Search results for "ULTRAVIOLET"
showing 10 items of 853 documents
Complexes of an anionic poly(p-phenylene) polyelectrolyte and dioctadecylammonium bromide at the air–water interface
1999
Abstract By spreading dioctadecyldimethylammonium bromide on a subphase containing rigid rod-like anionic poly( p -phenylene) sulfonate, a complex monolayer is formed in situ at the air–water interface. Complexation results in an increase of the area per amphiphile molecule compared to the amphiphile on pure water. The change in structural order upon complexation and subsequent compression of the monolayer can be demonstrated employing UV/Vis spectroscopy: A red-shift of the polymer absorption band upon compression and a subsequent partial reversion of this shift after monolayer collapse can be observed. The peak shift is discussed to be a result of the electronic interaction of the π -syst…
Visible photothermal deflection spectroscopy using microcantilevers
2012
International audience; Photothermal deflection spectroscopy based on bi-material cantilevers combines the sensitivity of miniature sensors and the selectivity of optical spectroscopy. In this paper, we report on the photothermal response of the microcantilevers functionalized with nanometer thin organic films in the visible region. Unlike responses in the infrared regime, in the optical region, light absorption by all the cantilever constituents must be considered for extraction of the physical parameters of the organic layer. A model of photothermal deflection for the optical region has been developed for two absorbing layers consisting of a thick metal (>200 nm) and a thin organic film. …
Vacuum-ultraviolet absorption of amorphousSiO2: Intrinsic contribution and role of silanol groups
2008
We present a study on the vacuum-ultraviolet (VUV) absorption properties of amorphous ${\text{SiO}}_{2}$ $(a{\text{-SiO}}_{2})$ with high concentrations of silanol groups (Si-OH). We found that the absorption spectra are made up of a couple of exponential profiles. The first, in the range from $\ensuremath{\sim}7.5$ to $\ensuremath{\sim}8.1\text{ }\text{eV}$, was attributed to Si-OH group absorption, while the second, in the range from $\ensuremath{\sim}8.1$ to $\ensuremath{\sim}8.25\text{ }\text{eV}$, was ascribed to the intrinsic absorption. The VUV absorption cross section of Si-OH groups in $a{\text{-SiO}}_{2}$ was determined as well. The intrinsic absorption was found to be affected by…
<title>Advances in silica-based glasses for UV and vacuum UV laser optics</title>
2003
The origins of pre-existing and laser-induced ultraviolet (UV) and vacuum ultraviolet (VUV) optical absorption in state-of-the-art glassy silicon dioxide and the ways to improve it are reviewed. The main causes of pre-existing absorption in UV/VUV are oxygen vacancies, hydroxyl (silanol) groups, and strained bonds/localized states due to glassy disorder. The main absorption bands induced by UV/VUV excimer lasers are due to oxygen vacancies and due to silicon and oxygen dangling bonds (E'-centers and non-bridging oxygen hole centers, respectively). The optimized glasses are achieved via an intricate balance between a good stoichiometry, use of network modifiers (F or OH) to reduce the number…
Effects of the Buffer Layers on the Performances of (Al,Ga)N Ultraviolet Photodetectors
2004
The fabrication of (Al,Ga)N-based metal–semiconductor–metal (MSM) photovoltaic detectors requires the growth of high-quality (Al,Ga)N films. Inserting a low-temperature deposited buffer layer enables the growth of an epitaxial layer with a reduced density of defects. Two structures using GaN and AlN buffer layers have been deposited by low-pressure metalorganic chemical vapor deposition and used to fabricate MSM interdigitated detectors. The devices have been characterized to investigate the effects of the buffer layers on the detector performances.
A Simple “Plastic Bag” Technique for Visible Spectra of Solid Metal Complexes
1979
The techniques commonly used to study the visible spectra of transition metal complexes in the solid state involve diffuse reflectance from the powdered sample or transmission through a mull of the compound in mineral oil on filter paper. Pressed KBr (for anhydrous compounds) and AgCl (for compounds containing water or other highly polar ligands) disk techniques have been used even for low temperature spectra. All of the transmission techniques mentioned are based on mixing the sample with another compound which may induce changes in the compound under study via chemical reactions. Air- and water-sensitive complexes also need special care. These interferences may be reduced by the use of th…
Ultra-broad spectral photo-response in FePS3 air-stable devices
2021
Van der Waals materials with narrow energy gaps and efficient response over a broadband optical spectral range are key to widen the energy window of nanoscale optoelectronic devices. Here, we characterize FePS as an appealing narrow-gap p-type semiconductor with an efficient broadband photo-response, a high refractive index, and a remarkable resilience against air and light exposure. To enable fast prototyping, we provide a straightforward guideline to determine the thickness of few-layered FePS nanosheets extracted from the optical transmission characteristics of several flakes. The analysis of the electrical photo-response of FePS devices as a function of the excitation energy confirms a …
Study of Gasdynamic Electron Cyclotron Resonance Plasma Vacuum Ultraviolet Emission to Optimize Negative Hydrogen Ion Production Efficiency
2019
Negative hydrogen ion sources are used as injectors into accelerators and drive the neutral beam heating in ITER. Certain processes in low-temperature hydrogen plasmas are accompanied by the emission of vacuum ultraviolet (VUV) emission. Studying the VUV radiation therefore provides volumetric rates of plasma-chemical processes and plasma parameters. In the past we have used gasdynamic ECR discharge for volumetric negative ion production and investigated the dependencies between the extracted H$^-$ current density and various ion source parameters. It was shown that it is possible to reach up to 80 mA/cm$^2$ of negative ion current density with a two electrode extraction. We report experime…
Intensity-correlated spiking of infrared and ultraviolet emission from sodium vapors
2021
The directional spiking infrared and ultraviolet emission from sodium vapors excited to the 4D5/2 level by a continuous-wave resonant laser pump, that constitute a novel feature of the cooperative effects, has been analyzed. Cascade mirrorless lasing at 2207 and 2338 nm on population-inverted transitions and ultraviolet radiation at 330 nm that is generated due to four-wave mixing process demonstrate a high degree of intensity correlation.
Synthesis of cubic and hexagonal NaYF4:Er3+
2012
Up-conversion luminescence process, which is related to absorption of several light photons (usually infrared) followed by emission of light in the visible or even ultraviolet spectral regions, has attracted interest of scientists due to its potential practical use in various applications including biolabels, temperature sensors, light sources etc. Although observable in d- and f-ions doped materials, the highest efficiency of up-conversion luminescence is usually attained in lanthanides doped hosts. Among huge variety of materials suitable as up-conversion hosts the most prominent is considered to be NaYF4, both due to its low phonon energy and multisite nature of the crystalline lattice. …