Search results for "Absorption"
showing 10 items of 2701 documents
Sintering process of amorphous SiO2 nanoparticles investigated by AFM, IR and Raman techniques
2011
We report an experimental investigation on the effects of thermal treatments at different temperatures (room-1270 K) and for different duration (0-75 h) on amorphous silica nanoparticles (fumed silica) in powder tablet form. Three types of fumed silica are considered, comprising nearly spherical particles of 40 nm, 14 nm and 7 nm mean diameter. The experimental techniques used here are Raman and infrared absorption (IR) spectroscopy together with atomic force microscopy (AFM). Raman and IR spectra indicate that the structure of nanometer silica particles is significantly different with respect to that of a bulk silica glass. In particular, the main differences regard the positions of the IR…
Effects of heat treatments on the properties of copper phthalocyanine films deposited by glow-discharge-induced sublimation
2006
Copper phthalocyanine films have been deposited by glow-discharge-induced sublimation. The films have undergone postdeposition heat treatments in air at 250 and 290 °C for different times, ranging from 30 min to 14 h. The properties of as-deposited and heated films have been investigated by different techniques in order to determine the effects of heat treatments on the film properties. Fourier transform infrared analysis and UV−visible optical absorption analysis point out a gradual evolution of the film structure from a mixture of α and β polymorphs to the only β polymorph in the sample heated at 290 °C for 14 h. A pronounced decrease of carbon and nitrogen atomic percentages against an o…
Electronic and optical properties of pristine, N- and S-doped water-covered TiO2 nanotube surfaces
2019
For rational design and improvement of electronic and optical properties of water-splitting photocatalysts, the ability to control the band edge positions relative to the water redox potentials and the photoresponse as a function of environmental conditions is essential. We combine ab initio molecular dynamics simulations with ab initio many-body theoretical calculations to predict the bandgap and band edge energies, as well as the absorption spectrum of pristine and N- and S-doped TiO2 nanotubes using the DFT+U and G0W0 approaches. Both levels of theory show similar trends, and N+S-codoping appears to be the optimal system for photocatalytic water splitting both in dry and humid conditions…
Photo-Induced Cluster-to-Cluster Transformation of [Au37–xAgx(PPh3)13Cl10]3+ into [Au25–yAgy(PPh3)10Cl8]+: Fragmentation of a Trimer of 8-Electron Su…
2021
We present the photoinduced size/structure transformation of [Au37-xAgx(PPh3)13Cl10]3+ (M37) into [Au25-yAgy(PPh3)10Cl8]+ (M25) cluster. Single-crystal X-ray diffraction revealed that M37 has a tri-icosahedron M36 metal core assembled via the fusion of three Au7Ag6 icosahedrons in a cyclic fashion and that the M36 core is further protected by phosphine and chloride ligands. The M37 cluster is found to be highly sensitive toward ambient light, and the M37 → M25 transition is observed with 530 nm irradiation, monitored by time-dependent UV-vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and femtosecond transient absorption spectroscopy. Linear-response time-dependent DFT…
Searching for new borondifluoride β -diketonate complexes with enhanced absorption/emission properties using ab initio tools
2018
International audience; The rational design of fluorophores with enhanced absorption/emission properties increasingly relies on theoretical chemistry, as new ab initio methods suited for electronically excited-states reduce the gap between calculated and experimental results. In this framework, Time-Dependent Density Functional Theory (TD-DFT) emerges as an attractive option as it often provides accurate results at a moderate computational cost. Here, we perform a TD-DFT-SOS-CIS(D) study of a panel of 18 borondifluoride β-diketonate complexes that can be classified as: curcuminoids, hemicurcuminoids, their ethynylene analogues, and 2′-hydroxy-chalcones. First, we reproduce the experimental …
A Raman calibration for the quantification of SO42-groups dissolved in silicate glasses: Application to natural melt inclusions
2017
Sulfur is an important volatile element involved in magmatic systems. Its quantification in silicate glasses relies on state-of-the-art techniques such as electronprobe microanalyses (EPMA) or X-ray absorption spectroscopy but is often complicated by the fact that S dissolved in silicate glasses can adopt several oxidation states (S6+for sulfates or S2-for sulfides). In the present work, we use micro-Raman spectroscopy on a series of silicate glasses to quantify the S content. The database is constituted by 47 silicate glasses of various compositions (natural and synthetic) with S content ranging from 1179 to 13 180 ppm. Most of the investigated glasses have been synthesized at high pressur…
Methane line parameters in the HITRAN2012 database
2013
International audience; The compilation of methane molecular line parameters was updated to include new global analyses and measurements for 12CH4, 13CH4 and 12CH3D. Over 70% of the methane parameters in HITRAN2008 were replaced; existing parameters retained were the microwave lines and the Dyad of 13CH4 near 7 μm and ν6 of 13CH3D near 8.7 μm, 12CH3D (7-4076 cm-1), hot bands of 12CH4 (1887-3370 cm-1) and normal sample CH4 (4800-5550 cm-1 and 8000-9200 cm-1). With a minimum intensity at 296 K in units of cm-1/(molecule cm-2) set to 10-37 for the far-IR and 10-29 for the mid- and near-IR, the methane database increased from 290,091 lines in HITRAN2008 to 468,013 lines, and three-fourths of th…
Measurement of UV-induced absorption and scattering losses in photosensitive fibers
2018
UV-assisted fabrication of gratings using photosensitive fibers is a well-established technique, based on the UV-induced permanent modification of the refractive index of the fiber material. As a result, the absorption coefficient is also changed. Here, we exploit the thermal sensitivity of whispering gallery mode resonances of the fiber itself to measure the profile of the heating along an irradiated fiber versus the input power and for different UV radiation intensities. Our technique allows discriminating between the absorption and scattering contributions to the overall losses, by comparing the results obtained with our technique with direct transmission measurements. Different photosen…
Photocatalytic H2 production over inverse opal TiO2 catalysts
2019
Abstract The influence of BiVO4 and CuO on the chemico-physical properties of TiO2-based systems is reported. The performances of these systems were investigated in the photocatalytic H2 production both under UV and solar light irradiation. The characterization data pointed out that the obtained TiO2 samples have highly porous inverse opal structures with interconnected macropores. Inverse opal TiO2 exhibited higher activity in the H2 production than the commercial TiO2 due to the peculiar porosity that allows photons to enter inside the photocatalyst. A further improvement in terms of photoactivity was verified by addition of increasing amounts of BiVO4. On the contrary a small CuO content…
Ein kalorimeter für hochenergetische elektronenstrahlen
1968
Abstract Construction details and experimental data are given for a total absorption calorimeter used for electron beams of several hundred MeV and for beam power up to 15 kW. In order to obtain high precision, precautions were taken to obtain very high heat insulation, specially by using a temperature controlled radiation shield. The heat loss of the 700 kg copper block corresponds to less than 10 −3 °C/h. Due to design calculations and confirmed by preliminary comparison tests with other beam monitors we consider the absolute accuracy to be 1% or probably better.