Perpendicular magnetic anisotropy in chemically disordered FePd-FeV(100) alloy thin films

We find that the use of V(100) buffer layers on MgO(001) substrates for the epitaxy of FePd binary alloys yields to the formation at intermediate and high deposition temperatures of a FePd¿FeV mixed phase due to strong V diffusion accompanied by a loss of layer continuity and strong increase of its mosaic spread. Contrary to what is usually found in this kind of systems, these mixed phase structures exhibit perpendicular magnetic anisotropy (PMA) which is not correlated with the presence of chemical order, almost totally absent in all the fabricated structures, even at deposition temperatures where it is usually obtained with other buffer layers. Thus the observed PMA can be ascribed to the V interdiffusion and the formation of a FeV alloy, being the global sample saturation magnetization also reduced.

Microstructure of highly oriented, hexagonal, boron nitride thin films grown on crystalline silicon by radio frequency plasma-assisted chemical vapor deposition

We present a high‐resolution electron microscopy study of the microstructure of boron nitride thin films grown on silicon (100) by radio‐frequency plasma‐assisted chemical vapor deposition using B2H6 (1% in H2) and NH3 gases. Well‐adhered boron nitride films grown on the grounded electrode show a highly oriented hexagonal structure with the c‐axis parallel to the substrate surface throughout the film, without any interfacial amorphous layer. We ascribed this textured growth to an etching effect of atomic hydrogen present in the gas discharge. In contrast, films grown on the powered electrode, with compressive stress induced by ion bombardment, show a multilayered structure as observed by other authors, composed of an amorphous layer, a hexagonal layer with the c‐axis parallel to the substrate surface and another layer oriented at random

Oxygen content and inhomogeneity effects on the electrical properties of YBa2Cu3Oy thin films

Oxygen content is a very important factor influencing the electrical properties of YBa2Cu3Oy. In this work the electrical properties of laser deposited YBa2Cu3Oy thin films on LaAlO3(100), in the whole range 6 y 7, are studied. An electrical network model, which randomly assigns oxygen contents and R(T) characteristics to the different elements in the circuit according to an arbitrary distribution, is used to analyze several features in the measured R(T) characteristics as a function of oxygen homogeneity. The model takes into account both short-range and long-range oxygen inhomogeneities. Good agreement between estimated oxygen contents from x-ray diffraction data in our samples and the average oxygen contents used to reproduce their R(T) characteristics is found. The model points out that oxygen homogeneity is very important in order to get the best and reproducible properties, and for conduction and superconductivity analysis through the shape or derivatives of R(T) characteristics.

Competing tunneling and capacitive paths in Co-ZrO2 granular thin films

The ac electrical response is studied in thin films composed of well-defined nanometric Co particles embedded in an insulating ZrO2 matrix which tends to coat them, preventing the formation of aggregates. In the dielectric regime, ac transport originates from the competition between interparticle capacitive Cp and tunneling Rt channels, the latter being thermally assisted. This competition yields an absorption phenomenon at a characteristic frequency 1/(RtCp), which is observed in the range 1010 000 Hz. In this way, the effective ac properties mimic the universal response of disordered dielectric materials. Temperature and frequency determine the complexity and nature of the ac electrical paths, which have been successfully modeled by an Rt-Cp network.

Competing tunneling and capacitive paths in Co-ZrO2 granular thin films

The ac electrical response is studied in thin films composed of well-defined nanometric Co particles embedded in an insulating ZrO2 matrix which tends to coat them, preventing the formation of aggregates. In the dielectric regime, ac transport originates from the competition between interparticle capacitive Cp and tunneling Rt channels, the latter being thermally assisted. This competition yields an absorption phenomenon at a characteristic frequency 1/(RtCp), which is observed in the range 1010 000 Hz. In this way, the effective ac properties mimic the universal response of disordered dielectric materials. Temperature and frequency determine the complexity and nature of the ac electrical paths, which have been successfully modeled by an Rt-Cp network.

Growth and characterization of CoO ultra thin films

In this report we present the growth process of the cobalt oxide system using reactive electron beam deposition. In that technique, a target of metallic cobalt is evaporated and its atoms are in-flight oxidized in an oxygen rich reactive atmosphere before reaching the surface of the substrate. With a trial and error procedure the deposition parameters have been optimized to obtain the correct stoichiometry and crystalline phase. The evaporation conditions to achieve the correct cobalt oxide salt rock structure, when evaporating over amorphous silicon nitride, are: 525 K of substrate temperature, 2.5·10-4 mbar of oxygen partial pressure and 1 Å/s of evaporation rate. Once the parameters were optimized a set of ultra thin film ranging from samples of 1 nm of nominal thickness to 20nm thick and bulk samples were grown. With the aim to characterize the samples and study their microstructure and morphology, X-ray diffraction, transmission electron microscopy, electron diffraction, energy dispersive X-ray spectroscopy and quasi-adiabatic nanocalorimetry techniques are utilised. The final results show a size dependent effect of the antiferromagnetic transition. Its Néel temperature becomes depressed as the size of the grains forming the layer decreases.

Optical response of Cu3Ge thin films

We report an investigation on the optical properties of Cu3Ge thin films displaying very high conductivity, with thickness ranging from 200 to 2000 Å, deposited on Ge substrates. Reflectance, transmittance, and ellipsometric spectroscopy measurements were performed at room temperature in the 0.01-6.0, 0.01-0.6, and 1.4-5.0 eV energy range, respectively. The complex dielectric function, the optical conductivity, the energy-loss function, and the effective charge density were obtained over the whole spectral range. The low-energy free-carrier response was well fitted by using the classical Drude-Lorentz dielectric function. A simple two-band model allowed the resulting optical parameters to be interpreted coherently with those previously obtained from transport measurements, hence yielding the densities and the effective masses of electrons and holes.

Cationic Diffusion in La2/3Ca1/3MnO3 Thin Films Grown on LaAlO3 (001) Substrates.

Microstructural features of La2/3Ca1/3MnO3 layers of various thicknesses grown on top of 001 LaAlO3 substrates are studied by using transmission electron microscopy and electron energy loss spectroscopy. Films are of high microstructural quality but exhibit some structural relaxation and mosaicity both when increasing thickness or after annealing processes. The existence of a cationic segregation process of La atoms toward free surface has been detected, as well as a Mn oxidation state variation through layer thickness. La diffusion would lead to a Mn valence change and, in turn, to reduced magnetization.

Nitrogen incorporation effects in Fe(001) thin films

Nitrogen incorporates into Fe thin films during reactively sputtered TiN capping layer deposition. The influence that this nitrogen incorporation has both on the structure and magnetic properties is discussed for a series of Fe~001! thin films grown at different temperatures. A higher nitrogen content is accompanied by distortion in the Fe lattice and by reduction in the Fe magnetization saturation as well as in the effective anisotropy constant, K. The reduction of K brings as a consequence lowering in the coercive field with respect to equivalent Fe films with no nitrogen present.