Defect structure of web silicon ribbon

The results of a preliminary study of two dendritic web samples are presented. The structure and electrical activity of the defects in the silicon webs were studied. Optical microscopy of chemically etched specimens was used to determine dislocation densities. Samples were mechanically polished, then Secco etched for approximately 5 minutes. High voltage transmission electron microscopy was used to characterize the crystallographic nature of the defects

Defect structure of EFG silicon ribbon

The defect structure of EFG ribbons was studied using EBIC, TEM and HVEM. By imaging the same areas in EBIC and HVEM, a direct correlation between the crystallographic nature of defects and their electrical properties was obtained. (1) Partial dislocations at coherent twin boundaries may or may not be electrically active. Since no microprecipitates were observed at these dislocations it is likely that the different electrical activity is a consequence of the different dislocation core structures. (2) 2nd order twin joins were observed which followed the same direction as the coherent first order twins normally associated with EFG ribbons. These 2nd order twin joins are in all cases strongly electrically active. EFG ribbons contain high concentrations of carbon. Since no evidence of precipitation was found with TEM it is suggested that the carbon may be incorporated into the higher order twin boundaries now known to exist in EFG ribbons

Employment Changes Play Major Role in Access to Employer Health Coverage

Highlights findings on the factors that drive short-term changes in employer-sponsored health insurance coverage, including the rising cost of health insurance and changes in employment rates and availability of better jobs during macroeconomic cycles

Predicting Intermediate Storage Performance for Workflow Applications

Configuring a storage system to better serve an application is a challenging task complicated by a multidimensional, discrete configuration space and the high cost of space exploration (e.g., by running the application with different storage configurations). To enable selecting the best configuration in a reasonable time, we design an end-to-end performance prediction mechanism that estimates the turn-around time of an application using storage system under a given configuration. This approach focuses on a generic object-based storage system design, supports exploring the impact of optimizations targeting workflow applications (e.g., various data placement schemes) in addition to other, more traditional, configuration knobs (e.g., stripe size or replication level), and models the system operation at data-chunk and control message level. This paper presents our experience to date with designing and using this prediction mechanism. We evaluate this mechanism using micro- as well as synthetic benchmarks mimicking real workflow applications, and a real application.. A preliminary evaluation shows that we are on a good track to meet our objectives: it can scale to model a workflow application run on an entire cluster while offering an over 200x speedup factor (normalized by resource) compared to running the actual application, and can achieve, in the limited number of scenarios we study, a prediction accuracy that enables identifying the best storage system configuration

Competition between magnetic field dependent band structure and coherent backscattering in multiwall carbon nanotubes

Magnetotransport measurements in large diameter multiwall carbon nanotubes (20-40 nm) demonstrate the competition of a magnetic-field dependent bandstructure and Altshuler-Aronov-Spivak oscillations. By means of an efficient capacitive coupling to a backgate electrode, the magnetoconductance oscillations are explored as a function of Fermi level shift. Changing the magnetic field orientation with respect to the tube axis and by ensemble averaging, allows to identify the contributions of different Aharonov-Bohm phases. The results are in qualitative agreement with numerical calculations of the band structure and the conductance.Comment: 4 figures, 5 page

Aharonov-Bohm differential conductance modulation in defective metallic single-wall carbon nanotubes

Using a perturbative approach, the effects of the energy gap induced by the Aharonov-Bohm (AB) flux on the transport properties of defective metallic single-walled carbon nanotubes (MSWCNTs) are investigated. The electronic waves scattered back and forth by a pair of impurities give rise to Fabry-Perot oscillations which constitutes a coherent backscattering interference pattern (CBSIP). It is shown that, the CBSIP is aperiodically modulated by applying a magnetic field parallel to the nanotube axis. In fact, the AB-flux brings this CBSIP under control by an additional phase shift. As a consequence, the extrema as well as zeros of the CBSIP are located at the irrational fractions of the quantity $\Phi_\rho={\Phi}/{\Phi_0}$, where $\Phi$ is the flux piercing the nanotube cross section and $\Phi_{0}=h/e$ is the magnetic quantum flux. Indeed, the spacing between two adjacent extrema in the magneto-differential conductance (MDC) profile is decreased with increasing the magnetic field. The faster and higher and slower and shorter variations is then obtained by metallic zigzag and armchair nanotubes, respectively. Such results propose that defective metallic nanotubes could be used as magneto-conductance switching devices based on the AB effect.Comment: 11 pages, 4 figure

The Amplitude of Non-Equilibrium Quantum Interference in Metallic Mesoscopic Systems

We study the influence of a DC bias voltage V on quantum interference corrections to the measured differential conductance in metallic mesoscopic wires and rings. The amplitude of both universal conductance fluctuations (UCF) and Aharonov-Bohm effect (ABE) is enhanced several times for voltages larger than the Thouless energy. The enhancement persists even in the presence of inelastic electron-electron scattering up to V ~ 1 mV. For larger voltages electron-phonon collisions lead to the amplitude decaying as a power law for the UCF and exponentially for the ABE. We obtain good agreement of the experimental data with a model which takes into account the decrease of the electron phase-coherence length due to electron-electron and electron-phonon scattering.Comment: New title, refined analysis. 7 pages, 3 figures, to be published in Europhysics Letter

Finite-temperature magnetism of Fex_xPd1−x_{1-x} and Cox_xPt1−x_{1-x} alloys

The finite-temperature magnetic properties of Fe$_x$Pd$_{1-x}$ and Co$_x$Pt$_{1-x}$ alloys have been investigated. It is shown that the temperature-dependent magnetic behaviour of alloys, composed of originally magnetic and non-magnetic elements, cannot be described properly unless the coupling between magnetic moments at magnetic atoms (Fe,Co) mediated through the interactions with induced magnetic moments of non-magnetic atoms (Pd,Pt) is included. A scheme for the calculation of the Curie temperature ($T_C$) for this type of systems is presented which is based on the extended Heisenberg Hamiltonian with the appropriate exchange parameters $J_{ij}$ obtained from {\em ab-initio} electronic structure calculations. Within the present study the KKR Green's function method has been used to calculate the $J_{ij}$ parameters. A comparison of the obtained Curie temperatures for Fe$_x$Pd$_{1-x}$ and Co$_x$Pt$_{1-x}$ alloys with experimental data shows rather good agreement.Comment: 10 pages, 12 figure

Superconductivity on the localization threshold and magnetic-field-tuned superconductor-insulator transition in TiN films

Temperature- and magnetic-field dependent measurements of the resistance of ultrathin superconducting TiN films are presented. The analysis of the temperature dependence of the zero field resistance indicates an underlying insulating behavior, when the contribution of Aslamasov-Larkin fluctuations is taken into account. This demonstrates the possibility of coexistence of the superconducting and insulating phases and of a direct transition from the one to the other. The scaling behavior of magnetic field data is in accordance with a superconductor-insulator transition (SIT) driven by quantum phase fluctuations in two-dimensional superconductor. The temperature dependence of the isomagnetic resistance data on the high-field side of the SIT has been analyzed and the presence of an insulating phase was confirmed. A transition from the insulating to a metallic phase is found at high magnetic fields, where the zero-temperature asymptotic value of the resistance being equal to h/e^2.Comment: 5 pages, 4 eps figures, RevTeX4, Published versio