María Tarsy Carballas Fernández

Calcium phosphate coatings prepared by aerosol-gel

The aerosol-gel process has been assayed for the deposition of calcium phosphate (CaP) coatings. The deposition conditions have been preliminarily studied in order to obtain polycrystalline hydroxyapatite (HAP) coatings. The evolution of composition, structure and morphology was monitored by FTIR, XRD and SEM techniques as a function of the sintering temperature. HAP coatings deposited on TiAlV substrates were further characterized by Auger and indentation techniques in order to measure their quantitative composition and adhesive strength, respectively. The results corroborate the high quality of aerosol-gel derived HAP coatings.

Properties of a-SiN x .: H films deposited at room temperature by the electron cyclotron resonance plasma method

Abstract a-SIN x :H films with a wide composition range (0·27≤×≤1·38), and some of them with low oxygen content, have been deposited at room temperature by the electron cyclotron resonance plasma deposition method. Auger electron spectro-scopy, infrared absorption, and transmittance and reflectance of the films in the ultraviolet/visible/near-infrared range are reported. Three different types of film are obtained: silicon rich, near stoichiometric and oxygen contaminated. At x =1·00, the hydrogen content, calculated from the infrared spectra, is a minimum (about 10 at.%), the N-H bond density becomes higher than the Si[sbnd]H density, and the slope of the Tauc plot (B) and the Urbach tail (E u), obtained from absorption coefficient results, reach minimum and maximum values, respectively. Hydrogen incorporation into the network is found to be related to that of nitrogen. A relationship between the hydrogen content and the optical properties of the films is deduced by comparing the results with those publis...

Surface and interface analysis of hydroxyapatite/TiO2 biocompatible structures

Abstract The properties of hydroxyapatite (HAP) coatings deposited onto sol–gel derived TiO 2 coatings are evaluated for applications involving the enhancement of biocompatible prostheses. HAP coatings were initially characterized by X-ray diffraction (XRD) to confirm the absence of calcium phosphate phases with lower stability at physiological pH. The surfaces of these HAP/TiO 2 structures were subsequently analyzed in a two-fold manner. A morphologic evaluation of the microstructured surface was made by using atomic force microscopy (AFM) before and after a chemical etching process in acetic acid. Furthermore, the HAP/TiO 2 interface composition could be analyzed in depth by using Auger electron spectroscopy (AES). In the case of structures grown onto TiAlV alloys, the composition profiles confirm the presence of apatite nuclei onto the surface, even after etching in acidic conditions. The properties derived from these analyses support the suitability of these structures for the development of orthopedic devices.

ROLE OF OXYGEN ON THE DANGLING BOND CONFIGURATION OF LOW OXYGEN CONTENT SINX:H FILMS DEPOSITED AT ROOM TEMPERATURE

SiNx:H films with a wide composition range and, some of them, with low oxygen content are deposited at room temperature. The defects observed in the films are attributed to Si-dangling bonds, with a structure depending on film composition. For the N-rich films they are of the form . Si=(N-3), whereas for the films with similar [N]/[Si] ratio but containing oxygen, the predominant defect is proposed to be Si=(Si2O), despite of the high N content and the low O content of these films. The spin density of the films has been related to the bonds that hydrogen establishes (either Si-H or N-H), with the maximum value corresponding to the minimum hydrogen content. Both maximum and minimum values, respectively, are obtained at the silicon percolation limit of the Si-Si bonds into the SiNx:H network, x similar to 1.10.

Analysis of the oxygen contamination present in SiNx films deposited by electron cyclotron resonance

Silicon nitride (SiNx:H) films are deposited by the electron cyclotron resonance method at different microwave powers and nitrogen to silane gas flow ratio (R). Auger electron spectroscopy (AES), infrared (IR) absorption, and refractive index (n) measurements are used to determine deposition conditions resulting in oxygen contamination of the films as well as those conditions that result in good quality films without oxygen incorporation. Oxygen contamination of the films is produced at high microwave powers and R ratios as shown by the oxygen content determined by AES and different features in the IR spectra: the shift to higher frequencies for the positions of the Si–N and Si–H peaks, the presence of the N–H bending mode, and the broadening of the Si–N peak with its frequency. Low n values confirm the oxygen incorporation into the films, as they decrease when the oxygen content increases. The characteristic dependence of the oxygen presence in the films with the deposition conditions indicate that the o...

DEPENDENCE OF THE MECHANICAL AND STRUCTURAL PROPERTIES OF (TI, AL)N FILMS ON THE NITROGEN CONTENT

(Ti,Al)N films with increasing nitrogen content were grown by reactive cosputtering and characterized by auger electron spectroscopy, grazing x-ray diffraction, polarization curves, electrochemical impedance spectroscopy, nanoindentation, and atomic force microscopy. For Ti/Al ≈ 1 the Ti 1− x Al x N phase is always present, but lower nitrogen contents lead to an additional phase, probably α–Ti(Al), which causes a decrease in hardness and Youngs modulus. The increase of nitrogen content results ina decrease of surface roughness or a more compacted surface coating, according to the impedance results.

Generation of positive charge in SiO2 thin films during electron irradiation

The positive shifts in the energy position of the Si(L2,3VV) Auger peak produced by 1–3 kV electron irradiation of SiO2 thin films have been quantitatively explained as related to the electron trapped charge distribution. However, the electron beam also induces negative Auger shifts for certain experimental conditions. This result is interpreted in terms of a buildup of positive charge, associated to the bond breaking processes in the oxide bulk, with a formation cross section σf+≊10−17 cm2. The centroid of the spatial positive charge distribution depends on the primary beam energy, and it is not necessarily located at the SiO2/Si interface.

Influence of oxygen on the morphological and structural properties of Ti thin films grown by ion beam-assisted deposition

Abstract Ti thin films have been deposited on silicon wafers by electron beam evaporation of Ti powder with and without simultaneous assistance of argon ion bombardment (IBAD technique). We have investigated the influence of the oxygen content on both the morphological and mechanical properties of the films. We found that the oxygen content in the films is minimum when a Ti pre-evaporation treatment is performed just before the deposition process. Moreover, the concentration of oxygen (∼5 at.%) found in non-assisted films grown with Ti pre-evaporation is very similar to that measured in Ti films deposited with the assistance of argon ions with different bombardment energies. The influence of the ion-beam acceleration voltage and the incident angle on the film properties was also investigated. It was found that the film oxygen concentration is critical for determining both the material film morphological performance (best at lower oxygen contents) and the film hardness, which is maximum with high and low oxygen contents in non-assisted and ion-assisted films, respectively.

Electron trapping characterization by Auger electron spectroscopy in silicon oxynitride thin film

The study of the kinetics of Auger peak shifts with low doses of electron injection (ΔQ≤10−3 C cm−2) in silicon oxynitrides thin films is presented. The nature of these shifts is clearly related with the trapping charge phenomena in the film. The parameters associated with the different traps involved are quantitatively established. Two methods of data acquisition have been developed. The former uses several energy channels in the derivative Auger spectrum (dN/dE) in order to determine each point of the kinetic curve. This method has allowed to measure capture cross sections σ≤5×10−18 cm2. The second method uses only one energy channel for each point in the curve, and reduces the acquisition time up to a factor of 50, measuring faster cross sections σ≤8×10−17 cm2. The numerical values of σ agree satisfactorily with those obtained by conventional C–V injection measurements, as well as the trap densities obtained at 1 kV of primary energy. The discrepancy for the values of N obtained at higher primary energ...

Electrical properties of co-sputtered tantalum silicides

Abstract The electrical properties of SiTa films of different compositions Si:Ta in the range from 3.4:1 to 1.0:1 were investigated in relation to their applications as interconnects and contact gates in microelectronic circuits. The SiTa films were co- sputtered onto oxidized silicon substrates in a magnetron sputtering system. After they had been annealed in vacuum at 950°C the sheet resistance of the films decreased by a factor of about 3 yielding the best results for relative Si:Ta compositions of about 2:1. Very low values of the temperature coefficient of the resistance, around 10 ppm°C -1 , were obtained in the as-deposited films. The sputtered silicides were also characterized by Auger electron spectroscopy, scanning electron microscopy and X-ray diffraction.