INVESTIGATIONS OF THIN TITANIUM OXIDE FILMS GROWN BY REACTIVE PULSED LASER DEPOSITION

Titanium oxide thin films were deposited on Si monocrystalline substrate using the pulsed laser ablation technique in a reactive oxygen atmosphere. The films were obtained starting from Ti and TiO2 targets which were ablated using a KrF* excimer laser (λ = 248 nm). During the deposition, the Si substrates were heated at 300 °C under various high purity oxygen atmosphere of 1.0, 0.5 and 0.1 mbar. Grazing incidence X-ray diffraction investigations revealed the presence of a nanostructured film consisting of a mixture of several titanium oxides, with crystalline grains size of few nm to 10 nm. Only the film deposited from the Ti target at a pressure of 1.0 mbar exhibited crystalline grains of 30-40 nm. Thin films surface morphology and topography, studied using atomic force and scanning electron microscopy, revealed a relatively smooth surface with the presence of some submicron droplets, typical for laser ablation technique. Films deposited at 0.5 mbar pressure from both targets were significantly rougher than the other deposited film

Hydrogen-discriminating nanocrystalline doped-tin-oxide room-temperature microsensor

Highly hydrogen (H-2)-selective [relative to carbon monoxide (CO)] sensor, operating at room temperature, has been fabricated using the micronanointegration approach involving the deposition of the nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin film on microelectromechanical systems device. The present microsensor exhibits high room-temperature sensitivity towards H-2 (S=12 700); however, it is insensitive to CO at room temperature. In view of the different gas selectivity mechanisms proposed in the literature, it is deduced that the In2O3 doping, the presence of InSn4 phase, the low operating temperature (room temperature), the mesostructure, the small sizes of H-2 and H2O molecules, the bulky intermediate and final reaction products for CO, and the electrode placement at the bottom are the critical parameters, which significantly contribute to the high room-temperature H-2 selectivity of the present microsensor over CO. The constitutive equation for the gas sensitivity of the semiconductor oxide thin-film sensor, proposed recently by the authors, has been modified to qualitatively explain the observed H-2 selectivity behavior

ZnO Nanowires Synthesized by Vapor Phase Transport Deposition on Transparent Oxide Substrates

Zinc oxide nanowires have been synthesized without using metal catalyst seed layers on fluorine-doped tin oxide (FTO) substrates by a modified vapor phase transport deposition process using a double-tube reactor. The unique reactor configuration creates a Zn-rich vapor environment that facilitates formation and growth of zinc oxide nanoparticles and wires (20–80 nm in diameter, up to 6 μm in length, density <40 nm apart) at substrate temperatures down to 300°C. Electron microscopy and other characterization techniques show nanowires with distinct morphologies when grown under different conditions. The effect of reaction parameters including reaction time, temperature, and carrier gas flow rate on the size, morphology, crystalline structure, and density of ZnO nanowires has been investigated. The nanowires grown by this method have a diameter, length, and density appropriate for use in fabricating hybrid polymer/metal oxide nanostructure solar cells. For example, it is preferable to have nanowires no more than 40 nm apart to minimize exciton recombination in polymer solar cells

Oligohydramnios: A review of etiology and management options

Oligohydramnios is both a consequence of fetal malformations and of uteroplacental insufficiency. Its existence is associated with a high rate of both antepartum and intrapartum complications. It is vital that its occurrence is detected as early as possible so that we can manage it correctly. The main causes of its occurrence are identified and described in this review. The management of oligohydramnios is most often expectant, the timing of delivery also being determined by Doppler examination and changes in parameters measuring fetal growth and development

Subthreshold Laser Ablation Measurements by Langmuir Probe Method for ns Irradiation of HfO₂ and ZrO₂

The unbiased Langmuir probe (LP) method was used to perform measurements on HfO2 and ZrO2 samples around the laser ablation threshold on a wide range of irradiation conditions. Important changes in the lifetime (from ms to μs) and the shape of the charge particle current were seen with the increase of the laser fluence. The ablation threshold was estimated by evaluating the overall average ablated charge as a function of the laser fluence. Above the ablation threshold, the generation of high kinetic species is seen, which can reach several keV. An important jump in ion acceleration potential is observed for values above 1 J/cm2, which coincides with the dominant presence of negative ions in the plasma. The evolution of several plasma parameters (ion density, expansion velocity, electron temperature, Debye length) was investigated and correlated with the fundamental ablation mechanism involved in various irradiation regimes. The LP data were correlated with COMSOL simulations on the maximum surface temperature reached during irradiation. Important correlations between the evaporation and melting processes and ablation threshold fluence and ion acceleration phenomena are also reported

Analysis of Multi-elemental Thin Films via Calibration-Free Laser-Induced Breakdown Spectroscopy

International audienceElemental analyses of thin films with complex composition are challenging as the standard analytical techniques based on measurement calibration are difficult to apply. We show that calibration-free laser-induced breakdown spectroscopy (LIBS) presents a powerful solution , enabling quantitative analyses of multiele-mental thin films with analytical performances better than those obtained with other techniques. The demonstration is given for a nickel-chromium-molybdenum alloy film of 150 nm thickness that was produced by pulsed laser de-position. The LIBS spectra were recorded in experimental conditions that enable simple and accurate modeling of plasma emission. Thus, a calibration-free approach based on the calculation of the spectral radiance of a uniform plasma in local thermodynamic equilibrium was applied to deduce the elemental composition. Supported by analyses via Rutherford backscat-tering spectrometry and energy-dispersive X-ray spectroscopy, the LIBS measurements evidence nonstoichiometric mass transfer of the alloy during the thin film deposition process. This technique could be used even for thinner films provided that the film-composing elements are not present in the substrate

Local thermodynamic equilibrium in a laser-induced plasma evidenced by blackbody radiation

International audienceWe show that the plasma produced by laser ablation of solid materials in specific conditions has an emission spectrum that is characterized by the saturation of the most intense spectral lines at the blackbody radiance. The blackbody temperature equals the excitation temperature of atoms and ions, proving directly and unambiguously a plasma in local thermodynamic equilibrium. The present investigations take benefit from the very rich and intense emission spectrum generated by ablation of a nickel-chromium-molybdenum alloy. This alternative and direct proof of the plasma equilibrium state reopens the perspectives of quantitative material analyses via calibration-free laser-induced breakdown spectroscopy. Moreover, the unique properties of this laser-produced plasma promote its use as radiation standard for intensity calibration of spectroscopic instruments

Structural Parameters and Behavior in Simulated Body Fluid of High Entropy Alloy Thin Films

The structure, composition and corrosion properties of thin films synthesized using the Pulsed Laser Deposition (PLD) technique starting from a three high entropy alloy (HEA) AlCoCrFeNix produced by vacuum arc remelting (VAR) method were investigated. The depositions were performed at room temperature on Si and mirror-like polished Ti substrates either under residual vacuum (low 10−7 mbar, films denoted HEA2, HEA6, and HEA10, which were grown from targets with Ni concentration molar ratio, x, equal to 0.4, 1.2, and 2.0, respectively) or under N2 (10−4 mbar, films denoted HEN2, HEN6, and HEN10 for the same Ni concentration molar ratios). The deposited films’ structures, investigated using Grazing Incidence X-ray Diffraction, showed the presence of face-centered cubic and body-centered cubic phases, while their surface morphology, investigated using scanning electron microscopy, exhibited a smooth surface with micrometer size droplets. The mass density and thickness were obtained from simulations of acquired X-ray reflectivity curves. The films’ elemental composition, estimated using the energy dispersion X-ray spectroscopy, was quite close to that of the targets used. X-ray Photoelectron Spectroscopy investigation showed that films deposited under a N2 atmosphere contained several percentages of N atoms in metallic nitride compounds. The electrochemical behavior of films under simulated body fluid (SBF) conditions was investigated by Open Circuit Potential (OCP) and Electrochemical Impedance Spectroscopy measurements. The measured OCP values increased over time, implying that a passive layer was formed on the surface of the films. It was observed that all films started to passivate in SBF solution, with the HEN6 film exhibiting the highest increase. The highest repassivation potential was exhibited by the same film, implying that it had the highest stability range of all analyzed films. Impedance measurements indicated high corrosion resistance values for HEA2, HEA6, and HEN6 samples. Much lower resistances were found for HEN10 and HEN2. Overall, HEN6 films exhibited the best corrosion behavior among the investigated films. It was noticed that for 24 h of immersion in SBF solution, this film was also a physical barrier to the corrosion process, not only a chemical one

E-MRS spring meeting 2019, Symposium O: Synthesis, processing and characterization of nanoscale multi functional oxide films VII. May 27–31, 2019, Nice, France

International audienceNice, France This Special Issue records another in an established tradition (since 2006) of interdisciplinary E-MRS symposia, bringing together scientists and engineers involved in all aspects of the synthesis, processing, characterization, device integration and theoretical modeling of multifunctional oxide-based thin films, multilayers and nanostructures. Symposium O was one of 28 parallel symposia at the European Materials Research Society Spring Meeting and, in a joint session, shared an afternoon of oral presentations with Symposium Q: Polar oxides: synthesis, science and applications. The final programme included 79 oral presentations (16 from invited speakers) and 93 posters, making up a full week of fascinating science and technology, covering a wide range of interest in oxides, oxide-based thin films, and device structures. Questions and discussions following presentations were often lively and wide-ranging. The very high standard of presentations in the poster sessions was of note, and these sessions also offered opportunities for discussion and debate with the many attendees. We thank those at E-MRS Headquarters for the organization of the meeting, and all their help and support. Also, GDR OXYFUN and EU Action NFFA (www.nffa.eu) for generous sponsorship of this Symposium. And thank you to all participants: scientific committee members, speakers, poster presenters, session chairs and assessors for poster prizes, and all those who attended, asked questions, and took part in the events. Once again, the Symposium Proceedings are published in collaboration with Thin Solid Films, and we are extremely grateful to Elsevier, and the editorial team, for all their assistance in the Editorial process. And we have greatly appreciated the invaluable, and very prompt, input to these proceedings by all authors and reviewers