J. A. Mendes

Physical and morphological characterization of reactively magnetron sputtered TiN films

c ´´ Abstract The present paper reports the influence of growth conditions on the properties of TiN thin films deposited by rf reactive magnetron sputtering in the low-pressure range.The effects of rf power at the Ti target and the negative bias voltage at the substrate in the morphology, structure, electrical resistivity and colour of the samples were studied in detail.X-Ray diffraction results showed that the d-TiN phase (a ;0.430 nm) is detected in all the samples.The sample prepared with grounded substrate 0 revealed a lattice parameter close to the bulk value (0.424 nm), which is a consequence of a low stress state, due to the absence of ion bombardment.The sample deposited at 1000 W has a lattice parameter of 0. 426 nm, close to that of the stress-free material (a s0.424 nm), probably due to some stress relief.All films have a columnar-type structure, lying in the T and I zone of the 0 Thornton Model.The resistivity of the TiN films is almost constant and close to 60 mV cm independently of the preparation conditions, except for the films deposited at 1000 W, r;215 mV cm, and for the grounded sample, r;153 mV cm.These values are probably due to cracks associated with stress relieves, in the first case, and the lack of ion bombardment that leads to films with lower density and higher number of defects in the second.No significant variations in colour were observed. 2002 Elsevier Science B.V. All rights reserved.

Chain Reorientation in β-PVDF Films Upon Transverse Mechanical Deformation Studied by SEM and Dielectric Relaxation

Chain reorientation may be induced in polyvinylidene fluoride (PVDF) in its β-phase by applying a deformation perpendicular to the pre-oriented polymeric chains. This reorientation begins right after the yielding point and seems to be completed when the stress-strain curve stabilizes. We have studied the chain reorientation mechanism by scanning electron microscopy (SEM) and dielectric relaxation methods and we have analyzed its influence in the α- and β-relaxations of the polymer. SEM images confirm the existence of a reorientation upon transversal deformation. The decrease of crystallinity with increasing reorientation and the dependence of the dielectric permittivity upon deformation indicate that a model of stress-induced melting followed by an incomplete recrystallization properly describes the reorientation mechanism.

Cobalt ferrite thin films deposited by electrophoresis on p-doped Si substrates

The structural and magnetic properties of cobalt ferrite (CoFe2O4) thin films deposited by electrophoresis on p-doped Si(001) substrates have been characterized. The films were polycrystalline and composed by cobalt ferrite with the cubic spinnel structure. The observed decrease of the coercive field with the sixth power of the grain size was indicative of a competition between the magnetocrystalline anisotropy and the exchange coupling energy, on these randomly oriented nanosized grained films.

Electrophoretic deposition of CoFe2O4 nanograins dispersed in a laser ablated BaTiO3 matrix

Thin film nanocomposites composed by CoFe2O4 grains, deposited by electrophoresis, and subsequently covered by a laser ablation deposited BaTiO3 layer, were prepared with different cobalt ferrite concentrations (x). The cobalt ferrite phase was under a compressive strain that relaxed as the CoFe2O4 concentration increased. Consequently, a blueshift of the Raman peaks of CoFe2O4 was observed, that decreased with increasing x. The dielectric permittivity of the films was found to decrease with increasing cobalt ferrite concentration, due to the decrease of the barium titanate layer grain size with increasing CoFe2O4 content in the films.

Cooperative and Local Relaxations in Complex Systems: Polymers and Crystals

A method for investigating the nature of thermally activated relaxations in terms of their cooperative character is tested both in low molecular weight crystals and polymers. This approach is based on the analysis of the activation entropy. In the betaine arsenate/phosphate (BABP) mixed systems we will study the effect of pressure and concentration, whereas in the rubidium ammonium dihydrogen arsenate (RADA) mixed crystal system the effect of concentration and deuteration in the relaxation processes will be studied. Several relaxations have been also studied in polymeric systems, trying to cover representative processes such as the slow g -relaxation in polymers, the i -relaxation in liquid crystalline polymers and the crystalline f -relaxation of semicrystalline polymer ( f c ).

Reactive DC Magnetron Sputtering of Vanadium Oxide Thin Films

Vanadium oxides are a class of materials with outstanding physical and chemical properties. They find a wide field of technological applications such as optical and electrical switching devices, light detectors, temperature sensors, micro batteries, etc. There are several studies regarding the production of vanadium oxide films by radio-frequency (RF) magnetron sputtering, and with increasing interest on the thermochromic VO2 phase. However, literature with focus on vanadium oxide films deposited by direct current (DC) magnetron sputtering is very limited. In this work, we have successfully deposited vanadium oxide thin films by reactive DC magnetron sputtering under several processing conditions. The effect of substrate type, temperature, and O2/Ar flow ratio on phase formation has been studied. Structural analysis and phase determination have been carried out by X-ray diffractometry (XRD). Some single phase samples were also analysed with respect to surface morphology by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermochromic behaviour of single phase VO2(M) films has been evaluated by optical spectrophotometry.

Annealing Induced Ordering of SrTiO3 Thin Films Deposited by Laser Ablation Over Si Substrates

Strontium titanate thin films have been prepared at different oxygen pressures and with different post deposition annealing treatments. The films were deposited by laser ablation at room temperature on Si(001) substrates with a silica buffer layer. The as-deposited films are amorphous with smooth and uniform surface. As the annealing temperature increase they become more crystalline, presenting a cubic SrTiO3 phase. The infrared characterization show that the silica layer also grows due to the annealing. The characteristics of this SrTiO3 crystalline depend on the oxygen partial pressure. At low oxygen pressures the annealed films are polycrystalline. As the oxygen pressure increase the films become more textured so that at longer enough annealing times the films become (200) oriented. The results are discussed in terms of atomic diffusion in the films.

Structural Characterization of Lead Metaniobate Thin Films Deposited by Pulsed Laser Ablation

The ferroelectric polymorph of lead metaniobate (PbNb2O6) presents an orthorhombic structure that is metastable at room temperature. This phase is obtained by quenching from high temperature. The fabrication of lead niobate thin films with this orthorhombic form has been reported to be difficult due to the presence of phases with the rhombohedric form or other nonstoichiometric phases. In this work, lead niobate thin films have been prepared by laser ablation, at different oxygen pressures and with different substrate temperatures. Their structure was studied by X-ray diffraction and their surface was examined by scanning electron microscopy (SEM). The results show that for low deposition temperatures the films presented a rhombohedric-PbNb2O6 structural phase. As Tdep increases the films started to develop an orthorhombic- PbNb2O6 structure that appeared at 400°C and remains up to 600°C. For lower oxygen pressure during deposition, a mixture of this phase and other orthorhombic lead deficient phases are present in the films. On the other hand, by increasing the oxygen pressure the lead deficient phases are strongly reduced and the films present only the orthorhombic- PbNb2O6 structure.

Ferroelectric/Antiferroelectric Phase Coexistence in the Intermediate Concentration Regions of the BAxBP1−x Phase Diagram

Temperature and frequency dependent hysteresis loop measurements have been carried out along the phase diagram of ferroelectric (FE) betaine arsenate (BA) and antiferroelectric (AF) betaine phosphate (BP) mixed crystal system (BA x BP1 -x ). Coexistence regions characterized by competing ferro- and/or antiferroelectric interactions are detected by multiple hysteresis loops.