C.J. Tavares

Hard nanocomposite Ti–Si–N coatings prepared by DC reactive magnetron sputtering

Abstract Films resulting from Si additions to TiN matrix were prepared with Si contents in the range 0–19 at.%, using a closed field unbalanced DC magnetron sputtering system. Transmission Electron Microscopy (TEM) analyses revealed the nanocrystalline nature of these coatings, confirming the results of grain size evaluation from X-ray diffraction (XRD) patterns. Nanoindentation tests and scratch tests were carried out for the mechanical characterisation. Regarding the results, the samples show hardness values as high as 45 GPa. Best hardness values were found for Si content in the range 4–10 at.%. Almost all samples showed high critical loads for total adhesion failure, generally higher than 80 N, although the critical load for the first adhesion failure was found to be lower than 20 N for several samples. XRD patterns revealed the presence of only one phase that can be assigned to a cubic B1 NaCl structure, typical for TiN, with a lattice parameter of approximately 0.430 nm. The preferential growth, as a function of Si content, changes from a strong (111) orientation at the lowest Si additions to a weak (200) orientation at the highest Si content. Density values in the range 3.0–3.7 g/cm3 were obtained for most of the samples prepared with deposition rates between 0.5 and 1.1 μm/h, although higher density values were obtained for higher Ti deposition rates, with maximum of approximately 4.7 g/cm3 for the case of samples with low Si content.

Structural, electrical, optical, and mechanical characterizations of decorative ZrOxNy thin films

The main objective of this work is the preparation of decorative zirconium oxynitride, ZrOxNy, thin films by dc reactive magnetron sputtering. Film properties were analyzed as a function of the reactive gas flow and were correlated with the observed structural changes. Measurements showed a systematic decrease in the deposition rate with the increase of the reactive gas flow and revealed three distinct modes: (i) a metallic mode, (ii) a transition mode (subdivided into three zones), and (iii) an oxide mode. The measurements of target potential were also consistent with these changes, revealing a systematic increase from 314to337V. Structural characterization uncovered different behaviors within each of the different zones, with a strong dependence of film texture on the oxygen content. These structural changes were also confirmed by resistivity measurements, whose values ranged from 250to400μΩcm for low gas flows and up to 106μΩcm for the highest flow rates. Color measurements in the films revealed a chan...

Micro and nanofilms of poly(vinylidene fluoride) with controlled thickness, morphology and electroactive crystalline phase for sensor and actuator applications

Poly(vinylidene fluoride), PVDF, thin films have been processed by spin-coating with controlled thickness, morphology and crystalline phases. The influence of the polymer/solvent mass ratio of the solution, the rotational speed of the spin-coater and the temperature of crystallization of the films on the properties of the material has been investigated. It is shown that high-quality films with controlled thicknesses from 300 nm to 4.5 µm and with a controlled amount of electroactive crystalline phases can be obtained in a single deposition step, which allows tailoring the material characteristics for specific applications.

Pvd grown (Ti, Si, Al)N nanocomposite coatings and (Ti, Al)N/(Ti, Si)N multilayers: structural and mechanical properties

Abstract In the last few years a considerable effort has been undertaken in order to optimise the production techniques of thin films and improve their quality. In this work, nanocomposite films resulting from Si additions to a (Ti,Al)N matrix have been prepared by RF and/or DC magnetron sputtering, with deposition rates varying from 0.21 μm/h to 4.6 μm/h. Rutherford Backscattering (RBS) and Electron Microprobe Analysis (EMPA) were used in order to access the chemical composition as well as the density of the films. For samples prepared with low deposition rates (deposited by a combination of RF and DC reactive magnetron sputtering) both symmetric and asymmetric XRD scans showed the development of crystalline phases whose structure is very similar to that of bulk TiN. The peak positions revealed changes of the lattice parameter from 0.420 to 0.428 nm with an increase of Si content dependent on the deposition rate. The lowest lattice parameter corresponds to a Ti–Si–Al–N phase where some of the Si and Al atoms are occupying Ti positions in the f.c.c. TiN lattice, while the highest lattice parameter corresponds to a system where at least a partial Si segregation can be enough to nucleate and develop the Si 3 N 4 phase that forms a layer on the growth surface, covering the (Ti,Al)N nanocrystallites and limiting their growth. As for the (Ti,Al,Si)N crystalline texture evolution, a (111) preferential growth for (Ti,Al)N and for low Si content was observed, while at intermediate Si content the texture changed to (200). With the increase of the Si content there is a corresponding decrease in the size of the diffracting grains. For samples prepared with high deposition rates (DC sputtered samples) High-Resolution Transmission Electron Microscopy (HRTEM) micrographs revealed a columnar growth associated with the f.c.c.-type structure of both phases. Small crystallites with sizes between ±7 and ±10 nm were observed. The use of (Ti,Al) and (Ti,Si) targets, relatively high deposition rates and an alternate deposition resulted in a multilayer of (Ti,Si)N/(Ti,Al)N. This system was produced with modulation periods between 5 and 10 nm, as shown by HR-TEM results, when the samples were grown with a deposition rate between 2 and 4.6 μm/h, respectively. Their average ultramicrohardness can be as high as 50 GPa. The residual stress values for the multilayer system are significantly lower than that of (Ti,Si,Al)N nanocomposite coatings.

Deposition and characterization of multilayered TiN/ZrN coatings

Abstract TiN/ZrN multilayers deposited by combined dc and rf magnetron sputtering on Si substrates have been studied by X-ray diffraction (XRD) and Rutherford Backscattering Spectrometry (RBS). The periodicity of the TiN/ZrN system was determined by the low angle XRD spectra and varied from 5.7 nm to 12.3 nm. These spectra showed a well defined TiN and ZrN layers, but with interfaces not perfectly planar. The individual layers have (111) and (200) orientations perpendicular to the plane of the film. The interfacial roughness was calculated by simulation of the high angle XRD patterns. The rms roughness values ranges from about 3.5 A or approximately ±1.4 atomic plane in the case of samples grown by static deposition mode and about 9.3 A or approximately ±3.5 atomic planes in the case of samples grown by rotating deposition mode. With the RBS technique it was possible to measure a superior limit for the average roughness.

Enhancement in the photocatalytic nature of nitrogen-doped PVD-grown titanium dioxide thin films

Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N2:O2 during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 °C the ...

Synthesis of iron-doped TiO2 nanoparticles by ball-milling process : the influence of process parameters on the structural, optical, magnetic, and photocatalytic properties

Titanium dioxide (TiO2) absorbs only a small fraction of incoming sunlight in the visible region thus limiting its photocatalytic efficiency and concomitant photocatalytic ability. The large-scale application of TiO2 nanoparticles has been limited due to the need of using an ultraviolet excitation source to achieve high photocatalytic activity. The inclusion of foreign chemical elements in the TiO2 lattice can tune its band gap resulting in an absorption edge red-shifted to lower energies enhancing the photocatalytic performance in the visible region of the electromagnetic spectrum. In this research work, TiO2 nanoparticles were doped with iron powder in a planetary ball-milling system using stainless steel balls. The correlation between milling rotation speeds with structural and morphologic characteristics, optical and magnetic properties, and photocatalytic abilities of bare and Fe-doped TiO2 powders was studied and discussed.

Mechanical characterisation of TiN/ZrN multi-layered coatings

Ultra-microhardness, adhesion and residual-stress analysis tests were performed on reactive sputtered deposited TiN/ZrN multi-layers. Hardness values as high as3600 Vickers were achieved for this material. Scratch tests of coatings deposited on steel substrates confirmed the existence of different mechanisms associated with total adhesion failure, depending essentially on multi-layer deposition control parameters. Stress-relaxation measurements indicated the compressive nature of these thin films. The inherent mechanical characterisation was broadened regarding the induced contributions from film thickness, total interfacial roughness, number of bi-layers and corresponding modulation periodicity. Complementary analyses with data extracted from structural XRD studies have been undertaken. # 1999 Elsevier Science S.A. All rights reserved.

A structural and mechanical analysis on PVD-grown (Ti,Al)N/Mo multilayers

Abstract (Ti,Al)N/Mo multilayered hard coatings have been designed to fulfil future applications concerning wear-prevention on tool steels. They have been deposited by reactive dc magnetron sputtering on high-speed steel substrates with modulation periods between 6.5 and 8 nm. Experimental X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and computational modelling of those patterns has undergone to survey structural properties such as modulation periodicity, interfacial roughness and density. Asymmetric XRD measurements confirmed that the textured grains, although being randomly distributed, possess a slight misorientation of ±11° due to their mosaic structure. Atomic force microscopy (AFM) analysis revealed a dome-rounded structure with columnar grain sizes between 90 and 120 nm in diameter, depending on deposition process parameters. The average ultramicrohardness of these multilayers can be as high as 36 GPa with a maximum Youngs modulus of 445 GPa, while the adhesion critical load may reach 60 N.

Comparative efficiency of TiO2 nanoparticles in suspension vs. immobilization into P(VDF–TrFE) porous membranes

Photocatalytic processes based on titanium dioxide (TiO2) nanoparticles have attracted increasing attention in the last decades. However, approaches based on nanoparticles show some drawbacks, in particular due to the need for expensive and time consuming post-treatment of nanoparticles filtration/separation. This hindrance demands the development of immobilized configurations with tailored properties, as an alternative to allow simple recovery of the photocatalytic particles. Thus, this work reports on the development of photocatalytic membranes based on TiO2 nanoparticles immobilized into a poly(vinylidenefluoride–trifluoroethylene) (P(VDF–TrFE)) membrane and the comparative study of their performance with dispersed TiO2 nanoparticles. Photocatalytic nanocomposite membranes with a highly porous structure (∼75%) and controlled wettability by NaY addition were successfully produced. These properties were paramount to achieve a methylene blue degradation efficiency of 96% in 40 min under ultraviolet (UV) irradiation, corresponding to an efficiency loss of just 3% regarding the TiO2 nanoparticle assays.