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Composition-driven amorphous-to-crystalline transition is widely observed in sputter-deposited thin films. We have recently shown that peculiar two-phase crystalline–amorphous nanostructures can be obtained for compositions in the transition zone between single-phased amorphous and crystalline films, offering a new possibility to control surface topography and related functional properties. Here, the growth kinetics of the two-phase nanostructures formed in the transition zone is explored and related to residual stress measurements. From the analysis of top-view scanning electron microscopy images, the evolution with the film thickness of relevant parameters describing the growth process was extracted, i.e., surface coverage, volume fraction, and perimeter per unit area of the crystalline regions growing in competition with the amorphous ones. We demonstrate, supported in the aforementioned parameters, that residual stress evolution in the transition zone is governed by the nucleation, growth, and interaction of the crystalline regions during the competitive growth process. Our results shed new light on the kinetics of the crystalline–amorphous competitive growth phenomenon and demonstrate the relevance of residual stress measurements for exploring the growth mechanisms of complex film microstructures. [ABSTRACT FROM AUTHOR]

Yb3+ ions hold promises for high power emission in the near infrared (NIR). Yet, relevant matrices, comprising mediators to excite Yb3+, have to be found and the optical mechanisms have to be studied in detail. The purpose of this study is to report on the optical excitation and emission mechanisms of NIR photoluminescence (PL) of Yb-doped crystalline aluminum oxynitride thin films prepared at room temperature using reactive magnetron sputtering. Crystal structure and chemical composition are analyzed by transmission electron microscope and Rutherford backscattering spectrometry, respectively. Photoluminescence spectroscopies are used to investigate the excitation and emission mechanisms. NIR emission at 985 nm is obtained under indirect optical excitation using the 325 nm line of a He-Cd laser, the excitation mechanism is explored by photoluminescence excitation measurement (PLE), and the fine structure of the emitted energy levels is investigated by performing PL measurements at low temperature (LTPL). PLE shows that the host defects play the role of mediators to transfer the excitation energy to Yb ions. This offers different possibilities for the development of multiple excitation channels for Yb3+. Stark splitting of the energy levels of the 2F5/2 and 2F7/2 transitions is evidenced using LTPL in the 78 to 295 K range. Electronic transitions are ascribed to experimental emission lines based on good agreement with theoretical values. Moreover, the activation energies for PL thermal quenching are determined and correspond to the energy difference between highest energy quenched lines and thermally activated “hotlines.” [ABSTRACT FROM AUTHOR]

Cu2O thin films have been grown on glass substrates at room temperature by reactive magnetron sputtering. As-deposited films exhibit high electrical resistivity and low optical transmittance. To improve the film properties, post annealing treatments in air at various temperatures have been performed. Low temperature annealing (<300 °C) avoids the film oxidation into CuO and the films remain single-phased. In this temperature range, the annealing in air enhances the transmittance in the visible region due to the decrease of the defect scattering. Moreover, the optical band gap of Cu2O thin films is enlarged from 2.38 to 2.51 eV with increasing annealing temperature. The increase of optical band gap accompanying the reduction of Urbach energy indicates that the widening of optical band gap may result from the partial elimination of defect band tail after thermal annealing in air. Combining experimental results with recent reported calculations, the peak at about 1.7 eV in photoluminescence spectra is assigned to the recombination of first conduction band minimum to copper vacancy. [ABSTRACT FROM AUTHOR]

A direct band gap of 1.6 eV has been identified in wurtzite CoO thin films, which matches the required value to achieve a theoretically high conversion efficiency solar cell. Its p-type conduction has been determined and an intense sub-gap absorption between 0.7 and 1.1 eV has been observed. [ABSTRACT FROM AUTHOR]

Nitrogen-doped Cu2O thin films have been deposited at room temperature by reactive magnetron sputtering. It is demonstrated that nitrogen doping in Cu2O can significantly improve the electrical properties by increasing the carrier concentration. The nitrogen chemical state in doped thin films has been investigated by electron energy loss spectroscopy, which reveals that nitrogen is in the form of molecular N2 in Cu2O thin films rather than the N-anion. Such experimental results are well consistent with the recently reported calculation, suggesting that in N-doped Cu2O, nitrogen mainly substitutes Cu in the molecular form, (N2)Cu, rather than in the atomic form at the oxygen site (Nq). [ABSTRACT FROM AUTHOR]

The room temperature growth of highly ＜111＞ oriented sputtered NiO thin films on glass and silicon substrates previously covered with a ＜111＞ oriented Cu2O film is reported. The results are compared to those obtained from single layer NiO thin films using the same deposition conditions. Electron microdiffraction analyses indicate that NiO columns are heteroepitaxially grown on the columns of a Cu2O seed layer. The well-matched atomic configurations between the Cu atoms in the {111} planes of Cu2O and the O atoms in the {111} planes of NiO may provide a strong driving force to promote this local heteroepitaxial growth. Such heteroepitaxial growth behavior in the columns can significantly improve crystallization. Moreover, valence electron energy loss spectroscopy has been employed to investigate the interband transition properties of the NiO films, which shows that the interband transition intensity can be tuned by this local heteroepitaxial growth. [ABSTRACT FROM AUTHOR]

Single-domain epitaxial ZnO films are grown near-room temperature (below 40 ℃C) on (0 0 0 1)-sapphire using reactive magnetron sputtering of a zinc target in the transition between the metallic and compound sputtering regimes. As the oxygen content in the reactive gas mixture is increased, the in-plane six-fold symmetry of hexagonal wurtzite ZnO, probed by ?-scan measurements, develops. Transmission electron microscopy analyses confirm that single-domain epitaxial layers are formed. This is accompanied by the incorporation of oxygen interstitial defects associated with oxygen over-stoichiometry and by compressive stresses. A model is proposed to explain the observed behaviour based on the transformation of the kinetic energy of fast oxygen particles into the mobility of the adatoms. [ABSTRACT FROM AUTHOR]

A set of Cu-Mn-O and Ag-Cu-Mn-O films were sputter-deposited onto polished Ti-6Al-4V coupons and the microbiological adherence of Staphylococcus sp. was studied in these biomedical surfaces modified by using advanced ternary and quaternary oxides, these latter incorporated micrometric silver islands. Silver is known to have a natural biocidal character and its presence in the surface of Ti-6Al-4V forming large micrometric islands. In principle, predicted to enhance the antimicrobial properties of biomedical surfaces. Microbial adhesion tests were performed using collection strains and six clinical Staphylococcus aureus and Staphylococcus epidermidis strains. The adherence study was performed using a previously published protocol by Kinnari et al. Collection strains and clinical strains showed decreased adherence to modified materials; however, only on the clinical strains were there statistically significant differences between Cu-Mn-O and Ag-Cu-Mn-O containing silver islands. Nanocrystalline silver dissolves and releases both Ag+ and Ag0 whereas other silver sources release only Ag+. We can conclude that nanocrystalline silver coating, confirmed by XRD, appears to alter the biological properties of the solution, particularly antimicrobial activity. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2012. [ABSTRACT FROM AUTHOR]

Abstract: Zr1−x W x nanocrystalline films of Zr-W solid solutions and ZrW2 Laves phase were synthesized by magnetron co-sputtering. Large values of the H/E ratio up to 0.09 are observed for grain sizes in the nanometer range along with a hardness above 10GPa and Young''s modulus below 230GPa. H/E values are correlated with the developed surface of grain boundaries suggesting an elastic deformation mostly handled by the grain boundaries. This is associated to friction coefficients comparable to those of metallic glass surfaces. In contrast to fragile bulk Laves phases, no cracks were detected at the film surface after indentation and scratch test of nanocrystalline ZrW2. The friction coefficient of such films against diamond tip was in the range 0.08–0.15, similarly to metallic glass surfaces. [Copyright &y& Elsevier]

Abstract: Transparent Al-doped ZnO thin films were deposited by reactive magnetron sputtering with different oxygen flow rates. The electronic resistivity, measured by the 4 point-probe method, is very sensitive to the sample position relative to the magnetron axis: the closer the magnetron from the axis the higher the resistivity. This is more pronounced for the films deposited under higher oxygen flow rate. Neither Rutherford backscattering spectroscopy nor Zn–K edge X-ray absorption near-edge structure (XANES) analyses evidenced any change in chemical composition such as a measurable variation of the oxygen stoichiometry. XANES at the Al–K and O–K edges show that (i) a portion of the aluminum atoms get positioned in octahedral conformation with oxygen, consistent with the formation of an Al2O3(ZnO) m nanolaminate structure, (ii) the films exhibit relaxed O-terminated (0001) surfaces with a higher density of empty states in more resistive samples. These two findings are believed to play a significant role on the electrical measurements by dopant deactivation and by creating an insulating barrier at the film surface, respectively. [Copyright &y& Elsevier]

Abstract: W x Zr1−x thin films were deposited at room temperature on glass substrates by co-sputtering tungsten and zirconium targets in argon. The composition was found in the range 0≤ x ≤0.81. The grain size deduced from X-ray diffraction analysis ranged from 1.3nm to 16nm depending on the composition. The events in the resistivity, optical reflectivity and thickness evolutions were correlated with the X-ray diffraction analysis. Depending on the composition, the local organization can be attributed to a nanocrystalline solid solution of W in Zr, to a nanocomposite structure involving ZrW2 nanograins embedded in an amorphous matrix, to ZrW2 Laves phase nanograins and to a nanocrystalline solid solution of Zr in W. For 0< x ≤0.72, the equivalent grain size is very small (less than 2nm) and the evolution of the resistivity can be fitted by the estimated volume of the material perturbed by the grain boundaries. [Copyright &y& Elsevier]

Abstract: Methane total oxidation was studied between 250 and 800°C in a specific quartz reactor for Pd, PdO y , Pd0.6Pt0.4O y and Pd0.4Pt0.6O y thin films deposited on yttria stabilized zirconia (YSZ) substrates. Pt containing films exhibited poor activity and a rapid thermal decomposition. Pd and PdO y films showed good activity and transformed to particles dispersed on the YSZ substrates. The higher reaction rate of PdO y films was explained by a better dispersion of the catalyst. A drop of the reaction rate was observed when the temperature exceeded 735°C and 725°C for initially Pd and PdO y , respectively, which can be associated with the decomposition of PdO into Pd and O2. The good cycling stability and catalytic efficiency of the latter films render it promising for the pollution control in methane combustion. [Copyright &y& Elsevier]

Abstract: Ag–Cu–O films were deposited on glass substrates by reactive magnetron cosputtering of silver and copper targets. In this manuscript, the current applied to the copper target and the oxygen flow rate introduced into the deposition chamber were kept constant, whereas the current applied to the silver target (I Ag) was varied. Films deposited without silver crystallised into the paramelaconite structure (Cu4O3). At low silver target current, incorporation of Ag into Cu4O3-based did not modify the film structure. Silver atoms substituted some Cu(+I) atoms leading to the formula: Ag2−x Cu2+x O3. On the other hand, when I Ag exceeded a critical value, X-ray diffraction analyses revealed a biphased structure: Ag2−x Cu2+x O3 and Ag. Contrary to the diffraction peak intensity of the Ag2−x Cu2+x O3 phase, that of silver was increased with I Ag. For the highest value of I Ag, no silver–copper oxide was detected and the mean crystal size of silver grains was close to 2nm. Due to the occurrence of the nanocrystallised silver phase, the film electrical resistivity strongly decreased. Optical reflectance measurements confirmed the structural changes versus the silver target current. [Copyright &y& Elsevier]

Abstract: Despite the discovery of sodium superionic conductivity in Na1+x Zr2Si x P3−x O12 (0.4< x <0.8) compounds in 1976, up to now their synthesis in homogeneous thin films has not been achieved on wide surfaces. In Part I, we have shown the limitations of the classical radiofrequency sputtering methods for depositing this kind of films with high microscopic and macroscopic chemical homogeneities. The present paper (Part II) proposes a new sputtering method based on the reactive co-sputtering of ZrSi alloy and Na3PO4 targets. The last one is powered by a high frequency pulsed direct current (DC) generator. It is possible to tune the discharge voltage as the current is regulated thanks to the modifications of the discharge frequency and/or the pulse off-time. The deposition rate of the Na3PO4 target is strongly influenced by the discharge voltage. Thin films were deposited in the Na2O–ZrO2–SiO2–P2O5 system with a high physical quality. The experimental configuration allows to adjust the Na/Si atomic ratio by varying the intensity dissipated by the ZrSi target and the target–substrate distance. Hence it is possible to reach on a large area the ratio 1.5 characteristic for Na3Zr2Si2PO12 compound. The structural analysis of a selected film showed an amorphous film in the as deposited condition. After annealing at 700 °C the monoclinic structure, which corresponds to the superionic conducting phase Na3Zr2Si2PO12 was obtained. [Copyright &y& Elsevier]

Abstract: Despite the discovery of sodium superionic conductivity in Na1+x Zr2Si x P3−x O12 (0.4< x <0.8) compounds in 1976, up to now their synthesis in homogeneous thin films has not been achieved on wide surfaces. In order to study the efficiency of classical sputtering methods for the synthesis of such compounds, thin films have been prepared by sputter deposition from two types of targets with the Na3Zr2Si2PO12 stoichiometry. The first one, associated with a NASICON (Sodium (Na) SuperIonic CONductor) structure, presented strong mechanical and chemical instabilities during sputtering that prevented a good experimental reproducibility. On the other hand the second one, a composite mixture of Na3PO4 and ZrSiO4, was stable. Nevertheless, strong macroscopic and microscopic chemical heterogeneities were observed for the corresponding deposited films. These features are interpreted in terms of sodium mobility in the coating and re-sputtering of light elements during the deposition process. [Copyright &y& Elsevier]

Abstract: Ag2Cu2O3 films were deposited on glass substrates by reactive sputtering of a composite silver–copper target. The deposited films were annealed in air at 100, 200 and 300°C. The structure of the films was studied using X-ray diffraction (XRD), their surface morphology was characterised using scanning electron microscopy (SEM) and their electrical resistivity at room temperature was measured using the four point probe method. The 100°C annealing did not modify either the film structure or the film morphology. On the other hand, Ag2Cu2O3 films were partially decomposed into Ag and CuO after a 200°C annealing. The decomposition was complete for a 300°C annealing. The evolution of the film surface morphology as a function of the annealing temperature was discussed in connection to the evolution of the molar volume of the phases constituting the films. [Copyright &y& Elsevier]