Search results for "Toe"
showing 10 items of 3824 documents
Initial stages of TiO2 thin films MOCVD growth studied by in situ surface analyses
2005
Abstract In situ chemical surface analyses using X-ray photoelectron spectroscopy (XPS) were performed to understand the initial stages of TiO 2 thin-film MOCVD growth. Deposits on Si (1 0 0), a few nanometres thick, were obtained at a fixed temperature of 650 °C and for two different pressures, 2.9 and 0.05 mbar, using titanium tetraisopropoxide (TTIP) as precursor. Pressure lowering led to a higher deposit growth rate. Reduction of titanium with respect to stoichiometric titanium dioxide and oxidation of the wet-cleaned silicon substrate are observed from decomposition of the Ti 2p and Si 2p peaks. The formation of a TiSi x O y mixed oxide is also pointed out and confirmed by the presence…
Interfacial reaction during MOCVD growth revealed by in situ ARXPS.
2006
International audience; Angle-resolved X-ray photoelectron spectroscopy (ARXPS) experiments were performed to study in situ the reaction at the film–substrate interface during metal organic chemical vapor deposition (MOCVD) growth of TiO2 thin films deposited on the silicon substrate. The in-depth distribution of chemical species was determined using several ARXPS thickness calculation models considering either single or bilayer systems. By the comparison of two single-layermodels, the presence of a second layer composed of silicon oxidewas evidenced. High-resolution transmission electron microscopy (HRTEM) observations confirmed the stratification of the film in two layers, as well as the …
Au/CeO2-SBA-15 catalysts for CO oxidation: Effect of ceria loading on physic-chemical properties and catalytic performances
2012
In this work gold catalysts supported over SBA-15 with different CeO 2 loadings (5-30 wt%) were prepared, characterized by N 2 physisorption analyses, SAXS, XRD, STEM and XPS techniques and their catalytic performances were evaluated in the CO oxidation, chosen as reaction test. Over a selected catalyst, Au/CeO 2(20 wt%)-SBA-15, the effect of CO 2 and of the mixture (CO 2 + H 2O) on the CO conversion to CO 2 was also evaluated. Characterizations by SAXS, XRD, STEM and XPS were carried out on selected spent catalysts after CO oxidation. The results were discussed in terms of relationship between morphological, structural, electronic and catalytic properties as a function of the ceria loading…
Photoelectric fields in doped lithium niobate crystals
2019
Photoinduced light scattering (PILS) in nominally pure stoichiometric and congruent lithium niobate single crystals (LiNbO3), and ones doped with B³⁺, Cu²⁺, Zn²⁺, Mg²⁺, Gd³⁺, Y³⁺, Er³⁺ cations was studied. All crystals have a relatively low effect of photorefraction and are promising materials for frequency conversion, electro-optical modulators and shutters. It was found that the photovoltaic and diffusion fields for some crystals have a maximum at a wavelength of 514.5 nm. All the crystals studied are characterized by a maximum of the integral intensity of the speckle structure of the PILS at a wavelength of 514.5 nm.
Metalenses with high-NA, enhanced resolution and apodization
2017
Dielectric microlenses employed in imaging and focusing for optoelectronics are currently prospects to be substituted by metalenses showing an extraordinary optical performance within notably reduced volumes. Here we present some proposals to achieve an enhanced resolution in metallodielectric metasurface-based lenses established on either efficient arrangements with high numerical aperture or spatial filtering enabling to surpass the limit of resolution derived by the Rayleigh criterion.
High Resolution X-Ray Spectroscopy with Compound Semiconductor Detectors and Digital Pulse Processing Systems
2012
The advent of semiconductor detectors has revolutionized the broad field of X-ray spectroscopy. Semiconductor detectors, originally developed for particle physics, are now widely used for X-ray spectroscopy in a large variety of fields, as X-ray fluorescence analysis, X-ray astronomy and diagnostic medicine. The success of semiconductor detectors is due to several unique properties that are not available with other types of detectors: the excellent energy resolution, the high detection efficiency and the possibility of development of compact detection systems. Among the semiconductors, silicon (Si) detectors are the key detectors in the soft X-ray band (15 keV) and will continue to be the c…
Hard X-Ray Response of Pixellated CdZnTe Detectors
2009
In recent years, the development of cadmium zinc telluride (CdZnTe) detectors for x-ray and gamma ray spectrometry has grown rapidly. The good room temperature performance and the high spatial resolution of pixellated CdZnTe detectors make them very attractive in space-borne x-ray astronomy, mainly as focal plane detectors for the new generation of hard x-ray focusing telescopes. In this work, we investigated on the spectroscopic performance of two pixellated CdZnTe detectors coupled with a custom low noise and low power readout application specific integrated circuit (ASIC). The detectors (10x10x1 and 10x10x2 mm3 single crystals) have an anode layout based on an array of 256 pixels with a …
Transmission Efficiency of the SAGE Spectrometer Using GEANT4
2013
The new SAGE spectrometer allows simultaneous electron and γ-ray in-beam studies of heavy nuclei. A comprehensive GEANT4 simulation suite has been created for the SAGE spectrometer. This includes both the silicon detectors for electron detection and the germanium detectors for γ-ray detection. The simulation can be used for a wide variety of tests with the aim of better understanding the behaviour of SAGE. A number of aspects of electron transmission are presented here.
A review of the development of portable laser induced breakdown spectroscopy and its applications
2014
Abstract In this review, we present person-transportable laser induced breakdown spectroscopy (LIBS) devices that have previously been developed and reported in the literature as well as their applications. They are compared with X-ray fluorescent (XRF) devices, which represent their strongest competition. Although LIBS devices have advantages over XRF devices, such as sensitivity to the light elements, high spatial resolution and the possibility to distinguish between different layers of the sample, there are also disadvantages and both are discussed here. Furthermore, the essential portable LIBS instrumentation (laser, spectrograph and detector) is presented, and published results related…
Spin-polarized photoelectrons resonantly excited by circularly polarized light from a fractional Ag film on GaAs(100)
2013
We demonstrate a finite spin polarization of photoelectrons emitted from GaAs(100) covered by a fractional Ag film. The photoemission yield shows a sharp maximum for intermediate coverage and the spin polarization increases with increasing laser intensity. Photoelectrons are excited by circularly polarized 100 fs laser pulses of 800 nm wavelength. We recorded the photoemitted electrons using a photoemission electron microscope combined with a Mott spin polarimeter. The spin polarization is analyzed in dependence on the excitation frequency and intensity and on the average thickness of the silver film. The results are explained by a model combining multiphoton photoemission and optical field…