Controlled growth of complex oxide thin films

Pulsed laser deposition (PLD) is attractive for research on complex oxides. The growth of oxide materials with PLD is the control of the surface morphology. For most materials it is necessary to control the thickness and roughness of the thin films down to an atomic scale. Such well-controlled growth can also be used to manufacture artificially layered structures of different materials with different propertie

In-situ growth studies of sputtered ybco thin films by spectroscopic ellipsometry

Using spectroscopic ellipsometry we studied in-situ the growth of off-axis sputtered YBa2Cu3O6+x thin films on (001) SrTiO3 as a function of the deposition parameters. Especially in the very first growth stage (<5 nm) we observed that the optical properties of the grown layer differs from the "bulk" optical properties of YBCO and strongly depends on, both, the deposition temperature and the oxygen partial pressure. Both properties are well established as influencing the superconducting properties of thin YBCO films. YBCO thin film growth under optimal deposition conditions (Tcnot, vert, similar90 K; jc>106A cm¿2 @ 77 K) is smooth and homogeneous, except for the first unit cell layer (initial stage regime). The smoothness of the response is indicative for a step-mode like growth mechanism. In contrast, the initial stage regime is governed by a 2D nucleation mechanism. This behaviour changes when the deposition temperature is lowered. Due to increased disorder, the initial stage regime is extended to larger thicknesses and a true 2D growth mode is no longer apparent. Similar behaviour is observed with increasing oxygen partial pressure, where the optical response is shifted from a step-flow mode like mechanism to an island-growth mode

X-ray and electron spin resonance on YBa2Cu3O7 prepared by citrate synthesis

YBa2Cu3O7 samples were prepared by a citrate synthesis technique. Powder X-ray diffraction and resistance measurements were performed for sample characterization. This single-phase material has a Tc(R=0) of 91.2 K. Electron spin resonance experiments indicate the presence of 10 to 15% of Cu3+

Observation of the AC Josephson effect up to THZ frequencies in YBCO/PBCO/YBCO ramp-type Josephson junctions

We present the response to 100 GHz irradiation of high-Tc Josephson junction devices for mixer/detector applications in the (sub-) mm wave range. These devices consist of a YBCO/PBCO/YBCO ramp-type junction combined with a planar logarithmic periodic antenna. The critical current and the first two Shapiro steps modulate with 100 GHz power according to the resistively shunted junction (RSJ) model. At 10 K clear Shapiro steps have been observed up to a voltage of about 7.5 mV. This corresponds to phase locking of 3.6 THz AC Josephson oscillations by the 36th harmonic of the 100 GHz signal. The number of observed steps is currently limited by the available power, but they are present up to voltages strongly exceeding the IcRn product of the junction at all temperatures

Fabrications aspects of microwave devices, including ramp-type high-Tc Josephson junctions and log-periodic antenna's

We describe the development of high-Tc Josephson junction devices for applications at millimeter wave frequencies. These devices consist of ramp type YBCO/PBCO/YBCO Josephson junctions that are equipped with a noble metal log-periodic antenna. Growth conditions of all layers, as well as etching, cleaning and annealing procedures are being optimized, to guarantee well-defined device properties. Lowering the deposition temperature of the thick PBCO layer strongly improved its isolating properties, which is of extreme importance for good reproducability of junction fabrication. Special attention is being focused on the optimization of the contact of noble metal to YBCO as well its adhesion to the substrate. Best results are obtained using sputtered gold contacts, after a soft Ar ion sputter clean treatment of the damaged YBCO surface, followed by an anneal procedure

Synthesis and characterization of microporous titania membranes

A procedure for the preparation of microporous titania membranes by the polymeric sol-gel technique is reported. The influence of acid/titanium ratio, water/titanium ratio, method of mixing components and refluxing time on particle size and sol stability was investigated. The thermal evolution, structural characteristics and liquid permeation properties of calcined materials were studied. Highly reproducible amorphous microporous titania layers with pore sizes le0.8 nm were obtained on both mesoporous gamma-alumina and titania/zirconia coated substrates. The upper limit of thermal stability of the amorphous phase is sim300°C. Higher calcination temperatures led to phase transformation into anatase, which was accompanied by a collapse of the microstructure. The material was found to be chemically stable in a wide pH interval

Superconducting weak links in YBa2Cu3O7-δ an AC magnetic susceptibility study

AC magnetic susceptibility, X' and X'', and ac resistivity, ρ, of two different samples of superconducting YBa2Cu3O7-δ have been measured. The results show a strong non-linear behaviour and are very sensitive to the exciting amplitudes. From the analysis of the data and comparison with appropriate models and other superconducting compounds, evidence for the existence of weak superconducting links is inferred. Finally, the utility of acX measurements for detection of different superconducting phases is made evident. \u

Pulsed laser deposition of PZT/Pt composite thin films with high dielectric constants

PbZr0.53Ti0.47O3 (PZT) thin films containing nanoparticles of Pt (3–10 nm) were produced using pulsed laser deposition (PLD). The Pt content can be tuned by varying the energy density of the laser beam. Phase and microstructure analysis of the thin films was performed using XRD, SEM, TEM and AFM. The electrical properties were investigated by C–V and I–V measurements. The effective dielectric constant of the composite films increased substantially through the Pt dispersion. These films are promising candidates, for instance, for high-density dynamic random access memory (DRAM) devices

Tetragonal CuO: A new end member of the 3d transition metal monoxides

Monoclinic CuO is anomalous both structurally as well as electronically in the 3$d$ transition metal oxide series. All the others have the cubic rock salt structure. Here we report the synthesis and electronic property determination of a tetragonal (elongated rock salt) form of CuO created using an epitaxial thin film deposition approach. In situ photoelectron spectroscopy suggests an enhanced charge transfer gap $\Delta$ with the overall bonding more ionic. As an end member of the 3d transition monoxides, its magnetic properties should be that of a high $T_N$ antiferromagnet