F.J. Espinoza-Beltrán

Effect of the substrate bias potential on crystalline grain size, intrinsic stress and hardness of vacuum arc evaporated TiN/c-Si coatings

Abstract TiN coatings were deposited on c-Si substrates by the vacuum arc evaporation process varying the substrate bias potential in the range from 100 to 450 V. The distribution in the crystalline grain size, the residual intrinsic stress and the hardness of the coatings were analyzed as a function of the substrate bias potential. Using the Warren–Averbach method, the X-ray diffractograms were analyzed to obtain the behavior of the crystalline size distribution and root mean square microstrains as a function of substrate bias potential. Vickers microindentation measurements were performed to obtain the substrate/coating hardness. The hardness of the TiN coatings as a function of crystalline grain size shows a behavior according to the Hall–Petch relation.

Structural, optical and electrical characterization of In/CdS/glass thermally annealed system

Abstract Chemical bath deposited CdS thin films coated with an evaporated indium thin film were analyzed by electrical, optical absorption, spectroscopic ellipsometry, X-ray and AFM measurements. As-deposited and thermally annealed (250–400°C) samples were evaluated. Heat treatments promote the formation of an external In 2 O 3 layer, as revealed by X-ray data. Indium atoms diffuse to the CdS layer from an intermediate indium layer. CdS doped with In with resistivities of approximately 10 −1 –10 −2 Ω/cm were obtained after annealing the In/CdS/glass system at 350 and 400°C. From the ellipsometry spectra, the evolution of the initial two-layer structure, In/CdS/glass, with thermal annealing was investigated. The analysis shows a more complex structure than the In 2 O 3 /In/CdS/glass structure previously proposed.

Oxygen diffusion in silicon oxide films produced by different methods

Thin films of silicon oxide were prepared on copper substrates using several techniques, such as DC sputtering, sol-gel and microwave decomposition of gases (SiH4 and O2). The sol-gel films were made using a conventional mixture of tetraethoxysilane (TEOS), water and ethanol, with various TEOS/water ratios. The oxygen diffusion coefficient is found from the thickness of the copper oxide layer formed at the copper–SiO2 interface, which was estimated from reflectivity and Auger spectroscopy measurements. Thermal treatments at various temperatures allowed us to determine the temperature dependence of the diffusion coefficient. It is found that the diffusion coefficient depends on the method of preparation of the SiO2 layer, which could be related to differences in the structure of the oxide layer. This conclusion is confirmed by the dielectric breakdown measurements. It follows from the results obtained that the oxygen diffusion constants and the dielectric breakdown field could be the indicators of the structural quality of silica.

Nanoindentation initiated dislocations in barium titanate (BaTiO3)

Plastic behavior during loading of ferroelectric bulk materials is commonly explained by domain switching processes. In this study the authors show that dislocation induced deformation also occurs during nanoindentation of BaTiO3. Studies were conducted using a spheroconical shaped indenter together with observations using atomic force microscopy (AFM) and focussed ion beam cross sections for transmission electron microscopy (TEM) of the contact areas. Force/displacement measurements showed the sudden appearance of “pop-in” events, which AFM/TEM observations revealed were associated with plastic deformation and dislocation arrays at the surface. TEM cross sections of the indents showed paired parallel slip lines with 45° to the original surface.

ZnO/CdS bilayers prepared by concurrent deposition from a chemical bath

ZnO/CdS bilayer films have been prepared by the chemical bath deposition (CBD) technique from a single reaction bath. The bilayer films were obtained by using solution concentrations of 1 M for ZnSO4 and 0.1 M for CdCl2. The pH was adjusted by the use of an ethanolamine‐ammonia system. A solution 1 M of thiourea was used as the source of sulfur ions. The thickness of each layer in the resultant film were 2 and 0.3 mm for ZnO and CdS, respectively. We report here the optical and structural characterization of this ZnO/CdS bilayer system. q 2001 Elsevier Science Ltd. All rights reserved.

Qualitative evaluation of sol-gel SiO2 as a protective layer for soft surfaces

Abstract In this paper, it is shown that SiO 2 sol–gel coatings deposited on glass and acrylic substrates (polymethyl methacrylate) considerably improved the mechanical resistance of the surface of these materials. We have used new methods to test the mechanical resistance and to measure the damage produced to the surface of the coated and bare substrates. The qualitative method employed to evaluate the mechanical resistance of the bare and coated surfaces consists of exposing the samples to the constant impacts and friction of zirconia balls. For that, the samples were fixed to the inner wall of a ball mill containing the zirconia balls. It is observed that during the mechanical treatment, the bare acrylic substrates lose their transparency, due to a large amount of surface defects created by the mechanical treatment. The presence of the defects is monitored measuring the transmitted light from a laser beam. Long exposure times to the mechanical test show that small amounts of materials are removed from the surface of the coating.

Structural Evolution of Colloidal Particles in Porous SiO2 Coatings.

The sol-gel method has been used to produce samples having colloidal copper-based particles embedded in a SiO2 matrix. The particle composition depended on: the atmosphere in which the samples were annealed, the annealing temperature and the time after the treatment. The optical properties of the colloidal system were determined, as a function of the sample history. For that, the model proposed by Mie was used with effective values for the optical constants of the colloidal particles. From this analysis, characteristic parameters of the colloidal system and particle composition were determined.

Presence of oxygen in the lattice of CdTe thin films

Polycrystalline CdTe thin films, with oxygen concentrations (x) in the range of 0.01–15 at. %, were grown at room temperature on 7059 Corning glass by means of the rf sputtering method. For low oxygen concentrations (x⩽0.3 at. %) the CdTe develops compressive stress during growth, making the films mechanically unstable. The stress normally relaxes when films are exposed to air, making stable films. In some cases, in films with low oxygen concentration, the stress relaxes abruptly immediately after they are exposed to air, and this results in either some fractures or in a loud explosive cracking of the film. In the latter case, the film is reduced to small pieces and violently dispersed over a wide area. Surface images of the fractures, obtained by atomic force microscopy, show detachment and liftup of the films in the regions adjacent to fractures. This indicates that the films were originally under compressive stress. Values of x in the bulk of the films were measured by means of Auger mass spectroscopy....

Stabilization of copper-based colloidal particles in sol–gel SiO2 thin films

Abstract SiO 2 amorphous thin films containing two different concentrations of copper-based colloidal particles were prepared by the sol–gel method. Thermal treatments in air at 350°C result in the segregation of cupric oxide particles. Subsequent reducing treatments in a CO atmosphere at 300 and 500°C for one hour partially reduces the cupric oxide into particles with metallic copper as the main component. The optical properties of the reduced films were characterized measuring the optical absorption spectra as a function of the elapsed time after the reduction process. The absorption data were analyzed in terms of the Mie model for colloidal systems. The fitting of this model to the experimental data provides the temporal evolution of the volume fractions of the three components of the colloidal particles, that is; Cu, Cu 2 O and CuO. It is found that the exposure to air of the films treated at 300°C under the reducing atmosphere, results in a gradual reoxidation of the colloidal particles modifying their chemical composition and therefore the optical properties of the composite film. On the other hand, the reduction treatment at 500°C results in the stabilization of the composition of the colloidal particles, producing stable films with a high optical density.

Rosette screw arms created by ac-domain structures and dislocations in barium titanate during nanoindentation

The nanoindentation in out-of-plane domains of a {001} oriented BaTiO3 single crystal was performed with a conical indenter of 0.9μm tip radius. The first pop-in occurs at 5±0.5mN load. The surface deformation was studied with atomic force microscopy and piezoresponse force microscopy. In addition to dislocation structures inside the remanent indentation, a rosette arm pattern is observed. The four identified screw arms are due to created a-domains as well as to at the free surface emerging dislocations of the {110}⟨11¯0⟩ glide system. For parts of the screw arms, a detailed analysis of the domain and dislocation structure is presented.