Search

With the increase of the laser powers and the decrease of the pulse durations, materials with very large optical nonlinearities are of great interest for the laser community. Indeed, depending on the type of the nonlinearities, they can be used for several applications including frequency conversion and self-focusing. In particular, saturable absorbers are widely studied, as they allow mode-locking of laser systems or super-resolved laser writing. In this work, we have studied the saturable absorption efficiency of Sb2Te3 thin layers. Layers with thicknesses ranging from 2.5 to 30 nm have been deposited using electron beam deposition (Buhler SYRUSpro 710). These films were then annealed in a temperature-controlled furnace at 250°C during 1h to ensure that the layers are completely crystallized. These layers were then thoroughly inspected with X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Backscattered electron detector (BSD) and Transmission Electron Microscopy (TEM). The nonlinear optical properties under nanosecond and femtosecond pulse duration were also studied for each layer using the Z-Scan technique. These studies allowed the determination of the nonlinear absorption and the nonlinear refraction of the samples under two different wavelengths at each pulse duration regime. In this paper we present a correlation between the structure of the Sb2Te3 thin films and the observed nonlinearities.

International audience; In this work, the conductance behavior of tungsten trioxide based chemoresistive ozone sensors under ultra violet illumination was investigated. The tungsten trioxide sensitive layers were deposited on a SiO2/Si substrate by reactive radio frequency magnetron sputtering with several Argon / Oxygen ratios. The detection principle is based on a change in the conductance of the semiconductor oxides when ozone is present around the surface. We demonstrate the influence of Argon / Oxygen during the deposition of the sensitive layer, on ozone detection at 50°C under light illumination. The sensor shows good sensitivity to ozone, with a stable baseline, fast response and recovery time. These results are promising for the detection of ozone at low temperature.

International audience; Sb 2 Te 3 thin films are very promising candidates for nonlinear optics and several applications including super-resolution and nano-photoinscription. This work aims to offer a detailed study of the preparation of the thin films and their nonlinear optical properties under nanosecond laser excitation. Thin Sb 2 Te 3 films have been deposited by the electron beam deposition technique. The films have been protected by a thin silica layer, then annealed in order to enhance their nonlinearities by material crystallization. The annealing has been optimized by simultaneously recording the X-Ray diffraction diagrams. After this optimization, the annealing could be safely performed by heating in an oven. The nonlinear optical properties of the Sb 2 Te 3 thin films have been studied by means of the Z-scan technique employing 11 ns laser pulses at 1064 nm and 532 nm. High nonlinear absorption has been found showing the possibility to employ these materials for super-resolution, mode-locking and other applications.

A barium titanate thin film was deposited by drop coating for carbon dioxide detection. The measurements are based on a resistance change and provided a sensitive response to different CO2 concentrations under a humidity environment. The concentration measurement range was between 100 and 5000 ppm of CO2 in synthetic air, and likewise, the relative humidity was between 20 and 70%. The response and recovery times of the BaTiO3 based resistive sensors were determined to 2 min and 4 min, respectively, for 400 ppm of carbon dioxide and 50% relative humidity.

Samples of cesium polymolybdates Cs2MonO3n+1 with n = 2, 3, 5, and 7 have been synthesized by melting and cooling stoichiometric mixtures of commercially available Cs2MoO4 and MoO3 powders. The sin...

2D materials are currently very promising candidates for various photonic applications. Optimizing their optical nonlinearities requires a thorough adjustment of several properties including the film thickness. In thiswork thin Sb2Te3layers with different thicknesses (ranging from 2.5 nm to 50 nm)are prepared by the electron beam deposition technique, then they are properly annealed in order to achieve significant third order nonlinearities. The film structure and morphology are extensively studied by means of X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and Energy-dispersive X-Ray spectroscopy. The presence of nanocrystals with sizes highly dependingon the film thickness has beenobserved.Optical studies are carried out by Vis-NIR spectrophotometric studies. Finally, a thickness dependent study of the ultrafast third order nonlinear optical properties of the Sb2Te3thin films is performed. This study is carried out by means of the Z-scan technique, employing 400 fs laser pulses at 1030 nm. The observed optical nonlinearities are veryhigh, comparedwith those of state-of-the-art nonlinear optical materials. Moreover they are highly dependent on the thickness of the layers. The findings demonstrate the importance of a fine adjustment of the Sb2Te3thickness in order to enhance its nonlinear optical efficiency.They are expected tobe of significant importance for mode-locking of laser systems and super-resolved direct laser writing.

Surface treatments are considered as a good alternative to increase biocompatibility and the lifetime of Ti-based alloys used for implants in the human body. The present research reports the comparison of bare and modified Ti6Al4V substrates on hydrophilicity and corrosion resistance properties in body fluid environment at 37 &deg, C. Several surface treatments were conducted separately to obtain either a porous oxide layer using nanostructuration (N) in ethylene glycol containing fluoride solution, or bulk oxide thin films through heat treatment at 450 &deg, C for 3 h (HT), or electrochemical oxidation at 1 V for 3 h (EO), as well as combined treatments (N-HT and N-EO). In-situ X-ray diffraction and ex-situ transmission electron microscopy have shown that heat treatment gave first rise to the formation of a 30 nm thick amorphous layer which crystallized in rutile around 620 &deg, C. Electrochemical oxidations gave rise to a 10 nm thick amorphous film on the top of the surface (EO) or below the amorphous nanotube layer (N-EO). Dual treated samples presented similar results with a more stable behavior for N-EO. Finally, for both corrosion and hydrophilicity points of view, the new combined treatment to get a total amorphous N-EO sample seems to be the best and even better than the partially crystallized N-HT sample.

International audience; The optimization of thin Sb 2 Te 3 films in order to obtain giant ultrafast optical nonlinearities is reported. The ultrafast nonlinearities of the thin film layers are studied by the Z-scan technique. Giant saturable absorption is obtained, which is the highest ever reported, by means of the Z-scan technique. There is a growing interest in materials exhibiting signicant ultrafast nonlinear optical (NLO) properties. 1 In particular, the saturable absorption is currently intensively being investigated because it can be directly applied to the mode-locking of laser systems. 2 Many different materials, for example, carbon nano-tubes, 3 graphene 4 and perovskites 5,6 have been reported in the past to exhibit a signicant saturable absorption. Moreover, nowadays, intense research is being carried out in the eld of nano-patterning materials in order to offer them unique optical/nonlinear optical properties. 7 This has a strong impact in many applications, for example, optical ltering, 8,9 diffractive element fabrication 10 and optical data storage, 11 to name a few. The direct laser writing technique, 12 using fs laser pulses, is one of the most promising and cost-efficient techniques used in order to pattern the matter with custom shapes. However, the resolutions are usually limited by diffraction. The latter can be surpassed by nonlinear phenomena, but the resolutions obtained are very highly dependent on the material used for patterning. 13,14 An improved way to surpass the diffraction limit is to use a super-resolution mask exhibiting a signicant saturable absorption. 15 A family of 2D materials, called topological insulators, exhibiting a "graphene-like" energy band gap structure, is currently very intensively being investigated, as these materials exhibit very high optical nonlinearities. 16,17 Among them, Sb 2 Te 3 is currently among the best candidates for the mode-locking of ultrafast laser systems. 18,19 Despite the high interest of this material for photonic applications, its NLO parameters at the ultrafast regime, are rather unknown. There is currently only one study reporting on the nonlinear absorption coefficient (b) of Sb 2 Te 3 using ultrafast pulses. 20 An optimization of its NLO response is very complex because it highly depends on its crystallization state. Research on this topic is of high interest because it will further enhance the applicability of Sb 2 Te 3 in the eld of photonics. Our group is aiming at using thin Sb 2 Te 3 layers as super-resolution masks in the ultrafast regime. Towards this objective , a thorough optimization of the crystallization state of Sb 2 Te 3 thin lms was initiated in order to obtain an optimal saturable absorption. In this work deposition, post treatment and NLO studies are presented. The crystallization was done by oven and laser annealing. In both cases, unprecedented nonlinear absorption parameters have been found, which are compared with state-of-the-art materials. The Sb 2 Te 3 thin lms were deposited using the electron beam deposition technique. The thickness of the lms has been determined to be 24 nm, by locally removing the thin layer and performing atomic force microscopy measurements (Fig. S1 †). A 10 nm thick silica layer was deposited over Sb 2 Te 3 , which allowed us to perform annealing in air without the oxidation of the layers. The substrate and the thin silica layer have been found to exhibit no optical nonlinearities under the experimental conditions used in this work. Aer the deposition, annealing was performed in two different ways. Firstly, the thin lms were annealed by using an oven at 300 C for 24 hours, following a procedure previously reported by our group. 21 A second alternative way to crystallize the thin lms has been employed in this work. In this case, laser annealing was performed by using a pump-probe setup (Fig. S2 and description in the ESI †). 22 During laser annealing the temperature on the sample was in situ measured by using a thermal camera throughout crystallization. Moreover, the relative reectance, which is well-known to be strongly dependent upon the crystallization state of the Sb 2 Te 3 material, 23 was

The optimization of thin Sb

In situ X-Ray diffraction, Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) were used to investigate the structure and the chemistry of the first phase formed after solid-state diffusive reaction between a Ni thin film (f) and an InAs substrate (s) at low temperature. The results show the formation of a single phase for which the Ni3InAs stoichiometry and the P63/mmc-hexagonal (a = b = 4.00 A and c = 5.10 A) structure were evidenced. Investigations in Electron Diffraction are in agreement with a disordered B8~1.5 structure in which additional Ni atoms are randomly distributed with In and As on the equivalent interstitial sites. The epitaxy relationship was also found, namely the [001]s//[210]f zone axes as well as the (220)s//(-120)f and (002)s//(100)f atomic planes. These findings were discussed taking into account atomic size effects.

Introduction Environmental safety is attracting significant attention due to the increase of dust particles, and toxic gas species (e.g. CO, NOx, etc.) [1]. CO is identified as a major threat for human health. Since CO is a colorless, odorless, and tasteless gas, it can't be detected by human senses. Therefore, sensitive sensor operating in humid air is required for CO gas detection [2]. For metal oxide (MOX) gas sensors, the humidity interferes with the low-level detection of reducing and oxidizing gases. The performances of MOX gas sensors such as SnO2 or CuO can be enhanced, by metal doping, material functionalization or MOX composite [3]. In this work, a comparison between resistive sensors based on CuO and on BaTiO3-CuO bi-layer film will be presented. The sensor responses to three CO gas concentrations in dry air and in 50% of relative humidity (RH) will be discussed. Method BaTiO3 nanoparticles (NPs) (2 powder (0.2 g) was dissolved in acetic acid (5 ml), water (7 ml) and ethylene glycol (2ml). These two solutions were deposited by drop coating on a silicon oxide substrate provided with interdigitated platinum electrodes (figure 1). CuO films were prepared with one drop of Cu(OH)2 solution. BaTiO3-CuO films were fabricated with one drop of BaTiO3 NPs, an ambient drying for 5 minutes followed by one drop of Cu(OH)2 solution on the top of it. Then, the sensors were annealed at 500°C for 1 h. The sensing properties of these sensors were investigated by CO exposure. NI PXIe-4140 sourcemeter was used to measure the sensor resistance variations for an optimum operating temperature found at 280°C. Results and Conclusions Figure 2 shows the x-ray diffractograms of CuO and BaTiO3-CuO materials. The XRD patterns of CuO film indicate the existence of CuO nanoparticles in the monoclinic phase without CuO2 nanoparticles [4]. BaTiO3-CuO bilayer consists of a tetragonal phase of BaTiO3 in addition to monoclinic CuO [5]. Figure 3 presents the responses of CuO and BaTiO3-CuO to CO gas. In dry air, CuO gives a response equals to 1.22, while the response is more important for BaTiO3-CuO (1.41). In 50% RH, the sensor responses with CuO have almost disappeared while the sensors based on BaTiO3-CuO film gave a response equals to 1.32. Therefore, BaTiO3-CuO films have an enhanced response to CO in dry air as well as in the presence of 50% RH. The CO concentration effect on BaTiO3-CuO films was tested for 10, 50, and 100 ppm of CO in dry air and 50% RH (figure 4). Linear responses under CO in dry or wet air make BaTiO3-CuO bilayer films a potential candidate for the CO gas detection application. We have developed sensors based on BaTiO3-CuO composite for the CO gas detection under dry and wet air. The sensing properties are based on the resistance variation under CO gas. Our results show enhanced responses of BaTiO3-CuO concerning CuO in dry air and 50% RH. Future work will be focused on the proportion of BaTiO3 and CuO investigations to enhance the sensor response under CO. References [1] A. Kumar, A. Sanger, A. Kumar, et R. Chandra, « Highly sensitive and selective CO gas sensor based on a hydrophobic SnO2/CuO bilayer », RSC Adv., 6, 52, (2016), 47178–47184. doi: 10.1039/C6RA0653 [2] K. Sircar, J. Clower, M. Kyong Shin, C. Bailey, M. King, et F. Yip, « Carbon monoxide poisoning deaths in the United States, 1999 to 2012 », Am. J. Emerg. Med., 33, (2015), 1140–1145. doi: 10.1016/j.ajem.2015.05.002 [3] M. Hijazi, M. Rieu, V. Stambouli, G. Tournier, J.-P. Viricelle, et C. Pijolat, « Ambient temperature selective ammonia gas sensor based on SnO2 -APTES modifications », Sens. Actuators B Chem., 256, (2018), 440–447. doi: 10.1021/acsomega.9b02185 [4] K. Martin, G. McCarthy, North Dakota State Univ., Fargo, ND, USA., ICDD Grant-in-Aid, 1991. [5] S. B. Rudraswamy et N. Bhat, « Optimization of RF Sputtered Ag-Doped BaTiO3-CuO Mixed Oxide Thin Film as Carbon Dioxide Sensor for Environmental Pollution Monitoring Application », IEEE Sens. J., 16, (2016), 5145–5151. doi: 10.1109/Jsen.2016.2567220 Figure 1

International audience; In situ X-Ray Diffraction, X-Ray Reflectivity and High Resolution Transmission Electron Microscopy were used to investigate the sequence and the texture of phase formation during the solid-state reaction of Ni thin film with GaAs substrate. These results show the formation of a unique Ni3GaAs crystalline phase at 200 degrees C that remains stable until 400 degrees C. The epitaxial relationships between this phase and the GaAs substrate were also evidenced. The formation of this unique phase, along with the variation of its lattice parameters when Ni is totally consumed, can be explained by local thermodynamic equilibrium and kinetics arguments. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The SrNiP2O7 compound was prepared by a solid-state reaction method. Electrical properties and modulus analysis were studied using complex impedance spectroscopy in the frequency range 200 Hz–5 MHz and temperature range 609–728 K. The difference of the value of activation energy for the bulk obtained from analysis of equivalent circuit (0.88 eV) and modulus relaxation (0.77 eV) confirms that the transport is not due from a simple hopping mechanism. The AC conductivity is studied using the following equation: σ ac ( ω ) = σ s 1 + τ 2 ω 2 + σ ∞ τ 2 ω 2 1 + τ 2 ω 2 + A ω s . The temperature dependence of the power law exponent s and a.c conductivity σac is reasonably interpreted by the overlapping large polaron tunneling (OLPT) model. The mechanism of conduction is probably due from the displacements of the Sr2+ ion in the tunnel-type cavities along the a and b axis.

In this study we investigated the influence of cobalt thickness (from 50 nm to 10 nm) on the kinetics and texture of CoSi 2 layers. In-situ X-ray diffraction measurements were performed during isothermal annealing to determine CoSi 2 kinetics as explained in a previous publication. Decreasing the initial cobalt thickness (50 nm, 30 nm, and 10 nm) induces a slowdown of the formation rate, especially for the 10 nm Co layer. A model based on CoSi 2 nucleation is used to explain this phenomenon.

In situ sheet resistance and x-ray diffraction measurements were used simultaneously during heat treatment to study Ti electrodes in contact with Ge-Te phase change materials. Ti is found to react with GeTe forming TiTe 2 and Ge. Atom probe tomography analyses confirm the presence of these two phases after a 400°C heat treatment.

International audience; Secondary γ′ precipitation in a commercial single crystal Ni-based superalloy after the 1100 °C isothermal aging has been investigated by atom probe tomography. After the isothermal aging for 300 s, 1800 s and 3600 s, a bimodal size distribution of larger primary γ′ precipitates and numerous smaller secondary γ′ precipitates was obtained. It is proposed that the secondary γ′ precipitated via a non-classical nucleation mode. The coarsening of secondary γ′ precipitates well obeys the classical LSW theory.

International audience; The precipitation of γ′ phase in a commercial single crystal Ni-based superalloy with different cooling rates has been investigated by atom probe tomography. Numerous irregular interconnected γ′ precipitates in the size range of ~30 to 50 nm were obtained even utilizing the fastest possible cooling rate. Diffuse γ/γ′ interface and far from equilibrium composition of γ′ phase were observed in the fast-cooled sample, suggesting that γ′ precipitation occurs via a spinodal decomposition at the very early stage.

International audience; The L10 martensite formed in a Pt-modified NiCoCrAlYTa bond coating has been investigated by atom probe tomography. It was found that obvious segregation of Co and Cr occurred in the micro-twins zone inside the martensite lath. Based upon the compositional analysis, it is known that Pt destabilizes the β phase and Co and Cr act as β stabilizers with respect to the β→L10 martensitic transformation. In addition, some α-Cr particles precipitated inside the martensite lath.

In-situ X-Ray diffraction was used to determine CoSi 2 kinetics growth from 100 nm CoSi. In this work, we discuss about an unexpectedly slow reaction that is observed at the end of CoSi 2 formation. A 1D model has also been developed from these experiments in order to reproduce the sequential growth of cobalt silicides and the end of the reaction experimentally observed in this study.

International audience; Wetting of ìm-sized Pb droplets on thin polycrystalline films of decagonal Al13Co4 and cubic crystalline AlCo phases is reported. The sample preparation is crucial to have Pb droplets lying on a clean surface. Decagonal and cubic films were prepared under high vacuum conditions, by sequential deposition and annealing of specific stackings of Al and Co layers of nanometric thicknesses. A 300nm-thick Pb slab was then deposited on the top of the films. Dewetting experiments were performed in situ in a scanning Auger microprobe where the surface chemistry can be monitored: the Pb slab dewetts into droplets. The wetting of Pb on both substrates was found to be similar with contact angles around 45°.

The formation of Ni silicide during the reaction between Ni(5% Pt) and a Si(100) substrate has been analyzed by differential scanning calorimetry (DSC), in situ x-ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), and H4e+ Rutherford backscattering. The DSC measurements show evidence of the Ni2Si nucleation followed by lateral growth formation. In situ XRD and TEM have been used to investigate the sequence of formation of the silicides. These experiments show that the formations of Ni2Si and NiSi occur simultaneously in the presence of the Pt alloy. The redistribution of platinum at different stages of the Ni silicide growth has been determined. We have estimated the solubility limit of platinum (1 at. % at 573 K) in the Ni2Si phase by extrapolation from a measured value at 1073 K. This redistribution is explained in terms of the solubility limits and the diffusion of Pt in the Ni2Si and NiSi phases. Pt is more likely to reside at the silicide grain boundaries and the interface...

Wetting with ?m-sized Pb droplets on thin polycrystalline films of decagonal Al13Co4 is reported. The films were prepared under high vacuum conditions in order to have Pb droplets lying on a clean surface. The method used is sequential deposition and annealing of specific stackings of Al and Co layers of nanometric thicknesses. A 300?nm thick Pb slab was then deposited on top of the films and dewetting experiments were followed in situ in a scanning Auger microprobe. The contact angle between the Pb droplet and the surface of the film is measured to be 49? ? 7?. Further investigation performed by cross section transmission electron microscopy allows us to better characterize the interface. Taking into account the rugosity of the film, it is concluded that there is partial wetting of the film, which corresponds to a smaller contact angle. The comparison with other results obtained either with pure metals or with a cubic AlCo compound leads to the conclusion that the wetting behaviour of Pb on the surface of a decagonal compound is close to that of a metal with a high melting point and not significantly different from that of a crystalline compound with a small unit cell.

Experimental procedure allowing the measurement of kinetic factors controlling the reaction of a nanometric film with a monocrystalline substrate by differential scanning calorimetry (DSC) is described. This technique is shown to be of great interest for characterization of silicide formation during microelectronic industrial processes. Combining both in situ x-ray diffraction measurements (crystal structure) and DSC measurements (formation enthalpy), the interface reaction coefficient Kr and the effective diffusion coefficient Kd characterizing Pd2Si growth have been measured.

International audience; Atom probe tomography assisted by femtosecond laser pulses has been performed on a Ni(Pt) film on (100)Si. Two phases with different compositions were found to form during deposition at room temperature: a NiSi layer with a relatively constant thickness of approximately 2 nm and a particle of Ni2Si. The shape of the Ni2Si particle is in accordance with nucleation followed by lateral growth formation. This confirms the growth model deduced from calorimetric measurement of silicides and intermetallics and from atom probe tomography studies of the Al/Co system. A nonuniform redistribution of Pt was also observed. (c) 2006 American Institute of Physics.

In-situ X-ray diffraction was used to determine CoSi"2 growth kinetics from 100nm CoSi films. In this work, we discuss about an unexpectedly slow reaction rate that is observed at the end of CoSi"2 formation. A 1D model has also been developed from these experiments in order to reproduce the sequential growth of cobalt silicides and the end of the reaction experimentally observed in this study.

International audience; Hydrogen is a promising gas for greenhouse gas emission reduction but also a reactive one. Thus, sensor for hydrogen detection in various atmospheres is mandatory. While leak sensors in air environments have been widely studied, only few researches have been done for hydrogen detection in anaerobic environments. In this work, the electrical resistance variation of a PdAu alloy as a sensitive film, is studied at various temperatures for hydrogen exposures in an anaerobic (N2) environment. The Pd0.8Au0.2 alloy was deposited on a Si/SiO2 substrate using magnetron sputtering followed by annealing at 200°C in N2. The sensor was then tested at various temperatures for 0.3% H2 exposure, the best operating temperature was found to be 50°C. Finally, sensor was able to detect at 50°C, concentrations from 0.3 to 3% H2. These preliminary results are promising for further development of hydrogen sensors in anaerobic environment.