P. Bartolo-Pérez

CORROSION BEHAVIOUR OF CHROMATED ZN AND ZN ALLOY ELECTRODEPOSITS

Abstract The influence of a chromate film on the corrosion behaviour of Zn, Zn–Co and ZnFe coatings was investigated. XPS, AES techniques were applied for characterisation of the iridescent chromate films, while the XRD method was used for the corrosion product analysis. Atmospheric field (4 years data), accelerated (neutral salt spray and SO 2 cabinet) tests and electrochemical measurements were applied for the corrosion resistance studies. The beneficial influence of alloying for chromated Zn electrodeposits was observed under the conditions, where Cl − ions were the dominant pollutant (marine test site, Cl − cabinet, Cl − aqueous solution). The degree of protection from the chromate film, in spite of their lower thickness, was detected to be higher for the alloyed samples. A higher concentration of Cr(VI) compounds in the passive chromate layers of alloyed samples may be the reason of their superior corrosion resistance.

First stages of growth of CdS films on different substrates

Cadmium sulfide films were grown on glass, silicon, and ITO substrates by chemical-bath deposition (CBD) at 358 K, and studied by atomic force microscopy, Auger electron microscopy and X-ray diffraction. CdS film growth initiates immediately and thickness increases with deposition time. The rms roughness of CdS films grown for 1 to 10 min (thicknesses of 10 to 70 nm) was measured by atomic force microscopy. The roughness of films grown on ITO remains similar to that of the substrate regardless of deposition time. On the other hand, the roughness of CdS films grown on glass and silicon increases with deposition time, finally reaching a roughness similar to that of films grown on ITO. Auger profiles show that the CdS/substrate interface is not abrupt and depends on the substrate. Substrate roughness plays an important role during the initial CdS growth process. X-ray studies show that silicon substrates are not appropriate for CdS film growth by CBD. The most appropriate substrate is ITO.

X-ray photoelectron spectroscopy study of CdTe oxide films grown by rf sputtering with an Ar-NH3 plasma

Abstract CdTe oxide films were prepared on glass substrates using the rf-sputtering technique and a controlled plasma of Ar–NH 3 . Films were studied by X-ray photoelectron spectroscopy and X-ray diffraction. The changes in chemical composition as a function of NH 3 partial pressure during deposition indicate that oxygen incorporates in the films up to approximately 62 at.%, while the Cd and Te contents decrease from ∼43 to 19 at.%. At NH 3 partial pressure of 1.3×10 −2 Pa, the Te–Cd bonds are strongly reduced and the Te in the films is mainly bonded to oxygen. The Cd MNN X-ray Auger feature shows a shift in energy of approximately 0.8 eV as a function of NH 3 partial pressure. This shift appears to be related to the change in Cd bonding from Cd–Te to Cd–O. Films prepared at NH 3 partial pressure of 4×10 −4 Pa present crystallinity with a [111] cubic CdTe orientation, while those prepared at higher NH 3 partial pressure show an amorphous structure. The amorphous material formed at NH 3 partial pressure saturation appears to be mainly amorphous CdTeO 3 .

Chemical and phase composition of SnOx:F films grown by DC reactive sputtering

Abstract Using X-ray diffraction and X-ray photoelectron spectroscopy we studied the structural variations of SnO x :F films grown by DC reactive sputtering. We used a metallic tin target and an Ar–O 2 –Freon plasma. We found that a mixture of compounds, i.e. SnO, Sn 3 O 4 , Sn 2 O 3 and SnO 2 were formed in the films. From the analysis of the deconvoluted peaks of the X-ray diffractograms and from the X-ray photoelectron spectroscopy results, we obtained the Sn 2+ /Sn and Sn 4+ /Sn molar fractions present in the films. The dependence of the Sn 2+ /Sn and Sn 4+ /Sn molar fraction with oxygen content was fitted by applying a combinatory model. The Sn 2+ /Sn and Sn 4+ /Sn molar fractions obtained from XRD and XPS were compared with theoretical values and showed good agreement. When the cathode voltage used to grow the films is varied, the Sn 4+ /Sn molar fraction shows two well-defined regions, related to the SnO and SnO 2 stoichiometries. This is related to the Sn 2+ →Sn 4+ transition in the cathode, as described in a previously proposed phase diagram for DC reactive sputter deposition of SnO x :F films. Sn 2+ and Sn 4+ are both present in the films at low current densities, and SnO and SnO 2 are the only species found in these conditions. Sn 2 O 3 and Sn 3 O 4 are formed at current densities over 30 mA cm −2 , when the growth takes place near the transition region in the phase diagram. The growth rates are also affected and closely related with the variations of the cathode voltage in this region.

Discharge diagnosis and controlled deposition of SnOx:F films by dc-reactive sputtering from a metallic tin target

Abstract Fluorine-doped tin oxide (SnO x :F) films on glass substrates have been prepared by reactive magnetron DC-sputtering in Ar–O 2 –Freon plasma from a metallic tin target. We studied the relationship between the discharge characteristics and film properties and found the discharge conditions in which the films belong to the SnO 2 or to the SnO stoichiometry, by proposing a phase diagram for this system. We showed that the film stoichiometry is closely related to the tin valence changes at the target. We found that there is a narrow voltage band and a limit value in the oxygen content where the films have SnO 2 stoichiometry; outside this region SnO films are obtained. We studied the crystallinity and the optical properties of the SnO 2 films. The results show that crystalline films have cassiterite-like diffraction patterns with preferred orientation in the (110) planes. The crystallinity of the films is improved when the discharge voltage and oxygen content increase. A thermal annealing of the amorphous films at 500°C leaves them in the crystalline cassiterite-like form. The films have a transmittance of ∼80% in the visible region of the spectrum and a uniform thickness.

CDTE OXIDE FILMS GROWN BY RADIO FREQUENCY SPUTTERING UTILIZING ARGON-NITROUS OXIDE PLASMA

Cadmium telluride oxide films (CdTe:O) were grown by a radio frequency sputtering technique using a controlled plasma (Ar–N2O) on glass slide substrates. The films were studied by Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and x‐ray diffraction. We demonstrate that with N2O the oxidation process occurs in a narrow range of partial pressures of nitrous oxide. We find that the films are amorphous and the amount of oxygen incorporated in the films depends on the N2O partial pressure and saturates at about 55 at. % oxygen. As the amount of oxygen increases the number of Te–O and Cd–O bonds increases. The compounds formed depend on the partial pressure of the N2O and are of the form CdxTeyOz. When saturation of oxygen is obtained the compound formed is probably CdTe2O5.

Auger electron spectroscopy analysis of oxidation states of Te in amorphous CdTe oxide thin films

Amorphous CdTe oxide (a-CdTe:O) thin films with different concentrations of oxygen were grown by rf sputtering and analyzed by Auger electron spectroscopy. A slight change of shape in the Cd MNN peak as a function of oxygen content in a-CdTe:O is observed. This peak resembles the Cd MNN peak of CdTe, at one extreme, and that of CdTeO3, at the other. The Te MNN and the O KLL peaks have similar shapes and lower intensities for a-CdTe:O oxygen saturated films than those in CdTeO3. On the other hand, there is a large and gradual difference in shape, intensity, and energy observed in the Te MNN peak among a-CdTe:O with low, intermediate, and high concentration of oxygen. Different Te oxidation states, as Te−2 and Te+4, contribute to this change as evidenced by a simulation with combinations of CdTe and of CdTeO3 spectra, or by combinations of a-CdTe:O spectra with low and high oxygen content.

CHEMICAL COMPOSITION AND CRYSTALLINE PHASES IN F-DOPED TIN OXIDE FILMS GROWN BY DC REACTIVE SPUTTERING

We study by x-ray diffraction (XRD) the structural variations on a series of SnOx:F films grown by dc reactive sputtering from a metallic tin target in an Ar-O2-Freon plasma. We found that the films tend to be crystalline when the stoichiometry approaches to that of SnO or SnO2, being amorphous in between. We fitted the x-ray diffractograms and found that films are composed by a mixture of compounds, i.e. SnO, Sn3O4, Sn2O3 and SnO2, given by the simultaneous presence of Sn+2 and Sn+4. From the analysis of the deconvoluted areas under the x-ray diffractograms we calculate the Sn+2/Sn and Sn+4/Sn molar fraction present in the films. The same calculations are done for the x-ray photoelectron spectroscopy (XPS) results. By applying a combinatory model we fitted the general behavior of SnOx films with different oxygen content versus the Sn+2/Sn and Sn+4/Sn molar fraction. Both XRD and XPS results are compared with the theoretical curve, showing a well agreement.