Inter- and intra-layer excitons in MoS2_2/WS2_2 and MoSe2_2/WSe2_2 heterobilayers

Accurately described excitonic properties of transition metal dichalcogenide heterobilayers (HBLs) are crucial to comprehend the optical response and the charge carrier dynamics of them. Excitons in multilayer systems posses inter or intralayer character whose spectral positions depend on their binding energy and the band alignment of the constituent single-layers. In this study, we report the electronic structure and the absorption spectra of MoS$_2$/WS$_2$ and MoSe$_2$/WSe$_2$ HBLs from first-principles calculations. We explore the spectral positions, binding energies and the origins of inter and intralayer excitons and compare our results with experimental observations. The absorption spectra of the systems are obtained by solving the Bethe-Salpeter equation on top of a G$_0$W$_0$ calculation which corrects the independent particle eigenvalues obtained from density functional theory calculations. Our calculations reveal that the lowest energy exciton in both HBLs possesses interlayer character which is decisive regarding their possible device applications. Due to the spatially separated nature of the charge carriers, the binding energy of inter-layer excitons might be expected to be considerably smaller than that of intra-layer ones. However, according to our calculations the binding energy of lowest energy interlayer excitons is only $\sim$ 20\% lower due to the weaker screening of the Coulomb interaction between layers of the HBLs. Therefore, it can be deduced that the spectral positions of the interlayer excitons with respect to intralayer ones are mostly determined by the band offset of the constituent single-layers. By comparing oscillator strengths and thermal occupation factors, we show that in luminescence at low temperature, the interlayer exciton peak becomes dominant, while in absorption it is almost invisible.Comment: 17 pages, 4 figure

Evaluation of the Mineral Element Profile of Wastes of Some Wine Grape (Vitis Vinifera L.) Varieties

In this study, the level of macro and micro elements of six wine grape cultivars were determined in seeds, bagasse (skin and pulp) and pomace (seed, skin and pulp) by inductively coupled plasma mass spectrometry and atomic absorption spectroscopy after microwave digestion (ICP-AES). The levels of macro and micro elements exhibited a genotype dependent alteration and affected by the part of the berry sampled. Potassium was the predominant macro element in bagasse and pomace, varying from 6.78 g/kg dry weight in pomace (Carignane) to 21.05 g/kg dry weight in bagasse (Cabernet Sauvignon). However, the level of calcium was higher than potassium in seeds and varied between 4.95 g/kg (Kalecik karası) and 6.73 g/kg (Carignane). Seeds were also richer than the bagasse and pomace related with phosphorus, magnesium, and sulfur. Among the micro elements, Fe had the highest amount in all parts of the berries. Its content ranged from 13.9 mg/kg dry weights in bagasse of Semillon to 24.8 mg/kg dry weight in seeds of Syrah. Iron, manganese, zinc and molybdenum in seeds; copper and boron in bagasse were higher amount than the other groups analyzed. The results of this study show that all parts of the grape berries are potentially rich sources of mineral elements. So, they could be used as a food supplement to improve the nutritive value of the human diet and for some engineering processes in food industry

MEMS-Based Terahertz Detectors

A MEMS based novel THz detector structure is designed and realized by micro fabrication. The detector is then characterized to extract its mechanical performance. Operating in 1-5 THz band, the detector has a pixel size of 200 μm × 200 μm. Bimaterial suspension legs consist of Parylene-C and titanium, the pair of which provides a high mismatch in coefficients of thermal expansion. The pixel is a suspended Parylene-C structure having a 200 nm-thick titanium metallization. Operation principle relies on conversion of absorbed THz radiation into heat energy on the pixel. This increases the temperature of the free-standing microstructure that is thermally isolated from the substrate. The increase in temperature induces mechanical deflection due to bimaterial springs. The detector is designed to deliver a noise equivalent temperature difference (NETD) less than 500 mK and a refresh rate of 30 Hz

Recent Progress of RF Cavity Study at Mucool Test Area

In order to develop an RF cavity that is applicable for a muon beam cooling channel, a new facility, called Mucool Test Area (MTA) has been built at Fermilab. MTA is a unique facility whose purpose is to test RF cavities in various conditions. There are 201 and 805 MHz high power sources, a 4-Tesla solenoid magnet, a cryogenic system including a Helium liquifier, an explosion proof apparatus to operate gaseous/liquid Hydrogen, and a beam transport line to send an intense H- beam from the Fermilab Linac accelerator to the MTA hall. Recent activities at MTA will be discussed in this document.Comment: 4 pp. 13th International Workshop on Neutrino Factories, Superbeams and Beta beams (NuFact11) 1-6 Aug 2011: Geneva, Switzerlan

A Suspended Array of Square Patch Metamaterial Absorbers for Terahertz Applications

A suspended array of square metallic patches on a thin dielectric layer is introduced as a terahertz absorber. The absorber is fabricated on a metalized substrate and the device exhibits metamaterial behavior at specific frequencies determined by the size of the patches. It is feasible to place patches with different sizes in an array formation for a broadband absorber. Design of the absorber is described using electromagnetic simulations. The absorber structure was fabricated on a silicon wafer and its characteristics were measured using a terahertz time domain spectroscope. The measured data match well the simulations indicating strong absorption peaks in a band of 0.5-2 THz

Computer models of saliency alone fail to predict subjective visual attention to landmarks during observed navigation

This study aimed to understand whether or not computer models of saliency could explain landmark saliency. An online survey was conducted and participants were asked to watch videos from a spatial navigation video game (Sea Hero Quest). Participants were asked to pay attention to the environments within which the boat was moving and to rate the perceived saliency of each landmark. In addition, state-of-the-art computer saliency models were used to objectively quantify landmark saliency. No significant relationship was found between objective and subjective saliency measures. This indicates that during passive observation of an environment while being navigated, current automated models of saliency fail to predict subjective reports of visual attention to landmarks

Polysulfone/Clay Nanocomposites by in situ Photoinduced Crosslinking Polymerization

Cataloged from PDF version of article.PSU/MMT nanocomposites are prepared by dispersing MMT nanolayers in a PSU matrix via in situ photoinduced crosslinking polymerization. Intercalated methacrylate-functionalized MMT and polysulfone dimethacrylate macromonomer are synthesized independently by esterification. In situ photoinduced crosslinking of the intercalated monomer and the PSU macromonomer in the silicate layers leads to nanocomposites that are formed by individually dispersing inorganic silica nanolayers in the polymer matrix. The morphology of the nanocomposites is investigated by XRD and TEM, which suggests the random dispersion of silicate layers in the PSU matrix. TGA results confirm that the thermal stability and char yield of PSU/MMT nanocomposites increases with the increase of clay loading