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Atom interferometry in free flight

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Published on 10 December 2009

Philippe Bouyer and co-workers in France performed a range of impressive experiments with an atom interferometer in free flight, onboard an Airbus aircraft making "micro-gravity jumps". These experiments successfully demonstrate that when atoms are sufficiently cooled and controlled, their wave properties can be used to perform interferometry in a way analogous to standard interferometry with light. This moves the field closer to the implementation of a range of sensors for e.g. gravity, rotation and inertia with unprecedented accuracy. Such devices will be potentially very useful in satellites and in space missions.

Tidal waves on liquid Helium-4

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Published on 17 November 2009

An analytical theory explains why a probe molecule such as Na₂ on the surface of a liquid ⁴He droplet creates soft vibrations which can be used to study the dynamics of the droplet surface with optical spectroscopy.

Microscopic modeling of electronic quantum nanodevices reviewed in a Colloquium paper by D. Taj, R.C. Iotti and F. Rossi

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Published on 02 November 2009

Quantum devices represent an important topic of modern nanoscience, characterized by its multi-disciplinary flavor where condensed matter physics, quantum theory, and information technology merge into a unique body of knowledge. In this Colloquium paper Taj and co-workes review and discuss how to work out a microscopic modeling of state-of-the-art electronic quantum devices. The emphasis is on the description of energy-relaxation and decoherence phenomena. Finally, the authors propose an alternative formulation of the problem in terms of a generalized Fermi's Golden Rule.

The unusual electronic and transport properties of graphene-based nanostructures reviewed in a Colloqium paper by Dubois, Zanolli, Declerck, and Charlier in EPJ B

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Published on 16 October 2009

Graphene-based nanostructures are expected to display the extraordinary electronic, thermal and mechanical properties and are thus promising candidates for a wide range applications and opening alternatives to present silicon-based electronics devices. This paper reviews the electronic and quantum transport properties of these carbon nanomaterials in which confinement effects are playing a crucial role. After reviewing the transport properties of defect-free systems, doping and topological defects are also proposed as strategy to tailor quantum conductance in these materials.

Time stamping in Einstein-Podolsky-Rosen experiments

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Published on 14 October 2009

Using the time of detection of each single photon, the authors falsify a class of non-ergodic local models that have not been tested in previous experiments on the Bell inequality.

Kurt Becker to lead the plasma physics sections of EPJ D

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Published on 10 July 2009

As of July 2009 The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics has a third Editor-in-Chief. Kurt H. Becker (NYU-Poly) has been appointed and will work alongside Franco Gianturco and Claude Fabre, toward strengthening EPJ D. His particular emphasis will be on low-temperature plasma physics.

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Photoinduced Switching of Charge Carrier Mobility in Conjugated Polymers

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Published on 26 June 2009

In this paper we investigate theoretically a mode of heating thick layers using a laser beam where the temperature of the layer propagates in a steady-state self sustained fashion from the bottom of the layer towards the surface and may exhibit a very steep front. The propagation of the thermal front happens at a constant speed, related to the intensity of the power flux. To achieve this heating mode the absorption coefficient of the layer has to remain low in weak temperatures and increase rapidly as a function of temperature in higher temperatures. Additionally, a significant temperature increase must be generated to trigger this propagation mode, for example through the presence of a strongly absorbing layer beneath the transparent layer. The mode is well suited to semiconductors, especially silicon . The theoretical approach is confirmed by a simulation in the case of a low doped silicon layer 150 micrometers thick above a highly doped substrate ; the low doped silicon is heated homogeneously at 1476 K by a 2E6Wcm^-2 CO₂ laser beam throughought the entire thickness in a timescale of 20µS.

EPJ launches EPJ Web of Conferences

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Published on 04 May 2009

EPJ launches EPJ Web of Conferences an open-access publishing service dedicated to the publication of conference proceedings and the related archiving of conference web pages. Maximum speed of publication and visibility are combined with a maximum of flexibility regarding formats.

For further information have a look at the website of EPJ Web of Conferences

Evaluation of organic sub-monolayers by X-ray based measurements under gracing incident conditions

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Published on 28 March 2009

The structural investigations of model organic systems like pentacene in the monolayer regime is very important for fundamental understanding of the initial nucleation process together with the electronic performance of transistor devices. The fact that the transistor performance saturates after deposition of some monolayers of the active organic material motivates a basic investigation of the submonolayer and monolayer regime in more detail. In this paper a method for the evaluation of the island formation and the island growth within the first monolayer is introduced. The method is based on X-ray scattering under grazing incident condition by means of specular X-ray reflectivity and off-specular X-ray scattering. From the specular reflectivity the electron density can be obtained which is directly correlated with the coverage of a submonolayer. Within the presented experiment coverages ranging from 7% up to 97% could be identified and are in excellent agreement with atomic force microscope results. Lateral information on the islands is obtained by rocking curve and detector scan measurements under grazing incident condition. The observed correlation peaks are evaluated by using Distorted Wave Born approximation, whereby mean island sizes ranging from 300nm to 1.5µm and mean island separation of about 2µm could be determined for the various samples. The obtained results encourages the use of this type of investigation for in-situ growth experiments to obtain a better understanding of the first monolayer formation.

Laser heating of thick layers through a backwards, self-sustained propagation of a steep, steady state thermal front

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Published on 05 January 2009

Presented paper reports on switching device based on reversible modulation of charge carrier mobility by photochromic additive distributed in polymer matrix. The light induced photochromic conversion of the additive is accompanied by significant increase of its dipole moment. The presence of the dipole moment induces change of electrostatic potential in its vicinity and shifts the site energies of individual polymer repeating units. Since the position and orientation of the photochromic additive with respect to the polymer chain are essentially random the effect results in broadening of the distribution of the transport states and consequently in the lowering of the charge carriers mobility. These notions suggested by quantum chemistry modeling are proved by experimental characterization of the optical and electrical switching properties of the suggested switch. The observed current-voltage characteristics showed reversible decrease of the currents after the photochromic switching of the additive to its metastable state with high dipole moment. This behaviour was explained on the basis of charge carrier mobility decrease due to the presence of charge traps. Impedance spectroscopy revealed a drop of the bulk conductivity when the polar state of the photochromic molecules was present. The induced conductivity decrease is proportional to the drop observed by current-voltage characterization.