High Absorption Cross Section Research Articles

Maximizing the ultimate absorption efficiency of vertically-aligned semiconductor nanowire arrays with wires of a low absorption cross-section

Single semiconducting nanowires with sub-wavelength diameters exhibit superior light absorption, and hence triggered a vivid discussion regarding the application of these nanostructures into future generations of high efficiency solar cells. We examine the transition from a single highly absorbing silicon wire into an array composed of such individuals in order to validate the application of these into solar harvesting devices. We use finite-difference time-domain simulations to show that the coupling of the Fabry–Perot oscillations with the waveguide resonances inside the wires has a significant effect on the array absorption. For example, the ultimate absorption efficiency of a square-tiled wire array under normal incidence (array period of 0.5µm, wire diameter of 0.4µm and wire height of 2) is 81% higher than a 2µm thin-film when the Fabry–Perot oscillations are considered and 37% higher when these oscillations are not considered. This coupling screens out the contribution of the waveguide modes to the array absorption and therefore, unlike previously published work, we eliminate the contribution of the Fabry–Perot oscillations. In this manner we demonstrate the absorption enhancement due to waveguide modes, and general correlations between the nanowire geometry and the overall array absorption are presented. First, we show that once an isolated wire with high absorption cross-section is nested inside an array its absorption decreases due to wire proximity effects. Secondly, the array absorption is maximized with relatively wide wires of low absorption cross-sections. We show that a 75nm wire inside an square-tiled array with 2µm period has an average absorption efficiency factor of 6.5 and the average relative absorption of the array is 0.5%, while the same wire nested inside an array of a 0.25µm period exhibits 2.3 average absorption efficiency factor and the array exhibits average relative absorption of 9.85%. Finally, there is an optimized wire diameter that once exceeded the array absorption converges to that of a continuous film. For example, the maximum absorption of 0.5µm array is obtained with wire diameter of 0.4µm where a decrease in relative absorption is recorded for arrays with wires exceeding 0.4µm.

Characterization and determination of catechins in green tea leaves using UV-visible spectrometer

In this paper, characterizations of pure major catechins and method for determination of total catechins in green tea leaves have been reported using UV-visible spectrometer. Most research activities have been focused on chromatographic methods, however spectrophotometirc method is preferred because of its rapidity, high accuracy, and reproducibility. The optical transition properties of Epigallocatechin Gallate (EGCG) and Epicatechin Gallate (ECG) in water, methanol, ethanol, acetonitrile and Epigallocatechin (EGC) and Epicatechin (EC) in water were measured. The results show that, EGCG has highest molar decadic absorption coefficient in methanol than in the other solvents. ECG has the highest absorption cross-section, transitional dipole moment, and oscillator strength of all the catechins in water. On the other hand, EGC has the least optical transition properties of all the catechins in water. Limits of detection (LOD) were comprised in the range 3.1×10-2gmL-1 to and reproducibilities with RSD lower than 2%. After characterization of the electron transition, a method was developed for UV-Visible determination of total catechins. Using the developed method, the content of total catechins in Ethiopian and Sri Lanka green tea leaves at room temperature was determined. The result of the experiment indicates that, Ethiopian green tea leaves has the greater total catechins (17±0.01%) than Sri Lanka green tea leaves (7.17±0.12%). Key words: Tea leaves, catechins, extraction, UV-visible spectrometer, optical transition properties.

Neutronic effects of rhenium, gadolinia and uranium dioxide addition to a tungsten based fast spectrum space reactor

The neutronic effects of rhenium (Re), gadolinia (Gd2O3) and uranium dioxide (UO2) addition to a W–60vol.% UO2 fast spectrum fuel form were investigated relative to a prismatic reactor type using the MCNP5 Monte Carlo code with the ENDF/B-VII.1 cross-section database. The effects of rhenium addition to the cladding tubes and sleeves were studied over the range of 2–25at.% as well as the corresponding effects on the reactor mass and control drum reactivity swing and neutron energy spectrum. The effects of rhenium addition to the tungsten matrix over the range of 1–5at.% was also investigated. Lastly, the UO2 concentration was varied from 55 to 60vol.% UO2 and the UO2 was mixed with Gd2O3 at concentrations ranging from 2 to 10mol.%. Each configuration was investigated for its effects on the control drum shut down margin both in a dry state and in a submerged state where the reactor was surrounded and flooded with fresh water. The high thermal spectrum absorption cross-section of tungsten, rhenium and gadolinium proved excellent in maintaining the reactor in a subcritical state when submerged in fresh water. However, increases in the concentration of rhenium and gadolinia to the matrix, cladding and fuel kernels were also accompanied by an increase in reactor mass. The control swing within the drums was not influenced by the material compositions; however, the increase in reactor size with varying UO2 and Gd2O3 concentrations did prevent a large fraction of the neutron population from reaching the control drums. The decrease in neutron population with access to the reflector region containing the control drums caused a loss of reactivity swing in the drums by up to 2.8% Δk/k ($4.36).

Introduction to the Application of Organic Polymers for Photovoltaic Devices Organic Electronics Approach: Critical Review

Photovoltaic effect is the emergence of a voltage between electrodes attached to a solid or liquid system up on shining light on to this system. Conjugated polymer is a molecular entity whose structure is represented as a system of alternating single and double bonds which give rise to their semi-conductor properties. Conjugated polymers are used for photovoltaic devices because, Intrinsically stable up on photoexcitation with visible light, High absorption cross-section for photon harvesting, Tunable band gap with in the entire visible spectral range and High yield of charge generation when mixed with electron acceptor materials. The important physical process in the energy conversion process that take place in polymers for photovoltaic cells are; Absorption of a photon of light by photoactive material and generation of excitons, diffusion of excitons in conjugated polymers, dissociation of charge carriers (electron-hole pair) at the donor-acceptor interface in to free carriers, transport of free carriers towards the electrodes, and extraction of the charge carriers at the respective electrode interfaces. The efficiency of converting solar to electrical energy by a solar cell depends on the band gap of the light absorbing semiconductor. Band gap (Eg) is the difference in energy between the HOMO and LUMO and there by the maximum amount of energy required for an excitation or is the energy difference between the edges of the conduction band and valence band. The power conversion efficiency is a function of band gap. For device architectures of conjugated polymer based photovoltaic cells; there are three types Single layer photovoltaic cell, Bilayer hetero junction photovoltaic cell and Bulk hetero junction Photovoltaic cell.

Logging identification of the Longmaxi mud shale reservoir in the Jiaoshiba area, Sichuan Basin

Compared with conventional gas reservoirs, shale gas reservoirs are not sensitive to petrophysical properties, making it much difficult to identify this kind of reservoirs with well logging technologies. Therefore, through a comparison of the logging curves of the Lower Silurian Longmaxi marine shale in the Jiaoshiba area, Sichuan Basin, it is found that the mud shale on conventional log curves generally features high gamma ray, high uranium, low thorium, low kalium, relative high resistivity, high interval transit time, low neutron, low density and low photoelectric absorption cross section index, while on elements logging curves, it features an increase of silicon content and a decrease of aluminum and iron content. Based on the logging response characteristics of mud shale, the logging curves most sensitive to shale, gamma ray, neutron and density logging were selected and overlaid to identify mud shale effectively. On the basis of qualitative identification, the density logging value can identify the non-organic-rich mud shale from organic-rich mud shale, because the former has a density of 2.61–2.70 g/cm3, while the latter has a density of less than 2.61 g/cm3. The identification results agree well with the results of field gas content test, TOC experiment, and gas logging, so this study can provide reference for the logging interpretation.

Emission turn-on and solubility turn-off in conjugated polymers: one- and two-photon-induced removal of fluorescence-quenching solubilizing groups.

The synthesis of highly efficient two-photon uncaging groups and their potential use in functional conjugated polymers for post-polymerization modification are reported. Careful structural design of the employed nitrophenethyl caging groups allows to efficiently induce bond scission by a two-photon process through a combination of exceptionally high two-photon absorption cross-sections and high reaction quantum yields. Furthermore, π-conjugated polyfluorenes are functionalized with these photocleavable side groups and it is possible to alter their emission properties and solubility behavior by simple light irradiation. Cleavage of side groups leads to a turn-on of the fluorescence while solubility of the π-conjugated materials is drastically reduced.

Localized Electric Field of Plasmonic Nanoplatform Enhanced Photodynamic Tumor Therapy

Near-infrared plasmonic nanoparticles demonstrate great potential in disease theranostic applications. Herein a nanoplatform, composed of mesoporous silica-coated gold nanorods (AuNRs), is tailor-designed to optimize the photodynamic therapy (PDT) for tumor based on the plasmonic effect. The surface plasmon resonance of AuNRs was fine-tuned to overlap with the exciton absorption of indocyanine green (ICG), a near-infrared photodynamic dye with poor photostability and low quantum yield. Such overlap greatly increases the singlet oxygen yield of incorporated ICG by maximizing the local field enhancement, and protecting the ICG molecules against photodegradation by virtue of the high absorption cross section of the AuNRs. The silica shell strongly increased ICG payload with the additional benefit of enhancing ICG photostability by facilitating the formation of ICG aggregates. As-fabricated AuNR@SiO2-ICG nanoplatform enables trimodal imaging, near-infrared fluorescence from ICG, and two-photon luminescence/photoacoustic tomography from the AuNRs. The integrated strategy significantly improved photodynamic destruction of breast tumor cells and inhibited the growth of orthotopic breast tumors in mice, with mild laser irradiation, through a synergistic effect of PDT and photothermal therapy. Our study highlights the effect of local field enhancement in PDT and demonstrates the importance of systematic design of nanoplatform to greatly enhancing the antitumor efficacy.

Photoluminescence study of Sm3+–Yb3+co-doped tellurite glass embedding silver nanoparticles

We report on the upconversion emission of Sm3+ ions doped tellurite glass in the presence of Yb3+ ions and silver nanoparticles. The enhancement of infrared-to-visible upconversion emissions is achieved under 980nm excitation wavelength and attributed to the high absorption cross section of Yb3+ ions and an efficient energy transfer to Sm3+ ions. Further enhancements are attributed to the plasmonic effect via metallic nanoparticles resulting in the large localized field around rare earth ions. However, under excitation at 406nm, the addition of Yb3+ content and heat-treated silver nanoparticles quench the luminescence of Sm3+ ions likely due to quantum cutting and plasmonic diluent effects, respectively.

Diketopyrrolopyrrole-porphyrin conjugates with high two-photon absorption and singlet oxygen generation for two-photon photodynamic therapy.

Two-photon photodynamic therapy is a promising therapeutic method which requires the development of sensitizers with efficient two-photon absorption and singlet-oxygen generation. Reported here are two new diketopyrrolopyrrole-porphyrin conjugates as robust two-photon absorbing dyes with high two-photon absorption cross-sections within the therapeutic window. Furthermore, for the first time the singlet-oxygen generation efficiency of diketopyrrolopyrrole-containing systems is investigated. A preliminary study on cell culture showed efficient two-photon induced phototoxicity.

Effect of heating rate on the thermoluminescence and thermal properties of natural ulexite

Boron-rich compounds are of interest in the nuclear industry because they exhibit a high neutron absorption cross section. The manufacture of these materials involves the application of thermal and chemical treatments. This paper focuses on the study of the effect of the heating rate (HR) in two thermal techniques, differential thermal analysis (DTA) and thermoluminescence (TL), performed on natural ulexite from Bigadiç-Balıkesir (Turkey). The TL measurements were performed at six different heating rates in the range of 25–240°Cmin−1. The UV–blue TL emission of natural ulexite shifted toward higher temperatures with increasing heating rate, whereas the intensity decreased. The kinetic parameters of the ulexite (Ea=0.65(9) eV and s=1.22×1012s−1) were calculated using the variable heating rate method. DTA measurements performed in the range of 0.5–10°Cmin−1 displayed similar behavior to that of the TL response, despite the differences in technique and HR values. The DTA results indicated that natural ulexite exhibits two endothermic peaks originating from different processes: (i) a phase transition between the pentahydrated ulexite phase and a triple-hydrated phase and (ii) dehydration, dehydroxylation and alkali and earth-alkali self-diffusion processes in the ulexite lattice. The main endothermic peak shifted from 160°C to 250°C as the heating rate was increased.

Nanostructured organosilicon luminophores and their application in highly efficient plastic scintillators.

Organic luminophores are widely used in various optoelectronic devices, which serve for photonics, nuclear and particle physics, quantum electronics, medical diagnostics and many other fields of science and technology. Improving their spectral-luminescent characteristics for particular technical requirements of the devices is a challenging task. Here we show a new concept to universal solution of this problem by creation of nanostructured organosilicon luminophores (NOLs), which are a particular type of dendritic molecular antennas. They combine the best properties of organic luminophores and inorganic quantum dots: high absorption cross-section, excellent photoluminescence quantum yield, fast luminescence decay time and good processability. A NOL consists of two types of covalently bonded via silicon atoms organic luminophores with efficient Förster energy transfer between them. Using NOLs in plastic scintillators, widely utilized for radiation detection and in elementary particles discoveries, led to a breakthrough in their efficiency, which combines both high light output and fast decay time. Moreover, for the first time plastic scintillators, which emit light in the desired wavelength region ranging from 370 to 700 nm, have been created. We anticipate further applications of NOLs as working elements of pulsed dye lasers in photonics, optoelectronics and as fluorescent labels in biology and medical diagnostics.

A Polyurethane-Based Positive Photoresist.

Polyurethane (PU) monomer mixtures containing commercially available o-nitrobenzyl-based photocleavable monomers have been formulated and tested as low-cost positive tone photoresists. The photolysis reaction is studied by UV spectroscopy. Well-defined micropatterns on 2 μm thick photodegradable PU films are obtained using 365 nm light exposure. This strategy is also extended to improved formulations based on synthesized o-nitrobiphenylpropyl derivatives with enhanced photochemical properties for single photon excitation and high two-photon absorption cross-sections. Improved pattern resolution in 2D and the capability of 3D resolution using a scanning laser at 780 nm is demonstrated. This work demonstrates the potential of PUs as readily available, versatile, and easy-to-use photoresist materials for low-cost lithography applications.

"m=1" coatings for neutron guides

A substantial fraction of the price for a supermirror neutron guide system is the shielding, which is needed because of the gamma radiation produced as a result of neutron absorption in the supermirror layers. Traditional coatings have been made of nickel-titanium heterostructures, but Ni and Ti also have a fairly high absorption cross section for cold and thermal neutrons. We examine a number of alternatives to Ni as part of a study to reduce the gamma radiation from neutron guides. Materials such as diamond and Be have higher neutron scattering density than Ni, smaller absorption cross section, and when a neutron is absorbed they emit gamma photons with lower energies. We present reflectivity data comparing Ni with Be and preliminary results from diamond coatings showing there use as neutron guide coatings. Calculations show that Be and diamond coatings emit two orders of magnitude fewer gamma photons compared to Ni, mainly because of the lower absorption cross section.

An Autonomous Reactivity Control system for improved fast reactor safety

The Autonomous Reactivity Control (ARC) system is a new safety device that can passively provide negative reactivity feedback in fast reactors that is sufficient to compensate for the positive coolant density reactivity feedback even in large low-leakage cores. The ARC system is actuated by the inherent physical property of thermal expansion, and has a very small effect on core neutronics at standard operating conditions. Additionally, the ARC system does not have an identified failure mode that can introduce positive reactivity in to the core. An ARC system can be installed in conventional fuel assemblies by replacing a limited number of fuel rods with rods that fill a safety function, providing negative reactivity to the core in the event of coolant temperature rise above nominal. These rods are of the same outer dimensions as the fuel rods, but contain smaller-diameter inner rods that are connected to liquid-filled reservoirs at the top and bottom of the assemblies. The reservoirs are filled with two separate liquids that stay liquid and immiscible throughout the applicable temperature range of fast reactor operation. The lower reservoir contains a “neutron poison” liquid with a high neutron absorption cross-section. The upper reservoir is filled with a separate liquid with a small neutron absorption cross-section. As the temperature in the assembly increases, the liquids in the reservoirs thermally expand, effectively pushing the absorbing liquid up toward the active core region while compressing the inert gas that fills the volume above the liquid between the inner and outer tubes of the ARC rods. The ARC system can be installed, or retrofitted in to existing systems, in every fuel assembly in the core. Since ARC installations in individual fuel assemblies operate independently, the system has a high level of redundancy. ARC-systems respond to local transients as well as core-wide accident scenarios. After actuation, the system automatically returns to its initial state as temperatures decrease, without the need for intervention by reactor operators. The ARC system concept and design considerations are described and illustrated.

Extraordinary High Microwave Absorption Cross Section of Ultralong Carbon Nanotubes

The microwave-induced heating of nanoparticles has been actively studied in pursuit of more efficient microwave absorbers. Here we systematically investigated the microwave absorption cross section of conductive particles (Al), magnetic particles (Fe3O4), and carbon nanotubes with different lengths. The particles were suspended in silicone oil and irradiated with a microwave at 2.45 GHz using a single-mode microwave reactor. The experimentally measured heating rate was analytically modeled based on the modified Lambert–Beer law to obtain the microwave absorption cross section per mass. The microwave-induced heating rate was primarily dependent on optical absorbance, which is proportional to the mass concentration of suspended particles. Under the similar optical absorbance, longer nanotubes provided greater microwave absorption cross section which could be described by the short dipole antenna theory. The microwave absorption cross section of 5 mm long multiwalled carbon nanotubes was ∼4080 times greater ...

Preparation of <sup>10</sup>B Enriched B<sub>4</sub>C Ceramics by Pressureless Sintering

Boron carbide is an attractive neutron absorbing material used both in Fast Breeder Reactors (FBR) and in Pressurised Water Reactors (PWR) owing to its very high absorption cross section for thermal neutrons, chemical stability and refractory character. In the present paper, 10B enriched B4C ceramics are prepared by pressureless sintering at 19602160°C, under argon, using 10B boron carbide powder as raw material, 18 wt% phenolic resin as sintering aid. In the sintering temperature range, with the increasing of sintering temperature, both the relative density and flexural strength increase linearly, the average particle sizes increase from about 3μm at 1960°C to more than 30μm at 2160°C. The sample sintered at 1960°C has a 91.7% of relative density and 192 MPa of flexural strength and a homogeneous texture with 3-4μm particle size, which are enough for pellet application of reactors.

High spectral resolution ozone absorption cross-sections – Part 1: Measurements, data analysis and comparison with previous measurements around 293 K

Abstract. In this paper we discuss the methodology of taking broadband relative and absolute measurements of ozone cross-sections including uncertainty budget, experimental set-ups, and methods for data analysis. We report on new ozone absorption cross-section measurements in the solar spectral region using a combination of Fourier transform and echelle spectrometers. The new cross-sections cover the spectral range 213–1100 nm at a spectral resolution of 0.02–0.06 nm in the UV–visible and 0.12–0.24 nm in the IR at eleven temperatures from 193 to 293 K in steps of 10 K. The absolute accuracy is better than three percent for most parts of the spectral region and wavelength calibration accuracy is better than 0.005 nm. The new room temperature cross-section data are compared in detail with previously available literature data. The temperature dependence of our cross-sections is described in a companion paper (Serdyuchenko et al., 2014).

High spectral resolution ozone absorption cross-sections – Part 2: Temperature dependence

Abstract. We report on the temperature dependence of ozone absorption cross-sections measured in our laboratory in the broad spectral range 213–1100 nm with a spectral resolution of 0.02–0.24 nm (full width at half maximum, FWHM) in the atmospherically relevant temperature range from 193 K to 293 K. The temperature dependence of ozone absorption cross-sections was established using measurements at eleven temperatures. This investigation is superior in terms of spectral range and number of considered temperatures compared to the previous studies. The methodology of the absolute broadband measurements, experimental procedures and spectra processing were described in our companion paper together with the associated uncertainty budget. In this paper, we report in detail on our data below room temperature and compare them with literature data using direct comparisons as well as the standard approach using a quadratic polynomial in temperature fitted to the cross-section data.

Heavily Eu3+-doped boroaluminosilicate glasses for UV/blue-to-red photoconversion with high quantum yield

We report on the photoluminescence of heavily Eu3+-doped SrO–La2O3–Al2O3–B2O3–SiO2 glasses. The specific glass system enables highly efficient photoemission for a dopant concentration of up to 8 mol% of Eu2O3 before concentration quenching is observed. This allows for the realization of high absorption cross section combined with an internal quantum efficiency of greater than 60% without further optimization of batch materials and processing conditions. In this way, the problem of luminescence quantum yield from active glass substrates in smart windows, greenhouses or solar energy harvesting may be overcome. In the present case, more than 50% of the photons coming in at the peak excitation wavelengths of 394 or 464 nm are converted to red.

Composite Conjugated Polymer/Fullerene Nanoparticles as Sensitizers in Photodynamic Therapy for Cancer

The fabrication and study of composite conjugated polymer nanoparticles doped with fullerene for application in photodynamic therapy (PDT) is reported. The nanoparticles are not intrinsically cytotoxic and show specificity towards cancer cells without surface modification. The high absorption cross-section and efficient charge transfer from conjugated polymer to fullerene in the composite nanoparticles results in only moderate light levels being necessary for PDT. The PDT scheme was tested in vitro for MDA-MB-231 (human breast cancer), A549 (human lung cancer), and OVCAR3 (human ovarian cancer) cell lines. While the treatment was observed to be only marginally effective for the MDA-MB-231 cell line, 60 % and complete cell death was observed for the A549 and OVCAR3 cell lines, respectively. Differences in PDT efficiency are attributed to the difference in nanoparticle uptake between these cell lines, and is potentially related to differences in metabolic rate. Through live/dead cell staining apoptotic cell death was observed for OVCAR3. This is a promising finding for potential development of treatment for ovarian cancer by the PDT scheme discussed herein.