National Institute Of Materials Physics - Romania

A novel method for the synthesis of nanostructured films produced by depositing gas-phase magnetic nanoparticles is presented and the properties of the films are reported. The technique mixes metal vapour and small argon clusters produced in a supersonic expansion. The condensed clusters are subsequently deposited in situ onto copper grids. The cluster size is controlled by the vapour pressure of the metal inside the pick-up chamber. Detailed analysis of the transmission electron micrographs of the Fe clusters shows that there is a simple linear relationship between the average metal cluster diameter and the metal vapour pressure during deposition. Furthermore, the nanoparticles show a relatively narrow size distribution for a given set of experimental conditions. Structural and magnetic investigations have been performed on Fe cluster samples, and the influence of the metal vapour pressure has been studied. Detailed analysis of the magnetic and structural data has been performed and valuable information such as cluster size distributions, strength of the interparticle dipolar interactions and average magnetic moment per cluster are derived. It is shown that, at room temperature, the magnetic behaviour of the films is consistent with nanoparticle supermoments interacting via dipolar interactions.

Electrical properties, i.e., dielectric hysteresis and leakage current, of epitaxial Pb(Zr0.2Ti0.8)O-3 films with bottom SrRuO3 electrode and different metals as top contact were investigated. The leakage current is largely insensitive to the work function of the top metal but increases with decreasing electronegativity as well as with decreasing number of electrons on the d-shell of the top metal. The best rectifying properties are obtained for metals with complete d-shell (Cu, Au, Ag, Pd), while the metals with few electrons on the d-shell (Ta, Cr) form Ohmic-like contacts. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3021293]

There was investigated the application of inorganic photo-resist based on three-component chalcogenide films for fabrication of submicrometer periodic relief on silicon wafers using interference lithography. For this purpose. technological process of resistive two-layer chalcogenide-Cr mask formation on a silicon surface was developed, and silicon anisotropic etching was optimized, too. This technology has been used for the fabrication of diffraction gratings and two-dimensional periodic structures on Si (100) surface. The obtained relief patterns were used to form photonic structures by oblique deposition of silicon monoxide in vacuum.

An optimized electroless deposition procedure to form Pd membranes onto ceramic substrates involving the thermal decomposition of a Pd complex compound ([Pd (NH3)(4)] [PdCl4]) is discussed. This allowed a reaction efficiency of about 90-95%. The proposed method significantly diminishes the Pd wastes as compared with the classical procedure involving hydrazine based reduction step. A Pd layer of about 3-5 mu m has been uniformly deposited on the inner surface of the alpha-Al2O3 based substrate, being characterized by a very good adherence and light grey metallic appearance. Homogeneous films of Pd were obtained by annealing the deposited Pd layers at temperatures higher than 500 degrees C in a hydrogen atmosphere. XRD and laser confocal microscopy techniques have been proved to be suitable to characterize the composition, thickness and uniformity of the formed Pd membranes.

This paper presents investigations on the electrical transport phenomena in perylene and PTCDA emphasising the particularities of the charge carrier injection at the contacts with inorganic semiconductors (Si) and metals (Cu, Al) and the effect of the supplementary organic layer (ZnPc, alpha-NPD) on the electrical conduction. The I-V characteristics for different delay and integration times, at forward and reverse bias, have evidenced a dominant ohmic behaviour of these SIS and MIS structures at low voltage (<0.1 V) and limitations of the current induced by the space charge and trap charge at voltages >1 V. An intermediate organic layer (ZnPc) with higher ionisation potential than PTCDA and lower electron affinity than perylene improves the charge carrier injection and the conduction properties of the Si/PTCDA/Si and forward biased Cu/perylene/Si heterostructures. No increase in the hole injection was obtained in Si(p)/perylene/Si(p) heterostructure introducing an a-NPD layer. (C) 2008 Elsevier Masson SAS. All rights reserved.

Nanowires made of CdTe were produced by using a template method. Polymer ion track foils (30 micrometers thick) were used as templates, after a proper chemical etching. Nanowires were electrochemically grown in the resulting pores. A discussion of the observed correlations between the morphological/structural properties of the wires and the growth conditions is given. Electrical properties of the arrays of nanowires were studied in the temperature range of 40 K - 300 K, after contacting them by sputtering a gold layer on top of the membranes. Symmetric, non-linear I-V characteristics were recorded in the voltage range used and an activated electrical resistance was observed in the ohmic regime.

This paper presents the obtaining of copper sulfide CuS (covelite) from Cu(CH3COO)(2)center dot H2O and thioacetamide (TAA) system. The reaction was conducted in presence or absence of sodium-bis(2-ethylhexyl) sulfosuccinate (Na-AOT). The effects of various reaction parameters on the size and on the shape of nanoparticles have been examined. CuS obtained was characterized by X ray diffraction, IR spectroscopy, TEM - transmission electron microscopy and SAED selected area electron diffraction. The influence of surfactant to the shape and size of CuS (covellite) nanocrystals was established. The size of the nanocrystals varied from 10-60 nm depending on the reaction conditions such as quantity of surfactant.

We measured directly the depth-dependent Fe spin rotation upon magnetization reversal in exchange-coupled Fe/MnF2 bilayers using nuclear resonant scattering of synchrotron radiation from an Fe-57-probe layer buried at different depths within the Fe film. Our results show that the exchange-biased ferromagnetic layer develops a noncollinear spin structure along the film normal direction, reminiscent of a partial domain wall parallel to the Fe/MnF2 interface. This is contrary to most theoretical models of exchange bias which assume a collinear spin structure in the ferromagnetic layer.

The temperature T dependence of the normalized magnetization relaxation rate S in optimally doped YBa(2)Cu(3)O(7-delta) films with the external dc magnetic field H oriented along the c axis exhibits the well-known plateau in the intermediate T range, associated with the presence of elastic (collective) vortex creep. The disappearance of the S(T) plateau in the high-H domain (H >= 20 kOe) is not completely understood. We show that in the case of high-temperature superconductors with significant quenched disorder the S(T) plateau is directly related to a crossover in the vortex-creep process generated by the macroscopic currents induced in the sample. In dc magnetization measurements the creep-crossover temperature decreases rapidly with increasing H, reaching the low-T region where the magnetization decay is dominated by micro flux jumps. Consequently, at high H no well-defined elastic-creep domain is present and the S(T) plateau disappears.

Spherical arsenic chalcogenide glass microlenses have been attached to optical fibers. The assembly was subjected to UV-radiation for different time intervals in different conditions of temperature. As a consequence, the focusing of the beam changes due to the modification of the refractive index, and of the structure, induced by photo-melting followed by crystallization. In the same time for high irradiation times the habitus of the lens changes into a prismatic one due probably to photomelting of the glass accompanied by a crystallization process.