Comparative analysis of different preparation methods of chalcogenide glasses: Molecular dynamics structure simulations

Two different preparation methods (liquid-quenching and evaporation) of chalcogenide glasses have been investigated by molecular dynamics simulations. Our particular aim was to determine how the structural changes occur due to the different preparation methods. We applied a classical empirical three-body potential of selenium to describe the interactions between atoms. Our simulation shows that a significant difference can be observed in the homogeneities

Physical rehabilitation for critical illness myopathy and neuropathy (Protocol)

Protocol for a review - no abstract

Scanning Tunneling Spectroscopy of Bi2Sr2CuO6+d: New Evidence for the Common Origin of the Pseudogap and Superconductivity

Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi2Sr2CuO6+δ between 275 mK and 82 K. Below Tc = 10 K, the spectra show a gap with well-defined coherence peaks at ±Δp≃12 meV, which disappear at Tc. Above Tc, the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T*≃68 K. The comparison with Bi2Sr2CaCu2O8+δ demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin

Structure and photo-induced volume changes of obliquely deposited amorphous selenium

Atomic scale computer simulations on structures and photo induced volume changes of flatly and obliquely deposited amorphous selenium films have been carried out in order to understand how the properties of chalcogenide glasses are influenced by their preparation method. Obliquely deposited a-Se thin films contain more coordination defects, larger voids than the flatly deposited ones. To model the photo induced volume changes the electron excitation and hole creation were treated independently within the framework of tight-binding formalism. Covalent and interchain bond breakings and formations were found. The obliquely deposited samples containing voids showed a wide spectrum of photo induced structural changes in microscopic and volume changes in macroscopic levels.Comment: 14 page

Negative frequency tuning of a carbon nanotube nano-electromechanical resonator

A suspended, doubly clamped single wall carbon nanotube is characterized as driven nano-electromechanical resonator at cryogenic temperatures. Electronically, the carbon nanotube displays small bandgap behaviour with Coulomb blockade oscillations in electron conduction and transparent contacts in hole conduction. We observe the driven mechanical resonance in dc-transport, including multiple higher harmonic responses. The data shows a distinct negative frequency tuning at finite applied gate voltage, enabling us to electrostatically decrease the resonance frequency to 75% of its maximum value. This is consistently explained via electrostatic softening of the mechanical mode.Comment: 4 pages, 4 figures; submitted for the IWEPNM 2013 conference proceeding

Photo-induced volume changes in selenium. Tight-binding molecular dynamics study

Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se$_8$ ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyse the photo induced instability inside the amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photoinduced volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination

Scanning Tunneling Spectroscopy on Single Crystal MgB2

We report on the results of scanning tunneling spectroscopy measurements on single crystals of Mg2. Tunneling was performed both parallel and perpendicular to the crystalline c-axis. In the first case, a single superconducting gap (Delta_pi = 2.2 meV) associated with the pi-band is observed. Tunneling parallel to the ab-plane reveals an additional, larger gap (Delta_sigma ~ 7 meV) originating in the highly two-dimensional sigma-band. Vortex imaging in the pi-band was performed with the field and tunnel current parallel to the c-axis. The vortices have a large core size compared to estimates based on Hc2, and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. A comparison to specific heat measurements is performed.Comment: 12 pages, 7 figs. Submitted to Physica

Comprehensive Analysis of Two H13-Type Starting Materials Used for Laser Cladding and Aerosol Particles Formed in This Process

Laser cladding with H13 steel powders was performed and the related material transformations were studied for the particles emitted during this process. Fractions of various sizes of the aerosol particles formed during the laser cladding were collected on a cascade impactor, while the electromobility and the aerodynamic size of the particles were measured using a scanning mobility particle spectrometer and an aerodynamic particle sizer, respectively. The aerosol particles deposited onto the impactor plates were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy, as well as total-reflection X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Both the concentration and mean oxidation state of the major components were correlated with the aerosol particle size. The ultrafine aerosol particles (with a diameter less than about 100 nm) were predominantly oxidized and formed as the result of an evaporation–oxidation–condensation process sequence. The larger particles (>200 nm in geometric diameter) were primarily the residues of the original metal powder and exhibited a composition change as compared to the as-received metal powder. Correlations between the changes in the concentration ratio of the components were detected and explained