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Search Results: 1 - 10 of 9830 matches for " Stefan Wundrack "
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Versatile sputtering technology for Al2O3 gate insulators on graphene
Miriam Friedemann, Miros?aw Woszczyna, André Müller, Stefan Wundrack, Thorsten Dziomba, Thomas Weimann and Franz J Ahlers
Science and Technology of Advanced Materials , 2012,
Abstract: We report a novel, sputtering-based fabrication method of Al2O3 gate insulators on graphene. Electrical performance of dual-gated mono- and bilayer exfoliated graphene devices is presented. Sputtered Al2O3 layers possess comparable quality to oxides obtained by atomic layer deposition with respect to a high relative dielectric constant of about 8, as well as low-hysteresis performance and high breakdown voltage. We observe a moderate carrier mobility of about 1000 cm2 V 1 s 1 in monolayer graphene and 350 cm2 V 1 s 1 in bilayer graphene, respectively. The mobility decrease can be attributed to the resonant scattering on atomic-scale defects, likely originating from the Al precursor layer evaporated prior to sputtering.
All-carbon vertical van der Waals heterostructures: Non-destructive functionalization of graphene for electronic applications
Miroslaw Woszczyna,Andreas Winter,Miriam Grothe,Annika Willunat,Stefan Wundrack,Rainer Stosch,Thomas Weimann,Franz Ahlers,Andrey Turchanin
Physics , 2014, DOI: 10.1002/adma.201400948
Abstract: We present a route to non-destructive functionalization of graphene via assembly of vertical all-carbon van der Waals heterostructures. To this end, we employ singlelayer graphene (SLG) sheets grown by low-pressure methane CVD on Cu foils and large-area dielectric ~1 nm thick amino-terminated carbon nanomembranes (NH2-CNMs) generated by electron-beam-induced crosslinking of aromatic self-assembled monolayers. We encapsulate SLG sheets on oxidized silicon wafers with NH2-CNMs via mechanical stacking and characterize structural, chemical and electronic properties of the formed heterostructures by Raman spectroscopy and X-ray photoelectron spectroscopy as well as by electric and electromagnetic transport measurements. We show that functional amino groups are brought in close vicinity of the SLG sheets and that their transport characteristics are not impaired by this functionalization; moreover, we demonstrate a functional response of the heterostructure devices to the protonation of the amino groups in water. Due to its relative simplicity, the suggested approach opens broad avenues for implementations in graphene-based electronic devices where non-destructive chemical functionalization of graphene is required (e.g., for engineering electrical transducers for chemical and bio-sensing) or as complementary dielectric to graphene in hieratical heterostructures.
Epitaxial graphene on SiC: Modification of structural and electron transport properties by substrate pretreatment
Mattias Kruskopf,Klaus Pierz,Stefan Wundrack,Rainer Stosch,Thorsten Dziomba,Cay-Christian Kalmbach,André Müller,Jens Baringhaus,Christoph Tegenkamp,Franz J. Ahlers,Hans W. Schumacher
Physics , 2015, DOI: 10.1088/0953-8984/27/18/185303
Abstract: The electrical transport properties of epitaxial graphene layers are correlated with the SiC surface morphology. In this study we show by atomic force microscopy and Raman measurements that the surface morphology and the structure of the epitaxial graphene layers change significantly when different pretreatment procedures are applied to nearly on-axis 6H-SiC(0001) substrates. It turns out that the often used hydrogen etching of the substrate is responsible for undesirable high macro steps evolving during graphene growth. A more advantageous type of sub-nanometer stepped graphene layers is obtained with a new method: a high-temperature conditioning of the SiC surface in argon atmosphere. The results can be explained by the observed graphene buffer layer domains after the conditioning process which suppress giant step bunching and graphene step flow growth. The superior electronic quality is demonstrated by a less extrinsic resistance anisotropy obtained in nano-probe transport experiments and by the excellent quantization of the Hall resistance in low-temperature magneto-transport measurements. The quantum Hall resistance agrees with the nominal value (half of the von Klitzing constant) within a standard deviation of 4.5*10(-9) which qualifies this method for the fabrication of electrical quantum standards.
Functional single-layer graphene sheets from aromatic monolayers
Dan G. Matei,Nils-Eike Weber,Simon Kurasch,Stefan Wundrack,Miroslaw Woszczyna,Miriam Grothe,Thomas Weimann,Franz Ahlers,Rainer Stosch,Ute Kaiser,Andrey Turchanin
Physics , 2014, DOI: 10.1002/adma.201300651
Abstract: We demonstrate how self-assembled monolayers of aromatic molecules on copper substrates can be converted into high-quality single-layer graphene using low-energy electron irradiation and subsequent annealing. We characterize this two-dimensional solid state transformation on the atomic scale and study the physical and chemical properties of the formed graphene sheets by complementary microscopic and spectroscopic techniques and by electrical transport measurements. As substrates we successfully use Cu(111) single crystals and the technologically relevant polycrystalline copper foils.
Comparison of Different Control Algorithms for a Gantry Crane System  [PDF]
Stefan Bruins
Intelligent Control and Automation (ICA) , 2010, DOI: 10.4236/ica.2010.12008
Abstract: For a gantry crane system, this paper presents a comparison between four control algorithms. These algo-rithms are being compared on simplicity, stability and robustness. Goal for the controller is to move the load on a gantry crane to a new position with minimal overshoot of the load and maximal speed of the load. An-other goal is to provide an insight in the behaviour of the possible controllers. In this article a parallel P-controller, cascade P-controller, fuzzy controller and an internal model controller are used. To be able to validate and design the controllers a model is derived from the gantry crane. The controllers and the model are being implemented in Matlab Simulink. Finally the controllers are validated and tuned in Labview on a laboratory gantry scrane scale model. Main conclusion is that all presented controllers can be used as a con-troller for the gantry crane system but the fuzzy controller is showing the best performance.
Simulation and Injection Molding of Ring-Shaped Polymer Bonded Nickel Braze Metal Composite Preforms Based on Rheological and Thermal Analyses  [PDF]
Stefan Kirchberg
Open Journal of Composite Materials (OJCM) , 2013, DOI: 10.4236/ojcm.2013.32004

Rheological and thermal properties of LD-PE and LD-PE + 65 vol% Ni composite were examined by viscosity, pvt and thermal conductivity measurements at a wide range of shear rate, temperature and pressure. The typical shear-thinning viscosity of LD-PE polymer melt was enhanced up to four times by adding 65 vol% Ni braze metal particles. LD-PE show increasing specific volume versus temperature, decreasing with pressure and braze particle filler content. Variation of specific volume of LD-PE was reduced to 5% by admixing 65 vol% rigid Ni braze metal particles. Thermal conductivity of LD-PE was increased up to 15 times in the composite, reduced by decreasing pressure at temperature exceeding 80. Furthermore, thermal analysis was performed in modulated DSC to determine the specific heat capacity in wide temperature range. Viscosity and pvt-data were fitted using Cross-WLF equation and 2-domain Tait-pvt model, respectively. Simulation of LD-PE and LD-PE + 65 vol% Ni composite was performed based on rheological and thermal properties to define processing parameters. Simulation and injection molding of ring-shaped LD-PE + 65 vol% Ni composite braze metal preforms were performed successfully.

Creating a Strategic Partnership for Educating Nurse Practitioner Students about Sexual Health  [PDF]
Stefan Rowniak
Creative Education (CE) , 2014, DOI: 10.4236/ce.2014.515156

Sexual health is an essential and often neglected component of primary care. Nurse practitioners are ideal members of the healthcare team to be providing sexual health information, diagnoses, and treatments. Unfortunately, this is an area that has been lacking in the education of all healthcare providers. This paper describes a program that incorporates sexual health into the curriculum for nurse practitioner students through collaboration between the university school of nursing and the local health department. Given the increasing shortage of clinical sites and the need to train nurse practitioners to be competent in the delivery of sexual health, this is a model that could benefit other schools of nursing.

On the Stability of Stochastic Jump Kinetics  [PDF]
Stefan Engblom
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.519300
Abstract: Motivated by the lack of a suitable constructive framework for analyzing popular stochastic models of Systems Biology, we devise conditions for existence and uniqueness of solutions to certain jump stochastic differential equations (SDEs). Working from simple examples we find reasonable and explicit assumptions on the driving coefficients for the SDE representation to make sense. By “reasonable” we mean that stronger assumptions generally do not hold for systems of practical interest. In particular, we argue against the traditional use of global Lipschitz conditions and certain common growth restrictions. By “explicit”, finally, we like to highlight the fact that the various constants occurring among our assumptions all can be determined once the model is fixed. We show how basic long time estimates and some limit results for perturbations can be derived in this setting such that these can be contrasted with the corresponding estimates from deterministic dynamics. The main complication is that the natural path-wise representation is generated by a counting measure with an intensity that depends nonlinearly on the state.
Product Repositioning in the UK Newspaper Industry  [PDF]
Stefan Behringer
Theoretical Economics Letters (TEL) , 2016, DOI: 10.4236/tel.2016.65099
Abstract: This paper investigates the alleged predatory behaviour in the UK quality newspaper industry in the 1990s in terms of product repositioning using a horizontal differentiation model and industry data. It supports the call for an effects based approach to competition law by showing that non-price conduct can be a critical and less visible, complementary means to achieve a predatory goal than mere price cuts.
Revenue Sharing in a Sports League with an Open Market in Playing Talent: A Comment  [PDF]
Stefan Szymanski
Theoretical Economics Letters (TEL) , 2016, DOI: 10.4236/tel.2016.66123
Abstract: Szymanski [1] and Szymanski and Késenne [2] showed that, in the standard model of a sports league, gate revenue sharing will tend to increase competitive imbalance between weak and strong teams, a seemingly perverse result. Dobson and Goddard [3] claim that “this analysis is flawed. If the revenue function is specified appropriately, gate revenue sharing always reduces competitive inequality.” This comment points out the analytical error in their paper which leads to their erroneous conclusion. Once their error is corrected, it is shown that the earlier results stand.
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