Search

Highlights: [•] Results on AFM surface imaging of Ge x Sb(As)40−x S50Te10 films are reported. [•] The films are continuous, isotropic, considerably smooth and show fractal behavior. [•] The protruding grains suggest a columnar growth mechanism. [•] The nanoscaled grain size is larger for the films with Ge x As40−x S50Te10 composition. [ABSTRACT FROM AUTHOR]

Penetration depth is an important factor critical to the quality of a laser weld. This paper presents a 3D heat conduction model with a moving line source to correlate the temperature measured on the bottom surface of the workpiece to the weld penetration, weld bead width and welding speed. Temperatures on the bottom surface of the workpiece are measured using infrared thermocouples located behind the laser beam. The averaging effect due to the temperature measurement spot size is analyzed. This paper provides a model-based approach for laser weld penetration monitoring instead of a pure empirical correlation between a measured signal (e.g., acoustic, infrared) and the penetration depth. Experiments were conducted to compare the depth estimation based on the model to bead-on-plate welds on low carbon steel plates of varying thickness at different laser power levels and speeds. It is shown that the temperature on the bottom surface is a consistent indicator of penetration depth and that the correlation is also sensitive to the sensor location as well as other process conditions such as weld shape, width, and the plate thickness. The proposed model is computationally efficient and is suitable for on-line process monitoring application.

Abstract: N-doping is often used to improve the photocatalytic properties of TiO2 films in order to achieve visible light response. In this work, we study the effect of annealing treatment (temperature and atmosphere) on the structural and optical properties of undoped and N-doped TiO2 films by means of X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE) and UV–VIS optical transmission spectroscopy. Porous five-layer TiO2 films were deposited by sol–gel method on quartz substrate and thermally treated in oxygen or NH3 flow at 500 and 600 °C. Significant doping effect was achieved after annealing at 600 °C in NH3 and a shift in optical bandgap value down to visible range (2.69 eV) was observed. [Copyright &y& Elsevier]

The article presents a study on nanostructured TiO2(Fe) thin films prepared by sol-gel and dipping method on SiO2/glass substrate in the depollution of contaminated water against Escherichia coli using methods such as X-ray diffraction, spectroscopic ellipsometry, and atomic force microscopy. It cites the effect of iron and polyethylene glycol (PEG) on the porosity, amorphous to anaphase transition, and on the antibacterial activity of TiO2. The correlation of the inhibitory effect towards the E. coli with PEG is shown.

Abstract: With a view to analyse multiresidues of pesticides in soil samples, a new ultrasonic solvent extraction (USE) was compared to the European Norm DIN 12393 for foodstuff (extraction with acetone, partitioning with ethylacetate/cyclohexane and clean-up with gel permeation chromatography (GPC)), the QuECheRS method and a pressurised liquid extraction (PLE) method. Pesticides were analysed with both GC-MS and HPLC-MS/MS. The reference materials were the EUROSOIL 7 and its subsoil SO26 as well as a sea sand. All the substances were observed to be linear in the range of 4–800ngg−1 for the European Norm DIN 12393, 7–1400ngg−1 for the USE method and 20–4000ngg−1 for the QueCheRS and the PLE methods. Limits of detection (LOD) and limits of quantification (LOQ) were with HPLC between 0.006 and 0.23ngg−1 and between 0.022 and 0.77ngg−1, respectively, with the exception of diuron (LOD up to 11.8ngg−1; LOQ up to 39.2ngg−1). With GC they ranged from 3.0 to 87.5ngg−1 and from 10 to 292ngg−1, respectively. All substances could be recovered with USE as well as with the QuECheRS method; the European Norm DIN 12393 could not recover carbendazim and metamitron; the PLE carbendazim, metamitron and monolinuron. For the remaining substances, recoveries at a 500ngg−1 fortification level ranged from 10.9 to 96.3% with the USE. In comparison, the QuECheRS method was the most efficient extraction method with recoveries from 27.3 to 120.9%. It was followed by the European Norm DIN 12393 with recoveries between 6.8 and 108.1% and the PLE with recoveries from 12.2 to 153.2%. Recoveries were higher from the EUROSOIL 7 than from the SO 26. The repeatability expressed in term of standard deviation was below 20% for all substances and all materials. [Copyright &y& Elsevier]

The paper describes a simple low-temperature synthesis route of preparing bismuth ferrite thin films through a wet chemical process, using nitrates of bismuth and iron and two chelating agents (citric acid and polyvinyl alcohol). The films were successively deposited on different type of substrates (silica glass, steel and sintered alumina) using the immersion technique. After specific annealing, in air, the samples were characterized by scanning electron microscopy (SEM), spectroellipsometry (SE), X-ray diffraction (XRD), X-ray photoelectron (XPS) and Raman spectroscopy. The influence of chelate agent and the nature of substrates on the mechanism formation of BiFeO3 is emphasized. [ABSTRACT FROM AUTHOR]

The article presents a study which explored the usefulness of thin films in microelectronics, sensing, nano-photonics, optoelectronics and as ionic conductors. In order to secure a precursor for obtaining layers, a systematic study of the sol-gel film preparation using various phosphorous predecessors was undertaken. The test result showed that only in the films obtained with H3PO4 and P could be detected after thermal treatment. This is explained, according to the author, by the fact that the phosphorous easily evaporated.

Abstract: A comparative study of the sol–gel films prepared in the SiO2–P2O5 system starting with triethylphosphate, triethylphosphite and phosphoric acid as P precursors was performed. The work addresses basic aspects of physics, chemistry, and engineering of oxide films for applications in microelectronics, sensing, nano-photonics, and optoelectronics by establishing the influence of different precursors on the composition, structure and optical properties of the obtained films. The influence of the type of substrate (glass and indium tin oxide coated glass) and of the thermal treatment (200 and 500 °C) on their structure and properties was studied. By spectroscopic ellipsometry, X-Ray photoemission spectroscopy and atomic force microscopy measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when P-alkoxides were used. The phosphoric acid that forms chemical bond with silica network during the sol–gel process leads to better incorporation of P in the silica network as compared to the P-alkoxides. [Copyright &y& Elsevier]

We intend to prepare periodic multilayered structures for photonic applications. With this goal we have performed a study of some characteristics of SiO x -P2O5 films deposited by the sol–gel method on glass and ITO (InSnO x )-coated glass. The as prepared films were annealed to different temperatures (150 and 200°C). The chemical composition of the samples was determined by X-ray Photoelectron Spectroscopy (XPS). The XPS results revealed the presence of P in the as-deposited films. The structural an optical properties were examined by Fourier Transform Infrared Spectroscopy (FTIR), Spectroellipsometry (SE) and UV Transmission Spectroscopy. IR spectra of the deposited films attest the interaction of an amorphous SiO2 with the H3PO4 used as a P-precursor. Refractive indices for individual SiO x -P2O5 determined from SE measurements show a densification of the layer structure with the increasing temperature in the thermal treatment. The UV transmission spectra revealed a lower transmission for the sol-gel SiO x -P2O5 films as compared to ITO/glass substrate. AFM images proved the densification of the films with annealing in agreement with the ellipsometric results. [ABSTRACT FROM AUTHOR]

Abstract: BaTiO3 thin films were deposited on Pt/Ti/SiO2/Si by rf planar-magnetron sputtering. The films thickness increases with the decrease of both deposition pressure and sample-discharge centre distance. The films annealed at 900°C, for 8h, present direct band gap energy ranged between 3.57 and 3.59eV. The dependence of the structure and microstructure (texture, degree of crystallinity), as well as of the optical characteristics on the deposition parameters, was analysed. Using spectroscopic ellipsometry (SE) measurements coupled with the Bruggeman Effective Medium Approximation (B-EMA), the layer structure and the surface roughness, were determined. The root mean square roughness values of the surface layer, estimated by atomic force microscopy (AFM) analyses, are ranged between 10 and 20nm and were in good agreement with SE data. The obtained films have tetragonal unit cell and show densely packed, non-columnar morphology and hexagon-like crystallite shape. [Copyright &y& Elsevier]

Abstract: Multilayered TiO2(Fe3+, PEG) films were deposited on glass and SiO2/glass substrates by sol–gel dipping method. The influence of Fe3+ and PEG(polyethylene glycol) concentrations, the number of layers, the thermal treatment time and the temperature on the optical and microstructural properties of the TiO2 films were studied. As-deposited TiO2(Fe3+, PEG) films were very porous, but after the thermal treatment at 500°C, the PEG decomposed and burned out to porosity decreasing. Homogeneous nanostructured films were obtained, where the amorphous and the anatase phases coexist. XRD analysis showed that no rutile phase is observed in the films deposited on SiO2/glass as compared with those deposited directly on glass and that the presence of the anatase phase in the films without PEG is more evident in the three-layers film. The XRD intensity of the main peak of anatase from 25° decreases with the increase of PEG concentration. The optical gap of the TiO2(Fe3+, PEG) films is found in 2.52–2.56eV range and does not essentially depend on the PEG content. [Copyright &y& Elsevier]

Abstract: InGaN layers were grown by molecular beam epitaxy (MBE) either directly on (0001) sapphire substrates or on GaN-template layers deposited by metal-organic vapor-phase epitaxy (MOVPE). We combined spectroscopic ellipsometry (SE), Raman spectroscopy (RS), photoluminescence (PL) and atomic force microscopy (AFM) measurements to investigate optical properties, microstructure, vibrational and mechanical properties of the InGaN/GaN/sapphire layers. The analysis of SE data was done using a parametric dielectric function model, established by in situ and ex situ measurements. A dielectric function database, optical band gap, the microstructure and the alloy composition of the layers were derived. The variation of the InGaN band gap with the In content (x) in the 0< x ≤0.14 range was found to follow the linear law E g =3.44–4.5x. The purity and the stability of the GaN and InGaN crystalline phase were investigated by RS. [Copyright &y& Elsevier]

TiO2 based nanustructured coatings have been prepared by sol–gel method on glass and SiO2/glass substrates. The films were thermally treated in oxidative and reductive conditions at 500 °C. The influence of the substrate and of the thermal treatment on the optical properties of the films was studied. The samples were characterized by spectroscopic ellipsometry (SE), scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS) and Raman spectroscopy. SE results supported by other optical and structural measurements have proven the transformation of CuO from as-prepared samples into Cu2O in samples heated in oxidative conditions and into metallic Cu in samples heated in reductive conditions as well as the transformation of the amorphous TiO2 in anatase. [Copyright &y& Elsevier]

Structures containing silicon nanocrystals (nc-Si) are very promising for Si-based light-emitting devices. Using a technology compatible with that of silicon, a broader wavelength range of the emitted photoluminescence (PL) was obtained with nc-Si/SiO2 multilayer structures. The main characteristic of these structures is that both layers are light emitters. In this study we report results on a series of nc-Si/SiO2 multilayer periods deposited on 200 nm thermal oxide SiO2/Si substrate. Each period contains around 10 nm silicon thin films obtained by low-pressure chemical vapour deposition at T=625°C and 100 nm SiO2 obtained by atmospheric pressure chemical vapour deposition T=400°C. Optical and microstructural properties of the multilayer structures have been studied by spectroscopic ellipsometry (using the Bruggemann effective medium approximation model for multilayer and multicomponent films), FTIR and UV–visible reflectance spectroscopy. IR spectroscopy revealed the presence of SiOx structural entities in each nc-Si/SiO2 interface. Investigation of the PL spectra (using continuous wave-CW 325 nm and pulsed 266 nm laser excitation) has shown several peaks at 1.7, 2, 2.3, 2.7, 3.2 and 3.7 eV, associated with the PL centres in SiO2, nc-Si and Si–SiO2 interface. Their contribution to the PL spectra depends on the number of layers in the stack. [Copyright &y& Elsevier]