Single domain transport measurements of C60 films

Thin films of potassium doped C60, an organic semiconductor, have been grown on silicon. The films were grown in ultra-high vacuum by thermal evaporation of C60 onto oxide-terminated silicon as well as reconstructed Si(111). The substrate termination had a drastic influence on the C60 growth mode which is directly reflected in the electrical properties of the films. Measured on the single domain length scale, these films revealed resistivities comparable to bulk single crystals. In situ electrical transport properties were correlated to the morphology of the film determined by scanning tunneling microscopy. The observed excess conductivity above the superconducting transition can be attributed to two-dimensional fluctuations.Comment: 4 pages, 4 figure

A high etendue spectrometer suitable for core charge eXchange recombination spectroscopy on ITER

A feasibility study for the use of core charge exchange recombination spectroscopy on ITER has shown that accurate measurements on the helium ash require a spectrometer with a high etendue of 1mm2sr to comply with the measurement requirements [S. Tugarinov et al., Rev. Sci. Instrum. 74, 2075 (2003)]. To this purpose such an instrument has been developed consisting of three separate wavelength channels (to measure simultaneously He/Be, C/Ne, and H/D/T together with the Doppler shifted direct emission of the diagnostic neutral beam, the beam emission (BES) signal), combining high dispersion (0.02 nm/pixel), sufficient resolution (0.2 nm), high efficiency (55%), and extended wavelength range (14 nm) at high etendue. The combined measurement of the BES along the same sightline within a third wavelength range provides the possibility for in situ calibration of the charge eXchange recombination spectroscopy signals. In addition, the option is included to use the same instrument for measurements of the fast fluctuations of the beam emission intensity up to 2 MHz, with the aim to study MHD activity

Electrical transport measurements on self-assembled organic molecular wires

The electrical properties of supermolecular assemblies of oligo(p-phenylene vinylene) were studied. These materials self-assemble into well-defined cylindrical structures in solution with lengths in the range of 100?nm–10??m and diameters between 5 and 200?nm. Atomic force microscopy showed that by adjusting the concentration, either individual molecular wires or a dense film could be deposited. The molecular wires showed poor electrical conduction. Several tests were performed that show that it was the molecular wires themselves, not the contacts, that limit the conductivity.Kavli Institute of NanoscienceApplied Science

Fluctuation BES measurements with the ITER core CXRS prototype spectrometer

The ITER core CXRS diagnostic system collects the light emitted from the interaction of the diagnostic neutral beam with the core plasma and guides it via a mirror labyrinth through the upper port plug #3 towards a fiber bundle, which then transmits the light into a set of spectrometers for spectral analysis. In order to test the accessibility of the special parameter range required for the ITER measurement, a prototype spectrometer was built and operated successfully at the TEXTOR tokamak. In addition to the He/Be, C/Ne and H/D/T regular spectral channels, a fluctuation beam emission spectroscopy (BES) system has been integrated to measure core MHD activity, and validate corresponding ITER simulation results. The fluctuation system can be operated as an alternative to the spectral BES measurement, and has 8 spatial channels sampled at 2 MHz. In this paper, we present details of the fluctuation BES system and its interface to the ITER prototype spectrometer along with simulation and measurement results at TEXTOR. We show that the measurement fully confirms the simulation results on achievable photon current at the detector and on the signal to noise ratio

Fluctuation Bes measurements with the ITER Core CXRS prototype spectrometer

The ITER core CXRS diagnostic system collects the light emitted from the interaction of the diagnostic neutral beam with the core plasma and guides it via a mirror labyrinth through the upper port plug #3 towards a fiber bundle, which then transmits the light into a set of spectrometers for spectral analysis. In order to test the accessibility of the special parameter range required for the ITER measurement, a prototype spectrometer was built and operated successfully at the TEXTOR tokamak. In addition to the He/Be, C/Ne and H/D/T regular spectral channels, a fluctuation beam emission spectroscopy (BES) system has been integrated to measure core MHD activity, and validate corresponding ITER simulation results. The fluctuation system can be operated as an alternative to the spectral BES measurement, and has 8 spatial channels sampled at 2 MHz. In this paper, we present details of the fluctuation BES system and its interface to the ITER prototype spectrometer along with simulation and measurement results at TEXTOR. We show that the measurement fully confirms the simulation results on achievable photon current at the detector and on the signal to noise ratio