S. Kaciulis

Sol-gel derived hydroxyapatite coatings on titanium substrate

Biomaterials, in particular those used for orthopaedic prostheses, consist of a metallic substrate, exhibiting excellent mechanical properties, coated with a ceramic layer, which guarantees resistance to the corrosion and an elevated bioactivity. In this paper the preparation of sol-gel films of hydroxyapatite, HA (Ca10(PO4)6(OH)2), on titanium substrate is described. The samples were obtained through the dip-coating method, starting from a colloidal suspension of hydroxyapatite. In order to increase the adhesion between the HA film and the metallic substrate, the same substrate has been preliminarily coated either with titanium oxide, TiO2 (in the anatase or rutile phase), or calcium titanate, CaTiO3 (perovskite). Also these latter films have been deposited from a sol-gel solution. The characterization of the films through XRD, SEM, and AFM gave good results for the crystallinity of the deposited HA; for what concerns the sample morphology, the films turned out to be homogeneous and crack-free.

SURFACE CHEMISTRY OF TIN OXIDE BASED GAS SENSORS

Four types of gas sensors based on SnOx thin film with and without additives (Pt and Sb) were investigated by means of x‐ray photoelectron spectroscopy and scanning Auger microscopy. The sensors were deposited on Si substrates by using reactive dc magnetron sputtering. The temperature dependencies of the electrical resistivity response to CO gas exposure were measured in order to characterize all types of fabricated sensors. The surface chemical composition before and after various treatments (Ar+ ion sputtering, thermal annealings in ultrahigh vacuum, and oxygen up to 400 °C) was determined from core level and valence band spectra. The three main types of oxygen species were found on the sensors’ surface: oxygen in SnOx, adsorbed hydroxyl groups and adsorbed water. An ultrathin Pt overlayer, which enhances the gas sensitivity in a low operating temperature range, was found to be very porous. The addition of a Pt overlayer was promoting a formation of hydroxyl groups, while the surface oxygen species was ...

XPS study of apatite-based coatings prepared by sol-gel technique

Abstract Biocompatible layers of hydroxyapatite and fluorhydroxyapatite were grown on Ti substrates by means of dip-coating into sol–gel. In order to improve the adhesion of apatite-based coatings, the substrates were a priori covered with calcium titanate. Therefore, the hydroxyapatite, fluorhydroxyapatite and CaTiO 3 coatings were produced and analysed. The chemical composition of the coatings (CaTiO 3 , CaTiO 3 +hydroxyapatite, and CaTiO 3 +fluorhydroxyapatite) was studied by using X-ray photoelectron spectroscopy (XPS). The data of quantitative XPS analysis displayed the different features (cleanness, homogeneity, etc.) of CaTiO 3 , hydroxyapatite, and fluorhydroxyapatite films after the growth and after the treatment in vitro.

Properties of CuxS thin film based structures: influence on the sensitivity to ammonia at room temperatures

Abstract Surface and electrical properties of thin CuxS films grown on different substrates (polyethylene and micro-porous-Si layer) sensitive to ammonia at room temperature are investigated. The resistance response to ammonia is measured in the CuxS in air with relative humidity from 15 to 100% at temperatures from 290 to 350 K. The surface chemical composition and the morphology are analysed. A honeycombed construction of the CuxS films deposited on a micro-porous Si-layer and proportions between components in the chemical composition are found to correlate with the higher sensitivity to ammonia in air at room temperature.

Surface analysis of biocompatible coatings on titanium

The coatings of hydroxyapatite, which is widely used for orthopaedic and dental prothesis, were deposited by using the dip-coating method. The layers of hydroxyapatite were grown on commercial Ti substrates. In order to improve the adhesion of hydroxyapatite, the substrate was a priori covered with titania or calcium titanate by using the sol-gel technique. For comparison, commercial samples of hydroxyapatite coating (manufactured by means of plasma-spray apparatus) were analysed. The chemical composition and the structure of the coatings (TiO2, CaTiO3 and hydroxyapatite) were studied by using X-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), X-ray diffraction (XRD) and secondary electron microscopy (SEM) techniques. The data of quantitative XPS analysis and the surface images (SAM and SEM) displayed the superior quality (cleanness, homogeneity, etc.) of hydroxyapatite deposited by sol-gel in comparison with commercial samples investigated.

Investigation of sol-gel prepared CeO2-TiO2 thin films for oxygen gas sensing

Abstract The oxygen gas sensing performance of semiconducting CeO 2 –TiO 2 thin films have been investigated. These thin films have been prepared by the sol–gel process utilizing a non-alkoxide as the main precursors. For gas sensing measurements, the films were deposited by the spin coating technique onto alumina substrates with interdigital transducers located on the top and a micro-heater on the bottom. For the microstructural characterization, the thin films were deposited onto single crystal silicon substrates. X-ray photoelectron spectroscopy (XPS), Auger electron spectrometry (AES) and scanning electron microscopy (SEM) were employed to analyze the films. These films were exposed to various concentrations of O 2 gas and their electrical responses were measured.

Surface studies of in vitro biocompatibility of titanium oxide coatings

Titanium oxide coatings are normally used for orthopaedic and dental prostheses. Nevertheless, their chemical, biological and mechanical properties can be still improved by the development of new preparation technologies. In this paper a surface characterisation of the titanium oxide layer, grown on commercial Ti substrates by metal organic chemical vapour deposition (MOCVD) technique, is reported. The biocompatibility of the samples is tested upon in vitro treatment as a function of the exposure time. The surface characterisation of the titanium substrate and the oxide coatings is performed by using different analytical techniques. Surface chemical composition and morphology of the coatings are investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and scanning tunnelling microscopy (STM). Quantitative XPS analysis and surface physical images show a good quality (cleanness, homogeneity, roughness) of the oxide coating deposited by MOCVD and the surface modifications induced by the interaction with osteoblast cells.

Hydroxy- and fluorapatite films on Ti alloy substrates: Sol-gel preparation and characterization

In this paper we describe the preparation of hydroxyfluorapatite (HFA) and fluorapatite (FA) films deposited on titanium alloys by means of the dip-coating method starting from a sol-gel prepared colloidal solution. These materials are compared with hydroxyapatite (HA) films prepared via sol gel and commercial films prepared by means of plasma spray. The film characterization from the point of view of the composition and crystallinity, performed by means of XRD, FTIR and Raman Spectroscopies, has shown a good purity degree, and compositional homogeneity for the sol-gel materials, though traces of carboxy-hydroxy apatite were found. Also, the samples exhibit a good crystallinity. SEM pictures, taken on HA coating deposited via sol-gel, revealed a homogeneous surface structure and optimum features to set up a good prosthesis-tissue interface.

Interaction of mercury vapour with thin films of gold

Thin films of gold deposited on a silicon substrate were used as electrical sensors of mercury vapour. The samples were exposed to mercury vapour at room temperature, changing the Hg concentration and the exposure time. The chemical composition and morphology of the films exposed to mercury vapour were studied by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), scanning Auger microscopy (SAM) and secondary electron microscopy (SEM). In the samples exposed for a short time, the mercury was adsorbed by thin surface sublayer of Au film. In the case of long exposures, the transformation of the uniform Au film to a dendritic-like coalesced AuHg amalgam occurred, i.e. the morphology of the film was modified irreversibly. This transformation is caused by insufficient adhesion of gold to the substrate.

Peculiarities of surface doping with Cu in SnO2 thin film gas sensors

It is demonstrated that a small amount of Cu impurity (less than 1 at.%) significantly modifies the properties of tin oxide thin films used for the gas sensors. Different amount of Cu (between 0.5 and 7 at.%) was sputtered on the top of the films. The structure, surface chemical composition, optical and electrical properties are studied for these films. It is shown that the surface doping with the sputtered Cu leads to nearly constant doping level in all the volume of the polycrystalline tin oxide thin film. It is shown experimentally that the selectivity of the resistance response to CO, H2 and Cl2 gases is improved for the tin oxide sensors by the small amount of the sputtered Cu. A correlation is revealed between the Cu effect and the electronic surface states that were detected by the XPS and the optical analysis.