B. Vengalis

MgO by Injection CVD

Abstract Epitaxial YBa 2 Cu 3 O 7 layers with 45° in-plane orientation have been grown by Injection CVD on MgO substrates polished off-axis to within 1.4–1.9° of the [100] direction. This new single-source CVD process is based on computer-controlled injection of precise microdoses of a metal–organic precursor solution into a CVD reactor. A wide range of solution compositions was tested to investigate compositional effects on phase purity, surface morphology, texturing and superconducting properties of the prepared films. The highest quality films with pure 45° texture had a smooth surface, zero resistance T c ( R =0) of 88–89 K, and critical current density J c (77 K) above 10 6 A/cm 2 .

Manganite Based Strong Magnetic Field Sensors Used for Magnetocumulative Generators

The effects of strong pulsed magnetic field and shock waves on the electrical properties of La 0.67 Ca 0.33 MnO 3 and La 0.7 Sr 0.3 MnO 3 thin films were investigated. It was demonstrated that these films could be used to measure the magnetic fields produced by magnetocumulative generators. Possible ways to design fast magnetic field sensors operating at room temperature are also discussed.

Growth and investigation of p-n structures based on Fe3O4thin films

We report preparation and investigation of p-n heterostructures based on Fe3O4 thin films grown on n-Si(111) substrates as well as indium oxide (IO) and tin doped indium oxide (ITO) layers deposited on lattice-matched monocrystalline ZrO2:Y2O3(100). Thin Fe3O4 films with thickness ranging from 100 to 300 nm were grown in situ at 400 K using dc magnetron sputtering technique. The measurement of microstructure revealed polycrystalline quality of Fe3O4 films on silicon substrate and epitaxial growth on (IO)ITO/YSZ. Investigation of surface composition by X-ray Photoelectron Spectroscopy (XPS) showed that Fe 2p peak consists of three main peaks, namely, metallic iron Fe(0), Fe(II) and Fe(III). Transport measurements of Fe3O4/n-Si heterostructures demonstrated rectifying behaviour in a wide temperature range (T = 78÷300 K) while those prepared by growing Fe3O4 layers on indium oxide (IO) demonstrated nonlinear current-voltage (I-V) dependencies at low temperatures (T<120K).

Microwave Response of La2/3Ca1/3MnO3 Thin Films

The investigations of microwave (MW) response of both epitaxial and polycrystalline La0.67Ca0.33MnO3 (LCMO) thin films, magnetron sputtered onto lattice matched NdGaO 3(100) and MgO(100) substrates, respectively, are presented. Both the MW radiat ion nduced anomalous resistance increase and fast resistance relaxation observed in this work for epitaxial LCMO film just below the paramagnetic (PM) to ferromagnetic (FM) transition t emperature Tc demonstrate a clear evidence of dynamical phase coexistence in the material. Similar investigations of LCMO/MgO films exhibited the importance of intergrain boundaries on the high fre quency conductivity of polycrystalline material. The MW response of the films, both below and above Tc, has been explained assuming influence of strong microwave radiation on the hopping c onductance of high resistance intergrain material.

Fast damaging processes in the TaN thin film absorbers under action of nanosecond electrical pulses

Purpose The purpose of this paper is to investigate damaging processes in TaN thin film absorbers under action of high-voltage electrical pulse of nanosecond duration. Despite having mechanical origin of crack opening, estimation based on the readings from oscillograms shows uncharacteristically high velocities of the crack propagation. Design/methodology/approach Microscopic images of damaged absorbers showing the final result of the damaging process provided initial information about its geometrical peculiarities. Then, to clarify the dynamics of the process, the authors create the model of the crack, having elements of self-similarities and multiple stage opening. The influence of heating induced by current concentration at crack tip and of magnetic stress of this concentrated current are both included in the model. Findings Using physical parameters of TaN layers with flowing current and performing calculations the authors define the conditions required to initiate the damaging process and to sustain it. Danger of such damage is relevant for high-Tc superconducting thin films after their switching to normal state which is induced by the high-voltage pulse. Practical implications There were made recommendations to manufactures aiming to improve electrical durability of the absorbers in an effort to prevent the damaging influence of power nanosecond electrical pulses. Originality/value Three stage opening model implies the appearance of zone of high-energy dissipation that can lead to detonation-like destruction of the film and, therefore, explain the high velocities of crack propagation.

Preparation and Electrical Properties of the Bi0.9La0.1Fe0.9Mn0.1O3/SrTiO3:Nb p-n Heterojunctions

We report synthesis of single phase highly [100]-axis oriented Bi0.9La0.1Fe0.9Mn0.1O3 (BLFMO) thin films grown by RF sputtering at 650–750°C under Ar/O2 (1:1) gas pressure. The current-voltage characteristics of the p-n heterostructures prepared by growing the BLFMO films on highly conductive 0.7 weight % Nb-doped SrTiO3(100) (STON) have been investigated. The current-voltage dependencies in a case of a forward bias have been modeled taking into account linear current-voltage relationship caused by space charge-limited current at low bias voltages, as well as major contribution of Shottky emission and current limiting effect by series resistance at higher forward bias voltages.