B. León

Influence of the non-bridging oxygen groups on the bioactivity of silicate glasses

The effect of the composition and bonding configuration of the bioactive silica-based glasses on the initial stage in vitro bioactivity is presented. Information of the IR active Si–O groups of glass in the system SiO2–P2O5–CaO–Na2O–K2O–MgO–B2O3 was obtained by fourier transform Infrared (FTIR) spectroscopy. Two different bands associated to non-bridging oxygen stretching vibrations (Si–O–1NBO and Si–O–2NBO) and a gradual shifting of the bridging oxygen stretching vibration (Si–O) have been observed and evaluated. Both effects are attributed to a decrease of the local symmetry originating from the incorporation of alkali ions into the vitreous silica network. The Si–O–NBO(s)/Si–O(s) absorbance intensity ratio increases with a gradual incorporation of the alkali ions (diminution of SiO2 content) following a linear dependence up to values close to 50 wt % of SiO2. In vitro test analysis by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) showed a correlation between the amount and type of the non-bridging oxygen functional groups and the growth of the silica-rich and CaP layers. It was found that a minimum concentration of Si–O–NBO bonds in the glass network is required in order to have an efficient ion exchange and dissolution of the silica network. Finally, the bioactivity of the glass is favored by the presence of the Si–O–2NBO groups in the glassy network. The role of these functional groups in the dissolution of the silica network through the formation of silanol groups and the adsorption of water is discussed.

Micro- and nano-testing of calcium phosphate coatings produced by pulsed laser deposition

Micro- and nano-testing methods have been explored to study the thin calcium phosphate coatings with high adhesive strength. The pulsed laser deposition (PLD) technique was utilised to produce calcium phosphate coatings on metal substrates, because this type of coatings exhibit much higher adhesive strength with substrates than conventional plasma-sprayed coatings. Due to the limitations of the conventional techniques to evaluate the mechanical properties of these thin coatings (1 microm thick), micro-scratch testing has been applied to evaluate the coating-to-substrate adhesion, and nano-indentation to determine the coating hardness and elastic modulus. The test results showed that the PLD produced amorphous and crystalline HA coatings are more ductile than titanium substrates, and the PLD coatings are not delaminated from the substrates by scratch. Also, the results showed that the crystalline HA coating is superior in internal cohesion to the amorphous one, even though the lower elastic modulus of amorphous coating could be more mechanically compatible with natural bone.

Extensive studies on biomorphic SiC ceramics properties for medical applications

Biomorphic silicon carbide ceramics are light, tough and high-strengt h materials with interesting biomedical applications. The fabrication method of the biomor phic SiC is based in the infiltration of molten-Si in carbon preforms with open porosity. The fina l product is a biostructure formed by a tangle of SiC fibers. This innovative process allows the fabrication of complex shapes and the tailoring of SiC ceramics with optimised properties and cont rollable microstructures that will match the biomechanical requirements of the natural host tiss ue. An interdisciplinary approach of the biomorphic SiC fabricated from beech, sapelly and eucalyptus is presented. Their mechanical properties, microstructure and chemical composition were evaluated. The biocompatible behaviour of these materials has been tested in vitro .

Stoichiometric transfer in pulsed laser deposition of hydroxylapatite

Abstract Hydroxylapatite (HA, Ca10(PO4)6(OH)2) is a calcium phosphate used as coating for dental and orthopaedical implants because its composition and structure is similar to the mineral part of bone. As an alternative to traditional plasma sprayed coating technique, pulsed laser deposition (PLD) has been applied due to its ability to reproduce complex stoichiometries. A hydroxylapatite target was ablated with an ArF laser in a water vapor atmosphere to investigate in which range of fluences the stoichiometric transfer to a titanium substrate is possible. The Ca/P ratio of the coatings was measured by energy dispersive spectroscopy (EDS), while their OH− and CO32− content was evaluated by Fourier transform infrared spectroscopy (FT-IR) spectroscopy. The irradiated target surface was analyzed by scanning electron microscopy (SEM) and the ablation rate measured with a profilometer. While at higher fluences all the target material is congruently ablated and stoichiometry is transferred to the coatings, at lower fluences (

Influence of the Network Modifier Content on the Bioactivity of Silicate Glasses

The influence of the substitution of calcium oxide for sodium oxide in the composition of silica-based glasses on the in vitro bioactivity is presented. Valuable information on the active Si-O groups present in the glasses is obtained by Fourier Transform Ra man and Infrared spectroscopies. In vitro test analysis by Scanning Electron Microscopy and Energy Dis persive X-ray Analysis show a correlation between the network disruption induced by the modifier type and the bioactive process. It is demonstrated that glasses with high SiO 2 content can be bioactive depending on the alkali/alkali-earth modifiers ratio included into the vitreous silica network. Introduction Bioactive glasses are interesting materials for medical pur poses due to their ability to bond chemically to living bone and soft tissues when soaked in physiologica l fluids [1, 2]. The clinical applications of bioactive glasses are numerous, especially in maxi llofacial reconstruction, otorhinolaryngology, oral surgery and periodontal repair [1]. The bioactive silica-based glass network is basically the same of vitreous silica, where the structural units consist of slightly distorted SiO 4 tetrahedra. This structure enables the accommodation of alkali and alkali-earth cations which create non-bridging oxygen s it s (Si-O-NBO) throughout the glass network [3]. When the bioactive glasses are soaked in human plasma or an analogous solution, it is known that a partial dissolution of the glass surface oc urs leading to the formation of a silica-rich gel layer and, subsequently, the precipitation of a c alcium phosphate film on the bioactive material takes place. The formation rate of this lay er is a critical parameter, which is directly related to the type and content of the network modifiers [1]. Several spectroscopic techniques, such as Infrared and Raman spectrosc opies, are sensitive to changes in the composition and the bonding configuration of the glasses, and they provide valuable information on the local structure of the silicate glasses. Thus, the aim of this work is to evaluate, through spectroscopic tec hniques and in vitro tests, the role of content and type of network modifiers on the bioactivity of silica-based gla sses. Materials and methods Glasses of different compositions in the quaternary system Na 2O-C O-P2O5-SiO2, with a systematic substitution of CaO and Na 2O concentrations, have been investigated (Table 1). Glasses were obtained by melting the appropriate quantities of analytical grade CaCO3, Na2CO3, CaHPO4·2H2O and commercial Belgian quartz sand in a Pt-crucible at 1360 oC for 3 h. The glasses were cast, annealed, crushed, and remelted to improve homogeneity. In the final casting, a graphite mould of 20 mm diameter and 100 mm long was used. The test pieces were obtai ned by sawing discs of 2 mm thick. The discs were washed and stored in ethanol. The structure of the glasses was studied by X-ray Diffract ion (XRD). Information on the active SiO groups present in the glasses was obtained by Fourier Transfor m Infrared (FTIR) and Raman spectroscopies. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 23-26 doi:10.4028/www.scientific.net/KEM.254-256.23

Extensive Studies of the Plume Deflection Angle During Laser Ablation of Si Target

The plume deflection effect during long laser irradiation of a Si target has been extensively studied. Two different laser ablation experiments were performed to study the plume deflection angle and the ablation rate versus the number of laser pulses/site. Scanning electron microscopy (SEM) analyses and profilometry of the Si target surface were performed to examine the continuous morphological changes produced by the laser irradiation. The roughening of the target surface strongly influenced the formation and expansion of the Si plume. Plume deflection angles higher than 30° have been observed by a digital camera. Complementary mass spectrometer measurements confirmed that the ion flux distribution is strongly oriented along the laser beam direction. In addition to laser ablation experiments, two other laser deposition experiments were performed: with the conventional configuration and with a new approach, termed frontal off-axis deposition. The new pulsed-laser deposition configuration provides much better control of uniformity and film thickness than the conventional deposition configuration.

Laser crystallisation of poly-SiGe for microbolometers

Abstract Bolometers based on micromachined poly-SiGe as active elements have recently been demonstrated. The advantage of using poly-SiGe relies on its low thermal conductivity, high coefficient of temperature resistance and perfect compatibility with the IC silicon technology. In order to simplify a device integration of such elements, a combination of laser-assisted low thermal budget techniques such as laser-induced chemical vapour deposition and laser-assisted crystallisation has been proposed. The present paper shows the first results obtained using this “all laser-assisted” process for producing amorphous as well as polycrystalline SiGe alloys and the simulation of the crystallisation processes via numerical analysis for tuning the parameters of the crystallisation process.

Temperature distribution in laser marking

A theoretical model describing the temperature distribution on plastic material during the laser marking process has been developed. The heat conduction differential equation was solved analytically by the Green function method, and numerically, based on the finite element method using ANSYS®(5.5). The experimental irradiation of a methacrylate piece by a CO2 laser was carried out in order to check the validity range of the model.

ArF-excimer laser induced chemical vapour deposition of amorphous hydrogenated SiGeC films

Abstract The growing interest in the development of silicon germanium carbon (SiGeC) based devices for micro- and optoelectronics provoked an increasing attention in alternative low thermal budget techniques capable to produce such alloys on large areas as well as on small selected regions. Excimer laser-induced chemical vapour deposition (LCVD) in parallel configuration is a “soft” alternative deposition technique that has already proved to be a feasible method for the production of various thin film semiconductors. This contribution will investigate the possibility to exploit the technique for producing the ternary SiGeC alloy and demonstrate that coatings with uniform composition, structure and thickness can be deposited at low substrate temperature. The samples have been extensively analysed by different techniques for identifying the most important experimental parameters determining the growth rate, and the homogeneity in stoichiometry and structure.

Influence of laser fluence in ArF-excimer laser assisted crystallisation of a-SiGe:H films

Abstract Polycrystalline silicon germanium (poly-SiGe) coatings are drawing increasing attention as active layers in solar cells, bolometers and various microelectronic devices. As a consequence, alternative low-cost production techniques, capable to produce such alloys with uniform and controlled grain size, become more and more attractive. Excimer laser assisted crystallisation, already assessed in thin film transistor production, has proved to be a valuable “low-thermal budget” technique for the crystallisation of amorphous silicon. Main advantages are the high process quality and reproducibility as well as the possibility of tailoring the grain size in both, small selected regions and large areas. The feasibility of this technique for producing poly-SiGe films has been studied irradiating hydrogenated amorphous SiGe films with spatially uniform ArF-laser pulses of different fluences. Surface morphology, structure and chemical composition have been extensively characterised, demonstrating the need of using a “step-by-step” process and a careful adjustment of both, total number of shots and laser fluence at each “step” in order to diminish segregation effects and severe damages of the film surface and of segregation effects.