended Fe particles is investigated. This microstructure leads to c-axis correlated pinning, both due to the GBs and the Fe particles and manifests in a c-axis peak in the Jc anisotropy at low magnetic fields and a deviation from the anisotropic Ginzburg-Landau scaling at higher fields. Strong pinning at ellipsoidal extended defects, i.e. the Fe particles, is discussed, and the full Jc anisotropy is fitted successfully with the vortex path model. The results are compared to a sample without GBs and Fe particles. 45{\deg} GBs seem to be good pinning centers rather than detrimental to current flow., Comment: 8 pages, 7 figures, CEC-ICMC 2013 proceeding, accepted for publication in Advances in Cryogenic Engineering (Materials)

Thin TiN films have been grown using reactive ion-beam assisted pulsed laser deposition. The texture development was in situ analyzed using reflection high-energy electron diffraction. Above 300°C a sharp cube textured nucleation layer is observed using an ion beam with energies above 400eV under an angle of 45° relative to the substrate normal. The cube texture is not stable during further ion-beam assisted growth but can be preserved using homoepitaxial growth. Resulting films showed an in-plane orientation of about 13°. The texture development can be described in terms of energy considerations and anisotropic sputter rates.

Epitaxial BaZr x Ti1−x O3 (BZTO) thin films with Zr contents of x = 0, x = 0.12 and x = 0.2 were grown by pulsed laser deposition on (0 0 1)-oriented single crystalline SrTiO3 substrates utilizing an additional conducting SrRuO3 buffer layer. It was found that the oxygen pressure during the deposition heavily influences the lattice constants and the microstructure of BZTO. A low of 0.01 mbar gives rise to a significant tetragonal distortion. Texture measurements reveal that an undisturbed epitaxial growth is only achieved for BZTO films prepared in 0.01 mbar oxygen. In contrast, the formation of twins was observed for higher . A detailed microstructural analysis indicates that the sample preparation in low prevents a preferential growth of columnar grains within the BZTO layers and leads to smoother film surfaces. BZTO thin films deposited with optimized deposition parameters show characteristic ferroelectric polarization behavior. The saturation polarization at room temperature declines with increasing Zr content and the characteristic ferroelectric hysteresis diminishes. Temperature-depended measurements of the relative permittivity reveal the existence of a broad transition range and a significant shift of the phase transition temperature to lower values for increasing Zr content.

Biaxially textured MgO films have been grown using ion-beam assisted pulsed laser deposition. Above 250 °C a cube texture with a 〈1 1 0〉 direction parallel to the ion beam is observed in films thinner than 10 nm at ion incidence angles between 35° and 55°. The in-plane alignment determined using RHEED analysis was better than 21°. A strongly anisotropic sputter rate is responsible for this oriented nucleation. During further growth the nucleation texture changes in such a way that the 〈1 0 0〉 direction becomes parallel to the ion beam. This change can also be explained by the anisotropic sputter rate of MgO found in sputtering experiments on single crystals selecting grains with a 〈1 0 0〉 direction parallel to the ion beam during growth.

The angular-dependent critical current density, ${J}_{\text{c}}(\ensuremath{\Theta})$, and the upper critical field, ${H}_{\text{c}2}(\ensuremath{\Theta})$, of epitaxial $\text{Ba}{({\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x})}_{2}{\text{As}}_{2}$ thin films have been investigated. No ${J}_{\text{c}}(\ensuremath{\Theta})$ peaks for $H\ensuremath{\parallel}c$ were observed regardless of temperatures and magnetic fields. In contrast, ${J}_{\text{c}}(\ensuremath{\Theta})$ showed a broad maximum at $\ensuremath{\Theta}=90\ifmmode^\circ\else\textdegree\fi{}$, which arises from intrinsic pinning. All data except at $\ensuremath{\Theta}=90\ifmmode^\circ\else\textdegree\fi{}$ can be scaled by the Blatter plot. ${H}_{\text{c}2}(\ensuremath{\Theta})$ near ${T}_{\text{c}}$ follows the anisotropic Ginzburg-Landau expression. The mass anisotropy increased from 1.5 to 2 with increasing temperature, which is an evidence for multiband superconductivity.

Ion-beam assisted deposition (IBAD) offers the possibility to prepare thin textured films on amorphous or non-textured substrates. It was shown within the last decade that the ion beam influences the nucleation in material with a rocksalt structure leading to a strong cube texture already within the first 10 nanometres. Among these materials, transition metal nitrides exhibit interesting physical properties as superconductivity, metallic behaviour or superior hardness. Therefore, a reactive IBAD process was applied for the preparation of highly textured transition metal nitride layers using pulsed laser deposition of pure metals in combination with a nitrogen-containing ion beam. The results on the in-plane textured growth of TiN are promising for the development of conducting buffer layer architectures for YBCO coated conductors based on the IBAD approach. Furthermore, this approach was used to prepare other highly textured transition metal nitride thin films like NbN and ZrN.

MgO thin films were deposited on amorphous substrates using ion-beam assisted pulsed laser deposition. The texture formation was investigated in-situ with RHEED. The microstructure of the films was observed by AFM. Using an ion beam at an angle between 35° and 65° with respect to the substrate normal, strong nucleation textures develop. Under certain deposition parameters a cube texture is observed in films thinner than 10nm. During further growth this nucleation texture changes in such a way that the «100» direction becomes parallel to the ion beam. This change can be explained by the anisotropic sputter rate of MgO seen in sputter experiments on single crystals. Moreover, MgO films were deposited homoepitaxially on MgO single crystals above 250° C with internal stresses decreasing with increasing deposition temperature. In contrast, films grown further on the thin cube-textured nucleation layer without ion-beam assistance show a texture change towards fibre textures.

Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magn...

In this work, fully alpha-axis oriented SrTiO3 thin films were synthesized by ink-jet printing of water-based precursor inks. The developed precursor solution or 'ink' was optimized in terms of rheology, leading to the ejection of single droplets showing a maximum contact angle of 12 degrees on (100) oriented single crystal LaAlO3 substrates. By using the appropriate ink-jet deposition parameters and thermal treatment, well-textured and dense SrTiO3 films of 130 nm thickness were obtained. The biaxial texture is maintained up to the surface of the films, leading to the formation of (h00)-oriented terraces. As shown by transmission electron microscopy, excellent texture transfer was achieved from the SrTiO3 film to the YBa2Cu3O7 - delta layer deposited by pulsed laser deposition. Outstanding superconducting properties were obtained with critical current densities up to 3.6 MA cm(-2) in self-field at 77 K, demonstrating that these sustainable SrTiO3 films meet the requirements to be used as growing template for high quality superconducting coatings.

MgO thin films were deposited on amorphous substrates using ion-beam assisted pulsed laser deposition. The texture formation was investigated in-situ with RHEED. The microstructure of the films was observed by AFM. Using an ion beam at an angle of 55° with respect to the substrate normal, strong nucleation textures develop. Above 250°C a cube texture is observed in films thinner than 10 nm. During further growth this nucleation texture changes in a way that the direction becomes parallel to the ion beam. This change can be explained by the anisotropic sputter rate of MgO found in sputter experiments on single crystals. Moreover, MgO films were deposited homoepitaxially on MgO single crystals above 250°C with internal stresses dreasing with increasing deposition temperature. This result gives rise to hope that homoepitaxial growth of MgO on the nucleation layer without ion-beam assistance should be possible in future PLD-experiments keeping the desired cube texture in thicker films.

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

Low-temperature magnetic force microscopy is used for the direct visualization of vortex distribution in high-temperature superconducting films. With the scanning probe microscope (Omicron Cryogenic SFM) magnetic fields up to 7 T (vertical) and 3 T (transversal) can be applied to the sample during in situ imaging at temperatures ranging from 7 K to 300 K in ultra high vacuum. The samples investigated were 300 nm thick YBa 2 Cu 3 O 7− δ films grown epitaxially on SrTiO 3 (0 0 1) substrates by off-axis pulsed laser deposition with a mean roughness less than 10 nm. Prior to imaging, the samples were cooled down in the microscope to 7.7 K in a magnetic field of 3 mT. Flux lines have been successfully imaged by measuring their stray field in the scan height of 40 nm above the sample surface. The number of vortices observed corresponds to the theoretically expected one. Whereas a constant current leads to unacceptable heating of the sample, the use of current pulses allows transport measurements without thermal movement of vortices.