On the origin of bistable resistive switching in metal organic charge transfer complex memory cells

Electrical characteristics of Cu:tetracyanoquinodimethane (TCNQ) devices with different electrodes were studied. The comparison of impedance spectroscopic measurements on devices with Al and Pt top electrodes proved the existence of a high resistive interface layer between Cu:TCNQ and Al. An equivalent circuit was modeled and the resulting values suggest that the interface layer is composed of naturally formed aluminum oxide. Devices with deliberately formed aluminum oxide and without Cu:TCNQ were fabricated and revealed a similar behavior. The authors propose that the switching effect in Cu:TCNQ thin film devices is a Cu ion based electrochemical effect occurring in a thin aluminum oxide layer. (C) 2007 American Institute of Physics

Preparation and characterisation of amorphous Cu: 7,7,8,8-Tetracyanoquinodimethane thin films with low surface roughness via thermal co-deposition

We demonstrate a physical vapor deposition process for preparing amorphous Cu:Tetracyanoquinodimethane (Cu:TCNQ) thin films. Samples made by this co-evaporation process exhibit a smooth surface in the scanning electron microscope. Spectroscopic studies confirmed the formation of a charge transfer (CT) complex with a degree of CT of 0.68. Reproducible resistive switching is observed in a glass/NiCr/Al/Cu:TCNQ/Al sandwich structure. OFF/ON ratios of 10 to 10(2) and impedance values between 100 k Omega and 10 M Omega have been measured. Switching voltages for the prepared samples with a film thickness of around 100 run are in the range of 4 +/- 2 V and are fairly symmetrical. The devices have a life time of more than 10(4) switching cycles. (c) 2006 Elsevier B.V. All rights reserved

Production of a highly ionized plasma with low impurity level, with and without magnetic bias fields for magnetic compression experiments

For the compression of a cylindrical plasma by fast rising axial magnetic fields, the initial state of this plasma is of critical importance (1). Therefore experiments with a preheating discharge for the production of an initial plasma with known and reproducible properties were started at this laboratory simultaneously with the first experiments on the compression of a weakly preionized deuterium gas.An electrodeless ring discharge was chosen. The absence of electrodes makes a high degree of purity of the plasma possible. Kolb's experience with a preheating discharge for magnetic com-pression experiments (2) confirmed this conception and gave further impulse to this work. Early experiments were made with a RF-transmitter as current generator, in pulsed as weIl as in stationary operation. Dueto the low inductance of the compression coil considerable difficulties are met in coupling the RF power to the discharge. The maximum available power is limited to some hundred kilowatts. By discharging a low inductance condenser on the compression coil a damped RF pulse with apower of 100 M Watt is easily obtained. To avoid prefiring of the main condenser bank, the voltage of the coil must be lirnited. With the spark gaps used at this laboratory the maximum permissible voltage at the coil was about 5 kV. This voltage, however, is sufficient to start an electrodeless ring discharge in hydrogen. Investigations on this electrodeless ring discharge were made with and without a steady magnetic bias field in a wide pressure range. Preliminary results, concerning the breakdown of the gas, the formation of a highly ionized plasma, and the subsequent decay of the plasma dtie to end losses and recombination are reported in this paper

The toroidal pump limiter ALT-II in TEXTOR

The Advanced Limiter Test (ALT) project is the focus of a fruitful and intense International Energy Agreement collaboration on TEXTOR. The pump limiter is a mechanical boundary that is laid out for taking the full heat load of TEXTOR, namely 8 MW (assuming 2 MW radiated power)for 10 s, and provides a pumping efficiency of at least 5% of the working gas. This layout is adopted from the requirements of a fusion reactor: It is mandatory to remove both the full power that is convected to the limiter or divertor and the helium ash that is generated in the fusion process. In order to obtain pumping for all gases, the ALT-II is equipped with turbomolecular pumps. A short description of ALT-II is given, and the power and particle fluxes to the limiter surface and into the exhaust scoops are discussed. Requirements of the helium removal rate for a reactor and relevant measurements are discussed, and particle removal and the power distribution to the limiters are treated. Related topics of the ALT-II program were hydrogen recycling and the measurement of turbulence-induced anomalous particle transport in the plasma edge