X-ray photoelectron spectroscopy for resistance-capacitance measurements of surface structures

Cataloged from PDF version of article.In x-ray photoemission measurements, differential charging causes the measured binding energy difference between the Si 2p of the oxide and the silicon substrate to vary nonlinearly as a function of the applied external do voltage stress, which controls the low-energy electrons going into and out of the sample. This nonlinear variation is similar to the system where a gold metal strip is connected to the same voltage stress through an external 10 Mohm series resistor and determined again by x-ray photoelectron spectroscopy (XPS). We utilize this functional resemblance to determine the resistance of the 4 nm SiO2 layer on a silicon substrate as 8 Mohm. In addition, by performing time-dependent XPS measurements (achieved by pulsing the voltage stress), we determine the time constant for charging/discharging of the same system as 2.0 s. Using an equivalent circuit, consisting of a gold metal strip connected through a 10 Mohm series resistor and a 56 nF parallel capacitor, and performing time-dependent XPS measurements, we also determine the time constant as 0.50 s in agreement with the expected value (0.56 s). Using this time constant and the resistance (8.0 Mohm), we can determined the capacitance of the 4 nm SiO2 layer as 250 nF in excellent agreement with the calculated value. Hence, by application of external do and pulsed voltage stresses, an x-ray photoelectron spectrometer is turned into a tool for extracting electrical parameters of surface structures in a noncontact fashion. (c) 2005 American Institute of Physics

Extracción en fase sólida de β-sitosterol y α-tocoferol de destilados de aceite de girasol desodorizado utilizando zeolita desilicada

In this study, the efficiency of using zeolite-based adsorbents in a solid phase extraction (SPE) procedure of α-tocopherol and β-sitosterol isolation from Sunflower Oil Deodorizer Distillate (SuDOD) with­out pre-treatment was investigated. The results showed that 99.2% α-tocopherol and 97.3% β-sitosterol were suc­cessfully isolated as pure fractions from SuDOD, when desilicated ZSM-5-type zeolite (DSiZSM-5) was used as adsorbent on a SPE. A simple and rapid HPLC method for simultaneous α-tocopherol and β-sitosterol analysis was developed and validated according to AOAC guidelines. It was found that the inclusion of a DSiZSM-5 SPE step increased the precision of the α-tocopherol and β-sitosterol analysis. In conclusion, DSiZSM-5 zeo­lite was proven to be an efficient adsorbent which can be used not only for the recovery of α-tocopherol and β-sitosterol from SuDOD in industrial scale, but also in a laboratory scale clean-up method prior to the analysis of α-tocopherol and β-sitosterol.En este estudio, se investigó la eficacia del uso de adsorbentes a base de zeolita en el procedimiento de extracción en fase sólida (EFS) para el aislamiento de α-tocoferol y β-sitosterol a partir de destilados de aceites de girasol desodorizados (SuDOD) sin ningún tratamiento previo. Los resultados mostraron que el 99,2% de α-tocoferol y el 97,3% de β-sitosterol se aislaron con éxito como fracciones puras de SuDOD, cuando se usó zeolita de tipo ZSM-5 desilicado (DSiZSM-5) como adsorbente en una EFS. Se desarrolló y validó un método HPLC simple y rápido para el análisis simultáneo de α-tocoferol y β-sitosterol de acuerdo con las directrices de la AOAC. Se encontró que la inclusión del paso DSiZSM-5 EFS aumentó la precisión del análisis de α-tocoferol y β-sitosterol. En conclusión, se demostró que la zeolita DSiZSM-5 es un adsorbente eficiente que puede usarse, no solo para la recuperación de α-tocoferol y β-sitosterol de SuDOD a escala industrial, sino también en un método de limpieza a escala de laboratorio antes del análisis de α-tocoferol y β-sitosterol

Melting of Flux Lines in an Alternating Parallel Current

We use a Langevin equation to examine the dynamics and fluctuations of a flux line (FL) in the presence of an {\it alternating longitudinal current} $J_{\parallel}(\omega)$. The magnus and dissipative forces are equated to those resulting from line tension, confinement in a harmonic cage by neighboring FLs, parallel current, and noise. The resulting mean-square FL fluctuations are calculated {\it exactly}, and a Lindemann criterion is then used to obtain a nonequilibrium `phase diagram' as a function of the magnitude and frequency of $J_{\parallel}(\omega)$. For zero frequency, the melting temperature of the mixed phase (a lattice, or the putative "Bose" or "Bragg Glass") vanishes at a limiting current. However, for any finite frequency, there is a non-zero melting temperature.Comment: 5 pages, 1 figur

Effect of solvent refractive index on the surface plasmon resonance nanoparticle optical absorption

Optical properties of plasmon coupled silver and gold nanoparticles were studied as a function of the refractive index of the surrounding medium. Our studies confirmed that the effect of changes in the refractive index of the surrounding medium was more difficult to demonstrate from an experimental point of view, because of the very high susceptibility of nanoparticles to aggregate in aqueous and organic solvents. Whereas the position of the absorption bands of triiodide in these solvents shows a clear dependence on medium's refractive index, the surface plasmon band position of silver and gold nanoparticles do not exhibit the same dependence. This is attributed to a non-negligible interaction of these solvents with nanoparticle surfaces. Copyright © 2007 American Scientific Publishers All rights reserved

Facet Formation in the Negative Quenched Kardar-Parisi-Zhang Equation

The quenched Kardar-Parisi-Zhang (QKPZ) equation with negative non-linear term shows a first order pinning-depinning (PD) transition as the driving force $F$ is varied. We study the substrate-tilt dependence of the dynamic transition properties in 1+1 dimensions. At the PD transition, the pinned surfaces form a facet with a characteristic slope $s_c$ as long as the substrate-tilt $m$ is less than $s_c$. When $m<s_c$, the transition is discontinuous and the critical value of the driving force $F_c(m)$ is independent of $m$, while the transition is continuous and $F_c(m)$ increases with $m$ when $m>s_c$. We explain these features from a pinning mechanism involving a localized pinning center and the self-organized facet formation.Comment: 4 pages, source TeX file and 7 PS figures are tarred and compressed via uufile

XPS analysis with external bias: A simple method for probing differential charging

The XPS spectra of thermally grown oxide layers on Si, Al, W and Hf substrates have been recorded while the samples were subjected to external d.c. voltage bias. The bias induces additional shifts in the measured binding energy differences between the XPS peaks of the oxide and that of the metal substrate in Si and Al (as probed both in the 2p and the KLL Auger regions), but not in W and Hf (as probed in the 4f region). These bias induced shifts are attributed to differential charging between the oxide layer and the substrate, which in turn is postulated to be related to the capacitance and inversely to the dielectric constant of the oxide layer. Accordingly, silicon dioxide with the smallest dielectric constant undergoes the largest differential charging, aluminium oxide is in the middle and no appreciable charging can be induced in the high-k tungsten and hafnium oxides, all of which are ∼6 nm thick. Copyright © 2004 John Wiley & Sons, Ltd

Heating of magnetic fluid systems driven by circularly polarized magnetic field

Cataloged from PDF version of article.A theory is presented to calculate the heat dissipation of a magnetic suspension, a ferrofluid, driven by7 circularly polarized magnetic field. Theory is tested by in vitro experiments and it is shown that, regardless of the character of the relaxation process, linearly and circularly polarized magnetic field excitations, having the same root-mean-square magnitude, are equivalent in terms of heating efficiency. (C) 2010 Elsevier B.V. All rights reserved

Self similar Barkhausen noise in magnetic domain wall motion

A model for domain wall motion in ferromagnets is analyzed. Long-range magnetic dipolar interactions are shown to give rise to self-similar dynamics when the external magnetic field is increased adiabatically. The power spectrum of the resultant Barkhausen noise is of the form $1/\omega^\alpha$, where $\alpha\approx 1.5$ can be estimated from the critical exponents for interface depinning in random media.Comment: 7 pages, RevTex. To appear in Phys. Rev. Let

Evaluation of Probabilistic Streamflow Forecasts Based on EPS for a Mountainous Basin in Turkey

AbstractWhen designing water structures or managing a watershed it is a challenging task to determine the response of a basin to storm and/or snowmelt. In this study, the Upper Euphrates Basin (10,275 km2 area and elevation range of 1125-3500 m) located at the headwater of Euphrates River, one of Turkey's most important rivers, is selected as the application area. In this region, snowmelt runoff constitutes approximately 2/3 in volume of the total yearly runoff, therefore, runoff modeling and forecasting during spring and early summer is important in terms of energy and water resources management. The aim of the study is to make a forward-oriented, medium-range flow forecasting using Ensemble Prediction System (EPS) which is a pioneer study for Turkey. Conceptual hydrological model HBV, which has a common usage in the literature, is chosen to predict streamflows. According to the results, Nash-Sutcliffe model efficiencies are 0.85 for calibration (2001-2008) and 0.71 for validation (2009-2014) respectively. After calibrating/validating the hydrologic model, EPS data including 51 different combinations produced by ECMWF is used as probability based weather forecasts. Melting period during March-June of 2011 is chosen as the forecast period. The probabilistic skill of EPS based hydrological model results are analyzed to verify the ensemble forecasts

A computerized volumetric segmentation method applicable to multi-centre MRI data to support computer-aided breast tissue analysis, density assessment and lesion localization.

Density assessment and lesion localization in breast MRI require accurate segmentation of breast tissues. A fast, computerized algorithm for volumetric breast segmentation, suitable for multi-centre data, has been developed, employing 3D bias-corrected fuzzy c-means clustering and morphological operations. The full breast extent is determined on T1-weighted images without prior information concerning breast anatomy. Left and right breasts are identified separately using automatic detection of the midsternum. Statistical analysis of breast volumes from eighty-two women scanned in a UK multi-centre study of MRI screening shows that the segmentation algorithm performs well when compared with manually corrected segmentation, with high relative overlap (RO), high true-positive volume fraction (TPVF) and low false-positive volume fraction (FPVF), and has an overall performance of RO 0.94 ± 0.05, TPVF 0.97 ± 0.03 and FPVF 0.04 ± 0.06, respectively (training: 0.93 ± 0.05, 0.97 ± 0.03 and 0.04 ± 0.06; test: 0.94 ± 0.05, 0.98 ± 0.02 and 0.05 ± 0.07)