Eric Tomasella

Structural and optical studies of ZnO thin films deposited by r.f. magnetron sputtering: influence of annealing

Abstract Zinc oxide thin films were deposited on various substrates by sputtering from a ZnO target. The sputtering gas was obtained from an argon–oxygen mixture (95–5%), at 1 Pa pressure and using a r.f. power density of 0.89 W cm −2 . The structural and optical properties of ZnO deposits, submitted to an annealing treatment in the 373–673 K ranges are studied by X-ray diffraction (XRD) and UV-visible spectrometry. XRD measurements show that all the films are crystallised in the wurtzite phase and present a preferential orientation along the c -axis. Only one peak, corresponding to the (002) phase (2 θ≈ 34.4°), appears on the diffractograms. The crystallite size, the density and the O/Zn atomic ratio increases with the treatment temperature. These modifications influence the optical properties. The refractive index n , the absorption coefficient α and the optical gap E g , increase with the treatment temperature, and are sensitive to the oxygen incorporation.

Structural and optical properties studies of sputtered a-SiCN thin films

Amorphous silicon carbonitride (a-SiCxNy) thin films were deposited by reactive sputtering from SiC target and N2/Ar mixtures. Their structural study was carried out by mean of RBS, FTIR, Raman and electron spin resonance analysis. The optical properties were determined by UV-visible spectroscopy. The fact to introduce different amounts of nitrogen with argon in the gas phase induced structural changes which are visible since 5 % of N2. For more than 30 % of nitrogen in the gas mixture, a N-saturated Si–C–N film were formed. The increase of nitrogen gas concentration induced the appearance of C-C sp2 character, an increase of the C≡N and dangling bonds densities. All these structural variations leaded to an increase of optical band gap from 1.75 to 2.35 eV.

Structural and ellipsometric study on tailored optical properties of tantalum oxynitride films deposited by reactive sputtering

Oxynitride materials, which offer the possibility of merging oxide and nitride properties, are increasingly studied for this reason. This paper focuses on assessing the optical properties of tantalum oxynitride thin films deposited by pure tantalum target sputtering in an Ar/O2/N2 reactive atmosphere. First, by changing the oxygen to reactive gas flow rate ratio, and using thermal post-treatment, we deposited films with elemental compositions studied by Rutherford backscattering spectroscopy, ranging from a nitride (close to Ta3N5) to an oxide (close to Ta2O5) with various structures analyzed by x-ray diffraction. Their optical properties were investigated in depth by spectroscopic ellipsometry and UV-visible spectroscopy. For the ellipsometry investigation, we propose a model combining the Tauc–Lorentz law and additional Lorentz oscillator: the first contribution is linked to a semi-conductor or insulator film matrix, and the second one to the presence of conductive TaN crystals. Ellipsometry thus appears as a powerful tool to investigate complex materials such as tantalum oxynitrides. Moreover, we demonstrated that using this deposition method we were able to finely tune the film refractive index from 3.4 to 2.0 (at 1.96u2009eV) and the optical band gap, specifically from 1.3 to 2.7u2009eV.

Enhancement of the photoprotection and nanomechanical properties of polycarbonate by deposition of thin ceramic coatings

The chemical reactions resulting from ultraviolet radiation produce discoloration and significant changes in the surface properties of polycarbonate (PC). To prevent photon absorption from irradiation and oxygen diffusion and to enhance the surface nanomechanical properties of PC, thin ceramic coatings of ZnO and Al2O3 (both single- and multi-layer) were deposited on bulk PC by radio-frequency magnetron sputtering. The samples were irradiated at wavelengths greater than 300nm, representative of outdoor conditions. Despite the effectiveness of ZnO to protect PC from irradiation damage, photocatalytic oxidation at the PC/ZnO interface was the limiting factor. To overcome this deficiency, a thin Al2O3 coating was used both as intermediate and top layer because of its higher hardness and wear resistance than ZnO. Therefore, PC∕Al2O3∕ZnO, PC∕ZnO∕Al2O3, and PC∕Al2O3∕ZnO∕Al2O3 layered media were fabricated and their photodegradation properties were examined by infrared and ultraviolet-visible spectroscopy. It wa...

Coupled effects of bombarding ions energy on the microstructure and stress level of RFPECVD a-C:H films: correlation with Raman spectroscopy

Abstract In this work a-C:H films have been prepared in a capacitively coupled RF-PECVD device (ν=13.56 MHz) from methane as the gas source. By the use of ERDA, IRTF and X-Ray reflectometry techniques, we have first investigated the structural evolutions of the films as a function of the ion energy. In the second part, we have measured mechanical properties (hardness and Youngs modulus) by nanoindentation. Concerning the stress level, according to Stoneys equation, the magnitude of the internal stress has been determined by substrates deflection measurements: this finally leads to a quantification of the adhesion through the calculation of the interfacial fracture energy (Gic). Raman spectroscopy has been used as a probe of both film quality and mechanical properties. The position of the G band is correlated with the sp3 carbon content and the stress level. One observes that the G peak position moves to high frequencies when the ion energy increases, indicating a graphitization of the samples. The relationship linking the Raman wavenumber shift to stress is discussed.

FTIR and XPS investigations of a-SiOxNy thin films structure

Amorphous silicon oxynitride (a-SiOxNy) thin films with large composition variation were deposited by reactive sputtering. Their structural study was carried out by mean of FTIR and XPS analysis. The IR absorption peak maximum was found to shift towards higher wavenumbers as the oxygen content increases and the absorption peaks of Si-O and Si-N bonds also appear. The Si 2p photoelectron peak was decomposed considering five tetrahedra of SiOvN4-v (where v = 0, 1, 2, 3 and 4) following the Random Bonding Model (RBM). But the comparison between RBM theoretical and experimental predictions and the non-linear behaviour of the modified Auger parameter (α) showed that the a-SiOxNy structure can be well described only considering a mixture of SiO2, Si3N4 and SiOxNy phases.

Determination of optical properties of a-SiOxNy thin films by ellipsometric and UV-visible spectroscopies

Optical properties of silicon oxynitride thin films of variable composition were investigated. Their refractive index was found to decrease linearly from 1.94 to 1.46 when their composition varies between silicon nitride and silicon oxide. Spectroscopic ellipsometry showed that all samples were transparent over the visible range and that the layer structure also influences their optical properties. Using UV-visible spectroscopy, it was found that the film absorption decreases with increasing the oxygen amount in their composition. The optical gap determined from the transmission spectra showed high values increasing with the oxygen concentration. The Urbach energy was also estimated and linked to the film structure and composition.

In-Situ Cu(In,Ga)Se 2 composition control by Optical Emission Spectroscopy during hybrid co-sputtering/evaporation process

In this work, we have developed a hybrid one-step co-sputtering/evaporation Cu(In,Ga)Se2 process, where Cu, In and Ga are sputtered simultaneously with the thermal evaporation of selenium, thus avoiding the use of H2Se. An appropriate control of the selenium flux is very important to prevent the target poisoning and hence some material flux variations. Indeed, the control of the CIGS composition must be rigorous to ensure reproducible solar cell properties. In this regard, a study of the correlations between plasma species, thin film composition and morphology has been performed by varying Se evaporation temperature in the 170 to 230 °C range.

Potential of TaOXNY Thin Films Deposited by Reactive Sputtering as Antireflective Coatings: Composition and Optical Properties

Tantalum oxynitride thin films are deposited by radio-frequency magnetron sputtering using a pure tantalum target under argon/oxygen/nitrogen gas mixture. The argon flow is kept constant while the oxygen and nitrogen flows are changed simultaneously in a way to keep constant the total flow of these reactive gases. We succeed to deposit TaOxNy films with stoichiometry ranging between those of TaN and Ta2O5. All films are deposited at room temperature and are amorphous. Spectroscopic ellipsometry and UV-visible spectrometry investigations show a direct relation between the optical properties and the stoichiometry of the films. In particular, the results show a variation of the refractive index from pure tantalum nitride-like films (3.76) to tantalum pentoxyde-like films (2.1), which confirms the possibility to deposit graded antireflective coatings with tantalum oxynitride.

Reactive gas pulsing sputtering process, a promising technique to elaborate silicon oxynitride multilayer nanometric antireflective coatings

The oxynitride materials present a high versatility, which enables their properties to be controlled by tuning their elemental composition. This is the case for silicon oxynitrides used for multilayer antireflective coatings (ARCs), where several thin films with various refractive indexes are needed. Different techniques allow for the modification of the thin film composition. In this paper, we investigate the reactive gas pulsing sputtering process to easily tune the thin film composition, from an oxide to a nitride, by controlling the averaged oxygen flow rate, without reducing the deposition rate, compared to a conventional reactive process (CP). We then demonstrated that the refractive indexes of films deposited by this pulsing process (PP) can be varied in the same range compared to films obtained by CP (from 1.83 to 1.45 at 1.95 eV), whereas their extinction coefficients remain low. Finally, the multilayer ARC has been simulated and optimized by a genetic algorithm for wavelength at 600 nm and for the silicon substrate. Various optimized multilayer (mono-, bi- and tri-layers) structures have been deposited by the PP technique and characterized. They are presented in good agreement with the simulated reflectivity. Hence, the PP allows for an easy depositing tri-layer system with a reasonable deposition rate and low reflectivity (8.1% averaged on 400–750 nm visible light range).