Elastic properties of chemically derived single graphene sheets

The elastic modulus of freely suspended graphene monolayers, obtained via chemical reduction of graphene oxide, was determined through tip-induced deformation experiments. Despite their defect content, the single sheets exhibit an extraordinary stiffness ( E = 0.25 TPa) approaching that of pristine graphene, as well as a high flexibility which enables them to bend easily in their elastic regime. Built-in tensions are found to be significantly lower compared to mechanically exfoliated graphene. The high resilience of the sheets is demonstrated by their unaltered electrical conductivity after multiple deformations. The electrical conductivity of the sheets scales inversely with the elastic modulus, pointing toward a 2-fold role of the oxygen bridges, that is, to impart a bond reinforcement while at the same time impeding the charge transport.     

Electronic transport properties of individual chemically reduced graphene oxide sheets

Individual graphene oxide sheets subjected to chemical reduction were electrically characterized as a function of temperature and external electric fields. The fully reduced monolayers exhibited conductivities ranging between 0.05 and 2 S/cm and field effect mobilities of 2-200 cm2/Vs at room temperature. Temperature-dependent electrical measurements and Raman spectroscopic investigations suggest that charge transport occurs via variable range hopping between intact graphene islands with sizes on the order of several nanometers. Furthermore, the comparative study of multilayered sheets revealed that the conductivity of the undermost layer is reduced by a factor of more than 2 as a consequence of the interaction with the Si/SiO2 substrate.     

Improved high-power twin-channel laser with blocking layer

We present an improved version of the twin-channel laser as a prototype for a new concept in semiconductor laser array structures with a well controlled far-field beam pattern. The laser device constitutes the first CW semiconductor laser array structure on a p-type GaAs substrate using current-blocking layers and yields improved current utilisation and efficiency over previous structures.     

Der Kernphysiker Rudolf Fleischmann und die Medizin an der Reichsuniversität Straßburg (1941–1944)

Under German occupation in World War II,Alsace-Lorraine was subjected to politically enforced Germanization. One means was science policy. The newly founded research institute of the medical school of the University of Strasbourg for instance was modeled on the Heidelberg Kaiser Wilhelm Institute for Medical Research of Ludolf von Krehl, incorporating institutes for internal medicine, physics and chemistry, and housing very modern research facilities. The expansion created tremendous professional opportunities for young German scientists like Rudolf Fleischmann, who worked in Strasbourg until the liberation, when he was taken as prisoner by the allied intelligence mission "Alsos." Released in 1946, Fleischmann started a second career in Hamburg and Erlangen, where he died in 2002. In one of his last interviews, which he gave to the author of this paper, he called the Strasbourg period a prerequisite for establishing his own scientific reputation.     

Wirklichkeitsnahe Brandeinwirkungen für die Planung und Nachrechnung von Tunnelschalen

Realistic fire loads for design and re‐analysis of tunnel linings Meanwhile, the development of numerical systems for the simulation of flow phenomena has reached a level, which even allows the analysis of complex scenarios such as tunnel fires, within acceptable time‐periods. On the one hand, this provides the possibility to critically question fire‐curves from standards (derived and calibrated for the general case) against the background of tunnel‐specific temperature fields. On the other hand, both temperature and smoke development as well as expected structural impairment may be assessed on a relatively realistic basis without large‐scale conflagration tests being necessary. In addition to general options of non‐linear structural analyses (i.e. utilisation of load re‐distribution and activation of additional bedding reactions) [1] the simulation‐based evaluation of fire loads particularly provides a valuable potential for the re‐analysis of existing tunnel linings. This especially applies in such cases where the calculation with conventional fire‐curves requires extensive strengthening and retrofit, whereas more favourable loading conditions may be expected by taking into account the tunnel‐specific boundary conditions. In the present paper, firstly tunnel fire accidents and the derivation of fire‐curves are generally discussed. Then, the possibilities, the theoretical background and limits of CFD modelling of fire scenarios are presented and finally, major influence factors on the thermal loading (in particular the cross‐sectional size of the tunnel) are investigated by sensitivity studies.     

Growth of Single‐Walled Carbon Nanotubes from Microcontact‐Printed Catalyst Patterns on Thin Si3N4 Membranes

Single‐walled carbon nanotubes have been grown by chemical vapor deposition from methane and hydrogen on catalyst patterns prepared by microcontact printing on 20 nm thick silicon nitride substrates. A higher yield of single‐walled carbon nanotubes was obtained by the simple expedient of introducing hydrogen during deposition. Based on atomic force microscopy and transmission electron microscopy measurements, we found that high‐quality single‐walled carbon nanotubes with a broad diameter distribution were obtained.