Hans-Rudolf Elsener

High-temperature processable carbon–silicate nanocomposite cold electron cathodes for miniature X-ray sources

We report on the fabrication, Raman characterization and electron emission behavior of cold electron cathodes that are specifically designed to be used in miniature X-ray sources. The cathodes are fabricated by screen-printing a nanocomposite paste comprising multiwall carbon nanotubes as fillers in a matrix of graphite, glass and bentonite clay. The cathodes can resist high temperatures up to 880 °C and, as such, can survive most high-temperature brazing steps required for vacuum-tight sealing of the sources. We demonstrate peak emission current densities around 300 mA cm−2 at an applied electric field of 175 kV cm−1 and stable emission around 50 mA cm−2 at 125 kV cm−1 for at least 5 hours without significant degradation. X-rays were successfully generated at 3.2 watts of peak power (80 μA, 40 kV) with a commercial X-ray tube modified to accommodate a paste cathode.

MCP detector development for WSO-UV

The spectrographs of WSO-UV cover the wavelength range of 102 - 310 nm. The essential requirements for the associated detectors are high quantum effciency, solar blindness, and single photon detection. To achieve this, we develop a microchannel plate detector in a sealed tube. We plan to use cesium activated gallium nitride as semitransparent photocathode, a stack of two microchannel plates and a cross strip anode with advanced readout electronics. Challenges are the degradation of the photocathode under atmospheric conditions and the sealing process. We present the detector concept, details of the transfer and sealing processes under UHV, and the current status.

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

Abstract The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag–Cu–Ti alloy and at 880 °C with a Cu–Sn–Ti–Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm−1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.

An introduction to the World Space Observatory-Ultraviolet spectrographs

The World Space Observatory Ultraviolet (WSO-UV) is a multinational mission under the leadership of Russia with contributions of Spain and Germany. The mission is part of the Spektrum series and launch is currently scheduled for 2016. It consists of a 1.7m mirror focusing on spectrographs in the range of 102-310 nm withh a resolution of R ≥ 55,000 for high resolution spectral observations, a long-slit-spectrograph for spatially resolved observations and an imager. According to the Phase-B-Study all spectrographs will use the same detectors built by the IAAT. These spectrographs are designed to observe cosmic plasma with temperatures of several ten thousands Kelvin and atomic transition lines of all important atoms and molecuules like H2, CO, OH eetc. In knowledge about the formation of galaxies and analyze the atmospheres of extrasolar planets and protoplanetary discs. To achieve these goals the IAAT designed in cooperation with the Leibniz-Institute for Analytical Sciences (ISAS Berlin) the spectrographs. In addition Tubingen develops and builds a new type of michrchannel plate detector based on gallim nitride cathods and a cross-strip-anode.