Substrate Crystalline Structure Research Articles

Influence of microstructure on the mechanical integrity of plasma-sprayed TiO2 splat

The TiO2 splats with different microstructures were deposited by controlling the deposition temperature and the substrate crystalline structure, in order to investigate the effect of microstructures on the mechanical integrity of TiO2 splat. It was revealed that the cracking of TiO2 splat occurs by two different modes, i.e. intergranular cracking and intragranular cracking, which depend on splat microstructures. Both the morphologies and the spacing of cracks are significantly affected by the cracking mode. The area average crack spacing ranges from 5.0 to 10.4μm with the increase of splat grain size. In addition, it was found that the coarse grain splat and especially the monocrystalline one with (110) orientation spall off the substrate, while the fine grain splat is well bonded to the substrate. The cracking modes of TiO2 splat was discussed based on the stress-relieving mode, which is related to the accumulation and the relaxation of quenching stress.

Characterization of Co–Cr–Mo alloys after a thermal treatment for high wear resistance

The cobalt–chromium–molybdenum alloys are characterized by a high resistance to wear and corrosion, as well as good mechanical properties, allowing their use in the substitution of hip and knee joints.Five alloys were used as substrates for a coating deposition by a thermal treatment in molten salts, as reported elsewhere, in order to form a tantalum‐rich coating on the sample surface, able to improve the biocompatibility and wear resistance of the materials. However, the temperature (970°C), reached during this process, is considered critical for the phase transformation of the Co-based alloys.The aim of this work is the evaluation of the temperature effects on the structure, microstructure, mechanical and tribological properties of the considered substrates, after the removal of the coating by polishing. The substrates are characterized through X-ray diffraction (XRD), scanning electron microscopy with energy dispersion spectrometry (SEM-EDS) and profilometry. The mechanical behavior is evaluated by the macro- and micro-hardness and bending tests, whereas the tribological properties are analyzed through a ball on disc test. A comparison between the as-received alloys and thermal treated substrates is reported. The biocompatibility feature is not reported in this work.The substrate crystalline structure changed during the heat treatment, inducing the formation of the hexagonal cobalt phase and the decrement of the cubic one. This crystallographic modification does not seem to influence the tribological behavior of the substrates. On the contrary, it affects the strength and ductility of the substrates.

Development of Multi-Step Procedure for Epitaxial Growth of Crystalline Silicon on Rare-Earth-Metal Oxide for SOI-Applications

Two new methods for fabrication of silicon-on-isolator (SOI) structures are studied. The first one is based on the formation of a template single crystalline Si-layer and combines encapsulated solid-vapor-phase epitaxy of silicon on rare-earth-metal-oxide layer, developed for fabrication of oxide/silicon/oxide heterostructures, subsequent chemical etching of the second oxide layer, followed by vapor-phase epitaxial growth of silicon on the template-silicon layer. In the second method, crystalline silicon islands serve as template for further growth of crystalline Si layer. Structural investigations show no interface and no noticeable differences in structure quality between these two silicon sub-layers grown on each other. Silicon-substrate/oxide/silicon heterostructure exhibits transition of the substrate crystalline structure with A/B/A twinning relationship. Initial stage of deposition of the template silicon is crucial for its structural quality. [DOI: 10.1380/ejssnt.2009.405]

YSZ thin films deposited by e-beam technique

YSZ thin films were grown evaporating cubic and tetragonal phase ZrO 2 stabilized by 8 wt.% of Y 2O 3 (8% of YSZ) ceramic powders by using e-beam deposition technique. Operating technical parameters that influence thin film properties were studied. The influence of substrate crystalline structure on growth of deposited YSZ thin film was analyzed there. The YSZ thin films (1.5–2 μm of thickness) were deposited on three different types of substrates: Al 2O 3, optical quartz (SiO 2), and Alloy 600 (Fe–Ni–Cr). The dependence of substrate temperature, electron gun power, and phase of ceramic powder on thin film structure and surface morphology was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The substrate temperature was changed in the range of 20–600° C (during the YSZ thin film deposition) and its influence on the crystallinity of deposited YSZ thin films was analyzed. It was found that electron gun power and substrate temperature has the influence on the crystallite size, and texture of YSZ thin films. Also, the substrate has no influence on the crystal orientation. The crystallite size varied between 20 and 40 nm and increased linearly changing the substrate temperature. The crystal phase of evaporated YSZ powder has the influence on the structure of the deposited YSZ thin films.

Effect of the substrate crystalline structure on the magnetic, electrical, and crystallographic characteristics of La0.35Nd0.35Sr0.3MnO3 epitaxial films

A study has been made of the electrical resistivity ρ, magnetoresistance Δρ/ρ, and magnetization of La0.35Nd0.35Sr0.3MnO3 epitaxial films on ZrO2(Y2O3), SrTiO3, LaAlO3, and MgO substrates. The first film can exist in four equivalent crystallographic orientations in the sample plane, while the other three have only one orientation. The maxima of ρ and Δρ/ρ of the first film are broadened considerably in the vicinity of the Curie point TC compared to the three others, the magnitude of ρ itself being larger by 1.5 orders of magnitude, and a large negative magnetoresistance (|Δρ/ρ| ∼ 10% in a field of 8.4 kOe) is observed at temperatures 80≤T≤200 K. In all films, the magnetic moment per molecule at 5 K is ∼46% smaller than the pure spin value, due to the existence of magnetically disordered regions. The larger value of ρ of the film deposited on ZrO2(Y2O3) is due to the electrical resistance of the boundaries separating regions with different crystallographic orientations, and the magnetoresistance is associated with polarized carriers tunneling through the boundaries coinciding with domain walls. The low-temperature magnetoresistance in fields above technical saturation is caused by the strong p-d exchange coupling within spin-ordered regions.

The influence of substrate crystalline structure on DAES profiles of ultrathin silver layers on a Cu(001) face

The influence of the substrate crystalline structure on DAES profiles for ultrathin silver (111) layers deposited on a Cu(001) substrate was investigated. For Ag MNN Auger electrons and for primary electron energies E P ≥ 800 eV, the DEAS profiles characteristic of the substrate structure were observed for a 0.8 ML silver layer, while for E P = 600 eV such a profile was flat. On the other hand, DAES profiles characteristic of the silver layer structure were observed for thicker silver films, for E P ≥ 600 eV. This can be explained if one takes into account that the Auger electrons are excited in the silver layer by primary electrons and by electrons backscattered in the substrate. The flux of the Auger electrons is determined by the forward focusing and channelling of primary electrons in the substrate. For E P = 600 eV the backscattering factor is close to unity and only the primary electrons are responsible for the Auger electron emission from the overlayer. Thus, as low as possible energies E P should be used to eliminate the influence of the substrate crystalline structure on the DAES profiles of ultrathin adsorbed layers.