G.G. Fuentes

Optical and electronic properties of TiCxNy films

The optical and electronic properties of TiCxNy(x+y∼1,0<y<1) thin films have been investigated by spectroscopic ellipsometry in the 1.5–4.5 eV energy range and by valence band x-ray photoemission spectroscopy as a function of the composition. The dielectric functions measured in the energy range of intraband transitions are analyzed in terms of a Drude-like approximation. Both the free plasma energy and the damping constant are observed to depend on the nitrogen content of the samples, suggesting a certain tunability of the optical and electronic properties of these films. Analysis of the valence band reveals that the C 2p band shifts toward higher binding energies upon an increase of the nitrogen content, in good agreement with the shift observed in the minimum of the optical reflectivity associated with the threshold of the interband transitions. The enhancement of the metallic character of the films as the nitrogen content increases is also evidenced by x-ray photoemission spectroscopy as a continuous ...

Study of the growth of ultrathin films of NiO on Cu(111)

We have studied the early stages of growth of the layers formed by Ni evaporation in an oxygen atmosphere at room temperature on a Cu(111) single crystal. The layers have been analysed by XPS and x-ray absorption spectroscopy as a function of the deposition time. A background analysis of the XPS spectra has also been performed. We have found a Stranski-Krastanov way of growth, i.e. the formation of a metallic Ni monolayer followed by the formation of defective NiO islands. Further deposition leads to the formation of stoichiometric NiO.

Elastic properties of hard TiCxNy films grown by dual ion beam sputtering

Abstract The nano-hardness (HV) of TiC x N y ( x + y ≈1) thin films has been investigated by nano-indentation as a function of the ion beam assistance for different contact depths and annealing temperatures. The hardness at low indentation depths (i.e. 10 nm) is observed to decrease abruptly from 55 down to 26 GPa when the carbon content in the films decreases from x ≈0.2 to x ≈0.05 (∼TiN). On the contrary, hardness measured at penetration depths of 40 nm is observed to decrease very slightly. After annealing in UHV the hardness of the coatings becomes independent of the penetration depths. Moreover, the values of the hardness of the annealed coatings are similar to the values measured for the untreated coatings at high penetration depths. All this suggests that, the surface of the films are hardened significantly, and that this hardening can be reduced not only by annealing but also by increasing the ion beam bombardment during the growth process. The mechanism of the film hardening has been addressed in terms of the content of lattice defects and its dependence on the ion bombardment.

New technique for determining the critical loads of a thin coating on a tool–steel substrate by considering the initiation of cracks in the coating

In this article, a mathematical algorithm is derived to accurately determine the critical load of indentation for the initiation of cracks on the surface of a hard coating on a soft substrate, based on the measurement of the diameter of circumferential cracks in micro-indentation impressions. The critical load required for the initiation of the first crack predicted using this technique is shown to be in good agreement with experimental results, indicating the feasibility of the technique proposed. The rationality of the approach proposed was further explored by investigating the fracture mechanism of the surface in a multilayer-coated surface using a finite element model, which was developed with the parameterised modelling approach, in combination with the cohesive-zone model.

Metodología de preparación superficial para la nanoindentación de recubrimientos de alta rugosidad

El presente trabajo muestra una metodologia de preparacion superficial previa a ensayos de nanoindentacion que permite reducir las imprecisiones producidas por una rugosidad superficial excesiva. En aplicaciones en las que el tamano maximo de indentacion es dimensionalmente comparable con la rugosidad de la muestra, la dispersion y falta de exactitud de los resultados puede resultar excesiva. Son estos casos a los que se dirige la metodologia desarrollada. El desarrollo del metodo se ha realizado para capas finas en las que el recubrimiento presenta mayor dureza que el sustrato. Para ello, este se ha validado y aplicado utilizando recubrimientos PVD de TiO2 depositados sobre Inconel 718, los cuales han sido posteriormente sometidos a temperaturas entre 600 °C y 1100 °C, produciendose un aumento en la rugosidad de las muestras. Modificando diferentes parametros del ensayo ha sido posible analizar la mejora en los resultados que aporta el procedimiento y sus fuentes de incertidumbre, y compararlo con la metodologia habitual de nanoindentacion. PALABRAS CLAVE/KEYWORDS: Nanoindentacion, capas finas, rugosidad, abrasion superficial, PVD, oxido de titanio. Nanoindentation, thin coatings, roughness, surface abrasion, PVD, titanium oxide.

TRATAMIENTOS TERMOQUIMICOS PARA ACEROS MARAGINGNITRURACION POR PLASMA ASISTIDO POR ARCO CATODICO

Los aceros maraging son aleaciones Fe-Ni, con concentraciones de Ni de entre 15-25% en peso, y con concentraciones de carbono muy bajas (<0.03%). Estos aceros pueden contener otros aleantes como Cromo, Titanio, Niquel, Molibdeno, Cobalto o Aluminio.

Effects of the low energy-ion beam assistance in the properties of TiCxNy thin films

Abstract The stoichiometry, structure and mechanical properties of ion beam sputtered TiC x N y thin films have been studied as a function of the assistance conditions. Tuning the ratio between the current density of assisting N 2 + ions and the target sputtering rate allows us to achieve films with stoichiometries in the range of 0.6> x >0.25, keeping x + y ≈1. The surface topography is also sensitive to the assisting conditions where the RMS roughness is an increasing parameter as the ion beam bombardment increases. In terms of the Ar + ion beam assistance, the films undergo a significant amorphisation and a steep increase in lattice strain as the current density and energy of the impinging ions are increased. The observed changes are discussed in terms of the energy transfer of the bombarding Ar + ions to the layers below the surface of the growing films, leading to vacancies and defects and to a sharp decrease in film crystallinity.