Search results for "I.2"
showing 10 items of 662 documents
Insight into the defect-molecule interaction through the molecular-like photoluminescence of SiO2 nanoparticles
2016
Luminescence properties due to surface defects in SiO2 are the main keystone with particles that have nanoscale dimensions, thus motivating their investigation for many emission related applications in the last few decades. A critical issue is the role played by the atmosphere that, by quenching mechanisms, weakens both the efficiency and stability of the defects. A deep knowledge of these factors is mandatory in order to properly limit any detrimental effects and, ultimately, to offer new advantageous possibilities for their exploitation. Up to now, quenching effects have been interpreted as general defect conversion processes due to the difficulty in disentangling the emission kinetics by…
Qualitative Models for the Photoresponse and Capacitance of Annealed Titania Nanotubes
2015
Physicochemical characterization of annealed TiO2 nanotubes (TNTs) was conducted by using photocurrent spectroscopy and differential capacitance techniques. It has been shown that the geometry and architecture of nanotubes determine how photogenerated electrons and holes are separated and transferred. Photocurrent generation in TNTs is a consequence of two phenomena; drifting of holes into the electrolyte and diffusion of electrons toward the substrate. These two processes have been shown to be independent of the anodic polarization. The capacitance of TiO2 nanotubes is also affected by their geometry. In anodic potentials, with respect to the flat band potential of the underlying barrier l…
Pickering Emulsions of Fluorinated TiO2: A New Route for Intensification of Photocatalytic Degradation of Nitrobenzene
2020
International audience; Fluorination of the TiO2 surface has been often reported as a tool to increase the photocatalytic efficiency due to the beneficial effects in terms of production of oxidizing radicals. Moreover, it is shown that the unique amphiphilic properties of the fluorinated TiO2 (TiO2-F) surface allow one to use this material as a stabilizer for the formulation of Pickering emulsions of poorly soluble pollutants such as nitrobenzene (NB) in water. The emulsions have been characterized in terms of size of the droplets, type of emulsion, possibility of phase inversion, contact angle measurements, and optical microscopy. The emulsified system presents micrometer-sized droplets of…
Photocatalytic CO2 reduction in gas–solid regime in the presence of H2O by using GaP/TiO2 composite as photocatalyst under simulated solar light
2014
GaP/TiO2 composites exhibited a remarkable photocatalytic activity for CO2 reduction in the presence of water vapor producing methane. By decreasing the GaP:TiO2 mass ratio an increase in the photocatalytic activity of the composite was observed for up to a 1:10 mass ratio. The photocatalytic activity of the composite can be attributed to the band structures of the solids as well as to the efficient charge transfer between GaP and TiO2 heterojunction.
Electronic Properties of Thermal Oxides on Ti and Their Influence on Impedance and Photoelectrochemical Behavior of TiO2 Nanotubes
2017
Thermal oxidation of titaniumwas carried out at 350◦C, 450◦C, and 550◦C for 2 h or 12 h.X-rayDiffraction and Raman Spectroscopy suggest that the thermal oxides are scarcely crystallinewhen the annealing temperature is low, while both anatase and rutile are present for high annealing temperature and time. Photoelectrochemical measurements allowed estimation of a bandgap decreasing from 3.35 eV to 3.15 eV with increasing annealing temperature. The impedance spectra confirmed the formation of n-type semiconductors, with an impedance strongly decreasing on going from a reverse bias toward a forward bias regime. TiO2 nanotubes grown by anodizing Ti in NH4F and water containing ethylene glycol so…
Tensile strength and impact strength of color modified acrylic resin reinforced with titanium dioxide nanoparticles
2017
Background Poor mechanical properties are among the main limitations of acrylic resins. Addition of titanium dioxide (TiO2) nanoparticles to acrylic resin has been shown to improve its mechanical properties with an adverse effect on its color. Thus, this study sought to assess the tensile and impact strength of a color modified heat cure acrylic resin reinforced with TiO2 nanoparticles. Material and Methods In this in vitroexperimental study, 1wt% TiO2 nanoparticles were added to SR Triplex Hot heat-cure acrylic resin powder and mixed. Pigments and color fibers were also added and 18 samples were fabricated of this paste for tensile and impact strength testing (n=9) according to ISO5271. Ei…
Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate
2017
Financial support from the Estonian Research Council (IUT2-25, PUT170, PUT1096, PUT748, PUTJD680), the Estonian Centre of Excellence in Research Projects “Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics” TK141 (2014-2020.4.01.15-0011), “Emerging orders in quantum and nanomaterials” TK134 and the Development Fund of the University of Tartu, are all gratefully acknowledged.
Residual crystalline silicon phase in silicon-rich-oxide films subjected to high temperature annealing
2002
Structural properties of silicon rich oxide films (SRO) have been investigated by means of micro-Raman spectroscopy and transmission electron microscopy (TEM). The layers were deposited by plasma enhanced chemical vapor deposition using different SiH4/O2 gas mixtures. The Raman spectra of the as-deposited SRO films are dominated by a broad band in the region 400-500 cm-1 typical of a highly disordered silicon network. After annealing at temperatures above 1000°C in N2, the formation of silicon nanocrystals is observed both in the Raman spectra and in the TEM images. However, most of the precipitated silicon does not crystallize and assumes an amorphous microstructure. © 2002 The Electrochem…
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 …
Angle resolved X-ray photoemission spectroscopy double layer model for in situ characterization of metal organic chemical vapour deposition nanometri…
2007
International audience; In situ Angle Resolved X-ray Photoemission Spectroscopy (ARXPS) characterizations of TiO2 thin films grown on silicon by Metal Organic Chemical Vapour Deposition were performed in order to get information on interfacial reactions at the first stages of the growth, one of the aims being to understand the influence of deposition conditions. Thickness measurements were also carried out from ARXPS analyses. As the real structure of the films was shown to be a double layer system such as TiO2/SiO2/Si, an ARXPS model of thickness and surface coverage determination was applied to each layer independently. However, the application of this model to very thin films underestima…