Search results for "Radiation"
showing 10 items of 5298 documents
Momentum-resolved photoelectron absorption in surface barrier scattering on Ir(111) and graphene/Ir(111)
2017
Physical review / B 96(15), 155108 (2017). doi:10.1103/PhysRevB.96.155108
Hydrogen-bonded liquid crystals with broad-range blue phases
2019
We report a modular supramolecular approach for the investigation of chirality induction in hydrogen-bonded liquid crystals. An exceptionally broad blue phase with a temperature range of 25 °C was found, which enabled its structural investigation by solid state 19F-NMR studies and allowed us to report order parameters of the blue phase I for the first time.
Temperature and excitation energy dependence of decay processes of luminescence in Ge-doped silica
2003
We report experimental results on the time decay of photoluminescence at 4.2 eV in Ge-doped silica. This optical emission is assigned to a singlet-singlet transition between electronic states localized on an oxygen deficiency nearby a Ge atom and its radiative decay rate is in competition with an intersystem crossing mechanism that populates an excited triplet state. We investigate the dependence of the lifetime of this photoluminescence on the temperature, in the 6--295 K range, and on the excitation energy, in the ultraviolet and vacuum ultraviolet region. The mean value of the decay time decreases on increasing the temperature, in agreement with the phonon-assisted nature of the intersys…
Doped ZnS:Mn nanoparticles obtained by sonochemical synthesis.
2010
A study of sonochemically synthesized ZnS:Mn nanoparticles is presented. The particles prepared at low rf power (about 20 W) and room temperature coalesce to form morphologically amorphous large species (30-100 nm in diameter). As the power is increased in the range from 20 to 70 W, and the solution temperature is raised to 60 to 80 degrees C, finer particles are produced with the size ranging from 2 to 20 nm and improved crystallinity. The results indicate the dispersion of the Mn(2+) ions at near-surface sites in the particles. It is shown that the sonochemically fabricated particles approach the quality of the ones obtained by a standard chemical route and show a reasonable luminescence …
Luminescence and vacuum ultraviolet excitation spectroscopy of samarium doped SrB4O7
2020
Abstract Sm2+ and Sm3+ co-doped SrB4O7 could be utilized in several high-level optical devices and fundamental knowledge about the optical behavior of these materials benefits the development of luminescent applications. Herein, we report luminescence and its vacuum ultraviolet (VUV) excitation spectra in samarium doped SrB4O7. Both, Sm2+ and Sm3+ luminescence centers have been examined and distinguished in the emission and the excitation spectra investigated under synchrotron radiation. The contribution of either Sm2+ or Sm3+ emission lines into the emission spectra heavily depended on the excitation energy, and strong f-f transitions of both Sm2+ and Sm3+ were detected. At 10 K, a broad i…
Colloidal electro-phoresis in the presence of symmetric and asymmetric electro-osmotic flow
2018
We characterize the electro-phoretic motion of charged sphere suspensions in the presence of substantial electro-osmotic flow using a recently introduced small angle super-heterodyne dynamic light scattering instrument (ISASH-LDV). Operation in integral mode gives access to the particle velocity distribution over the complete cell cross-section. Obtained Doppler spectra are evaluated for electro-phoretic mobility, wall electro-osmotic mobility and particle diffusion coefficient. Simultaneous measurements of differing electro-osmotic mobilities leading to asymmetric solvent flow are demonstrated in a custom made electro-kinetic cell fitting standard microscopy slides as exchangeable sidewall…
Fluoride-Induced Negative Differential Resistance in Nanopores: Experimental and Theoretical Characterization
2021
We describe experimentally and theoretically the fluoride-induced negative differential resistance (NDR) phenomena observed in conical nanopores operating in aqueous electrolyte solutions. The threshold voltage switching occurs around 1 V and leads to sharp current drops in the nA range with a peak-to-valley ratio close to 10. The experimental characterization of the NDR effect with single pore and multipore samples concern different pore radii, charge concentrations, scan rates, salt concentrations, solvents, and cations. The experimental fact that the effective radius of the pore tip zone is of the same order of magnitude as the Debye length for the low salt concentrations used here is su…
Absorption edge in silica glass
2005
Measurements of optical absorption in the v-UV range in a variety of silica glass are used to determine the width of the absorption edge (Urbach energy). Measured values range from 60 meV up to 180 meV. So high a variability over silica types is tentatively ascribed to the different disorder degree, which characterizes different materials.
Ultrathin Organic Multilayer Films Via Salt Formation: Easy Access To Tailor-made Coatings In The Thickness Range Of 1 Nm To 500 Nm
2005
The state of the art technologies for the preparation of well defined ultrathin films in the submicron range are the Langmuir-Blodgett (LB) technique and self-assembly (SA) methods based on chemisorption [l]. Whereas the LBtechnique requires sophisticated apparatus and is generally limited to small film areas [2], the SA-methods are relatively simple [3,4], hut have not been employed for the preparation of films thicker than 8 layers ( 20nm) [4], probably due to the loss of chemical functionality. Our approach avoids these limits and extends the SA-concept by emploing salt formation as the driving force for the construction of multilayer supramolecular assemblies.
Number, Mass and Volume Distributions of Mineral Aerosol and Soils of the Sahara
1983
Abstract A direct method will be described to determine the complete mineral size distribution in aerosol (xylene-insoluble component) and soils (water-insoluble component) covering a size range from 0.01 up to 100 μm and 1000 μm radius, respectively, by using a combination of a scanning electron microscope, optical microscope and sieving. Aerosol and soil samples from the Sahara have been investigated. All mineral aerosol size distributions indicate a maximum between 0.06 and 0.08 μm radius and mineral particles have been found in the Aitken size range down to 0.02 μm radius. The concentration decrease toward larger particles is not uniform and shows considerable variations below 0.5 μm an…