F. Vaz

Characterisation of Ti1−xSixNy nanocomposite films

Abstract Ti 1− x Si x N y films were synthesised by RF reactive sputtering from Ti and Si elemental targets, in an Ar/N 2 gas mixture. XRD results revealed the development of a two-phase system, composed of a nanocrystalline f.c.c. TiN (phase 1: B1 NaCl type) and a second one (phase 2), where Si atoms replaced some of the Ti ones, inducing a structure that we may call a solid solution. An amorphous phase, supposed to be of silicon nitride, within grain boundaries seems to be also present, especially for high Si contents. TEM experiments confirmed the f.c.c.-type structure for phase 2, which is the only phase that develops without ion bombardment. The higher lattice parameter of phase 1 (∼0.429 nm compared to 0.424 nm for bulk TiN) may be explained by the residual stress effect on peak position. The Ti replacement by Si would explain the low value of the lattice parameter for phase 2 (∼0.418 nm). All samples showed good results for hardness (Hv≥30 GPa), and Ti 0.85 Si 0.15 N 1.03 at a deposition temperature of 300°C showed a value of approximately 47 Gpa, which is approximately double that of pure TiN. For higher deposition temperatures, an increase in hardness is observed, as demonstrated by this same sample, which at 400°C reveals a value of approximately 54 GPa. Similar behaviour was observed in adhesion, where this same sample revealed a critical load for adhesive failure of approximately 90 N. In terms of oxidation resistance, a significant increase has also been observed in comparison with TiN. At 600°C, the oxidation resistance of Ti 0.70 Si 0.30 N 1.10 is already 100 times higher than that of TiN. For higher temperatures this behaviour tends to be even better when compared with other nitrides.

Thermal oxidation of Ti1-xAlxN coatings in air

Abstract (Ti,Al)N coatings prepared by combined DC and RF magnetron sputtering were annealed in air at temperatures between 500 and 900 °C, in order to obtain information regarding the oxidation behaviour. The depth concentration profile of the oxidized layers was measured by Rutherford Backscattering Spectrometry (RBS). During the heat treatment at 500 °C, the Ti 0.35 Al 0.65 N coating forms a Ti and Al mixed oxide with about 10 at% of nitrogen. After the annealing at 600 °C of Ti 0.62 Al 0.38 and Ti 0.35 Al 0.65 N coatings, the nitrogen amount disappears and the oxide layer is still homogeneous. At temperatures between 750 and 900 °C, a two-layer structure is formed, consisting generally in a protective superficial layer of Al 2 O 3 with traces of Ti, followed by a titanium-rich zone. The Ti 0.35 Al 0.65 N system showed a slightly higher oxidation resistance than the Ti 0.62 Al 0.38 N one. On the other hand, the Al-rich coating, Ti 0.19 Al 0.81 N, revealed the worst oxidation resistance, similar to the AlN coating, and the oxide layer is always homogeneous.

Structural transitions in hard Si-based TiN coatings: the effect of bias voltage and temperature

Abstract (Ti,Si)N films were grown by reactive magnetron sputtering. X-Ray diffraction experiments (XRD) showed the development of a mixture of two crystalline phases with lattice parameters higher ( a =0.429 nm: phase 1 — indexed with TiN) and lower ( a =0.418 nm: phase 2 — indexed to a Ti–Si–N phase) than that of bulk TiN ( a =0.424 nm). Transmission electron microscopy revealed nanocrystalline grains of an fcc structure in both crystalline phases. X-Ray absorption spectroscopy results indicated that in these films there are Si atoms bonded to Ti. This means that in phase 2 there must be some Si atoms occupying Ti positions within the TiN lattice, which explains the lower lattice parameter for that phase. Phase 2 was the only phase observed for low surface mobility conditions of the deposited material (low temperature =300°C and absence of ion bombardment of the growing film). This low surface mobility conditions of the deposited material might explain the claimed substitution of Ti with Si in TiN. When present, the lattice parameter of phase 2 is approximately the same for all Si contents, which ranged from 2.5 up to nearly 20 at.%. The enhancement of the surface mobility, either by a temperature increase or by ion bombardment during film growth, induces higher phase segregation, and therefore the XRD diffraction peaks from phase 2 disappear. For deposition temperatures near ∼ 500°C, and/or biased substrates, the complete segregation of phases was observed (no traces of phase 2), thus forming a nanocomposite structure composed of nanocrystalline grains of TiN embedded in an amorphous silicon nitride phase-nc-TiN/a-Si 3 N 4 .

Oxidation resistance of (Ti,Al,Zr,Si)N coatings in air

We prepared TiN-based multicomponent hard coatings by combined d.c. and r.f. magnetron sputtering with different contents of Ti, Al, Zr and Si on high speed steel substrates at 300°C. These coatings, with thicknesses ranging from 1 to 3 μm, were annealed in air at temperatures between 500 and 850°C in order to obtain information on their oxidation behaviour. The composition-depth profiles of heat-treated coatings were then measured by Rutherford backscattering spectrometry (RBS). The results show that the introduction of aluminium improves the oxidation resistance in all cases. During the heat treatment of Ti0.62Al0.38N at 600°C, a mixed oxide of Ti and Al is formed. At temperatures between 700 and 850°C, a protective superficial layer of Al2O3 with traces of Ti is formed, which is followed by an aluminium-depleted zone. However, for Ti0.57Al0.38Zr0.05N coatings, no protective Al2O3 layer was found on the surface after heat treatment. At 600°C, the oxidation resistance of Ti0.57Al0.38Zr0.05N is similar to that of (TiAl)N, but is about 30 times poorer at 700°C due to the absence of the protective Al2O3 layer. The Ti0.62Al0.26Si0.12N system shows a slightly lower oxidation resistance than (TiAl)N (Kp = 9.0 × 10−12 kg2 m−4 s−1 and Kp = 6.4 × 10−12 kg2 m−4 s−1 at 800°C respectively). It also forms a two-phase scale as in (TiAl)N, but the amount of Ti in the Al-rich outer layer is about 10 at.%, instead of 4at.% found in the (TiAl)N system. In the temperature range 700–850°C, oxidation is thermally activated with activation energies of 187 kJ mol−1 and 296 kJ mor−1 for (TiAl)N and (TiAlSi)N coatings respectively.

Preparation of magnetron sputtered TiNxOy thin films

Within the frame of this work, r.f. reactive magnetron sputtered TiNxOy films were deposited on steel, silicon and glass substrates at a constant temperature of 300 °C. The depositions were carried out from a pure Ti target, under the variation of process parameters such as the substrate bias voltage and flow rate of reactive gases (a mixture of N2/O2). Film colours varied from the glossy golden type for low oxygen content (characteristic of TiN films) to dark blue for higher oxygen contents. X-ray diffraction (XRD) results revealed the development of a face-centred cubic phase with 〈111〉 orientation (TiN type; lattice parameter of approx. 0.429 nm), and traces of some oxide phases. Scanning electron microscopy (SEM) revealed a mixture of very dense and columnar type structures. All these results have been analysed, and are presented as a function of both the deposition parameters and the particular composition, and crystalline phases present in the films.

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...

Physical, structural and mechanical characterization of Ti1-xSixNy films

Abstract Within the frame of this work, Ti 1− x Si x N y hard coatings with 0≤ x ≤0.37 and thicknesses ranging from 1.2 to 3.5 μm, were prepared by r.f. reactive magnetron sputtering in an Ar/N 2 gas mixture. X-ray diffraction and Fourier analysis of X-ray profiles were used to investigate the structure and grain size, and its correlation with hardness behaviour, as a function of the Si content, bias voltage and working gas (argon) flow rate. In this respect, the results show that a double cubic phase of NaCl type was developed with lattice parameters of 4.18 and 4.30 A, revealing the (111) orientation for low Si content ( x =0.05), (220) for intermediate Si contents (0.13≤ x ≤0.22) and (200) for the highest Si contents (0.30≤ x ≤0.37). Regarding the results of ultramicrohardness tests, and although all samples with 0.05≤ x ≤0.30 present a hardness value higher than 30 GPa, the Ti 0.85 Si 0.15 N 1.03 revealed the highest hardness value, around 47 GPa, which is more than twice as high as that of common TiN. Furthermore, the study of hardness as a function of the applied bias voltage revealed that best results are achieved between −50 and 0 V. The variation in hardness as a function of the argon flow showed that best results in hardness are obtained when working with flow rates around 110 cm 3 /min.

Tuning of the surface plasmon resonance in TiO2/Au thin films grown by magnetron sputtering: The effect of thermal annealing

Nanocomposites consisting of a dielectric matrix, such as TiO2, with embedded noble metal nanoparticles (NPs) possess specific optical properties due to the surface plasmon resonance (SPR) effect, interesting for several applications. The aim of this work is to demonstrate that these properties are sensitive to the nanostructure of magnetron-sputtered TiO2/Au thin films, which can be tuned by annealing. We study the role of the shape and size distribution of the NPs, as well as the influence of the crystallinity and phase composition of the host matrix on the optical response of the films. All these characteristics can be modified by vacuum annealing treatments of the deposited films. A theoretical interpretation and modeling of the experimental results obtained is presented. The model involves a modified Maxwell-Garnett approach for the effective dielectric function of the composite (describing the SPR effect) and the transfer matrix formalism for multilayer optics. Input data are based on the experiment...

Residual stress states in sputtered Ti1−xSixNy films

Abstract The present paper reports on the influence of Si addition on the properties, namely stresses and thermoelastic behaviour, of r.f. reactive magnetron sputtered TiN coatings, in order to reach a further increase of coating performance in industrial application. Residual stresses were determined by two distinct methods, one of them being the so-called mechanical method. In this method, the deflection of the substrates, before and after deposition, is measured using a high precision co-ordinate measuring unit as well as an interference optical microscope (deflection method). The second method used is X-ray diffraction using the sin 2 ψ method. By heating the samples and in situ observation of substrate deflection evolution with temperature, the analysis of thermally-induced stresses was also carried out. Regarding the results, compressive residual stresses up to approximately 11 GPa were observed. The stress magnitude was found to depend on the total amount of Si addition to TiN matrix; for large Si additions (>12 at.%) a significant reduction was observed. Furthermore, the analysis of thermally-induced stress allowed the determination of the real effective deposition temperature, which led to a value of approximately 200 °C for the conditions employed within this work.

Influence of the chemical and electronic structure on the electrical behavior of zirconium oxynitride films

This work is devoted to the investigation of decorative zirconium oxynitride, ZrOxNy, films prepared by dc reactive magnetron sputtering, using a 17:3 nitrogen-to-oxygen-ratio gas mixture. The color of the films changed from metallic-like, very bright yellow pale, and golden yellow, for low gas mixture flows [from 0 to about 9SCCM (SCCM denotes cubic centimeter per minute at STP)] to red brownish for intermediate gas flows (values up to 12SCCM). Associated to this color change there is a significant decrease of brightness. With further increase of the reactive gas flow, the color of the samples changed from red brownish to dark blue (samples prepared with 13 and 14SCCM). The films deposited with gas flows above 14SCCM showed only apparent colorations due to interference effects. This change in optical behavior from opaque to transparent (characteristic of a transition from metallic to insulating-type materials), promoted by the change in gas flow values, revealed that significant changes were occurring in...