1,721,105 research outputs found
Verification of layered structures in Sno2/metal-based gas sensors by X-ray microanalysis: Comparison with X-ray photoelectron spectroscopy
No full textThe depth profile of thin film layers on bulk substrate, avoiding the cross-sectioning of samples, is commonly performed by techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron Spectroscopy (AES), and secondary ion mass spectroscopy (SIMS). Techniques based on X-ray emission intensity measurements by energy dispersive spectroscopy (EDS), with conventional matrix or ZAF correction, are normally applied to cross-sectioned samples. This article compares XPS with surface Xray intensity measurements by EDS, carried out with a more realistic X-ray generation and absorption model, known as the phi(rho Z) model. The phi(rho Z) approach has been adopted together with Monte Carlo simulation for the proper selection of SEM accelerating voltages, in conjunction with the analysis of SEM morphological images for thin film density correction. The method discussed hereafter and compared with the XPS technique, has advantages of higher lateral resolution, non-destructive elemental analyses, morphological visualization, low cost, and faster performance. This methodology has been followed to verify the layered structure of SnO2/metal-based gas sensors. X-ray intensities were measured using an EDS ultra-thin window detector. Two different porous layers, 25-nm thick of SnO2 and 10-nm thick of Cu, were detected, showing better agreement with their nominal thickness compared to results obtained using XPS measurements where porosity affects XPS data. If confirmed to be reliable and as effective as XPS depth profiling, this technique may be adopted for process quality control purposes
HT-XRD analysis of W thick coatings for nuclear fusion technology
No full textW is a promising material to use as protection for thermal shields in future nuclear fusion reactors, however the joining to other metals is really challenging. For realizing such joints plasma spraying (PS) has been used for its simplicity, the possibility to cover complex and extended surfaces and the relatively low cost. An appropriate interlayer must be optimized to increase the adhesion of W on the substrates and to provide a soft interface for better thermo-mechanical compatibility. The present work demonstrates that high-temperature X-ray diffraction (HT-XRD) permits to quickly assess the reliability and quality of the coating-interlayer-substrate system by measuring the strain of coating. This is very useful to orientate the work for optimizing the structure and composition of the interlayer and the parameters of deposition process
IN792 DS superalloy: Optimization of EB welding and post-welding heat treatments
No full textElectron beam (EB) welding has been used to realize the seams on 2 mm thick plates of directionally solidified (DS) IN792 superalloy. A grid of the samples has been prepared by varying the pass speed v from 1 to 2.5 m/min, while the other process parameters (power P = 1 kW, acceleration voltage T = 50 kV, beam current I = 20 mA) were kept constant. Experiments were carried out both at room temperature and with pre-heating at 200 °C or 300 °C. Once found the best process conditions (pre-heating at 300 °C; v = 2.5 m/min) the effect of postwelding heat treatments at 700 and 750 °C for increasing time up to 2 hours has been investigated
Verification of Layered Structures in SnO2/Metals-based Gas Sensor by X-ray Microanalysis: Comparision with X-ray Photoelectron Spectroscopy
No full textVerification of layered structures in SnO2/metal based gas sensors by x-ray microanalysis
No full textXPS investigation of 5N purity Al thin foils for MEMS devices
No full textThin Al foils are promising materials for applications in devices of microelectromechanical systems (MEMS). In this work, three foils of high purity (5N) Al with different thickness (10, 50, and 125 μm) were analyzed by means of X-ray photoelectron spectroscopy (XPS), before and after annealing (720 K for 30 min). XPS surface analysis and depth profiling of chemical composition were performed to investigate the distribution of Al oxide. Electron energy loss spectroscopy (EELS) measurements were also carried out in order to identify the plasmon losses and chemical state of Al. The loss peaks in the 5N-Al thin foils were compared with those of an Al foil of commercial purity (99.95 wt%). The thickness of the oxide layer on the sample surface of all the samples is not constant and oxide is thicker in the samples of high purity than in those of commercial quality. Moreover, the thinnest foils of 5N-Al (10 μm) exhibit the thinnest oxide layer. These findings have been discussed by considering the size effect, that is, mechanical properties of thin foils are improving as the thickness decreases. The complex morphology of the metal-oxide interface may contribute to enhance the mechanical performances of Al foils with a thickness below ~50 μm, because the free dislocations pile up against the interface which represents an obstacle for their motion hindering plastic deformation. Obtained results suggest that Al foils to be used in MEMS devices should be of high purity and annealed to get a surface completely covered by the oxide layer
Gold corrosion: red stains on a gold Austrian Ducat
No full textStains of different colours have been observed on historic and modem gold coins in several countries. An Austrian Ducat at the Kunsthistorisches Museum in Vienna has developed some red spots on its surface over the years. The same defects have also been observed in modem coins of higher gold purity. The spots have been examined by OM, SEM, EDS, XPS and AES. Optical microscopy showed that "red" defects exhibit in fact a nuance of colours. The surface analysis put in evidence the presence in the stains, in addition to gold, of silver and sulphur. The values of the modified Auger parameter alpha' of silver correspond to those of A(g2)S; thus, it can be assumed that the stains are composed of silver sulphide (A(g2)S). It was not possible to determine whether the presence of silver on the surface is due to segregation towards the surface or to external particles of silver embedded in the matrix. Depth profiling performed on modem coins suffering from the same problem allowed us to demonstrate that the nuance of colours is due to the inhomogeneous thickness of the spots. Moreover, it was demonstrated that spots are formed by two layers: an outer layer of silver sulphide and an inner layer of silver
Verification of Layered Structures in SnO2/Metals-based Gas Sensor by X-ray Microanalysis: Comparision with X-ray Photoelectron Spectroscopy
No full textCorrelation between atomic composition and gas sensing properties in tungsten-iron oxide thin films
No full textMixed tungsten and iron oxide thin films were prepared with reactive RF sputtering. The electrical response of thin films of W-Fe oxides toward CO, NO2, ozone and ethanol was investigated. Moreover, XPS technique was employed to study the chemical composition of the samples' surfaces and the depth profile through the whole thickness of the films. The oxidation states of W and Fe were determined from the photoelectron spectra. Iron addition always increases the response towards ozone, carbon monoxide and ethanol. For nitrogen dioxide, the introduction of iron concentrations lower than 10% produce an enhancement in the response. (c) 2007 Elsevier B.V. All rights reserved
Surface analysis of biocompatible coatings on titanium
No full textThe coatings of hydroxyapatite, which is widely used for orthopaedic and dental prothesis, were deposited by using the dip-coating method. The layers of hydroxyapatite were grown on commercial Ti substrates. In order to improve the adhesion of hydroxyapatite, the substrate was a priori covered with titania or calcium titanate by using the sol-gel technique. For comparison, commercial samples of hydroxyapatite coating (manufactured by means of plasma-spray apparatus) were analysed. The chemical composition and the structure of the coatings (TiO2, CaTiO3 and hydroxyapatite) were studied by using X-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), X-ray diffraction (XRD) and secondary electron microscopy (SEM) techniques. The data of quantitative XPS analysis and the surface images (SAM and SEM) displayed the superior quality (cleanness, homogeneity, etc.) of hydroxyapatite deposited by sol-gel in comparison with commercial samples investigated. (C) 1998 Elsevier Science B.V. All rights reserved
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